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instrumentation study- black liquor solids content

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1. Group Project 4025 Page 11 Report One WATER TO SOLIDS RATIO 0 ho 80 120 160 200 240 280 320 A gt DILUTION WATER ADDED 1b Figure 2 Interrelation Between Measured Solids Content and Dilution Water Page 12 Groun Project 5025 Report One from the same mill five weeks after Liquor A A third liquor Liquor C was obtained from a northern kraft mill pulping softwoods to conventional kraft yiela levels The results of chemical analyses of these liquors are shown in Table T It should be noted that although Liquors A and B were obtained from the seme mill and have similar inorganic contents there is a difference in the degree of oxida tion of the sulfur compounds Liquor C contains significantly more sulfur and also has a distinctly higher inorganic content In all cases the liquors were obtained at high solids concentration and were shipped to the Institute in sealed drums TABLE I CHEMICAL COMPOSITION OF BLACK LIQUORS All results are expressed as weight percent on black liquor solids and are based on TAPPI Procedure T 625 A B C Sulfated ash 34 0 32 6 56 5 Organic gt 66 0 67 4 63 5 n Total sodium 19 4 19 3 21 9 p Total sulfur 3 4 3 1 5 0 Nass 1 05 0 29 4 14 Na2S203 3 95 3 16 4 10 NasS04 5 43 7 05 5 11 Inorganic sulfur 3 24 2 99 4 53 Group Project 3025 f Page 13 Report One EMC REFRACTOMETER DESCRIPTION OF INSTRUMENT The EMC
2. O K 4 al s 7 Round bottom flask TN Solvent Weighed black liquor and boiling chips Heater Figure 32 on Black Liquor Group Project 3025 4 Cooling water Solvent layer Water layer distilled from the black liquor sample Distillation Apparatus for Solids Determination Group Project 3025 Page 91 Report One Proponents of the distillation method believe that it offers several advantages over residual solids methods It is a faster method than oven drying methods since a distillation determination can be completed in about an hour It is also more precise than a moisture balance approach Among the advantages claimed for the method are the following l With concentrated liquors the relatively large size sample of liquor used increases accuracy by permitting a more representative sample It is not necessary to weigh out liquor samples to a specific weight as with the moisture balance method Distillation is a direct means for determining water content Solids can then be defined in an unambiguous manner as the total nonaqueous part of the liquor The black liquor is heated at a controlled temperature The temperature remains close to the boiling point of water until evaporation is essentially complete The maximum temperature is limited to the boiling point of the solvent Absorption of oxygen from the air is eliminated because the s
3. doo 38a JO UBIZBTA TIROS T mr uredp OL uN y MN P o o T2 O amp 5 o H 9 UreJp or dumd dumd Te9nird4uo oulon T V d Q N NA gt JIogueuoxa 3e9H J v N de CN aTdueg E X d Ueo3g 1939 UToOT9A TossoA pogoxyoel UBS 197 9004 28179H NE Jo4eTnumooy niil NNNSNNNNNNNUN ANY Page 6 Report One uorTqo uuoo umnogA E JO rnss zq Group Project 3025 Page 7 Report One observation of the liquor level At the top of the accumulator provisions were made for pressurizing the loop with nitrogen and for evacuating the loop The return leg to the circulating pump was taken from the bottom of the accumulator A bypass line ran directly from the heat exchanger to the accumulator to permit control of flow through the instrument test zone With the Moyno pump 8n additional mode of flow control was available nada adjusted of the pump PEN with a Reeve s drive A separate bypass line around the refractometer was installed to permit reducing the velocity through the smaller refractometer adapter if desired With the exception of the piping in the immediate vicinity of the instruments all piping in the main loop containing the centrifugal pump was 2 in diameter pipe The feed lines from the storage vessel and the piping around the Moyno pump were of l in diameter pipe The capacity of the flow loop was about 15 gallons The rated capacity of the
4. INSTRUMENTATION STUDY BLACK LIQUOR SOLIDS CONTENT Project 3025 o Report One A Summary Report to A MEMBERS OF GROUP PROJECT 3025 February 23 1972 THE INSTITUTE OF PAPER CHEMISTRY Appleton Wisconsin INSTRUMENTATION STUDY BLACK LIQUOR SOLIDS CONTENT Project 3025 MacMillan Bioedel Research Limited LIBRARY 3350 East Broadway Vancouver 12 B C Report One A Summary Report to MEMBERS OF GROUP PROJECT 2025 February 25 1972 MEMBERS OF GROUP PROJECT 3025 American Can Company Bowaters Southern Paper Corporation Container Corporation of America Continental Can Company Inc Crown Zellerbach Corporation W R Grace amp Co Green Bay Packaging Inc Hammermill Paper Company Hoerner Waldorf Corporation Inland Container Corporation International Paper Company Kimberly Clark Corporation Longview Fibre Company MacMillan Bloedel Limited The Mead Corporation St Regis Paper Company Scott Paper Company Weyerhaeuser Company TABLE OF CONTENTS SUMMARY INTRODUCTION APPARATUS AND PROCEDURES EMC Flow Loop Procedures Solids Measurement Liquor Analysis REFRACTOMETER Description of Instrument Instrument Checks Instrument Calibration Basie Instrument Response Spent Liquors Temperature Compensation System Variables Composition Effects Refractive Index Measurement On Line Calibration VELOCIMETER Principle of Operation Specifi
5. 6 SPAN ADJUST This permits a change of gain on the output meter to either increase readout resolution or indicate solids content changes directly The action is one of dividing the gross span by any number between O and 10 00 If no adjustment is to be made this control is set at 1 00 A convenient feature of this instrument is that all settings and adjust ments are mad on calibrated switches or dials Once a calibration procedure has been performed it can be precisely reset at a later date for exactly the same operating conditions Even more significant is the fact that the numbers on the dials and switches have actual physical meaning For example the TEMPERATURE NULL dial markings are equivalent to degrees centigrade COMPENSATION ADJUST markings are equivalent to n sec 9C and SPAN ADJUST markings give ihe divider factor on gross span The numbers on the LOW END ADJUST switches are an octal representation of a number which is proportional to sing around frequency and can be used to compute the mean sonic velocity setting In summary it is possible to read the following quantities with this instrument Page 58 Report One Group Project 3025 Sonic velocity of the solution in meters per second This is obtained by reading the sonic velocity S N deviation on the meter multiplying by the setting on the S N range switch and adding the result algebraically to the value SP ene velocity corresponding to the
6. l l Sucrose NasC0s Solution Group Project 3025 Page 51 Report One composition are all nearly parallel regardless of temperature and whether the compensated or uncompensated response is used Establishing linearity of response to output solids variation is basic to use of adjustable ZERO and SPAN pots for direct readout of percent solids The parallel nature of the curves shows that the temperature effects can be separated out and handled by temperature compensation circuitry It also shows that the temperature compensation circuitry does not introduce any nonlinearity into the response In essence these data confirm the adequacy of the controls provided ZERO SPAN and TEMP for calibrating the instru ment to give a direct readout of solids content SPENT LIQUORS Pupas aus carried out with the three different black liquors discussed previously The temperature compensation circuitry was connected for all of these runs The runs were carried out in the order Liquor C then Liquor A and finally Liquor B The run with Liquor C was initiated immediately after the completion of the work with sucrose and NasCOs solutions The ZERO pot was adjusted so that the meter reading corresponded to an initial estimate of the solids content in the loop The SPAN pot was not adjusted The TEMP pot was given one turn counterclockwise No known changes were made in the pot settings during the remainder of the test program Since the pots on th
7. A decrease in temperature of the sucrose solution would increase its index of refraction and thus cause a higher output reading Allowing for the changing temperature it appears that the output did not change by more than 0 1 solids over the twenty four hour period Group Project 3025 Page 21 Report One INSTRUMENT CALIBRATION The major part of the program regarding the EMC refractometer was devoted to an evaluation of the ability of this instrument to measure solids PREA of black liquor and to study those datas which could affect its usefulness under industrial conditions Since the b sibosent Seventy measures refractive index it must be calibrated to give liquor solids content as an output Any variable affect ing the index of refraction such as temperature or chemical composition would affect the response of the unit For this reason the calibration procedures employed are important in interpreting the results of this study The output of the EMC refractometer is a reading on a meter having a linear scale ranging from h5 to 75 solids This is because this instrument is intended for use in measuring high solids content black liquors TT factory adjusted is the refractive index range of such liquors There are three adjustable potentiometers which are used to calibrate the instrument to read directly in percent solids these are ZERO SPAN and TEMP The ZERO pot serves to set a base line for the output meter The SPA
8. Report One gravity of the solutions increases but along different curves for different sub stances This is very interesting because the equation indicates that if the bulk modulus B remained constant then the sonic velocity would decrease as specific gravity increased The fact that the sonic velocity of solutions increases as specific gravity increases both due to an increase in solids content means that the bulk nodis increases more rapidly than density B p increases as solids content increases Hence the measurement is responding more to changes in bulk modulus than to changes in density In particular this indicates that sonic velocity is a unique property of a given solution like refractive index or density and is not simply another way of measuring density A sonic velocimeter and a densitometer are not equivalent The fact that the various methods of measuring solids Saran of liquor are susceptible to errors due to changes in liquor composition is a CORREGUES of their Waaa se of indirect E for determining solids The problem arises because the sonic velocity or refractive index at a given solids content and temperature of a solution is a function of its composition This would be expected to be true at least to some Segoe for all indirect methods of determining black liquor solids content In order to illustrate this point some handbook data on specific gravity as a function of solids content are shown in Fig 21 The dat
9. temperature of the sucrose solution in the loop cycled somewhat as the room cooled overnight and then reheated All of the observed changes in the meter reading are essentially caused by the temperature changes This is readily apparent in Fig 20 in which the sonic velocity deviation meter readings and the counter readings are plotted versus the temperature of the solution Since the counter reading is essentially the sing around frequency the change in the meter reading with temperature is reflecting actual changes in sonic velocity with temperature Thus the instrument appears to be stable over at least a twenty four hour period TEMPERATURE MEASUREMENT A check on the NUS temperature measuring system was carried out early in the program An iron constantan thermocouple Conax was installed in the flow loop immediately upstream of the velocimeter probe An ice bath was used as the cold junction and the passa emf was read with a Cambridge Portable Potentiometer No L 316688 The NUS temperature was determined by adjusting the temperature null control until the temperature deviation read zero and then adding 209C to the vernier readings on the null control dial This check on the temperature measurement system was carried out with 50 sucrose solution circulating in the loop The results of this test are presented in Table VI It can be seen that the NUS instrument tended to read a slightly lower value over the whole range from 50 to 120 C
10. 11120134 ANNOG I 9203112372 i m E 396wua Kho qA Qrinog Noto Dam Ovan 1v1S Ovni Y ee amas eror HOILYANG Liv amp Ge al DINOS 10d1no Outan Indino NLDA jiii v o gt SIHDIIMS LENPGY ONA MOI a 8 Du3i12 noiviaza E O ALDOWA Annes iN P Z a ai at s i ird LINN 108 LNOD nO Oon eS do As 10ayno amp e A5N300243 Group Project 3025 Page 55 Report One At the pipeline the temperature sensing element generates a d c signal which is proportional to temperature A temperature reference is also provided These signals are sent to the TEMPERATURE NULL control which is used to null out the temperature signal The NULL control is a vernier helipot calibrated in terms of degrees centigrade The noinuli s portion of tie signal is sent to the meter where it can be read as the teqse pues deviation By reading the mull setting and the temperature deviation the temperature at the probe can be monitored The temperature deviation signal which is proportional to the difference between the actual temperature and the null setting is also sent to the temperature COMPENSATION ADJUST This varies the gain on the temperature deviation signal to generate the desired sonic velocity related signal for compensation The adjusted signal is then sent to GodpEdnetion electronics where it is effectively added to the sonic velocity signal coming from the digital to analog converter A switch is provided to allow compensat
11. E 60 1 solids E f 58 4 solids g i lt 60 i B g 55 0 solids 0o oco B x 52 47 2 solids O L O_O 70 l 80 90 100 110 120 TEMPERATURE 9C Figure 12 Temperature Compensated Response for Liquor C l Group Project 3025 Page 35 Report One 16 72 68 S 64 58 9 solids o 00 69 Vy m E 60 S E56 T 51 7 solids 47 6 solids 80 90 100 110 120 TEMPERATURE 9C Figure 15 Temperature Compensated Response for Liquor Page 36 Group Project 3025 Report One different solids levels This would indicate that the amount of compensation needed is not a strong function of solids content The data in Fig 15 for Liquor A also show excellent temperature compensation The largest difference i output at any solids level is 0 4 of a unit on the meter over a 40 C temperature range There is a slight tendency toward a drop in indicated output at the high temperature end It should be noted that the TEMP pot was not adjusted for this particular liquor This would indicate that the effect of temperature on refractive index of Spent liquors is not a strong function of composition This could be important from the standpoint of industrial use of the instrument because a Simple setting of the TEMP pot based on laboratory tests could be adequate One final point should pe noted in connection with the slight deviation present in Fig
12. Page 9 Report One SOLIDS MEASUREMENT tea Direct measurement of solids content of liquor samples was used as a reference in interpreting instrument response Several m thods were used for these determinations including different ovendry procedures and a distillation method The most successful procedure was that taken from a final draft of a proposed revision of TAPPI Standard T 625 ts 64 Solids Content of Black Liquor as submitted to the Standards Editor of TAPPI in June 1969 In this procedure which follows many of the eumd T e Parker et al 2 liquor samples are dried at 1059C for a minimum of six hours An inert surface extender and a controlled flow of dried air are used to increase drying rate and eliminate moisture entrapment Strong black liquors are diluted to allow volumetric handling and to reduce scum formation Measurement of the solids content by the distillation method bonded to give slightly lower values of solids content than the ovendry method In order to keep a single Base for evaluating the instruments all of the data reported herein related to the NUS velocimeter or the EMC refractometer are based on ovendry solids values In the runs with black liquor in the flow loop liquors were progressively diluted to vary solids content The amounts of dilution water used were recorded and used to minimize uncertainty in measured solids values The method of doing this is described below It was assumed that the accu
13. adjustment of zero only adjustment of zero and span and adjustment of zero span and temperature compensation The first would require only amp single point calibration and the second a two point calibration The third would normally require only two different concentrations to set zero and Page 8h Group Project 3025 Report One span plus the freedom to vary temperature however the manufacturer recommends a three point calibration since the temperature compensation should be set at the mid range concentration say Examination of the data in Fig 26 showing sonic velocity vs solids data for the three different black liquors indicates that the major effect of composition changes will be amp zero shift The slope of the sonic velocity vs solids curves the span appears to be less affected If the instrument is set up to monitor solids over a reasonably narrow range say 50 60 solids then the main effect of composition changes would be a zero offset The proper corrective action in such a situation is a change in the LOW END ADJUST switches and not a change of the SPAN ADJUST pot When the liquor sample is taken for a laboratory measurement of the o d solids the s v deviations temperature attenuation and output readings should be recorded along with the settings on one pots and control switches When the true solids content Site becomes available it honid be compared with that obtained from the meter output The so
14. control console Fig 18 The probe contains the sonic velocity transducer while the control console contains the electronics and signal conditioning equipment The instrument also measures the temperature of the solu tion under test This measurement can be fed to appropriate circuits to provide a sound velocity signal which is compensated for temperature over a given range Figure 19 is a simplified block diagram showing the basic operation of the instrument The probe is inserted into the process solution and the transducer transmits and receives sonic pulses In the control unit the sound velocity electronics operate to produce the sing around frequency The S V electronics also monitor the attenuation of the sound pulse in passing through the solution The frequency and attenuation are examined and the information passed to the NORMAL and OUT OF RANGE lamps on the front panel The outputs from the S V electronics are the sing around frequency and the attenuation signal essentially amplitude ratio of detected and transmitted pulse The attenuation signal is routed to the front panel meter where it can be read The sing around frequency then passes through the SOUND VELOCITY RANGE selector apparently a frequency divider to a Scaling counter In the scaling counter the sound velocity signal is offset by the value set on the LOW END ADJUST switches These latter are set up to operate off an octal code The digital output of the scaling
15. for a delib erate comparison of the two methods The other set was taken with Liquor A during flow Laos tests and includes a eek estimate of the solids content taking into Eikos the amounts of dilution water added It can be seen that with Liquor C the distillation method Sanda to give consistently lower values of percent solids than does the ovendry method The disagreement between the two methods is less in the data taken with Liquor A although the distillation method does seem to give slightly lower values at high solids contents It should be emphasized that these tests were not intended to be a conclusive comparison between the ovendry and distillation methods No great pains to achieve maximum accuracy were taken gt a ERE Am x4 i C O Group Project 3025 Page 95 Report One Many of the tests were not run in duplicate However the tendency for the distil lation method to give somewhat lower values does appear to be real TABLE VII COMPARISON OF SOLIDS VALUES FROM OVENDRY AND DISTILLATION METHODS Ovendry Distillation Best Method Method Estimate Data on Liquor C solids 69 9 68 2 61 3 59 2 55 5 2 55 1 h2 5 40 7 36 9 35 1 28 3 25 5 15 9 13 1 Data on Liquor A solids 61 2 58 9 58 6 54 8 54 9 52 7 51 7 48 0 46 7 47 6 43 2 42 8 43 3 39 2 59 0 59 5 35 2 35 6 35 0 30 4 30 5 30 5 25 4 24 6 25 4 20 9 21 4 20 9 15 8 16 0 In interpreting the meaning of the apparently lower
16. not intended as a rapid or routine control method Tt may be used to calibrate such procedures One of the big drawbacks to oven drying procedures is the length of time needed to carry out the test TAPPI Method T 625 ts 64 called for a 24 hour drying s mmYr J H Page 88 I Group Project 3025 Report One procedure The r vised procedure discussed above would still require from 7 to 10 hours to obtain results In order to overcome this problem moisture balances combined with an infrared lamp for heating the sample are used for rapid drying and simultaneous weighing The weight loss can be followed continuously and the end point of very slow loss or constant weight easily determined The scale on these devices can be calibrated to read solids content directly provided one starts with a fixed initial weight of sample With such a balance a solids determination can be made in a fraction of an hour as opposed to the many hours required with the TAPPI procedure It is thus suitable for use in the mill as a routine method to enable operetors to rum a Pis furnace efficiently and safely operet tne moisture balance should be considered a derived method requiring dulibsation and not as a primary Aedes method Tha PERO js that the high liquor surface temperatures which are associated with the higher drying rate may lead to thermal decomposition formation of an impervious skin
17. overcome the problems mentioned above Parker et al discuss the latest Proposed Method in their paper In this revised procedure black liquor samples are dried at 105 for a minimum of six hours An inert surface extender such as sand or alundum and a controlled flow of dried air are used to increase drying rate and eliminate moisture entrapment Strong black liquors are diluted to allow volumetric handling and to reduce scum formation The procedure can be summarized as follows 1 Dry and weigh 25 50 g of inert material in a wide shallow glass container Add sufficient liquor sample to give 1 5 g of dry solids and weigh Add 10 20 ml of water to dilute and distribute samples in excess of 30 solids 2 Dry the liquor for a minimum of 6 hours in a gravity convection oven controlled at 1059C 59C with an air space of one cubic foot or less adapted to pass dried preheated air at a replacement rate of about twice per minute After E the initial drying and weighing drying is repeated for one hour intervals until the weight loss is less than 0 1 solids per hr 3 Duplicate determinations on the same sample should differ by no more than 0 3 solids It is important when using this procedure to keep the sample size within the recommended range An excessively large sample will lower the surface volume ratio of the liquor and lead to scum formation All tests should be run in dupli cate This procedure is
18. refractometer model BL 168 uses the principle of critical angle refractometry by which dissolved solids content is related to the refractive index of the solution The basic unit consists of a sensing head and control console Fig 5 The sensing head is mounted on the adapter installed in the process line and the process solution is viewed through a transparent window The surface of the solution which is in contact with the window is optically scanned by a motor driven octagonal prism The refractive index is determined by a beam of light from the prism which repeatedly sweeps at a varying angle at the surface of the solution At a point in the cycle as the angle between the incident light beam and the surface decreases the light beam instead of refracting into the solution is reflected back into the optical system The point of change from refraction to reflection depends on the refractive index of the solution and is known as the critical angle The prism scans the beam of light through the critical angle at the rate of 480 Hz A photodetector measures the alternating light and dark periods and its electrical output is used to provide a readout of refractive index in the required units R I concentration degrees Brix etc A principal advantage of this method is that it measures the index of refraction at the surface of the process solution Since the light beam does not penetrate into the solution the instrument can be used for opaqu
19. to a boil while stirring in the steam jacketed vessel The loop was then filled from the bottom by pumping the liquor from the vessel with the Moyno pump When the loop was filled the valving was adjusted so that the Moyno pump served as the circulat ing pump also In nearly all cases where a high attenuation of the sonic pulse occurred the problem could be ascribed to air bubbles In the flow loop there were no indications that black liquor itself became opaque to sound waves No discernible trend of increased attenuation with increasing solids content was observed The only evidence of liquor opacity was obtained in some beaker tests with Liquor C At temperatures of 40 C and solids contents above 50 attenuation of the sound pulse became significant This is apparently associated with the high viscosities of low temperature high solids liquors Otherwise the cause of high attenuation was air in the liquor Zacharias 3 has stated Bubbles and solid particles larger than 50 microns may cause erroneous readings Also emulsions containing large liquid droplets may be opaque to sound at high concentration levels and slurries with large quantities of suspended particles may scatter the sound excessively This could indicate that undissolved salt cake could also cause difficulties The rreobs nP the presence of undissolved salt cake were not tested for the reasons described earlier in the section on the refractometer BLACK LIQUOR MEASUR
20. 090 range would certainly appear adequate In all cases the compensated response has an S shaped characteristic The output rises more steeply over the midrange of temperatures than it does at either end The reasons for this behavior are not known but it should be noted that this occurs over a much wider temperature range than the hO F compensation range stated in the instrument specifications The basic response of the instrument general form of the curves was not significantly affected by changes in organic inorganic ratio The data in Pig 5 6 and T may be cross plotted to show output versus Solids content at fixed temperature levels These results are shown in Fig 8 9 and 10 It can be seen that a linear relationship between output and percent solids does exist for all cases shown In addition the lines for a given liquor Group Project 3025 Page 25 Report One 76 I Compensated 50 solids T 68 40 solids 6h e 60 E 30 E solids Uncompensated E 50 solids E 56 52 40 solids 30 solids 48 l hh e 20 LO 60 80 100 120 140 TEMPERATURE C Figure 5 Refractometer Output on Sucrose Solution E E eg ee ee Page 26 Group Project 3025 Report One 76 72 Compensated 40 solids 68 35 solids 2 6h H 3 30 solids 8 col p B e 25 solids i 5e Uncompensated 40 solids 35 solids 48 30 solids 25 solids 20 L
21. 15 The tempera ture range over which the tests were carried out 40 C is nearly twice as great as the 40 F range for which temperature compensation is claimed in the instrument specifications SYSTEM VARIABLES The effect of several other variables on refractometer response was also examined Flow rate through the refractometer adapter had no oouervable effec over the range from dead stop to 50 gal min The pressure in the system was varied from atmospheric to 60 p s i g with no observable effect on the reading The refractometer also aid not appear to be affected by the presence of air bubbles in the liquor This was most apparent in initial runs with Liquor C when the centrifugal pump was used In these cases liquor aeration was severe enough to prevent sonic velocity readings yet refractometer response was unaffected Stopping flow which would permit bubbles to rise also did not affect the response An attempt was made to see how the refractometer response was seege sea by undis solved solids This was not successful The main problem was finding a method Group Project 3025 Page T Report One for characterizing the amount of undissolved solids in a circulating loop A second problem was a tendency for undissolved solids to plug the pump COMPOSITION EFFECTS One of the main of this investigation was to gain some insight into the effects of liquor composition on refractometer response It is clearly Sh
22. EMENT There are at a minimum two requirements which must be met for the sonic velocimeter to be useful for measuring solids content of black liquor First the instrument must be capable of measuring sonic velocity in black liquor and second there must be a reasonable functional relationship between the sonic velocity of the Group Project 3025 Page 65 Report One liquor and the solids content The first question was alluded to in the previous section As long as air bubbles are not present in the liquor the instrument does measure sonic velocity and the black liquor is not opaque to the sound pulse The second question is best examined by determining ihe sonis eleit response curves of black liquor as functions of s lids ptenb ani qaqas s The most complete set of data on the sonic velocity response was obtained with Liquor A Some additional data were obtained with Liquor B When Liquor C was used in th flow loop the problem of EU liquor had not yet pesn solved In thes early runs the velocimebet HB out of range nearly all of the time and the only sonic velocity data on Liquor C ess obtained in small beaker tests at Loc The sonic velocity data on eigen d are shown Sp atro of temperature at different solids contents in Fig 21 Across plot of these data to show the dependence on solids content directly is regentes in Fig 22 Similar data for Liquor B are given in Fig 23 and 2h m f E There are a feature
23. In this evaluation study it was decided that more useful information could be obtained by minimizing pot adjustments than would be obtained by setting up the instrument to read solids directly for each Ti duo tested The emphasis is then on instrument response d a wide range of Naptubles including solids content rather than on deviations between meter reading and solids content In particular attention was focused on the items listed below 1 A determination of whether or not for a given liquor at a given temperature a linear relationship exists between the meter output and the solids content of the liquor If amp linear relationship does exist proper adjustment of the ZERO and SPAN pots would put the meter reading into a one to one correspondence with the liquor solids content 2 A determination of the ability of the temperature compensation circuitry to handle the effect of temperature changes on the refractive index For tempera ture compensation to be useful it should not be necessary to adjust the TEMP pot at different solids levels 5 A determination of the effect of liquor flow rate system pressure degree of liquor aeration and the presence of undissolved solids on instrument response Group Project 3025 Page 23 Report One h Examination of the relationship between chemical composition of the liquor and x the refractometer response In order to cover a wider range of variables than was possible in the fl
24. N pot adjusts the proportionality between the output reading 8nd refractive index The TEMP pot determines the amount of temperature compensation employed These pots are twenty five turn trim pots and are not susceptible to ready determination of pot settings Thus if a given pot is adjusted to a new value it cannot be easily returned to its original setting In commercial operation it is of course highly desirable to adjust the instrument so that the output meter reading corresponds to the true solids content of the liquor In order to do this a two point calibration is used to set ZERO and SPAN This should be carried out at a fixed temperature in the midrange of expected temperature variations A known value sample in the low solids range is put in and the ZERO pot adjusted until the meter reading corresponds to the known Page 22 Group Project 3025 Report One i value of the sample Next a known sample from the high end of the range is put in and the SPAN pot adjusted until the meter reading corresponds to the known value Since Bd aspen of the SPAN can affect the offset the Qosaqa may have to be repeated Note that ihis c iibration procedure assumes an essentially linear per tiene Pein the measurement refractive index and the percent solids The TEMP pot is adjusted to hows the meter reading constant as the liquor is heated or cooled Adjustment of the TEMP pot normar requires a readjustment of the ZERO also
25. O 1800 n a 56 1 solids 48 8 n N n Hg O 4 5 E 4 Oo E 21700 1600 160 180 200 220 240 260 280 TEMPERATURE OF Figure 25 Sonic Velocity Data for Liquor B Group Project 3025 Page 69 Report One O Q o Sonic Velocity meters sec HP q e o 1600 20 50 hO 50 60 70 LIQUOR SOLIDS Figure 24 Sonic Velocity ys Solids Content for Liquor B Page 70 Group Project 3025 Report One of temperature dependence shown in these data should make it easy to provide temperature compensation because little error would be introduced by linearizing a the curves over a 20 40 F range The relationship between sonic velocity and solids content is shown in Fig 22 and 24 The curves tend to be steepest and most linear at the low solids end and then bend over and Pedone curved and less steep at high solids Both linearity and steepness increase at lower liquor temperatures Slopes of the response curves for Liquor A span the range from 6 7 to 3 0 n sec solids At the low solids end linearization of the curves over a wide range of solids contents would be adequate At high solids linearization would be valid only over a small say 2 5 solids range of solids contents It is evident that the sonic velocity response of black liquor is surricient y straightforward to permit its use for monitoring solids content A comparison of Fig 22 with Fig 24 shows that co
26. O 60 80 100 120 140 TEMPERATURE C Figure 6 Refractometer Output on a 3 1 Suerose NasC0s Solution Group Project 3025 Page 27 Report One 76 72 Compensated 40 solids 68 35 solids ON 30 solids REFRACTOMETER METER READING ON o Mul ON Uncompensated 40 solids 52 35 solids 30 solids 20 40 60 l 80 100 120 140 a TEMPERATURE C Figure 7 Refractometer Output for a 1 1 Sucrose NasCOs Solution wawww rr cc rIssarrrrmacam Page 28 Group Project 3025 Report One 16 72 68 Compensated ON ON O F REFRACTOMETER METER READING MI ON Uncompensated 52 48 bby a ks 50 25 30 35 j 4O SOLIDS CONTENT Figure 8 Refractometer Output vs Solids Content Sucrose Solution Group Project 3025 Page 29 Report One 16 T2 1000c 800c 68 Compensated S 64 E vi ga B 5 60 E OPC 50 C O 56 8o c 1000c 52 Uncompensated 48 yh 25 30 35 40 45 50 SOLIDS CONTENT Figure 9 Refractometer Output vs Solids Content 3 1 Sucrose NasC0s Solution Page 30 Report One 16 68 ON ON o F REFRACTOMETER METER READING n ON 52 48 hh Figure 10 Group Project 5025 80 C f 5090 Compensated A 50 C o Ww N A 809c Uncompensated I 25 20 55 LO l5 50 SOLIDS CONTENT Refractometer Output vs Solids Content
27. Os NaCl sucrose NasS04 and oxalic acid Phenol has a high value for the solids content at which the measurement was made Examining these data there is no obvious ranking of e Page 38 Report One 139 INDEX OF REFRACTION 1 41 1 38 1 57f 1 36 Z Es 22 X 1 34 1 43 O Arte 20 PERCENT SOLIDS Oxalic Acid x lt Group Project 3025 Sucrose Liquor C Nacl Na2COs 50 50 Mixture of NasC0s and sucrose Sucrose Na2S04 E Oxalic Acid Phenol 50 Figure 14 Refractive Indices of Various Solutions Group Project 3025 Page 59 Report One organic and inorganic substances Liquor C which is mostly organic has the highest refractive indices sucrose is significantly lower while oxalic acid is very low Phenol on the other hand seems to have high values The inorganic compounds also vary considerably NasCOs is nearly as high as the black liquor while NasSO4 is much lower Further insight into composition effects can be gained by examining the behavior of mixtures This is most easily done with solutions of two pure compo nents but it is also enlightening to look at the addition of various amounts of a pure material to black liquor Both approaches were used in this study Refractive index data for various mixtures of sucrose and NasCOs at both 20 and 30 solids are given in Fig 15 It is seen that refractive indices of the mixtures li
28. The deviation is largest at the nes about 19C and is smaller in midrange about 0 5 C It should be noted that the instrument Sp ci fications make no claim on accuracy of temperature measurement What is specified Page 61 Group Project 3025 Report One S V DEVIATION READING 13h 900 134 800 134 700 COUNTER READING Hertz 134 600 1553500 27 28 29 30 31 32 33 l TEMPERATURE C Figure 20 Data from Stability Test on NUS Velocimeter Page 62 Group Project 3025 Report One is a repeatability of 0 059 and the ability to provide first order correction of sound velocity for temperature variations to within O 19C The instrument certainly appears capable of doing this Because of the reasonable agreement between the NUS temperature measurement and the thermocouple and the convenience of the NUS method the NUS instrument was used for all temperature measurement in the flow loop TABLE VI ACCURACY OF NUS TEMPERATURE MEASUREMENT Thermocouple Thermocouple NUS Temp NUS T C emf mv Temp 9C oc G 1 75 31 2 33 3 0 9 2 73 52 8 52 5 0 5 3 75 71 8 71 4 0 4 Mas 07 84 8 84 2 0 6 5 27 100 0 99 1 0 9 5 72 108 3 107 2 1 1 6 42 121 2 119 9 1 3 OPERATIONAL VARIABLES The effects of several operational variables on instrument response were examined These included the flow r te of liquor past the probe system pressure and the presence of entrained air in the liquo
29. URE C Figure 25 Temperature Compensated Response of Velocimeter Group Project 3025 Page 73 Report One COMPOSITION EFFECTS The investigation of the ertette of chemical composition on velocimeter response paralleled the study on the refractometer Figure 26 clearly shows that composition effects are present This curve shows the 1800F lines for Liquors A and B taken from Fig 22 and 2h The response curve for Liquor B lies below and to the right of the curve for Liquor A This same behavior occurs at other temperatures Thus at the same temperature and solids contents Liquor A gives a higher sonic velocity Sonic velocity data for Liquor C are also shown in Fig 26 Unfortunately these data were taken at 40 C 1040F so that a direct comparison with Liquors A and B cannot be made In order to make such a comparison the data in Fig 21 were used to estimate he change in sohic velocity with temperature from 180 to 104 F at various solids contents These estimated values were then sub tracted from the Liquor C curve to give an estimated curve for Liquor C at 1800F This latter curve is shown as the dashed line in Fig 26 This line indicates that Liquor C would give a higher value of sonic velocity than either A or B at the same solids content and temperature Thus the data indicate that sonic velocity decreases at a given solids level and temperature from C to A to B It is of interest that this is essentially the s
30. Under normal operating conditions the attenuation of the sound pulse was low on the order of 5 or less When bubbles were present the attenuation would rise to over 90 Under some conditions the attenuation reading might bounce from very high to very low values Pressurizing the flow loop to 60 p s i g did not overcome the air bubble problem It is not known if conditions could occur where aeration would cause significant changes in sonic velocity without also causing sufficient attenua P tion to trigger the out of range signal In all of these tests aeration did cause the out of range light to come on In thts program the biens Basocieted with aerated liquors were over come by preheating the liquor to a belie condition in the steam sss vessel see Fig 1 which allowea the air bubbles to rise to the top and by eliminating the use of the centrifugal pump for recirculation All of the liquors which were used in this program were aerated when received from the mills most probably because of aeration during direct contact evaporation The aerated nature of the CHO as received could be seen by USE ne the alkennste expansions and contractions in volume of a quer sample exposed to vacuum and atmospheric pressure Thus the EEE EE aaa Page 6 Group Project 3025 Report One problem with aeration in this program had to be solved by first deaerating the liquor and then M ass The deaeration was carried out by heating
31. a on black liquor are taken from the TAPPI data sheets It is obvious that the use of solution density to determine solids content is fraught with the same problem as is the use of sonic velocity or refractive index One advantage to the sonic velocimeter may be that the interpretation of composition effects appears to be much more straightforward than it is for the refractometer There seems to be a definite correlation between high sonic velocities for inorganic solutions and lower velocities for organic solutions Group Project 3025 Page 81 Report One Sucrose SPECIFIC GRAVITY 1 100 1 000 O 10 20 50 hO 50 60 SOLIDS CONTENT Figure 51 Specific Gravity Data for Various Solutions Page 82 Group Project 3025 Report One It seems quite reasonable to assume that the major variable affecting sonic velocity in black liquor is the organic inorganic ratio Although refractive index also responds to changes in organic inorganic ratio the dependence is not as clear cut or direct ON LINE CALIBRATION im changes in liquor composition affect the sonic velocity response and it is essential to avoid iHteropett s eompositional changes as changes in solids content it would be necessary to maintain instrument calibration during on line drerit As with the refractometer the major problem would seem to lie with f changes in the functional dependence of sonic velocity on solids content and temper amp ture ra
32. ae velocity Bid pressure as desired and observing tuo E den Poeran Liquor samples vei taken for off line solids measurement At the completion of amp uM the liquor would be forced back to the storage vessel by the gue iredsuricstion of the loop Water would be added at that point to reduce solids concentration the liquor heated to boiling and the procedure repeated The flow loop was used for a series of runs with industrial black liquors and some introductory runs with sucrose solutions Much of the work on the effect of composition on measurement TURA was made external to the flow ean The main reason for doing this was to cover a wider range of compositional variables than was possible in the flow Loop The difficulty with using the flow loop itself for studies of compositional effects was the relatively large volume of liquor Sequine about 15 gallons abd the time needed to make up a sample feed it into the loop and carry out Bru To ieseare sonic velocity the NUS probe was simply inserted into a beaker containing the P vith a water bath used for temperature control The EMC refractometer was not used in out of loop studies because the geometry of the adapter section was not suitable for this mode of testing Instead a laboratory refractometer was used to determine the effect of changes in composition on the refractive index The laboratory instrument was amp Bausch and Lomb Type 334558 refractometer Group Project 3025
33. alysis of solids content 5 The instrument should periodically be removed from the line for two point ZERO and SPAN adjustment and to check on the ability to compensate for temperature variations h The ealibration should not be changed to handle the effect of solids deposits on the window The window prism should be cleaned instead Group Project 3025 Page 49 Report One NUS VELOCIMETER PRINCIPLE OF OPERATION The NUS velocimeter provides an indirect determination of black liquor solids content through measurement of the velocity of sound in the liquor The instrument operates on the sing around principle for measuring sonic velocity A sound velocity transducer transmits a sound pulse through the solution under test to a reflector which is separated from ih fo nsduceP by a fixed distance x The pulse is then reflected back to the transducer which also serves to detect the pulse After detection of the reflected pulse a new pulse is transmitted and the sequence repeated The result is a train of pulses at a frequency sing around frequency which is dependent on the sonic velocity of the solution The sing around period time from the start of one pulse to the start of the next is determined by the sum of the pulse transit time path length divided by sonic velocity and the electronic delay time time between detection of one pulse and transmission of the next This results in the following equation re
34. ame order in which refractive index increases see Fig 11 In order to gain some insight into why these changes occurred sonic velocity data were obtained on some simple solutions and mixtures These data were obtained outside of the flow loop at 40 C Sonic velocity data were obtained for Liquor C various mixtures of sucrose and NasC0s NasS04 NaCl oxalic acid and phenol These data are shown in Fig 27 Several trends are apparent in these data The general form of the curves is somewhat nonlinear with an increasing Slope at higher solids content This may be contrasted with the data on black Page 74 Group Project 3025 Report One 1900 Liquor C 1800 ta a H O 9 B E z E O Q1700 Liquors A and B at 1809F Liquor C at 104 Dashed line is for Liquor C extrapolated to 180 F 1600 O 10 20 30 ho 50 60 SOLIDS CONTENT Figure 26 Effect of Liquor Composition on Sonic Velocity Response Group Project 3025 Page 75 Report One 1900 Liquor C am 75 25 1800 o Q n lt a 4 D p H Sucrose 5 H 9 d 1700 gt o n g A 1600 Mixtures of sucrose and Na2COs A Liquor C D NaCl Na2S04 gum eh X Oxalic acid xx amp Phenol 1500 0 10 20 50 ho 50 60 SOLIDS CONTENT Figure 27 Sonic Velocity Data for Various Solutions Page 76 Group Project 3025 Report One liquor in Fig 22 and 2h taken at higher temperatures and solids levels showin
35. ample is covered by solvent Since solids are determined from the amount of water present oxidation of the liquor after the initial weighing would not cause error unless water were produced Results are independent of the time of distillation once the end point is reached The time for carrying out an analysis about one hour compares favorably with the long times needed for oven methods Page 92 Group Project 3025 Report One 8 The distillation method is reproducible Measured amounts of water added to black liquor can be recovered quantitatively poi up A The distillation method would seem to be sound in principle It may be somewhat less precise than the TAPPI method because weighing the liquor and deter mining the amount of water are done only to within 0 1 gram However it should give correct results if carried out properly COMPARATIVE TESTS In this work both the ovendry and the distillation methods were employed for the direct determination of solids content Although all of the data presented on the refractometer and velocimeter are in terms of ovendry solids values the experience with the distillation method was quite good There was seeing in the course of making the tests that directly indicated one method was inherently more accurate than the other It is interesting to compare values obtained by the two methods Such i 4 data are shown in Table VII One set of data was taken with Liquor C
36. asurement of black liquor solids content These include instruments based on refractive index nucl ar attenuation specific gravity sonic velocity and vibration amplitude In addition the ammeter reading of the cascade evaporator motor drive is often used as an indica tion of liquor solids content In the proposal for this project it was indicated that a general review of the state of the art of black liquor solids ensein would be carried out This was to include a review of measurement methods instru ment manufacturers and the extent of application in the industry An extensive survey of the use of black liquor solids monitoring devices in the kraft industry has been recently carried out by the Instrumentation Subeommittee of BLRBAC 1 The following conclusions were reached Group Project 3025 Page 3 Report One l Instruments are available for successfully measuring black liquor solids concentration continuously These instruments have sufficient dependability amp ccuracy and reliability to permit their use in promoting safe operation of recovery boilers 2 Refractive index type instruments are more widely accepted and far more successful with less maintenance requirements than other types of instruments presently or previously used for this service 5 Refractometer installations have proven sufficiently reliable and accurate to be used for automatic alarming on low black liquor solids concentration 4 Th
37. cations Description of Instrument Instrument Checks Temperature Measurement Page O AN wi M 10 15 15 18 21 25 31 25 56 2T ll 45 49 49 50 51 58 60 iv Operational Variables Black Liquor Measurement Temperature Compensation Composition Effects On Line Calibration DIRECT MEASUREMENT OF SOLIDS CONTENT Residual Solids Methods Distillation Method Comparative Tests CONCLUSIONS ACKNOWLEDGMENTS LITERATURE CITED 62 6h E 15 82 85 86 88 95 9T THE INSTITUTE OF PAPER CHEMISTRY Appleton Wisconsin INSTRUMENTATION STUDY BLACK LIQUOR SOLIDS CONTENT SUMMARY A comparative evaluation of two commercial instruments for measuring black liquor solids content an Electron Machine Corporation refractometer and an NUS Corporation sonic velocimeter was carried out The study showed that both instruments have the capability of measuring black liquor solids The sonic xe odii tay is quite sensitive to air bubbles and would probably be limited to use before the direct contact evaporator unless Special provisions for deaerating the liquor were made Both instruments are sensitive to changes in chemical composi tion of the black liquor and would require frequent recalibration Procedures and limitations of on line calibration are discussed in the report The response of the velocimeter increases as the inorganic to organic ratio in the liquor increases The response of the refractometer to such changes
38. centrifugal pump was 100 g p m while the maximum capacity of the Moyno pump was about 10 g p m The heat exchanger was rated at 20 000 B t u hr and provided the capability to control temperature over the range from 60 to 140 C The loop was capable of being pressurized up to 140 p s i g A r A E was installed in the tee which hel the Sosa tuyo Once it was established that the temperature measurement in the NUS instrument was reliable the NUS temperature PENON was used for the bulk of the work n sample tap was provided immediately ahead of the velocimeter A This was used for taking samples for off line measurement of solids content PROCEDURES The normal operating procedure was to start with high solids liquors as obtained from the mills The semisolid liquor was scooped into the steam jacketed eT Page 8 l Group Project 3025 Report One storage vessel and heated to boiling while stirring When this point was reached all valves in the flow loop were opened the accumulator vent was opened to the 3 atmosphere and the liquer was then pumped slowly into the flow loop until the desired level in the accumulator was reached The storage vessel was then valved off the 8028 Sasawi d with nitrogen to the desired level bypass valves adjusted and circulation of liquor begun With black liquor the Moyno pump was used almost exclusively as the circulatory pump A run would theh be carried out aaku
39. cessary to set it up according to instructions provided in the instrument manual The liquor is brought to the desired midrange temperature and the TEMPERA TURE NULL set so that the temperature deviation reads zero The LOW END ADJUST switches are then set so that s v deviation reads zero The product temperature is then changed to an extreme point and the temperature COMPENSATION ADJUST turned to bring the output meter back to zero This inserts the correct amount of temperature compen sation The results of the compensation test are shown in Fig 25 It is evident that for the sample for which the compensation was set up number 1 excellent compensation is obtained over the 109C range There were no deviations over the compensated range With the progressively diluted liquors the instrument was overcompensating for temperature This simply reflects the fact that the sonic velocity vs temperature curves are not parallel but rather are steeper at high solids Thus the compensation settings are valid only for amp narrow range of solids content comparison of the compensated and uncompensated response shows that the compensation circuitry is indeed important Page 72 Group Project 3025 Report One High solids 1870 P Co NES o Co o SONIC VELOCITY meters sec Co H O X Uncompensated DN O Compensated Compensated a Range q o o 1770 60 70 80 90 100 110 TEMPERAT
40. ck liquor can be considered to consist of two substances something called liquor solids and water It is of course possible to make this distinction and the solids are then identified with the total nonaqueous constituents of the liquor However it is important to make a distinction between the nonaqueous constituents and the residual solids remaining after evaporation of the moisture from the liquor These are not normally the same since volatile matter other than water may be removed during evaporation Because of the loss of volatiles residual solids should always be less than the total nonaqueous constituents It is a somewhat philosophical question to decide which quantity is truly desired since black liquor is evaporated as part of the firing procedure No attempt will be made to resolve that question in this report Parker et al 2 discuss the measurement of black liquor solids in some detail They list two basic approaches to the problem The first and most common is to measure the material in the liguor which is nonvolatile under specific test Page 86 Group Project 3025 Report One conditions This might be called the residual solids approach The second amp pproach is to measure the water content of the liquor and calculate the solids by difference Residual solids Wekhods include those based on the use of drying ovens e g TAPPI procedures as well as the use of infrared lamps and a moisture balance e g Cenco moi
41. composition although some of the difference might be due to long term drifts in the instrument since the runs were carried out over amp period of several weeks A detailed discussion of composition effects will be given later however some E are of interest The lines for Liquor A and Liquor B are nearly parallel This is interesting because Liquors A and B were obtained from the same mill and according to the data in Table I have similar chemical compositions The differences between Liquors A and B could be taken care of simply by adjustment of the ZERO iiodor C which has a sigdi Pivantiy inorganic content and much more sulfur shows a different slope as well as an offset The fact that the line for Liquor C nearly parallels the line of direct correspond ence must be considered coincidental TEMPERATURE COMPENSATION The ability of the instrument to provide temperature compensation was examined in some detail At each solids content the temperature of the liquor was varied over a range of about 40 C and the compensated output recorded The results of these tests are shown in Fig le for Liquor C and in Fig 13 for Liquor A The small initial adjustment of the TEMP pot was made for Liquor C and it is clear that excellent compensation was obtained There was no observable change in the meter reading over the temperature range from 80 to 1109C for each of four Page 5h Group Project 3025 Report One 76 72 68 E 64
42. cording the output reading run an analysis of the liquor solids content and then adjust the ZERO pot to make up the difference between the indicated output and the analytical solids content If the effect of composition change is mainly to cause amp zero shift this procedure would be adequate The asda case is spe complicated because adjustment of the ZERO and SPAN pots requires a two point calibration and thus liquor analyses should be run at both the low and high ends of the concentration range This is not a very suitable procedure for on line calibration since it requires a significant change in liquor solids content and freedom to vary liquor solids does not usually exist in a mill situation The time lag in asya yu solids content in liquor samples also would cause problems in a two point on line calibration There are two alternatives which can be used here Either the A E would be calibrated off line adjust ing ZERO and SPAN or it would be calibrated on line adjusting only the ZERO In the first case two batches of liquor of known solids content would be used in the x normal calibration procedure The second approach could be used if the change in Under these conditions only small errors result if the ZERO is kept in adjustment There is a hazard in this second approach Over a period of time the SPAN setting may differ appreciably from the proper value and large errors could occur if there were large changes in solids content Fo
43. counter essentially the digital overflow beyond the offset is routed to a digital to analog converter The resulting analog signal is sent to the meter where it can be read as sonic velocity deviation and is also routed to the compensation electronics Page 52 Report One Group Project 3025 Photograph of NUS Sensing Probe Figure 17 Group Project 3025 Page 53 Report One SONIC PANON INTRO Eis NUSNC MODEN CJE3 Gee CIRO AEN Figure 18 Photograph of NUS Control Console LN S Xe48UroOT 23A SAN JOS werSetq OOT 6T IMIA NN p o Y bum o HOMME 0123126 HLM VILIN IWrollonns UNA e BNO 39n Ysoow GUVQNVIS a 22S MOF o 9X 8 304 Ui OO 4x do 226 E OS T 3x 226 MST ix SBorvy A112012A ANNOS loii s E UR E k m n A EH TE E AQ O andano dwat AAINO NOLLWIAIQ m OLLES iag SAIBA ACI O NOLUVIAG0 DYNI UJANI Ni n BALBBANOD BOWLION insano NOLayiARG i x 1N3Uun2 32N38313u Oi BOWLIOA Sunivuagvn wv E ann ASII o 12313 SWBTICULNOD NOUNSN34v05 1NIOd132S Tunivi24wW3l addo Po De S ts 01 03 F anws l ano Agi AQULNOS AQUINO 390u4 NOUVEN ISVO NN C mnivuidina m gunivu3awar 3univu3e 3i o uau au E ao o Sonya jazaa N3Quo 3s MUTO 21N0u12313 N Vu oz v OL 39w11OA PUITA QWnOS 44112013 MoO LV S N340 N02 e x ALIDONSA ANNOG Q31v9N34vt02 annos aom Q3LVENDS NONO Qalcneov mus kuti O15333S FONVU 1031N02 AVES o W
44. e sensitive to changes in chemical composition of the liquor The relationships of sonic velocity or refractive index to solids content and temperature are functions of composition Page 96 Group Project 3025 Report One Thus changes in chemical composition may be interpreted as changes in solids content of khe ue This can easily cause an error of several percent in the solids sdntent reading The velocimeter tends vo be quite sensitive e the E ratio of the Tiguors The sonic velocity increases nich would be interpreted as an increase in solids content as the inorganic cantent increases The Pelapionohip appears straightforward and may eventually be a pe to quantitative treatment of an empirical Gua The enfecg of p 19 changes on E response was more difficult to interpret It does appear that the reied TEN tends to EP which vould be interpreted as a decrease in solids content as the inorganic content increases This is the opposite direction from the velocimeter B cause of the composition dependence of the response of both shin nts it is EER RNN to recalibrate them bericiicafiy se account for changes in liquor composition The frequency of calibration would be dese nan on the experience of a given mill however it would appear that the instrument should be checked at least once each shift The procedures to be followed in changing the calibration on line are discussed in the body of the report and need not be repeated
45. e as well as transparent materials The optical system is shown in Fig h The light from the tungsten lamp source passes through a collimating lens and an aperture to give a narrow beam The octagonal prism rotated at 60 r p s causes the beam to oscillate as each face of the prism traverses the beam the light exiting from the prism is displaced by an amount equal to the width of the faces The cycle is repeated for each face Group Project 3025 Page 14 Report One Xe4euo4osd1joH OWA JO udexsogoud omBT psouy Sursu s Page 15 Report One Group Project 3025 939Uo4oe1jeH JO UDIS S TEDTI O JO or48Usuog y IMBP o 9ue pa oeryoy uoranTos Ssaoo4d IENNE b wstad aatyddeg P zeuugos ustad Sur4940M I Su T aqn BUTSNDOT T9A9J4 wesq JO UOI3909JI xzmaz dyv ae SUdST SUIj9UITTOO dure Page 16 Group Project 3025 Report One so that the frequency of oscillation is 8 x 60 h80 c p s This beam is focused at the interface of the sapphire prism and the process solution The effect of focusing is to cause the light to enter the process solution at an angle which varies as the light beam oscillates At the higher angles the light is refracted into the auiutios At the shallower angles the light is reflected through the sapphire through a lens assembly to the anais tania The ratio of refracted to reflected light varies with the refractive index of the solutions b
46. e between those of the pure substances However the curves are not aged This would mean that a simple linear combination rule based on the addition of the fraction of the refractive index of each pure substance would not predict the refractive index of mixtures Refractive index data for mixtures of black liquor with sucrose and sodium chloride are given in Fig 16 The data for liquor sucrose mixtures are at 60 solids For solubility reasons the data for liquor and salt are at 25 solids In both cases the refractive index increases as the proportion of liquor increases This is not surprising since the data in Fig 14 showed that both sucrose and NaCl solutions had lower refractive indices than Liquor C at the same solids content With liquor and NaCl a linear relationship is observed while amp curved relation exists with liquor and sucrose In general it appears that the refractive index of mixtures lies between the indices of the pure compounds but a linear combination of each component is the exception rather than the rule The tendency toward nonlinear combinations indices of each component not additive seems to increase as the solids content increases Page hO Group Project 3025 Report One 1 3924 1 388 40 solids 1 384 1 380 REFRACTIVE INDEX Xx 1 ON 1 368 i 20 solids 1 364 1 360 o 25 l 50 75 PERCENT SUCROSE OF SOLIDS Figure 15 Refractive Indices of Sucrose NasCOs Soluti
47. e carried out a comprehensive review of methods for off line measurement of solids content and have Uipeupped the PODIGNE involved The problems of accuracy in methods for merece Jeremia ion of black EPE solids are fundamental to the general problem of measurement of this quantity and will be discussed later in this report The major emphasis of this project was directed toward a comparative evaluation of two commercial instruments for black liquor solids measurement The two instruments which were chosen were as follows 1 An Electron Machine Corporation Model BL 168 Black Liquor Analyzer which is whe based on measurement of the refractive index of black liquor 2 An NUS Corporation Model 6161 139 Sonic Solution Monitor which employs a measurement of sonic enor tty of the liquor The evaluation was directed mainly toward the applicability of these instruments in on line measurement of black liquor solids and investigation of potential sources of errors in their use A major objective was a study of the effect of liquor composition on instrument response Group Project 3025 Page 5 Report One APPARATUS AND PROCEDURES FLOW LOOP The two instruments were installed in a flow loop which was constructed to permit simulation of on line operation A schematic diagram of the flow loop is shown in Fig 1 The instruments were mounted in amp vertical leg of the flow loop with the sonic velocimeter located
48. e refractometer did not bear markings which would indicate what the settings were it was not possible to verify that no changes were made A plot of the refractometer output meter reading versus liquor solids content is shown in Fig 11 for Liquors A B and C The line of direct corre spondence between the meter reading and the percent solids is also shown The indicated output is an average of the temperature compensated output over the temperature range covered at each point It is evident that a reasonably linear Page 32 Group Project 5025 Report One te 68 Liquor B 2 6u Liquor A E H E Liquor C m 6o m E O b 56 I Line of x Direct Correspondence 48 4 I lt hO s hh LIE EE 52 56 60 64 LIQUOR SOLIDS CONTENT Figure ll Refractometer Output vs Solids Content for Black Liquors Group Project 3025 Page 33 Report One relationship between refractometer output and solids content exists for all three liquors This would indicate that proper adjustment of the ZERO and BERN pete could shift any of these response curves into direct correspondence It must be emphasized that the fact that no response curve is in direct correspondence is to be expected since the necessary calibration procedure to bring this about was not employed The fact that the response curves are not identical is primarily an indi cation of the effects of liquor
49. eing measured The light and dark periods on the photodetector Srodu s a 480 Hz a c output from the device which is transmitted to the control console The function of the electronics in the console is to condition the signal so that the light and dark periods can be compared The resulting signal which is proportional to refractive index is used to drive the front panel meter which reads directly in percent solids The signal passes through a preamplifier the output of the preamplifier is squared the positive and negative portions averaged and compared by a differential amplifier the output of which drives the meter The signal conditioning provides an output which is dependent on light and dark periods reflection and refraction periods and hence the output is not sensitive to changes in the light intensity Temperature compensation is applied at the input of the differential amplifier This compensation is necessary because the refractive index of the solution changes with temperature The temperature is sensed by a thermistor located close to the sapphire prism on the sensing head An Heseron ain elbow adapter Fig 3 supplied with the petua tomate was used to mount the sensing head on the process line The adapter not only provides for physical attachment of the sensing head but also serves to direct the black liquor flow against the window Thus fresh liquor is continuously brought into intimate contact with the window This is im
50. er is distilled over The connection between the flask and the trap should be insulated to prevent condensation of water at that point so as to facilitate capturing all of the water in the collecting trap The temperature of the contents in the flask will remain close to the boiling point of water until essentially all of the moisture has been driven from the liquor Then it will rise to the Dolving point of the solvent The end point of the distillation is signalled by the rise in temperature and when the volume of the water in the trap no longer increases with time The volume of water in the trap is then read and the percent solids calculated The precision of the test is such that duplicate determinations should agree within 0 5 solids Parker et al 2 make the following comments with regard to distillation methods Allowable sample sizes are normally small and vary directly with the sample solids content Thus weak liquors with high moisture contents require smaller sample sizes to keep the amount of water distilled within the capacity of the collecting trap Consequently test accuracy varies widely as solids content changes Calibration and cleanliness of the apparatus are of utmost importance in the distillation methods rendering agreement between different laboratories some what difficult Page 90 Report One Odor trap gt gm Condenser Distilling trap H f X K q Insulation
51. ere remains a considerable need for improvement of instruments presently available and for the development of new techniques and or instruments for monitoring and control of black liquor solids concentration In view of the fact that a survey such as we had Soneenpia codon id duplicate the work done by BLRBAC and the fact that most sponsors of this project are members of BLRBAC it was decided not to carry out a survey Specific details of the mill survey are on file with the BLRBAC subcommittee and are available to any member of BLRBAC upon request We are not free to divulge the findings of that study All of the methods for continuous measurement of black liquor solids are indirect methods in that they measure some property of the black liquor which is dependent on solids content Thus they must ultimately be calibrated in terms of some method for the direct determination of solids content The accuracy of the continuous methods is thus ultimately dependent on the accuracy of the direct measurement and the calibration procedure employed Direct measurement of black liquor solids content is not completely straightforward Black liquor is amp complex Page 4 Group Project 3025 Report One I l o mixture of organic and inorganic compounds and at the present time there exists no laboratory method for determination of black liquor solids content which is accept able to all segments of the kraft pulping industry Parker et ale 2 hav
52. es who supplied us with the instruments and the liquors which were used Page 98 Group Project 3025 Report One Pech kB et LITERATURE CITED 1 Black Liquor Recovery Boiler Advisory Committee BLRBAC Instrumentation Subcommittee Report on use and application of black liquor solids monitoring devices BLRBAC Oct l 1969 2 Parker Je Le Hensel R P and Wagoner C Le Tappi 53 no 5874 7 May 1970 5 Zacharias E M Instruments and Control Systems 45 no 9 112 113 Sept 1970 4 Phillips J H and Rubright M M Tappi 36 no 9 392 Sept 1953 THE INSTITUTE OF PAPER CHEMISTRY T M L Research Associate Division of Materials Engineering and Processes Robert N Larsen Research Fellow Division of Materials Engineering and Processes N ll L y EES IES q E 6 a III E
53. f sonic velocity response data was obtained for each sample the instrument could be easily readjusted The calibrated dial settings on the velocimeter pots aid such an adjustment How ever it is not possible to run a full set of calibration curves on each sample and less data would be available for changing the calibration Normally only the actual solids content of the liquor sample and the velocimeter readings would be known The adjustments needed E set a calibration are a zero a span and the amount of temperature compensation employed The zero amounts to selecting a particular meter reading to correspond to a particular solids content usually the lowest expected and is basically determined by the LOW END ADJUST switch The span is the change in sate meter reading which corresponds to a given change in solids content usually selected so that the meter covers the full range of solids expected and is controlled primarily by the SPAN ADJUST pot The amount of temperature compensation is determined by the gain applied to the temperature deviation signal which is controlled by athe COMPENSATION ADJUST pot The setting of the S RANGE switch amp ffects both the Seo ard peti and would not normally be changed during a minor adjustment of the calibration The adjustments required to maintain calibration depend on the degree to which the sonic velocity response function has changed As with the refractometer this could take on three forms
54. g a decrease in the slope at higher solids values Another feature in Fig 27 is that all of the curves seem to be converging to about a value of 1525 m sec at zero solids content which is the approximate sonic velocity of water at this temperature Perhaps the most striking feature of these data is the distinct separation between organic and inorganic compounds Solutions of NasC0s Na2804 and NaCl all have high values of sonic velocity while the organics sucrose phenol and oxalic acid all have relatively low values of sonic velocity The curve for Liquor C containing organics and inorganics lies somewhere in between This behavior may be contrasted with the index of refraction data on thiene same materials Fig 14 which did not show trends of this nature The data in Fig 28 showing sonic velocities at various proportions of sucrose and NasC0s and those in Fig 29 for mixtures of black liquor and sucrose and NaCl all show the same basic response The sonic velocity of these organic inorganic mixtures increases as the inorganic content increases in a linear manner The sonic velocity of the mixtures is a linear combination of the sonic velocities of the pure components in all four curves This may again be contrasted with the data on refractive index which tended to give nonlinear results It should not be concluded that a linear combination law is generally valid for the sonic velocity of mixtures However it does appear that
55. hanical vibrations It was found that the sonic velocity deviation reading was unaffected by line voltage variations from 95 to 125 volts The reading was also unaffected by the presence of a magnetic field near the probe console or connecting cable Mechanical vibration had no noticeable effect on the meter reading It was noticed in a later test with the probe lying on a table that the arcing from a motor running nearby caused the meter to go off scale In this particular situation the probe did not have the benefit of being shielded by the mounting flange and tee section An overnight 24 hour stability check was run on the velocimeter concur rently with the test on the refractometer The results of that test are given in Table V TABLE V TWENTY FOUR HOUR STABILITY TEST ON NUS VELOCIMETER Time of S V Counter NUS Temp Day Deviation Hz 9 1650 0 0 154920 32 1 1940 0 5 134750 29 5 2240 0 7 134630 27 8 0805 0 9 134540 27 0 0900 0 9 134550 27 0 1015 0 9 134570 27 2 1200 0 8 134600 27 6 1300 0 7 134630 gt 28 2 1500 0 6 134690 28 7 Page 60 Group Project 3025 Report One The performance of the instrument was monitored by observing the readings on the sonic velocity deviation meter as a function of time Although the tempera ture compensation selector switch was turned off during this test the sonic velocity deviation r ading would not be affected by compensation anyway The
56. here If experience indicates that frequent adjustments of the calibration are necessary to maintain agreement between indicated solids and laboratory test values the instruments should be taken off line occasionally for a full recalibration It would appear that these two stpanente could be effectively operated in tandem so as to male use of the fact that they tend to respond in opposite direc tions to changes in danse Pr re This would certainly permit a distinction to be made between changes in solids content and changes in composition If both instruments responded together it would indicate real change in solids content On the Giles hand if they moved in opposite directions it would indicate a composition change It would appear possible that after a certain period of data Group Project 5025 Page 9T Report One logging use of a refractometer and velocimeter in tandem would permit simultaneous monitoring of solids content and inorganic organic ratio based on an empirical algorithm ACKNOWLEDGMENTS The SCE would like to acknmwitedge the following people who contributed significantly to this work Mr O C Kuehl and Mr A O Johnson erected the flow loop and helped keep it running Messrs H J Grady D G Sachs and C Piette assisted in taking data and running the liquor analyses Mrs E A Cary did her usual fine job in typing the manuscript We would also like to thank the paper and instrument compani
57. ich is unlikely it may be simplest to periodically recalibrate the refractometer off line with known solutions Changes in chemical composition of the liquor are probably the major reason for refractometers getting out of calibration The degree to which composition changes cause difficulty depends on the detailed effect of composition on response It is possible to distinguish three cases 1 A composition change that affects the actual value of refractive index at a given solids level hence the meter zero but has little or no effect on the change in refractive index per unit change in solids slope of index vs solids curve or span or the effect of temperature 2 A composition change that affects the slope and intercept of the refractive index solids curve hence zero and span but which does not affect the temperature coefficient 5 A composition change that affects the entire refractive index vs solids curve and the temperature coefficient hence zero span and temperature compensation The first case can be handled by a simple adjustment of the ZERO pot The second involves adjustment of both ZERO and SPAN pots and hence a two point calibration The third requires simultaneous adjustment of ZERO SPAN and TEMP Group Project 3025 Page 47 Report One The first case is readily adapted to on line calibration since it involves z single point calibration It is necessary only to take a sample of liquor while re
58. immediately below the refractometer The sonic velocimeter was mounted in a standard 4 in tee The refractometer was mounted on amp special Electron Machine elbow adapter which was furnished with the instrument The adapter was sized for a standard flanged connection to a l in process line The flow loop consisted of a circulating pump a heat exchanger the Heimen a pressurized accumulator and the necessary piping A steam jacketed vessel with an integral stirrer was used for making up liquors prior to their introduction into the flow loop This vessel could be sealed and evacuated to permit deaeration of the liquors before feeding them into the main loop A Moyno pump was used to pump the liquor from this storage vessel into the test loop In the initial configuration of the flow loop a La Boor centrifugal pump was used as the only circulating pump with the Moyno pump used solely for feeding liquor to the system In order to avoid the possibility of introducing air into the system at the centrifugal pump the piping was changed to permit using the Moyno pump as a circulating pump as well as a feed pump In the final configuration either the centrifugal pump or the Moyno pump could be used as a circulating pump The accumulator located at the high point in the loop was simply a cylindrical pressure vessel 10 in i d and 30 in long with a side arm attached halfway up for incoming black liquor A sight gage was installed to permit
59. ion upward or downward as needed as well as to shut off the com pensation The signal from the compensation electronics is sent through SPAN ADJUST another variable gain and then to the output position on the meter This last gain adjustment allows the operator to increase readout resolution or to set up the reading for a particular set of units such as percent solids The output meter has a dial indicator with two ranges on the dial 10 to 10 and Oto 10 The signal which is being displayed on the meter is con trolled by a METER SELECTOR switch The four funetions which can be monitored are as follows 1 S N DEVIATTON This reading in conjunction with the SOUND VELOCITY RANGE selector zas sa His deviation in the sound velocity from the value dex it dfe LOW END ADJUST switches The value on the meter 10 full Sente should be multiplied by the setting on the SOUND VELOCITY RANGE selector for a true sound velocity deviation Page 56 Report One 2 Group Project 3025 ATTEN This displays the attenuation of the sonic pulse in the solution in percent of full seale If attenuation exceeds 90 measurements should not be performed TEMP DEVIATION This displays the deviation in temperature up to 10 C of the solution from that set on the TEMPERATURE NULL control OUTPUT This displays the sonic velocity deviation signal after temperature compensation if selected and after SPAN ADJUST This would e
60. is less distinct but t nds to be in the opposite direction This leads to the possibility that use of the two instruments in tandem could provide a means for detecting changes in liquor solids content and in chemical composition simultaneously Page 2 ETT x Group Project 3025 Report One INTRODUCTION Reliable continuous measurement of black liquor solids content is a Subject of considerable importance to the pulp industry The solids content of liquor Tnerogucen into a Eecovery furnace can have a pronounced influence on firing behavior Current treads toward better control of the recovery ande for reasons of RIEN and reduced s emissions require a rester degree of control over incoming solids content ana appropriate adjustment af operating conditions to handle varia tions in solids s content This in turn requires a reliable eoa qux continuously monitoring solids du ten An mposntane factor influencing the need for on line measurement of solids content is the recommendation by BLRBAC Black End Recovery Boiler Advisory Committee that a inimigo tida content of 55 be eines on firing to avoid Puy bev ss explosion hazards The need for solids measurement is nat restricted to high solids liquors connected with furnace operation There is niso a need for solids measurement on weak Liquors to permit con ros of NAHE or End solids concentration pi a He ae furnace enye seges A number of devices are available for on line me
61. land O Chemical Rubber Pub lishing Co 1958 Page lh I Group Project 3025 Report One Composition effects would certainly be an important factor in the reliability of refractometers in the field since changes in composition could be read as changes in solids content It appears very likely that a change in organic inorganic ratio would change the refractometer response Wood species and pulp yield would also play an important role The effects of chemical composition re emphasize the need for proper calibration during use REFRACTIVE INDEX MEASUREMENT An interesting observation was made during the refractive index measure ment with the laboratory peppaceancter There are two methods for determining refractive index with such a refractometer In the first method an incident beam of light shines through a thin film of the solution and the beam of light emerging on the other side is observed through a lens system This lens system is rotated until the critical angle appears at a a of cross hairs in the eyepiece What the observer sees is a circle with the cross hairs at the center and when set properly the lower half of the circle is dark and the upper half is light The only differ ence in the second method is that the incident beam of light is on the same side of the solution as the observation lens system This permits the observation of opaque solutions and this is the same type of arrangement as is used in the EMC refractome
62. lating the ns sonic velocity to the sing around frequency T Bf dg where c sonic velocity in meters per second A sonic path length in meters B electronic delay time in microseconds aq coefficient of thermal expansion of the velocimeter probe material c 7 t temperature C and f sing around frequency hertz t L SL LIGLGLLLLU ULULLLUOOGOGLUGGLLUAGLSLILL IU COS X ZZ Page 50 Group Project 3025 Report One The factor of 7 appears in the denominator because the actual frequency is electron ically multiplied by 7 in the instrument SPECIFICATIONS The manufacturer gives the following specifications on the Model 6161 159 Sonie Solution Monitor which was tested in this program Sound Velocity Range 900 to 2250 meters sec Operating Temperature Range Probe 20 to 12090 Electronics Oto 50 Output Sound velocity 4 20 milliamperes and 0 10 volts Temperature 4 20 milliamperes and 0 10 volts Repeatability Sound velocity 0 025 Temperature 0 059 Temperature Compensation First order correction of sound velocity for temperature variations to within O 190 Compensation coefficient is continuously adjustable from O to 10 00 meters second c Probe Material 316 SS platinum and teflon Group Project 3025 Page 51 Report One DESCRIPTION OF INSTRUMENT The instrument consists of a sensing probe Fig 17 which mounts on the process line and a
63. mperature compensation Continuous over full range adjusted to compensate within 0 1 over 20 F range specified by customer Page 18 f Group Project 5085 Report One Although the instrument is factory calibrated there are several adjust ments provided in the control console These are a ZERO and SPAN to calibrate the lower and upper ends of the meter scale TEMP to provide the proper temperature compensation for the solution being measured and AGC automatic gain control which insures that the circuit is operating in the proper range The operating and service manual which is provided with the instrument NE simple instructions for making these adjustments If a major sands in the range iu desired the manufacturer recommends uso De instrument be returned to the factory for secutis bration since this requires a mechanical adjustment in the optical system No information is available as to the life expectancy of the various components in the instrument However the manufacturer recommends that the following spare parts be keston hand exciter PEET transformer phototube prism motor encapsulated ocean module fuses and replacement printed circuit Mie cards INSTRUMENT CHECKS At the start of the program several tests were made on the effect of environmental conditions on the refractometer These included checks on the effects of line voltage aieticad TR magnetic fields and vibration A twenty fou
64. mposition of the black liquor affects sonic velocity response also The curves for Liquor B fall below and to the right of Liquor A This means that at the same solids content and temperature Liquor A gives a higher sonic velocity than Liquor B This effect of composition has several implications First of all it is fruitless to attempt to discover an algorithm for describing the concentration and temperature dependence of sonic velocity in black liquor because it would change with each change in liquor composition Secondly since liquor composition would be expected to vary it would be necessary to continuously maintain calibration during on line operation Composition effects will be discussed in more detail a little later as will the problems of on line calibration Group Project 3025 Page 71 Report One TEMPERATURE COMPENSATION The effectiveness of the temperature compensation circuitry which is provided in the velocimeter was checked over the specified temperature range of 10 C using Liquor C and a midrange temperature of 90 C The adjustments of the amount of compensation were made on a high solids content liquor which was then progressively diluted Unfortunately no direct determinations of liquor solids content were made for this series and so all of the data are on a relative basis ranging from about 60 solids down to 30 solids The temperature compensation is not a factory calibration ana it is ne
65. nable the operator to monitor the concentration of the solution after the instrument has been adjusted controls which are available to the operator include the following SOUND VELOCITY RANGE Selector This brings the Control Unit into the mode most compatible with the sound velocity range of the solution under test This control works directly with the S V DEVIATION display LOW END ADJUST Switches These Shave the operator to select the operating range of the instrument by offsetting the sound velocity span which is below the low range of the solution being monitored The numbers on the switches which are in octal may be used together with the S N DEVIATION reading to determine an actual sound velocity value TEMPERATURE NULL Control This enables the operator to select the average temperature to which readings are corrected This control in conjunction with the TEMP DEVIATION reading permits determination of the process temperature Group Project 3025 I Page 57 Report One 4 TEMP COMP SELECT This is a switch that connects or disconnects temperature compensation and also the polarity of the compensation for a positive temperature coefficient and for a negative temperature coefficient 5 COMPENSATION ADJUST This enables the operator to set the correct amount of temperature compensation After the setting has been made the control scale will indicate the temperature coefficient of the Solution
66. nic TEA disperdmos associated with any discpepe ancy between the indicated and true solids content should be calculated and used to make the necessary change in the LOW END ADJUST switches This E not be the simplest procedure because the switches are based on an octal code and a base conversion would be niicishky over period of ime otis procedure may lead to significant error in the span and the dudas should be taken off line for full recalibration of zero span and temperature Gol penas bon according to the manu facturer s recommended procedure Group Project 3025 page 85 Report One DIRECT MEASUREMENT OF SOLIDS CONTENT A common theme running through much of the Previous discussroH is that the Instrumental methods for determining solids content are indirect peruse passes on the measurement of some property dependent on solids content and that these instru ments must be calibrated by means of a direct measurement of solids content Regardless of the stability ana precision of these instruments their ultimate accuracy is no greater than the accuracy of the solids determination iue in calibration Since all methods for monitoring solids content are ultimately based on some direct method some attention must be paid to this subject This report on the refractometer and velocimeter would be incompiete without some discussion of direct measurement of liquor solids The use of the term solids content or concentration implies that bla
67. nics The tests were carried out at several solids levels and over a wide range of a temperatures Both uncompensated and temperature compensated outputs were obtained The results for tests on sucrose solutions solutions containing 3 parts of sucrose ee Page 24 Group Project 3025 Report One I dE to 1 part of NasCOs and solutions containing equal parts of sucrose and NasCOs are shown in Fig 5 6 and 7 There are several interesting features of these data The offset due to temperature P E S is clearly shown This is the reason a change in the TEMP pot would normally require a readjustment of ZERO It also shows why the tempera ture compensation should be connected and the temperature held at the midpoint of the operating range when setting ZERO and SPAN It is also clear that the instru ment is overcompensating for the effects of temperature in these runs This is not surprising since the TEMP pot was not set to provide the correct amount of compensa tion for these solutions The uncompensated responses are nearly linear functions of temperature over the range tested There is however amp tendency for the output to drop more steeply at the high temperature end The only exception to this behavior is the set at 0 solids of the equal parts sucrose NasC0s solution The reason for this anomalous behavior is not known The degree of curvature of the uncompensated curves is not very extreme and a linear approximation over a 3
68. o the front of the sensing head away from the flow loop did not affect the reading Locating the field near the console unit and the interconnecting cable did not affect the reading The vibration test vis run by AT SS a Lightnin model F motor with an off centered shaft to a flange on the refractometer adapter in the loop r Sufficient vibration was produced to be felt at both the refractometer sensing head and at the NUS probe mounted below The vibration did not affect the refractometer rea ing x Page 20 Group Project 3025 Report One The twenty four hour stability check was run by allowing the system to stabilize for two hours and then taking readings periodically The temperature compensation on the refractometer was disconnected for this test The reason for this was that the temperature compensation pot was adjusted for a black liquor while a sucrose solution was used for the test The results are shown in Table III TABLE III STABILITY CHECK ON REFRACTOMETER Time Refractometer Output Temperature hr min solids I oc 16 30 53 4 32 1 19 40 52 55 29 5 22 40 55 64 27 8 8 05 53 7 27 0 9 00 55 7 27 0 10 15 55 7 27 2 12 00 BAT x 27 6 13 00 55 0 28 2 15 00 53 7 28 7 In general the stability of the output over a twenty four hour period is quite good The slight increase in rea ing corresponds with a decrease in tempera ture as the sucrose solution responded to changes in ambient temperature
69. of correlating refractive index data fv ebaapie compounds by means of an R factor is described in Table IV Higher R values give higher refractive indices It should be noted that the presence of double or triple bonds aromatic structures and rings tends to increase R values It is especially interesting to note the high R values associated with sulfur bonds The following generalizations although by no means proved are consistent with all of the data examined An increase in the inorganic content of a black liquor will tend to lower the refractive index at a given solids content An increase in organically attached sulfur will tend to increase the refractive index The main contributor to the refractive index of black liquor is of ligneous origin Group Project 3025 Page 43 Report One TABLE IV REFRACTIVE INDEX OF ORGANIC COMPOUNDS The following equation can be used to correlate refractive indices of organic compounds s t n 1 M R lt n 2 a where n index of refraction M molecular weight and d density g cc R in units of ec mole is additive for bonds which are present A partial tabulation follows C 2 591 C H 25 463 ethylenic bond 1 575 5 H 1 028 Cy ofl 43 00 acetylenic bond 1 977 0 2 122 gt s 7 729 4 member ring 0 317 gt o 1 643 s 7 921 3 member ring 0 614 OH 2 553 Taken from Handbook of Chemistry and Physics 4th ed C D Hodgman ed Cleve
70. ons 100 Group Project 3025 Page 41 Report One 1 50 1 48 O iquor Sucrose 60 solids 1 46 E 1 44 z fa g H 1 42 m 1 40 n Liquor Nacl 1 38 25 solids 1 36 1 34 O 20 hO 60 80 100 PERCENT LIQUOR OF SOLIDS Figure 16 Refractive Indices of Mixtures of Black Liquor and Other Substances Page 42 Group Project 3025 Report One It is impossible to make any quantitative predictions about the effect of liquor eomposition on refractive index Black liquor is simply too complex to permit this The organic material originates from lignin and carbohydrates in the wood and is at least partially substituted with sodium and sulfur In addition there will remain a aortara amount of cooking chemicals Thus the composition and refractive index of the black liquor would depend on wood errr as well as cooking conditions The most simplistic treatment of liquor would have to consider it made up of a ligneous fraction aromatics EP E E fraction sugars and the inu indo NaOH NasCO3 NaS etc If it is assumed that black liquor can be described in this manner then the data in Fig 1h 15 and 16 would Seem to indicate that the high refractive indices of black liquor originate mainly with the ligneous material The inorganies tested and sugar sucrose all lie below the black liquor line Phenol on the other hand an aromatic compound lies almost on the black liquor curve A means
71. or oxidation of the liquor Parker et al state th t use of the so called moisture balances for rapid drying and simultaneous weighing have been evaluated with ambiguous results It would appear that the moisture balance is suitable for monitoring the more indirect methods refractometers velocimeters etc in order to detect drifts and as a check on sudden changes However etui pices in the calibration should be based a more accurate procedures DISTILLATION METHOD Distillation methods for moisture analysis in pulp paper board and other materials are well known and have been applied to black liquor analysis Basically the approach consists of distilling off the water from the liquor in the presence of an organic solvent and collecting it in a trap From the amount Group Project 3025 Page 89 Report One of liquor originally present and the amount of water collected the solids content can be caleulated A schematic diagram of the apparatus for determining solids content by the distillation method is shown in Fig 32 A weighed amount of black liquor is introduced into the flask along with the solvent The distilling trap is initially filled with solvent Upon heating both solvent and water are vaporized in the flask and recondensed up in the condenser As the condensate drops down the denser water collects in the trap and the solvent is refluxed to the flask The procedure is continued until all of the wat
72. ow loop data from a laboratory refractometer were used to complement data from the EMC instrument regarding these effects The instrument as obtained vas factory adjusted for a particular high solids black liquor The instrument checks discussed previously were made with the loop filled with a sucrose solution The ZERO was adjusted at that time to obtain an on scale reading Initial runs were carried out with sucrose NasCO3s solutions of various proportions and with temperature compensation connected and disconnected At the start of these series of runs the ZERO and SPAN pots were adjusted to keep the meter on scale ver the temperature range employed The SPAN pot adjustment was relatively small At the completion of the sucrose NasCOs runs actual black quer was used in the loop Liquor C was the first liquor tested The ZERO pot was adjusted to give a meter reading corresponding to a preliminary estimate of solids content The TEMP pot was given one turn counterclockwise The SPAN pot was not adjusted These pot settings were then held constant for all remaining I tests The TEMP pot was given one turn clockwise at the completion of the program to restore its original setting BASIC INSTRUMENT RESPONSE The initial runs were carried out with specific mixtures of sucrose and Sodium carbonate These were done to obtain some idea of the basic response of the instrument with simple one and two component solutions of organics and inorga
73. own in Fig 11 that liquor composition can have a significant effect At the same actual solids content Liquor B gives a reading which is 2 6 units higher than Liquor A This is of particular interest since both A and B were obtained from the same mill only five weeks apart and the data in Table I indicate only minor differences in composition Based on the sulfated ash determination the organic content of Liquor B is 67 4 while that of Liquor A is 66 0 In addition there is a slightly piece degree of oxidation of the sulfur compounds in taquer B The response line for Liquor C is generally below th other two curves and hee a smaller slope Liquor C is from a different mill has a smaller organic content and a higher M E than A and B Thus it is not too surprising that its response curve has a different slope In order to gain greater insight into this behavior the refractive index was measured as a function of solids content for several solutions including single components and mixtures These data were taken on the laboratory vebractoneter described previously at a constant temperature of 28 C Refractive index data were obtained for Liquor C and for solutions of NasC0s sucrose a 50 50 mixture of NasCOs and sucrose NaCl Nag2S04 oxalic acid and phenol These data are shown in A Fig lh It can be seen that Liquor C has the highest values of all the substances tested Refractive index values fall off in the order NasC
74. portant because the index of Group Project 3025 Page 17 Report One refraction of the liquor is measured at the solution window interface nd misleading readings could be obtained with a relatively stagnant film of liquor hext to the window The turbulence associated with the jet of liquor impinging on the window also helps to minimize the build up of deposits It is necessary to provide cooling water for the scanning prism motor There is also provision in the hesd for a steam purge nozzle for cleaning deposits B from the Window In this evs iuation ho use was made of any prism cleaning apparatus and the ARTT was simply plugged There was never any indication of deposits during the test period and the window was found to be clean whenever the head was removed from the loop The unit is factory calibrated for each specific application and the manufacturer states that it normally requires no adjustment when installed The unit which we evaluated was factory calibrated to read percent solids over the range of h5 to 75 and the temperature compensation was set for a particular liquor Manufacturer s specifications for the instrument are Range 1 2 to 1 7 R I converted to indicate percent soluble solids within this range Accuracy 1 meter span standard meter spans 5 soluble solids 10 soluble solids 20 soluble solids 40 soluble solids Response time 1 0 second Solution temperature range O to 400 F Te
75. r It was found that the instrument was unaffected by variations in liquor velocity past the probe over the range from O to 5 ft per second A small effect due to system pressure changes was found This was observed with Liquor A at 15 solids and a temperature of 27 9 C Increasing the total pressure in the system from O to 60 p s i g caused an increase in the sing around frequency measured by the counter from 131 770 Hz to 131 800 Hz or an increase in sonic velocity of 0 023 This would amount to a change in sonic velocity of about 0 0004 per p s i This observed effect seems to be quite small Group Project 3025 Page 63 Report One and would not seriously affect the use of the instrument If maximum measurement precision is desired variations in total pressure should be avoided It should be noted that a pressure effect was not unexpected since sonic velocity depends on the density and bulk modulus of the solution and these could be pressure dependent Entrapped air sesta affected the operation of the velocimeter partic ularly at high solids contents Aeration of the liquor resulted in an attenuation of the sound pulse by more than 90 thus causing the out of range light on the front panel to come on In all cases when air bubbles were present the instrument went out of range rather than simply giving an erroneous reading Observation of the attenuation signal provided a ready means of detecting aeration problems
76. r example if a liquor is being monitored at a normal solids content of 65 and the calibration is maintained by ZERO adjust ment only there could be considerable error at solids contents on either side of 65 such as at 55 solids for automatic alarming purposes If ZERO adjustment x calibration is used the instrument should be taken off line occasionally for ZERO and SPAN adjustment m UT c nn ca Page h8 Group Project 3025 Report One In the third case where composition affects the temperature coefficient also the instrument must almost certainly be taken off line for recalibration The interaction between ZERO and TEMP settings and the need to cycle temperature practically requires off line operation Fortunately the indications of this test program were that composition changes had a relatively small effect on the amount of temperature compensation needed It would appear that the TEMP setting should be checked occasionally when the instrument is pulled off line for two point ZERO and SPAN adjustment The following summary statements regarding calibration of the refractometer can be made 1 The absolute accuracy of the refractometer in reading percent solids is deter mined primarily by the accuracy of the analytical procedure for solids measure ment employed in calibrating the refractometer 2 The only suitable method for on line calibration is adjustment of the ZERO pot based on single point an
77. r hour stability check was also run All of these tests were run with the loop filled with a sucrose solution but with no circulation In the test of the effect of line voltage on instrument response the instrument was plugged into a 15 amp powerstat The output of the powerstat was monitored with a GE type P 5 voltmeter The loop was filled with a sucrose solution and Ciera pened ouster was adjusted to read about 53 solids with the temperature compensation disconnected The solution was at a temperature of 35 C Group Project 3025 Page 19 Report One The line voltage was adjusted from 95 volts to 125 volts The results of this test are shown in Table II TABLE TI EFFECT OF LINE VOLTAGE ON REFRACTOMETER OUTPUT Refractometer Output Line Voltage Temp Compensation On Temp Compensation Off volts solids solids 115 53 1 56 8 7 105 53 1 56 8 95 55i 56 8 a 125 53 1 56 8 115 53 1 56 8 It can be seen that variation in the line voltage between 95 and 125 volts had no effect on the meter reading In order to check the effect of stray magnetic fields a coil of wire connected to a 60 cycle line was used to generate the field and this was moved to various locations around the probe and console The only location of the field that affected the instrument output was at the top and side of the probe sensing head In this case the reading was increased from 53 1 to 53 6 Placing the field t
78. racy of the solids determina tion improved as the liquor became more dilute and so the most dilute liquor was used as a base The working equation for the solids smoothing was Page 10 Group Project 3025 Report One where X solids content of Iun sample x total solids in loop at end lb W katai water in loop at end lb and A dilution water added from ith sample to end lb i Inverting Equation 1 gives A 1 W i We ae Pa 2 1 or A 1 W i 1 3 i Equation 3 was used to minimize the uncertainty in the solids data The solids content Xi and the amount of dilution A were measured quantities A plot of x l vs was then made The best straight line consistent with a acusa estimate of the initial solids X which relates to the slope and the greater reliability of low solids samples was used to determine the set of values of solids content in the runs An example of this method of handling the solids data is shown in Fig 2 These particular data show an excellent agreement between measured solids content and amounts of dilution water The agreement was generally poorer with higher solids content liquors LIQUOR ANALYSIS Three different commercial liquors were used in the tests Two liquors labeled A and B were obtained from a southern kraft mill pulping southern pine to high yiel and mixtures of pine and hardwoods to low yields Liquor B was obtained
79. s which are apparent in these data The sonic velocity EE With Femera over the full t Wperature and solids range Curves of sonic velocity vs temperature Bre steepest and essentially linear at the highest solids contents and become less steep E tens ued at the low solids end No maximum in iU ents velocity the curve was observed over the range of variables tested These data indicate that the temperature dependence of sonic velocity in black liquor is better behaved than might be expected Zacharias 3 says that aqueous solutions or emulsions generally exhibit nonlinear character istics in which velocity increases to some maximum value and then decreases As Bonssntpcti H increases the velue of sound velocity would change so that the maximum would occur at lower comera ME data in Fig 21 and 23 show that if a maximum exists at all it exists outside the range of normal interest The kind Page 66 Group Project 3025 Report One 1900 1800 f 1700 SONIC VELOCITY meters sec 1600 140 gt 160 180 200 220 240 260 TEMPERATURE OF 2 Figure 21 Sonic Velocity Data for Liquor A Group Project 3025 Page 67 Report One 1800F 1900 2009F 2200F 2400F 1800 meters sec SONIC VELOCITY 1700 1600 10 20 30 hO 50 60 TO SOLIDS CONTENT Figure 22 Sonic Velocity vs Solids Content for Liquor A Page 68 Group Project 5085 Report One 1900 oO
80. setting of the low end adjust switches The percent attenuation of the sonic pulse sent through the solution This is read directly on the meter when the meter selector switch is set on attenuation Temperature of the solution in degrees centigrade This is obtained by reading the temperature deviation on the meter adding it algebra ically to the vernier reading on the temperature null control dial and adding 20 A temperature compensated output proportional to some quantity which in turn is proportional to sonic velocity such as percent solids This would be read directly on the meter after proper calibration and adjustment of the S N range switch low end adjust switches tempera ture compensation adjust and the span adjust In addition to the outputs and controls normally provided with the instru ment amp connection was made to tap the sing around frequency signal and send it to a Hewlett Packard 5512 A digital counter This provided additional information and a way to get sonic velocity data independent of the meters INSTRUMENT CHECKS A series of checks on the effect of environmental conditions on the NUS velocimeter were carried out simultaneously with the checks on the refractometer Group Project 3025 Page 59 Report One described previously These runs were made with sucrose solution in the loop and included tests on the effects of line voltage variations stray magnetic fields and mec
81. sonic velocity is more susceptible to linear addition of each component than refractive index On theoretical grounds the sonie velocity c in any liquid is related to density p and bulk modulus B the reciprocal of GonigrebadUi lity by the expression c B p 2 In order to gain some understanding of what duas occur in solutions the sonic velocity data were plotted versus specific gravity as shown in Fig 30 These data show that the sonic velocity increases as the specific Group Project 3025 Page 77 Report One 1900 25 solids 1800 O n ao HT D 4 U H E 20 solids l O Q B 1700 O E Q Ww 1600 1500 I m o 2o hO 60 80 100 NasCOs PERCENT SUGAR ON SOLIDS Sucrose Figure 28 Sonic Velocities for Sucrose NasC0s Solutions Page 78 Group Project 3025 Report One 2100 2000 Sucrose liquor 60 solids o O n a n Q 42 o HB 1900 z E oO O O n 1800 8 O I NaCl Liquor O 25 solids 1700 o 16 7 33 3 50 66 7 83 3 PERCENT LIQUOR IN SOLUTE Figure 29 Sonic Velocities of Mixtures of Black Liquor and Other Substances 100 a Group Project 3025 pa Q o SONIC VELOCITY meters sec 1600 o Phenol 1500 1 000 Figure 50 Page T9 Report One o Na2S04 Liquor C Sucrose 1 2000 1 1000 SPECIFIC GRAVITY Sonie Velocities as Functions of Specific Gravity Page 80 I Group Project 3025
82. sponse js a monotonically inenesaine function SP solide content which can be Yineafi ed over reasonable concentration Jonges The effect of tenperatur on the response is sufficiently ER o eee so that temperature compensation can be Sa 182 q Thus with f proper calibration either instrument can be used to measure black liquor solids No major operational limitations were found regarding the refractometer The response was not affected by changes in liquor flow or system pressure Aeration of the liquor did not affect the response No problems with deposits on the window were encountered however the loop was drained and washed with water frequently so the possibility of build ups over a longer time period remains The only significant limitation to the use of the velocimeter was the effect of air bubbles in the liquor It was practically impossible to obtain meaningful data with the velocimeter until the liquors which were obtained already aerated were deaerated This would not hinder the use of the velocimeter within or after the multiple effect evaporators or a high solids indirect concentrator since the evaporation process would keep the liquor free of air However it is expected that a direct contact evaporator would aerate the liquor Thus the velocimeter would not be very applicable beyond the contact Ayh api unless some means for on line deaeration of the heavy liquor were employed Both the refractometer and the velocimeter ar
83. sture balance The amount of water in black liquor can be deter mined by titration using a modified Karl Fischer method 4 Another approach to determining the amount of water present is an azeotropic distillation with an organic solvent anions Wbocedures employing distillation for black liquor solids measurement have been developed RESIDUAL SOLIDS METHODS The main problem in evaporating liquors to a solid residue for gravimetric determinations of solids contents are as follows 1 The liquor may form a scum which greatly retards the rate of water removal This results in excessive evaporation times and leads to erroneous high values for solids content due to unevaporated moisture 2 There may be thermal decomposition of the liquor and subsequent volatilization of organic materials especially if long drying times or excessive temperatures are employed Volatilization would tend to cause measured values of solids content lower than the true values 5 In the presence of air oxidation of various components of the liquor may take place Since the oxidation would not normally occur to the extent to which volatile combustion products are formed the effect of the oxygen uptake would be to cause erroneously high values for solids contents Group Project 3025 Page 87 Report One Oven drying procedures have been the basis for TAPPI methods for black liquor solids determinations These procedures have evolved to try to
84. ter In observing the critical angle of black liquor by the second method it becomes immediately obvious that the line of separation between dark and light is much less distinct than it is with transparent solutions using the first method In fact when viewing through the eyepiece it is sometimes difficult to see the separation unless one sweeps back and forth through the critical angle It is difficult to quantitatively determine what effect this has on the EMC refractom eter precision however it does imply that the refractive index might not be determined as precisely as is possible with transparent solutions Group Project 3025 Page 45 Report One ON LINE CALIBRATION The basic response of the ak showing a linear jnre podes sa uaqta output and solids content along with the demonstrated capability to provide temperature compensation indicates the potential of the refractometer for reliable measurement of black liquor solids content in industrial use The basic requirement affecting reliability is the ability to maintain the proper sa bretion of the instrument in the industrial environment Accordingly it is necessary to consider the question of calibration in some detail There would appear to be three major factors which could cause significant deviations between indicated Gubput and actual solids content for an instrument which is initially properly calipratedi 1 Build up of deposits on the window 2 Long
85. term drifts in the instrument and 3 Changes in the chemical composition of the liquor Any solids which deposit on the window will interfere with proper agaba ment because the optics will tend to see the deposits rather than the liquor The proper action to take in this case is to clean the window and not adjust the instrument calibration to compensate Changing the calibration could cause erroneous results In the extreme case solids deposits could completely isolate the liquor from the opties If solids deposits are found to cause trouble a prism cleaner should be installed and operated on a regular schedule Provisions should also be made for isolating the instrument from the flow line for inspection as needed Any long term drifts in instrument response due to changes within the instrument should be corrected by changing the calibration pot settings No direct evidence for such drifts was obtained in these tests The instrument is stable for Page 16 Group Project 3025 Report One at least 24 hr but stability tests over a period of weeks were not run If the drift is only in the zero adjustment of the ZERO pot will correct for the drift This would require only amp singile doseru nsbion of solids content The problem is more severe if there is drift in range or span Since two point calibration is required to Bet ZERO and SPAN Soke If instrument drift is a more serious problem than liquor sdiponitl n variability wh
86. ther than with arifts or other problems in the instrument itself Thus a program for on line calibration is a major factor in obtaining reliable solids monitoring of black liquor The NUS velocimeter is a versatile instrument which can give several measurements on the solution under test These include sonic velocity temp rature and sound pulse attenuation in the solution It can also be set up to read directly some other quantity such as percent solids which is a function of sonic velocity This latter signal can be compensated fos Aanpenetane variatie It is of course such an output which would be used in monitoring solids content of black liquor This instrument is quite easy to use for measurement of sonic velocity and temperature It is also easy to set up for reading solids content if the sonic velocity of the solution as a function of solids and temperature is known Because of the effects which liquor composition may have on sonic velocity response it is inadvisable to rely on a single set of curves such as Fig 21 or 22 in inter preting instrument response It would be necessary to take periodic samples of the Group Project 3025 Page 83 Report One liquor and run a direct determination of solids content and then use this informa tion to adjust the calibration of the velocimeter The basic problem in on line calibration is making the Need san adjust ments on minimal information Obviously if a complete set o
87. values obtained with the distillation method it must be borne in mind that the value is obtained from the amount of water collected Thus a lower value of solids content means a greater amount of water was collected Most of the errors associated with the Page 9i Group Project 3025 Report One distillation method stopping sh rt of the end point incomplete condensing or trapping water droplets on the side arm would tend to reduce the amount of water collected and hence cause an overestimation of solids content The two errors which could lead to low solids values are either the solubility of some solvent in the dites layer or a consistent underestimation of the initial weight of liquor It may well be that consistently lower values by the distillation method are actually indicative of a systematic error in the oven drying procedures Such an error could be due to oxidation of the liquor during drying or to an inability to drive off the final amounts of moisture These errors would tend to be greatest with heavy black liquors Thus it is possible that the distillation method is more accurate for high solids liquors while the ovendry method is more accurate for weaker liquors Group Project 3025 Page 95 Report One CONCLUSIONS The results of this d TEP A show that both the refractometer and the sonic velocimeter are capable of effectively monitoring black liquor solids content on a continued basis In both cases the re

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