Graphic Instruments in Chemical Processes R. NOAHIS SHREW Purdue University, Lafayette, Ind.
VERY chemical process has some optirnuni set of Many chemical processes involve factors tlult are not conditions under which the niadmum yield of useful readily susceptilde to direct measurement, but that can product is obtained with a minimum expenditure of be measured easily and accurately through electrical means. labor, power, and raw materials. Tlie variables entering In some cases these factors are of a complex nature which into any given chemical process are usually numerous; some cunnot be expressed by customary units of measurement but of them are easy t.o measure and control, others are difficult. must be given in terms of purely arbitrary empirical standVariables found in many chemical reactions are: nature of ards. For such factors an electrical method often affords raw material, proportion of ingredients, temperature, hu- the only convenient form of mrasuremcnt or quantitative midity, rate of flow, pressure, speed, reaction time, acidity, expression. The use of electrical recording instruments to conserve or alkalinity, etc. I n order to control a process exactly, the quruititative value power, save labor, control processes, increase yields, and mainof each of these variables should be known cont~innoosly tain higher qiiality will be described. throughout theentire cycle. Automatic RECoKnING CHEXICAI,CHANGES recording instruments are being used CHEMICAL ANALYSISTKltOUGH ELECwidely for tbis purpose. They make it TXICAL CONDUCTIVITY MEASUREMENT. unnecessary for a human operator to One of the most obvious applications take those readings that give a com$etc picture of the process (both during of electrical recording to strictly cheminormal and abnormal conditions) and cal problems is the nicasnrement of concentration of certain components in that provide a permanent and indisputable record of occurrences within the solution by means of the electrical concycle, uncolored by human opinion. d u c t i v i t y method. In general, this Such instrument records show whether method is applicable when any one of the or not the operators follow prescribed eomponenbs of the chemical mixture is an All c a s w r o d u c d !u Co*rte=u OJ ionizable electrolyte. The conductivity schediilee and whether or not antoEsfdrne-dwua eo. CONCENTRATION method is continuous and may often be matic controls function p w e r l y ; they F,uunr: I,AnGE E ~ applied ~ for ~analytical ~ or control ~ purposes , ~ supply information from which a- REcoRnEn rN where complicated mixtures would make h w E n PLANT ciency and cast data can be calculated; when the process goes wrong, they show o r d i n a r y analysis difficult, or where just, what variables have changed and often enable tbe en& turbidity or presence of interfering compounds renders usual mer in charge to locate the source of the trouble and thus to methods useless. correct it. A typical application of this measurement is in the control The use of recording thermometers and pyrometers is of ammonia concentration in the ammonia-soda alkali process. familiar to every chemical engineer; the use of recording Some of the largest alkali plants control this important factor pressure gages and flowmeter8 is fairly common. However, continuously by circulating animoniacal liquor through electhere are other variables entering into the chemical process trode cliarnbers to wliich are connected graphic recording which can be measured best by electrical means, sucli as speed, instruments. These instruments are really ohmmeters time, electrical conductivity, mechanical power, etc. The measuring electrical resistance but, are calibrated in terms of
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............................................... FIGURE 2. ACTUALRECORDFROM
CONCENTRATKIN H s C o R o E R O N A
LARGEBOILER
Each hump represents B blow-down.
nietLsurement of variables in chemical processes by electrical means has been neglected in the past but is receiving a great deal of attention a t present, and the commercial success of many modern processes is largely dependent on such measureinen&%
chemical concent.ration. The electrical inctiiod gives a continuous picture of the concentration a t all times, which is not possible with discontinuous chemical analysis, and is particularly valuable in this instance because the solution is iinstable. 1021
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I N D U S T R I A L A N D E N G I N E E H I N G C H E M I ST R Y
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FIGURE 3. RECORD SHOWING CAUSEOF HEAVYREJECTIOVS DUETO FAULTYOPERATIONOF B ~ T CMIXER H PREPARING PASTE FOR PLATES IN STORAGE BATTERY PLANT Use of the instruments stopped losses.
[The multiplier for scale (0to 1.0) is 100 to give actual readings in kilowatts.]
Another characteristic example of the conductivity method present day use automatic recording instruments of this type is the continuous measurement of concentration of dissolved as watchdogs on their power-generating equipment to detect solids in a steam boiler. By continuously drawing off a foaming or priming of boilers, or leakage in surface condensers. minute stream of water from the steam drum of a boiler and An interesting problem has come up recently in a large measuring the electrical conductivity of this water under power plant on the Atlantic seaboard using exceedingly high standardized conditions of temperature and pressure, i t is steam pressure and temperature, and high circulating vepossible to know a t all times the total concentration of the locities. Severe trouble was experienced because of carrydissolved solids in the boiler. If this concentration becomes over of small quantities of raw boiler water with the steam, too high, the boiler will tend to foam, carrying over particles and unusual measures were taken to insure the highest posof liquid water with the steam. This causes salt deposits in sible steam quality. The plant has been finally perfected the superheater tubes and results in burn-outs of the tubes; to a point where the steam contains only an average of 0.4 it may carry over into the turbine, deposit on the blading, and part of solid per million, and under some conditions runs a5 reduce the capacity of the machine. The tendency of the low as 0.14 part per million. The analysis of this solid concentration of dissolved salts continuously to increase in content n-as carried out entirely by electrical conductivity the boiler is offset by blowing-down the concentrated solution methods. In this plant, owing to the absolute freedom at regular intervals. If blow-downs are too infrequent, foam- from dissolved gases and the high rate of circulation, even ing of the boiler will take place; if blowing-down is carried though the water is in contact with metals, the resistivity of out too often, valuable heat and treated water are lost. Us- the condensate runs 2,000,000 ohms per centimeter cube or ing the conductivity method, it is possible to obtain a con- higher; this is many times that of laboratory-distilled water tinuous record of salt concentration in the boiler and to sound handled in glass ves+elo. An unusual application of a n alarm when this concentration exceeds p r e s c r i b e d 50 this same principle was made by the engineer of a southern limits. All this is done auto345 y40 chemical p l a n t which was matically, leaving the trained chemist free to employ his turning acid waste i n t o a 235 river. At times the acid contime and talent for more productive purposes than boiler 530 c e n t r a t i o n was sufficiently high to kill the fish in the water analysis (Figures 1 river, and a hydraulic power and 2). plant f a r t h e r downstream The same method of electrical conductivity is applied ‘5 claimed corrosion damage of to the condensate from steami t s e q u i p m e n t . At first samples of the water downpropelled prime movers to 05 stream from the plant disdisclose important operating conditions. Under n o r m a l charge were taken and anaconditions the condensate in MILL LOAD IN POUNDS lysed, and dumping of the plant effluent was guided by FIGURE 4. L 0 4 D CHARACTERISTICS OF A BALLM I L L a closed circulating system is the results of these analyses. essentially distilled water and has an exceedingly high resistivity (usually in the neighbor- Later an electrode was installed a t a downstream point and hood of 150,000 ohms per centimeter cube or higher). How- connected to a recorder in the plant superintendent’s office. ever, if the boiler foams and carries over concentrated boiler This electrode showed continuously the acid concentration water with the steam, or if a leak develops in a surface con- in the river water and saved the time of the man who took denser and allows raw cooling water to enter the condensate, the samples and of the chemist who ran the analyses. the presence of even small quantities of ionizable salts will This same conductivity method is applicable to a great greatly reduce the resistivity of the solution and thereby mani- variety of chemical problems. It is being used successfully fest these effects. -411 the larger steam power plants of the in connection n-ith plating baths, with continuous control of
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A T T M E T E R RECORDS FROM A BEATER MOTOR FIGURE 5. G R . ~ P HWI ~ Above: Brand of pulp required that beating be continued 1 75 hours; below: 3 hours,. Load, length of t i m e for each operatlon in t h e cycle, and time cxonaumed in emptying and refilling are shown.
concentration in rayon manufacture, and in alkali and chlorine plants.
~ I E A S U R E VOF E XPOWER T COXSUMPTIO~ ELECTRICAL METHODOF MEASURING COKSISTENCY.A typical situation encountered in chemical procehses, where the important property is not readily susceptible to absolute measurement and where the indirect electrical method is most useful, is the measurement of the consistency of plastic materials. Thus in the manufacture of brick and other clay products, the plastic clay mass that is introduced into the extrusion machine is a complex physico-chemical system whose plasticity is dependent upon a number of factors. Despite this complexity the consistency of the mass must be maintained within narrow limits if a product o f satisfactory quality is to be made. d mix which is only slightly too wet or too dry mill give s n unsatisfactory product, causing shrinking, cracking, brittleness, abnormal porosity, and other undesirable properties Chemical analysis will not tell the complete story, and the only available physical tests are purely empirical in nature. This problem can be solved with ease and certainty by the simple device of placing a recording wattmeter in the circuit of the motor which drives the mixing machine. Since the mixer usually revolves a t an essentially constant speed, a n y change in consistency of the mass will be reflected immediately in the power consumption required to revolve the mixer. -1recording wattmeter plots directly and continuously this power consumption as a function of time, and thus produces a chart showing the consistency of the mass from instant to instant and its tendency to increase or decrease with any
change in conditions. The recording instrument also enables the operator t o follow the average power, independent of the swings which take place on each revolution of the mixer; this is not possible with a simple indicating instrument. The use of such recording wattmeters in large brick plants has enabled them to produce a more uniform product, to reduce spoilage, and to increase the production from a given equipment without any increase in fixed charges. This same method of measuring consistency through the use of a recording wattmeter is applicable to almost any type of plastic material, and has been applied successfully to such diversified operations as the freezing of ice cream and the milling of rubber. This method of plasticity measurement is valuable in the mixing of dough for bread. I n fact, some of the largest commercial dough mixers are regularly equipped with a graphic recording instrument as an integral part of their mechanism. Since the flour which forms the raw material for the dough is unaroidably variable in nature, the recording instrument is serviceable in detecting and correcting these variations, and it forms a useful adjunct to standard physical and chemical tests. An experienced operator can recognize different types of flours merely by the shape of the curve produced when this flour is mixed with water under certain specified conditions. Furthermore, through observing the form of this curve, the operator can tell just what changes to make in the standard process to offset any abnormalities in the material and thus to obtain a uniform product in spite of these abnormalities. Another valuable application of this same idea is in the mixing of storage battery paste. This is a process where
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Vol. 26, No. 10
FIGURE 6. RECORDS FROM MOTORDRIVING A JORDAN ENQINE Record above shows good operation: the load is steady and uniform with no shutdowna or interruptions. is wrong.
Record below indicates that aomething
for these changes. (3) These records have enabled the engineering department of a t least one battery plant to study its paste-mixing process critically, to simplify the process, to shorten the total time, and to reduce the power consumption; thus the output of the machinery is increased and the unit cost of the mixed paste is reduced. (4)The use of the meter has reduced maintenance costs by almost eliminating breakage of mixing machines. Some of the chemical reactions which occur in the mixing of battery paste are exceedingly rapid; if the paste is not manipulated properly, i t is possible for the consistency t o i n c r e a s e so TABLEI. OPERATIOlhi O F STORAQE B.4TTERY PASTE MIXER rapidly as to stall the BATCH3. FINALTEMP.93' F. BATCE 4. FINAL TBMP.99' F. OPERATION . Timea Power Remarks Timea Power Remarks mixer, often with disKw. Kw. astrous results. The Mixer loaded 8: 13 4 ... 9:07 6 ... ... 9:14 8 ... Dry mixing completed 8:22 6 recording meter shows Water added 8:23 11 max. ... 9:15 10 max exactly how hard each OK 9:17 80 max:, 32 kv. Stiff paate,' mixer labors Acid added 8:25 62 max., 27 av. 21 ... ... 9:25 Dilator added 8:29 26 mixer is working at all ... 9:35 17 ... Reworked paste added 8:41 16 ... Consistency adjusted 8:48 21 ... 9:40 20 t i m e s a n d gives the 8:54 18 9:48 1s ... o p e r a t o r fair warning Slightly granular Mixer dumped 8:57 16 smoddi paste IO:OZ 17 a Figures indicate start of an operation. before a dangerous condition is reached. I n not the plant workmen are following prescribed schedules one nationally known battery plant the saving from this factor accurately. Since the addition of each ingredient to the alone paid for the installation and maintenance of the instrupaste causes a pronounced change in consistency, i t is easy t o ment. Table I and Figure 3 show two methods of recording what tell from the finished curve whether or not the different ingredients were added at the proper time and in proper goes on in a battery paste mixer. The tabulation shows the amounts. (2) Just as in the case of dough mixing, the operator's record of the same data presented by the graphic use of the continuous recording instrument has enabled opera- instrument on the chart depicted in the figure. The greater tors to recognize changes in behavior of materials due to ease of picking out the differences in the two pastes from the causes beyond their control and to make suitable corrections graphic chart is worthy of note.
the raw materials are variable to a certain extent, where the chemical reactions are complicated and not completely understood, where the exact crystalline form and particle size of materials are just as important as their chemical analysis, and where the slightest change in the character of the final mixed paste will have a profound effect on the properties of the battery plates made from that paste. The use of graphic wattmeters, permanently installed on the paste mixers in battery plants, has accomplished four distinct results : (1) They provide an easy and simple check as to whether or
411 applicatiun to consistency Ineasmeirient that is attracting a great deal of attention at the present time is the use of a graphic meter connect.ed to a concrete mixer tu show uniformitv of handling different batelks of concrete and final consistency of mix. This method is being successfully used in large g o v e r n m e n t undertakings at the present time, and special wattmeters have been constructed for this purpose. Thus the graphic meter is doing its share in insuring safety in some of the gigantic dams which the government now has under construction
~~1scE:LL.ASEOUS APPLIC.4TIONS OF ELECTRICAL POWER x63ASUitEMEXTs
Anotiicr typical caaeiri wliioli a11electrical instruiuent wiil obtain information not readily d e t e r m i n e d in a n x other nmnner is in the casc of ball or tube mills and similar grinding machinery. In such equipment the pmwr required to drive the mill at a fixed speed denends uuon the weight of charge coiitaincd io the mill. The grinding conditions usually vary with the weight of charge; in order to obtain t,lir maxininm tonnage output froin the mill and still maintain a satisfactory character of product, it is usually necessary to rnaintain the amonnt of rnat,erial in the mill within certain definite limits. While this can be integated over a period of time by noting the ainoiint of raw material fed in and the amount uf product discharged, the only practical method of knowing a t any instant the load in the mill is througli the use of a wattmeter in tlrc circuit of the motor driving the mill. Ry itsing a recording instrument , the trend of the load, whhcther u p or donri, cart easily be noted by the slope of the curve, and the foed rate adjusted to mairit,aiii the load at the opt,imumpoint. Figure I
4 shuws the load chariictcristic of a ti-ton ball mill as given by
an initial series of tests. From this figure the amount of material in the will can be dct,ermined a t any time by noting the wattmeter reading. Similar considerations apply to ~ u c l iequipment as impact pulverizers, shredders, and the like, where the readings of a recording w a t t m e t e r in the driving-motor circuit form the most p r a c t i c a l and reliable ineans of controlling the feed rate uf raw material8 tu the machine. The application r d electric power measurement to a chemical process is also found in the wide use of graphic wattmeters iiii paper beaters. IIere the time for wliicli the heating is carried o u t ( a n d often the speed of beating) is critical if good quality is to be obtained, and both theje fxctors will vary with different types of stock. Fortunately, each of t h e s e factors is readily m e a s u r e d continuously by the recording wattmeter. The meter shows the exact time a t which the beater is started and stojiped; if the speed is changed, this is instiiiitly reflected in the power connuniption. In this case the graphic instrument performs a double function of nieasuring poaer and of measuring the time element. This is important irecause, in generai, the strongest paper will he obt,ained with a definite beating tinie, and either underbeating or cimrbeating will weaken the product (Figure 5). Tlic same considerations as described above in cunnection with beaters apply also to Jordan engines in paper mills where a certain setting uf the Jordan engine is necessary in miler to obtain thc best product. Clinnging the setting of t.he Jordan engine will alter the perfoniianae uf the pulp on the paper machine, bot all snch changes will be immedi-
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CH.4RT FIGURE 9. RECORD
SHOWING VARIATIONS IN
GUN OPERATIONS IN
ately and permanently recorded by a graphic wattmeter in the driving motor of the Jordan engine (Figures 6 and 7 ) . DIRECTMEASUREMENT OF THE TIMEFACTOR Time is one of the most important factors in chemical processes. Typical examples are found in the vulcanization of rubber and the curing of synthetic plastics where the properties of the final product depend upon the time duration of the chemical reaction. Again the graphic instrument comes to the rescue. This type of measurement has been found so important that special instruments have been devised exclusively for the purpose of recording time intervals varying from many hours down to fractional parts of a second. These special time recorders measure the time of occurrence and the duration and sequence of events, rather than some electrical quantity such as is done by the instruments described thus far. However, the instruments themselves are operated by electrical means, suitable electric circuits forming the connecting links between the recording instruments and the various process units under supervision. TheEe time recorders are constructed with a multiplicity of recording pens, all operating on a single moving chart so that a number of process units can be supervised simultaneously and their operations compared. A typical application of such time recording is made in the extraction of cottonseed oil, as shown in Figure 8. Insufficient pressure will not remove all the oil from the seeds, while excessive pressure makes the cake too dense. Tnsufficient time again prevents the removal of oil from the mass, while excessive time merely restricts production without any compensating advantage. This problem has been solved by the use of contact-making pressures gages, arranged to close an electrical circuit when the pressure is between the desired minimum and maximum limits. These circuits are connected to the individual pens of a multipen time recorder, arranged so that, as long as pressure is applied and maintained within the desired limits, the pen will move from its rest position. The record of the instrument thus shows the exact time for which the correct pressure was applied. This record not only assists the operators in controlling the machines but aids the management in determining whether or not the operators are following instructions. This method proved so valuable a t one extraction plant in the South that it swung the financial reports out of the red ink column into the black. This same method has been applied to artificial ice plants in order to schedule accurately the harvesting periods and hence the freezing time of ice. I n one midwestern ice plant, through
CHEMISTRY
SEPTEMBER, 1 9 3 0 , AND M A R C H ,
Vol. 26, No. 10
1931
the use of instruments of this kind, ice production was increased 13 per cent without any change in machinery or without any increase in labor. When it is realized that this 13 per cent increase in output was made without any increase in overhead charges, a n idea can be gained of the effectireness of the graphic instrument as a tool for increasing efficiency of processes. The same instruments are a t work daily in rubber plants and plastic molding plants. Here the properties of the finished article depend largely on the temperature and time of vulcanization or cure. I n order to increase output from a given amount of equipment and given expenditure of labor, the modern tendency is to compound the materials in such a manner as to shorten the curing time as much as possible. With such raFid curing processes the time factor is more critical than ever, because a slight Tariation in the time of the cycle represents a greater percentage of change. On this account the use of automatic time recorders has in some cases meant the difference between success and failure of certain rapid xulcanii.ing procefses. These instruments are being used regularly on such diversified articles as automobile tires, rubker heels, compcsition battery boxes, victrola records, and buttons. A type of process which is receiving increasingly widespread application is the steam explosion process, applied, for example, to the manufacture of breakfast food and of wall board from sawmill refuse. I n some of these processes costly equipment is used and large amounts of expensive highpressure superheated steam are needed. The economic success of the process often depends on being able to produce the maximum output of satisfactory material from given installed equipment and with a minimum steam consumption. By using pressure and time recorders operated a t high chart speeds (since the total time of cycle is very short), a large southern wall-board plant increased by 20 per cent the output of its “gun” department, using the same mechanical equipment and the same labor (Figure 9). The curves of Figure 9 show how the preheating time has been reduced by preheating to a higher pressure for a shorter time. The effect of shooting a t low boiler pressure is also indicated. The shot recorded by curve 1 was made at approximately 900 pounds per square inch pressure and required five blows to empty the gun. The shot recorded by curve 2 was made at 10.50 pounds and required only three blows to empty the gun. Shooting at low pressure requires more steam per shot which, in turn, tends to reduce the pressure still more. The use of natural gas fuel in the high-pressure boilers, closer coopera-
October, 1934
I K D U S T K I A L A N D E N G I N E E 1%1 N G C A E M I S T R Y
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FIGURE 10. RECORDS OF KILNA N D FEEDER SPEEDS IN CEMENT MIM, Kiln eposd ia ~oouiatelyfallowed by the feeder, giving uniform loading of the kiln snd makiox it possible to obtain B uniform product; twin metem on the board reoord the weed of kilns nnd the respective feeders.
tion between the gun and boiler departments, and the adoption of a biJnuS deduction for shooting helow 950 pounds have eliminated this wasteful practice. AfEAsUREMENT OF THE TIME ELEMENT THROUOH MEASUREMENT OF SPEED There are many processes where the time element OS the process can be ascertained most conveniently through the measurement of speed which, in turn, is casy to record continuously through electrical means. Such a record not only has the advantage of indicating the exact speed a t which the equipment was operated at all times hut of showing at a glance the timeoi occurrenceanddurationoS any shutdounsor delays. In the manufacture of cement the time required for any portion of the charge t.o pass through the kiln depends upon the kiln speed. By taking simultaneous records ol kiln speed and feeder speed, one la.rge eastern cement mill u w able to increase its clinker output 30 per cent. This was donc solely through accurate control of the time factor, properly coordinating slurry speed t.o kiln speed, and this in turn to comhustion conditions (Figure 10). Another instance where specd measurement and control are OS extreme importance is in the operation of paper machines. Here the speed must be absolutely constant to p r o vent costly breakages OS the paper web and yet must be as high as possible in order to ohtain the maximum output from the extremely costly machinery. A plant in Oregon installed a 234-inch newsprint mill designed for operation at a maximum speed of 700 feet per minute. Frequent and expensive breakages of the paper web prevented satisfactory operation a t any speed over 500 Sect per minute; thus production was reduced to ahout 70 per cent of that which should have been possihle from the machine. A carefully coordinated study of the speed and rmwer conditions, made through tlie use of elect,rical recording instruments, so reduced the trouble that csentually it wm found possihle to speed the machine up to 1000 feet per minute; this increased the output 40 per cent above that which the machine manufacturer himse!f had considered the maximurn,
esses described above and for completely different typos of applications. Once it is learned that a graphic instrument can furnish useful data when applied to a certain process, the only question to decide is the simple one OS economics: How soon will the instrument pay for itself? An analysis of a great variety OS applications ha shown that the cost of owning and using a graphic instrument vi11 range hetwen 10 and 25 cents per 24-hour day. This includes not only the cost of charts, ink, and necessary maintenance or occasional repairs, hot also depreciation and interest on the investment. In considering instrumentation in general, it is natural to compare the continuously reconling type with simpler and less expensive indicating instruments. To visualize the scope oE both types, it is necessary to hear in mind that the only time the indicating instrument has any value is during . the instant when an operator is looking at it; Sor the rest of the time, no matter how valiiable its story, i t is lost. Contrast this with the permanent recording instrument which works 24 hours a day. The graphic instrument never rests; it records every minor detail, every unsuspected change; it obtains the facta just as completely and accurately during times of stress, when things have gone wrong and the operators are too busy correcting trouble to read meters, as it does when everything is progressing smoothly. Best of all, i t puts all these facts down in permanent forin so that they can he studied on the following shift, the folloning day, or the following year, and in the one form which appeals most directly to the brain-a two-dimensional graphic chart. R ~ c m v ~A nw u t 6. ISM.
AnnENnnM. Anather sentence should have been added to footnote 2, page 753, of my article on “Critical Temperatures in Silicate Glasses” I m . ENQ.CXEM.,25, 74855 (1933)J. The : “These electrical conductivity measureer a fellowship at Purdue University under , and the viscosity dat,a on the by Lillie (9). Lark-IIorovitz and Bahcock have represented these data by the formula:
INSTALLATION AND OPERATION OF GRAPHICINSTRUMENTS Obviouslv there are manv other Dossihie uses of these instruments, both Sor purposes similar to thosr chemical proc-
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