Unit Consumption Factors - ACS Publications - American Chemical

Unit Consumption Factors R. NORRIS SHREVE

Downloaded by RUTGERS UNIV on May 29, 2018 | https://pubs.acs.org Publication Date: June 17, 1954 | doi: 10.1021/ba-1954-0010.ch008

Purdue University, Lafayette, Ind.

Unit consumption factors are the quantitative data that enable calculations to be made in determining the amount of raw materials necessary to make, for in stance, 1 pound of finished product. The conditions under which these unit consumption factors vary are discussed as is how they can be used, both in checking products and in planning for raw material supply and for the sale of chemicals. Nine functions wherein the unit consumption factors have been used are listed.

^Quantitative data form the basis of the chemical industry. This has long been recog nized i n the design and implementation of factories, and i n the supplying of the necessary raw materials. The quantitative aspect is just as important i n sales planning and i n marketing surveys. T h e difficulty is obtaining quantitative data i n the marketing area. Though much has become available i n recent years, more is needed. The retarding con dition is the confidential nature of many of the basic figures. E v e n i n the area of marketing or sales, the application of the quantitative figures available requires technical training and understanding. The universities are giving such training as the backbone of the education imparted to chemical engineers wherein the emphasis is upon material balances, energy balances, flow sheets, and the yields and conversions of the chemical changes.

Definition of Unit Consumption Factors A s a foundation to the treatment of this subject, a frequent misunderstanding be tween yields and conversions must be clarified, because the unit consumption factors are based on the chemical yields and not on the conversions. The operational efficiency of chemical plants is interpreted i n terms of the yield and conversion. These terms may be defined as follows: Ρ cent e 'eld — 100 X moles of main product moles of main product equivalent to net disappearance of chief reactant ^ . moles of main product Percentage conversion = 100 X — ; ζ : ;— :—;—— rr-z — moles of main product equivalent to chief reactant charged Based on the synthesis of ammonia at 300 atmospheres and 500° C , the yield is frequently above 9 8 % while the conversion will be limited b y the equilibrium figure of around 2 0 % . This means that 8 0 % of the hydrogen and nitrogen charged are not converted and must be recirculated after the removal of the ammonia. Somewhat higher figures prevail for the methanol synthesis. I t is from the yields that the unit consumption factors are calcu lated. The aim of the chemical engineer, concerned with the cost, is to arrange for such conditions of temperature, pressure, and proportions that the conversion figures approach 71

LITERATURE RESOURCES Advances in Chemistry; American Chemical Society: Washington, DC, 1954.

72

ADVANCES IN CHEMISTRY SERIES


the yields as closely as feasible. This is, of course, not possible for ammonia because of the low equilibrium of this reaction at practical temperatures and pressures. A s a corol lary of the low ammonia and methanol conversions, larger equipment is required than would be necessary were the conversion figures nearer to those of the yield. When making any market study i n the chemical field the unit consumption factors are needed because they are a measure of the average realized chemical change that takes place when a raw material is converted chemically into a salable finished product. This can be demonstrated most easily i n conjunction with flow sheets (Figures 1, 2, 3, and 4) wherein the raw materials are put through a coordinated sequence of physical changes (unit operations) and chemical changes (unit processes) to convert them into products of enhanced value and usefulness. These latter products may enter directly into sales i n the consumption areas or they may be consumed within the factory where they are manu factured i n order to be turned into salabje products of still further enhanced value and usefulness. I t might also be pointed out here that the chemical industry is its own best customer, consuming much of its own products.

Variations in Unit Consumption Factors The literature sometimes uses the words unit conversion factors when they really mean unit yield factors. The latter, as explained above, represents the net change of a given raw material into the main product. A s a corollary to this consideration, the actual yields should be compared to the theoretically possible yields. While i t is not the func tion of the market investigator to endeavor to change conditions i n the factory i n order to make the realized yield approach as closely as possible to the theoretical yield, yet in case of wide discrepancy between these, he should recognize that, with advancing knowl-

FATTY ACIDS

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Figure 1.

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S0AP F/N/SHiNG BARjFLAKB Oft

FMfZfR MRATBÙ BAR SOAP

Flow Sheet for Finished Toilet Soap with 2 0 . 5 % Moisture Pounds per pound of soap 0.85 Make-up water

Fat Lye (as 5 0 ° Β ' caustic soda) Salt Sodium silicate ( 4 9 ° Be. solution)

0.236 0.0067 0.005

Steam (150-lb.) Electricity (kw.-hr.)


0.833 1 .2 0.025

73

SHREVE—UNIT CONSUMPTION FACTORS Rosin y'F}rsf%gre" HCI Filter Γ7=3— Lye Soap Soap treating . kettle , kettle (second (first batchtf Lye_ batch Soap Salting evaporators

Melting from containers

Oils and fats

mm

Settling tank Steam

Stcam\ Lye/ Soap' /iake-up salt [Second Nigrel used for {Recovered dark soap j> salt

Water* Filter Na OH or jcausticizing

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Na C0 Steam\ Sodium ~~ or water Silicate,etcJ

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Figure 2.

Flow Sheet for Laundry Soap

Per ton of a typical laundry soap (plus 70 pounds of 8 0 % glycerol) Oil, fats Sodium hydroxide ( 7 6 % N a 0 ) Rosin Salt (make-up)


2

653 111 90 4

pounds pounds pounds pounds

Steam Water Soda ash ( 5 8 % N a 0 ) Sodium silicate ( 1 8 ° Be.) 2

2 230 37 822

tons gallons pounds pounds

edge, the actual yields tend to approach theoretical ones. I n the parlance of the factory superintendent this happens when the chemical yield of the process is improved. Through out the entire chemical field a certain proportion of the funds assigned to research are devoted to the improvement of chemical yields. When this occurs the principal unit consumption factor will decrease. Published unit consumption factors are subject to variations with advances i n the chemical industry. This industry is characterized by change; i n its entirety i t spends the largest percentage of sales dollars and probably the largest actual number of dollars i n research and development. While much of this goes into developing new chemicals and chemical products like D D T , Dacron, D y n e l and many others, a certain proportion of research expenditures are employed for improvement of processes. The improvement of these processes proceeds along three general lines. First is the enhancement of yields with elimination of wastes and consequent decrease of unit consumption factors. This is fairly simple and is illustrated by the great improvements i n the sulfonation process for making phenol wherein the consumption factor for sulfuric acid (66° Bé.) has been much decreased to 1.4 pound per pound of phenol. The second approach involves a change of products or their proportionate conversions and may be illustrated b y chlorination of benzene. Although monochlorobenzene was the product commercially needed, some o- and p-dichlorobenzene were always formed i n the process. These were stored by the wise manufacturer until excellent markets for these products were developed. A t present certain manufacturers conduct the chlorina tion of benzene to make the maximum amount of the dichloro derivatives. Here the unit consumption factor of chlorine, for example, varies with the proportion of the polychloro derivatives made. When benzene is chlorinated i n this fashion, there will be not one conversion factor but two series, giving for each the conversion factor of benzene or of chlorine to chlorobenzene, p-dichlorobenzené, and o-dichlorobenzene. F o r this multipleproduct manufacture the over-all picture can be obtained only b y the summation of the individual product conversion factors. The third aspect of improvement may mean an entirely different process for making an old substance. F o r many decades soap has been manufactured by caustic soda saponi fication of fats i n the batch process. I n recent years plants have been installed for the high pressure, high temperature rapid hydrolysis of fats i n the countercurrent liquid mixed phase using water and a catalyst. I n this case the sodium fatty acid or the soap may be prepared b y neutralizing the free fatty acid hydrolysis product with caustic soda or soda ash depending upon convenience and the market. Naturally the unit consumption factors changed when the improved process was used. Figure 1 gives the unit consumption factors for one pound of a finished toilet soap with 20.5% moisture. Figure 2 represents a flow sheet for laundry soap wherein chemical reactions and physical changes (unit processes and unit operations) are involved i n the LITERATURE RESOURCES Advances in Chemistry; American Chemical Society: Washington, DC, 1954.


74

manufacture. Note the change i n the unit conversion factors between the two different kinds of soap. Figure 3 represents a flow sheet for the concentration to suitable purity of glycerol obtained from the preceding flow sheet, together with the recovery of the cyclical salt (unit operations). Judgment and technical experience will enable an approximation of a unit consump tion factor to be made i n certain areas. The approximation will be nearer to the actuality, the more experienced the calculator is i n the particular field. F o r instance, a man versed in the manufacture of chlorinated insecticides with knowledge of yields can calculate the unit consumption factor for chlorine consumption for an analogous new chlorine-contain ing product with fair accuracy.

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N a OH

glycerine 95-98% COURTESY

Figure 3.

MCGRAW-HILL BOOK CO.

Flow Sheet for Glycerol Manufacture

To produce 1 ton of glycerol and 2.2 tons of salt Spent lye (glycerol, . % ) Sodium hydroxide Aluminum sulfate Ferric chloride Steam Electricity

22 tons 200 pounds 22 pounds 110 pounds 8000 pounds 10 kw.-hr.

Direct labor 4 man-hr. Activated carbon 5-10 pounds Steam still condensers 1, 2, and 3 are, respectively, a vapor superheater, an air or warm-water partial condenser for 8 5 % glycerol, and a cold-water final condenser for sweet water.

Where no chemical change is involved, the unit conversion factor is the measure of the average realized extraction or crystallization or other physical change. This is illus trated by Figure 4 wherein a salable product is extracted out of a mixture. This may be done by solvents, by crystallization, or by distillation. Figure 4 typifies this type of extractive procedure as applied i n Sugar refining. The principal unit consumption factor is greater than unity, or 1.06 pounds of raw sugar to furnish one pound of refined sugar. M a n y other flow sheets with the data for the unit consumption factors, are available i n the references described.

Evaluation U n i t consumption factors enable the caustic soda manufacturer to determine how much caustic soda is going to be needed for a million or a billion pounds of soap of the quality and type for which the unit consumption factors are available. The composition of soaps vary greatly according to their use and market areas, and as these and the quality change, the unit consumption factors must change. This illustrates how a technical understanding is required for the evaluation of unit consumption factors. Another example is the determination of sulfur needed for sulfuric acid on the basis of the equivalent of 1 ton of 100% sulfuric acid. The consumption figure for sulfur will vary from 677 pounds to make 9 3 % sulfuric acid to 688 pounds to furnish 2 0 % oleum. Plants for chamber acid, concentrated acid, or oleum vary greatly i n the costs and slightly so for the yields, and hence for the unit consumption factors. The Government i n their statistical.reports reduces the various strengths of sulfuric acid to 50° Bé. acid (62.18%) in order to have the same yardstick for statistical reports. I n marketing surveys, an investigation should be made between different grades of a chemical because their costs vary. M a n y chemicals, other than the sulfuric acid, are sold i n different purities and forms. Solid chemicals like soda ash and sodium sulfate may be anhydrous or crystalline; and LITERATURE RESOURCES Advances in Chemistry; American Chemical Society: Washington, DC, 1954.

75

SHREVE—UNIT CONSUMPTION FACTORS

even the number of molecules of crystal water may vary as illustrated by sodium carbon ate monohydrate ( N a C 0 . H 0 ) and decahydrate or sal soda ( N a C 0 . 1 0 H O ) . Other chemicals are sold i n solutions of different strengths as sodium silicate (water glass) or even with different ratios of constituents ( N a 0 to S i 0 ) . Because of great variations i n the active constituents: nitrogen ( N ) , potash ( K 0 ) , and phosphoric acid anhydride ( P 2 O 5 ) , fertilizers are commonly evaluated by the percentages of these constituents i n the single, more or less pure, salt; or by the percentages of the three i n a mixed fertilizer (e. g., N : P 0 : K 0 = 10:6:4). Here and elsewhere, solutions such as ammonium nitrate solutions or " U . A . L . " (urea-ammonia liquors), are articles of commerce. A l l of the variations i n purity or composition effect the unit consumption factors, so the purity or composition of products must be specifically stated. 2

3

2

2

2

2

2

2

5

3

2

2

2

2


Preparation The writer has participated i n obtaining and publishing unit consumption factors; it seems worthwhile to record how these have been made available. The procedure was to work up a flow sheet of a selected process and material and energy balances including, when possible, hours of labor and kilowatt hours of electricity used i n the process. If the data, from which the flow sheet and unit consumption factor calculations were made, were reliable and based upon wide experience, the result was satisfactory. If the data for material, energy, and labor balances were not deemed reliable, i m proved data were frequently obtained b y sending tentative figures to be checked to certain individual factories whose cost and production figures embodied the data needed. A s some requested data was considered confidential, some companies rightly did not consider it good business to release such figures. This confidential aspect largely pertains to new processes, and as the competitive picture widens and more plants use the same process, the figures become more readily available.

Sources References from which unit consumption factors can be obtained are listed. T h e books that are most usable are those i n which the unit consumption factors are given with a flow sheet, since these factors cannot be used properly without a knowledge of the tech nical procedures concerned. Earlier flow sheets published several decades ago did not, as a rule, contain data for the calculation of the factors of material, energy, or labor. I n recent years there have appeared a number of books and publications containing annotated and enlarged flow sheets. I t seems to the writer that the most useful way of presenting these data are as tabulations underneath the technical flow sheets as shown i n Figures 1, 2, 3 and 4. The books by Shreve (IS), Olive and Shreve (11), Lee (8), Perry (12), and Faith, Keyes, and Clark (2) have the quantitative data arranged i n the most convenient manner. I n certain books these quantitative data are included i n the text descriptive of the accompanying flow sheet. The 'Chemical Process Industries" by Shreve (15) contains many flow sheets with quantitative data. T h a t book was published i n 1945 and a revision is underway. There is now being written, for 1953 publication, the " C h e m i c a l Business Handbook" (12) i n which one of the co-editors, J . R . Skeen, has very carefully recalculated and arranged in tabular form all the available unit consumption factors that he can find. F o r many years Chemical and Metallurgical Engineenng, now called Chemical Engineering, has pub lished separately a book of flow sheets. The last edition was revised b y Olive and Shreve (11). Nine-tenths of these flow sheets with comments are i n " C h e m i c a l Process Indus tries" (IS). "Industrial Chemicals" by Faith, Keyes and Clark (2) is extremely valuable for its flow sheets with quantities, but no further references to the literature are given. Currently there is being published under the editorship of K i r k and Othmer (7) the " E n cyclopedia of Chemical Technology." This very excellent encyclopedia has numerous flow sheets, and occasionally these flow sheets or the adjacent text contain the data neces sary to calculate unit consumption factors. I t will be very helpful to have this encyclo1



76

[Whit? sogqr Weighing, "gaging, shipping

Soft sugars Packaging,


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COURTESY MCGRAW-HILL BOOK CO

Figure 4.

Flow Sheet for Refined Cane Sugar

Per 100 pounds of refined sugar (about 4 pounds of residual sirup also produced) Raw sugar (97 Pol.) Hydrated lime Kieselguhr Bone char (in process) Bone char (revivified) Bone char (new)

106 0.05 0.25 150-250 35-75 0.25-0.3

pounds pounds pounds pounds pounds pounds

Condensing water 2000-3500 Pure water 600 Process steam and power steam 175 Char kiln fuel 20,000-25,000 Employees (total) 0.3

pounds pounds pounds B.t.u. man-hr.

pedia i n English to supplement Ullmann's "Enzyklopaedie der technischen Chemie" (17). It is surprising how much data the Germans have been able to obtain. A third edition of Ullmann is to appear very shortly. Groggins and his coauthors i n the fourth edition of ' 'Unit Processes i n Organic S y n thesis" (4) have brought together many flow sheets, with quantities. This is also true of "Industrial Chemistry" b y Riegel (14) and "Chemical Engineers' Handbook" b y Perry (12). I n the electrochemical field M a n t e l l (9) i n his third edition of "Industrial Electro chemistry" has a large amount of data, both i n tabular form and i n flow sheets. Nelson (10) i n the third edition of "Petroleum Refinery Engineering" has many flow sheets and much material data for the petroleum industry. Furnas (3) in the sixth edition of " R o g ers' M a n u a l of Industrial Chemistry" was able to include many flow sheets and an occa sional compilation of data. "Chemical Engineering Plant Design" i n the third edition by Vilbrandt (16) uses a flow sheet for making hexachlorobenzene to illustrate in great detail various principles of plant design. It is doubtful whether any process is described as quanti tatively as this one. This book also has a few other flow sheets with some quantitative data. T h e first volume of the series on "Chemical Process Principles" b y Hougen and Watson (5) includes an excellent description of the data and calculations necessary for the determination of energy and material balances on which unit conversion factors are based. Certain of our chemical journals have been extraordinarily valuable i n recent years i n supplying flow sheets and quantities for material and energy balances. This has been particularly true of the monthly pictured flow sheets i n Chemical Engineenng (1) and i n the Staff Industry Reports appearing monthly i n Industrial and Engineering Chemistry (6). W i t h technical development, the unit consumption factors change, both for materials and energy and labor—in most cases decreasing with the advances i n technology. F o r this reason, any published unit consumption factors should be checked from time to time.

Applications A rather interesting use of unit consumption factors was related to the writer b y Albert B . Newman. Immediately following W o r l d War I I , Professor Newman was techLITERATURE RESOURCES Advances in Chemistry; American Chemical Society: Washington, DC, 1954.


SHREVE—UNIT CONSUMPTION FACTORS

77

nical advisor to the American occupation group i n Germany. One of the important plan ning jobs was to determine just how much sulfuric acid, caustic soda, and nitric acid or other chemical would be needed to supply the peace time demands of the German nation for fertilizers, soap, insecticides, medicines, dyes, and a l l the other products required for making explosives or other war chemicals. Professor Newman told the writer that with out the data that were available i n the American literature on unit consumption factors it would have been impossible for h i m to have checked the tonnages of the various chemi cal raw materials that the Germans said they needed i n order to make the finished m a terials which everyone acknowledged they must have to carry on their technical civiliza tion. The applications of unit consumption factors are varied. A tabulation of these figures serves to check production and yields i n any process, whether batch or continuous. Indeed i n many plants the quantities of materials consumed to produce a given quantity of a finished chemical, are charted from day to day, from week to week, and from year to year. If these charts for materials are extended to include energy, labor, and other factors entering into the cost of a product, there is presented the best series of comparisons for cost control of manufacturing operations. A further comparison of such figures for the different procedures for making the chemical will indicate the relative position i n the economic picture of different processes and point out the cheapest one. This may lead to the abandonment of a high cost process. The use of unit consumption factors i n sales and marketing development is just as important as i n production. This may be looked at from two viewpoints—i.e., markets for new products and markets for old products. I n the consideration of the advisability of undertaking the manufacture of any product, the unit consumption factors will enable a prospective manufacturer to determine how much raw material he is going to consume and, therefore, he will be able to investigate properly the avenues for obtaining that raw material. Also, the unit consumption factors will enable a prospective supplier of this raw material to ascertain the quantities that will be consumed i n a given area if he can obtain the tonnages of the sales. Turning to new products the unit consumption factors will permit exact calculations to be made for raw materials for specified areas and facili tate proper planning for managements' decision regarding the risk involved i n introducing new products. Certainly such calculations should precede the expenditure of any con siderable amount of money i n research and development and should be continued as the process reaches the pilot plant and before any large sum is spent for plant and equipment. Finally the unit consumption factors can be employed from year to year to check and to compare sales, both from the consumption and the production viewpoints for a given area. In summary unit consumption factors have been used to carry out the following functions : Reduce the costs in manufacturing processes. Eliminate obsolete processing. Stimulate research for new and better processes. Enable management to make wiser decisions regarding both processing and marketing. Point out quantitatively declining markets in given areas. Point out quantitatively advancing markets in a given area. Enable markets for new products to be studied more quantitatively. Guide research and development in a profitable direction by studying markets quanti tatively at the time research and development is being carried on. Enable sales to be predicted more certainly for those products for which these factors are available. Literature Cited (1) Chemical Engineering, McGraw-Hill Publishing Co., New York, Pictured Flow Sheets and Chementator, monthly. (2) Faith, W. L., Keyes, D. B., and Clark, R. L., "Industrial Chemicals," New York, John Wiley & Sons, 1950. (3) Furnas, C. C., ed., "Rogers' Manual of Industrial Chemistry," 6th ed., 2 vols., New York, D. Van Nostrand Co., 1942. LITERATURE RESOURCES Advances in Chemistry; American Chemical Society: Washington, DC, 1954.


78


(4) Groggins, P. H., ed., "Unit Processes in Organic Synthesis," 4th ed., New York, McGraw-Hill Book Co., 1952. (5) Hougen, Ο. Α., and Watson, Κ. M., "Chemical Process Principles," Vol. I, New York, John Wiley & Sons, 1943. (6) Industrial and Engineering Chemistry, AMERICAN CHEMICAL SOCIETY, 1155 Sixteenth Street, N.W., Washington 6, D. C., Staff Industry Reports, Monthly, February 1948. (7) Kirk, R. E., and Othmer, D. F., "Encyclopedia of Chemical Technology," New York, The Interscience Encyclopedia, 1947. (8) Lee, J. Α., "Materials of Construction for Chemical Process Industries," New York, McGrawHill Book Co., 1950. (9) Mantell, C. L., "Industrial Electrochemistry," 3rd ed., New York, McGraw-Hill Book Co., 1950. (10) Nelson, W. L., "Petroleum Refinery Engineering," 3rd ed., New York, McGraw-Hill Book Co., 1949. (11) Olive, T. R., and Shreve, R. N., "Chemical and Metallurgical Engineering's Chemical Engi neering Flow Sheets," 4th ed., New York, McGraw-Hill Publishing Co., 1944. (12) Perry, J. H., ed., "The Chemical Business Handbook," New York, McGraw-Hill Book Co., forthcoming publication. (13) Perry, J. H., ed. "Chemical Engineers' Handbook," 3rd ed., New York, McGraw-Hill Book Co., 1950. Bibliographies. (14) Riegel, E. R., "Industrial Chemistry," 5th ed., New York, Reinhold Publishing Corp., 1949. (15) Shreve, R. N., "The Chemical Process Industries," New York, McGraw-Hill Book Co., 1945. (16) Vilbrandt, F. C., "Chemical Engineering Plant Design," 3rd ed., New York, McGraw-Hill Book Co., 1949. (17) Ullmann, Fritz, "Enzyklopaedie der technischen Chemie," 2d ed., 10 vols., Berlin and Vienna, Urban & Schwarzenberg, 1928-1932. RECEIVED April 22, 1952. Presented before the Division of Chemical Literature, Symposium on Literature Sources for Chemical Market Research, at the 121st Meeting of the AMERICAN CHEMICAL SOCIETY, Buffalo, Ν. Y.


Unit Consumption Factors - ACS Publications - American Chemical

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