October, 1930
I S D USTRIALS Ah'D ENGINEERIA'G CHEMISTRY
1113
Gas-, Coke-, and By -Product-Making Properties of American Coals and Their Determination' A. C. Fieldner, J. D. Davis, a n d D. A. Reynolds PITTSBURGH EXPERIMENT STATION,U. S BUREAUOF MINES, PITTSBURGH, PA.
A n apparatus and method are described for determining t h e gas-, coke-, and by-product-making properties of coal a t various carbonization temperatures ranging from 500 ' t o 1100" C. The advantages of this new procedure may be summarized as follows: (1) T h e yields (except NH,), as shown by tests on two well-known gas coals, check those obtained i n practice without any correlating factors. ( 2 ) The effect of carbonization temperature on yields and quality of coke, gas, a n d by-products is obtained throughout t h e range from low- t o high-temperature coking. (3) The temperature and other coking conditions can be closely controlled, t h u s affording a means of comparing t h e carbonizing properties of various coals on a uniform basis, and also a means of studying t h e influence of various factors such as moisture, inerts, size of coal, a n d preoxidation or preheating of coal.
(4) The autogenously welded sheet-iron retort is gastight and permits uniform heating from all sides. ( 5 ) The 75-pound charge of coal is large enough to yield sufficient coke and by-products for analysis and physical tests and yet small enough for convenient laboratory manipulation and accurate control. ( 6 ) It is possible with this uniform method of carbonizing at various temperatures to study and correlate carbonizing properties with t h e constitution of coal as shown by microscopic examination, extraction with solvents, a n d various methods of analysis. (7) The agglutinating value, softening temperature, plastic range, a n d other physical tests of coal can be correlated with coking value. (8) The value of laboratory distillation assay testa using only a few grams of coal can be determined by comparing their results with those obtained in this new test which uses 75 t o 90 pounds of coal, a n d which gives actual plant yields.
...... . . ...... HE rapid advance of t,he coke and gas industry and the search for new methods of produring smokeless fuel require a much more compreliensivc knowledge of the physical and chemical properties of the many varieties of American coals than is now available in the published coal analyses of the U. S. Bureau of Mines ( 5 ) . Analyses and B. t. u. determinations may be sufficient for evaluating coal for ordinary fuel purposes, but they are inadequate for selecting coal for the production of gas, coke. and by-products. The coal-processing industries need to know the yields and quality of these products, and the effect of different temperatures and methods of carbonization. Obviously; such a study should be comprehensive and broadly fundamental. The chemical and physical properties of the coal and the method of heat treatment should be correlated with the yields and nature of the products obtained; furthermore, the results of the laboratory investigation should be correlated as far as possible with commercial results obtained in the gas and coking industries. Intcrcst in this problem was crystallized by the Carbonization Committee of the American Gas Association, which, in a report a t the 1927 convention of the association ( 2 ) , recommended cooperation with the Bureau of Mines in a preliminary study of laboratory and small-scale testing methods for determining the carbonizing properties of coals. The association accepted this rccommtmdation, and appointed a subcommittee on Survey of Gas- and Coke-hlaking Properties of American Coals to represent the association in a coiiperative study of present-day knowledge on the subject of testing coal for gasand coke-making properties. In carrying out this study a review was made of various present and past methods of testing, ranging from the smallscale lahorntory t'ests using only a few gram9 of coal, such as the well-known U. S. Steel Corporation test, to full-scale commercial oven tests. Also, the leading gas anti coke tech-
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Received August 2, 1930. Cooperative investigation, IT,S. Bureau of Mines and American Gas Association. Published by permission of the Director, U. S. Bureau of Mines. ( r o t subject t o copyright.)
nologi~tsin America and Europe were consulted and questionnaires on ( I ) optimum scale of test, (2) best dwign of rrpparatus, and (3) data to be obtained were sent to chemists and engineers experienced in coal-carbonization testing. The results of this preliminary investigation, which were reported to the association a t the 1928 convention (S), indicated, first, that fundamental information on the mechanism of carbonization tliroughout the entire range from lowto high-temperature coking is desired; and second. that a uniform basis on which to compare the carbonizing properties of different coals should be developed. Since fundamental information on mechanism is fragmentary a t present, the comparison method developed must needs be largely empirical; nevertheless the aim should be so to conduct the romparative testing that it will furnieh data fundamental to any carbonizing proress. These considerations indicate use of an experimental retort or oven small enough for definite temperature control and accurate measurerncnt of yields, yet large enough to obtain coke in sufficient quantity and of sufficient size for the usual physical and chemical tests. Seventy-five pounds of coal is probably the minimum amount that mill yield sufficient coke and by-protlucts for examination; 300 pounds is about the upper limit beyond which the cost of apparatus and operation becomes rather high and accurate control of conditions becomes more difficult. The other important requirements in the proposed carbonization investigation may be summarized briefly as follows : (1) Carbonization tests should be made a t 100-degree intervals in the range from 500" t o 1100" C. (2) T h e retort should be of metal to avoid leakage. (3) T h e shape of retort should be either cylindrical, heated on all sides, or rectangular, heated on the two opposite sides only. (4) The temperature of the outside of t h e retort should be kept constant and uniform during t h e entire test. ( 5 ) The coals for test should be subject to all possible analyses and tests that may have any bearing on their carbonizing properties.
INDUSTRIAL AND ENGYNEERING CHEMISTRY
1114 I
(6) The yields and quality of all products should be determined. (7) The first series of coals to be tested should be selected from wellknown gas and coking coals, on which commercial oven and retort test data are available so that c o r r e l a t i o n with commercial yields may be obtained.
Development of Apparatus
Vol. 22, No. 10
wells were removed after the flow of heat through the charge had been investigated, and the method of heating had been adjusted to secure uniform flow. I n subsequent routine tests, thermocouples were maintained a t the following points: three couples, A , B, and C,in the space between jacket and retort; three couples in well 2: No. 1, 5 inches from bottom of retort; No. 2, in the middle of retort; and KO 3, 5 inches from the top of retort. Three couples, Nos. 4, 5, and 6, were similarly placed in well No. 5, making six couples inside the retort and three couples just outside the retort in the space between the retort and the wall. The outside couples A , R , and C determine the carbonization temperatures of the tests. FURNACE-The retort is protected from direct contact with flame by a jacket (Figure l ) , consisting of a high-chrome steel cast cylinder (with top and bottom plates) of internal diameter 1 inch larger than the external diameter of the retort and inches high. The jacket wall 1 inch thick equalizes the temperature around the retort and serves as a muffle in the pot furnace. The flames from two Maxon-Premix burners entering tangentially a t the bottom of the furnace whirl around in the 3-inch annular space between the jacket and the furnace wall. The combustion gases leave the furnace through two 4-inch flues a t opposite sides of the top. These are fitted with dampers and are connected to a stack. The furnace (Figure 1) consists of a cylindrical steel casing 39 inches in diameter and 46 inches high, lined with firebrick to a thickness of 4l/*inches, and provided with a hinged, divided cover.
RETORT-TO minimize operating expense it was decided to design the experimental carbonizing apparatus for the minimum acceptable charge of coalLe., 75 to 100 pounds. Themost difficult problem was the retort material. Silica and other refractories are difficult. to keep gastight under testing conditions that involve frequent heating and cool ing. High-t e m p e r aFigure 1-Retort, Jacket, a n d S e t t i n g ture resisting alloys, such as iron-chromium or nickel-chromium, are expensive and of questionable durability under the proposed test conditions. It was desired to have a ret'ort that could be charged with the coal, made gastight, and then placed in a furnace at the desired carbonization temperature in a manner similar to making a volatile-matter determination with an electrically heated vertical tube furnace. After some preliminary experimentation it was found that a gas-heated pot furnace and an autogenously welded cylindrical canister of ordinary l/leinch sheet steel answered these requirements. The steel canister served as a retort in a similar manner 89 the platinum crucible in the volatile-matter determination. It was expected that a single retort would serve for only one test a t the highest temperatures, but it was found that two or three tests could be made before oxidation penetrated the metal. At the lower temperatures the same retort served for a number of tests. As shown in Figure 1, the retort is simply a steel can 26 inches high and 13 inches in diameter. The cylinder is rolled from I/,a-inch steel sheet and the ends are cut from '/r-inch material. All seams are welded autogenously with an OXYacetylene torch, the bottom being left open for welding after charging with coal, The standpipe is a 11/2-inch iron pipe 12 inches high and is welded to the center of the retort top. For heat-flow experiments five 1jr-inch iron pipes, which served as thermocouple wells, were let through the head as shown in Figure 2, and welded into place. The spacing of the wells was as follows: Well No. 1, 1 inch, No. 2: 2 inches, ~ l & . a d ~ @ I w pylm k e ~ t)mrmaapa m wbonNo. 3, 3 inches, No. 4,4 inches, and No. 5, 5 inches. respecFigure 2-Position of Thermocouples i n Retort a n d Jacket tively, from the retort wall. Since the retort is 13 inches in diameter, well No. 5 was 11/? inches from its center. These CONDENAINQ, TAR-PRECIPITATINQ, AND SCRUBBING TRAIN wells were placed on concentric circles on the retort top SO that no two of them fell on a vertical principle plane. With -The condensing and scrubbing train for the recovery of this arrangement it was believed that the pipes would least the by-products is shown diagrammatically in Figure 3. affect horizontal heat flow through the charge. The flow of Figure 5 is a photograph of the entire apparatua, showing heat in a coking charge. as illustrated in Figure 4, is based on the charged retort heing lowered into the furnace. The disa continuous record from couples so spaced. Some of these tillation products pass from the retort offtake first to a dry
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October, 1930
I N D U S T R I A L A N D EiVGINEERING CHEMISTRY
1115
p a c k e d with Knight standard 6/8-inch cylindrical stoneware tower packing. The gas enters at the bottom into a 5-inch space between the bottom cap and the packing support, which consists of a l / ~ inch steel plate drilled with 3/8-inch holes. R a s h oil is admitted from a reservoir at the tower top, passing to a cuptype distributor and thence through the packing countercurrent to the gas. The wash oil is not recirculated; it is admitted a t such a rate that approximately 4l/2 gallons will have passed the tower during a run. This quantity of wash oil is, of course, a large excess for the low-temperature runs where the gas make is small, but is required for the high-temperature runs since here the gas make is high. This scrubber was installed after the runs on coal No. Figure 3--Condensing, Tar-Precipitating, and Scrubbing Train 1 had been completed; accordingly only trap, b (Figure 3), and then to a tubular water-cooled con- the gas from coal No. 2 was scrubbed before passing to the denser, d , of large capacity. This is an 8-inch vertical pipe, recording calorimeter. Before passing to the small meter this portion of the gas 39 inches in length, with welded heads into which twelve '/*-inch seamless copper pipes are brazed, These are the gas (2l/2 to 12 cubic feet, depending on the carbonization tempassages. Two Cottrell precipitators, e and f. follow in perature) is scrubbed for light oil by passage through a tube of series. Each is a &inch standard pipe, 36 inches in length, active charcoal. This oil is recovered from the charcoal by with a standard flange a t the top. To this is bolted a cover steaming a t t.he end of each run. MEASURING APPARATUS-Retort temperatures (couples 1 disk of fiber, 1 inch in thickness, through which passes the stem of a squirrel-cage electrode. The electrode is suspended to 6, inclusive) are recorded by an 8-point Leeds & Northrup vertically in the pipe extending to within 3 inches of the bot- potentiometer. The thermocouples are made from B. & tom. The gases enter centrally at the bottom and are dis- S. KO. 18 chromel-alumel* wire of a grade especially selected charged through a 1-inch pipe welded to the side of the 3-inch for uniformity and for reproducibility of electromotive force. pipe, 4 inches from t,he top. The suspended electrode con- The couple leads are insulated from each other, and from the sists of a 1/4-inch brass rod passing through two ll/s-inch brass disks at the top and bottom. Eight No. 22 steel wires are soldered to the peripheries of the disks at equal intervals. A 1-kilowatt 26 transformer supplies the power at about 20,000 volts. The output of the transformer is rectified by highly insulated commutator of the disk type driven by a l/4-horsepower synchronous motor. The trap, condenser, and precipitator are provided with drip cocks and with steam connectioris for removing adhering tar after a run is completed. @ The detarred gas then passes upward through R 5-inch lead tower, h, 57 inches high, supplied with g 2 N sulfuric acid for removing ammonia. It then passes through a similar iron tower, i, supplied with caustic liquor for removing hydrogen sulfide. The circulat'ing liquor in both towers passes through perforated distributors in the tower tops. It then -1 descends through the tower packing (Knight 5/8inch hollow cylinders form packing) countercurrent to the gas stream. The liquor leaves the tower base through a trap and is caught in a 5-gallon bottle. The scrubbed gas is now metered by two stantlard American Meter Company's wet-test meters in parallel. A large meter, m ,takes 49//50 of the make 0 6 4 gas and a small one, I , takes 1/m of it, which Figure 4-Flow of Heat i n a Coking Charge is collected in a 10-cubic foot holder for analysis. The remai+nder of the gas is burned. The spindles of the iron wells, by the usual clay insulators, 2- or 4-hole insulators two meters are geared together so that the small meter being used depending on the number of wires. The three continuously takes '/'w of the make gas, regardless of what the couples in each well are formed by welding with oxyacetylene gasification rate may be. A pressure equalizer insures ac- flame three different alumel leads to one chrome1 lead at the curate proportioning of the sample. Just before entering points shown in Figure 2. That part of each lead which exthe make-meter the gas passes through the light-oil scrub- tends from the top of the well to the potentiometer distributher, k, which consists Of a 7-foot piece Of standard pipe 2 At temperatures above a red heat alumel wire must be protected from fitted with standard flanges and caps at top and bottom, and gases containing carbon monoxide; otherwise i t rapidly disintegrates.
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INDUSTRIAL AND ENGlNEERING CHEMISTRY
1116
Figure 5--Charged Retort Being Lowered
Info
Furnace
ing panel is insulated vith asbestos loom. Carbonization or furnace temprratiircs (couples -4, R, and C) are measured at 15miniit,e int,ervals with a Leeds & Northmp portable potentiometer. The gases are analyzed by a Burrell gar apparatus. A standard Thomas rerording gas calorimeter is connected to thegas line a t the outlet of the make-meter, so t.liat the Iieating value of the scrubbed gap as made is recordcd continiiously. At the end of a test the cnlorimetrr is connected to the holder whicli contains the scnibbed composite sample, and the Iicating value of this gas is det,ermined. A llanarex standard specific gravity recorder is connoctrd in par~llelwith the calorimeter. This can be used to record tlie gravity of the scnibbed gas from the make-meter or can he ronnected to the holder vvhich contains the composite sample at will. Rot11the recorded calorific value and the specific gravity of the romposite gas sample are checked, the former by calculation lrom the gas audysis and the latter by the effusionieter. Gaspressure readings in inches of water are read at 15-minute intervals at points e, p, and j. (Figure 3)
Vol. 22, KO. 10
A.S.T.M. apparatus, I n general, tlie gtas tar. light oil, and ammonia are tested by methods describrd in t,hr Cnr Chemist's Handbook. 1929 edition. and the coal and r:ol;c i,,v mrthoils of the American Society for ?'est,ing Mntcrial?. I l w cnieulation of yields is based on coal "as testcd." and gas measiiremcnts apply to gas scrubbrd for light oil and saturated with waterat 15.5"C. ((iO"F.)and 7fX)mm. (30inches!ofioarcury. Duplicate carhonization tests are made at ,500".fOO", 700', Soon, WO", 1000": and 1100" C . , the temperatiires being measurcd outside the retort in the spare betu\~eenthe retort and jacket. This tempratiire (couplra A . I?, and C) isdesignated the furnace or carbonization trmpcratiire. To insure uniformity of compositioii of rod t.hroii~lioutthe series of tests. a 1-ton lot of the roal is croshed in n Sturterant roffee mill-type crusher to pass a '/cincl~ square-mesh wire screen. The produrtion of an rxcess of fine size8 of coal is %voidedas far ns possible by setting the crusher iyith a comparativrly Iargc owning, screening tlir product, and again rrnshinp the ovcrsize. The l/
