Oil Dehvdration of North American Lignites J
E. P. SCHOCH
The University of Texas, Austin, Texas
When lignite is covered with a thin oil and heated under atmospheric pressure it gives up its water without disintegrating, but the resulting product is oil-soaked. The amount of water thus obtained up to 225" C. may be logically considered to be its moisture content, and this furnishes a good method of moisture determination. Attempts have been made to remove the oil from this oil-soaked product, but none of them appear to be economical. The following method of operation was evolved: The lignite with its cover of oil is heated in a closed vessel to 210' C., the major part of the moisture is allowed to blow off slowly, the oil is allowed to drain, and the pressure is reduced to 5 cm. of mercury for a few minutes. Thus a lump product is obtained which contains only a few per cent of water and of oil, is practically waterproof, and has an average heating power of 11,000 B. t. u.
R U E lignite is found in two distinct areas of our prairie regions: one in and around North Dakota (Saskatchewan, South Dakota, and Montana), the other in Texas and other Gulf states farther east (Arkansas, Mississippi, Louisiana, Alabama, and Tennessee). I n most of these states the amounts are relatively small, but in three of them the tonnages are very large: Texas, 23 billion; North Dakota, 600 billion; Saskatchewan, 63 billion. Such large quantities of fuel are worthy of technical consideration. Yet in spite of many efforts, the economic production of an improved fuel from lignite has not been attained. This work on oil dehydration is the result of protracted efforts to attain this end.
T
Properties and Attempts to Briquet Lignite North American lignites are woody in texture and have a moisture content ranging from 30 to 45 per cent, determined by heating in kerosene. When they contain 36 per cent moisture thus determined (or 32.5 per cent determined by drying in air a t 105" C. or 221 " F.) and 7 per cent ash, their heating power may be about 7400 B. t. u. per pound, and lignite of this composition may be said to be of good quality. When exposed to relatively dry air, raw lump lignite loses much of this moisture and disintegrates into fine particles or loosely coherent lumps; such a mass is practically unburnable because, unlike bituminous coal, it does not fuse together or coke in a fire. Lump lignite undergoes this same disintegration in a fire, and hence much of the fuel drops through the grate bars unburned. It also undergoes this disintegration when heated in a dryer or retort, and hence a dehydrated lump lignite cannot be made by direct drying. Lavine, Gauger, and associates (4, 7, 8) made a careful study of the behavior of North Dakota lignites during dehydration with the view of ascertaining whether the moisture might be removed by air drying under controlled conditions of relative humidity and temperature, and reached the conclusion that this can be done only when the lignite is first heated to a high temperature in a steam atmosphere. The disintegrated residue from lignite has none of the pasty quality of some of the European lignites; hence, unlike the latter, i t will not cohere when partially dried and pressed into briquets. I n other words, European briquetting methods do not apply to North American lignite. The only way to briquet it is to mix i t hot, with about 10 per cent of its weight of a n asphaltic binder. However, to make such briquets serviceable, the lignite powder must first be freed not only of all its moisture, but also of some of its carbon dioxide and other easily evolved gases; in other words, the solid must be carbonized or retorted to a temperature above 400" C. (752' I?.). Otherwise, the briquets made from it will "explode" when put into a fire. The above outlined manufacture of briquets was first attempted commercially through the efforts of Babcock ( I ) . It was repeated by the Canadian Government (IO) and simultaneously by the Texas Bureau of Industrial Chemistry (report not published); finally it was tried by the United
States Bureau of Mines ( 5 ) . The conclusion reached from these studies is that the cost of the fuel produced is too high to make the procedure profitable. It was thought a t one time that careful attention to the by-products might reduce the high cost, but this was found impossible; the retorting of this lignite produces no by-products of present commercial value. The ammonia obtainable amounts to only 11 to 13 pounds of ammonium sulfate per ton; the so-called lignite tar amounts on a n average to about 2 per cent of the weight of the raw lignite, and is a thin liquid composed of unsaturated, straight-chain hydrocarbons usable only as a fuel. The best gas production results in a yield of 4200 cubic feet per ton with a heating power of 415 B. t. u. per cubic foot; this is evidently of no value except to be used as fuel in the retorting plant. Since the quantities of ammonia and of tar oil are too small to be significant, and since the gas must be used where it is produced-i. e., a t the mine or briquetting plant-it follows that there are no by-products of significant or present commercial value. The latest process for making lignite briquets is that known as the Lurgi process (6). The new feature of this process is the method of drying and carbonizing the lignite which consists of heating it by direct contact with hot flue gas. Although this operation is undoubtedly cheaper than the retorting methods formerly employed, the high cost of the binder is still involved and so far no information as to the total cost is available. It is not known that the process is substantially cheaper than former briquetting processes.
1489
1490
INDUSTRIAL AND ENGINEERING CHEMISTRY
Dehydration without Disintegration I n 1920 the writer undertook to change lignite more directly into a n improved fuel. The solution seemed to require removing the water without disintegrating the lumps, and producing a material which would not reabsorb moisture. Lumps of lignite were placed in a beaker, covered with clear gas oil, and heated gradually to 230" C. (446" F.); moisture began to be evolved as the temperature rose above 100" C. (212' F.), but the material remained essentially intact. There was no formation of fines. Large lumps may crack, but portions ranging from 1 to 5 inches (2.5 to 12.7 cm.) in diameter remain solid (12). During this operation the lignite absorbs a relatively large amount of oil, equal to about two fifths of the weight of the water displaced, so that the product generally contains from 19 to 20 per cent of oil. Although this quantity of fuel oil costs no more than the asphalt for briquetting, and the material is about as strong as raw lignite, yet the product is not desirable as a fuel because the volatile matter is too large in amount and too flashy. Hence a t this point the problem of producing a fuel from lignite by means of oil dehydration became the problem of reducing the oil content of the lumps thus produced. Concerning the dehydration operation itself, the evolution of moisture occurs only while the temperature is rising and stops as soon as this stops. Further evolution of moisture occurs only when the temperature rises above the highest temperature previously attained. Hence a definite amount of moisture is retained by the lignite after i t has been heated to any particular temperature, and the later portions of moisture are progressively more difficult to remove (i. e., require higher temperatures) than t h e preceding portions. Figures 1 and 2 show the amounts of moisture retained by two samples of Texas and one of North D a k o t a l i g n i t e , respect i v e l y , w h e n t h e zeromoisture-content temperature is taken a t 225" C. (437 'F.). The two samples of Texas lignite used were from the same locality but differed greatly in moisture c o n t e n t . This difference affects the curves only in the region of lower temperatures; the curves merge a t 190" C. (374" F.). T h e curves for b o t h Texas and North Dakota lignite show that beyond 220" C. (428" F.) their inclinations to the temperature axis are less than before, and on these plots amount to only about one per cent per 10" C. (18' F.). This slight inclination continues until near 300" C. (572' F.). Here the rate of moisture evolution again increases sharply but is also
1 -
VOL. 31, NO. 12
accompanied by the evolution of carbon dioxide, of carbon monoxide, and of other compounds; this behavior indicates that a t this temperature the lignite is undergoing changes in chemical composition. Hence the water then obtained is no longer to be classed as moisture. But at all lower temperatures there is no indication of any chemical decomposition; hence all water liberated up to some temperature between 220" and 300" C. can be classed as moisture. This behavior has been found to be true with all lignites tried in this laboratory since 1924. Because near 225" C. the evolution of moisture per degree temperature rise is less than a t other temperatures, this point was chosen as the most convenient and logical end point for the determination of moisture. The following method is based on this idea.
Determination of Moisture by Oil Dehydration Lignite undergoes moisture changes readily. On this account lignite samples must be put promptly into airtight containers. Furthermore, the material is very irregular in composition, and to obtain a n average, one myst employ rather large samples. Grinding is not permissible because i t entails large losses of moisture. For these reasons the following procedure is advocated :
A sample of 2270 to 4540 grams is put promptly into an airtight can. To make a moisture determination this is broken up quickly into small lumps which will just pass through the neck of a 1-liter distilling flask; the mass is mixed briefly and replaced in the can. A portion of about 250 grams is quickly transferred to a 1-liter, dry, weighed, distilling flask; the flask is weighed again, and gas oil or kerosene is poured into the flask until the lignite is well covered. T h e flask is mounted on an iron stand (Figure 3), immersed in an oil bath, and connected with a vertical condenser which delivers its condensate into a thistle tube. The latter, in turn, extends into a 100-cc. volumetric flask. The flask stands in a 1-liter beaker. A thermometer is inserted in the distilling flask with the bulb immersed in the oil, and heat is applied so that a temperature of 225' C. is reached in about 80 to 90 minutes. The side neck of the flask is covered with a towel to prevent condensation. When the thermometer isat 225" C., the side neck of the flask is promptly withdrawn from the condenser, and heating is discontinued. The condenser tube is rinsed with a few cubic centimeters of kerosene to wash down any moisture clinging in it. Then water from a buret is run into the flask until it is filled to the mark, and the water thus added is subtracted from 100 cc. to obtain the weight of water obtained from the lignite.
The following results indicate the range of accuracy of this method. The four samples for the first column were drawn from the same sample bottle. About 350 grams from this same sample were then ground to pass 40 mesh and were well
DECEMBER, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
mixed, and four samples of 5 grams each were heated simultaneously in a n air bath a t 105" C. (221' F.) for 2 hours. T h u s the four results in the second column were obtained. % of Sample B y distillation 32.88 32.76 32.40 32.92 Av. 32.72
By air drying at 105' C. 28.98 29.44 29.50 29.71 29.41
Difference = 3.31% of samples, or 4.9270 of lignite oil-dried at 225' C.
T h e results by distillation are more nearly concordant than those obtained by air drying; furthermore they are definitely a measure of the moisture obtainable up to 225' C.; the results obtained b y air drying are partly due to unknown though slight amounts of other weight changes. This was shown by Brandis and Vergeer ( 2 ) who determined the moisture from the same sample of a European lignite by a number of different methods with the following results (in per cent) : Weight losa at 105: C. (221" F.)in Nz stream Weight loss at 105 in Oz stream in air stream Weight loss at 105" Distillation with gas oil t o 155' C. (311' F.) Distillation with xylene to 140' C. (284' F.) Collecting water in CaClz from Nz stream at 105' C. Collecting water in CaClz from 01stream
8:
1491
extent of 4 per cent (of the dry lignite) in the form of a heavy oil residue. However, while the natural binder in the lumps in a few Texas lignites was not impaired by this treatment, in other lignites, particularly those from North Dakota and Canada, it was practically destroyed. This fact, together with the relatively great fire risk involved in the operation of such a plant, led to the abandonment of this procedure. CARBONIZATION WITHOUT AGITATION.The next procedure for removing the excess oil from the oil-dehydrated lump lignite was based on the observation that all such lumps yield a firm charcoal when allowed to remain undisturbed or motionless while being heated from about 225' to 450" C. (437" to 842" F.) or higher (14). I n this temperature range lignite undergoes extensive changes; it evolves moisture, carbon dioxide, and a small amount of liquefiable hydrocarbons (the so-called lignite tar). These materials are evolved almost explosively within this temperature range. This period is followed by one in which there is a more quiet further evolution of gas.
54.66 54.11 54.10 54.12 53.72 53.68 53.46
These results show that the losses in weight are partly due t o the removal of other components than moisture, that these losses are complicated by oxidation changes, that a t 105" C. the moisture is only partially removed, and that the temperature limits of 140" and 155" C. employed in the above oil distillations are of no special significance because they were chosen merely to make these determinations conform to the gas drying results a t 105" C. Hence there is nothing significant about the results obtained with the 105' C. drying operation. For other determinations on lignite, the sample must be finely ground and well mixed, and since these operations will produce extensive moisture losses, a large portion of the powdered material should first be dried a t room temperature for 24 hours, mixed, and bottled, its moisture content again determined as above, and this material used for further determinations. It is advisable to express results on the weight of lignite, oil-dried at 225" C.
Attempts to Manufacture Oil-Dehydrated Lump Lignite PARTIAL DEHYDRATION. As pointed out above, the problem involved in the use of oil for dehydration is the reduction of the amount of absorbed oil, and hence the first attempt consisted of limiting the extent of dehydration. By heating to about 135' C. (275' F.), a product containing 11 per cent moisture and 11 per cent absorbed oil can be produced, but such a partially dehydrated product is worthless because it disintegrates wholly into small fragments within 2 to 3 weeks after its preparation. COMPLETE DEHYDRATION AND REMOVAL OF OIL WITH HOTFLUEGAS. I n the second attempt (IS) the lignite was first dehydrated by being heated in a light oil-i. e., gas oilto 200" C. (392' F.), its temperature was raised to 300" C. (572" F.) by heating in a higher boiling oil. Since practically all of the dehydration occurred in the gas oil, the absorbed oil in the product could be removed by heating it to slightly above 300' C. Hence, after the heavy oil was drained off at 300" C., producer gas a t 500' C. (932" F.) was passed through the lump lignite until its temperature was raised to 350' C. (662" F.). The effluent gas was passed through a condenser and a scrubber or filter, to strip it as completely as possible Qf the vaporized oil. Thus a product was obtained which was entirely free of moisture and which retained oil only to the
The above fact indicated that the oil-dehydrated lignite should be carbonized while it is being kept a t rest. The first attempt to carbonize lignite in this manner showed that a mass of lump coal cannot be heated readily when it lies directly on the heating surface. But, when the lump lignite is held in .trays with bottoms made of iron wire screen and these trays are suspended about 2 inches (5 cm.) above the bottom heating surface, then the heating of the lump lignite takes place readily because the gases rising from the bottom pass through the lignite. The heated gas must be replaced by cool gas from the sides, and thus a continuous circulation of gas through the lignite must be made possible. Since the gas rising through the lignite becomes charged with petroleum vapors, it has to be passed through a condenser before i t is returned to the bottom of the trays for recirculation because the oil vapors would be cracked if they came in contact with the hot bottom. Hence, the operation of such a retort requires taking the hot gas out of the retort a t the top, passing it through a condenser, and returning it a t the bottom. With this arrangement it was found possible to retort this oil-dehydrated lump lignite to temperatures of 500-550' C. (9321022" F.) and remove and collect not only all the oil which had been taken up by the lignite, but also the so-called lignite
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INDUSTRIAL AND ENGINEERING CHEMISTRY
tar. The latter is a material which resembles ordinary gas oil in volatility, and hence i t compensates for any oil losses. It was on this account that in the laboratory unit it was actuslly possible to gain a slight amount of oil. The resulting charcoal amounts to a little less than half the weight of lignite, and the yield naturally varies with the composition of the raw M.iateiisl lignite, With lignite frorn Bienfait, Sashtohewan, a yield of 46 per cent w&s obtained. Rsriignite
The heating power of the product retorted to pIduotI 550' C. was 12,000 B. t . u. per pound. Product2 The resultins material alwavs has a ereat tendency to take &e when i t is krst exposed to the air; this is a general property of all retorted lignite and requires that the retorted mass be cooled and that air be admitted to i t gradually. Before above observationswere used in the design of a continuous plant for dehydrating and retorting lump lignite, it was decided t.o test them i n a pilot plant. Such a plant was built and operated at Estevan, Saskatchewan, in the summer of 1929. A view of the plant is shown in Figure 4. It consisted essentially of one dehydrator and one oven, each with a capacity of 0.75 ton of raw lignite. A plan and side view of the assembly of these two are shown in Figure 5. The lignite was placed in baskets, and four of these baskets were lowered into the dehydrator tank by means of ail elevator frame. The oil was heated by steam coils and pumped to the bottom of the dehydrator; then it rose through the lignite and at the top flowed sideways to the heating coils to be returned to the bottom under the lignite. When a maximum temperature near 200" C. (3'22" F.) hltd been reachrd the elcvat.or with its four baskets or cars was raised, and the baskets were rolled into the oven by nicans of their suspensions from two lateral rails. IIere the baskets were suspended so that their bottoms were about 2 inches above the b e d bottom of the oven. The latter was made of a nickel-chrome steel, and the whole oven was designed to allow for "heat" expansion. Wheii the maxiinurn temperature was attained at the top, the fire was cot off, and the insulating covers at the top were removed t,o allow the oven to cool more rapidly.
This material was dehydrated by being heated to 190" C. (374" F.) in gas oil, transferred to the oven, and gradually heated until the given temperatures were attained. TABT.E I. RESGIXSx1mx Fixed
Volatile hlstter
Carbon
%
%
%
39
22.1 14.9
Moistuie
.. ..
2a.l
PiiiOT
I ' ~ . w rAT E~TEUAN oven
%
Heating Power B.c.v.
*C.:"F.)
31.4
09
7.3 18.1
7,070 iz.070
62.4
14.6
11.900
i%'&iio>
Ash
Bottom
SBO(1040)
Oven Top 'C.("F.)
Yield %
......
B ~ O ( I O Z ~ I 16:+ 450(842) 51.8
Hence, on a n average, 2 tons of raw lignite yield I ton of product. The fuel requirements were estimated on a boiler furnace efficiency of 55 per cent and a retort furnace efficiency of 40 per cent, and found to be 1000 pounds of raw lignite per ton of product, plus all the gas obtained from the retorting. Hence, altogether 5000 pounds of raw lignite are required to produce 1 ton of product; and since the lignite tar obtained will compensate for any losses, the only other costs are for labor and for plant investment. The process appears to have a iriuch better possibility of commercial success than the hriquetting processes, yet it did not produce an improved fuel a t a sufficiently low cost to justify commerciai enterprises.
Final Process-Dchydratinn under Conditions Preventing Extensive Oil Absorption The difficulties attending the removal of absorbed oil from the dehydrated lignite made it desirable to try to prevent or minimize the alrsorption of oil during the dehydration operation. The basic idea for accomplishing this is to prevent the evaporation of moisture from the pores of the lignite during the heating-;ripperiod by employing a closed vessel capable of standing the vapor pressure obtained at maximum temperature and filled niainly Tvith lignite and oil; thus only a negligibly small itmount of moisture is vaporized to establish the pressure inside so that the pores of the lignite will remain
FXCURE 4. LIGNITE DEHYDRATING PLANT, ESTEVAX
About 3 hours were required for dehydrating, 5 hours for carbonizing, and 10 hours for cooling because it had to be done in the oven. In a specially built cooler the material could be cooled in a few hours. The product thus obtained was of excellent quality. The data taken from two operations are presented in Table I.
filled with moisture. Furthermore, i t was primarily contemplated to use a high-boiling oil, which would not add a p preciably to the vapor pressure and thus avoid an excess of outside pressure for forcing oil into the lignite. Contrary to expectations, it was found that less volatile oils than gas oil cannot be used because they bring about extensive disinte-
INDUSTRIAL AND ENGINEERING CHEMISTRY
DECEMBER, 1939
1493
R
OIL- CIRCULATING
i
OVEN AND FURNACE SIDE VIEW
DEHYDRATOR SIDE VIEW
FIGURE 5. LIGNITE DEHYDRATION PLANT
choice between the following three operations to determine which would give the most desirable results:
gration of the lumps, but that oils which are much more volatile can be used because the total vapor pressures of oils saturated with water are less than their theoretical pressures and there are some volatile oils which produce total pressures no greater than that of water alone (Table VII). The latter are particularly serviceable because they are removed, extensively or wholly, with the steam after the oil has been drained
I. Opening a cock at the bottom and draining off the oil and then allowing the hot charge t o evaporate its moisture and thus t o blow out most of the oil that may have been absorbed on the surface. 11. Opening a cock at the t o p and allowing vapors t o blow off until the vapor pressure had been reduced to atmospheric pressure and then draining off the oil. 111. Allowing some suitable fraction of the vapors to blow off through the top cock, but sto ping this operation while a substantial amount of vapor is stif retained within the lignite, then opening the bottom cock, draining off,the oil, and allowing the rest of the moisture t o evaporate from the lignite and blow out much of the absorbed oil.
Off.
The first part of this process consists of nearly filling a strong vessel with lignite and oil, closing it so that no vapors can escape, and heating i t with steam coils or a steam jacket t o a temperature near 210' C. (410' F,). Then came the
Operation No. ---Jacket Lb.
TABLE 11. OILDEHYDRATIONS IN A CLOSED VESSEL Oil
InsideC.(" F . )
Lb.
2
C . ( " F.) gage 313 219(426.2) ZOQ(408.2) 239 281 213(415.4) 198(388.4) 180
Kero. 1 Gas Oil
3
308 218(424.4) 209(408,2) 239
Kero. 1
4 5
242 206(402.8) 198(388.4) 180 242 206(402.8) lgS(388.4) 180 346 224(435.2) 218(424.4) 293
Gas Oil Gas Oil Gas Oil
324 ZZl(429.8) 208(406.4) 230 315 Zlg(426.2) 203(397.4) 210 345 223(433.4) 214(417.2) 271
Kero. 1 Kero. 2 Kero. 3
354 344 382 386 376 292 308 324 313 324 335 344 376 416 397 397 397
Naphtha Mixt. Aa Mixt. A Mixt. A Mixt. A Naphtha Naphtha Mixt. Bb Mixt. Bb Mixt. Bb Mixt. Bb Gasoline Mixt. C c Mixt. C Mixt. C Mixt. C Mixt. C
gage
1
6
7 8
9
O
ZZG(438.S) 212(413.6) 223(433.4) ZlZ(413.6) 12 229(444.2) 213(415.4) 13 229(444.2) ZlZ(413.6) 14 22q442.4) ZlZ(413.6) 15 210(410) 215(437) 16 21q424.4) 210(410) 220(428) 210(410) 17 18 Zlg(426.2) 210(410) 19 219(426,2) 210(410) 20 222(431.6) 210(410) 21 224(435.2) 21 l(411.8) 22 228(442.4) 218(424,4) 233(451.4) ZZl(429.8) 23 24 231(447.8) ZlS(424.4) 231(447.8) 219(426,2) 25 213(415,4) Zlg(426.2) 26 a One part oil t o 3 parts naphtha 1. b One part oil to 3 parts naphtha 2. One part oil t o 3 parts gasoline.
10 11
274 274 280
274 274 272 272 272 272 272 272 303 335 348 335 335 335
Blowoff
CS2 Eut.
H ~ 0 i n from Produot Product
Lb. gage % None 11.2 Complete t o 1 atm. 5.5 Rapid t o 50 lb. 5.2 To 100 lb. 6.6 Same 9.9 To 140 lb. in 10 min. 10.1 T o 150 lb. 5.9 Same 5.25
T o 150 Ib.
in 28 min. Same Same Same Same Same Same Same Same Same Same Same Same Same Same Same Same Same
5.78 6.36 6.0
4.9 6.0 5.6
3.2 2.75 3.83 2.64 3.4 2.3 6.67 5.86 6.66
6.46 5.0 7.8 c
% 3.2
14.4 8.1
9.45 10.92 8.5
5.3 6.9 8.28
2.25 4.0 4.33 3.5 3.0 1.57 2.79 4.11 6.53 4.86 4.1 7.55 L55
8.25 7.25 6.5 7.75
Operation I would employ merely the sensible heat in the lignite to evaporate the moisture, and this might not suffice to evaporate enough of it. [The Fleissner process (S), in which lignite is heated in a steam atmosphere up to a maximum pressure of 220 pounds, depends mainly on the sensible heat in the lignite to evaporate the moisture. However, as Lavine, Gauger, and Mann (9) showed, the material absorbs moisture from the steam, and hence the sensible heat has additional evaporating to accomplish, which is not the case in the above oil dehydration process. While Fleissner also provides a hot air blast at the end to aid in evaporating moisture, the moisture removal is incomplete. ] In operation I1 the oil would supply all the heat for evaporating the moisture, and in this respect this operation would be like the former oil-dehydration procedure, but it would be unlike the former in the fact that the evolution of moisture could be allowed to take place so rapidly that the simultaneous entrance of oil into the pores could be prevented or hindered thereby. Operation I11 is evidently designed to evaporate a part of the moisture by means of heat furnished
IKDUSTRIAL AND ENGINEERING CHEMISTRY
1494
by the surrounding oil, and to evaporate the rest by means of the sensible heat in the lignite; thus it might be operated to secure complete moisture removal while providing a n adequate amount of moisture to remove absorbed oil left after draining the latter. With the above objects in view, a series of trials was made which gave the results presented in Table 11. The apparatus (Figure 6) is essentially a steam-jacketed autoclave made of a 10-inch (25.4-em.) iron pipe with an inside length of 17 inches (43.2 cm.). The lignite is held in a wire screen basket on feet which keep the bottom of the lignite about one inch above the bottom of the autoclave. The steam jacket is heated direct with gas flames and hence serves also as a boiler, The inner vessel is connected a t the bottom and a t the top with the condenser. The latter consists of 25 feet (7.6 meters) of copper tubing, inch (9.6 mm.) in diameter. Pressure gages and a thermometer well are provided as shown. The usual charge was about 5000 grams of lignite and 15 liters of oil. About 30 minutes were necessary to heat the whole apparatus to 100' C. (212' F.), and then about 90 minutes more to heat it to the maximum temperatures given in Table 11. The amount of gas heat applied was always the same. When the maximum temperature was reached, the blowoff from the top was operated as stated in Table 11. The length of time for the blowoff to 150 pounds was about 30 minutes except when the exact time is given. As soon as the upper valve was closed to end the blowoff, the lower valve was opened to allow the oil to drain as rapidly as possible (usually in about 3 minutes), and the steam pressure was allowed to expend itself. Then the gas burners were cut off and the vacuum pump was applied a t the end of the condenser to reduce the pressure in the system to 50 mm. of mercury as rapidly as possible, usually in 2-3 minutes. The autoclave could then be opened and the charge removed while hot. Table I11 presents the distillation ranges of the oils useda gas oil, three kerosenes, two naphthas, and one gasoline. Mixtures of 1 part by volume of the gas oil with 3 parts of the naphthas or gasoline, respectively, were also used.
' RANGES(" C.) TABLE 111. DISTILLATION Initial distn. point
ixg %% 90 distd.
Endpoint
Kero.
1
Kero. 2
Kero. 3
Naph. 1
Naph. 2
Gaso-
190 232 312 410
198 219 249 265 280
169 203 237 265 284
183 209 225 237 252
155 175 183 194 209
124 139 160 191 209
42 65 126 191 217
.,,
TABLEIV. Product No. 10 11 12 13 14 15 16 17 18 19 20
line
COMPOSITION OF PRODUCTS IN TABLE I1
% Moisture
Av.
OILSIN TABLE I1
OF
Gas Oil
6.36 6.0 4.9 6.0 5.6 3.2 2.76 3.83 2.64 3.4 2.3 4.27
% Oil Absorbed 0.25 2.0 2.33 1.5 1.0 -0.43 t-0.79 2.11 4.53 2.86 2.1 1.73
% Ash 9.1 11.15 9.76 14.85 10.84 14.3 14.18 13.84 13.64 13.77 13.93 12.67
€3.
t. u./Lb. 10,800 10,843 11,163 10,667 11,259 11,100 11,090 10,990 10,900 10,890 11,088 10,980
REMOVED TABLE V. RATIOSOF OILTO WATERIN VAPORS Vapor No. 6 8 9
10 11
21 22
Kind of Oil Gas oil Kero. 2 Kero. 3 Naphtha 1 Mixt. A Gasoline Mixt. C
-Ratio In blowoff Cc. 390/930 1750/1200 670/970 2600/1100 2400/1040 4900/1500 3600/1150
Oil/WrtterIn vacuum
cc .
140,420 350/250 210/200 250/250 2ii/i70 130/160
VOL. 31, NO. 12
All these trials were made with lignite from Bastrop, Texas; when fresh from the mine, i t had the following average composition: Moisture at 225' C., % Ash, % Heating power, B. t. u./lb.
38.75 9.05 7000
Table IV presents the composition and heating powers of some of the products. The oil in these products does not increase the heating power more than 100-150 B. t. u. per pound because the dry, ashless, lignite substance itself has a heating power of 13,415 B. t. u. per pound and its displacement by oil increases the heating power about 60 B. t. u. for each per cent of oil. TABLE VI. WATERREMOVED IN DIFFERENT PARTS OF OPERATION Operation 13"
%
Grams
Net weight of !ignite Water in raw lignite, by oil distn. t o 225' C. Total water Water in product Water collected from blowoff Water in drained oil Water in vacuum Water not accounted for Weight of product Number of operation in Table 11.
...
5180 1955 224 1100 200 200 240 3520
37.8 100 11.45 56.3 10.24 10.24 12.26
...
Operation 18" Grams
yo
5060
...
2050 370 1050 200 200 230 3680
40.6 100 18.05 51.3 9.76 9.76 11.22
...
Q
Table V shows the ratios of oil to water present in the vapors removed from the vessel during the blowoff and the vacuum operation, respectively, and Table VI gives a complete account of what happens to the total water present in the raw lignite. The "water not accounted for" is probably lost equally in the blowoff, draining the oil, and drawing the vacuum. The amounts of moisture in the products were determined by oil distillation to 225' C. (437" F.) and this must be borne in mind when comparing these results with those obtained by air drying a t 105' C. (221' F.) (see section on "Determination of Moisture by Oil Dehydration"). The amounts of carbon-disulfide-extractable matter were determined in a Soxhlet apparatus. I n order to determine how much of the material is thus obtained from the lignite (i. e., how much is lignite tar), a charge of the same lignite was heated in the same manner but immersed under water instead of oil; the total extractable matter was determined to be 2.9 per cent of lignite oil-dried a t 225' C . Another test was then made as follows: Two thousand grams of product 22 (Table 11) were ground and extracted repeatedly with carbon disulfide; 100 cc. of extract with a specific gravity of 0.9265 (at 32' C.) were thus obtained. This amounts to 4.63 per cent of the product, whereas the total carbon disulfide extract for this product amounted to 5.55 per cent; hence 0.92 per cent was not extracted in this largescale operation. This extracted portion was examined by distilling, determining the specific gravities of the various portions, and comparing the results with corresponding observations made on the gas oil. The results are tabulated below; gravities (in parentheses) are a t 32' C. and amounts in weight per cent: Pressure, Mm. H g Atm. Atm. 38 38
..
Temp., O F. (" C.) 110-184 (43.3-84.4) 184-366 (84.4-185.6) 2 0 8 5 2 0 (97.8-271.1) j20-552 (271.1-288.9) Residues
Gas Oil (0.826), yo
Ext. (0.9263), % ' 1 4 . 8 (0.73) 1.63' 5 4 . 0 (end point) (0.83) 3 (end point) decomposed 9 29.57
0 0 88 (0.828)
Since the 208-520 ' F. fractions have practically the same gravities, we may assume them to be identical; and the fraction of gas oil present in the 520-552' F. fraction of the ex-
INDUSTRIAL AND ENGINEERING CHEMISTRY
DECEMBER, 1939
tract may be assumed to be proportioned to these amounts. Thus we obtain: (54/88) X 12 = 7.4% 54 7.4 = 61.401,
+
This fraction (61.4 per cent) of the extract may have been derived from gas oil; but the remainder is certainly of a different origin, and the latter amounts to 22.2 X 4.63, or 1.03 per cent of the product.
FIGURE6. AUTOCLAVE FOR DEHYDRATING LIGNITE 1. Thermometer 2. Steam vent 3. T o condenser 4. Steam jaoket 5, 7. Pressure gages 6. Oil drain 9. Lignite
1495
A comparison of the results obtained with gas oil and with kerosene, respectively, showed the latter to be preferable; hence, progressively more volatile liquids were tried-i. e., naphtha 1, naphtha 2, and gasoline (Table 111). The best results were obtained with naphtha 2. I n order to understand why the still more volatile gasoline gives less desirable products, one must note that the amount of oil retained in the product is determined by two different actions which produce opposite effects-the absorption of oil due to the net amount of pressure acting to inject oil into the lignite during the heating-up period, and the evaporation of the absorbed oil afterward when the liquid has been drained out of the autoclave. I n order to ascertain the net pressure exerted to inject oil into the lignite, mixtures of water with the respective oils were heated to determine their total vapor pressures a t 200" C. The results are given in Table VII. The last column shows that with oils less volatile than naphtha 1, the moisture in the lignite exerts less pressure than the vapor pressure of the moist oil, and hence some moisture probably leaves the lignite to mix with the oil until equilibrium is attained. But the opposite is the case with the more volatile oils. With naphtha 2 and with gasoline the vapor pressure of the moist oils is greater than that of the moisture in the lignite, and hence oil is pressed into the lignite. It appears that with naphtha 2 this latter effect is more than compensated by the greater volatility of this oil which serves to evaporate correspondingly more absorbed oil after the oil has been drained away from the lignite, but not so with the gasoline. Hence, there is a limit in the volatility of the oil to be used for this purpose. TABLEVII. DIFFERENCES BETWEEN VAPORPRESSURE OF WATER(225.5 POUKDS PER SQUARE INCH)AND OF OIL-WATER MIXTURES, AT 200" C. (392' F.)
Since the portion not extracted in this large-scale operation is likely to be derived from the lignite rather than from the absorbed oil, the total amount of lignite tar thus indicated is 1.03 0.92, or 1.95 per cent. This result agrees fairly with the preceding determination, in view of the fact that the darkening of the oil used indicates appreciable extraction of lignite tar. I n order to avoid underestimating the amount of oil absorbed, the amount of lignite tar in the carbon bisulfide extract will be considered to be only a part of the above results; hence the figures in Table IV, column 3, are derived from those in Table 11, last column, by subtracting 2 per cent from each of the percentages of extract. Operation 1, Table 11, corresponds to operation I above; there was no blowoff, and as soon as the charge attained 209" C. (408.2" I?.), the lower valve on the autoclave was opened, and the oil was allowed to drain rapidly, and the moisture was evaporated by the sensible heat of the charge. The results show that the amount of oil absorbed is only 3.2 - 2.0, or 1.2 per cent, and hence very small in amount. But the amount of moisture retained is still fairly large (11.2 per cent). Operation 2, Table 11, was carried out as described under operation I1 above; as soon as the charge had attained 198" C. (388.4" I?.), the top valve on the autoclave was opened, and the vapors were allowed to blow out until the pressure had dropped to 1 atmosphere (in about 30 minutes). This operation reduced the moisture content to a desirable extent but left a fairly large content of oil (12.4 per cent). All other trials were made as described under operation I11 above. Operations 3 , 4 , 5, and 6 of Table I1 show the effect of blowing off to different final pressures. These results indicated that a blowoff to 150 pounds appeared to secure generally the most desirable results, and hence all other operations were made in this manner.
+
Material Gas oil Kerosene 2 Naphtha 1 Naphtha 2 Gasoline
Vapor Pressure Oil f Water, P
B. P.
c. 312 237 183 160 126
Lb.per
F.) (593.6) (458.6) (361.4) (320) (258.8) ( 0
204 215 228 256 298
P minus 225.5 sq. in.
-21
5
-10.5 + 2.5 +30.5 +72.5
Properties of Oil-Dehydrated Lignite I n order to determine the aqueous-vapor-absorbing tendency of this oil-dehydrated lignite, samples were exposed to a water-saturated atmosphere a t temperatures varying from 80" to 95" F. (26.7" to 35" C,), and the following increases in weight were obtained in per cent of original weight: Sample No. After 24 hr. 48 hr. 91 hr.
3 1.22 1.44 1.52
12 1.75 3.38 3.5
22 3.8 6.06 6.06
I n order to determine its resistance to liquid water, 500gram portions of samples 3 and 22 were placed in a basket made of wire netting (16 mesh per inch), weighed, submerged under water for the following respective periods of time, then allowed to drain for 30 seconds, and weighed again; this procedure was repeated as shown: Time of Immersion 15 sec. 1 min. 5 min. 1 hr. 24 hr. 91 hr.
Increase as % of Original Weight No. 3 No. 22 .. 2.08 2.37 2.67 2:65 2.67 2.54 6.35 6.47 16.20
..
These tests show that with water this material behaves like ordinary coal rather than like wood charcoal. The freshly produced material is entirely free of fines and is in lumps with diametric lengths varying from 1 to 5 inches
INDUSTRIAL AND ENGI NEERING CHEMISTRY
1496
(2.5 to 12.7 em.). It does not change noticeably with time. Figure 7 shows some material made more than a year before, which has been handled repeatedly in transferring i t from one container to another. The following screen analyses and strength tests were all made with such aged material.
FIG1:HE
7. OILDEHYDRATED LUMP L l G N l T E
VOL. 31, NO. 12
revolutions in 1.5 hours with a drop of 19 ern. (7.5 inches). Table IX presents the screen analyses of the material resulting from this test. This material is wholly different from any now on the market, and when handled in the usual manner it will he shattered so extensively as to destroy largely the advantage of being initially in lump form. The mat.eria1could be produced so as to have much greater strength by leaving larger amounts of moisture in it; but this advantage defeats the main purpose of the process-to produce a material with tire maximum possible heating power. If the material is poured through troughs or chutes instead of being tossed, i t call probahly be loaded, shipped, and unloaded in carload lots without undue disintegration. However, for domestic useit should be put up in paper bags, a practice which has been employed successfully in several instances and can be done economically by employing strong double paper bags with a capacity of 40 pounds. If the product is made like Kos. 10 to 20 (Table II), the properties of the raw lignite and of the product compare as shown in Talde X.
The samples were subjected to a drop test similar to the A. S. T. M. standard method of shatter test for coke ( S o . D-
141): A 4540-gram (10-pound) portion of coal was pbaced in a box
4.27 1.91
bottom of the box
was
12.67 10,980 40.6 10,541
a'smooth sheet of metal, which when
1.G5
41
I . 406
paratus, and finallJ'subjeeted to the same s&en &ai& (#ahtable VIII-R).
a
In order to show that this process may he applied equally well to lignite from other places in North America, a sample was secured from the Onakawana lignite field in Canada near the southern end of Hudson Hay. The sample was taken from the lower seam of the deposit (ZI), and two portions were treated like samples 17 to 20 (Table 11). The products obtained have the same physical properties as those from Texas lignite, and their composition and heating powers are as follows: Sample
% Moisture
%Oil Absuibed
A I3
8.0 7.8
0.81 0.91
70 Ash a. 33 6.36
13.
t. u./Lb. 11.145 10.664
It is evident that this material needs a slightly more extensive hlowoff to reduce its moisture content to 4 per cent; then its oil content will be about 2 per cent, and its average heating power ahout 11,120 R. t. u. Literature Ciled (11 Bsboock. E. J., U. S. Bur. Mines. BdZ. 89 (19161.
TABLEIX. SCREENANALYSES OF RESULTS FIWM TUMEJ.ING TEsTs MADE~ ~ 1 IJJMPY~ ~ 1 1 FROM MIXTURE OF S A M F L10-18 E~ Teat
_ _ _ . . ~ Sire, ~ Cm.:.~ 00 On 0" 0" 1.88
0.47
0,117
%
%
%
%
21.7
R.3
13.9 33.7 19.6 30.0 " O n 3.81 throucli 2.54 om.
I 2
20 0
0.0642
9.2
(21 Brandie and Vergcer, Biennstof-Chem., 3,353 (1922). (31 Flsissner. U.5. Patents 1,632,829(June 21. 1927). and 1.679,078
(July 1, 1928).
Gordon, Lavine. and Harrington. IND.Eno. Cesw.. 24, 928 ~ . ~ ~ . _ _(41_ On l'hiouzli (19321. 0.0074 0 0074 ( 5 ) Hood. 0.P.. and Ode& W. W.. U. S. Bur. Mines. BUZZ. 255 % % (19261. 11.2 11.2 (61 Hubman. B7ennslofl-Chem., 11. 219 (1930). _?
12.6
s.7
~~~
The second strength toat was aiirrilarto the A. S. T. M. standard method of tumbler test for coke (No. D-294). It oonsisted of placing 1200 grams of material passing 3.81-cm. (1.5-inch) screen and retained on 2.54cm. (1-inch) meen in an AbhB mill jar of approximately 19 cm. (7.5 inches) internal diameter, fitted with metal bafflesto prevent the material from slipping. Comeepondin to the A. s. T. M. requirements of 1400revolut.ions in 1 hour wi?h a drop of 91.4 em. (36 inches) this test employed 6300
(71 Larian. Lavine. Mann. and Gauger, INU.ENB. CXEX..22. 1231 (19301. (81 Lavirie and Gauger, Zbid., 22, 1226 (1930). (91 Lavine, Gauger. and Mann. Ihid., 22. 1347 (1930). (101 Lignite Utilization Board of Cenada, 1st Gene~alRept.. March 15, 1924. (Ill Ontario Dept. Mines. Ann. Kept., 42, Pt. 111 (1933). (12) Schoeh, U. S. Patznt 1,508.617 (Sept. 16. 1924). (131 Ib
