Low-Temperature Carbonization of Coal
Engineering Factors Relating to the Utilization
of the Cannel Coals of Southern Utah
by S.C. Jacobsen & G.W. Carter
Thesis submitted to the Faculty of the University of Utah (15 May 1933)
Table of Contents ~
Frontispiece: The Great White Throne (showing members contiguous to the cannel coal measures) [Not included here]
3. Cannel Coal
4. Utah’s Cannel Coal Deposit
5. Object of Plant Tests
6. Description of Apparatus
7. General Test Procedure
8. Description of Individual Tests
9. Heat Calculation for Test Run # 6
10. Discussion of Results
1. Acknowledgement ~ [Not included here]
2. Introduction ~ [Not included here]
3. Cannel Coal ~
Ashley (11) states that, "Cannel coal is a massive, non-caking, tough, clean block coal of fine, even, compact grain, dull luster, commonly conchoidal cross fracture, having a low fuel ration, a high percentage of hydrogen, easy ignition, long yellow flame, black to brown greasy streak, and moderate ash, which is pulvurent in burning. It is essentially a rock derived by solidification and partial distillation or oxidation of water-laid deposits consisting of or containing large quantities of plant spores and pollen grains and more or less comminuted remains of low orders of water plants and animals".
David White (12, in writing about his microscopical study of the Utah cannel coal, says, "The fuel contains very little if any vestiges of the cell structures of higher plants, being made up largely of lemon-yellow, more or less lenticular, or globular, translucent bodies embedded in a brownish black groundmass of somewhat flocculent aspect. Some of the translucent matter is probably resinous, while it is possible that some of the lemon-yellow substance, less in quantity may be gelatinous, tough that is not at all certain. On the whole, the microscopical composition of the coal is essentially that of a high-grade cannel".
It is generally accepted that bituminous coals resulted from woody materials whereas cannel coals appear to have been formed from decayed spores, pollen, leaves and the cuticle material from plants, thus these waxy ingredients account for the high oil yield which is possible from most cannel coals, being usually two to three times the yield from bituminous coals. The same organic constituents are largely responsible for the oil obtainable from oil shales.
Cannel coal is adapted to the common uses of bituminous coals excepting coke manufacture. It is especially an ideal fireplace fuel and for a long period has been accepted as a "deluxe" fuel for this purpose. It is very clean to handle, attractive in appearance, ignites very easily, gives a cheerful, large, bright, orange-colored flame, and the ash is in pulvurent form. It burns without disintegration and therefore does not yield as much smoke as the common high volatile bituminous coals, thus making for a very popular domestic fuel.
Because of the high volatile content and high candle power of the volatiles, cannel coal has been in use extensively in former years in the eastern USA for coal gas enrichment. In the early days in Utah, cannel coals and oil shale were imported from Australia for use in the first gas plant to increase the candle power of the city gas. The principal use of cannel coal in the USA in past years was for the production of oil for refining into the common oil products. As early as 1846 oil was manufactured from coals and in the year 1860, when the first reqal discovery of petroleum occurred, there were 55 coal-oil plants operating in the US, the largest having a distilling capacity of 6000 barrels of oil per day. Kerosene (coal oil), light lubricants, greases, and wax were the principal refined producrts, gasoline having no market value at that time. Most of the plants were in Pennsylvania, Kentucky, and West Virginia, although one large plant was in Boston. The principal cannel coal deposits are in Pennsylvania, Kentucky, West Virginia, Indiana, Ohio, Tennessee, Missouri, Iowa, Arkansas, Texas and Utah.
4. Utah’s Cannel Coal Deposit ~ [Not included here]
5. Object of Plant Tests ~
In the visit to the cannel coal deposit in 1932 information was obtained by the writers showing that the coal deposit was sufficiently extensive and accessible to large markets by truck and rail to justify its early development. It was also concluded that because of the pronounced superiority of this coal as compared with all other local coals for domestic fuel and as a source of road oil and motor fuel -- that a need existed and an impetus could be given the development of this Utah resource if a study were made of the processing of the slack coal from the deposit. Consequently a study was planned of the heat requirements in treating this coal as well as an investigation of the products formed.
Advantage was taken of the studies made of this coal in 1920 by the State of Utah and the Federal Government in which laboratory processing data were obtained (9) and by which excellent yields and quality of oil were obtained. The destructive distillation method used steam as the heat transferring fluid, the exhaust steam from power plant engines or turbines being superheated and then passed directly through bodies of sized, dust-free coal. This method [the Karrick LTC Process] (13) had subsequently been developed (5) for commercial uses and appeared to have many advantages, so it was adapted for the thesis study of the cannel coal. In designing the test apparatus the primary objects were to minimize radiated heat losses under all processing conditions and then take temperature and heat-flow data throughout the coal charges and the apparatus, thus permitting a correlation of products obtained with the most economical use of heat.
This coal treating method used is one of a group being offered to the Utah Research Foundation [by Lewis C. Karrick].
6. Description of Apparatus ~
For the purpose of carrying out this investigation, a small distilling plant was constructed. Figures 2 and 3 are, respectively, a schematic plant layout and a photograph of the test setup.
The plant, Figure 2, consisted of a gas-fired superheater (a), a coal retort (b), and the condensers (c), (d), and (e).
The combustion chamber (f) of the superheater was constructed of common brick. Heating gas was supplied from the gas line through the control valve (g) an was measured in meter (h). The manometer (i) provided the operator with an instantaneous sight control of the volume of gas delivered to the two burners. These burners consisted of the nozzles (j) and the air and gas mixing tubes (k).
Above one end of the combustion chamber an supported from the wall by mean of a bracket, was the steam superheating coil consisting of approximately one hundred feet of 1/2" standard pipe formed into a coil 15" in diameter and 48" high. This coil was hung in the annular space between the cylindrical column (1) and the heat-insulating outer wall (m) so that the hot gases from the combustion chamber passed at high velocity over the coil counterflow to the steam. The outer wall was 4" thick and was comprised of two sheet metal casings filled with diatomaceous silica earth. This structure was supported on a frame work, about 10 ft above the floor. At the inlet to the insulating coil there were provided a steam gauge to show the pressure of the steam as it entered the coil, a steam-flow regulating valve, and a steam separator with a drain as shown on the drawing, Figure 2.
The coal-distilling retort (b) consisted of a thin-walled cylinder (n) of 18-gauge black iron with welded seams, 5" in diameter and 8 ft high. On the top and bottom ends of the retort were welded 5" pipe couplings with screw plugs to serve as removable closures. At the top of the retort a flexible connection with the superheater was provided from a multiple-elbow assembly of 1/2" fittings and nipples, thus relieving strains on the superheater and retort caused by changes of length with temperature. To further obviate any strains to the connection between the retort and superheater, the retort was made stationary by suspending it from a wall bracket with wires connected to arms welded to the top of the retort. Changes in length of the retort thus took place downwardly. Likewise a flexible multiple-elbow vapor outlet of 3/4" fittings was provided at the bottom of the retort leading into the condenser (c), this also preventing strains to the equipment due to thermal expansion. The retort was well-insulated against heat losses by surrounding the retort with a sheet iron jacket (o), spaced 6" from the retort and filling this annular space (p) with diatomaceous earth. The insulating material and jacket were supported 2 ft above the floor by a circular steel plate. The lower 4" of the retort and the vapor connections protruded through this plate allowing free vertical movement of the retort by thermal expansion and easy access to the lower retort plug for discharging the treated coal.
The superheated steam connections from the superheater into the top of the retort were buried in the same insulating material up to the top of the 5" coupling. The remaining exposed portions of the retort and plug were buried under a layer of ground asbestos-magnesia insulating material which was removed while the retort was being charged. A low-pressure steam gauge (q) was screwed into the charging plug and served to indicate the back pressure in the top of the retort above the coal. The lower plug was not covered, the coal being supported well up within the insulated retort shaft.
Six thermocouples (abbreviated to TC on Figure 2) were placed in firm contact with the retort walls through holes in the retort casing at 16" intervals, beginning at the bottom of the retort; also one thermocouple was inserted in the superheated steam connection at the top of the retort. The thermocouple leads were run to the selective switch board ® from which connections were made to the potentiometer (s).
Vapors from the bottom of the retort were carried to the top of the condenser (c) through a vertical 3/4" pipe. The condensed vapors were removed at the drain provided, and the remaining vapors were then carried out from the top of the second tube of this condenser to the condensers (d) and (e).
Condenser (c) consisted of two vertical 2" pipes (t) 6 ft long, joined at their lower ends and containing a spiral metal ribbing which caused rotation of the vapor stream and impingement of condensed particles against the tube walls. Each pipe was surrounded by a steam jacket of 4" pipe with steam inlets, blow off, pressure gauge and valves for regulating the steam pressure, and therefore the temperature on the 2" tube walls. An oil drain was provided in the bottom of the connection between the two 2" tubes. This condenser thus provided a means of condensing out of the vapor stream only the high-boiling oil vapors while preventing any condensation of water vapor. By thus removing the high-boiling oils, which were found to be heavier than water, the remaining oils and water could be condensed together in another condenser and thence separated by decantation. Without this selective condensation this crude oil, which has approximately the same specific gravity as water, could have been separated from the water only with great difficulty.
Condensers (d) and (e) consist of two coils of 2" pipe placed in series occupying separate compartments in the condenser box (u). Cooling water flowed counter direction to the vapors being cooled, the condensate from condenser (d) being maintained above 70° F so as to prevent the waxy oil condensed from congealing and clogging the coils. The oil and water condensates of condenser (d) were drawn off under a liquid seal and the remaining vapors and gases were passed into condenser (e) surrounded by cold water so as to condense the light oils, the latter being collected in a container shown. The non-condensable gases were measured in the meter (v) and were then burned at torch (w).
7. General Test Procedures ~
In conducting the test runs made in this study, the following procedure was practiced in obtaining the data and observations recorded on the accompanying data sheets.
A 50 lb representative sample of raw coal which had been previously sized was charged into the retort and the upper end of the retort closed and insulated with ground asbestos-magnesia material. The superheater fuel gas was then ignited and the superheater allowed to warm up. In the meantime, the steam separator drain was adjusted, condenser (c), Figure 2, was heated by raising its steam jacket pressure to 5 lb gauge, then condenser (d) was heated by bubbling steam into its cooling water in order to raise its temperature between 70° C and 80° C where it was maintained thereafter throughout the run by regulating the rate of flow of cooling water, and condenser (e) was cooled by turning cold water into its condenser box.
After containers had been placed under the condensate drains from each condenser, the meter (v) for registering generated gas flow was read and the retort temperatures were taken and recorded. The saturated steam was then admitted to the superheater at a pressure of 20 psi. The meter (h) registering the flow of gas supply to the combustion chamber, was read simultaneously with the admittance of steam. The superheated steam pressure indicate by gauge (q) at the top of the retort was then read and all readings were taken and recorded at 15 minute intervals during the superheated steam period. This is the period during which superheated steam was being used for distilling the charge.
At the beginning of each run a large volume of gas was supplied to the combustion chamber in order to obtain a rapid rise in the temperature of the superheated steam up to the predetermined distilling temperature (*1), and thereafter the gas supply was regulated at frequent intervals to maintain this temperature.
(*1 ~ The final distilling temperature is the approximately constant temperature at which the superheated steam was maintained during the superheated steam period.)
When generated fixed gases from the coal began issuing from the torch (w) they were ignited, the time was noted and meter (v) read. Condensed steam and the medium gravity oils were collected from condenser (d) in an oil separator, from which the water was driven off and measured for the duration of the superheated steam period.
The superheater gas supply was then shut off at either of the following two instants; first, at the time when the rate of evolution of the coal gas began to decline which accompanied a change of flame coloration from orange to light yellow, indicating nearly complete distillation of the charge; and second, the time at which it was estimated, by observing the rise of temperature indicated by the various thermocouples that the upper part of the retort and contents had reached a high enough temperature and contained enough heat to raise the lower portion of the retort to a temperature slightly above 360° C (the initial distilling temperature). It had proved that this final temperature would complete the distillation at the base of the charge and that it would be attained during the dry-quenching period and thus decrease the length of the superheated steam period.
Superheated steam of high initial temperature was used to cool the retort and its contents during the time designated as the "dry-quenching period", that is, the period in which steam was passed through the superheater and retort with the superheater fuel gas supply discontinued. Obviously, the residual heat within the superheater kept the steam superheated to some degree after the heating was stopped. This method of cooling was used in all runs except Test # 8 in which the retort and contents were cooled by the method set forth in the description for that test. The retort temperatures during the first part of the cooling period were read at 5 minute intervals in order to obtain more complete data on the rapid temperature changes that occurred during this time. Thereafter readings were taken every 15inutes as before. At the instant the evolution of generated fixed gases ceased, the time and meter (v) were read.
When all the thermocouples indicated temperatures throughout the retort approximating 250° C the steam was shut off and the coal residue was dropped out of the retort by removing the lower retort plug. This temperature has been demonstrated to be sufficiently low to prevent ignition of the discharged residue. A few moments were allowed for the condensers (c), (d), and (e) to drain, then the oil condensates were mixed together and stored for further study.
Each crude oil sample was distilled under pressure in a 2 gal still for the purpose of determining the water contained as emulsion in the crude oil. Thus the amount of dry crude oil was determined and recorded. Analytical distillation analyses have previously been made on the crude oil from this coal which had been produced by the same destructive distillation treatment, and consequently it was not necessary to make these analyses. However, the yield of crude oil and its properties were found to be identical in all the 8 runs and therefore a sample was subjected to a cracking and refining study. The distillation and cracking analyses determined from this sample are recorded herein. [Not included here]
The thermal value of an average sample of the generated fixed gases taken during a typical test run was also determined.
8. Description of Individual Tests ~
Test Run # 1: The retort was charged with 50 lb of coal sized to 1" to 1/2", which was distilled with superheated steam at 650° C (1202° F).
The accompanying temperature curves and operating data show that superheated steam first entered the retort at 244° C and was then raised to 650° C by the end of the first hour, whereupon its temperature was maintained substantially constant throughout the remainder of the "superheated steam period". By the end of this period, namely, 2 hours and 12 minutes, the formation of fixed gases had practically stopped, indicating that oil generation had practically ceased, whereupon the superheated steam was shut off.
In this test run an investigation was made of the thermocouples and each was found to indicate the same temperatures immediately before and after the flow of steam was stopped. This proved that the couples were reading the true temperature of the retort and contents at each of the respective points throughout the length of the retort shaft. Couple 6 was out of service during this run.
The dry-quenching steam was then admitted into the top of the retort and its flow continued until all thermocouples indicated temperatures within the retort approximating 250° C. This preliminary run was made for the purpose of observing the operating characteristics of the retort and to obtain the accompanying data, so no heat economies in the use of superheated steam were attempted.
LTC Test on Cannel Coal from S. Utah ~ Univ. of Utah (12 May 1933)
Test # 1 ~ Made by: S. Jacobsen & G. Carter
Size of Coal: -1" to 1/2"
Superheated Steam Temperature: 650° C ~ Pressure of Saturated Steam to Superheater: 20 psi ~ Average Superheated Steam Pressure: 2.54 psi. ~
Barometer: 25.34" Hg ~ Superheated Steam/Hour: 69 lb
Time ~ Retort Temperatures ° C ~ Ave T ~ Remarks
Thermocouple # 1 ~ 2 ~ 3 ~ 4 ~ 5 ~ 6 ~ 7
1:47 74 ~ 40 ~ 74 ~ 74 ~ 74 ~ -- ~ 244 ~ 97 ~ Supersteam admitted
2:00 85 ~ 62 ~ 85 ~ 85 ~ 85 ~ -- ~ 365
2:15 85 ~ 68 ~ 85 ~ 85 ~ 85 ~ -- ~ 484 ~ Generated gas began
2:30 84 ~ 74 ~ 120 ~ 184 ~ 224 ~ -- ~ 575
2:45 155 ~ 120 ~ 258 ~ 395 ~ 340 ~ -- ~ 650
3:00 308 ~ 198 ~ 388 ~ 428 ~ 452 ~ -- ~ 658
3:15 414 ~ 292 ~ 480 ~ 497 ~ 508 ~ -- ~ 620 ~ 468
3:30 455 ~ 334 ~ 508 ~ 520 ~ 536 ~ -- ~ 650 ~ Flame change O to Y
3:45 482 ~ 364 ~ 530 ~ 545 ~ 555 ~ -- ~ 652
4:00 508 ~ 390 ~ 545 ~ 555 ~ 565 ~ -- ~ 638
4:15 Ave Temperature of TC # 1: 265° C ~ Gas supply shut
4:30 498 ~ 405 ~ 518 ~ 518 ~ 512 ~ -- ~ 440
4:45 475 ~ 402 ~ 457 ~ 448 ~ 436 ~ -- ~ 316
5:00 376 ~ 357 ~ 375 ~ 367 ~ 365 ~ -- ~ 240
5:30 270 ~ 278 ~ 258 ~ 242 ~ 242 ~ -- ~ 160
End of Run
1. Weight of raw coal charged, lb = 50
2. Weight of residue from retort, lb = 23.5
3. Weight of volatiles, lb = 26.5
4. “ “ “, lb per ton of coal = 1060
5. Quantity of crude oil, gal = 1.6
6. “ “ “ “, gal per ton of coal = 64
7. Total gas generated, cu ft = 170
8. “ “ “, cu ft per ton of coal = 6800
9. Time required for destructive distillation, hr = 1.33
10. Time that superheated steam was used, hr = 2.27
11. Total time of run, hr = 3.72
12. Superheated steam required for destr. dist., lb = 92
13. “ “ “ “ “, lb per ton of coal = 3680
14. Total superheated steam used, lb = 156
15. “ “ “ “, lb per ton of coal = 6250
16. Heat required for destr. dist., Btu = 10,330
Btu per Ton of Coal = 413,000
Heat Distribution in Retort per Test Charge (Btu /% of Total):
1. Total heat content of superheated steam entering retort = 257,000 / 100 %
2. Heat given to retort = 3,380 / 1.31 %
3. Heat given to the residue = 2,290 / 0.89 %
4. Heat in volatiles plus fixed gases = 3,870 / 1.5 %
5. Heat content of a superheated steam leaving retort = 212,000 / 82.5 %
6. Heat unaccounted for = 35,460 / 13.8 %
Test Run # 2: [Details not included here] This run was made for the purpose of observing the formation of water gas from the coal residue, also the operating characteristics of the retort at a higher temperature, namely 760° C, and to obtain the accompanying data. No heat economies were attempted in utilization of the superheated steam.
Test Run # 3: [Details not included here] This run was made for the purpose of observing the operating characteristics of the retort under conditions applying better heat utilization, wherein it was demonstrated that by discontinuing the heating of the superheater during the latter part of the distilling period it was possible to completely distill the lower part of the charge by utilizing the sensible heat of the coke in the upper portions of the retort. Other data were also recorded.
Test Run # 4: [Details not included here] This run was made for the purpose of observing the operating characteristics of the retort at a lower temperature than was previously used, namely, 535° C, and under conditions applying economical heat utilization, and to obtain the accompanying data.
Test Run # 5: [Details not included here] This run was made for the purpose of observing the operating characteristics of the retort using the smaller sized coal, namely -1/2" to -1/4", and to obtain the accompanying data.
Test Run # 6: [Details not included here] This run was made for the purpose of observing the operating characteristics of the retort using mixed size coal under conditions applying economical heat utilization and to obtain the accompanying data.
Test Run # 7: [Details not included here] This run was made for the purpose of observing the operating characteristics of the retort using coal of 3 different sizes, also to obtain retort insulation temperature gradients, and to obtain the accompanying data. No heat economies were attempted.
Test Run # 8: [Details not included here] This run was made for the purpose of observing the operating characteristics of the retort when low temperature superheated steam was used for preheating the charge, also for cooling all of the residue, which results appear in the accompanying data.
9. Heat Calculations for Test Run # 6 ~
The following information is presented to show the bases upon which the tabulated results and the figures representing the heat distribution in the retort were calculated. Test # 6 is chosen for this purpose, since it is typical of the series of tests made. He numbers of the items appearing below correspond to similar numbers presented on page 4. For figures used in the calculations see data sheet, p. 46 [Not included here]. Items not listed are self-explanatory.
(3) Weight of Volatiles, lb ~ This is the difference between the weight of the raw coal charged and the weight of the residue, which is: 50 - 25 = 25 lb.
(6) Time Required for Destructive Distillation, hr ~ This is the total elapsed time from the instant superheated steam was admitted to the retort to the instant that thermocouple # 1 reached the initial distillation temperature, namely 360° C.
(7) Time that Superheated Steam was used, hr ~ This is the total elapsed time from the instant superheated steam was admitted to the retort to the instant that the superheater gas supply was shut off.
(8) Total Time of Run, hr ~ This is the total elapsed time from the instant superheated steam was admitted to the retort to the instant that thermocouple #1 reached 250° C while the retort was being cooled.
(9) Superheated Steam Required for Destructive Distillation ~ This is the total superheated steam used in the time specified in item (6) above.
(10) Total Superheated Steam Used, lb ~ This is the total superheated steam passed into the retort during the time specified in item (7) above.
(11) Heat Required for Distilling the Coal, Btu ~ This is the heat given to the coal charge itself during the time specified in item (6) above. This is the product of the weight of raw coal charged, times the specific heat of the raw coal, times the temperature difference between the figure representing the average of the thermocouple readings at the end and the figure for the average temperature at the beginning of the period specified in item (6) above. Substituting gives: 50 x 0.31 x 682 = 10,600 Btu.
Heat Distribution in Retort, Btu:
(1) Total Heat Content of Superheated Steam Entering Retort ~ Since the published steam tables do not give properties of superheated steam above 1000° F, it was found necessary to substitute in Goodenough’s empirical equation:
Hs = 0.320 Ta / 0.000063 T2s – 23.583 / Ts – C3p ( 1 / 0.0342o0.5 ) / T4s / 0.00333p / 948.7
Hs = Total heat of one lb superheated steam above 32 F
Ts = Superheated steam temperature F absolute
C3 = A constant, the logarithm of which is 10.7915
P = Pressure of superheated steam, psi absolute
The superheated steam temperature corresponding to 625 C (the average temperature during the superheated steam period) is: Ts = 1157 / 460 = 1617° F absolute
The average superheated steam pressure was found by adding the average reading of trhe gauge to the barometric pressure. Thus
P = 3.6 / (25.46 / 2.04) = 3.6 / 12.48 =16.08 psi absolute
Substituting the above values in Goodenough’s equation gives the total heat of one lb superheated steam as being 1616 Btu.
The total heat content of the superheated steam entering the retort is the product of heat content of one lb steam, the pounds of steam used per hour, and the time (*1) in hours, which is: 1616 x 56 x 1.15 = 104,000 Btu
(*1 ~ As herein used, this time is that specified in item 7 under "Tabulated Results")
(2) Heat Content of Retort ~ This quantity is equal to the product of the weight of the retort shell and the specific heat of the sheet steel, plus the product of the weight of the retort pipe couplings and plugs and the specific heat of cast iron, each product being multiplied by the temperature difference. (*1)
(*1 ~ As herein used, the temperature difference is the difference between the average of the thermocouple readings in degrees F at the end and beginning of the time as described in the preceding footnote)
Weight of retort equals weight in pounds of one sq ft of US Standard Gauge sheet metal times the sq ft of retort surface: 2.5 x 3.14 x 5/16 x 8 = 26 lb. Weight of 5" cast iron pipe plugs @ 5 lb each = 10 lb. Total = 30 lb.
Specific heat of sheet steel = 0.117
Sp. ht. of cast iron = 0.1298
Therefore the heat given to the retort is: ( 26 x 0.117 / 30 x 0.1298 ) ( 853 x 205 ) = 4550 Btu.
(3) Heat Given to the Residue ~ This quantity is equal to the product of the weight of the residue, the specific heat of the residue, and the temperature difference, between the average maximum temperature of the residue and the temperature of the coal as it entered the retort, is: 25 x 0.2 x ( 752 x 70 ) = 3410 Btu
(4) Heat in Volatilization Plus Fixed Gases ~ This quantity is equal to the product of the weight of the volatiles, the specific heat of the volatiles, and the temperature difference between the average temperature of the vapor as it left the retort during the superheated steam period and the temperature of the coal as it entered the retort, which is: 25 x 0.3 x ( 289 x 70 ) = 1640 Btu
(5) Heat Content of Superheated Steam Leaving Retort ~ This quantity is based on the average readings of #1 thermocouple during the time as herein specified, and a pressure of 14 psi absolute. This is higher than atmospheric pressure by the amount of the friction head in the condensers and the piping. The heat content of one lb steam based on an average temperature of the vapor as it left the retort at 289° F was found from steam tables to be 1182 Btu. Therefore the total heat of superheated steam was: 1182 x 62 x 1.15 = 84,500 Btu.
(6) Heat Unaccounted For ~ This quantity is the heat imparted to the insulating material, plus the heat lost by radiation from the retort casing surface, from the highly heated retort cap, and probably from errors in observed exit steam temperatures. This amounts approximately to 4,000 Btu the heat imparted to the insulation, assuming the 2" layer of insulation next to the retort fluctuates about 500° F in heating and cooling, and is unaffected beyond a point 2" from the retort, also 2000 Btu lost by radiation. This total of 6000 Btu subtracted from the 9910 Btu shown in the unaccounted for heat in the "Tabulated Results" for Test 6, still leaves 3910 Btu unaccounted for which must be the heat lost from the very high temperature surfaces at the top of the retort and probably errors in the observed temperatures of the discharged steam and volatiles. All thermocouples, excepting # 7 which was inserted within the superheated steam line, were placed in contact with the outer wall surface of the retort and undoubtedly gave low readings.
10. Discussion of Results ~
General: The purpose of the foregoing curves is to show the instantaneous temperatures and particularly the rate of change of temperature, of the superheated steam and the coal throughout the retort during the progress of the test runs. The thermocouples placed at regular intervals along the length of the retort, as previously described, are numbered from 1 to 6 inclusive, the one at the vapor outlet being designated as # 1. The temperature of the superheated steam as it entered the retort was determined by thermocouple # 7.
Except for the graph representing conditions of test # 8 in which the charge was preheated and finally dry-quenched with relatively low-temperature superheated steam, the curves herein presented are substantially of the same general shape (*1). Throughout all of the tests, it is interesting to note the consistent lagging of the temperature near 100° C, as indicated particularly by thermocouples # 1, 2, and 3 during the first part of the superheated steam period when the coal in the lower zones was being heated up by condensation of the steam, following this the subsequent rate of temperature increase as indicated by the slope of the curves, and then the crossing of the curves as the retort is cooled, ultimately resulting in reversing the final arrangement of the curves.
Coal Size vs Distilling Period: Tests # 1 and # 5 show the influence of the size of coal on the length of time required for distillation at the same final distilling temperature. The charge used in Test #1 was sized up to -1" to 1/2", and that used in Test # 5 to -1/2" to 1/4". Comparison of the distilling periods as indicated on the curves shows the period in #5, exceeding by 2 minutes that in #1 in which the larger coal was used. This appears to be in a direction contrary to the expected results. However, it was observed that this cannel coal tended to fracture when it was crushed, into flat laminated pieces which were thin in section and yet large enough in the other dimensions to be withheld by a 1/2" mesh. Hence, the larger size of coal was usually no thicker in its smallest dimensions than the smaller size and will distill in like periods of time, also the pieces became porous with many small cracks parallel to the bedding plane which made them permeable to the superheated steam. This effect would not be measurable in treating coal lumps of much larger sizes. Also it should be noted that the distillation progressed down through the 8-ft column of coal, in both instances, at the rate of 1 ft in each 10-minute interval. Or, if we consider the range of temperature within which the coal is distilled as 360° C to 450° C, then in each instance the average period that the coal particle is undergoing distillation is 20 minutes. Previous work, however, has demonstrated that coal of the two sizes used will actually distill in less than 20 minutes, and therefore the distilling period is in these tests entirely governed by the rate of heat supply and not by coal particle size. With coal charges composed of lumps having minimum dimensions of 1" the effect of lump size on distilling rate would be important. Lumps 1" minimum diameter will require approximately 1 hr to distill and 2" lumps nearly 3 hr under the above conditions.
Superheated Steam Periods vs Economy: The charge used in Test # 5 was heated until after the end of the distilling period, while in Test # 6 the heating gas supply of the superheater was shut off before distillation was completed in an effort to use the steam most economically (note the length of superheated steam period in each case). An inspection of the curves for Tests # 5 and # 6 shows that using the same final distilling temperature (650° C) and securing complete distillation in both cases, the superheated steam period was 20 minutes shorter in Test # 6 in which steam economy was practiced than in Test # 5. Obviously, then it is distinctly advantageous from the standpoint of economy to shut off the superheater gas supply before distillation is complete, since the same end conditions of distillation result. The practical application of the economy would be to divert the superheated steam into another retort at this moment. Curves for Tests # 2 and # 3 show a similar saving of superheated steam at a higher final distilling temperature (760° C).
Distilling Period vs Final Distilling Temperature: Tests # 3 and # 4 were both run with an attempt to secure superheated steam economy, but different superheated steam temperatures were used, # 4 being 535° C and # 3 being 760° C. By reference to the curves it is seen that the distilling period for # 4 at the lower temperature is 8 minutes longer than # 3. It will also be noted, however, that the rate of temperature increase as of thermocouple # 7, indicated by the slope of the curve, is much slower than in Test # 3 than in Test # 4. Hence if superheated steam had raised to its final temperature in equal periods of time, then, with the same flow of steam, the distilling period of Test # 3 at the higher distilling temperature would have been much further reduced. It may be concluded, therefore, that the higher superheated steam temperatures will decrease the length of the distilling period as well as the consumption of superheated steam.
Generation of Water Gas: It was found in the runs using superheated steam at temperatures of 650° C and above, that large quantities of gas were generated, as may be seen by reference particularly to the data sheet of Test #3, the steam temperature of which was 760° C. This gas was identified by the flame color and behavior in burning as blue water gas produced by the combination of the chemically reactive coal residue with the highly heated steam, in accordance with the following reactions:
C / H2O = CO / H2
C / 2H2O = CO2 / 2H2
Mixed with this gas was also some of the gas formed from the residual volatiles of the coke residue consisting of methane and hydrogen, also possibly some distillation gases.
Preheating Effects: The curves for Test # 8 show that thermocouple (TC) # 1 and # 2 reached a temperature of 135° C in 70 minutes while the preheating of the charge with superheated steam at 300° C was in progress. In Test # 3 made at 760° C the curves show that these TCs did not reach this same temperature until 55 minutes of the superheated steam period. Also in Tests # 2 and 7 made at 760 C at the end of 65 minutes of the superheated steam periods, these TCs indicated 250° C. It will be noted further that in dry-quenching the charges in all the various tests the lowest temperature reached by the steam leaving the retort, TC # 1, was approximately 250° C.
Therefore it is obvious that by the proposed method of using this steam leaving the retort, during the dry-quenching period, for preheating a fresh coal charge in another retort, that much high-temperature steam would be saved. The superheated steam period was 70 minutes in Test # 8, 95 minutes in Test # 7, 85 minutes in Test # 2, and 100 minutes in Test # 2. Had it been that the superheated steam used in Test # 8 was initially at 760° C, as would be the case in a commercial plant where the steam at constant temperature is diverted from one retort to the next, it is probable that the superheated steam period and the preheating period would each have been 60 minutes or less, making a total period of 120 minutes.
There are good evidences why the entire outflow of steam, oil vapors, and gases from the base of one retort should pass through the next retort of fresh coal enroute to the condensers, thus serving to preheat the new coal with both the exit superheated steam and the dry-quenching steam, and continuing until the new charge has stored within it the greatest quantity of heat. In the case of cannel coal, from which the coal residue will not have extensive market value because of its high ash content, the final cooling of the residue to a safe temperature for storing might be advantageously done by discharging it and spraying with water. This procedure serves to keep the retorts free for distilling purposes during the greatest percentage of their time, which would not be the case if they were used to serve as dry-quenching chambers. In the case of coals such as the Carbon County coals from which the smokeless fuel residue is the important product desired, the coke should be dry-quenched with steam in the retorts to the safe storage temperature, thus keeping the product physically dry. In this procedure, the dry-quenching steam might best be derived by recovering the sensible and latent heat of the volatiles issuing from one retort by condensing them in an evaporator type of condenser, the new low-pressure steam then being passed through the coal residue immediately following the diverting of the superheated steam into the next retort.
Distilling Graded Sizes of Coal: As shown above, there was no reduction in time consumed in distilling the charges comprising the different sizes of cannel coal, this being because of the fact that the largest lumps used, mainly -1" to 1/2", actually required much less time to distill them than the time for the distilling heat wave (360° C to 450° C) to pass entirely through the retort from top to bottom. Had the lumps been over 1" in minimum dimensions a coal charge of the height, or even greater or less height, and with the same flow of steam, would have consumed more time. However, there is the practical consideration to be met as to the best way to effectively distill the maximum quantity of the slack coal at the proposed cannel coal mine. It would appear from the foregoing data that the slack coal should be screened to several sizes and these placed severally into the retort with the coarsest at the base and the finest dust-free size, say 1/4" to 1/8", at the top as applied in Test # 7. The size from dust up to 1/8" would then serve for stoker fuel under the boiler or for heating the separately fired superheater. In a stoker this high oil-yielding fuel should undergo combustion much like an oil fire. In the treatment of carbon slack the physical properties, crushing strength and insipient fusibility of the coal while undergoing distillation, requires that the retort charge be composed of stratified layers with the coarsest (strongest) lumps at the base of the charge so as to avoid crushing and yet compress slightly while improving the density and hardness of the smokeless product.
Retort Insulation & Temperature Gradients: Figure 4 shows the temperatures along the retort surface and at 6 equidistant points throughout the thickness of the insulating wall at the thermocouples positions shown in Figure 2. These measurements were taken during Test # 7 after the production of oil had ceased and the retort had therefore been receiving heat for approximately 1-1/2 hr. The temperature readings on the retort wall were taken after the flow of steam had been shut off. Each thermocouple starting with # 1 was read and then moved out 1" from the wall into the insulation. After # 7 was read a second reading was made of # 1 and it was then moved out another inch. Thus the measurements were taken out to and including the surface temperature of the insulating wall, the entire set of temperature readings requiring about 50 minutes.
It is recommended that the temperature gradient through the wall at each thermocouple position should be a curve of logarithmic form if the temperature of the heat-receiving surface had been constant. This, however, was not the case since during the progress of the distillation al points along the retort had been gradually rising in temperature in accordance with the records shown in Test # 7 graphs. Consequently it may be stated that the points on each thermocouple curve above the abscissa, Figures 1 to 6, are instantaneous records of the temperature of the insulating material, which is the additive effect of an infinite series of heat impulses, of increasing potential, moving out through the insulating wall. Therefore the curve is steeper than if the temperatures had been stationary. The temperature of the outer surface will, of course, move up and down as the waves of heat pass down the retort in successive distillation tests. The figure shown on Figure 4 for the surface temperature was used in calculating the heat loss.
Yield of Products: It will be observed by referring to the data on each sheet that the oil yield was the same in all instances within the range of possible experimental error in collecting the oil and its distillation to remove the contained water. It is logical to conclude that the yields actually were the same considering that the particles of coal throughout the charge experienced practically the same rate of rise of temperature in all tests while passing through the distillation range (360° C to 450° C). Although the contents of the retort were heated hotter in some tests, this occurred after the oil was removed and carried out of the retort. (Ref. 14)
The average yield of crude oil in this study was 64 gal per ton of coal; that reported by Allen 68.8 gal.
The latter analysis was made by Karrick in the US Bur. Mines in which the following data regarding the oil also appear:
"Specific gravity of crude oil -.918 at 15.56° C; Baume 22.5; viscosity of crude oil at 60° C, –57 Saybolt. Setting point of crude oil –34° C. Residue waxy and oil probably will yield good percentage of high melting point wax."
Thesis cracking analysis at 120 lb pressure, gave 15 gal refined gasoline, 12 gal kerosene, 15 gal fuel oil from which diesel oil and road oil can be refined, 2 gal cresylic acid, 52 lb ashless coke from each tone of coal.
The cannel coal residue was easily kindled and burned very well without smoke.
11. Summary ~
An engineering investigation has been made of a valuable natural resource of the State of Utah, the cannel coal body in the Zion Canyon-Cedar Breaks area of southern Utah. The availablility of this undeveloped body is noted, also its probable economic importance to the State. Attention is now directed to the potential usefulness of this great body, offering many new Mechanical, Mining, and Chemical Engineering studies for engineering students of the University, also as a source of revenue for the Utah Research Foundation which has just been created.
A "heat and products" study has been made in the destructive distillation of this cannel coal. Superheated steam was used as the heat-transferring fluid, wherein the heat units involved have been measured and their distribution traced during the mechanism of the heat transfer while heating. Also while abstracting heat, "dry-quenching" the residue, with low temperature steam. The quantity of coal gas and the semi-coke were determined, also the crude oil product was refined into desirable petroleum derivatives.
Steam from turbine exhaust or other economical source, when reheated, provides an effectual way of transferring the necessary heat into batches of dust-free slack coal and accomplishing very rapid distillation. Important economies in steam consumption are obtained, (1) by preheating the coal, (2) by using maximum steam temperature, (3) by using physically dry coal, (4) by reducing heat absorption in walls of retort by using retort covering of low conductivity and heat capacity, therefore by using large diameter charge of coal to minimize surface loss factor, (5) by reducing radiation losses, (6) by utilizing the heat stored in top portion of coal charge to distill by transfer of its heat to the lower portion of coal charge, (7) by using sensible heat of coal residue to preheat new coal, (8) by condensing the issuing steam and oil vapors in an evaporator and using the new steam generated to dry-quench and preheat other new coal charges, (9) by using very tall retorts full of properly sized coal. The data indicate that the small diameter retort used in these studies can apply economies and distill coal with less than one pound of steam per pound of coal treated.
This cannel coal, unlike the fusing types of bituminous coking coals, has the desirable physical property of holding its form without crushing or cohesion while passing through the treatment. The solid residue is active chemically, though high in ash, and should be a good smokeless domestic fuel or fuel for industrial gas. The crude oil was readily cracked into a color-stable, non-gumforming gasoline with small refining loss.
The slack coal should provide a permanent supply of low-priced city gas and diesel powerplant oil, also motor fuel and road oil, and develop a new coal mining industry of a remarkable coal with steady employment for labor in southern Utah.
12. Bibliography ~
(1) See footnote on page 1.
(2) Gavin, M.: "Oil Shale", US Bur.Mines Bull. # 210
(3) Karrick, L.: "Methods of Analysis of Oil Shales & Shale Oils", US Bur. Mines Bull. # 249. See also: "The Analysis & Evaluation of Oil Shales", Monograph 25, Amer. Chem. Soc. See also: "A Shale Oil Industry", Mining Review, 23 August 1932.
(4) Schmutz, C: "Oil from Oil Shales & Coals of Utah & Factors Affecting their Production", Masters Thesis, Univ. Utah, 1932.
(5) Larsen, W. & Stutz, C.: "Design of Plant for the LTC of Utah Coals by the Karrick Process", Bachelor of Science Thesis, Univ.of Utah, 1932, Dept. of Civil Engineering.
(6) Karrick, L.: "The Economic Production of Smokeless Fuel from Utah Coals", Bulletin being written, Carnegie Inst. of Tech. & USBM.
(7) Speiker, E.: "Bituminous Sandstone near Vernal, Utah"; USGS Bull. # 822 (1931).
(8) Brighton, T.: Bachelor of Science Thesis, Univ. of Utah.
(9) Allen, Carl:"Cannel Coal in Southern Utah", US Bur. Mines Report of Investigation (1921).
(10) Richardson, G.: USGS Bull. # 431.
(11) Ashley, G.: "Cannel Coal in the United States"; USGS Bull. # 659.
(12) White, David & Thiessen, Reinhardt: US Bur. Mines Bull. # 38
(13) One of a group of Utah coal-treating patents offered by Mr L.C. Karrick to the University of Utah Research Foundation.
(14) Karrick, L.: "Some Factors Affecting the Destructive Distillation of Oil Shales", US Bur. Mines Report of Investigation.