Energy & Fuels 1987, 1 , 23-28 Registry No. I, 26811-28-9;111,105281-51-4;IV, 14039-14-6; V, 105281-52-5;Ph3C+,13948-08-8; g-PhXa-, 20460-07-5;TMCP', 26827-04-3;g-t-BuFlH-, 73838-69-4;FlHT, 12257-35-1;g-BzFlH-, 53629-11-1; 2-BrFlH-, 85535-20-2; g-PhFlH-, 31468-22-1; 9PhSFlI-I-? 71805-72-6;2-Br-9-PhSFlH-, 73838-76-3;9-PhS02F1H-, 71805-74-8; 9-CO2MeF1H-, 12565-94-5;g-CNFlH-, 12564-43-1; 2,7-Br2-9-C02MeF1H-,73838-70-7; m-CNPhMN, 99726-50-8;
23
m-CF3PhMN,99726-51-9;m-ClPhMN, 99726-52-0;p-ClPhMN, 91880-07-8; PhMN, 45884-26-2; p-MePhMN, 91880-08-9; pMeOPhMN, 85535-17-7;2-NaphthylAN, 19268-56-5; p-CF,PhAN, 100859-08-3;p-N02PhAN,48129-94-8;p-N02PhOH, 14609-74-6; 3,5-ClzPhOH,65800-69-3;4-t-BuPhOH, 28528-33-8;4,6-dinitroo-cresol,46325-40-0; xanthylium, 25187-66-0;xanthenol, 90-46-0; 9-phenylxanthenol, 596-38-3;trityl alcohol, 76-84-6.
Morphology of Retorted Oil Shale Particles D. C. Adamst and 0. P. Mahajan* Corporate Research, Amoco Research Center, Naperville, Illinois 60566 Received September 4, 1986. Revised Manuscript Received October 9, 1986
The formation of two distinct coked particle morphotypes, namely exfoliated and peripheral, during oil shale retorting and their implications toward the coking mechanism are discussed. Rapid heating causes swelling, exfoliation, and formation of a matrix of veinlets and cracks; these changes lead to uniform coking within the particle body. In contrast, slow heating produces the peripheral morphotype with a low coke density at the center and a high coke density at the periphery. The difference in the coking morphology of the two particle types has been explained on the basis of kerogen pyrolysis kinetics. Of the two morphotypes, peripheral coke makes the particles stronger and more resistant to size attrition. In addition to the formation of coke in the particle body of the two morphotypes, coke is also formed on the outer surface of both the particle types. It has been concluded that more coke is produced from the secondary decomposition reactions than directly from the kerogen itself.
1. Introduction Coke formation is recognized as a limiting factor that detracts from high oil yield during oil shale retorting. Approximately 20% of Green River oil shale organic matter is converted to coke during conventional retorting.I2 Various approaches have been used to reduce coke formation, such as retorting in the presence of hydrogen3g4 and steam"' and use of high sweepgas rates,'+ reduced pressure,9Jo and rapid heatup The objective of this study was to correlate the retorted oil shale residue characteristics with processing conditions and to determine the effect of particle morphology on particle strength. 2. Experimental Section 2.1 Samples. Two samples of Green River oil shale from the
Rio Blanco (Colorado) C-a tract were used in this study. They are designated as S1and S2 in the text. The two samples were of 41 and 15 gal/ton grade, respectively. Oil shale samples were mixed with dry ice and ground to the desired particle size. The ground samples were placed in a nitrogen-filled glovebox where they were riffle-divided and packaged and sealed in bottles under nitrogen; the inert atmosphere was used during grinding and riffling to minimize weathering of shale kerogen. We believe this is important because shale kerogen, like coal, undergoes weathering even under ambient conditions.12 2.2 Retorting. For particle morphology studies, oil shale particles were dropped into a preheated fluidized bed of &dumina particles in a quartz tube to pyrolyze them at a maximum heatup rate; the bed was fluidized with nitrogen gas and maintained at
* To whom correspondence should be addressed.
Present address: Energy Recovery Technology, Naperville, IL
60540.
0887-0624/87/2501-0023$01.50/0
540 "C. The particle heating rate was estimated to be -1000 "C/min. When oil shale particles were dropped into the fluidized bed, they agglomerated with the alumina particles. While it was possible to isolate retorted oil shale particles for coke morphology studies, the agglomeration of the coke particles with the alumina particles complicated the friability measurements on the spent shale particles. This problem was circumvented by retorting 15 g of oil shale particles in a N2flow (300 cm3/min) up to 540 "C in a custom-built thermogravimetric analyzer (TGA). The TGA runs were made at a heating rate of 200 "C/min (maximum rate possible in the TGA) and 1.5 "C/min. The sample prepared at 1.5 "C/min was also used for coke morphology studies. The TGA was also used for combustion of the spent oil shale samples. For the combustion studies, -5 g of sample was heated in flowing air (300 cm3/min) from ambient temperature to 500 "C at 10 "C/min; the soak time at 500 "C was 30 min. N
( 1 ) Baughman, G. Synthetic Fuels Data Handbook, 2nd ed.; Cameron Engineers: Denver, CO, 1978; p 46.
( 2 ) Singleton, M. Lawrence Liuermore Lab., [Rep.] UCRL 1982, UCRL-53273. ( 3 ) Feldkirchner,H. L. Synth. Fuels Oil Shale, Symp. Pap. 1979,1980, 489-524. ( 4 ) Greene, M. I.; Damukaitus, J. Energy Prog. 1985, 5 ( 3 ) , 143-146. (5) Campbell, J. H. Lawrence Liuermore Lab., [Rep] LTCID 1978, UCID-17770, ( 6 ) Allred, V. D. Oil Shale Symp. Proc. 1978, 12th, 241-251. ( 7 ) Wall, G. C. Oil Shale Symp. Proc. 1984,17th, 300-309. ( 8 ) Campbell, J. H. Lawrence Liuermore Lab., [Rep.] UCRL 1977, UCRL-79034. ( 9 ) Sohn, H. Y.; Yang, H. S. Ind. Eng. Chem. Process Des. Deu. 1985, 24, 265-270. (10) Yang, H. S.; Sohn, H. Y. Ind. Eng. Chem. Process Des. Deu. 1985, 24, 271-273. (11) Richardson, J. H. Lawrence Liuermore Lab., [Rep] UCID 1982, UCID-19548. (12) Adams, D. C., unpublished results.
0 1987 American Chemical Society
A d a m and Mahajan
24 Energy & Fuels, Vol. 1, No. 1,1987
C
r, In
-a
10
40
I
I
I
100
200
500
Figure 2. Particle agglomeration during retorting of S1 sample; lo()o
(magnification 5X).
Diameter (microns)
Figure 1. Effect of retorting and attrition on particle size distribution of S1 sample: (A) particles before retorting; (B) particles after retorting; (C)retorted particles after 2-min attrition; (D) retorted particles after 20-min attrition. 2.3 Microscopy and Elemental Microprobe Analysis. Spent oil shale particles were mounted in an epoxy resin, cut, and polished to obtain cross sections suitable for microscopic examination. The X-ray micrograph pictures were taken with a JEOL 733 electron microprobe with secondary electron imaging. Elemental line profiles were obtained with the same unit. Polarized light micrographs were obtained with a Leitz Ortholux microscope. 2.4 Infrared Spectroscopy. The diffuse reflectance Fourier transform infrared (FTIR)analyses were made on whole spent particles as well as on the fine powder obtained by grinding the whole particles. This approach allowed a comparison of the characteristics of the outer surface vs. the effective cross section of the powdered particles. 2.5 Attrition Test. The attrition test was an arbitrary test. Particle attrition was effected by using a SPEX Mixer. This device oscillated the container of particles for a predetermined time through a travel distance of 4.93 cm at a frequency of 24.2 Hz.
3. Results and Discussion 3.1 Particle Agglomeration during Retorting. The particle size distribution results for the SI sample retorted in the TGA a t 200 OC/min (figure 1) illustrate particle agglomeration during retorting and subsequent resistance of the agglomerates to attrition. Before being retorted, all the particles were
