LAWRENCE LIVERMORE NATIONAL LABORATORY OIL SHALE PROJECT QUARTERLY REPORT JULY - SEPTEMBER 1980

Transcription

1 UCID LAWRENCE LIVERMORE NATIONAL LABORATORY OIL SHALE PROJECT QUARTERLY REPORT JULY - SEPTEMBER 1980 J. F. Carley, Editor November 2, 1981 This is an informal report intended primarily for internal or limited external distribution. opinions and conclusions stated are those of the author and may or may not be those of the Laboratory. Work performed under the auspices of the VS. Department of Energy by the Lawrence Livermore Laboratory under Contract W-7405-Eng-48. DISCLAIMER FOR QUARTERLY OIL SHALE REPORTS This is a report of work in progress. The data and conclusions presented are preliminary and may change as additional information becomes available. For the above reasons only a limited distribution of these reports is made and the reader is requested not to quota conclusions or data. Completed results of the research will be published in conventional channels by appropriate authors.

2 DISCLAIMER This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement recommendation, or favoring of the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.

3 -i- TABLE OF CONTENTS I. RETORT MODELING 1 Page II. GAS EVOLUTION DURING PYROLYSIS OF VARIOUS 5 COLORADO OIL SHALES III. OXIDATION OF RETORTED SHALE 8 IV. PUBLICATIONS AND PRESENTATIONS 13

4

5 -1- I. RETORT MODELING A preliminary process flowsheet for a commercial-size, aboveground, countercurrent, gas-combustion retort system has been developed. Flowsheet data are based on an overall mass and energy balance code which uses the LLNL one-dimensional retort model in conjunction with models for the physical processes external to the retort (e.g., condenser and blowers). The principal purpose of the flowsheet is to predict the retorting results and the process interrelationships for conditions to be encountered in a typical commercial operation. After similar flowsheets are developed for a number of surface retort systems, they can be used to help assess the advantages and disadvantages of the various generic processes and to help determine the most important areas for additional experimental work. The principal element in the flowsheet model is the LLNL one-dimensional retort code. The validity of the retort model for simulating countercurrent, gas-combustion retorting has been tested by comparison with over 27 runs of the Paraho semiworks retort. In those runs, the exit gas was cooled to about 140 F (60 C), so a fraction of the oil vapor was recycled and burned. In our simulations, we estimated that fraction to be 10%; this gave a calculated oil yield that agreed closely with the average measured value of 89% of Fischer assay. In applying the retort model to commercial conditions, we assume that there is a much more efficient oil collection system and that none of the oil production is left in the recycle gas stream. Thus, the calculated oil loss is due only to coking and burning of the oil vapor near the original retorting zone and not to burning of recycled oil vapor as in the semiworks retort. model does not yet address the possible mechanism of oil-mist refluxing and further thermal degradation. The This is the main uncertainty of the calculations. The retort model was run with a sample case using 125-a/Mg shale, 45% bed porosity, 47.4 m/d linear shale velocity, 10 C raw-shale feed temperature, mol/m -s dry recycle gas (71% of the dry offgas), 3.81 p mol/nr's air and an ambient atmospheric pressure of 0.8 atm. The inlet fluxes for shale, recycle gas and air were taken directly from a representative Paraho semiworks run. However, the steam content of the

6 -2- semiworks recycle gas was replaced on an equivolume basis by dry recycle gas to reflect the lower condensation temperature of the offgas anticipated for the commercial process. The mass- and energy-balance code takes the retort data and results as predicted by the retort model and scales them up to a 50,000-barrel-per-day (bpd) shale-oil plant. The code then calculates temperatures, pressures and mass flow rates as they occur in the overall process. Condenser cooling requirements, heater requirements and compressor or blower power requirements are also calculated. Table 1 shows the resulting mass and energy balance. The plant flowsheet, shown in Figure 1, was designed by making a few modifications to the semiworks flowsheet. The main difference is that each recycle gas and air feed line has its own blower, rather than having one blower for the recycle gas and one for the air feed. Following through the system, beginning with inputs to the retort, 895 kg/s of raw shale must be crushed to produce the 761 kg/s needed for retorting. The difference represents the material that is too fine for processing (< 1.3 cm). The shale flows downward in the retort being swept by a countercurrent gas stream that originates at three locations in the retort. The cross-sectional area indicated (1181 m ) should not be interpreted as the cross-section of one retort unit; it is the total area required for a 50K bpd plant. Burned shale exits from the retort at 286 C, carrying a sensible heat of over 150 MW. However, the relatively low shale temperature may make it difficult to recover this heat efficiently. Pyrolysis and combustion products leave the retort and enter the cooling and separation train shown on the flowsheet as the precipitator and condenser. At this point the streams are cooled to 10 C, and the oil and foul water are separated and leave the system. The gas stream is now dry and has suffered a pressure drop of 0.05 atm. Approximately 29% of the dry gas stream is bled off as product gas through a blower, the remainder of the stream is recycled. As air is fed to the system, its pressure is raised by blowers from 0.80 atm, to a gage pressure equal to the sum of the pressure drops through the bed, the manifold and the valve. The air and recycle-gas temperatures are raised as they pass through their individual blowers; the temperature rise of the recycle gas (though not shown) is between 6 and 8 C. The preliminary process flowsheet presented here is meant only to serve as an example of a 50,000-bpd shale oil plant that uses a countercurrent, gas

7 -3- Table 1: Overall Mass and Energy Balance MATERIALS INPUT MASS (kg/s) ENERGY (kj/s) Raw Shale Air Reactions ir i Gas Blower Heat Unaccounted Gains Heat in Retort TOTALS OUTPUT Burned Shale Oil Products Gas Products Foul Water Distributor Cooler Condenser Reactions in/on Shale Wall Heat Losses TOTALS Difference Closure (%) Enthalpies are referenced to 250C

8 REJECTED T Rflu SHflLE is^ucs?! 895 KC'S 761 KG/S " I i GPS It VAPORS Kr,/S 135.3'C 9.8 PTM IRETORT OREO 1181 n*«2 DISTRIBUTOR COOLER LORD KU RSHX i36 AM WED., 30 SEPT, 1981 PRECIPITRTOR d CONDENSER GRS t RIR 147 KG/S 14.2'C.830 ATM GRSt. H1R 62.1 KG/S 16. 'C.835 RTH RECYCLE CRS 337 KG/S 16.1'C.821 PTM BURNED SHRLE 606 KG/S 286' LOPD KU RETORT GPS 587 KG'S 10.'C 0.75 ATM OIL URTER RECYCLE BLOUERS POWER REQUIREMENTS 4144 KU RECYCLE GRS -8-8^' -e^ K.758 PT S^J 10.0' C KG/S P1R O, 13.2'C.830 RTI1 23.S KG/S PIR 13.7'C.835 ATM PRODUCT BLOUER POWER REQUIREMENTS 916 KU -e "fr 8.8 KG/S PIR 0.0 'C 0.00 PTM & PIR BLOUER POWER REQUIREMENTS 483 KU CRS PRODUCT KG'S C.80 PTM OIL PRODUCT KG'S 18.8' C RETORT WPTE? 32.1 KG/S 10.0' C RIR FEED 18'C 130 KG/S.88 ATM FIGURE 1. Overall Process Flowsheet

9 -5- combustion retort. No attempt was made to optimize the process or any of its parameters. These results will be useful, however, for comparison with preliminary results of models which are being developed for other types of aboveground retort systems. II. GAS EVOLUTION DURING PYROLYSIS OF VARIOUS COLORADO OIL SHALES In a previous quarterly (January-March, 1981), we reported the rates of evolution of the gases C0_, CO, l-l, CH. and the C? and C 3 hydrocarbons during the pyrolysis of seven Colorado oil shales. These shales yielded from 9 to 61 gallons of oil per ton raw shale and were from various depths at two different sites. the retorting of all samples. We used a nonisothermal linear heating rate of 2 C/min for This study was done to reveal the variations in gas evolution with different initial shale compositions. In the past quarter 3 we have tested the ability of an existing kinetic model (Campbell et al ) to predict our gas-evolution results. Although the rate expressions work quite well, it is necessary to modify the stoichiometric coefficients slightly to obtain good agreement. The resulting kinetic model should adequately describe the behavior of the upper portion of the Green River formation. The kinetic expressions of Campbell et al. accurately predict the temperatures of maximum evolution rate for H?, CH-, and the C? and C~ hydrocarbons. These temperatures are 20 to 35 C higher than for oil evolution, which corresponds roughly to a factor of 3 to 7 in the rate constant. In addition, we have been able to show that the evolution of CO is 4 predicted reasonably well by the oil-evolution kinetic expression. Although neither we nor Campbell et al. derived a kinetic expression for COp evolution from kerogen pyrolysis, we also have found a very broad profile, possibly with several components, that peaks prior to the maximum rate of oil evolution. the kerogen. We have attributed the source of this C0 2 to carboxyl groups in We have found that Campbell's stoichiometric coefficients for hydrogen in char pyrolysis must be modified slightly to remove contributions from inorganic hydrogen in the retorted shale. Since Singleton et al. have also recently determined a more broadly based stoichiometry for assay pyrolysis, we have modified their stoichiometry to Campbell's more general form. The result is shown in Table 2. For completeness, we have also tabulated Campbell's

10 -6- Table 2. Kinetic scheme for pyrolysis of organic material in Colorado oil shale modified from Campbell et a!. I. Primary Pyrolysis (^ 450 C) CH 1.50 N CH K63 N 0<019 (oil) CH 064 N 0080 (char) CH C 3 Q H H C0 2 " CO H 2 0 II. Secondary Pyrolysis {* 550 C) CH 0.64 N (char) CH 0#20 N 0#06 (char') CH H 2 +(0.023 NH 3 ) III. Tertiary Pyrolysis (^ 750 C) CH 0.20 N 0.06 (char,) CH * 0.0*0.04^" > H 2 + (0.020 NH 3 )

11 -7- Table 3. Rate constants for pyrolysis of organic material in Colorado oil shale (19,33). Species Volume Evolved, \i f / 3, C) (cm /g org Preexponenti factor, A (s- 1 ) al Source Fractional contribution Activation energy (kj/mole) Distribution parameter, a (kj/mole) Oil x CO x C 3.0 H x CH 4 H x x l 2 [1 2 la a 0il volume calculated from an average carbon content of 84.1% and an average density at room temperature of g/cm3. Gas volumes are reported at STP.

12 -8- kinetic expressions in Table 3 along with the evolved gas volumes determined here or by assay. If half of reaction II occurs as in an assay, this scheme predicts products of CH Q 42 N Q 07Q, CH 4, and H«, in excellent agreement with that obtained by Singleton et al. III. OXIDATION OF RETORTED SHALE With approximately 20 percent of the fuel value of shale remaining as char in retorted shale there is strong motivation to burn it for process heat. Retorted shale retains most of the sulfur of raw shale as the insoluble iron sulfide FeS. Combustion of retorted shale produces heat in part from sulfide combustion, but not without the risk of S0? emissions and a more soluble waste product. We have reported how oxidation at temperatures above approximately 550 C reduces the loss of sulfur to 0, ±3 percent. (This was based on the difference in the sulfur content of the solid before and after oxidation in air for 30 min.) In order to confirm these initial conclusions, improve the accuracy and identify the sulfur-bearing gases, we analyzed the air stream used to oxidize retorted shale during oxidation. We made an analysis every five seconds for C0 2, S0 2, COS, and SO.. Only COp and SOp were found. The results, for an oxidation initiated at 505 C, are given in Figure 2. Knowing the initial amount of sulfur in the retorted shale, and the flow rate of air, the fraction of the sulfur lost was calculated as a function of time as shown in Figure 3. Note that when the oxidation was initiated at 505 C the temperature rose to a maximum of 555 C as a result of char and sulfide combustion, and the sulfur loss was only 0.3 ±0.1 percent. The loss is much greater at lower oxidation temperatures and decreases when the temperatures of oxidation are higher, in which case the amount is less than the sensitivity of our present mass spectrometer (thus the wide limits of error). In other experiments, samples of retorted shale weighing 5 g were oxidized in flowing air at temperatures from 350 C to 700 C and for periods of time ranging from 1 to 100 min. The fraction of the char burned was determined. The fraction of sulfur oxidized to sulfate was assumed to be equal to the fraction of sulfur dissolved in water. A direct correspondence between char

13 -9- and sulfide oxidation was found (Figure 4). It appears that the observed identical reaction rate of char and FeS was due to lack of available oxygen (a diffusion limitation) when the temperature was high. At 350 C, however, the observed rates may be limited by the rate of the oxidation processes rather than diffusion. We plan to measure these rates of oxidation under conditions where we have eliminated diffusional limits. We have leached oxidized shale samples in water and find that the principal soluble components are Ca and Mg sulfates. The atomic ratio of Ca/Mg in the leachate of these oxidized shale samples was found to be *1. The ratio in the oxidized shale was 1.9, corresponding to a dolomite/calcite mole ratio of *1. This suggests that the S0 and oxygen are reacting preferentially with dolomite. Two possible explanations for this preferential reaction are: (1) The rate of reaction with dolomite is faster than with calcite. (2) Dolomite may surround the FeS crystals and the SO- does not contact calcite. References 1. R. L. Braun, "Retort Modeling," in Oil Shale Project Quarterly Report, A. J. Rothman, ed., Lawrence Livermore National Laboratory Report UCID (1980). 2. J. B. Jones, Jr. and R. N. Heistand, "Recent Paraho Operations," Proc. 12th Oil Shale Symposium, Colorado School of Mines, Golden, CO (1979). 3. Campbell, J. H., Gallegos, G. and Gregg, M., Fuel, 59, 797, Campbell, J. H., Koskinas, G. J. and Stout, N. D., Fuel, 57, 372, LLNL Oil Shale Project Quarterly Report, April-June 1981, A. E. Lewis, editor, UCID (Information also available from manuscript in preparation by Singleton, M. F., Koskinas, G. J., Burnham, A. K. and Raley, J. H.) 1107K:kk

14 FIGURE BELEASE mmz CHAR SOHBUSTIOH 60 F60 a. 40 I s o 20 c Time (min)

15 -11- FIGURE 3 Percent S lost as S0 2 during combustion of retorted shale as a function of temperature of oxidation 100 in (A CO u CJ c 2 3 Oxidation time (min) 4

16 -12- FIGURE 4 When retorted shale is oxidized and then leached with water, the percent of char oxidized is equal to the percent of sulfur dissolved which is assumed to be equal to the percent of insoluble sulfide oxidized to soluble sulfate. I I J I I PERCENT CHAR OXIDIZED

17 -13- IV. PUBLICATIONS AND PRESENTATIONS UCID LLNL Oil Shale Project Quarterly Report, April-June 1981 A. E. Lewis, Editor, September 1, 1981 UCID A. K. Burnham, "Effect of Steam on H 2, C0 2> H 2 S, and COS Concentrations in Combustion-Retort Offgas," July 16, UCID J. H., Raley, W. A. Sandholtz and R. G. Mallon, "Oil Shale Project Run Summary, Large Retort Run L-2," August UCRL A. K. Burnham, P. C. Crawford and J. F. Carley, "Heats of Combustion of Retorted and Burnt Colorado Oil Shale," submitted to Industrial and Engineering Chemistry, Process Design and Development, July 15, UCRL R. W. Taylor, A. K. Burnham, R. G. Mallon and C. J. Morris, "SOp Emissions from the Oxidation of Retorted Oil Shale," submitted as a Letter to the Editor, Fuel, July 20, UCRL ABST. J. H. Richardson, E. B. Huss, J. R. Taylor and M. 0. Bishop, "Retorting Kinetics for Oil Shale from Fluidized-Bed Pyrolysis," prepared for AIChE Spring National Meeting, June 7-10, 1982, Anaheim, CA, August UCRL "Fluidized Bed Pyrolysis of Oil Shale," J. H. Richardson and Abstract E. B. Huss, prepared for presentation at the ACS Spring 1982 National Meeting, March 28-April 2, Las Vegas, NV. UCRL "Biological Markers from Green River Kerogen Decomposition," A. Burnham, J. Clarkson, M. Singleton, C. Wong, R. W. Crawford, prepared for submittal to Geochimica et Cosmochimica Acta.

18 -14-7/21-24/81 M. F. Singleton, presentation at CONFAB '81, Saratoga, WY, "Assay Products from Various Shales." 7/21-24/81 J. H. Richardson, presentation at CONFAB '81, Saratoga, WY, "Fluidized-Bed Pyrolysis and Gas Analysis by Raman Spectroscopy." 9/15/81 A. E. Lewis presented talk, "Mining Strategies and the MIS Process," at LBL invitational workshop on Hydrological Issues Associated with Oil Shale Development.