13 Mild Hydrocarbonization of Western Coal
Downloaded via UNIV OF CALIFORNIA SANTA BARBARA on July 9, 2018 at 07:23:07 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
H. D. COCHRAN, JR. and J. M. HOLMES Chemical Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830
Experiments with mild hydrocarbonization of Wyodak western coal at ORNL have led to a proposed process for the production of oil, gas, and low-sulfur char with a very low overall consumption of hydrogen. The process yields: (a) high-Btu pipeline gas, (b) a light oil that requires only mild hydrotreating, and (c) a high-quality char that can fuel a pressurized, fluidized-bed combustor (PFBC) without adding limestone for SO control or using high-pressure solid feeders. Preliminary heat and mass balances have been prepared for a commercial-scale facility which includes a PFBC for power generation. An economic analysis of this facility indicates that the oil product can be marketed at a very attractive price by using current published estimates for the prices of the product pipeline gas and electricity. Further development and technical evaluation of this promising coal conversion process are recommended. x
/^Vne way to reduce the overall costs of coal conversion is to reduce capital costs. This can be achieved by simplifying the process, using mild process conditions, and sharing part of the capital costs with a complementary facility such as a utility power plant. Experiments with Wyodak coal at O R N L have suggested such a process based on mild hydrocarbonization to produce oil, gas, and a low-sulfur char with a very low overall consumption of hydrogen. Preliminary economic evaluation of this process is highly encouraging. The experimental results will be presented, and a process flowsheet will be described. Product price estimates have been derived which are very attractive when compared with product prices from other coal conversion technologies. 0-8412-0468-3/79/33-183-225$05.00/0 © 1979 American Chemical Society
Oblad et al.; Thermal Hydrocarbon Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
226
THERMAL
HYDROCARBON
CHEMISTRY
Carbonization of coal at atmospheric pressure results in a net evolution of molecular hydrogen—up to 2-3 wt % [based on moisture- and ash-free ( M A F ) coal]. The use of elevated hydrogen pressure, on the other hand, results in a net consumption of hydrogen that increases substantially with increasing temperature and hydrogen partial pressure. Under milder, intermediate conditions it is possible to hydrocarbonize coal so the consumption of hydrogen is just offset by the small evolution of hydrogen; that is, mild hydrocarbonization with no net consumption of hydrogen. The elimination of hydrogen consumption permits the gasifier to be removed from the process flowsheet and, with it, the oxygen plant. Experimental A complete description of the experimental equipment, procedures, materials, run conditions, and results is available elsewhere (J); therefore, only minimal information on the experimental work is presented here. The 10 lb/hr bench-scale hydrocarbonization facility at O R N L is shown in Figure 1; the equipment flowsheet is presented in Figure 2. With this apparatus, yield data have been generated for the mild hydrocarbonization of Wyodak subbituminous coal. Table I summarizes the proximate and ultimate analyses of this coal. When Wyodak coal is hydrocarbonized at 1040°F under a hydrogen pressure of 300 psi (315 psia total pressure), the yields obtained (expressed as wt % of M A F coal fed) were as follows: oil, 20; gas, 21; water, 13; and char, 46. Figure 3 shows the variation of oil yield with temperature at a hydrogen pressure of 300 psi; as observed, a gentle maximum occurs at about 1040°F. The steady-state, make gas composition under these conditions is presented in Table II. The process to be described is based on four significant attributes of mild hydrocarbonization of western coal: (a) subbituminous coals are noncaking and do not agglomerate in the fluidized-bed hydrocarbonizer; (b) significant yields of oil and gas can be obtained with a very low overall consumption of hydrogen; (c) the residual solid char is a clean, efficient boiler fuel; and (d) the quality of the oil produced is such that only light hydrotreating is required. These attributes are illustrated in the next few figures. Figure 4 is a plot of hydrogen consumption vs. hydrogen partial pressure with temperature as a parameter. The solid lines are taken from a correlation (2) of published data (3); the point shown is our recent experimental verification of the zero net hydrogen consumption at a temperature of about 550°C ( 1 0 4 0 ° F ) and a hydrogen pressure of 300 psi. Table III summarizes the proximate and ultimate analyses of the char produced during this mild hydrocarbonization process. Figure 5 shows the distillation curve (simulated by the A S T M chromatographic procedure) for the oil produced by mild hydrocarbonization of Wyodak coal. Note that, in contrast to many other coal-derived liquids, more than 90% of this oil can be distilled at 900°F. Other properties of the raw product are presented in Table IV.
Oblad et al.; Thermal Hydrocarbon Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
13.
COCHRAN AND HOLMES
Hydrocarbonization of Coal
Figure 1. Hydrocarbonization apparatus
Oblad et al.; Thermal Hydrocarbon Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
227
Ω
Ο
Ω » 03
§
M W
H
to to 00
Χ
Oblad et al.; Thermal Hydrocarbon Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
13.
Table I.
229
Hydrocarbonization of Coal
COCHRAN AND HOLMES
Proximate and Ultimate Analyses of Wyodak Coal
(%)
Proximate Analysis Moisture Ash Volatile matter Fixed carbon
30.9 5.0 32.3 31.8
Ultimate Analysis(MAF) Carbon Hydrogen Nitrogen Sulfur Oxygen Calorific content:
2Ol
1
800
ι
72.40 5.63 1.04 0.85 20.08 12,500 Btu/lb
ι
ι
ι
900 IOOO TEMPERATURE (°F)
ι
1100
Figure 3. Liquid hydrocarbon yield vs. temperature for hydrocarboniza tion of subbituminous C coals at a hydrogen pressure of 300 psi
Table II.
Carbon Distribution in Make Gas from Wyodak Coal Hydrocarbonized at 300 psi and 1 0 4 0 ° F Component CH
4
C2He + C2H4
C 3 H 8 + CeHe
C* CO C0 4
2
Concentration (vol%) 51 13
4
nil 23 9
Oblad et al.; Thermal Hydrocarbon Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
230
200
400
HYDROGEN PARTIAL
600 PRESSURE
800
1000
(psia)
Figure 4. Hydrogen consumption during hydrocarbonization of subbituminous C coals Table III. Proximate and Ultimate Analyses of Wyodak Hydrocarbonization Char (%) Proximate Analysis Moisture Ash Volatile matter Fixed carbon
