Subsurface thermal conversion of coal into light gases and oils via pyrolysis potentially offers a more environmentally benign alternative to conventional coal combustion. Few studies have examined coal pyrolysis under conditions relevant to subsurface pyrolysis, such as very large particle sizes, confining pressures, and very slow heating rates. The presented work examines structural changes in the porous network of very large particles of Utah bituminous coal undergoing pyrolysis at atmospheric pressure at heating rates as slow as 0.1 °C/min. Several unique phenomena are observed, including an absence of plastic deformation at heating rates below 10 °C/min, the development of a bimodal macropore size probability distribution because of confinement effects when plastic deformation occurs, and a potential trapping mechanism for residual organic matter in the mesopore system. The pyrolysis behavior of very large bituminous coal particles at very slow heating rates is found to deviate substantially from those observed under conventional conditions.
With the continuously decreasing quality of crude oils, issues may arise with refining and transporting such oils. New technology must be developed to address these issues. Coupling a thermal cracker with a catalytic cracker in series was investigated as a possible method of directly treating heavy fractions as well as paraffinic whole crude oils. A potential application of this cracker configuration would be upstream treatment of high pour point crudes to improve flowability. The idea was to deposit a fraction of the coke on the thermal medium that would otherwise be deposited on the catalyst, thereby extending the life of the catalyst. This concept was tested using two transport reactors, one with sand and the other with catalyst, and with three feedstocks, atmospheric residuals, fluid catalytic cracker feed, and a waxy crude oil. Product distributions were determined for variations in thermal and catalytic cracker residence times, cracker temperatures, feedstock type, and catalyst/oil ratios. The data gathered show that coupling a thermal and a catalytic cracker may provide some definite advantages. The typical liquid yields for the combined thermal and catalytic cracker ranged from around 50 to 75%. One of the experiments produced a bimodal distribution of hydrocarbons in the liquid products, with the first distribution being olefinic and the second distribution being paraffinic, with a 68.4% liquid yield. Promising results were obtained with a waxy crude oil, wherein 34.6% by weight of the liquid products was naphtha.
Underground coal pyrolysis is a process similar to in situ oil shale production wherein heat is applied to deep coal formations to produce light hydrocarbons. Like enhanced coal bed methane, the injection of CO 2 post thermal treatment can improve hydrocarbon recovery and serves as a means of carbon sequestration. Little information exists pertaining to coals pyrolyzed to temperatures expected with this process. This work examines the development of meso-and micropores and their influence on methane and carbon dioxide adsorption and permeability on a thermally treated Utah bituminous coal. Residual tars were found to affect the pore size distributions in pyrolyzed coals. Generally, with increasing treatment temperature, there are more meso-and micropores. A correlation was established between the prevalence of mesopores in pyrolyzed coals and adsorption and, to a lesser extent, permeability. The treatment temperature of this particular coal is directly related to the amount of CO 2 said coal can store and how the plume of injected CO 2 moves through the formation.
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