Simulation of underground liquefaction of lignite

Abstract

There were three steps toward the final solution of this research. First, a kinetic model which was used to estimate the degree of lignite liquefaction was developed. Then the underground liquefaction process was simulated by a laboratory bench-scale system. Finally, with this knowledge, a mathematical model was developed to simulate the underground process. The kinetic data were obtained by use of a 60 ml mini-reactor at reaction pressures and temperatures of 20 to 70 atm and 375, 400, and 425 °C, respectively. Texas lignite predried in the air and about 5 mm in diameter was used throughout the experiments. Solvents that were tested were tetralin, SRC recycled solvent, anthracene oil and creosote oil. Devolatilization experiments were also conducted in order to determine the effect of the solvent in solubilizing the lignite. The lignite conversions were found to vary from 23.2% to 81.4% on an ash free basis. Results obtained for the creosote and anthracene oil were similar to results of the devolatilization experiments. The conversion increased with increasing temperature and reaction time. A continuous flow system with a semi-adiabatic tubular reactor was designed and built to simulate an underground liquefaction process. The tubular reactor was packed with lignite particles and hot solvent was passed through the reactor. The unsteady state temperature profile was measured and the rate of extraction was monitored by use of a gel permeation chromatograph. The conversions obtained from this system were similar to those obtained in the minibatch reactors. A one-dimensional mathematical model was developed to predict the unsteady state temperature distribution and the rate of extraction of the lignite. The model successfully estimates the unsteady state temperature profiles and the rates and extends of extraction that were obtained experimentally. The rate of extraction was limited mainly by the temperature. In experiments with tetralin and creosote, 58.7% and 28% respectively of the lignite charged was reacted within 6 hours. Loner extraction times were not necessary, because equilibrium conversion of the lignite was obtained...