Two-Dimensional Thermodynamic Model (Second Stage) of in Situ Underground Coal Gasification of Eastern Thin-SEAM Coals

摘要

The methodology and results of determining cavity growth via a side wall burn model in underground coal gasification (UCG) in Eastern, swelling coals is presented. Modeling techniques are still in preliminary stages but when perfected will aid in determining the feasibility of a particular site, dictate the design of the multi-well field pattern, and help control the product gas composition and cavity geometry during production. The computerized models generate a three-dimensional cavity based on the flow geometry and a two-dimensional boundary layer approach. The controlling mechanism for combustion is the diffusion of oxygen to the wall reaction zone. Specific results are presented for a simple, chemical energy balance Model IIA with specified wall and gas temperatures. Product gas composition and heating values are given, as well as reasonably good cavity comparisons with field tests at Hanna II, phase 2 in western, shrinking coals and predictions for the Pricetown I burn. Factors affecting the allowable flow rate schedule are found to be the cavity geometry, the oxygen diffusion rate to the reaction zone, and the remaining link zone flow resistance. Quantitative results are presented for Pricetown I. The complex wall-gas energy balance Models IIB and IIC are discussed in detail. The models include heat convection between wall and gas, radiation between walls (optically-thin gas case), and conduction into the wall, as well as the chemical energy transfers. Applications of the model include the Hanna II, phase 2 field test and predictions for the Pricetown I field test. Results from the models with various boundary conditions are compared in an attempt to identify viable mechanisms. The lack of sufficient field test data and the minor effect of the various boundary conditions precludes any definitive conclusion at this time. 45 references. (ERA citation 10:017810)