Two-Dimensional Pyrolysis Effects During In-Situ Coal Gasification: Preliminary Results
Authors: Forrester R.C. , Westmoreland P.R. 
Published: December 2007

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Introduction

Estimates are that 9.2% of all U.S. coal resources may be recovered by conventional deep-mining or strip-mining techniques. The approximately 3.9 trillion tons (3538 Pg) remaining comprise seams that are too thin or too deep to be recovered by such methods. The energy contained in many of these seams, however, could be recovered by in-situ or underground coal gasification (UCG) processes currently being developed.

UCG concepts differ in many fundamental respects from those defining surface processes for gasifying coal that has been mined, crushed, sized, and dried. An important incongruity is the large variation in coal-particle size that will be processed in an underground "reactor." Our inability to crush and screen the coal introduces difficult problems related to controlling operating conditions and, correspondingly, to the quality of the product gas. Past pyrolysis studies have been confined to the heating of small, finely ground samples of coals using thermogravimetric techniques, and most research has been performed using an inert cover gas (hydrogen was used in some studies). The effects of reactive gases from a gasification zone on pyrolysis processes are not understood. These problems were processes are not understood. These problems were addressed recently by experimental studies on the pyrolysis of large blocks of coal in hopes of developing pyrolysis of large blocks of coal in hopes of developing better understanding of the pyrolysis process. Improved models and, thus, better design and control of UCG processes are the ultimate goals. processes are the ultimate goals. Apparatus and Procedure

Studies of two-dimensional pyrolysis systems have consisted of experiments using large, instrumented blocks of subbituminous coal taken from the Roland-Smith seams near Gillette, WY. A 20-cm-diameter reactor is heated electrically and swept with a cover gas supplied from a cylinder. A specified heating rate is maintained within the reactor by using a three-mode controller that can provide heating rates of 0.1 to 10 degrees C/min, measured at the surface of the test specimen. Reactor pressure remains essentially 1 atm throughout the run.

Fluids produced during pyrolysis are swept into a water-cooled mist eliminator-condenser that traps most of the tars, oil, and water. Noncondensable gases are metered, sampled, and vented.

Laboratory procedure for preserving the original condition of samples during storage includessealing the sample blocks in plastic bags at the mouth of the mine,submersing the samples in water on receipt at the laboratory, andperforming all necessary machining and drilling operations under a water spray.

Preparation of pyrolysis test blocks requires that a 15-cm Preparation of pyrolysis test blocks requires that a 15-cm right circular cylinder be cut from larger, irregular blocks using a band saw. The blocks then are drilled to accommodate 1.0-mm thermocouples.

Once a test specimen has been sealed in the reactor and a stable cover-gas flow has been established, the reactor is heated at one of two heating rates chosen for these studies: 3.0 or 0.3 degrees C/min.

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