(621ey) Reaction Engineering Model for Underground Coal Gasification

Reaction
Engineering Model
for Underground Coal
Gasification

Vivek Ranade* and Akshay
Singan

Chemical Engineering and Process Development Division

CSIR ? National Chemical Laboratory

Pune 411008, INDIA;  vv.ranade@ncl.res.in

Coal is
the major source of energy in the Indian sub-continent with roughly 65-70% of
the electricity being sourced from coal fired power plants. Much of the coal resources are locked deep in the earth
with heavy costs in recovery, and even when recoverable they contain large quantity of ash and
require treatment for reducing ash content and transport to the point of
use. With adequate geological
characterization, Underground
Coal Gasification (UCG) offers a promising
way for
the utilization of such reserves to generate synthesis
gas without bringing the high ash coal above ground.
 UCG
 involves  drilling
 holes
 from  the  surface,  deep  into
 the
 seam  and
 allowing  the
gasification to happen in-situ,
and
gas comes to the surface via other wells.

Several parameters affect the combustion and gasification of underground coal
seam and therefore performance
of
UCG operations. Some of these include the temperature, pressure,
quality and quantity of the gasifying medium, quality of coal, presence and movement of
moisture from within
and
around the seam. The UCG operation by its inherent nature is difficult to monitor and control. It
is therefore essential to develop appropriate mathematical
models to describe and to some extent predict performance of UCG. In this work a chemical reaction engineering (CRE) framework is
developed to simulate UCG operations.

The overall framework includes formulation of detailed three-dimensional
models using the computational fluid dynamics (CFD) platform as well as formulation of a simpler one-dimensional
CRE model. The scope of this presentation is restricted to discussing the simpler one-dimensional
model. A detailed pseudo steady state one-dimensional packed bed model was developed for representing the seam with linking channel between the wells for injection and extraction
of
gas. All the key reactions are included along with
transport within the seam. The model was applied to seam sizes ranging from micro-UCG to block sized UCG and finally to seam scale UCG. The simulated
results are compared with some of the published results/ data.
The model was then used to understand influence of key design and operating
parameters on composition as
well
as quantify of generated gas.
The
model permits the analysis of variation
of
temperature within the seam with changes in condition of operation and their interplay in getting sustainable rates and composition of
syn-gas.
The results will
be useful
for further work on UCG modeling.

Considered geometry of UCG
and sample of typical
results