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