Applying spontaneous adiabatic test procedure to determine CO2 gasification reactivity and kinetics of coal for UCG applications

Abstract

UCG is a gasification process used to produce synthesis gas from coal in situ (underground in the coal seam) by injecting air or oxygen, with or without steam, into coal seams and extracting the product gas via the production well and may also be thought of as a thermo-chemical mining process. The coal face becomes a gasification front and results in high temperatures (>1000 oC) that cause the hydrocarbons contained in the coal to effectively re-form into gas. This resulting synthetic gas (“syngas”) can be used to produce electricity, as well as chemicals, liquid fuels, hydrogen and synthetic natural gas. The effectiveness and carbon efficiency of UCG can further be improved by applying CO2 gasification / recycling of waste captured CO2 as gasification agent (replacing part of the oxygen and steam as gasification agent). With CO2 based gasification, the most important reaction is the reduction process, (also known as the Boudouard Reaction, where CO2+C2CO above 850°C. CO2 gasification, and specifically applied to an Underground Coal Gasification process, is a practical solution to improve both carbon efficiency and lower the CO2 footprint. The main aim of this study is to determine the minimum O2 addition and mininmun CO2 temperature (350 °C). During a previous experimental study (Part 1 of this study), it was observed that at a higher mass flux of both CO2 and O2, an increase of 6% more CO was present in the reactor effluent stream. However, during both of the practical tests, the O2 concentration in the reactor agent stream remained approximately the same. This indicates that the CO2 gasification process is favoured at higher temperatures. At higher mass fluxes, the bed obtained an overall greater conversion, resulting in a lower residual bed height and increased ash bed height. Understanding the properties of a coal is critical to effectively and efficiently operating a UCG process under CO2 saturated environments andthe Spontaneous Combustion and Reactivity behaviour– may supply technical detail and scientific insight into gasification behaviour and carbon conversion of the coal. Adiabatic oven testing using R70 and SponComSIM™ tests is usually applied as a precautionary measurement of the self-heating properties of coal, e.g. to manage coal on stockpiles or during transport. In this study, we aim to show how the novel approach of using R70 and SponComSIM™ tests to quantify the optimal conditions (temperature, duration, self-heating, carbon conversion) at which a coal can be successfully gasified with CO2 as agent