ESTIMATION OF GAS EMISSIONS FROM SHALLOW SUBSURFACE COAL FIRES IN JHARIA COALFIELD, INDIA, USING FLIR DATA AND COAL FIRE GAS ANALYSIS

Jharia Coalfield is a highly populated area located in north east India. It encompasses an area of about 450 km2 and contains about 68 major coal fires. Fires occur both on the surface and underground. This is one of the densest congregations of coal fires in the world. Besides the environmental pollution and coal resource loss, the fires constitute a direct threat to the local residents who suffer from skin and pulmonary diseases, and for whom collapsing homes are a common sight.

The purpose of the project was to estimate the emission of greenhouse gases from shallow subsurface fires in the Jharia Coalfield using thermal imaging and direct gas collection and analysis. In May 2006, we carried out fieldwork in the coalfield to study several fire areas. Data collected included field photos of fire areas, sequences of temperature images recorded using a Forward Looking Infrared (FLIR) camera, and gas samples from shallow fires collected in stainless steel evacuated canisters. The sequence of FLIR images acquired over a typical subsurface fire for fixed length of time was used to estimate the gas velocities from subsurface fires. Field photos of the corresponding crack from which the gas was escaping helped to estimate the crack area. Using these two pieces of information the gas volume flux was calculated.

Chemical analysis of the gas in the laboratory provided a quantitative estimate of the amount of CO₂, CO and CH₄ in a fixed volume of gas. We assumed that once the coal fire gas cooled down to ambient temperatures, it had the same density as that of air. For hot coal fire gas, we therefore made corresponding adjustments, for estimating the amount of CO2, CO and CH4 emissions. To estimate gas emissions from the entire coalfield over a fixed length of time, we extrapolated our results with the crude assumption that the gas flux and crack areas are comparable over all known fires in the Jharia Coalfield. This lead to a conservative gas emission estimate of about 10⁸ kg/year for the study area.