Research On Groundwater Pollution Caused By Underground Coal Gasification

Underground coal gasification is a coal exploitation technique that underground coal is directly converted into gaseous fuel or raw materials by controlled combustion.It can reduce the coal gangue, dust coal due to development and utilization and other ecological environment damage, so it is known as the "green mining". But both of the gas products and gasification residue generated from UCG and residued in underground may pollute groundwater. In this paper, the gasification experiments of Neimeng lignite, Hebi bitumite and Jincheng anthracite were conducted respectively by using the tube furnace coal gasification experiment system and underground coal gasification model test system, the gas washing water and residual semi-coke leaching liquid were detected by GC-MS for studying the dissolving rules of gas pollutants and gasification residue into the groundwater. Furthermore, the gas washing water was purified by using self-made activated carbon. The main conclusions are as following:(1) Experiments by the tube furnace coal gasification experiment system show that the gasification temperature and gasification agents have important influence on coal gasification reactivity, gas calorific value of H2O(g) is higher than that CO2.The optimal gasification temperature is 1000 ℃; Coal gasification reaction characteristics are as follows: Neimeng coal > Hebi coal > Jincheng anthracite coal.(2) The pollutant in gas washing water from tube furnace coal gasification experiment are related to gasification temperature、gasification agent and coal and so on. The concentration of TOC and COD、ammonia and volatile phenols in gas washing water are increased with as the gasification temperature increasing; The types of organic and the concentration of volatile phenol, TOC, COD, ammonia and elements in gas washing water in gasification are higher than the CO2 gasification, and increased with the decrease of coalification.(3) The TOC and phenolic compounds in residual semi-coke leaching of liquid tube furnace gasification all decreases with the increase of leaching temperature; As the extension of leaching time, the concentration of ammonia and phenolic compounds in residual semi-coke leaching of liquid is increased before they are the same, While the concentration of TOC and most elements are constantly increasing; With time of coal influencing the concentration of TOC and ammonia follows: Neimeng coal > Hebi coal > Jincheng anthracite coal.(4) Underground coal gasification model test system experiments showed that the concentrations of phenol, polycyclic aromatic hydrocarbons, volatile phenol, TOC, COD, ammonia and elements in water-gas washing water when the steam as the gasification agent were greater than that in the air as the gasification agent.The rule of the leaching from the gasification residual pollutants and the leaching by tubular furnace are basically identical.Gasification residual semi-coke soaking experiment found that the static water pressure of the confined groundwater is helpful to control inorganic contaminants in groundwater pollution. But it may increase the pollution of organic pollutants.(5) Activated carbon exhibits well performance on the purification of gas washing water from UCG, the removal rate of volatile phenol can reach 99%, the removal rate of TOC was 88%, the removal rate of ammonia was 80%, the removal rate of elements can reach more than 99%.