The movement of gases in longwall coalface wastes liable to spontaneous combustion
The increasing depth, distance from surface connections and falling quality of coal mined are factors that increase the risk of spontaneous combustion in working areas. The trend towards high capital investment, high output faces significantly raises the economic consequences of spontaneous combustion. Much work has been directed towards methods of identifying the liability of a coal to spontaneously combust under given conditions. The cost of prevention and combat of spontaneous combustion underground is high, however this work is carried out with little knowledge of the likely location of a heating in a coalface waste. This thesis investigates the airflow patterns in a coalface waste, with a view towards improving the use of prevention and combat methods. The factors that affect the liability of a coal to spontaneously combust, and the methods of prevention and combat are discussed to provide a background to the subject area. An investigation into the flow of nitrogen that was injected from one hole into a coalface waste as a combat measure was conducted. The results of this showed how the amount of nitrogen entering the waste depended on the rise and fall of the atmospheric pressure. An attempt was made to develop a method of sampling gas from deep within the coalface waste. It proved impossible to sample further than 15m behind the face line. The results from this exercise are presented. The finite element method was used to model the pressure distribution in the waste under differing boundary pressure and waste permeability conditions. A suggested area at risk from spontaneous combustion is presented.