Stoichiometric calculations of combustion of Lakhra lignite

Lakhra coal field is largest productive coal field of Pakistan. About 1.5 millions tonne of this coal is, annually, mined and transported daily to various parts of the country in 500 trucks each of 10 tonnes of coal. The major consumers of this coal are brick kilns located in Sindh and Punjab. It is available at Rs. 500/- per tonne at mine head. A number of attempts were made for the production of power (electricity) by foreign companies. Feasibility studies were undertaken but no one set up power plant. It may be due to inferior quality of coal as it is lignitic in nature with high ash and sulfur contents. This coal is also, very sensitive to spontaneous combustion. Spontaneous combustion is the auto-ignition of coal at ambient conditions. Hence there are storage problems. In spite of these drawbacks, a 3(50) Mega Watt (3 units of each 50 mega watt power generation capacity) power plant, based on atmospheric fluidized bed combustion of coal technology (AFBC), was setup in early nineties. The performance of this plant remained poor. The main reasons might be poor quality of coal and limestone. Limestone is used with high sulfur Lakhra lignite, in fluidized bed combustor, to arrest sulfur of the coal, fixing sulfur as calcium sulfate to minimize hazardous emissions of sulfur dioxide (SO/sub 2/). Spontaneous combustion of Lakhra lignite is responsible for each fire of coal and conveyor belt etc. (author)