Effect of Moisture in Coal on Station Heat Rate and Fuel Cost for Indian Thermal Power Plants

Indian coals inherently contain low inherent moisture (IM) (5.5-9.5 % with an average of around 7.5 %) and moisture addition is through the surface moisture (SM) due to sources external to the coal. On the other hand imported coals contain very high IM (15-25 %) but negligible SM. Presence of surface moisture (SM) is a major liability to the power generating process and it’s and control needs to be understood on a broader national perspective. Great importance must be given during the transportation, handling, transfer and storage of coal to ensure that its heating value is preserved and there is no deterioration on account of SM addition enroute to the power plant or in the coal yard storage prior to its entry into the furnace of the boilers. It is the SM which affects the power plant operations. In the case of imported coals higher total moisture (TM) coals (higher inherent moisture and almost no SM) are cheaper and the marginally increased generation cost due to IM is offset by the cheaper purchase price. The same is not true for Indian coals where there is no provision for cost accounting of SM except for upper limits. The impact of 1 % TM (without considering the weight effect) is -4.2 kcal/kWh on design unit heat rate, -8.2 kcal/kWh on operating unit heat rate, -0.0226 p.u. of plant load on Station load, -4.0 % on Plant load factor,+0.2263 % of plant load on Auxiliary power, +0.0079 kg/kWh on Specific coal consumption,+1.1426 ml/kWh on Specific fuel oil consumption and +15.21 kcal/kWh on Station heat rate.