Effect of Ash on the Efficiency and Capacity of Coal Fired Thermal Power Plants

Abstract

This paper reports the effect of ash content in raw coal on the energy performance of coal fired thermal power plants of capacity range 30-500 MW. It also gives the extent of capacity reduction in equipment due tofiring of coals with higher ash contents. The effects of variation of ash in coal from 6% (taken as standard) up to 75% (extreme) on component performance are studied and overall unit performance is quantified based on experimental data and performance simulation. When the ash content increases from 6% to 57% and above, the effects on the system (without fuel oil support) are: (a) efficiency of boiler fans drop by 22-27%, (b) drum mills show an increase in SEC of 115% while ball-race mills and bowl mills show an increase in SEC of 30%, (c) ID, FD and PA fans shown an increase in SEC of around 30%, 6-14% and 2-7% respectively, (d) the gross and net overall efficiencies are reduced to 77% and 66% of their original values, (e) ratio of the specific fuel consumption at a given ash content to that at standard ash of 6% increases from 1 to 10, and (f) SEC gross increases from 0.35 to 3.0. When the ash content of coal goes beyond 57%, limitations in combustion space and flow arise and beyond this the unit has to be operated only at part load. When the ash in coal exceeds 75%, its UHV is reduced to zero.