Effect of Ash in Coal on the Performance of Coal Fired Thermal Power Plants. Part I: Primary Energy Effects

This article 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. The focus is on primary energy effects—combustion, heat transfer, and flow hydrodynamics. The effects of variation of ash in coal from 6% (taken as standard) up to 75% on component performance are studied and overall unit performance is quantified based on experimental data. When the ash content increases from 6% to 75%, the effects on the system (without fuel oil support) are as follows: (a) total boiler area requirement (excluding air preheater [APH]) increases by 69%, (b) efficiency of boiler fans drop by 22%–27%, (c) drum mills show an increase in SEC of 115% while ball-race mills and bowl mills show an increase in SEC of 30%, (d) induced draft (ID), forced draft (FD), and primary air (PA) fans show an increase in specific energy consumption (SEC) of around 30%, 6%–14%, and 2%–7% respectively, (e) the gross and net overall efficiencies are reduced to 77% and 66% of their original values, (f) the ratio of the specific fuel consumption at a given ash content to that at standard ash of 6% increases from 1 to 10, and (g) specific fuel consumption (SFC) _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 partial load. When the ash in coal exceeds 75%, its UHV is reduced to zero.

Keywords:

• ash content
• useful heating value
• energy efficiency
• specific energy consumption
• efficiency underrating