temperature drop of flue gas from 290.7 1 C to 199.7 1 C. The flue gas temperature is decreased from 845.4 1 C to 290.7 1 C by transferring heat to water/steam in superheater,boiler bank and economizer. In the model, the temperature drop in boiler is from 850 1 C to 300 1 C. The steam supply to turbine is 15.25 t per hour (TPH) in running plant during the observation. At the same operating conditions,thermal model results 14.5 TPH of steam. The deaerator pressure in the plant is 0.55 bar.The results are compared at 0.2 deaerator temperature ratio. At this temperature ratio, the deaerator pressure is 0.64 bar.