Stack Losses
• In steam power plants, the exhaust gases are discarded to the stack at a temperature in the range of between 100 to 150oC: to lift the trail of stack gas well above the ground level; and to evade corrosion in the fuel gas system by sulphuric acid, that will form when there is any sulphur in the fuel, and the gas temperature drops underneath the dew point.
• The thermal energy needed to increase the stack gases from ambient air temperature to the stack gas temperature generally symbolizes 10 to 20% of the heating value of the fuel.
• The stack losses rose as the quantity of excess air is raised above the stoichiometric value. When excess air is raised from 0 to 100%, the stack losses will twice. For maximum combustion efficiency, the quantity of excess air is to be not more than 10%.