Effect of operating condition on Boiler

Steam pressure and temperature are the key parameters of power generation for thermal power plants and also for process application. Steam pressure and temperature decide the amount of heat available, in the form of enthalpy, to do work in the turbine. A drop in both will reduce the plant heat rate in different magnitude.

1. Effect of superheating
2. Effect of max. pressure
3. Reheating

• Effect of superheating

Increase the efficiency

The average temperature at which heat is added to the steam can be increased without increasing the boiler pressure by superheating the steam to high temperatures.

Superheating the steam to higher temperatures has another very desirable effect: It decreases the moisture content of the steam at the turbine exit.

Heat loss due to radiation and convection: 

Heat losses from a boiler consist of the loss of heat by radiation and convection from the boiler casting into the surrounding the boiler house. Normally surface loss and other unaccounted losses are assumed based on the type and size of the boiler as given below 

For industrial fire tube / packaged boiler = 1.5 to 2.5% 

For industrial water tube boiler                = 2.0 to 3.0% 

For power station boiler                             =  0.4 to 1.0%

• Effect of max pressure-

 increase the efficiency

 Lowering the operating pressure of the condenser lowers the temperature at which heat is rejected. The overall effect of lowering the condenser pressure is an increase in the thermal efficiency of the cycle.

• Reheating

In Reheating, process waste heat is used to reheat the water before inserting to the boiler.

this lead to an increase in the thermal efficiency of the boiler.

The addition of one stage reheater utilization will increase the thermal efficiency of the Rankine cycle by 3-4%, the addition of two stages of the reheater increases the efficiency by 1.5-2%, the addition of the three-stage reheater increases efficiency by 0.75-1%, and so on.