Efficiency improvement in thermal power plants using waste heat recovery of flue gas – simulation study.

Abstract

In this paper an Organic Rankine cycle is used as waste heat recovery cycle for a 250 x 2 MW thermal power plant. The exhaust flue gas (80 to 130°C) in the thermal power plant is often released into the atmosphere as waste heat. This waste heat can be utilized as a form of heat source for the Organic Rankine Cycle. The treated flue gas form the Flue Gas Desulphurization plant will be fed to the heat exchanger where the heat transfer between the flue gas and the working fluid (e.g.: Ammonia, R245A) will take place. The working fluid will be fed to the (low pressure) turbine where the work done can obtained. After the expansion of the working fluid in the turbine, the working fluid is cooled in the condenser using water. Then this fluid is again sent to the heat exchanger using pump. The flue gas from the heat exchanger after the heat transfer will be then supplied to the stack. The cooling of the condenser water can be done using a cooling tower. As the load varies for the thermal power plant the temperature of the flue gas also changes and hence the turbine shaft output also changes this may result in tripping of the generator. In order to avoid this, a turbine governing system is designed with a step-up gear box and a torque converter. This governing system will keep the generating shaft in motion at constant speed even during low loads and high loads. This cycle will help the thermal power plants to obtain extra power output and will increase the efficiency of the plants.