Gas Turbine Cycle with Regeneration - Effect on Thermal Efficiency

Gas turbine cycle with regeneration is a modification of the simple gas turbine cycle. In this cycle, a fraction of the exhaust gas from the turbine is passed through a heat exchanger before it is discharged to the atmosphere. This heat exchanger is called a regenerator or a heat recovery steam generator (HRSG). The regenerator transfers heat from the exhaust gas to the compressed air before it enters the combustion chamber. The main purpose of the regenerator is to increase the thermal efficiency of the cycle.

Pressure Ratio and Work Output

The pressure ratio is the ratio of the compressor discharge pressure to the inlet air pressure. In a gas turbine cycle with regeneration, the pressure ratio remains the same as that of the simple gas turbine cycle. However, the work output of the gas turbine decreases due to the energy required to pump the air through the regenerator.

Heat Input

The heat input to the combustion chamber is the same as that of the simple gas turbine cycle. However, a fraction of the heat rejected by the turbine is recovered by the regenerator and returned to the cycle. This results in an increase in the available heat for the cycle.

Thermal Efficiency

The thermal efficiency of a gas turbine cycle with regeneration is higher than that of a simple gas turbine cycle. This is because the regenerator increases the temperature of the compressed air before it enters the combustion chamber. This results in a higher turbine inlet temperature and an increase in the cycle efficiency. The increase in thermal efficiency is due to the following reasons:

- The regenerator allows the recovery of waste heat, which is otherwise lost to the atmosphere.
- The regenerator preheats the compressed air, which reduces the fuel consumption required to achieve the same temperature rise in the combustion chamber.
- The regenerator reduces the temperature of the exhaust gas, which increases the temperature difference between the exhaust gas and the ambient air. This increases the heat transfer rate from the exhaust gas to the atmosphere.

Conclusion

In a gas turbine cycle with regeneration, the pressure ratio remains the same, the work output decreases, and the heat input remains the same as that of the simple gas turbine cycle. However, the thermal efficiency increases due to the recovery of waste heat by the regenerator. The regenerator preheats the compressed air, reduces fuel consumption, and increases the temperature difference between the exhaust gas and the atmosphere.