A Novel Combustion Air Preheating System in a Large-Scale Coal-Fired Power Unit

A novel hybrid system for combustion air heating, including flue gas cooling, air heating and heat regeneration has been proposed. In the reformative scheme, the air gains energy from four tubular heat exchangers and the flue gas releases heat in four tubular heat exchangers as well, instead of the rotary regenerative air preheater (APH) that is used in the conventional scheme. Consequently, the temperature differences between the fluids during heat transmission can be diminished, and the mixing of the hot-cold primary air and the severe leakages are avoided, which remarkably reduces the exergy destruction and enhances the thermal performance of the power unit. The new design was evaluated based on a 670 MW coal-fired supercritical power unit. The results show that the additional net power output of the power unit can reach 8.57 MW with a net efficiency promotion of 0.57 percentage points due to the novel configuration. And the energy saving mechanism of the proposed concept was revealed on grounds of the first and second laws of thermodynamics.