Collaborative optimization for deep peak-shaving and ultra-clean emission of coal-fired boiler using flue gas recycling technology

Abstract

ABSTRACT Nowadays, deep peak-shaving of coal-fired boilers is critical for energy saving. However, the deep peak-shaving performance of coal-fired boilers is constrained by the performance of the catalyst of the SCR. This is because deep peak-shaving working condition will cause the temperature at the entrance of the SCR (Selective Catalytic Reduction) to drop below 300 degrees, which makes the catalyst of the SCR lose its normal function. The malfunction of the catalyst eventually causes the NOx emission concentration to exceed the standards, which limits the peak-shaving capability of the coal-fired boilers abiding by the ultra-clean emission standard. This paper proposes a new method to improve the peak-shaving capability of the coal-fired boilers using flue gas recycling technology (FGRT). With this new method, part of the flue gas is mixed with the primary air, which postpones the combustion of the coal powder in the coal-fired boilers and moves the combustion center of the coal powder upward. Using this method will increase the flue gas temperature at the exit of the coal-fired boiler, and therefore the temperature at the entrance of the SCR is increased to 303 degrees to achieve the high-efficiency zone of the catalyst. Moreover, after adopting the FGRT, the oxygen concentration in the coal-fired boilers is lowered, which can effectively reduce the concentration of NOx generated in the boilers. With these advantages, the FGRT can finally enable the NOx emission concentration of the coal-fired boilers reduce to 40 mg/Nm3, which meets the requirements of the ultra-clean emission at low-load conditions, and also improves the peak-shaving capability of the coal-fired boilers. Namely, the collaborative optimization of the deep peak-shaving and ultra-clean emission can be achieved together.