To address the large temperature difference in the air heater (AH) inlet of a traditional exhaust heat utilization system and energy grade mismatch problems during the heat and mass transfer processes, this study proposed a new multi-level waste heat cascade utilization system. Based on a principle of “temperature-to-port and cascade utilization”, this system uses the boiler side high-temperature flue gas and low-temperature air, and the turbine side high-temperature feed water and low-temperature condensate water, to conduct cross heat exchange according to the energy grade matching principle. Combined with a typical 1000 MW coal-fired unit, the heat transfer characteristics and energy-saving benefits of the new system were analyzed. The results showed that the new system has excellent performance: the heat rate decreased by 91 kJ/kWh, coal consumption decreased by 3.3 g/kWh, and power generation efficiency increased to 49.39%.

By taking a 130 t/h water-cooled grate biomass boiler as the research object, the ANSYS software is applied to simulate the effects of the tail burnout air’s incidence angle, wind speed, and pipe diameter on flow field distribution in the furnace, the movement of unburned carbon particles at the tail of the grate under cold operation. The influence rules of the incidence angle, pipe diameter, and wind speed of the tail burnout air on the combustion in the furnace and the movement of the tail particles were obtained. The results show that the setting of burnout air at the tail of the grate can better organize the air flow field at the grate tail, change the particle distribution, prevent small density particles from directly falling into the ash hopper, and prolong the residence time of particles on the grate. Under the study conditions, with an increase in the outlet velocity and the pipe diameter of the tail burnout air, as the movement degree and the burnout degree of grate particles increase, the boiler efficiency increases. With an increase in the incidence angle of the tail burnout air, the flow field in the furnace and the reduction ratio of the tail particles increases at first and then decreases, and the optimal incidence angle is 11–13°.