Investigation Of The Flow And Heat Transfer Performance For A Water-Cooling Grate In A Biomass Boiler

Biomass direct combustion power generation technology can effectively take the advantage of the biomass resources. Water-cooled reciprocating grate has become the research hotpot of biomass boilers for its advantages such as excellent performance and controllable cost. This paper mainly studies the flow and heat transfer performance of the water-cooled reciprocating grate, according to the different combustion state, the boiler can be divided into four sections: the moisture evaporation section, the volatile release section, the char combustion section and the cooling section. A porous model is used to simulate the biomass combustion process in different sections. Results indicate that the porous model can show more details about the temperature distribution of the grate, which is closer to the real situation. Compared to the traditional model, the relative deviations of main parameters against the heat transfer performance are less than 5%. With the increase of mass flow rate, the descend amplitude of the temperature decreases, but the ascend amplitude increases sharply, which would increase the operation cost. The least mass flow rate needed to keep the temperature rise between the inlet and outlet less than 5 degrees C for the moisture evaporation section, the volatile release section, the char combustion section and cooling section are 0.46 kg center dot s(-1), 0.55 kg center dot s(-1,) 4.60 kg center dot s(-1), and 0.23 kg center dot s(-1), respectively. For the moisture evaporation section, the volatile release section and the cooling section, the temperature of the grate and cooling water is low on the middle but high on the tail, while it is opposite for the char combustion section, due to the variation of combustion state and biomass thickness in different sections. Besides, it is found that the longitudinal vortices could pose great influence on the uniform distribution of cooling water. To optimize the cooling effect, it is important to reorganize the water channel and reduce the longitudinal vortices.