Investigation of the flow and heat transfer performance for a water-cooling grate in a biomass boiler

ABSTRACT

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°C for the moisture evaporation section, the volatile release section, the char combustion section and cooling section are 0.46 kg·s⁻¹, 0.55 kg·s^−1, 4.60 kg·s⁻¹, and 0.23 kg·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.

KEYWORDS:

• Biomass boiler
• water-cooling grate
• porous model
• flow and heat transfer

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Shiqiao Yang

Shiqiao Yang is a Ph.D. student in the School of Energy and Environment, Southeast University, since 2019. He received his master's degree from the School of Environmental Engineering, Tsinghua University in 2016. His main research interests are theoretical research and numerical simulation of the flow and heat transfer performance of the water-cooled grate inside the biomass boiler.

Hrvoje Mikulčić

Hrvoje Mikulčić defended his PhD thesis in 2015 at the Department of Power Engineering, Energy and Environment, Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb. His main research area includes: Numerical modelling of fluid flow; Solid fuel combustion; Endothermic calcination reaction; Pollutant formation, Greenhouse gasses emissions analysis and accounting; Energy intensive industry; Energy system analysis; Renewable energy; Multiphase flows; Waste-to-Energy, Carbon capture and utilization; Pollution reduction; Green ammonia. He is an author of 71 scientific papers, in scientific journals (SCI). His current Scopus h-index is 25. He is the Associate Editor of the Journal of Cleaner Production. He serves as a Special Issue Guest Editor in the Journal of Environmental Management, in Optimization and Engineering, and in the international journal Fuel.