Experimental and numerical study of the characteristics of biomass suspension combustion in a hot-water boiler

Abstract

Biomass powder fuel is an abundant and widely available biomass resource with potential advantages including simple manufacturing process, low energy consumption during processing, high bulk density, convenient storage and transport and high combustion efficiency over other forms of biomass fuels such as bulk, compact block and grain fuels. However, the nature of biomass powder produces a series of issues during combustion including inferior combustion stability, which demands a deep investigation to enhance the energy production and utilization from powder biomass. In this paper, a combined experimental and theoretical study on combustion characteristics is carried out based on a recently developed biomass suspension hot-water boiler with a new design. When the fuel powder concentration is 450 g/m3 and the primary/secondary air ratio is 0.8, the biomass suspension combustion hot-water boiler reaches its optimal condition and the combustion chamber temperature and the thermal efficiency are at their highest levels. The thermal performance of the designed biomass suspension hot-water boiler is tested for the rated condition. Data show that the combustion efficiency and the thermal efficiency reach 97% and 83%, respectively, whereas the harmful gas (CO, SO2, NOx) content in the fumes meet the requirements of the national industrial boiler atmospheric pollutant emission standard in China. The computational fluid dynamics simulation of the temperature field in the furnace shows that combustion of a biomass powder fuel in a pre-combustion chamber and a furnace is not only closely related to the oxygen supply but also related to the airflow ratio and the furnace temperature. The simulated results show that the furnace temperature field, the primary and secondary airflow streamlines, the biomass powder grain movement trajectory and the component field distribution are in agreement with the experimental results. Our findings may help to design an efficient biomass suspension hot-water boiler.