Performance analysis of biomass gasification coupled with a coal-fired boiler system at various loads.

• A model of biomass gasification coupled with coal-fired boiler is proposed. • The performance of the coupled system at various loads is studied. • The coupled system efficiency reaches 84% at optimum conditions for various boiler loads. • The maximum reductions of NO and SO 2 emissions reach 5.99% and 16.80% respectively. • An efficient utilization method for straw in a coal-fired power plant is provided. The utilization of agricultural wastes in existing pulverized coal power plants is an attractive option to alleviate environmental pollution and reduce over-exploitation of fossil fuels. A coupled system model of biomass gasification coupled to a coal-fired boiler is established in Aspen Plus and successfully validated by experimental data. A 20 t/h straw gasifier operates at the rated capacity and the straw gas is introduced to the boiler running at different loads. The co-firing ratio increases with the reduction of boiler load. Results indicate that the main parameters, such as furnace combustion temperature, flue gas temperature, and NO and SO 2 emission decrease with the reduction of boiler load. Compared to pure coal combustion, co-firing can reduce the furnace combustion temperature and increase the flue gases temperature. More importantly, the coal consumption, and NO and SO 2 emissions are reduced at all loads, especially at lower loads. The excess air ratio should be adjusted to obtain the optimum combustion performance in the furnace, but there is still a slight drop of around 0.2% in boiler efficiency when co-firing. Meanwhile, the coupled system efficiency at various loads can reach slightly more than 84% under optimum conditions. [ABSTRACT FROM AUTHOR]