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

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 SO₂ 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 SO₂ 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.