Biomass energy has occupied an important position in boiler fuels due to energy shortages and environmental degradation caused by the large use of fossil fuels. Since biomass fuels, especially agricultural wastes, contain higher chlorine content and alkali metal content than fossil fuels, some technical difficulties occur in the combustion process, which need to be taken seriously, mainly: contamination, corrosion, agglomeration, SOx, NOx, HCI, and aerosol emissions. In response to these problems, countries have increased research and development on biomass boiler technology.
Biomass boilers burn biomass as a fuel and use the energy generated by combustion for power generation, heat resource and other applications. The main combustion types of today's biomass boilers are fluidized bed combustion boilers and layer fired boilers.
The biggest difference between fluidized bed combustion and ordinary combustion is that the fuel is in the shape of particles, and the fuel is in a fluidized state in the fluidized bed for combustion reaction and heat exchange. Biomass fuel has relatively high water content, and adopts fluidized bed technology, which is conducive to complete combustion of biomass and improve combustion efficiency. Biomass fluidized bed boilers can use sand, high-aluminum bricks, coal-fired slag, etc. as fluidization medium to form a dense bed with high heat storage and high temperature, providing superior ignition for high moisture and low calorific value biomass. Conditions, relying on the intense heat and mass transfer process in the bed and the longer residence time of the fuel in the bed, the biomass fuel is fully burned out. The fluidized bed boiler can maintain the combustion temperature at around 850 °C and is fully disturbed by the material layer, so the bed is not easy to slag, and low temperature combustion and desulfurization in the furnace reduce the generation of harmful gases such as NOx and SOx.
However, the fluidized bed boiler has strict requirements on the size of the fuel particles in the furnace. Therefore, a series of pretreatments such as drying and pulverization of the biomass are required to homogenize the size and condition to ensure the normal fluidization of the biomass fuel.
During the layered combustion process, different combustion stages are formed along the height of the upper bed of the grate. The grate of a layer-fired boiler mainly includes a reciprocating grate, a water-cooled vibrating grate, and a chain grate. The biomass energy boiler developed by the layer burning technology has a simple structure, convenient operation, and relatively low investment and operating costs. Due to the large grate area of the boiler, the moving speed or vibration frequency of the grate can be adjusted, and the furnace has sufficient floating space to prolong the residence time of the biomass in the furnace, which is beneficial to the complete combustion of the biomass fuel. However, the furnace temperature of the layer-fired boiler is relatively high and can reach above 1000 °C. Moreover, the requirements for boiler air distribution in the combustion process are relatively high. If the full combustion of biomass fuel cannot be guaranteed, the combustion efficiency of the boiler will be affected.
The biomass boilers produced by ZBG are mainly divided into two categories, fluidized bed boilers and chain grate boilers. The boilers use world-class technology to improve boiler performance. The boiler fuel is fully combusted after combustion, and the thermal efficiency is high, which reduces the power consumption during operation.