The Cold And Hot Experimental Research On Biomass Fluidized Combustion

Energy is the foundation of our world .Great change of energy structure results in the great development of human society. The increase of GDP always keep pace with the increase of energy consumption. Oil will be used out, and the new energy structure will be built up in the 21th century .Presence of multi-energy will be the characteristic of energy structure in the new century. The biomass energy is likely to be one of the main energy in 21th century .As a utilization mode of biomass energy , electricity generation technology of biomass combustion is simple and cost-effective. This will be a available approach of biomass usage in our nation. Combustion in CFB has its own particular strongpoints, such as wide flexibility of fuel, low temperature combustion,high combustion efficiency, favorable adjustment performance on load, so it is a good method to handle biomass fuel. Because of the particularity of shape and physical properties of biomass, complex flow happened in CFB and influence the combustion in the boiler. As above, the deep research on fluidization property, mix-separation property and particle concentration distribution property will be meaningful to the practice in engineering. On the base of cold research in boiler, carrying out research on combustion property of biomass will conduce to organization of combustion and improvement of combustion efficiency in CFB.In order to get our deep understand about fluidization property, mix-separation property and particle concentration distribution property of biomass in CFB, we review the influence of different factors, including different ratio, different size and different shape of biomass, on fluidization property on the cold CFB test-bed. With the experimental research, we find that ratio will influence the critical fluidization property remarkably when the big difference of size exists between biomass and sand. When the difference of size exist between biomass and sands is not obvious, the ratio influence will be small. As for different size of biomass particle, the big one will influence the critical fluidization property more remarkably. For different kinds of biomass with different shape, the one with special shape which can keep biomass particles inside will give more influence on the critical fluidization property. In the bubbling fluidized bed, the mixture of biomass and sands take on clear phenomena of delamination, that the distribution of biomass is uneven, more at the top and less at the bottom of boiler. In contrast with bubbling fluidized bed, the distribution of biomass in CFB is more uniformity. The particle concentration of biomass and sand in CFB decrease as the height of boiler, and the particle concentration of biomass follow the same rule.With the hot CFB test-bed, we carry out combustion experiment on rice straw and wheat straw to analysis the distribution of temperature and get the understanding on combustion in the bed. On the base of zoning heat balance, we use the ratio of effective decalescence to build modeling of combustion fraction along the height of boiler. With the modelling, we calculate the distribution of combustion fraction and get the deep understanding on combustionin bed . At last, we get the conclusion that distribution of temperature in boiler is uniformity, high temperature zone occurs in the median superior part of boiler and the temperature at the outlet of boiler decrease rapidly because of simulated heating surface . The portion of combustion in boiler dense zone is very low and in the free board is high.With the data collected from the biomass combustion CFB in demonstration project, we analysis the distribution of temperature under different load and get conclusion that the low temperature occurs in the outlet of boiler dense zone and the temperature increase after dense zone. The highest temperature occurs in the outlet of boiler. We use the idea used in the hot experiment to make research on the distribution of combustion fraction under different load. As a result, we find that the distribution of combustion fraction in demonstration project is the same with the hot experiment, that combustion mainly happened in free board, in contrast, the dense zone and outlet of boiler is less. At the end, we use the built model of combustion fraction to forecast the distribution of temperature in boiler and get the accurate result.