Study On Flow Hydrodynamics, Combustion And Abrasion Properties Of CFB Boiler Burning Anthracite

Recently, circulating fluidized bed technology has been greatly developed. For its favorable operation characteristic, circulating fluidized bed boiler is considered to be the first choice for burning anthracite. But due to its complex flow field, there is a problem to fully understand circulating fluidized bed system, especially for flow hydrodynamics, combustion and abrasion properties. Besides, existing researches are almost confined to round cross-section, so it's necessary to get a detailed study about circulating fluidized bed with rectangular cross-section. In this thesis, with the basis of 130t/h CFB boiler burning anthracite in Guizhou division of China Aluminum Industry Corporation, flow hydrodynamics and abrasion properties in rectangular circulating fluidized bed boiler were studied. Besides, optimizing combustion test was also carried on 440t/h CFB boiler burning anthracite of Guangdong province. The results have guidance on improvement of flow field, decreasing abrasion, optimizing operation and increasing boiler efficiency.Based on some anthracite circulating fluidized bed boiler, a bench scale cold test unit of rectangular circulating fluidized bed was built. Particle movement in rectangular CFB was studied by using a high-speed video camera and particle image velocimetry (PIV) technology. The results with velocity vectors and concentration distribution on different cross-section showed that furnace structure had important impact on flow hydrodynamics. Particle movement in dense phase was dominated by bubble wake. Particles were inclined to collision with back wall on the influence of expanding cross-section of back wall. Projection section in transition region caused the deflexion of particle movement and increasing particle lateral velocity. Besides, projection section was also a high particle concentration region. In dilute region, the corner between front wall and left wall was the most easily wear area on the influence of corner effect and outlet effect. Particle movement in Left wall of outlet region showed no core-annular distribution on the influence of outlet effect. In whole riser, Particle concentration was gradually growing from core region to annular region. The higher the axis situation, the lower the particle concentration was. With higher superficial gas velocity, the variety in annular region was greater than that in core region.In order to understand the effect of air stage on flow hydrodynamics and erosion distribution, numerical simulation was carried in different operation condition with two-fluid model. The operation condition included different superficial gas velocity, different rate between primary air and secondary air, different rate between up secondary air and under secondary air, different rate between front secondary air and back secondary air, different particle diameter, different outlet structure, different injection angle, different momentum. Besides, combustion products distribution of different operation condition was also analyzed and some measures were suggested to improve the burnout of anthracite. Reasonable controlling on excessive air ratio, reducing superficial gas velocity, proper increasing secondary rate, keeping equal rate on front wall and back wall, choosing rational feeding particle distribution, decreasing irregular region in furnace and injection momentum of secondary air, adopting bigger injection angle of secondary air.Optimizing test on 440t/h CFB boiler showed that operation parameters, especially oxygen content, secondary air ratio, load, bed temperature, bed pressure and Ca/S ratio had great impact on fume temperature, boiler efficiency, pollutant, carbon content of fly ash and bottom ash. Increasing oxygen concentration of dilute region properly could be helpful for the burnout of anthracite; improving coal quality was favorable for boiler efficiency. Increasing secondary air ratio properly could be helpful for the burnout of anthracite. According to test results, operation parameters were put forward to optimizing boiler performance.The influence of air distribution on boiler was related to both boiler structure and operation status. For the reason of non-uniform fluidization on air distributor, some measures, such as increasing secondary air injection, could not always be helpful for the optimization of boiler. To get the perfect performance of boiler, one should consider all kinds of factors carefully.