Flow Characteristics Research Of Fine Particles In Circulating Fluidized Beds

Fine particles carbon fuel is hard to burn because of its low violate content. The efficient combustion of low violate fuels could be realized by the circulating fluidized bed (CFB) preheating combustion technology proposed by the Institute of Thermophysics, Chinese Academy of Sciences. Whether the fine particles can be circulated in a CFB or not is the key to that this technology can be applied to fine particles. Based on those problems encountered, the flow characteristics of fine particles were researched in a CFB cold test rig and an experiment was conducted in the 30 kW preheating combustion test rig.Fluidization, separation and recirculation of the residual carbon fine particles were researched on the test rig. The results show that fine particles are elutriated considerably when the superficial velocity is larger than 0.5 m/s, and are transported entirely when the superficial velocity is larger than 0.9 m/s. The cyclone pressure drop decreases when the air mixed with the increasing of solid inlet loading and approaches to fixed values finally. There is a good agreement between the experiment values and the calculated values of the cyclone separation efficiency. The separation efficiency under different solid inlet loading is larger than 97.5% due to the particle agglomeration and sedimentation. The aeration of the recirculation valve in the supply chamber dose better in adjusting solid flux than it in the recycle chamber, and solid flux increases with increasing aeration in both chambers.In different CFB test rigs, the solid flux and pressure balance are researched with changeable operating parameters and are compared with each other. The results show that these structures can maintain their system pressure balance when changing operating parameters including superficial velocity and system inventory. It proves that these CFBs can be applied to preheated combustion processes. The solid flux of a CFB without air distributor is larger than other three CFBs. The pressure balance difference exists in the exit of the loop seal, and the loop seal pressure drop of the CFB without air distributor is smaller than that of the other three CFBs.The preheated combustion and nitrogen dioxide emissions of the Fine particles carbon fuel were researched in a 30 kW preheated CFB test rig. The results show that the residual carbon can be preheated to 900℃ in the CFB preheater with partial combustion, and it can burn well in the down fired combustor, and its combustion efficiency is 95.3%; NOx emission values can be declined by the combination of preheating and air classification; NO emission value in the exhaust is 102 mg/m3 and the conversion ratio of fuel N to NO is 7.92%. The preheated combustion process can achieve high efficiency combustion and low NOx emission for the residual carbon.