Experimental Study Of Characteristic Geometric Parameters Of Solid Return Valve In The High Density Circulating Fluidized Bed

High density circulating fluidized bed pulverized coal pressurizedgasification technology can adapt to low rank coal (high sulfur and high ash,high ash melting point) which is rich reserves in our country and satisfies therequirement of IGCC technology for coal gasification subsystem. It is veryimportant to master operating characteristics of the high-density circulatingfluidized bed for the development of IGCC. The characteristics of return valveare directly related to the safe and stable operation of the system. Return valve isone of the important parts of circulating fluidized bed. The characteristicgeometric parameters of return valve was studied in this thesis.The effects of the gas distribution methods, diameter and height of blowgas tubes, valve diameter, horizontal channel height and overflow port heighton the return flow rate, the system stability and resistance were investigated atdifferent structure size of L-valve, J-valve and U-valve in a cold high densitycirculating fluidized bed (Ф0.219×7m). Air was used as the fluidizing medium,quartz sand as recyclable solid materials in experiments. Through orthogonaltests, diameter and the height of the optimal combination schemes were obtainedfor L-valve and J-valve.The main results are as follows: (1) L-valveThe key factors of the return ability are the gas flow of ClassⅡ blow tubeas combined gas-blow mode is used. And the gas flow of ClassⅡis also aneffective method to reduce the resistance of the valve. The system operates morestably when the blow gas flow of ClassⅠincreases. The Influences of thediameter and height of blow gas tubes on the return flow rate (M), the systemstability (RSD) and resistance (△P) are different. The maximum M is453.3kg/m2s, and the corresponding GSis232.3kg/m2s. In this condition, high densityis realized. With the increase of GS, return ability is more and more small, andthe△P is generally larger in high density operation than in low densityoperation. Optimal geometric size was got with the orthogonal test which iscarried out according to M, RSD and△P.(2) J-valveReturn ability of J-valve is mainly decided by aeration of ClassⅠ, and thelarger aeration is, the stronger return ability is. Resistance is mainly determinedby the amount of Class Ⅱinflation, and the larger aeration is, the smaller△P is.When the ClassⅠaeration quantity increases, the system runs more stably. Theeffects of the diameter and height of blow gas tubes on M, RSD and△P aredifferent. Return characteristics of J-valve is better when the valve diameter is219mm. Compared with L-valves, return capability of J-valve is smaller while△P is larger. The maximum M is369kg/m2s, and the maximum GSis214.5kg/m2s. It is difficult to achieve high-density operation in such conditions.Optimal geometric size was obtained with the orthogonal test which is carriedout according to M, RSD and△P.(3) U-valveRegulatory effect of loose gas on return flow rate is more sensitive than thefluidization gas. The regulation performance of U-valve is better when h2/D0is1.19and h1/D0is from0.48to0.76(h1, h2, D0represents horizontal orifice height, overflow weir height and standpipe diameter, respectively). M reachesthe maximum value when h1/D0is0.76, and h2/D0is1.19. When h1increasesand h2decreases, and the distance between the upper edge of horizontal orificeand the lower edge of the overflow weir reaches in a certain extent, theresistance of U-valve significantly reduced. At the same time, it is not prone tostable operation.