Performance Estiation Of Venturi Scrubber For Coal Fly-ash

With the new venturi-annular flow washing combined purification technique developed for gasifier's outlet raw gas ash removal in coal chemical industry as the research background,this paper combines experimental research with computational fluid mechanics numerical simulation to conduct a systematic research on key equipment--venturi scrubber's hydraulic characteristics and coal-ash washing performance.First,scanning electron microscope(SEM)and Matersizer2000 laser particle analyzer are used to measure raw coal ash particles' surface characteristics and particle size distribution--the 0~50?m account for 80.8% of the total particle mass,and to analyze the main ingredients of each particle size range.Then,based on gas-liquid interface's solid dust trapping theory and micron-grade dust-containing liquid drops' separation characteristics,it discusses the following features of small-size particles and air.Last but not least,it analyzes the difficulty conventional venturi-bubbling bed wash washing has in trapping particles in low particle size range,and proposes an ash removal mechanism that combines venturi reinforced trapping and annular flow water washing reinforced separation.In the venturi scrubber gas-liquid two-phase hydraulic characteristics experiment,this paper examines the effect of two-phase flow patterns,operating gas velocity,fluid amount and throat length in the scrubber on pressure drop and its distribution.The results show that,under experimental conditions,the flow patterns in venturi scrubber are annular flow and slug flow,throat gas velocity is 75m/s~85m/s,and throat length and fluid amount have a significant effect on pressure drop.In addition,CFD simulation is carried out,and the simulation results basically tally with hydraulic data;through the simulation,we find the throat section of venturi scrubber has an unstable stage and a stable stage,with a throat length of 75 mm,the venturi tube's optimal throat gas velocity is 65m/s~90m/s,and optimal expansion angle is 7°;a single-phase pressure drop calculation model is built,and the model calculation values have a good agreement with the experimental values.Based on hydraulics experiment and CFD simulation,a gas-liquid-solid three-phase gas ash removal & washing experiment is conducted to examine the effect of operating gas velocity,fluid amount and liquid-gas ratio on total washing efficiency of coal-ash particles.The total washing efficiency,increases with the increase of operating gas velocity,tends to be a constant value at high gas velocity,and linearly increases with the increase of operating fluid amount.Under experimental conditions,the scrubber's optimal working conditions are: throat gas velocity 130m/s,operating fluid amount 1500L/h,and throat length 150 mm,when the total removal rate reaches 99.9998%,far higher than the requirement of engineering precision.Furthermore,this paper examines outlet purified gas' s dust-containing particle size distribution and washing efficiency to different particle size given various kinds of operating gas velocity and fluid amount,and analyzes the main factors affecting the efficiency to different particle size.150?m~200?m grade efficiency is low,which is mainly because the porous vitreous structure is not easy to be wetted,25?m~40?m grade efficiency is significantly affected by loss on ignition,1?m~3?m grade efficiency is low,which is mainly because the particles are so small that the particle surface is wrapped by gas film,and thus the wettability is reduced.