Research On Electrostatic Precipitation Of Fine Particle In High-temperature Gas

The development of coal staged conversion and power generation technology is very important for the sustainable energy supply of China.Different components in coal are separated by pyrolysis to achieve staged utilization.Particles produced from pyrolysis in high-temperature gas seriously affect the separation and utilization of different components?tar,fuel gas,et al?.Electrostatic precipitation is a promising particle collection technology which has advantages of high particle collection efficiency,large dealing capacity,low pressure drop,and high operation reliability.Particle collection in electrostatic precipitator?ESP?is of great relationship with gas temperature,gas composition and particle characteristics,which need further research for the collection of particles in high-temperature gas.This thesis focuses on the research of gas discharge and particle collection mechanism at different temperature,gas composition and particle characteristics by laboratory and pilot experiment.1.Studies on particle collection characteristics of electrodes with different geometries at high temperature.Results show rod electrode get higher operation voltage and electric field intensity,and achieved higher particle collection efficiency than screw electrode and saw electrode at 700 K and 900 K.Effect of electrode diameter and electrode interval to particle collection were investigated.Particle collection efficiencies of 5 mm diameter electrode were higher than 3 mm and 5 mm diameter electrode for all test temperatures.The 55 mm interval electrode achieved the highest particle collcetion efficiency at 300 K,but with the increase of temperature,110 mm interval electrode get higher particle collection efficiency than 55mm interval electrode and particle 165mm interval electrode,particle collection efficiency of 87.4%was achieved at 900 K by 110 mm interval electrode.2.Studies on mechanism of particle collection with different discharge parameters and gas parameters.The increase in temperature led to the decrease of spark voltage.The onset voltage and spark voltage were 17 kV and 39 kV at 300 K,but changed to 9 kV and 17 kV at 900 K.The decrease of operation voltage resulted in the decrease of particle collection efficiency from 99.8%to 95%with the temperature from 300 K to 900 K,and the input power was much higher at high temperature than low temperature'to get the same particle collection efficiency.Particle collection efficiency and migration velocity increased with the increase of particle concentration,while the increase of gas velocity resulted in the decrease of particle collection efficiency,but had little effect to particle migration velocity.3.Studies on mechanisms of gas composition and particle characteristic to corona discharge and particle collection was studied.Gas discharge characteristics were tested according to the analysis of gas ionic energy,gas electronegativity,and ionic mobility.A mixture of N2,CO₂ and He was used as substitute fuel gas in high-temperature particle collection.The electrostatic precipitation of particles from coal-fired power station?coal-fired particles?and coal-pyrolysis particles were studied in air and substitute fuel gas.The onset voltage of air was lower than substitute fuel gas while the spark voltage of air was higher than substitute fuel gas,which favored particle collection,but the viscosity of air was higher than substitute fuel gas',which had disadvantage to particle collection.Particle collection efficiency of coal-fired particles in air and substitute fuel gas were 99.5%and 99.3%at 300 K,while changed to 86.2%and 88.6%at 900 K.Particle collection efficiencies of coal-fired particles and coal-pyrolysis particles in substitute fuel gas were 99.3%and 99.1%at 300 K.The differences between particle collection efficiencies of the two particles were enlarged with the increase of temperature.Particle collection efficiencies of the two particles were 88.6%and 78.7%at 900 K.The particle specific resistivity of coal-pyrolysis particles is low for the high carbon content,which is 1.17×10⁵ ?cm,which is out the particle specific resistivity of the ESP application scope.Coal-pyrolysis particles release charges quickly with the attachment to collection plate,and went back to gas flow,which resulted in the lower particle collection efficiency than coal-fired particles'at 900 K.4.Studies on particle electrostatic precipitation characteristics of large amount practical flue gas in wide-gap high-temperature ESP.A 300 mm plate-plate distance wire-plate high-tmperature ESP was designed and built according to result of labractory experiment,and electrostatic precipitation characteristics of particles in practical high-temperature flue gas were studied in pilot-scale ESP.Gas velocity increase from 0.25 m/s to 0.45 m/s when the temperature increase from 563 K to 1020 K with the constant inlet air flow of 215 Nm3/h from combustor.The operation voltage of ESP was decrease from 43.5 kV to 17 kV with the increase of temperature.The decrease of operation temperature and increase of gas flow resulted in the decrease of particle collection efficiency from 99.2%to 73.2%.Particle collection efficiency decreased from 82.2%to 66.2%with the increase of gas velocity from 0.3 m/s to 0.52 m/s at 1020 K by the adjust of inlet air flow at 1020 K,but the particle migration velocity only changed from 2.4 cm/s to 2.6 cm/s,the increase of gas velocity has little effect to particle migration velocity.