Research On High Temperature Electrostatic Precipitation Based On Coal Pyrolysis Gas

The development of clean coal technology represented by coal pyrolysis polygeneration technology is an important aspect of achieving energy security and clean utilization in China.The coal pyrolysis polygeneration process can not only produce electricity,but also extract high-grade oil and gas resources in coal,which helps to achieve clean and cascade utilization of coal.However,the high-temperature gas produced by coal pyrolysis contains a large amount of dust particles.Subsequent utilization of components?tar,gas?has adverse effects.Electrostatic precipitator has the advantages of high efficiency,low pressure drop,and large flue gas volume,and has been widely used in conventional power plants.However,the research on high-temperature electrostatic dust removal technology for coal pyrolysis gas is not perfect,and the experience of optimal design and operation is seriously lacking.It cannot meet the requirements of coal pyrolysis polygeneration technology,and systematic research is urgently needed.In view of this,this paper carried out basic research on the application of discharge mechanism and dust removal characteristics of electrostatic precipitator in high-temperature coal pyrolysis gas environment,with a view to providing key data and theoretical guidance for the industrial application of high-temperature coal pyrolysis gas electrostatic dust removal technology.In this work,a high temperature discharge device of wire-cylinder configuration is first built,and the coupling effect of temperature and gas medium on the discharge characteristics is studied.High temperature can promote the discharge process,reduce the corona onset voltage and increase the current,but the increase in temperature shortens the operating voltage range of the electrostatic precipitator.During the discharge of an electronegative gas such as CO₂,as the output voltage increases,three types of discharge phases can be observed in turn,namely corona discharge,glow discharge and arc discharge.However,during discharge of non-electronegative gas such as H₂,only glow discharge was observed.During the discharge of CH₄ and CO,chemical reactions occur when gas molecules collide with high energy electrons,resulting in the formation of solid carbon.The chemical reaction has almost no effect on the discharge characteristics of CO.The impact on the discharge characteristics of CH₄ is mainly reflected in two aspects:?1?The process of growth and dropping of carbon filaments will cause the discharge electrode spacing to change and cause a sharp discharge current fluctuation;?2?In some cases,the growth of carbon filament is relatively stable,and it will touch the anode,causing a short circuit between the anode and cathode.Based on the experimental study of high-temperature discharge,a high-temperature discharge model is established,which is used to analyze the charge distribution and electric field intensity distribution during the discharge process.During the negative DC discharge of air,with the increase of radius r,the electron concentration first increases and reaches a maximum at the ionization boundary,then gradually decreases.The negative ion concentration distribution is similar to the electron distribution,but the negative ion reaches its maximum at the attachment boundary.The concentration of positive ions is the largest on the surface of the cathode,and the concentration decreases sharply in the ionization zone and drops to 0 at the ionization boundary.Under the same working conditions,during the gas discharge process with poor electronegativity,the electron concentration is higher,the negative ion concentration is lower,and the electric field strength is lower.Non-electronegative gases,such as N₂and H₂,negative ions do not exist during the discharge process,and the charge in the drift region is composed of electrons.In the process of positive polarity discharge,the electrons are mainly concentrated in the ionization zone.There are only a few electrons drifting from the ionization zone in the drift zone.The charge in the drift zone is mainly composed of positive ions,and the concentration of positive ions is 4 orders of magnitude higher than the electron concentration.A small-scale high-temperature electrostatic precipitator experimental device was built,and the influence of temperature and gas medium on the efficiency and energy consumption of electrostatic precipitator was studied.High temperature is detrimental to the operation of the electrostatic precipitator,and the increase in temperature leads to a reduction in dust removal efficiency and an increase in energy consumption.The atmosphere has a great influence on the operation of the electrostatic precipitator.At600?,the highest dust removal efficiency in the pyrolysis gas atmosphere is 77.12%,and the corresponding energy consumption is 58.35 W/?g/Nm³?.In view of the problems of low efficiency and high energy consumption in the process of electrostatic dust removal of high-temperature coal pyrolysis gas,this paper studied two imporovement methods of gas media conditioning and positive power supply.By adding CO₂ gas to coal pyrolysis gas,the maximum dust removal efficiency was increased by 6.02%at 400°C,and the energy consumption index was reduced by 4.08W/?g/Nm³?under the condition of 12kV output voltage.The positive power supply has an improvement effect on the dust removal efficiency and energy consumption of the high-temperature coal pyrolysis gas electrostatic precipitator,and as the temperature increases,the improvement effect of positive power supply on dust removal efficiency is enhanced.At 600?,by positive polarity power supply,the maximum dust removal efficiency of the high-temperature pyrolysis gas electrostatic precipitator is increased by 11.8%,and in the working condition of 10kV output voltage,the energy consumption indexes of the positive and negative polarity electrostatic precipitators were 17.01 W/?g/Nm³?and 39.54 W/?g/Nm³?.Based on the experimental research results,a pilot-scale high-temperature electrostatic precipitator was designed and built.Under 500?oily pyrolysis gas conditions,the electrostatic precipitator has good operation stability,and there is no short circuit.The dust removal efficiency fluctuates between 61-78%,but it does not decrease significantly in the operation process.Adding water vapor can improve the discharge characteristics,increase the breakdown voltage,and thus improve the dust removal efficiency.Under coal pyrolysis gas media and at 500°C,by steam purge,the water vapor concentration was increased from 6.89%to 18.53%,the breakdown voltage was increased from 35kV to 45kV,and the maximum dust removal efficiency was increased from 71%to 78%.