Characteristics Of The Secondary Reactions Of Volatiles From Coal Pyrolysis

Producing oil and natural gas by low rank coal pyrolysis is an effective way for clean utilization of coal.Secondary reactions of the volatiles generated by the pyrolysis of the coal occured in a high temperature environment during escaping process.Thus,increasing the yield of products that were needed by decreasing other products and changing gas,liquid,solid three-phase product distribution by controlling secondary reactions of the volatiles,played an important role in regulating coal pyrolysis process.In this thesis,the secondary reactions of the volatiles generated by coal pyrolysis were studied in different temperature,residence time and gas atmosphere.（1）Study on the product distribution from 20 g coal at different temperature with fixed bed quartz reactor.The result showed that the char yield decreased and the gas yield increased,while the tar yield increased first and then decreased with the increase of temperature.At550℃,the tar yield reached maximum of 5.56%,about 96.4%of Gray-King assay yield.（2）Study on the effect of temperature on secondary reactions when the residence time is 10 s.At lower temperature below 700℃,the tar mainly converted into gas product by secondary cracking of tar.At higher temperature above 700℃,the tar transformed into gas and deposited carbon products by the secondary cracking and coking of tar.（3）Study on the effect of residence time on secondary reactions at different temperature by changing the diameter of lower part of reactor.The result showed that the effects of residence time and temperature on secondary reactions were interrelated.With the increase of the temperature and the time of secondary reaction,the secondary reactions of volatiles intensified,resulted in the decrease of tar yield and the increase of yields of gas and carbon.With the increase of the temperature and the residence time of secondary reactions,the yields of H₂,CH₄ and CO increased while CO₂ yield decreased,also lead to the increase of the heavy PAHs（polycyclic aromatic hydrocarbons of>3 ring）and the decrease of the PCX,H/C and O/C ratios.Especially at high temperature of 900℃,the yields of H₂ and heavy PAHs increased rapidly with increasing the residence time,due to the occurrence of the violent condensation reactions among aromatic rings.（4）Different gas atmosphere have different influences on secondary reactions at the reaction temperature of 700℃,at the residence time of 10 s.the tar yield decreased at H₂atmosphere due to hydrocracking reaction.The influence of CO is similar to H2 because CO participated water-gas shift reaction to produce H2.CO2 caused the increase of tar yield due to reforming reaction,and also led to the reduction of the carbon yield as gasification agent.Tar yield increased,because radicals produced by CH4 at high temperature could inhibit condensation polymerization reaction of aromatics.