Study On Pyrolysis Characteristics Of Municipal Solid Waste Based On Microwave Pretreatment

With the rapid development of economy,the output of municipal solid waste(MSW)is increasing rapidly and increasing year by year,and the waste flooding has become a problem facing the whole world.Waste disposal methods are widely used at present in our country mainly includes landfill and incineration.Although incineration can significantly reduce the weight and volume of MSW,it is easy to form poly chlorinated dibenzop-dioxin and other harmful substances,which will cause second pollution.The pyrolysis technology of garbage can solve these problems better.The MSW mixture in Guangzhou city,which consists of five organic components and three inorganic components,including glass,bamboo,waste paper,textile,plastic and rubber,glass and ceramic,metal and others,is taken as the research object.The physicochemical properties,pyrolysis weight loss characteristics,product distribution and characteristics of MSW under microwave pretreatment were investigated,in order to provide a theoretical basis for the new way of MSW treatment.At first,the MSW mixture was pretreated by microwave oven,and by changing the microwave power and the pretreatment residence time to studythe changes of micro shape and appearance,material composition and element content of waste.The results showed that the microwave pretreatment can make the surface of the waste sample sag and produce pore structure,and with the increase of pretreatment power and residence time,the pore structure and the phenomenon of surface depression become more obvious.When the microwave power is too large(800 W)and the residence time of the pretreatment is too long(10 min),the pore structure breaks and even collapses.In addition,microwave pretreatment can promote the evaporation of internal moisture in MSW.With the increase of microwave pretreatment power and residence time,the internal moisture content decreased significantly but the content of ash and fixed carbon increased rapidly,while the content of volatile almost remained unchanged.When the microwave power is too large(800 W)and the residence time of pretreatment is too long(10 min),some volatile components and easily decomposed components will escape from evaporation and decomposition,resulting in the reduction of volatile content.What's more,with the increase of microwave pretreatment and residence time,hydrogen content decreased gradually,and the carbon content increased first and then decreased,however the oxygen content decreased first and then increased,and the content of sulfur and nitrogen is almost constant.And the low calorific value increased gradually and then decreased,with the increase of microwave pretreatment power.Then,the pyrolysis experiments of MSW mixture treated by microwave pretreatment under different working conditions were completed by using a tubular furnace,and the change of pyrolysis characteristics of the MSW mixture were studied.The results showed that microwave pretreatment can promote the pyrolysis reaction of MSW,and make the main pyrolysis reaction time ahead,and at the same time can also promote the formation of pyrolysis gas.When the microwave pretreatment power is 600 W and the residence time is 7 min,the main weight loss time of MSW pyrolysis is from 9 ~18 min ahead to 6 ~15 min,and pyrolysis gas production rate increased significantly and the maximum reached 48.42%,but the yield of liquid products decreased significantly and the lowest decreased to 37.54%,the pyrolysis residual solids content decreased slightly,the rate of decline was less than 1%.When the microwave power was too high(800 W),the pyrolysis gas yield decreased rapidly to 18.98%,much lower than the yield at 0 W.When the residence time of pretreatment is too long(10 min),the main weight loss time of pyrolysis process increased to 6 ~18 min,while the pyrolysis gas production rate decreased to 40.81%,but both the yield of liquid products and the amount of pyrolysis residual solids increased.Finally,the pyrolysis experiments of MSW mixture treated by microwave pretreatment under different working conditions was completed by PY-GC/MS,and the change of pyrolysis product components was studied.The results showed thatmicrowave pretreatment can promote the formation of hydrocarbons(chain hydrocarbons and aromatic hydrocarbons)in MSW pyrolysis,and reduce the generation of oxygencompounds(mainly including acids,esters,phenols,aldehydes,ketones,alcohols,sugars and furan etc.)and nitrogenous compounds(mainly hydrazine and nitrogen heterocyclic),so as to improve the quality of pyrolysis products.Besides,with the increase of pretreatment microwave power and residence time,the content of hydrocarbons in pyrolysis products increased gradually,and the total content of oxygen and nitrogen containing substances decreased rapidly.When the residence time of pretreatment is too long(10 min),the content of hydrocarbons in pyrolysis products decreased instead.Considering the physical and chemical characteristics,pyrolysis weight loss characteristics,distribution of three phase products in pyrolysis,and the characteristics of fast pyrolysis products of MSW,in the experimental conditions of this paper,the optimum power and residence time of microwave pretreatment were 600 W and 7 minutes,respectively.