Experimental Study Of Microwave Irradiation Influencing Coke Discharge And Micro-Characteristics

Microwave technology has the characteristics of clean,energy saving,convenience,efficiency,catalysis,expedite start-stop and excellent products,etc,which is having increasingly been receiving people's concerns.Then,this technique often has been used to numerous fields,including pyrolysis,synthesis of carbon-containing materials and removal of nitrogen(sulfur)oxides,etc.However,it is easy to cause discharge in the process of microwave radiating the carbon-containing materials.And some literature reports the discharge effect of carbon-containing materials that it can contribute to improve the heating of materials and removal of nitrogen oxide.In this,it is necessary to study the discharge mechanism of carbon materials in the microwave field,the factors influencing the intensity of discharge and the effects of discharge on the microscopic feature of carbon-containing materials.Zhundong coal was collected as the main carbon-containing raw material,and the coke samples were made over the temperature range of400~1200?in pipe furnace.Immediately after,this thesis researched the factors influencing the intensity of coke discharge and coke heating under microwave irradiation through the two aspects,including the experimental conditions(microwave power,irradiation time,carrier flow,gas sorts,environment pressure)and the characteristics of coke(carbonization temperature,carbonization time,coke sizes,coal type,coke quality)on the basis of coke discharge theory.And the surface morphology,phase structure,pore structure,surface functional groups and thermal stability of the cokes which were irradiated by microwave under the two conditions of inducing discharge and shielding discharge were studied by the related equipments.The results are as follows:(1)The larger the power,the stronger the discharge of coke.The discharge would destroy the surface tips of coke making the overall discharge intensity gradually decreased in the later stage.The nitrogen flow too low(40 ml/min)or too high(5000 ml/min)was not conducive to the discharge of coke;when the nitrogen flow was 200 ml/min,the overall discharge of coke was the most powerful.Compared with the atmosphere of carbon dioxide,the discharge of coke in nitrogen atmosphere was stronger.The higher the vacuum degree,the stronger the overall discharge of coke;when the vacuum reached to the mutational negative pressure,there were suddenly a large and sustained glow discharge over the coke owing to the gas pulleded away.At this point,the coke particles basically no longer generated electrical sparks and the temperature droped sharply.(2)The lower the carbonization temperature of coke(below 600?),the later the discharge of coke.The higher the temperature of coke(above 800?),the smaller the overall discharge of coke.The carbonization time of coke had little effect on the discharge strength.The coke over the size range of 2.8~4 mm generated the arc light discharge,while the coke over the size range of 0.22~1mm produced the spark discharge.The smaller the particle size of coke,the higher its the final temperature,and when the particle size of coke was less than98?m,the coke had good contact,just like a whole,without the phenomenon of discharge.The overall discharge intensity of Zhundong coke was greater than Jincheng coke becouse of that the surface structure of Zhundong coke was much more rough.It was very difficult to come into being discharge when the coke was laid flat in single layer,and the less the quality of coke,the stronger its overall discharge intensity.(3)The longer the time in discharge,the more fragmentations of the surface of coke.Discharge could promote the aromatic ring of coke opening and accelerated the transformation of fat hydrocarbon structure and oxygen functional groups of coke,however,when the time of microwave irradiating coke was 100 min,the degree of hydrogen rich(oxygen)degree of coke in the discharge condition was similar with that in the non-discharge condition.Discharge promoted the formation of interlayer compounds of carbon structure,and in 10 min it could significantly expand the carbon crystal surface distance of coke,but it was beneficial to the increase of carbon crystal size of coke,therefore,when using microwave technology to make coke,it should be preferred to choose raw coal with low potassium and sodium.(4)In the non-discharge condition,microwave heating hardly made the pore structure of coke change,and in the discharge condition,the specific surface area of coke changed from 4.4 m~2/g to 45.3 m~2/g in 30 min,but too long discharge time(60min)would transform the mesoporous of coke into the macropore,and reduce its specific surface area to 8.5 m~2/g.The short-term discharge would reduce the thermal stability of the coke,while the long-term discharge could make the ash melt,block the gasification channel of coke,so as to improve the thermal stability of coke,therefore,when the discharge time was30 min,the thermal stability of coke was the worst.