| Coal is not only an energy source,but also a valuable resource.It is especially important to develop a clean and high-efficiency coal utilization technology under the current background which petroleum and natral gas are increasingly scarce and current low-efficiency coal utilization is causing pollution issues.In traditional coal use patterns,coal is always burned directly and only heat energy is used,therefore,it is necessary to apply cascade utilization to coal resources according to different properties and transformation characteristics of coal component.In coal based poly generation system,coal is the raw material,coal gasification technology is the key point,multiple coal conversion technologies are integrated together,pyrolysis tar can be obtained,the tar component benzene,anthracene,indene and fluoranthene can be extracted and applied in chemical synthesis.Besides,pyrolysis gas can be also obtained and applied in metallurgy industry and civil fuel gas.What's more,char can be collected to burned to generate electricity.Thus,integrated utilization of coal resources and promotion of energy utilization efficiency are achieved.The goal of coal based poly generation system are the maximization of integrated productivity efficiency and minimum of pollutants emission,it achieves great economic benefit of coal utilization and it is a clean coal utilization technology that matches the fundamental realities of China.Pyrolysis and gasification technology are the key technologies in coal based poly generation system,in this paper,multiple pyrolysis and gasification reactor are used to investigate the regulate and control mechanism of directed coal pyrolysis.First of all,Shenhua coal,Pingzhuang coal,Huainan coal and Baiyinhua coal are selected as study objects,the effects of temperature and particle size on coal pyrolysis behaviors are investigated in the fixed bed tube furnace.The pyrolysis products coal char,tar and pyrolysis gas are deeply investigated.The pyrolysis temperature ranges from 600 ? to 1200? with a step of 100?,and the coal particle size ranged in 0?75 ?m,75?150 ?m,150?300 ?m and 300?900 ?m.The results showed that increasing pyrolysis temperature promoted production of pyrolysis gas,when temperature raised from 600 ? to 1200?,the volume of pyrolysis gas raised from 678 ml to 1932 ml for Shenhua coal,544 ml to 2077 ml for Pingzhuang coal,347 ml to 1903 ml for Huainan coal and 328 ml to 1918 ml for Baiyinhua coal.High temperature was conducive to the production of H2,but it suppressed the production of CH4 and CO2.In 700 ? pyrolysis of Huainan coal,the pyrolysis heat value reached to the highest point,the value is 27.2MJ/Nm3.Small coal particle size increased pyrolysis gas volume but decreased the content of CH4.The major components of Shenhua tar were aliphatic compounds with no benzene rings.Then,in order to create better pyrolysis environment which is more closer to that in actual industrial boiler,the investigation is performed in a self-designed one-dimensional drop tube furnace.The investigated operation parameters are temperature,coal particle size,residence time,pulverized coal concentration and pyrolysis atmosphere,among these,the temperature is studied in detail.Results showed that the coal particle size grew one time bigger after pyrolysis in drop tube furnace.Pyrolysis had significant effects on dehydration upgrading of lignite and was conducive to the remove moisture from lignite.With the temperature increased,H2 and CO increased significantly,CO2 and CH4 decreased continuously.Pyrolysis leaded to aromatization of coal structure and decrease of hydrophilic group,the dried coal char had a good ability for reducing moisture reabsorption.With the temperature increased,there were more multi-ring aromatic compounds in tar component,the content of aliphatic in tar increased first and then decreased.Multiple pyrolysis operation experiments showed that 900 ?m is an economic particle size which allowed fully pyrolysis of coal,when particle size was bigger,the production of CH4 was also better.Longer residence time in drop tube furnace promoted the pyrolysis reaction.There was no significant effects of pulverized coal concentration on pyrolysis gas component.The mass loss of coal increased from 3.99%to 30.35%when carrier gas increased,pyrolysis reaction had been better complete.Small addition of CO2 suppressed the pyrolysis reaction,however,with the increased CO2 concentration in carrier gas,the pyrolysis degree increased.When added O2 at lower position in drop tube furnace,it was more conducive to pyrolysis and gasification reaction in reactor,adding a small amount of O2 promoted the production of pyrolysis gas,especially CO.Finally,gasification device is the center of the coal based poly generation system.In order to develop a high-efficiency and low-pollutants gasification device,a 75-kg-feeding-level oxygen enrichment pulverized coal gasification furnace is designed and built.The gasification furnace is self-heated with no electricity aided.The height of the furnace is 4.3 m and the inner diameter is 0.3 m,the rated coal feeding amount is 75 kg/h,the rated oxygen feeding amount is 23 Nm3/h,gasification temperature is between 1000? and 1400?.The ratio of syngas in coal gas under rated working condition is over 90%,high heat value is 10.9 MJ/m3,carbon conversion efficiency is 72.20%,cold coal gas efficiency is 52.81%,every kilogram coal produce 1.25 m3 coal gas,the production efficiency of syngas is 63.87%.In air gasification,heat value of coal gas is 5.6 MJ/m3.Compared to pure oxygen gasification,oxygen enrichment gasification and pure air gasification has lower cold gas efficiency ranging from 50%to 53%.When oxygen concentration decreases,the production of coal gas increases,but useful gas decreases.In pure oxygen gasification,11,18%of carbon is burned,useful carbon accounts for 88.82%.When oxygen concentration is lower,more carbon burns and useful carbon is less. |
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