Research On Pyrolysis Characteristics Of Naomaohu Coal In Z-pafh Moving Bed

China's low-rank coal resources are abundant,accounting for about 50% of coal reserves.At present,the main utilization mode of low-rank coal is direct combustion and gasification,and it can not make full use of its inherent oil and gas resources.The pyrolysis of coal at medium and low temperature can get high value tar,heat value gas and cleaner char,which is an effective method to realize low-rank coal grading utilization.However,there is no mature low-rank coal pyrolysis technology in the market,the main problem is that the existing pyrolysis technology is difficult to use small particle size of coal,tar yield is low,heavy component content of tar is high,the dust content of tar is high.Aiming at the technical problems existing in the pyrolysis of coal,this paper puts forward a z-path moving bed pyrolysis technology,constructs a new type of z-path moving bed pyrolysis reactor,takes Naomaohu coal in Xinjiang as the research object.The feasibility of the technology was verified through cold experiment,and the influence of reactor structure on particle motion is studied,which provides the design basis for the establishment of the thermal experimental device.In the thermal experimental device,the pyrolysis characteristics of Naomaohu coal under different temperature,different residence time and segmented temperature control are studied,and the effect of the z-path moving bed to improve the tar quality is revealed by characterizing the content and composition of pyrolysis tar,char and gas.By comparing with the pyrolysis experiment of fixed bed,the advancement of z-path moving bed is verified.The main research contents and results of this work as follows:(1)The cold experiment of the z-path moving bed.The coal is stored evenly from top to bottom in the z-path moving bed,the particle flow is more stable.There is no obvious dead zone,trench flow phenomenon.By studying the flow condition of coal in the z-path moving bed,it is found that the smaller the angle between the plate and the reactor,the more serious of coal retention,the little influence when the angle is more than 45°.The faster the feeding speed,the less of ditch and dead zone are produced in the reactor,and the particle size has little effect on the particles movement characteristics in the z-path moving bed.(2)The pyrolysis experiment of coal in the z-path moving bed.The quality characteristics of Naomaohu coal in Xinjiang were analyzed firstly,and the pyrolysis experiments of different temperature(450?,550?,650?,750?),different residence time(2h,2.5h,3h)and segmented temperature control were carried out in the z-path moving bed.It is found that with the prolongation of pyrolysis residence time,the char yield is slightly reduced,the tar yield increases slightly,and the pyrolysis gas yield increases gradually.At the same temperature,the pyrolysis tar yield of Naomaohu coal in the z-path moving bed is mainly related to the volatiles release time.Through segmented gas collection,volatile can quickly leave the reactor.By segmented gas collection,the volatiles can leave the reactor quickly,reduce the second reaction of volatiles,which can produce high content of heavy components and high content of fatty compounds in tar.Compared with four layers of z-path moving bed control of the same temperature(such as 550?),there is a significant reduction in tar yield while a slightly increase in tar quality under three layers of 550? or two layers for 550?,indicating that it is difficult to improve the yield of tar,but can play a role in regulating tar quality.When the residence time is 3h and the pyrolysis temperature is 550?,the tar yield is up to 11.38%,which accounts for 85.49% of the G-K tar analysis,and the content of the heavy component with a boiling point greater than 360? in tar is 11%.(3)Pyrolysis characteristics of Naomaohu coal under different pyrolysis modes.When coal pyrolysis in the z-path moving bed,with the residence time is 2h and the pyrolysis temperature is 550?,the tar yield is 10.81 wt.%,which reaches 82.3% of the G-K tar yield.The tar yield is 8.44 wt.% when coal pyrolysis in the fixed bed,which is much lower than the yield of pyrolysis in the z-path moving bed.By comparing and analyzing two kinds of pyrolysis techniques,the existence of metal plate in the z-path moving bed can greatly improve the heat transfer in the reactor,the coal can heat up faster in the z-path moving bed.The volatiles can be derived in time by segmented gas collection in the z-path moving bed,which can greatly avoid the second reaction of volatile materials,which higher than the tar yield in the fixed bed.