Study On Thermochemical Conversion Of Typical Tobacco Wastes And Its Application

China owns the largest tobacco products market in the world,with a predicted annual growth rate of 0.7%according to the data of National Bureau of Statistics.During the productive process of cigarette,25%of tobacco will be abandoned as tobacco waste.Because of the special character of tobacco waste containing non-ignorable amount of alkaloids such as nicotine,a direct treatment of it such as combustion or landfill will be harmful to the environment.Then the treatment of tobacco waste as a significant problem attracts so much attention.Many researchers have made efforts to propose several utilization methods.Among these methods,thermal conversions such as pyrolysis and gasification are promising technologies.As a mainstay industry in China,cigarette industry ensures the stability of abundant tobacco waste supply,which overcome the main obstacle of biomass utilization.In this dissertation,the pre-treatments,potassium salts and alkaloid emission during thermal conversion of tobacco stem were investigated.Firstly,the influences of different pyrolysis conditions on the pyrolysis of tobacco stem were explored,focusing on the pyrolysis temperature and potassium salts.The characterization of three phase products obtained in pyrolysis uncovered the effects of pyrolysis condition.The results show that the weight loss section of pyrolysis is between 220and 400?,which is mostly attributed to the degradation of cellulose and semi-cellulose.As the temperature increasing,the char and gas yield increased,while the yield of tar reached its maximum at 600?.At temperatures below 500?,CO and CO₂ are the two main components in the gas,while at elevated temperature,H₂ increased significantly.High temperatures is benifitial to CO and H₂,but detrimental to the product of CO₂.After the loading of KCl and KAc,the product of char and gas was improved at the expense of tar,which was mainly attributed to the catalysis of potassium.Secondly,the effects of leaching with various solvents?water,erthyl alcohol and hydrochloric acid?on the structure and pyrolysis characteristics of tobacco waste were explored.In addition,the catalytic influences of the high content of potassium in tobacco waste were also studied by adding potassium chloride into the washed residues.The results show that nicotine and potasiium were mostly removed by leaching with either solvents,while calcium was stubborn to water or alcohol.Different from water and alcohol,acid can strongly influence the main structure of tobacco stem.The stability and gas product distribution during the pyrolysis of tobacco stem wer explored by TG-FTIR.The char yields were in order RTS>WTS=ETS>ATS,which is assitent to ash contents.The monitor of gases by FTIR shows that acid washing is uninfluent on the gases production in the two weight loss stages,while water and alcohol leaching can remarkably improve the emission of oxygen containing gases in the second stage.Besides,the addtion of KCl improved the production of CO₂.In addition,because of the absence of carbonas in the acid washed sample,no CO and CO₂ was generated at 650°C.According to the quantitative study on Py-GCMS,the recovery of nicotine declined to 86.88%at 600?and 77.22%at 700?seems that at higher temperature above 500?,nicotine becomes less stable and transforms into other nitrogenous compounds.KCl is uninfluential for the products distribution of nicotine pyrolysis based on the pyrolysis of model compounds mixed with KCl.Thirdly,the transformation of potassium during torrefaction and its effects on the subsequent gasification process were explored.Most of potassium in tobacco stem was removed by water washing,after which K₂SO₄,KCl,K₂CO₃ and KAc were added into the washed sample respectively.Then all samples were treated by torrefaction,and the existing forms of potassium in the char were characterized.The results show that the increase of temperature leaded to the emission of water soluble potassium.What's more,torrefaction aslo changed the water soluble potassium into insoluble.In addition,during gasification,it is obvious that potassium improve the transfer of solid into tar and gas.Furthermore,different kinds of potassium made different effects on the final weight loss.Inorganic potassium is more effective than organic potassium related with gasification improvement.Although torrefaction is influential on the subsequent gasification process,different kinds of potassium own the similar effects on the process.On the other hand,the release rate of potassium in baking samples will also increase as the gasification temperature rises.Finally,the basic characteristics of the combustion of tobacco stem,the analysis of the tendency of burning and slagging of tobacco stem,the design of fluidized bed boiler and the entralized heating supply system,and the application in tobacco nursery and tobacco curing were studied.The resulta showed that the determination of low temperature ash slagging index is more accurate than high temperature ash,and it is difficult to accurately determine the slagging characteristics of biomass ash using a single criterion.The characteristics of the bed material have different effect on the slagging characteristics of the tobacco stem.The quartz sand and the tobacco stem are prone to agglomeration and hinder the fluidization when mixed and burned,and therefore,it is not suitable as a bed material.The sieved coal ash can be used as a bed material which can realize stable combustion operation of the long-term cycle.When the bed temperature is greater than 600°C,the stem tobacco stem can be burned out and the combustion temperature should be controlled around 750°C.The ratio of primary air and secondary air plays a crucial role in the burning organization of the stem tobacco stems.Compared with the traditional coal-fired dispersed heat supply,the centralized heating technology of the tobacco stem combustion can optimize the temperature environment of the nursery system,shorten the nursery time,and improve the quality of tobacco seedlings.In addition,centralized heating is also beneficial to improve the quality of tobacco leaves,increase the economic value of tobacco curing and reduce the emission of pollutants such as dust,SO₂,and CO₂.