Study On Coal Gasification And Pyrolysis Based On Decoupling Conversion

Coal is the mainly primary energy in China,and it is also the only fossil resource which can produce aromatic chemicals in large amount. Presently,more than 80%of coal was burnt or gasified derectly,which surely destroy the aromatic structure contaning in coal.On the other hand, the production of motor oils and aromatic chemicals from coal is defitely needed in face of the serious shortage of petroleum resource.A so called "integrated thermal conversion(ITC)" idea was recently proposed to combine the technical superiorities of pyrolysis,gasification and combustion and thereby to implement coal casecade conversion and comprehensive processing.The innovation of ITC is decouling of pyrolysis,gasification and combustion reactions.The study is devoted to investigating the reaction fundamentals of gasification and pyrolysis involved in some typical processes based on the principle of ITC.Dual fluidized bed gasification(DFBG)is a technology based on decoupling combustion from pyrolysis and gasification reactions.The study investigated the reaction basis of gasification simulating the conditions of DFBG of coal.Pyrolytic topping is another kind of ITC technology established by decoupling pyrolysis from gasification or combustion.The second part of the study was thus devoted to the reaction fundamentals of coal pyrolysis in terms of pyrolysis oil production chracteristics,such as oil yield,necessary reaction time and chemical species present in the oil.All of these studies found surely the basis for reactor design and operating condition optimization.The results of gasification study demonstrated that the gasification of bituminous coal via dual fluidized bed(DFBG)is better to be under gasification temperatures of about 1123 K and run with coal having sizes below 4-5 mm.Coal should be generally supplied into the gasifier from a position nearby the surface of fluidized particles.The optimal oxygen and steam contents in the gasifying reagent appeared to be about 5 vol.%and below 35 vol.%,respectively.Under these conditions,the required reaction time for converting 60%fuel C into producer gas was about 600 s,offering essentially a designing criterion for the gasifier.Regarding pyrolytic topping,the results clarified that the highest pyrolytic oil yield was obtained under the temperature of 873K,reaction time of 3 min and in the simulated pyrolysis gas as atmosphere. Increasing coal particle size would decrease the oil yield,but coals in different sizes may have also different properties(such volatile and ash contents)to affect the oil yields.The test results demonstrated also that adding H₂ and CO₂ into atmospheric gas decreased oil yield,but the oil yield was likely to increase with raising CO and CH₄ contents.TG-FTIR analysis of pyrolytic oils revealed that the presence of H₂ in reaction atmosphere can increase the contents of phenolic and carboxylic chemicals,while adding of CO would lead to more aliphatic hydrocarbons,single-ring chemicals and aromatics.Adding CH₄ into the reaction atmosphere was likely to increase the contents of all the chemicals mentioned above,including phenol,aliphatic hydrocarbons, single-ring chemicals and aromaticscarboxylic group compounds.