Research On Gasification/Co-gasification Characteristics And Mechanism Of Coal,Waste And Other Carbonaceous Materials

Coal carbonaceous materials are affected by various factors such as carbon structure,gasification temperature,particle size and ash content and composition during gasification Mastering the influence of various factors on the physical and chemical structure evolution of carbonaceous materials during gasification/co-gasification can provide reference and guidance for improving carbon conversion in coal gasification process.In this research,different carbonaceous materials(coal,industrial gasification slag,biomass and food waste)were chosen as samples.The effects of carbonization,gasification temperature,particle size and internal diffusion on the gasification reaction process of materials were investigated.The different effects of the alkali metals and acid components present in coal ash on the physicochemical structure of the carbonaceous materials during gasification,and the differences in the gasification reactivity and physicochemical properties of the industrial fine slags with different particle sizes were studied,and the co-gasification reactivity of fine slags with petroleum coke were also tested.The co-gasification characteristics and mechanism of coal with biomass/food waste were studied.The main contents are summarized as follow:(1)The various effects of temperature,particle sizes and ash contents on sixteen coals with different coal ranks were studied at high conversion stage,and the char structure was further studied to understand the relationship between gasification reactivity and char structure.R0.95 was proposed to represent gasification reactivity at high conversion stage.As a result,the char with higher coal rank has lower gasification rate due to the more orderly crystalline structure.Ash is an important factor affecting gasification reactivity at high conversion stage.The gasification rate decreases significantly for coals with high ash content at mid-later reaction stage.The effect of particle size on gasification reactivity is much more significant for high rank coal than low rank coal.And the effects of particle size,gasification temperature and ash contents on char gasification are much greater for high rank conl.Volume control model fits high rank coal well and random pore model fits low rank coal.(2)The effects of alkali and alkaline metals(AAEM)and acid components present in coal ash on the evolution of char physicochemical structure during coal gasification were studied based on different acid-washing methods.The results show that the AAEMs react with char and form active sites,resulting in higher reactivity.Dealkalization dereases the initial gasification rate without changing the physical structure evolution.And demineralization changes the physical structure evolution of char during gasification.The ash present in char not only covers the surface of char,but also blocks the pore strucuture,resulting the decrease of specific surface area.The gasification rate of demineralized char is higher than that of raw char at mid-later reaction stage.Although the initial gasification rate decreases,the overall gasification rate is promoted by demineralization for bituminous coals and anthracites.(3)The gasification resid ues from industrial plant were selected to stud y the physical and chemical characteristics of coal fine slags with different particle sizes,and the effect of ash on the residual carbon in fine slags was further examined.The results showed that the carbon content of fine slag with small particle size(<40 ?m)was much lower than that with large particle size(>63 ?m).For fine slag with large particle size,the surface of residual carbon was significantly co vered by ash,although the carbon co ntent was low.Whereas,for slag with small particle size,the residual carbon particles was not packaged by ash and was separated from ash particles.Moreover,the residual carbon in fine slag with small particle size has lower graphitization degree and more active sites,resulting in the higher gasification reactivity.The fien slag with smaller particle size also has stronger catalytic effect on the gasification of petroleum coke.(4)The co-gasification reactivity of food waste and its different components with coal and biomass were tested and the interaction mechanism was further studied via a high temperature stage microscope.Results showed that coal and food waste presented synergetic effect during co-gasification,whereas no synergy was found between coal and sawdust.The migration of ash was the key factor of synergetic effect.Rice,lettuce and meat-bones were selected to study the interaction mechanism between food waste and coal,due to the complex components of food waste.Lettuce and coal presented the greater synergetic effect than meat-bones and coal.And rice and coal presented inhibitory effect during co-gasification.Moreover,the lettuce ash(rich in K)had significant catalytic effect on gasification,resulting in the great synergetic effect in the mid-early reaction stage,In the later reaction stage,the partly molten ash covered unreacted carbon and restricted char gasification.The ash with high Ca content from meat and bones has catalytic effect on char gasification and do not restrict the contact between char and gasification agent.