Studies On The Oil Shale Pyrolysis Mechanism And Bubbling Fluidized Bed Retorting For Shale Oil

Oil shale is one of the important alternative energy resources which could be transferred into shale oil by retorting.The oil shale resources are widespread and abundant in the global world,so the rational utilization of oil shale resources is of great importance in the world economic development and energy security.In the comprehensive utilization of oil shale,oil shale retorting is one of the important core processes.Retorting of oil shale is a complex process involving series of chemical reactions affected by the physical and chemical characteristics,retorting technology and reaction conditions.So deep studies of the oil shale retorting process,influences of reaction conditions on the retorting process and products,and gas emission regularities are of great importance to promote the efficient and comprehensive utilization,and improve the industrial value of oil shale.Pyrolysis of oil shale could be classified into slow pyrolysis and fast pyrolysis according to the heating rate.This paper mainly conducted researches on the fast pyrolysis of oil shale in both experimental and theoretical aspects aiming to study the oil shale fast pyrolysis process,find the influence factors of the fast pyrolysis results,and find ways to increase the yield of shale oil and improve the conversion efficiency.In this paper,influence of heating rate on the pyrolysis of oil shale under the slow pyrolysis condition was studied firstly with the TG-MS?thermogravimetry-mass spectrometer?method.Then,the fast heating rate condition was realized by using the Curie-point pyrolysis technology,and the effect of temperature on the pyrolysis products was studied with the CP-GC-MS?Curie-point pyrolysis-gas chromatography-mass spectrometer?method.Subsequently,a bubbling fluidized bed retorting experiment system for small oil shale particles was designed to study the influences of temperature,carrier gas flow rate,oil shale particle size,feed rate,bed materials,and catalysts on the oil shale retorting product yields,compositions and physicochemical properties.Finally,with a fragment of the Dachengzi kerogen macromolecule as the reactant model,the Gaussian quantum chemistry calculation method was used to simulate the oil shale pyrolysis process and explain the pyrolysis mechanism.In the research of oil shale slow pyrolysis,experiments were conducted on the oil shale and kerogen at two different heating rates respectively with the TG-MS equipment to study the influences of heating rate and minerals on the pyrolysis process and partial products.The results showed that the increase of heating rate could effectively restrain the secondary cracking reaction and reduce the yield of small molecular gas products.The presence of minerals catalyzed the pyrolysis reaction of kerogen,and at the same time increased the resistance to escape of the gaseous pyrolysis products within the particles,so that the yield of small molecular gas products increased.In the research of oil shale fast pyrolysis,experiments were conducted on the Dachengzi oil shale at different Curie temperatures with the CP-GC-MS equipment to study the influence of temperature on the fast pyrolysis products.The results showed that the fast pyrolysis reaction of oil shale was strengthened with the increase of temperature,and the reaction became violent after 485?.The pyrolysis products had the largest proportion of aliphatic hydrocarbons,among which n-alkanes could be pyrolyzed at higher temperatures,and further transferred into cycloalkanes and alkenes.Aromatic compounds were produced in large quantities at the temperatures above 485?,and mainly existed in the form of alkylbenzene in the shale oil,meanwhile the average molecular weight decreased with the increase of temperature.There were a lot of oxygen-containing organic compounds in the pyrolysis products including ketones,acids,alcohols,esters and phenols et al..At the same time,Gonghe and Gonglangtou oil shales were studied with this method at 485?and 590?to get knowledge about the influence of oil shale deposits on the products.The results showed that the macromolecule structures and fast pyrolysis products of the three oil shales had high similarities because that the deposits were all located in the Huadian basin.In the formation of oil shale deposits,dehydrogenation reactions of the aliphatic carbon chains occurred forming the aromatic rings,and some oxygen-containing functional groups were removed from the kerogen macromolecule,so the oil shale with deeper deposit depth had lower relative contents of aliphatic hydrocarbons and oxygen-containing organic compounds in the shale oil.In the research of oil shale bubbling fluidized bed retorting,influences of temperature,carrier gas flow rate,oil shale particle size,feed rate,bed materials and catalysts on the product yields,composition and physicochemical properties were studied by changing the reaction conditions.The results showed that the increase of retorting temperature could promote the pyrolysis of kerogen macromolecule,while at the same time promote the secondary cracking reaction of the products.The increase of carrier gas flow rate could enhance the heat and mass transfer in the reaction zone,reduce the residence time of the retorting products in the reactor,and thus promoted the retorting reaction.Increasing the oil shale particle size could reduce the adsorption of oil on one hand,and on the other hand increase the residence time of retorting products within the particles.Totally,increasing the oil shale particle size could reduce the secondary cracking reactions.The effect of increasing the feed rate of oil shale on the retorting products was consistent with that of decreasing retorting temperature.Both char and shale ash as bed materials could promote the retorting reaction,while inorganic minerals in shale ash were more effective in promoting the secondary reaction.Both char and shale ash had pore structures which could promote the adsorption of shale oil strengthening the coking reaction.FeCl₃ and H-ZSM-5 zeolite catalyst could promote the pyrolysis reaction of kerogen and the secondary reaction of shale oil?including cracking reaction and aromatization reaction?leading to the decrease of the shale oil yield and increase of the non-condensable gas yield.H-ZSM-5 zeolite catalyst had a greater impact on the product yields comparatively.In the research of oil shale pyrolysis mechanism,a fragment of kerogen macromolecule was used as the reactant model to simulate the path of pyrolysis reaction and impact of temperature on the pyrolysis process using the Gaussian quantum chemical calculation software.The results showed that the increase of pyrolysis temperature could affect the activation enthalpy?H and activation free energy?G in the reaction process.?G decreased significantly with the increase of temperature which means that increasing temperature could promote the pyrolysis reaction.