Study On The Effect Of Synergy Of Water And Oxygen On Pyrolysis Characteristics Of Oil Shale

With the continuous increase of global oil consumption and the increasing shortage of conventional resources,many countries in the world have begun to work on unconventional oil and gas resources.Oil shale,a low calorific value solid fossil fuel,has attracted the attention of researchers for its huge reserves and oil production capacity.In addition to being directly used as a solid raw material for combustion power generation,cracking kerogen to obtain a series of petrochemical products has become a common method of utilizing oil shale.According to statistics,China's oil shale resource reserves are about 978 billion tons,in situ converted to 61 billion tons of shale oil.Its efficient development and utilization are of great significance to safeguarding China's energy security and alleviating the contradictions in China's energy consumption.At present,in order to reduce mining costs and improve shale oil recovery and energy utilization,a large number of research work on oil shale pyrolysis process and characteristics has been carried out.However,the current research work was mainly aimed at the development of high-quality oil shale.Few studies have investigated the effects of operating conditions on the product yield and product composition properties from low-quality oil shale.Therefore,in view of the low-quality characteristics of oil shale resources in China,low-quality oil shale was selected as the research object,and its pyrolysis behavior was studied.The effects of heating rate,atmosphere and self-characteristics on pyrolysis behavior were discussed and detailed analyzed.And the effects of different pyrolysis conditions on the composition of pyrolysis products were compared.Secondly,according to the advantages of water and oxygen in the pyrolysis process,a method of synergistic action of water and oxygen to pyrolysis oil shale was proposed,and the pyrolysis products of oil shale with different water injection rates and different pyrolysis temperatures were discussed.The influence of distribution and composition of oil products and the variation of solid residues were analyzed in detail to reveal the synergistic mechanism.The main conclusions of research are as follows:1.The non-isothermal pyrolysis method was used to investigate the pyrolysis characteristics of oil shale from five areas:namely,Huadian,Nongan,Fuyu,Mongolia,and North Korea.The pyrolysis behaviours of the oil shale at different heating rates and different atmosphere were determined by thermogravimetric analysis?TG?and differential thermogravimetric analysis?DTG?.During pyrolysis,as the heating rate increased,the oil shale reaction zone moved to a higher temperature due to thermal hysteresis.And oil shale combustion was slightly delayed at 21%O₂/79%CO₂compared to the air atmosphere.With an increase in oxygen concentration,the initial temperature,burnout temperature,and maximum mass loss temperature decreased,and the combustion stability and comprehensive oxidation of the oil shale were improved.The activation energies of the oil shale samples from four areas were obtained by the Flynn-Wall-Ozawa?FWO?,Starink,and Friedman methods.The results showed that the activation energy was not stable throughout the conversion stage,and the overall trend showed increase with increase in temperature.The average activation energy in the second stage was 280,276,and 347 kJ mol^-11 for Huadian oil shale;304,307,and342 kJ mol^-1 for Fuyu oil shale;328,333,and 348 kJ mol^-11 for Nongan oil shale;341,347,and 422 kJ mol^-1 for North Korea oil shale;and 362,363,and 379 kJ mol^-1 for Mongolia oil shale by the FWO,Starink,and Friedman methods,respectively.The fluctuation of activation energy showed that thermal degradation in oil shale was a complicated multistep reaction,regardless of the production area.The quality and characteristics of organic matter and mineral impacted the pyrolysis process and kinetic characteristics.The Sestak-Berggren method was used to fit the data from oil shale pyrolysis.The results indicated that the main mass loss phase of oil shale pyrolysis was controlled by a nucleation mechanism.2.The pyrolysis behavior of oil shale was studied by a tubular furnace experimental device.The effects of pyrolysis temperature on the yield and product characteristics of low-quality oil shale products were discussed.The results showed that the main mass loss of oil shale was in the temperature range of 310–600°C and the maximum mass loss temperature was 465°C.The retorting experiments showed that temperature had an important influence on shale oil yield and the maximum oil yield was obtained at 550°C.The oil yield was reduced at higher temperatures resulting in an increase in gas.According to the analysis of shale oil compositions,the high pyrolysis temperature could promote the formation of short-chain hydrocarbons.Meanwhile,more alkenes and aromatics and less heteroatomic compounds were found at high temperature.The long-chain hydrocarbons and heteroatomic compounds were proved to be secondary products decomposed at higher temperature.In addition,the results of nitrogen adsorption/desorption and scanning electron microscopy indicated that the shale surface became more porous due to the decomposition of kerogen and more micro-and mesopores were found after the treatment at high temperature.3.The pyrolysis of oil shale were carried out under different temperatures and different water injections.The effects of different factors on the pyrolysis product yield and pyrolysis products of oil shale were discussed.The mass spectrometer and elemental analyzer were used to analyze the differences of oil composition under different conditions,and the mechanism of water and oxygen synergistic action to crack oil shale was analyzed.The results show that the pyrolysis temperature had an important influence on the decomposition of oil shale organic matter.When the oil shale was pyrolyzed under air conditions,the yield of shale oil in the range of400-480°C was higher than that in the nitrogen atmosphere.The yield of solid residue decreased with increasing temperature,and the presence of oxygen consumes a small amount of shale oil.The injection of water increases the yield of shale oil.At the temperature of 450°C and the Water/Oil shale ratio of 1:10,the highest oil yield was obtained.The main components of shale oil were aliphatic hydrocarbon compounds,aromatic hydrocarbon compounds,and heteroatom compounds.Compared to conventional pyrolysis,water injection increased the content of oxygen and sulfur in shale oil and reduced the content of carbon and nitrogen.Under the same water injection conditions,an increase in the pyrolysis temperature will significantly increase the yield of shale oil.As the pyrolysis temperature increased,the alkane content in the shale oil continued to decrease,and the content of alkenes and heteroatoms increased.High temperature had the effect of increasing the nitrogen and oxygen content of shale oil and reducing the carbon content.4.The variation of residues under the synergistic effect of water and oxygen was investigated by industrial analysis,Fourier transform infrared spectroscopy?FTIR?,thermogravimetric analysis?TG,DTG?,and nitrogen adsorption/desorption.The influence of different water injection and different temperature conditions on the micro-porous structure of solid residues was analyzed,and the fractal dimension calculation method was used to quantitatively describe the complexity of solid residues structure.The results showed that the injection of water had a certain influence on the chemical composition of the oil shale residues,resulting in an increase in the ash content of the residues and no significant effect on the decomposition of minerals.At the same time,the injection of water affects the formation of a small-amount of pores,resulting in a decrease in specific surface area.With the rise of pyrolysis temperature,the peak intensity corresponding to hydroxyl and aliphatic hydrocarbons decreased gradually,and the effect of temperature on pore development was more significant.Oil shale residue had obvious fractal characteristics.Under the condition of water injection,the fractal dimension fluctuated greatly,and the internal pore structure of the residue was more complicated than the surface structure.With the increase of pyrolysis temperature,the fractal dimension showed an increasing trend,indicating that the cracking of organic matter had a greater contribution to the fractal dimension.