| Current excessive dependence on oil can cause economic problem and instability of energy security because of the lack of total global recoverable oil reserves and increasing oil price. Therefore, it is necessary to develop various alternative energy sources of crude oil to ensure a balance between supply and demand of energy. Oil shale, a fine-grained sedimentary rock containing significant amounts of kerogen, is widely distributed throughout the world. The kerogen in oil shale can be converted into shale oil as an alternate to conventional oil and synthetic gas by retorting, representing a valuable potential source of liquid hydrocarbons and energy. China has enormous oil shale resources which are estimated at about 48 billion tones of shale oil in place. This huge reserve of energy sources is very significant for alleviating the pressure of oil supplies in the resource endowment characteristics of “rich in coal, oil-poor, less gas” in China. Oil shale retorting process is a multi-step chemical reaction process involving hundreds of chemical reactions and intermediates, which is affected by a variety of reaction conditions, such as the physical and chemical characteristics of oil shale samples, operating parameters and retorting medium, etc. Compared to crude oil, shale oil contains more unsaturated hydrocarbons, and non-hydrocarbon compounds containing oxygen, nitrogen, sulfur and others. For the energy potential of oil shale to be maximized and improving shale oil yield and quality, the conversion process of the oil shale to shale oil should be undertook under optimal process conditions.Base on the above, Dachengzi oil shales were retorted in a small fixed bed under argon atmosphere to determine the products yield and characteristic of shale oil and gases under the conditions of non-retorting medium, adding a mineral catalyst and adding shale ash composed of a variety of minerals. The distribution of elements, boiling point distribution, chemical class fractionation, and the chemical composition of aliphatic and aromatic hydrocarbons in the derived shale oil and volume percentage and mass percentage of the main gases in the non-condensable gases, as well as heating value of the non-condensable gases were analyzed. Shale ash, as a complex mineral consisted of a variety of minerals, is rich in acidic, basic and amphoteric oxides. All the shale ash samples exhibit a multimodal pore size distribution, and possess a reasonable amount of mesopores and a small fraction of micropores and macropores. And the physical and chemical properties of shale ash indicate that it possess good adsorption capability and catalytic properties. The 0.20 mm shale ash particle has the most developed pore structure with 3.928m2/g of specific surface area and 0.01348cm3/g of pore volume.The results indicate that compared to three crude oils(Daqing, Shengli, Xinjiang) produced in China, the atomic H/C ratio in the derived shale oil in this paper is close to that of crude oil. However, nitrogen, oxygen and sulfur content are higher. And the shale oil generated by retorting Dachengzi oil shale is classified as sweet and high-nitrogen crude oil in terms of the classification method of crude oil. Moreover, the boiling point distributions of the produced shale oils show that light naphtha fraction and the medium fraction in the derived shale oil in this study have normal distribution, with mean values of 134-151 oC and 274-285 oC, respectively. This distribution favors the cut of the shale oil as the naphtha and diesel oil in potential applications. Compared to three crude oils in China, the shale oil contains less heavy fraction and is much lighter. The aliphatic compounds content in the derived shale oils is about 50-66 wt.%, and the aromatic compounds content is about 7-17 wt.%. The organic compositions of the aliphatic compounds and polycyclic aromatic compounds are analyzed in this paper because polycyclic aromatic compounds in the shale oil may cause environmental pollutions and health hazards. The results indicate that the aliphatic fraction in the derived shale oil mainly consists of 1-olefin ranging from the number of carbon atoms C7-C28 and n-paraffin ranging from the number of carbon atoms C7-C35. The 1-olefin and n-paraffin are divided to four main groups respectively according the number of carbon atoms, i.e., C7-C12, C13-C18, C19-C24 and C25+. The results show that both C7-C12 n-paraffin and C25+ 1-olefin content are lower, and the total content of n-paraffin is about 2-4 times that of 1-olefin. The chemical composition of polycylic aromatic fraction was also studied. The PACs in the shale oil produced at different reaction conditions have similar characteristics. The PACs mainly contain naphthalenes, phenanthrenes and fluorenes followed by pyrenes, anthracenes, biphenyls, dibenzofurans and dibenzothiophenes, and then followed by low levels of chrysenes and benzo matters. The naphthalenes content is the largest which is close to half of the total content of PACs followed by phenanthrenes content which are far lower than the naphthalenes content and close to the fluorenes content. In addition, the produced shale oil in this study mainly consists of 2 and 3 ring compounds followed by 4 ring compounds and a very minor amount of 5 ring compounds. Except studying the characteristic of the derived shale oil, this paper also investigated the influence of different retorting conditions on the properties of non-condensable gases. In the non-condensable gases studied, the volume percentage of CO2, CH4 and H2 is much larger and those of CO and C2-C4 hydrocarbons are lower. The non-hydrocarbons, such as CO, CO2 and H2, are generated prior to hydrocarbon gases. On other hand, it was investigated that the mass percentage of main compositions in the non-condensable gases. The non-condensable gases mainly contain CO2 and CH4 and minor concentrations of C2-C4 hydrocarbons.When experiments were conducted without adding any retorting mediums, the effect of retorting temperature, heating rate and residence time were investigated. With increasing temperature and prolonging residence time, the shale oil yield goes up and the the heavy fractions content firstly decreases and then raises. Moreover, as heating rate improves, the shale oil yield firstly rises up and then reduces and the heavy fractions content reduces. Increasing temperature, prolonging residence time and raise heating rate contribute to producing high heating value gases.The optimal result is obtained when the sample was heated from room temperature to final retorting temperature of 520 oC at a fixed heating rate of 12oCmin-1 and held at 520 oC for 20 min. In this reaction condition, the maximum shale oil yield is achieved. Based on the optimal reaction condition, two different mineral catalysts(Ca CO3 and Fe2O3) were added into the oil shale samples to determine their effects on the properties of oil shale pyrolysis. The results indicate that adding catalyst is helpful for improving the reactivity of kerogen. Compared to the retorting experiment without adding any retorting mediums, the shale oil yield slightly increases after adding CaCO3 and obviously goes up after adding Fe2O3 to the oil shale sample. Moreover, the shale oil produced after adding Fe2O3 contains less N and S contents as well as less aromatics content, which can be seen as higher quality shale oil. On other hand, adding CaCO3 is more conductive to generating high heating value gases and reducing the heavy fraction content and boiling point of the obtained shale oil. So the suitable catalyst can be selected according to target products. In this paper, shale ash was added into the oil shale samples to investigate the effect of shale ash particle size and shale ash to oil shale mass ratio on the properties of oil shale pyrolysis. Adding shale ash with smaller grain size is helpful for raising shale oil yield and the heat value of non-condensable gases. Compared to the retorting experiment without adding any retorting mediums, adding shale ash with three grain sizes slightly decreases S content and has ucertainty effect on N and O contents. Adding the 0.20 mm shale ash produces the largest shale oil yield and the largest light fraction content in the derived shale oil. So the obtained shale oil has the lowest average boiling point. Moreover, O content in the derived shale oil decreases to the extreme extent. Compared to 0.60 mm and 1.25 mm shale ash, the obtained shale oil in the presence of 0.20 mm has less aromatics content. So adding the 0.20 mm shale ash is more helpful for improving the shale oil yield and quality. As SA/OS is larger than zero, both the shale oil yield and the light fraction content in the produced shale oil increase. In addition, the O content in the derived shale oil obviously decreases and N and S content.has no significant change. Additionally, changing SA/OS has small effect on the heating value of non-condensable gases. SA/OS=1:2 gives the largest shale oil yield, and decreases O content to the extreme extent in the derived shale oil. SA/OS=1:2 is optimal to improve the shale oil yield and quality compared to the other SA/OS mass ratios.In addition, two computation codes(HSC Chemistry for thermodynamic and Sandia PSR for kinetic simulations) were employed to investigate the integrated effects of thermodynamic and kinetic phenomena occurring in the oil shale pyrolysis process on the distribution of gaseous products, which will benefit the development and application of oil shale pyrolysis technology. Firstly, CH1.58O0.22N0.02S0.01 and CH1.58O0.22 are selected as the moral form of the oil shale and used for the HSC simulation. The simulation results based on the latter moral form are used as the basis of PSR kinetic simulation. And there are three ways to input the oil shale sample for the PSR simulation. In the first method, subtracting the nonvolatile carbon from the original carbon content in terms of CH1.58O0.22 can be used as the raw material of PSR In the second method, the normalized products after subtracting nonvolatile carbon from the component at the average temperature in every typical temperature range obtained by HSC simulation can be used as input raw materials to PSR. In the third method, the normalized products after subtracting nonvolatile carbon from the component at each typical temperature obtained by HSC simulation can be used as input raw materials to PSR. HSC simulation results show the other hydrocarbons except CH4 are unstable at the thermodynamic equilibrium state, so there are no other hydrocarbons except CH4. However the PSR simulation results under three input methods indicate that there are small amount of C2 and C3 except CH4 in the produced gases. In addition, the PSR simulation results based on the second input method show PSR has great sensitivity to the input feed at higher temperature. The results indicate high temperature easily results in the gas phase cracking reactions. Compared to the experiment result in the fixed-bed in this paper, the peak concentration of gases is lower and appears at higher temperature. It is possibly because the effect of mineral matter in the oil shale on the oil shale pyrolysis. Moreover, the simulation results based on the third input method show good continuity and the input feed components have no obvious effect on the composition of output products. All the gases generate at different times. C2 and C3 hydrocarbons produce later than CH4, CO, CO2 and H2 and mainly generate at medium temperatures region. Increasing the temperature enhances gas phase pyrolysis reaction of organic matter and improves the alkene content.Lastly, a novel comprehensive utilization technology for Huadian oil shale resources is recommended for shale oil production, electricity generation, oil shale ash processing, economical efficiency and environmental protection. The system integrated retorting oil shale for shale oil, circulating fluidized bed combustion of shale char and ash utilization system is simulated to explore the advantages of this comprehensive utilization technology and its optimal operating conditions. The simulation results are not only to guide industrial validation experiments, but also used for important reference to explore the comprehensive utilization of oil shale. To ensure the thermal balance and stable operation of the whole system, part of non-condensable gases from retort process, as auxiliary fuel, are introduced into a combustor connected before the CFB furnace. The system performance is simulated using ASPEN software tool in this paper. The influence of retorting temperature, residence time, temperature and pressure of the CFB furnace, content of oil shale for combustion, content of non-condensable gases for combustion on the system performance are discussed. In order to explore advantages of this system, a retort system and a combustion system are investigated. The results show that increasing retorting temperature, residence time, pressure of CFB furnace and content of non-condensable gases for combustion has positive significant effect on improving the total profit and the output energy efficient of the comprehensive utilization system. The solid heat carrier technology is more adaptable for this system. Compared with other utilization modes for oil shale, the comprehensive utilization system has higher utilization efficiency of oil shale resources, more diversified products, lower pollutants emission and higher total profit. |
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