Direct investigation of the changes of functional groups of organic matter in oil shale during the pyrolysis is important for understanding its thermal conversion for shale oil generation. In this paper, an in situ Fourier transform infrared (FTIR) analyzer with a heater was used to study the pyrolysis of Huadian oil shale and its demineralization samples (kerogen concentrates) during the heating up to 600 °C. Transition state theory (TST) was used to analyze the conversion mechanisms of different oxygen-containing functional groups to H2O, CH4, CO, etc. The pyrolysis of dried oil shale begins with the rupture of C—OH and subsequently progresses to the decomposition of thermosensitive oxygen-containing groups (C—O and C═O in sequences). Also, then, aliphatic compounds will begin to decrease obviously from 350 °C due to cracking and evaporation while aromatic compounds exhibit excellent thermostability. The minerals in oil shale produce catalytic effects on the conversion of kerogen to bitumen, making the pyrolysis reactions easier in oil shale than in pure kerogen.

This is the age of oil when many parts of the economy, particularly transportation, still rely heavily upon oil. The uncertainty in petroleum prices, its growing worldwide consumption and limited availability have motivated many countries rich in oil shale resources to investigate more efficient technologies to produce and use shale oil as an alternative to traditional petroleum. This review considers some aspects of oil shale based technologies. Among many differences in the flow and operational characteristics of several typical industrial oil shale retorting processes, one of the most important concerns how to treat semicoke and transfer the pyrolytic heat required for retorting oil shale. This will not only affect the yield and quality of shale oil, but also involves a series of serious issues related to energy and environment.Semicoke, one of the final products formed after retorting oil shale, is a potentially harmful solid waste often containing some toxic organic compounds and heavy metals, disposal of which can result in very great environmental contamination. However, the organic compounds remaining in semicoke lead to it having a potential heat of combustion, and thus semicoke may be considered for combustion utilization as a fuel. This paper reviews the fundamental characteristics and combustion utilization possibilities for semicoke that would allow treating and utilizing semicoke efficiently and in an environmentally friendly manner. Although properties of semicoke vary widely with both the retorting processes and their operational parameters, it generally contains significant amounts of inorganic minerals from the oil shale matrix, some organic compounds and lesser amounts of trace elements. Its leaching elutes have shown acceptable limit values at a landfill for non-hazardous waste and thus the leaching of heavy metals is not necessarily a problem. However the leaching of organic compounds may often exceed the limits for dissolved organic carbon. Thus, the incineration of semicoke will often be desirable both to ensure relatively low harm to the environment as well as efficient resource recycling for energy. Based on the current status and probable future development of oil shale industries, and the combustion characteristics of semicoke, two technical routes have been recommended for utilizing semicoke. These might also be regarded as references or benchmarks for evaluating the new development of oil shale retorting processes. One method involves an integrated utilization system for oil shale in which semicoke is actively treated and utilized in a circulating fluidized bed boiler for providing heat for both retorting the oil shale and for generating steam. The other option is to employ circulating fluidized bed technology to burn semicoke which has been previously produced and might still be a byproduct of some retorting technologies. With regard to both options, industrial circulating fluidized bed combustion results are discussed, in an effort to establish the feasibility of burning semicoke in a circulating fluidized bed boiler.

Combustion experiments of Shidongkou sewage sludge from China were carried out by using a small lab-scale fluidized bed, and the effects of moisture content and feed rate of sewage sludge and the transfer of heavy metals were analyzed. Studied sewage sludge with a moisture content of no more than 40% can stably burn in the fluidized bed without any auxiliary fuel input. Enhancing the bed temperature of the dense phase, strengthening the gas–solid mixing of dense phase, and increasing the feed rate of sludge are very necessary for the ignition of sludge with higher moisture content; however, higher feed rate will give rise to an increase of both the incomplete combustion heat loss and the physical absorbing heat amount of new sludge into the fluidized bed, reducing the bed temperature. Gaseous pollutants from the fluidized bed were discussed under different experimental conditions. At last, it was presented that heavy metals except Zn within sewage sludge are mostly concentrated in bottom ashes and bag filter ashes.

The devolatilization of solid fuels will cause remarkable changes to the pore structures of the resulting char particles, which has a significant influence on successive reactions, such as the combustion of the char particles and the formation of ash. In the present work, the pore structures of shale chars prepared under different retorting conditions were measured by employing a N2 adsorption−desorption method. On the basis of the measured results and thermal degradation mechanisms of the kerogen within oil shale, the effects of four retorting parameters on the pore structures of shale char were discussed. An elevating retorting temperature will notably increase the pore volume and specific surface area in shale char. However, at the higher retorting temperatures, the cracking and carbonization of residual organic matter within shale char become more intensive. Subsequently, the pores are easily blocked (especially small pores), and the specific surface area of the char particles decreases slightly. In terms of the residence time of retorting at a low temperature of 430 °C, sufficient residence time is required for forming more extensive porosity within shale char particles. The particle size and low heating rate were found to have little effect on the surface area and pore volume of shale char.

On the basis of the physical and chemical performance of Huadian oil shale and the design experience of Huadian 65 t/h oil shale-fired circulating fluidized bed (CFB) boiler operation, this paper introduces several main characteristics of oil shale, such as platy structure, high volatile and Ca/S content, and low ignition temperature, which are relevant to the design of CFB boiler, and analyses key design technologies of large-scale oil shale-fired circulating fluidized bed boiler. The design principles of large-scale oil shale-fired CFB boiler are suggested: (1) to adopt a II-shape configuration natural circulation mode with medium-temperature cyclone with downward gas exhaust, reliable antiwear technology and self-desulfurization technology; (2) to determine a circulating ratio of 6, hot state superficial air velocity of 5–6 m/s, combustion portion of about 0.5–0.6 in dense phase zone, and air velocity at the nozzle hole of air cap of 50–60 m/s; (3) to adopt an igniting system with hot gas generator below distributor plate and oil guns as auxiliary ignition device above distributor plate, and fluidized bed ash cooler retrieving the heat taken by hot slag. Lastly, the design scheme of 420 t/h superhigh pressure oil shale-fired CFB boiler is put forward and the general configuration and technical data are given at the end of this paper.

•The whole formation process of shale oil might be divided into four stages.•Higher ash/shale mass ratio intensified the cracking and coking of shale oil.•Ash/shale ratio of 1:2 was recommended for oil shale fluidized bed retort with fine oil-shale ash as solid heat carrier.For exploring and optimizing the oil shale fluidized bed retort with fine oil-shale ash as a solid heat carrier, retorting experiments of oil shale and fine oil-shale ash mixtures were conducted in a lab-scale retorting reactor to investigate the effects of fine oil-shale ash on shale oil. Oil shale samples were obtained from Dachengzi Mine, China, and mixed with fine oil-shale ash in the ash/shale mass ratios of 0:1, 1:4, 1:2, 1:1, 2:1 and 4:1. The experimental retorting temperature was enhanced from room temperature to 520 °C and the average heating rate was 12 °C min−1. It was found that, with the increase of the oil-shale ash fraction, the shale oil yield first increased and then decreased obviously, whereas the gas yield appeared conversely. Shale oil was analyzed for the elemental analysis, presenting its atomic H/C ratio of 1.78–1.87. Further, extraction and simulated distillation of shale oil were also conducted to explore the quality of shale oil. As a result, the ash/shale mixing mass ratio of 1:2 was recommended only for the consideration of increasing the yield and quality of shale oil.

The gradual decrease in conventional energy resources, and the growth of heavy industry, have placed great pressure on China's energy supplies. As a result of technological development, clean and diverse energy utilization facilities have become available in the energy market. Oil shale with combustible organic materials is widespread throughout the earth; many researchers have been motivated to investigate efficient means to use oil shale as an alternative energy as soon as possible.In China, the conventional utilization of oil shale is concentrated mainly on oil shale retorting, and burning oil shale in pulverized furnaces, or bubbling fluidized beds. To improve the availability of oil shale, many specialists have advocated burning oil shale in a circulating fluidized bed (CFB), which has a satisfactory combustion efficiency, low NOX and SO2 emission, adaptability to low-grade coal, etc. In Huadian, China, a plant incorporating three units of 65 t h−1 oil shale-fired CFB began successful commercial operation in 1996, proving that burning oil shale in a CFB produces both high combustion efficiency and environmental protection. For effective utilization of oil shale, its pyrolysis and combustion characteristics, emission performance of gaseous pollutants from an oil shale-fired CFB pilot setup, co-combustion characteristics of oil shale and high sulfur coal—as well as the operating performance of the Huadian CFB boiler—were further studied. The resulting experimental data and theoretical analysis prove that oil shale resources have significant potential use in the combustion field.This paper introduces these fundamental characteristics and the industrial application of oil shale in combustion. Three projects are recommended for the future use of oil shale, based on the current status of energy and the characteristics of oil shale: (1) co-combustion of oil shale and high sulfur fuel for furnace desulfurization; (2) large-scale development of oil shale-fired CFBs; (3) a comprehensive oil shale utilization project to produce shale oil, burn oil-shale semicoke in a CFB boiler to generate electricity and supply heat, and produce building materials with oil shale ash.