Experimental Study On Low Temperature Pyrolysis Process Of Oil Shale And Key Components Of Circulating Fluidized Bed

Oil shale is a combustible organic sedimentary rock with an oil content of 3.5%-18%, and also a main oil-gas alternative fossil fuel. The converted heat of its worldwide total reserves ranks second among all fossil energy resources and only after coal. Through the low-temperature pyrolysis technology, we are able to extract shale oil, an alternative liquid fuel oil, from oil shale and coal. At present, the long-term commercialized operations of low-temperature pyrolysis are all dependent on massive shale or coal as raw materials. The modern mechanized mining has produced abundant oil shale powder/coal powder that is not efficiently utilized and piled in open air, thereby causing huge resource waste and severe environmental pollution. Thus, the development of low-temperature pyrolysis process suitable for oil shale powder/coal powder is of significant economic benefit and environmental effect, since it will provide alternative liquid fuels urgently needed in the industry, and improve the utilization of oil shale/coal resources and product added values.In this study, the difficulties of the existing pyrolysis technology in a circulating fluidized bed were selected as the breakthrough point and investigated in order to improve the shale oil yield and quality and to reduce flyash in shale oil. Experiments were conducted to characterize the basic pyrolysis of oil shale and to develop a new process and its key components. This study provides basic data and design basis for further application of the new process.The microstructure and pyrolysis process of oil shales were analyzed via Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TG)-FTIR. Results show the total fat parameter IH0 is almost linearly related with the volatile matter of dry-ash-free basis (Fdaf) and the H/C atomic ratio, and all parameters represent the oil potential of raw materials. The aromatic/aliphatic hydrogen ratio (Har/Hal) is well linearly related to the ratio of fixed carbon to volatile matter (FCad/Fad). The thermal stability and metamorphism degree of oil shales change in consistent trends. The pyrolysis of Yaojie-1 oil shale is significantly promoted by the H2 atmosphere, but is inhibited by CH4, CO and CO2 atmosphere to different degrees.Pyrolysis of pulverized Yaojie-1 oil shale for oil extraction was tested in an electric heated bubbling fluidized bed reactor. It is found that the pyrolysis process, three-phase (gas, liquid, solid) product distribution and shale oil quality are mainly affected by pyrolysis temperatures, but slightly by the residence time of the solid-phase. Liquid yield and shale oil quality are maximized at the pyrolysis temperature 550 ℃ and the solid-phase residence time of 30 min. FTIR and curve-fitting were used to study the surface functional groups of pyrolysates produced in the bubbling fluidized bed and determine the source and basic composition of pyrolysates. Based on the principle of infrared spectrum superposition, the infrared spectra of fly ash and shale oil were combined to be compared with the infrared spectrum of toluene-insoluble matter (TIM). It is found that the infrared spectrum of TIM is highly consistent with the combined spectrum in terms of peak positions and shapes, which confirms that TIM is formed by ultra-fine fly ash and heavy shale oil.This study then presents a tube-type indirect heat transfer low-temperature pyrolysis process and we conducted 100-kg-level pilot experiments. The results confirm the feasibility of the indirect heat exchange process integrating a combustion furnace and a pyrolysis tube furnace, and clarify the effects of different fluidized states on heat transfer characteristics. However, the application of this process is limited by the low heat transfer efficiency. Thus, the key component of direct heat exchange low-temperature pyrolysis, the lower valve, was innovatively designed and experimentally studied. A traditional mechanical valve (butterfly valve) was selected as the lower valve and was used in a D400 cold pilot experiments to explore its stable operating range. A novel integrated return feeder was designed and installed on a D100 bench-scale device and a D400 pilot-scale device separately. Then the effects of operating parameters on solid flow rate and pressure profiles were studied. The results show its application is limited by the bad self-balance of the valves.Based on analysis of bulk flow characteristics and the operation mechanism of the pneumatic transport valve, a novel non-mechanical valve, named the jet-control solid material valve, is presented. The jet-control solid material valve was installed on the D400 pilot scale device, and its feasibility and performance were investigated. Compared with the conventional non-mechanical valve, the jet-control solid material valve can transfer solid particles steadily over a larger range, prevent artesian flow, and improve the leakage performance. The solid flow rate of the valve (W) at any relative position is equal to the summation of the solid flow rates of n jet pipes working individually (Wi). A two-valve model was proposed to explain the transport capacity of the valve for single jet pipe, and the opening degrees of the two valves jointly decide W. Furthermore, a semi-theoretical expression for Wmax was obtained based on the experimental data with a maximum deviation of 30%, providing useful guidance to scale-up the design.