Distinctive Oil Shale Pyrolysis Behavior in Indirectly Heated Fixed Bed With
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RSC Advances PAPER View Article Online View Journal | View Issue Distinctive oil shale pyrolysis behavior in indirectly heated fixed bed with internals Cite this: RSC Adv.,2017,7, 21467 Lanxin Lin,ab Dengguo Lai,ab Zhen Shi,ab Zhennan Hanab and Guangwen Xu *ac Intrinsic characteristics of oil shale pyrolysis in a fixed bed reactor with internals have been investigated in this study. Mounting particularly designed internals in fixed bed reactor improved shale oil production to up to 90% yield by Fischer assay. Comparing particle characteristics at different radial positions of the reactors with and without internals demonstrated that, inside the particle bed with internals, the product flow was regulated to move from the high-temperature zone (outer) to low-temperature zone (center), which reduced the secondary reactions of released volatiles. Terminating oil shale pyrolysis at central particle bed temperatures of 150, 300, 450, and 550 C showed that the contents of vacuum gas oil and heavy oil in the shale oil produced had increased from 9.63 wt% to 53.29 wt%. The volatile contents of particles in the inner layer of the reactor slightly increased in the early stage of pyrolysis and, in turn, decomposed to form pyrolysis products as the temperature was raised. The adsorption or condensation of liquids on Creative Commons Attribution 3.0 Unported Licence. the surface of particles gradually increased from the outer region to the central region of the reactor due to the regulated product flow direction and low temperatures in the central zone of the reactor causing heavy components to condense. Increasing the degree of pyrolysis was also found to decrease Received 25th February 2017 the alkene, aromatic, and cycloalkane contents in shale oil, but increased those of alkane and Accepted 3rd April 2017 heteroatomic compounds. These results demonstrate that adopting internals into oil shale pyrolysis DOI: 10.1039/c7ra02347b optimized the product flow direction and selectively directed secondary reactions to occur for heavy rsc.li/rsc-advances volatile species only. This article is licensed under a 1. Introduction Lurgi–Ruhrgas process in Germany, and the Fushun process in China.4–9 Of these, Tosco-II, Galoter, Enet-280, ATP, and Lurgi– Alternative and renewable energy sources have received Ruhrgas processes adopt a solid heat carrier method to heat oil Open Access Article. Published on 18 April 2017. Downloaded 10/2/2021 5:51:51 PM. increasing attention in recent years as fossil fuel consumption shale particles and achieve relatively high oil yields. However, has grown. Oil shale is among the most promising alternative the resultant liquid products usually exhibit high dust intake energy sources because of its enormous reserves and plentiful due to inherent technical defects. Many studies on oil-dust aliphatic organic compounds.1 Available oil shale utilization characteristics and separation have been conducted, but patterns have been established in several countries since the a comprehensive solution for the dust-intake problem in 1960s. Combusting oil shale to generate power could supply pyrolysis had yet to be developed.10 Gas heat carrier retorting domestic industrial users, with retorted shale oil considered technology is employed in the Petrosix, Kiviter, and Fushun a potential resource to offset the future crude oil scarcity. The retorting processes. However, these methods only process large- utilization of retorted shale oil requires a comprehensive utili- particle feedstock. Excessive air pumped into a Funshun zation mode, as reported by many studies.2–6 furnace causes oil combustion in the pyrolysis stage, lowering Several representative oil shale retorting processes have been the shale oil yield to 65% by Fischer assay. Process analysis is developed and are still in service, such as in situ underground applied to optimize operating parameters and improve oil retorting and Tosco-II technology in the USA, the Kiviter process production efficiency.11 An in situ retorting process has been in Estonia, the Petrosix process in Brazil, the Galoter process in proposed for deeply buried oil shale, but this technology Russia, Enet-280 technology in Germany and Estonia, the requires long-term verication for application.4 Therefore, no Alberta Taciuk process (ATP) in Australia and Canada, the existing retorting processes provide satisfactory pyrolysis performance for oil shale, especially for particle sizes below 10 aState Key Laboratory of Multi-Phase Complex Systems, Institute of Process mm. In particular, innovative retorting technologies are Engineering, Chinese Academy of Sciences, Beijing 100190, China. E-mail: gwxu@ required for small oil shale particles to achieve high oil yield ipe.ac.cn; Fax: +86 10 82629912; Tel: +86 10 82544886 and quality simultaneously. bUniversity of Chinese Academy of Sciences, Beijing 100049, China Particularly designed internals, comprising a central gas cInstitute of Industrial Chemistry and Energy Technology, Shenyang University of collection pipe and a number of metallic plates, have been Chemical Technology, Shenyang 110142, China This journal is © The Royal Society of Chemistry 2017 RSC Adv.,2017,7, 21467–21474 | 21467 View Article Online RSC Advances Paper employed to improve oil shale pyrolysis production in indirectly 2. Experimental section heated xed bed reactors.12–14 An innovative reactor with inter- nals was evaluated by comparing the heating rate of oil shale 2.1 Materials and apparatus particles and pyrolysis product distribution. With the heating Oil shale was obtained from Huadian oil shale mine, and was rate to particles improved, especially in the central region, the sieved to a particle size of 0–5 mm for use in experiments. The resultant shale oil yield was afforded in 90% oil yield by Fischer properties of Huadian oil shale are shown in Table 1. The dry- assay. Raising the reactor temperature from 600 C to 1000 C base oil content was 12.78 wt% by Fischer Assay. Silica sand beneted shale oil production, which was in contrast to almost (1–2 mm) was used in the study to replace a portion of the oil all other reports in the area, which show higher pyrolysis shale particles, which had been pretreated at 900 C for 3 h. temperatures lead to lower oil yield. In conventional indirectly A conventional xed bed reactor without internals was used heated xed bed reactors, it is generally difficult to achieve high as reference in this work. The pyrolysis investigation was con- oil yields at high reaction temperatures due to unavoidable ducted in a reactor mounted with a central collection pipe and signicant secondary reactions of volatiles.15–18 In contrast, four metallic plates. The plates were welded perpendicular to devised internals can reduce cracking in the reactor to achieve the xed bed reactor wall. Fig. 1 shows schematic diagrams of a higher shale oil yield at higher heating or reaction tempera- the two reactors used. The reactors had an inner diameter of 200 tures. Matching the product ow eld with temperature distri- mm, and effective volumes for loading oil shale of around 5600 bution in the reactor using internals has been speculated to mL. From the wall to the center of the reactor (Fig. 1), both avoid excessive cracking of primary products and improved reactors were demarcated into three layers (a–c) in a radial pyrolysis production. Therefore, further understanding of the direction. Three temperature measurement points were present detailed pyrolysis characteristics of the new reactor and its in layers a–c to record real-time heating curves inside these superiority are required to guide industrial applications of the layers. The experimental system was the same as used in our technology. previous work,14 consisting of four parts: pyrolysis, liquid Creative Commons Attribution 3.0 Unported Licence. Many studies have focused on the behavior and kinetics of collection, pressure control, and gas sampling. oil shale pyrolysis, which are needed for reasonable analysis and optimization guidance.15–22 Al-Ayed et al. adopted second- 2.2 Pyrolysis and analysis order kinetics to model liquid accumulation15 and rst-order kinetics to t the total weight loss of oil shale in a xed bed.16 The furnace was heated to 850 C and held until the pyrolysis In contrast, various parameters, such as heating rate, nal test was completed. For each individual experiment, dried temperature, particle size, density, and additional minerals, Huadian oil shale (4900 g) was loaded into the test reactor. In have been investigated to clarify their effects on oil shale some tests, the oil shale particles in the outboard layer were – À1 pyrolysis at various scales.22 32 A heating rate of 10 C min for replaced with silica sand of equal volume. A er connecting to This article is licensed under a oil shale particles is optimal for obtaining a high oil yield.26–29 the experimental system, the reactors were placed into the The internals adopted in the preceding reactor gave an obvious heated furnace and quickly covered with silica wool. The pres- improvement on heating rate.12–14 Nonetheless, this improve- sure in the reactor was maintained at 1 atm using a vacuum ff pump. Pyrolysis products were exhausted from the top of the Open Access Article. Published on 18 April 2017. Downloaded 10/2/2021 5:51:51 PM. ment was not as e ective at altering pyrolysis behavior in indirectly heated reactors.12,13 Lan et al. obtained a maximal reactor and cooled in a downstream condenser pipe. The cooled shale oil yield at a reaction-stopping temperature of 550 C.30 liquid product was collected in a bottle. Residual low-boiling Lai et al. demonstrated that the oil yield decreased with components in the gaseous product were adsorbed using increasing temperature by conducting an oil shale pyrolysis three acetone bottles. The pyrolysis gas was then passed series with and without ash.31 Zhang et al. investigated the through a wet gas meter to measure the volume and then impact of residence time on the pyrolysis product in a uidized successive through a few clean bottles to remove dust, moisture, bed.33 These studies were all performed in reactors without the and hydrogen sul de.