Article pubs.acs.org/EF
Pyrolysis of Huadian Oil Shale in an Infrared Heating Reactor Somprasong Siramard,†,‡ Yutthasin Bunman,†,‡ Dengguo Lai,†,‡ and Guangwen Xu*,† †
State Key Laboratory of Multi-phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China ‡ University of Chinese Academy of Sciences, Beijing 100049, China ABSTRACT: Pyrolysis of Huadian oil shale was investigated in a newly designed shallow fixed bed reactor mounted with infrared heating to clarify the pyrolysis behavior at different heating rates and pyrolysis temperatures under minimized secondary reactions to volatiles in an oil shale bed. The maximum shale oil recovery was obtained under the proper conditions of a heating rate of 0.5 °C/s, a pyrolysis temperature of about 550 °C, a reduced reaction pressure (0.6 atm in this work), and for a singlelayer oil shale bed. The highest shale oil yield under such conditions was close to 100% of the Fischer Assay oil yield (11.10 wt % of dry basis). For the adopted infrared-heating reactor, increasing the heating rate decreased the shale oil yield but increased the gas production. The total hydrogen in volatile products including shale oil and pyrolysis gas increased with raising the heating rate, and the total volatile production was higher for the infrared quick heating pyrolysis (heating rate: 25 °C/s) than that for the Fischer Assay. The shale oil from the infrared quick heating pyrolysis had also more light fraction. Experiment also found that pyrolyzing the multilayer oil shale bed lowered the shale oil yield in comparison with the pyrolysis of a single-layer material bed. Thus, adopting a single-layer oil shale bed, low infrared heating rates, and reduced reaction pressures obviously suppressed the secondary reactions toward volatiles to have consequently high shale oil yield. High infrared heating rate facilitated volatile and hydrogen production but led to more serious secondary reactions to lower the shale oil yield. to the reactor.15 According to the preceding understanding about pyrolysis reactions, we would emphasize that “fast” or “slow” cannot fully characterize the pyrolysis reaction process. In fact, heating rate affects more the primary reactions of volatile release from particles, even though its potential influences on secondary reactions to volatiles cannot be denied. There are many studies about effects of heating rate on pyrolysis, but they almost did not distinguish its actions on primary and secondary reactions. Results of slow pyrolysis show that increasing the heating rate to 0.17 °C/s would increase shale oil production owing to the higher self-generated gas sweep rate of volatile from the particle (shortening residence time). Further increasing the heating rate to 0.5 °C/s slightly reduced shale oil yield, possibly caused by a diffusion limited process of heat and product transfer that incurs secondary reactions of oil.16,17 Nonetheless, the productions of light oil and noncondensable gas are generally higher at higher heating rates.18 Fast pyrolysis is a well-known technique for acquiring high volatile production.19 Table 1 summarizes a few investigations on oil shale fast pyrolysis in terms of shale oil production against the Fischer Assay yield. Nieh et al.20 reported relatively lower oil yields for rapid pyrolysis of oil shale at a heating rate of 500 °C/s in a radiation-heated furnace as compared to the pyrolysis in an aluminum-made retort, but the shale oil had the higher light oil fraction for rapid pyrolysis. Using a grid reactor, Solomon et al.21 reported a higher shale oil yield but a slight effect on shale oil yield from heating rate varying in 0.17−600 °C/s. Suuberg et al.22 found little enhancement on oil yield
1. INTRODUCTION Utilization of oil shale, one of the major alternative oil resources, has been extensively studied worldwide especially in the countries having relatively rich reserves.1,2 Pyrolysis or retorting is the major technology converting oil shale into shale oil and shale gas which are further applied to many industries or civil utilizations. From a fundamental aspect, any pyrolysis of oil shale occurring in actual processes has to be composed of primary decomposition of oil shale molecules and its following secondary reactions on the formed vapor products or volatiles. Especially in a large-scale practical pyrolysis reactor, the volatile released from individual particles has to pass through an oil shale particle bed and to confront with a series of complex reactions. Thus, the reactions of oil shale pyrolysis can be treated as two distinctive stages, volatile releasing from a single oil shale particle and secondary reactions toward such volatiles during their flowing inside the reactor. While the intensity of volatile releasing (or primary pyrolysis) reactions from single particles is determinative to the total/overall volatile yield, the occurrence degree of such secondary reactions controls the distribution and composition or quality of final pyrolysis products. Many factors affect the volatile releasing from individual particles and secondary reactions to volatiles, including temperature and its distribution in the reactor,3−5 heating rate,4−7 residence or flowing time of volatiles in reactor or particle bed,8 reaction pressure,9,10 mineral matrix,11 and particle size of oil shale,12−14 and others. Heating rate and reaction temperature greatly act on the volatile released from oil shale particles. On the other hand, it is hard to separate the actions of temperature and heating rate because high heating rate is usually accompanied by high temperature. Pyrolysis is typically grouped into slow and fast pyrolysis according to heating rate to particles or in most cases © 2017 American Chemical Society
Received: April 6, 2017 Revised: June 14, 2017 Published: June 16, 2017 6996
DOI: 10.1021/acs.energyfuels.7b00964 Energy Fuels 2017, 31, 6996−7003
Article
Energy & Fuels Table 1. Literature Reports of Oil Shale Pyrolysis at Rapid Heating Rate in Different Reactors reactor type
pyrolysis temperature (°C) 20
radiation heated furnace heated grid reactor21 wire mesh reactor22 microwave irradiation reactor23 a
heating rate (°C/s)
500−600 550 500−1000 590
500 0.17−600 1000 0.2−1.2b
feedstock mass (g) a
0.07−0.5 0.01−0.03 20
shale oil yield against FAc (%) 93−77 150−160
