Article pubs.acs.org/EF
Co-pyrolysis Properties and Product Composition of Low-Rank Coal and Heavy Oil Yong-hui Song,* Qiao-na Ma, and Wen-jin He Metallurgical Engineering Technology Research Centre of Shaanxi Province, Xi’an University of Architecture and Technology, Xi’an, Shaanxi 710055, People’s Republic of China ABSTRACT: The co-pyrolysis characteristics of low-rank coal (SJC) and heavy oil (HS) were investigated using a thermogravimetric Fourier transform infrared analyzer and a vacuum tube-type furnace reactor. The structure and composition of the pyrolysis products were characterized through gas chromatography−mass spectrometry, Fourier transform infrared spectrometry, and gas analysis. The coke yield decreased by 20%, and the gas and tar yields increased by 7.74 and 12.18%, respectively, after combining with HS. Meanwhile, the number of hydroxyl groups on the coke surface decreased, and the alkane and phenol contents of tar decreased by 7.89 and 8.10%, respectively. The aromatic substance content increased by 21.60%. The HS was upgraded after the co-pyrolysis of SJC + HS. The HS did not affect the precipitation temperature of each component in the pyrolysis gas. The CO2, CH4, and CnHm contents were augmented by about twice the original amount, whereas the CO and H2 contents were diminished by 2.88 and 22.18%, respectively. The initial decomposition temperature of SJC + HS co-pyrolysis was greatly reduced. The cracking of the light component in the HS appeared in the first stage, but the maximum mass loss occurred in the second stage. Hydrogen donation and synergistic effects for the radicals produced by coal pyrolysis with the pyrolysis products of HS redistributed the co-pyrolysis products, increased the pyrolysis tar yield, and sharply reduced the CO and H2 contents.
1. INTRODUCTION China is a highly coal-rich country, with coal reserves much more substantial than those of petroleum and natural gas. Low-rank coal (long flame coal, non-caking coal, and weakly caking coal) in northern Shaanxi is rich in resources and is characterized by low ash, sulfur, and phosphorus contents and high volatility, calorific value, and activity.1 Such a coal type is an excellent fuel and thermal coal and a high-quality raw material of semi-coke. Low-rank coal produces considerable amounts of pulverized coal during coal production and transport. The internal heat type of an upright semi-coke stove can only use block coal of 30−80 mm particle size. Given the present lack of development in pyrolysis technology and equipment, a large amount of coal can only be used for direct combustion, which is a low-efficiency process. Under direct combustion, tar and gas are difficult to separate and recover, resulting in serious resource waste and environmental pollution. Therefore, the full use of low-rank coal in northern Shaanxi is a great challenge facing the advancement of the coal chemical industry in the region. Obtaining high-quality coke products from molding pyrolysis of low-rank coal to maximize tar recovery is a new approach of using low metamorphic coal resources. However, the caking property of low metamorphic coal is poor. Obtaining highquality coke products requires a certain amount of adhesive. Therefore, the co-pyrolysis properties of low-rank coal and additives as well as the bonding mechanism of coke formation must be understood. At present, many scholars are concerned with the co-pyrolysis of low-rank coal and oil shale, biomass, waste polymer plastics, and other organic materials. The studies mainly concentrated on two aspects. One is optimizing the tar yield and component, and the other is considering the synergies in pyrolysis. Abnisa and Wan Daud2 summarized the co-pyrolysis of biomass and found that such an approach © XXXX American Chemical Society
improves not only the yield and properties of tar but also the calorific value of coke, tar, and gas. Song et al.3 showed that adding low-rank coal to oil shale could enhance the tar yield and increase the gas contents of CO, CH4, and H2 under microwave heating. In addition, during the pyrolysis of low-rank coal and plastics, the yield of coke decreases, whereas the tar yield improves with the increase in plastic additive proportion.4 Mushtaq et al.5 studied the microwave-assisted co-pyrolysis of coal and biomass. Results showed that the microwave-assisted pyrolysis of coal and biomass in the presence of a microwave absorber provides a distinct environment to resolve these challenges. The microwave absorber can indirectly heat coal and biomass particles, which are relatively microwave-transparent and influence the product yield and quality by contributing as catalytic precursors. Soncini et al.6 investigated the product distribution of low-rank coal and biomass pyrolysis. Co-pyrolysis synergies become increasingly significant as the coal rank decreases possibly because the initial structure of these coals contains large pores and small clusters of aromatic structures, which are readily retained as tar in rapid co-pyrolysis. Aboyade et al.7 studied the co-pyrolysis characteristics of coal and agricultural wastes and found that the mixing ratio is the main factor affecting the yields and composition of tar and gas. The author indicated that the synergistic effect is significant during coal and biomass pyrolysis but minimal during co-pyrolysis. Miao et al.8 studied the co-pyrolysis characteristics of different ranks of coal and oil shale and noted synergy during the process. Coal provides hydrogen for oil shale, which Received: August 24, 2016 Revised: November 16, 2016
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DOI: 10.1021/acs.energyfuels.6b02106 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels Table 1. Proximate and Ultimate Analyses of SJC (Mass %) proximate analysis
ultimate analysis
sample
Mad
Aad
Vad
FCad
Cad
Oad
Had
Nad
St,ad
SJC
4.71
5.94
34.30
55.05
73.07
4.94
4.34
0.96
0.42
Figure 1. Laboratory equipment connections of the pyrolysis experimental setup. coal. After preliminary crushing, SJC was sieved to
