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Cite This: Energy Fuels XXXX, XXX, XXX−XXX
Comparison of HTSM and TGA Experiments of Gasification Characteristics of Different Coal Chars and Petcoke Ming Liu, Zhihao Zhou, Zhongjie Shen, Qinfeng Liang, Jianliang Xu, and Haifeng Liu*
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Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education, Shanghai Engineering Research Center of Coal Gasification, East China University of Science and Technology, P.O. Box 272, Shanghai 200237, People’s Republic of China ABSTRACT: The thermogravimetric analyzer (TGA) is an ideal experimental method to estimate the gasification kinetics. However, the diffusion resistance was significant in high-temperature gasification process. In this study, comparison of different coal chars and petcoke gasification characteristics between high-temperature stage microscope (HTSM) and TGA experiments at high temperature were carried out. The gasification reactivity of different coal chars and petcoke in HTSM was higher than that in TGA experiments. The gasification reactivity of lignite and bituminous char in HTSM was much higher than that in TGA experiments. Meanwhile, the reactivity index of anthracite and petcoke in HTSM was merely double of that in TGA experiments. Interparticle diffusion process limited the gasification reactivity of different coal chars and petcoke in TGA experiments. The diffusion resistance of lignite and bituminous char was severe in TGA experiments. Moreover, the complete reaction time of bituminous coal char in HTSM experiments at high reaction temperature showed an agreement with industrial operating data.
1. INTRODUCTION Entrained flow gasifier was an efficient technology that converted solid fuel (e.g., coal and petcoke) into syngas, which was widely used for chemical production, power generation (integrated gasification combined cycle), indirect liquefaction, and so on.1,2 Coal gasification reactivity was an important factor that affects the efficiency of gasifier.3−6 Thus, it was imperative to apply an approximate experimental method to study the gasification properties of coal. At present, the thermal gravimetric analyzer (TGA) was widely accepted as an applicable laboratory experimental method to estimate the gasification reactivity of coal.7−12 But the diffusion resistance was severe at high temperatures. The application of reaction kinetics parameters obtained at low temperatures to high-temperature reactions was not appropriate because of the ash melting at high temperatures. The drop tube furnace (DTF) reactor was an appropriate experimental method to study the gasification of coal and petcoke at high temperatures.3,13−16 But the limited residence time of the samples in DTF reactors restricted the reaction time of coal gasification. The wire mesh reactor also was applied to investigate the pyrolysis and gasification process of coal.17−19 However, the carbon conversion of samples during the gasification process was difficult to directly estimate. The high-temperature stage microscope (HTSM) system also was applied to investigate the gasification characteristics (morphological evolution and shrinkage rate) of coal char at high temperatures.20−22 And the experimental results showed novel characteristics. Thermogravimetric analyzer was generally applied to investigate the gasification kinetics of coal char, biomass char, and petcoke.23−27 It is an effective experimental method to study the gasification kinetics of coal char. The diffusion resistance of gasifying agent in the crucible also is a problem when studying the intrinsic reaction kinetics of coal char at high temperatures.28−34 The CO2 partial pressure in the © XXXX American Chemical Society
sample bed was extremely lower than that expected (atmosphere pressure).28 Ollero et al.35 found that the internal diffusion in the sample bed was significant during the gasification of wood matter. Besides, the internal diffusion in the sample bed should not be disregarded in kinetics evaluations. Gomez et al.36 pointed out that the maximum reaction rate during coal gasification process was caused by the switching of inlet gas. And, the reaction rate obtained from an improved gasification procedure was higher than from the novel TGA experiments. New experimental method was developed to reduce the interparticle diffusion.37 The sample bed thickness was reduced to decrease the diffusion resistance in this method. Even though, the diffusion limitation control the reaction process when the reaction temperature was above 900 °C. Single-step kinetics models were thought inappropriate for estimating kinetics parameters because of the diffusion hindrance. The high-temperature stage microscope system was initially used by Ding et al. to study the morphology evolution of coal char during the gasification process.38 Shen et al.20 studied the gasification characteristics of coal char particles on molten slag by a HTSM system. The conversion of coal char particles on molten slag was obtained by measuring the projecting area of char particles. It was found that the gasification rate of char particle on molten slag was higher than that of char particles. Combustion characteristics of coal char on molten slag also was investigated by a HTSM system.21 The reaction rate of coal particles on molten was lower than of coal char particles. Besides, the HTSM system was applied to investigate the gasification of coal char and petcoke by Shen et al. and Liu et Received: January 1, 2019 Revised: February 9, 2019 Published: March 7, 2019 A
DOI: 10.1021/acs.energyfuels.9b00005 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels Table 1. Proximate and Ultimate Analyses of Samplesa proximate analysis (wt %)
ultimate analysis (wt %, ad)
sample
Mad
Vad
Aad
FCad
C
H
N
S
XLT coal XLT char SM coal SM char GP coal GP char PC
1.49 0.60 3.08 2.60 1.17 1.79 0.71
29.60 2.24 32.95 1.93 9.23 1.63 7.99
15.60 26.92 9.53 19.93 14.26 14.49 2.03
53.31 70.24 54.44 75.54 75.34 82.09 89.27
60.01 65.10 72.86 82.28 76.17 81.37 91.63
4.10 0.50 4.83 0.84 3.03 0.77 3.46
0.90 0.82 1.05 1.26 1.06 1.11 1.68
1.27 5.18 1.04 1.31 3.58 3.38 2.78
M: moisture; V: volatile matter; A: ash; FC: fixed carbon.
a
al.22,39−42 Furthermore, Liu et al.43 studied the gasification characteristics of petcoke particle swarms using a HTSM system. It was found that the particle concentration significantly affected the gasification of the samples. It was inferred that the interparticle diffusion restricted the diffusion process. The gasifying agent concentration in particle swarms was lower than expected. It was suggested that gasification kinetics characteristics of coal char obtained from fixed-bed reactors should be re-evaluated. The gasification kinetics of coal char, biomass char, and petcoke could be well estimated by a TGA experimental apparatus at lower temperatures (
