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Research Papers: Fuel Combustion

Exergy Destruction Mechanism of Coal Gasification by Combining the Kinetic Method and the Energy Utilization Diagram

[+] Author and Article Information
Handong Wu

Institute of Engineering Thermophysics,
Chinese Academy of Sciences,
University of Chinese Academy of Sciences,
No. 11 North Fourth Ring Road West,
Haidian District,
Beijing 100190, China
e-mail: wuhandong@iet.cn

Sheng Li

Institute of Engineering Thermophysics,
Chinese Academy of Sciences,
University of Chinese Academy of Sciences,
No. 11 North Fourth Ring Road West,
Haidian District,
Beijing 100190, China
e-mail: lisheng@iet.cn

Lin Gao

Institute of Engineering Thermophysics,
Chinese Academy of Science,
University of Chinese Academy of Sciences,
No. 11 North Fourth Ring Road West,
Haidian District,
Beijing 100190, China
e-mail: gaolin@iet.cn

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received September 26, 2016; final manuscript received May 1, 2017; published online June 15, 2017. Assoc. Editor: Antonio J. Bula.

J. Energy Resour. Technol 139(6), 062201 (Jun 15, 2017) (9 pages) Paper No: JERT-16-1386; doi: 10.1115/1.4036957 History: Received September 26, 2016; Revised May 01, 2017

Gasification is the core unit of coal-based production systems and is also the site where one of the largest exergy destruction occurs. This paper reveals the exergy destruction mechanism of carbon gasification through a combined analysis of the kinetic method and the energy utilization diagram (EUD). Instead of a lumped exergy destruction using the traditional “black-box” and other models, the role of each reaction in carbon gasification is revealed. The results show that the exergy destruction caused by chemical reactions accounts for 86.3% of the entire carbon gasification process. Furthermore, approximately 90.3% of exergy destruction of chemical reactions is caused by the exothermal carbon partial oxidation reaction (reaction 1), 6.0% is caused by the carbon dioxide gasification reaction (reaction 2), 2.4% is caused by the steam gasification reaction (reaction 3), and 1.3% is caused by other reactions under the base condition. With increasing O2 content α and decreasing steam content β, the proportion of exergy destruction from reaction 1 decreases due to the higher gasification temperature (a higher energy level of energy acceptor in EUD), while the proportions of other reactions increase. This shows that the chemical efficiency is optimal when the extent of reactions 1 and 3 is equal and the shift reaction extent approaches zero at the same time.

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Figures

Grahic Jump Location
Fig. 1

Hypothetical subprocesses of the detailed gasification model proposed by Prins and Ptasinski Tr and P are the gasification temperature and pressure, respectively

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Fig. 2

Algorithm flow chart of carbon gasification. The matlab algorithm flow chart of carbon gasification, which is calculated using the kinetic method and obeys mass conservation and the first and second law of thermodynamics. ni represents the mole number of the component i. Rj represents the reaction rate of Reaction j. e, A, dH, and Ex are the interim parameters obtained at every time period.

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Fig. 3

Variation of reaction extents ej with time under the base condition

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Fig. 4

Variation of mole numbers ni with time under the base condition

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Fig. 5

EUD of the gasification process. ΔH is the enthalpy change and A is the energy level of each subprocess. The shadow areas represent the exergy destructions of each subprocess.

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Fig. 6

Key simulation results including reaction temperature, overall exergetic efficiency, and chemical efficiency under the carbon deposition boundary conditions [16]. α and β are the coupled O2/C and H2O/C under the carbon deposition boundaries.

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Fig. 7

Relationship of chemical efficiency and reaction extents. e1, e3, and e8 are the reaction extents of the partial oxidation reaction, steam gasification reaction, and shift reaction, respectively.

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Fig. 8

Distribution of the exergy destruction and physical exergy output under five representative conditions. Each color represents a specific exergy destruction of the corresponding subprocess, and the origin color represents the physical exergy output.

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