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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

# Coal Based Cogeneration System for Synthetic/Substitute Natural Gas and Power With CO2 Capture After Methanation: Coupling Between Chemical and Power Production

[+] Author and Article Information
Sheng Li

Laboratory of Integrated Energy System
and Renewable Energy,
Institute of Engineering Thermophysics,
P.O. Box 2706,
Beijing100190, China
e-mail: lisheng@iet.cn

Hongguang Jin

Laboratory of Integrated Energy System
and Renewable Energy,
Institute of Engineering Thermophysics,
P.O. Box 2706,
Beijing 100190, China
e-mail: hgjin@iet.cn

Lin Gao

Laboratory of Integrated Energy System
and Renewable Energy,
Institute of Engineering Thermophysics,
P.O. Box 2706,
Beijing 100190, China
e-mail: gaolin@iet.cn

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received September 28, 2013; final manuscript received February 19, 2014; published online March 21, 2014. Assoc. Editor: Paolo Chiesa.

J. Eng. Gas Turbines Power 136(9), 091501 (Mar 21, 2014) (11 pages) Paper No: GTP-13-1350; doi: 10.1115/1.4026928 History: Received September 28, 2013; Revised February 19, 2014

## Abstract

Cogeneration of synthetic natural gas (SNG) and power from coal efficiently and CO2 capture with low energy penalty during coal utilization are very important technical paths to implement clean coal technologies in China. This paper integrates a novel coal based cogeneration system with CO2 capture after chemical synthesis to produce SNG and power, and presents the energetic and exergy analysis based on the thermodynamic formulas and the use of ASPEN PLUS 11.0. In the novel system, instead of separation from the gas before chemical synthesis traditionally, CO2 will be removed from the unconverted gas after synthesis, whose concentration can reach as high as 55% before separation and is much higher than 30% in traditional SNG production system. And by moderate recycle instead of full recycle of chemical unconverted gas back into SNG synthesis, the sharp increase in energy consumption for SNG synthesis with conversion ratios will be avoided, and by using part of the chemical unconverted gas, power is cogenerated efficiently. Thermodynamic analysis shows that the benefit from both systematic integration and high CO2 concentration makes the system have good efficiency and low energy penalty for CO2 capture. The overall efficiency of the system ranges from 53%–62% at different recycle ratios. Compared to traditional single product systems (IGCC with CO2 capture for power, traditional SNG system for SNG production), the energy saving ratio (ESR) of the novel system is 16%–21%. And compared to IGCC and traditional SNG system, the energy saving benefit from cogeneration can even offset the energy consumption for CO2 separation, and thus zero energy/efficiency penalties for CO2 capture can be realized through system integration when the chemicals to power output ratio (CPOR) varies in the range of 1.0–4.6. Sensitivity analysis hints that an optimized recycle ratio of the unconverted gas and CPOR can maximize system performance (The optimized Ru for ESR maximum is around 9, 4.2, and 4.0, and the corresponding CPOR is around 4.25, 3.89, and 3.84, at τ = 4.94, 5.28 and 5.61), and minimize the efficiency penalty for CO2 capture (The optimized Ru for minimization of CO2 capture energy penalty is around 6.37 and the corresponding CPOR is around 3.97 at τ = 4.94, ε = 16.5). The polygeneration plant with CO2 capture after chemical synthesis has a good thermodynamic and environmental performance and may be an option for clean coal technologies and CO2 emission abatement.

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## Figures

Fig. 1

Fig. 2

Power losses for SNG synthesis at different conversion ratios in traditional SNG plant [5]

Fig. 3

(a) Coal based SNG and power PG plant with CO2 capture after chemical synthesis (b) PG plant with CO2 capture before chemical synthesis

Fig. 4

Diagram of IGCC with CO2 capture

Fig. 5

Main factors impacting polygeneration performance

Fig. 6

(a) Effects of recycle ratio on SNG conversion ratio and overall efficiency, and (b) effects of SNG conversion ratio on exergy losses of chemical synthesis in PG plant

Fig. 7

Effects of the CPOR on ESR (a) PG plant with CO2 removal after SNG synthesis, and (b) PG plant with CO2 removal before SNG synthesis (IGCC+CC and traditional SNG system as reference plants) [5]

Fig. 8

Effects of CO2 separation efficiency on η and ESR

Fig. 9

CO2 enrichment mechanisms in the polygeneration system

Fig. 10

The energy/efficiency penalty for CO2 capture

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