Gas Turbines: Coal, Biomass, and Alternative Fuels

Combustion Performance in a Semiclosed Cycle Gas Turbine for IGCC Fired With CO-Rich Syngas and Oxy-Recirculated Exhaust Streams

[+] Author and Article Information
Takeharu Hasegawa

 Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka-shi, Kanagawa-ken, 240-0196, Japantakeharu@criepi.denken.or.jp

J. Eng. Gas Turbines Power 134(9), 091401 (Jul 18, 2012) (10 pages) doi:10.1115/1.4006985 History: Received October 06, 2011; Accepted May 10, 2012; Published July 17, 2012; Online July 18, 2012

Our study found that burning a CO-rich gasified coal fuel, derived from an oxygen–CO2 blown gasifier, with oxygen under stoichiometric conditions in a closed cycle gas turbine produced a highly-efficient, oxy-fuel integrated coal gasification combined cycle (IGCC) power generation system with CO2 capture. We diluted stoichiometric combustion with recycled gas turbine exhaust and adjusted for given temperatures. Some of the exhaust was used to feed coal into the gasifier. In doing so, we found it necessary to minimize not only CO and H2 of unburned fuel constituents but also residual O2 , not consumed in the gas turbine combustion process. In this study, we examined the emission characteristics of gasified-fueled stoichiometric combustion with oxygen through numerical analysis based on reaction kinetics. Furthermore, we investigated the reaction characteristics of reactant gases of CO, H2 , and O2 remaining in the recirculating gas turbine exhaust using present numerical procedures. As a result, we were able to clarify that since fuel oxidation reaction is inhibited due to reasons of exhaust recirculation and lower oxygen partial pressure, CO oxidization is very sluggish and combustion reaction does not reach equilibrium at the combustor exit. In the case of a combustor exhaust temperature of 1573 K (1300 °C), we estimated that high CO exhaust emissions of about a few percent, in tens of milliseconds, corresponded to the combustion gas residence time in the gas turbine combustor. Combustion efficiency was estimated to reach only about 76%, which was a lower value compared to H2 /O2 -fired combustion while residual O2 in exhaust was 2.5 vol%, or five times as much as the equilibrium concentration. On the other hand, unburned constituents in an expansion turbine exhaust were slowed to oxidize in a heat recovery steam generator (HRSG) flue processing, and exhaust gases reached equilibrium conditions. In this regard, however, reaction heat in HRSG could not devote enough energy for combined cycle thermal efficiency, making advanced combustion technology necessary for achieving highly efficient, oxy-fuel IGCC.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Comparison of CO2 recovery processes for IGCCs; (a) precombustion system; (b) proposed oxy-fuel IGCC system

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Figure 2

Thermal efficiency of coal-base power plants with and without CO2 capture and compression. In the three conventional cases of post-, oxy-fuel and pre-combustion, currently available technologies are employed and CO2 recovery rate is set at 90% [8]. In the case of oxy-fuel IGCC employing technologies currently under development, CO2 recovery rate is set at 99% [2].

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Figure 3

Schematic diagram of oxy-fuel IGCC and semiclosed cycle gas turbine [1]

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Figure 4

Influence of carrier gas conveying pulverized coal into gasifier on oxygen-blown gasification performance under conditions of coal input of 118.5 t/h [1]

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Figure 5

Schematic flow diagram of demonstration plant of dry gas purification system for current IGCCs [13]

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Figure 6

Comparison of kinetic analyses with experimental data of Lyon [17] on concentration of NH3 and NO in the NH3 -NO-O2 -H2 system under conditions of selective noncatalytic reduction of NOx

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Figure 7

Schematic of algorism in semiclosed gas turbine for oxy-fuel IGCC under typical rated conditions. Recirculated gas turbine exhaust is injected into the PSR of the combustor alongside incoming stream of gasified fuel and oxidizer of O2 .

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Figure 8

Chemical species behavior over time in gasified fuel/O2 stoichiometric combustion with exhaust recirculation. Analysis conditions: mixture of gasified fuel, oxidizer and dilution at inlet to combustor is CO = 9.44 vol%, H2 = 3.39 vol%, CH4 = 0.043 vol%, CO2 = 55.6 vol%, H2 O = 21.7 vol%, Ar + N2 = 2.53 vol% and O2 = 7.33 vol%. Reaction temperature is set at 1573 K of adiabatic flame temperature of the mixture.

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Figure 9

Chemical species behavior over time in conventional CH4 /air combustion

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Figure 10

Comparison of emission characteristics with conventional air-fired combustions

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Figure 11

Chemical species behavior over time in H2 /O2 combustion with steam recirculation

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Figure 12

Stoichiometric combustion characteristics of each fuel; overall equivalence ratio φ is 1, markers (stars) are test data under conditions where combustion pressure is set at 2.5 MPa and recirculated steam temperature is 623 K [24]

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Figure 13

Influence of fuels and dilution gases on adiabatic flame temperature

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Figure 14

Influence of dilution gases on combustion emission characteristics, compared with case of CH4 fuel. Overall equivalence ratio is 1.

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Figure 15

Effects of apparent equivalence ratio (φ*) on combustion emission characteristics

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Figure 16

Typical stream history of exhaust temperature and pressure from gas turbine inlet to compressor inlet of recirculating exhaust

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Figure 17

Chemical species behavior of combustion and exhaust gas over time in semiclosed cycle gas turbine, using PSR + PFR combined model. Combustor inlet conditions are the same as those in Fig. 8.

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Figure 18

History of combustion emissions from gas turbine inlet to heat recovery steam generator (HRSG) outlet

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Figure 19

Influence of exhaust recirculation on thermal-NO emissions




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