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TECHNICAL PAPERS: Gas Turbines: Combustion and Fuels

Gas Turbine Combustion Technology Reducing Both Fuel-NOx and Thermal-NOx Emissions for Oxygen-Blown IGCC With Hot/Dry Synthetic Gas Cleanup

[+] 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

Takashi Tamaru

 Japan Aerospace Exploration Agency, 7-44-1 Jindaiji-higashi-machi, Chofu-shi, Tokyo 182-8522, Japantamaru@chofu.jaxa.jp

J. Eng. Gas Turbines Power 129(2), 358-369 (Oct 13, 2006) (12 pages) doi:10.1115/1.2432896 History: Received May 23, 2005; Revised October 13, 2006

In order to improve the thermal efficiency of the oxygen-blown integrated gasification combined cycle (IGCC) and to meet stricter environmental restrictions among cost-effective options, a hot/dry synthetic gas cleanup is one of the most hopeful choices. The flame temperature of medium-Btu gasified fuel used in this system is high so that NOx formation by nitrogen fixation results to increase significantly. Additionally, the gasified fuel contains nitrogenous compound, as ammonia, and it produces nitrogen oxides, the fuel NOx, in the case of employing the hot/dry gas cleanup. Low NOx combustion technology to reduce both fuel-NOx and thermal-NOx emissions has been required to protect the environment and ensure low cost operations for all kinds of oxygen-blown IGCC. In this paper, we have demonstrated the effectiveness of two-stage combustion and nitrogen injection techniques, and also showed engineering guidelines for the low-NOx combustor design of oxygen-blown gasified, medium-Btu fuels. The main results obtained are as follows: (1) Based on the basic combustion tests using a small diffusion burner, we clarified that the equivalence ratio at the primary combustion zone has to be adjusted according to the fuel conditions, such as methane concentration, COH2 molar ratio, and calorific values of gasified fuels in the case of the two-stage combustion method for reducing fuel-NOx emissions. (2) From the combustion tests of the medium-Btu fueled combustor, two-stage combustion with nitrogen direct injection into the combustor results in reductions of NOx emissions to 34ppm (corrected at 16% O2) or less under the gas turbine operational conditions of 25% load or higher for IGCC in the case where the gasified fuel contains 0.1% methane and 500ppm of ammonia. Through nitrogen direct injection, the thermal efficiency of the plant improved by approximately 0.3% (absolute), compared with the case where nitrogen was premixed with gasified fuel. The CO emission concentration decreased drastically, as low as 20ppm, or combustion efficiency was kept higher than 99.9%. The above results have shown that a two-stage combustion method with nitrogen direct injection is very effective for reducing both fuel-NOx and thermal-NOx emissions at once in IGCC, and it shows the bright prospects for low NOx and stable combustion technology of medium-Btu fuel.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Relationship between equivalence ratio and adiabatic flame temperature for various gasified fuels and CH4

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Figure 2

Combustor and diffusion burner of basic experimental device

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Figure 3

Effect of nitrogen injection on thermal-NOx emission characteristics in two-stage combustion, using a small diffusion burner

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Figure 4

Effect of nitrogen injection on the conversion rate of ammonia to NOx in two-stage combustion, using a small diffusion burner

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Figure 5

Effect of CH4 concentration in fuel on the conversion rate of NH3 in fuel to NOx in two-stage combustion, using a small diffusion burner

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Figure 6

Effect of CO∕H2 molar ratio on the conversion rate of NH3 in fuel to NOx in two-stage combustion, using a small diffusion burner

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Figure 7

Design concept of a medium-Btu fueled gas turbine combustor

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Figure 8

Axial distribution of inverse of equivalence ratio at the rated load condition

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Figure 9

Schematic diagram and specifications of experimental facility

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Figure 10

Combustion test rig

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Figure 11

Axial distributions of combustor wall temperatures using gas turbine combustor exit gas temperature as a parameter

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Figure 12

Effect of combustor-exit gas temperature on NOx emission characteristics

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Figure 13

Effect of sectional flow velocity of air in the combustor on NOx emission characteristics in the case of nitrogen injection

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Figure 14

Effect of bypassing nitrogen flow rate, premixed with combustion air on NOx emission characteristics

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Figure 15

Effect of nitrogen injection flow rate from the burner on NOx emission characteristics

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Figure 16

Effect of ammonia concentration in fuel on NOx emission characteristics

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Figure 17

Effect of pressure inside a combustor on NOx emission characteristics

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Figure 18

Effects of methane concentration and pressure in the combustor on NOx emission characteristics

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Figure 19

Effect of the gas turbine load on combustion emission characteristics

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