Influence of the Steam Addition on Premixed Methane Air Combustion at Atmospheric Pressure

Mao Li,Jens Klingmann,Yiheng Tong,Marcus Thern

doi:10.3390/en10071070

Abstract

Steam-diluted combustion in gas turbine systems is an effective approach to control pollutant emissions and improve the gas turbine efficiency. The primary purpose of the present research is to analyze the influence of steam dilution on the combustion stability, flame structures, and CO emissions of a swirl-stabilized gas turbine model combustor under atmospheric pressure conditions. The premixed methane/air/steam flame was investigated with three preheating temperatures (384 K/434 K/484 K) and the equivalence ratio was varied from stoichiometric conditions to the flammability limits where the flame was physically blown out from the combustor. In order to represent the steam dilution intensity, the steam fraction Ω defined as the steam to air mass flow rate ratio was used in this work. Exhaust gases were sampled with a water-cooled emission probe which was mounted at the combustor exit. A 120 mm length quartz liner was used which enabled the flame visualization and optical measurement. Time-averaged CH chemiluminescence imaging was conducted to characterize the flame location and it was further analyzed with the inverse Abel transform method. Chemical kinetics calculation was conducted to support and analyze the experimental results. It was found that the LBO (lean blowout) limits were increased with steam fraction. CH chemiluminescence imaging showed that with a high steam fraction, the flame length was elongated, but the flame structure was not altered. CO emissions were mapped as a function of the steam fraction, inlet air temperature, and equivalence ratios. Stable combustion with low CO emission can be achieved with an appropriate steam fraction operation range.

Highlights

Steam-diluted combustion in gas turbine cycles is an efficient, inexpensive, and environmentallyfriendly technology for power generation
The steam addition decreases the concentration of all the reactants, which results in a lower reaction reaction rate for the same equivalence ratio compared to the combustion case without steam rate for the same equivalence ratio compared to the combustion case without steam addition
The results indicated that to control CO below 200 ppm at the same steam fraction, a higher inlet temperature could extend the operation range to a smaller equivalence ratio

Summary

Introduction

Steam-diluted combustion in gas turbine cycles is an efficient, inexpensive, and environmentallyfriendly technology for power generation. The steam-diluted combustion can be combined with the CCS (carbon capture and storage) and applied as an environmentally-friendly technology to reduce the greenhouse emissions (mainly CO2 ). In this combined technology, the gas turbine combustion operates with sufficient steam dilution to extend the operability limits of low NOx to near-stoichiometric operating conditions [3,4], where the CO2 concentration in the combustion exhaust achieves the theoretical maximum value for the combustion of hydrocarbon fuel in air-breathing gas turbines.

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Conclusion