The Effects of LBG Composition and Combustor Characteristics on Fuel NOx Formation

Abstract

The low Btu gas (LBG) combined gas and steam turbine power cycle is a potentially attractive alternative to the direct coal fired steam cycle because of the potential for low sulfur emissions and high overall cycle efficiency. However, LBG may contain ammonia (NH3) which could be converted to nitrogen oxides (NOx) under typical combustion conditions. This paper examines the effects of LBG composition and combustor design on NOx emissions. Low Btu gases of varying compositions were synthesized from bottled gases and fired in three atmospheric pressure flame reactors: diffusion flame reactor, flat flame reactor and catalytic reactor. Nitrogen oxide emissions were found to be most sensitive to the concentrations of NH3 and hydrocarbon fuel gas in the synthetic LBG. Lowest NOx emissions were produced by the diffusion flame reactor operating at near stoichiometric conditions and the catalytic reactor operating fuel rich.

Calculations of Fuel NO Formation in a Gas Turbine Combustor

“…This conclusion may not be appropriate for different combustor designs. For example, staged combustion has been shown to decrease overall fuel nitrogen conversion (Flagan and Seinfeld, 1988) and has been suggested as an approach for low-Btu gaseous fuel combustor (Folsom et al, 1980). The predictions show a range of fuel nitrogen conversion of 35 to 86%.…”

Performance and Emission Levels in Gas Turbine Plants

“…A further contribution to NO,, formation is given by the nitrogenous species, like ammonia, contained in fuel which undergo a direct conversion into nitrogen oxides, named "fuel NO X ". This particular NO, formation occurs according to chemical mechanisms different from those of thermal NO (Folsom et al, 1980). The relative weight of this contribution is more significant for those fuels, such as low LHV coalderived gases, which manifest good behavior from the point of view of thermal NO.…”

“…Depending on fuel composition, a strong reduction in thermal NO production can be often obtained, but usually an increase in carbon dioxide arises from the higher carbon to hydrogen ratio which characterizes these kinds of fuels. In addition to that, the formation of "fuel NO x " can be due to the greater quantity of nitrogenous species, such as ammonia, that can be contained in the fuel (Hung, 1975, Folsom et al, 1980.…”

Gas Turbine Combustion and Ammonia Removal Technology of Gasified Fuels

“…The body of research into the basic combustion characteristics of gasified fuel includes studies on the flammability limits of mixed gas, consisting of CH 4 or H 2 diluted with N 2 , Ar or He [47]; a review of the flammability and explosion limits of H 2 and H 2 /CO fuels [48]; the impact of N 2 on burning velocity [49]; the effect of N 2 and CO 2 on flammability limits [50,51]; and the combustion characteristics of low calorific fuel [52,53]; studies by Merryman et al [54], on NOx formation in CO flame; studies by Miller et al [55], on the conversion characteristics of HCN in H 2 -O 2 -HCN-Ar flames; studies by Song et al [56], on the effects of fuel-rich combustion on the conversion of the fixed nitrogen to N 2 ; studies by White et al [57], on a rich-lean combustor for low-Btu and medium-Btu gaseous fuels; and research of the CRIEPI into fuel-NOx emission characteristics of low-calorific fuel, including NH 3 through experiments using a small diffusion burner and analyses based on reaction kinetics [58][59][60][61]. It is widely accepted that two-stage combustion, as typified by rich-lean combustion, is effective in reducing fuel-NOx emissions [62,63].…”