Mixture Preparation Effects on Distributed Combustion for Gas Turbine Application - Novel Combustion Concepts for Sustainable Energy Development - page 272

recirculation region which provides a low-velocity region for fl flame stabilization

with the evolution of high temperatures from the flames operating in

diffusion mode, the reaction zone is stabilized, resulting in large temperature gra-
dients and hot-spot regions in the entire combustion chamber that cause high NO x
levels from the combustion of fuels (Lefebvre 1999 ).
In previous studies on HiTAC

fl ame. For fl

flames for furnace applications (that are charac-
teristic of low combustion intensities of 0.1

fl

1 MW/m 3 -atm), avoidance of thin

-

concentrated reaction front flame has been achieved by the controlled

recirculation and mixing of large amounts of hot and active combustion gases with
the fuel and air streams prior to ignition of the mixture to provide distributed
mixture reaction zone (Tsuji et al. 2003 ). Preheating of the air stream has been
employed to provide spontaneous ignition of the fuel with volume distributed
combustion and stable

in the fl

fl flame without any fl flame-holding device. The pressure drop

is also very low compared to other fl flame stabilization devices. HiTAC has been

shown to provide signi cant fuel energy savings in furnaces. In the HiTAC tech-

nique, one may envision that high air preheats are required; however, preheating of
the combustion air or the fuel is neither necessary nor required to achieve dis-
tributed combustion reactions. Furthermore, no catalyst is used in this distributed
combustion mode. HiTAC has been successfully demonstrated and is now widely
used to achieve low NO x and CO emissions, stable combustion, and low noise and
simultaneously achieve significant energy savings using a range of gas, liquid, and
solid fuels for furnace applications (Tsuji et al. 2003 ; Gupta 2004 ; Wunning and
Wunning 1997 ; Katsuki and Hasegawa 1999 ). This work has been known as Hi-
TAC (Tsuji et al. 2003 ; Gupta 2004 ), excess air enthalpy combustion, and fl flameless

oxidation (FLOX) (Wunning and Wunning 1997 ).
In HiTAC technology, high temperature of the air is obtained by preheating with
the hot gases from a furnace or reactor. The hot gases can be harvested from within
the combustion zone or external to the combustion zone, using, for example, exit
gases. The peak temperature in the

flame zone is much reduced with the use of
diluted low oxygen concentration combustion air even though the air is preheated to
high temperatures. This low oxygen concentration or diluted air is obtained from
the exhaust gases by recirculating part of the combustion products into the
incoming hot combustion air. The effect of air preheat temperature and oxygen
concentration on HiTAC

fl

flames have been studied, where it was found that pol-
lutants emission, including CO 2 and NO x , was much lower with highly preheated
combustion air at low O 2 concentration than with normal air (Gupta et al. 1999 ).
The HiTAC technology has been also extended to other applications such as
thermal destruction of wastes (Gupta et al. 1996 ) and combustion in microscale
combustion devices wherein the combustor dimensions are smaller than quenching
distances (Vijayan and Gupta 2010 ; Shirsat and Gupta 2011 ).
CDC investigated here is focused on high combustion intensity for stationary gas
turbine combustion application, although other applications are also possible.
Therefore, the results presented here are also relevant for other power and pro-
pulsion applications. Previous investigations of CDC suggest signi

fl

cant improve-
ment in pattern factor, low sound emission levels, and ultra-low emissions of NO x