Effect of the distance between fuel and oxidizer nozzles on NOx emissions from spray combustion furnaces incorporating high-temperature preheated oxidizers

Abstract

The objective of the present study was to investigate the effect of the distance between fuel and oxidizer nozzles on NOx emissions from a laboratory-scale spray combustion furnace simulating an industrial high-temperature air combustion (HiTAC) furnace. The furnace employed in these trials was fueled with commercially obtainable kerosene in combination with highly preheated oxidizer gases. The oxidizer was pre-diluted by the addition of nitrogen in order to produce dilution levels equivalent to those in industrial HiTAC furnaces. The resulting NOx measurements indicate a trend opposite to that reported by previous studies, such that increasing the distance between the nozzles increases the NOx emissions, and a theory is advanced to explain this unusual observation. In a furnace within which the nozzle distance in the burner is small, the properties of the oxidizer supplied from the nozzle located near the spray nozzle greatly affect NOx emissions. The use of an oxidizer with a much lower preheat temperature and a lower O 2 concentration induces flame lifting further downstream, which significantly reduces NOx emissions through the formation of an invisible flame exhibiting a uniform temperature distribution throughout the furnace. In contrast, in a furnace in which the burner has a large nozzle distance, a highly luminous flame is anchored near the spray nozzle exit due to ignition of fuel vapor by high-temperature burned gases recirculated to the lower section of the furnace. This flame represents a zone with high combustion intensity and generates significant NOx emissions. In such cases, the influence of the oxidizer properties is moderated due to the widely separated nozzle locations.

110th Anniversary: MILD Combustion of Liquid Hydrocarbon–Alcohol Blends

“…As extensively discussed in the literature, − the geometry of the burner (with particular reference to the fuel and air jet nozzles) plays an important role since it allows to obtain large exhaust recirculation and turbulence intensity, as required to reach MILD combustion conditions.…”

“…Among the others, Weber et al 32 studied NOx emission from a semi-industrial highly preheated air furnace with light and heavy oils as fuels; they found that NOx reduction requires an optimized burner design in terms of distance between fuel and oxidizer injectors. The effects of the nozzle distance on NOx emissions were studied also by Nada et al 33 in a laboratory-scale furnace with kerosene as a liquid fuel. Derudi and Rota 34 investigated the sustainability of MILD combustion of liquid linear and branched hydrocarbons in a dual-nozzle laboratory-scale burner; they found that MILD combustion conditions seems more affected by the physical state of the fuel than by the chain length of the hydrocarbons.…”

Numerical investigation of the effect of constant velocity and constant residence time scaling criteria on the natural gas MILD combustion

“…There have been several studies on MILD combustion, both experimentally and numerically, such as; effects of geometry and operating condition, the effect of burner configuration (Nada et al, 2015;Lee et al, 2019a), furnace chamber configuration (Schaffel-Mancini et al, 2010;Tu et al, 2015a), jet velocity of reactant (Mi et al, 2011;Veríssimo et al, 2013), reactant temperature (Khoshhal et al, 2011;Huang et al, 2014), chemical composition of fuel and oxidizer (Dally et al, 2004;Tu et al, 2015b;Lee et al, 2019b), on NOx formation and reduction (Wünning and Wünning, 1997;Mancini et al, 2002) and microscopic characteristics (Jin and Zhou, 2015;Zhang et al, 2019;).…”