Combustion characteristics of CH_4 in low emission fractional burner

Volume 26, issue 1 March 2013 GAS TURBINE TECHNOLoGY V0l_26 no.1 Mar., 2013. Combustion characteristics of CH4 in low-emission graded burners: huang mingming, zhang zhedian, shao weiwei, xiong yan, liu yan, xiao yunhan (1).Institute of engineering thermophysics, Chinese academy of sciences, Beijing 100190, China;2.Abstract: flue gas reflux is a means of achieving soft combustion. In order to accurately control the reflux ratio, a fractional burner was established. The effects of reflux ratio, equivalent ratio on CH soft combustion flame morphology and NO and CO emissions were experimentally studied.When the equivalent ratio is 0.8 and the reflux ratio is 0.6-0.7, the soft combustion is realized, the reaction zone is dispersed without stratification, and the volume fraction of NO and CO in the flue gas is less than 1.2 ×10 and 4×10 ~ respectively.Diffusion combustion occurs when the reflux ratio is too small, and combustion is unstable when it is too large.NO emission is mainly generated in the flue gas producing area.When the reflux ratio is 0.6 and the equivalent ratio is 0.6 ~ 0.8, the efflux effectively mixes with the main stream and is accompanied by the lifting of the flame to achieve soft combustion.When the equivalent ratio is the same, NO emission from fractional combustion is lower than that from cyclone diffusion. When the equivalent ratio is 0.8, NO emission reduction from fractional combustion relative to cyclone diffusion reaches 44%.Key words: fractional combustion;NO;Gentle combustion;Diffusion combustion;Gas turbine combustion technology is developing towards the direction of high combustion efficiency and low NO emission. Gentle combustion, as A new combustion method that can simultaneously achieve the two goals of high combustion efficiency and low NO emission, has attracted the attention of scholars in recent years.The initial temperature of reactants is higher than the spontaneous combustion temperature, and the maximum temperature rise is lower than the spontaneous combustion temperature.Different scholars adopt different methods to achieve the soft combustion, there are mainly four: air preheating + thin air release (mode 1), air preheating + fuel dilution (mode 2), flue gas internal circulation (mode 3), fractional combustion (mode 4).Gupta et al. preheated the air to 900 ~ 1100 oc and diluted the air to oxygen mole fraction of 2% ~ 21% by using the residual heat utilization assembly. The combustion characteristics of fuel at different preheating temperatures and oxygen mole fraction of oxidant atmosphere were observed through the flame pictures, and the NO and CO discharges under different conditions were analyzed.When the pre-heating temperature of air is unchanged and the oxygen mole fraction decreases from 21% to 2%, the flame lifting distance increases and the brightness decreases.When the air preheating temperature is 1 100~C and the oxymol fraction increases from 2% to 21%, the NO emission increases from 2×10 to 2×10 (all emissions mentioned in this paper refer to the volume fraction).Daily et al. J used flue gas to preheat air to 600 -- 900~(2, C H and preheated air to produce NO emissions of 4×10 ~ 7.6 ×10 ~ in soft combustion boiler.If the fuel and air flow rate are kept unchanged, N: thin release of CH, and the proportion of thin release increases from 0 to 88%, NO emission decreases from 2×10 to 1×10 ~.In the soft combustion experimental burner of Szeg6 et al.Based on the momentum ratio of fuel and air injection, the author studied the conditions for steady and gentle combustion of natural gas, and defined NO emission less than 7×10 ~ and CO emission NO more than 1×10 as gentle combustion.In the soft combustion experiment burner of Dally et al. _8, the smoke generated by the auxiliary combustion chamber mixes with the air to form an oxidant with the temperature of 1 300 K and the oxygen content of 3% ~ 9%. The fuel burns gently in this oxidant atmosphere.When the oxygen mass fraction is 3%, NO emission is only 5×1