Stuay on effect of oxygen-enriched partial gasification on NOx formation during pulverized coal combustion

The problem of high initial emission of nitrogen oxides （NOx） is common in the operation of coal-fired boilers, which affects the economy of system operation. In order to reduce the amount of NOx generated during pulverized coal combustion from the origin, a new low- NOx combustion technology with oxygen-enriched partial gasification coupled combustion was proposed in this paper. The pulverized coal combustion generates strong reducing gases under the conditions of low excess air coefficient and oxygen-enriched atmosphere. The purpose of controlling the initial NOx emission from pulverized coal combustion was achieved by air-staging technology in the furnace. The FR/ED model was used to simulate the gas phase reaction, which took into account the gasification reaction of pulverized coal. It is more suitable for the simulation of oxygen-enriched partial gasification reaction of pulverized coal. According to the simulation results, when using a 25.9% oxygen-enriched atmosphere, the combustion reactions in the burner was improved sufficiently. The inner temperature and the exit temperature in the burner were increased from 897 ℃ to 1 007 ℃, and from 1 255 ℃ to 1 356 ℃, separately, while the CO content was increased from 5.48% to 7.17%, and the carbon conversion rate was increased from 61.54% to 86.27%. The oxygen-enriched experimental results of 7 MW double-cone burner showed a quite good agreement with that of simulation works, strong reducing atmosphere was achieved by proper oxygen content and excessive ratio in the burner, and the lower the excessive ratio, the stronger the reductive gas composition such as CO and CH4 at the burner outlet. When the oxygen content in the air of the burner was increased from 21% to 28.3%, the CO content in the outlet center of the burner was increased from 9.54% to 20.258%, and the NOx production at the outlet of the burner was zero. Industrial experiments showed that, oxygen partial gasification and air-staging can both reduce the initial emission of NOx from boilers, and the combination of the two methods could made a better low- NOx effect. When the oxygen enrichment ratio was 28.3% and the air distribution ratio was 41.2%, the initial emission of NOx from boilers can be reduced from 546 mg/m3 to 159 mg/m3.