Research on natural gas oxygen-enriched MILD combustion and NO emission characteristics
Combining MILD(Moderate or Intensive Low-Oxygen Dilution)combustion and oxygenation combustion to achieve low CO2 and NO emissions during natural gas combustion.Based on a 0.58 MW industrial furnace,a simulation study was conducted on natural gas MILD combustion and NO emission characteristics under the air premixed oxygenation method.The effects of oxygen concentration(19.5％-30.0％)and oxidant jet velocity(100-300 m/s)on the flow field,temperature,reaction zone distribution,and NO emis-sion characteristics inside the furnace under the oxygen-enriched MILD combustion method were analyzed.The results show that,under the condition of unchanged MILD burner structure,when the oxygen concentration increases from 19.5％to 30.0％,the high tempera-ture zone becomes more concentrated,the temperature distribution uniformity weakens,and NO emissions increase from 32.4 ×10-6 to 58.9 ×10-6,an increase of 82％.This means that the low nitrogen emission characteristics of MILD combustion under high oxygen conditions will disappear.However,at the same oxygen concentration condition,the elevated oxidizer inlet velocity promotes flue gas re-flux dilution,which leads to a decrease in peak temperature and enlarges the reaction zone of MILD combustion.At an oxygen concentra-tion of 26.5％,increasing the inlet jet velocity to 150 m/s leads to a reduction of NO from 49 ×10-6 to 31.2 ×10-6,resulting in NO emission levels equivalent to those under air conditions.In general,direct premixed oxygenation of air is not conducive to the formation of MILD combustion,but MILD combustion at high oxygen concentration conditions and maintaining low NO emissions can be achieved by increasing the oxidizer velocity.
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