家用燃具低氮燃烧技术分析

Analysis of Low Nitrogen Combustion Technology for Domestic Gas Appliances

分析燃气供暖热水炉和家用燃气快速热水器常用的低氮燃烧技术的原理和特点,包括完全预混燃烧、水冷低氮燃烧器、浓淡燃烧、烟气再循环以及增加单片燃烧器数量等技术。完全预混燃烧、水冷低氮燃烧器、浓淡燃烧均能实现额定热负荷时NO_(x)排放较低,但各技术也有相应的难点。完全预混燃烧对燃气空气比例控制要求高,只有在最优的空燃比下,完全预混燃烧才能有最佳效果,且经济成本较高。水冷低氮燃烧器容易产生离焰等问题,不易满足GB 25034—2020《燃气采暖热水炉》的要求。浓淡燃烧的过剩空气系数过小时,烟气中CO体积分数过高,不易满足GB 25034—2020的要求。对于烟气再循环技术,需要确定合理的烟气再循环比例才能够实现低氮燃烧。增加单片燃烧器数量能够降低额定热负荷下的烟气中NO_(x)体积分数,且使常规大气式热水炉的NO_(x)排放等级从3级升至4级,经济成本相比其他技术更低。由于热水炉和热水器的体积偏小,改变一次空气系数或助燃空气加湿虽然能够降低烟气中NO_(x)体积分数,但实际试验结果显示降低效果有限。

The principles and characteristics of low nitrogen combustion technologies commonly used in gas-fired heating and hot water combi-boilers and domestic gas instantaneous water heaters are analyzed,including fully premixed combustion,water-cooled low nitrogen burners,rich-lean combustion,flue gas recirculation and increasing the number of single-chip burner.Fully premixed combustion,water-cooled low nitrogen burner and rich-lean combustion can all achieve low NO_(x)emissions at rated heat load,but each technology also has corresponding difficulties.Fully premixed combustion requires high gas-air ratio control,only at the optimal gas-air ratio,fully premixed combustion can have the best effect,and the economic cost is high.Water cooled low nitrogen burner is easy to produce problems such as flame separation,which makes it difficult to meet the requirements of Gas-fired Heating and Hot Water Combi-boilers(GB 25034-2020).When the excess air coefficient of rich-lean combustion is too small,the volume fraction of CO in the flue gas is too high to meet the requirements of GB 25034-2020.For flue gas recirculation technology,it is necessary to determine a reasonable flue gas recirculation ratio to achieve low nitrogen combustion.Increasing the number of single-chip burner can reduce the volume fraction of NO_(x)in the flue gas at rated heat load,and increase the NO_(x)emission level of conventional atmospheric combi-boilers from level 3 to level 4,and the economic cost is lower than other technologies.Due to the small volume of combi-boilers and water heaters,changing the primary air coefficient or humidification of combustion air can reduce the volume fraction of NO_(x)in the flue gas,but the actual test results show that the reduction effect is limited.