生物质掺氨燃烧特性试验研究

Experimental Investigation on Combustion Characteristics of Cofiring Biomass With Ammonia

燃煤锅炉是中国CO_(2)的主要排放源之一,氨和生物质作为无碳、清洁替代能源用于燃煤锅炉,是中国实现“碳达峰、碳中和”目标的重要技术途径。为探究氨与其他燃料掺烧的可行性,利用清华大学25kW一维炉系统,通过调节气体流量、更换不同口径的氨气喷头,研究一种生物质燃料(玉米秸秆粉)与氨在多种掺烧比(热值比0~40%)和不同氨喷入速度下的燃烧特性、污染物及细颗粒物生成特性。结果表明,相较纯生物质燃烧,氨的掺入会吸收一部分热量用于自身预热,引起炉膛内烟气温度分布发生变化;提高氨的掺烧比,尾部烟气中NO_(x)的浓度近似线性增长,NH_(3)浓度无明显增加,飞灰中PM1~10质量占比增大,在氨的掺烧比低于40%时,烟气中NH_(3)浓度不高于2mg/m^(3),不存在氨逃逸现象,但纯氨燃烧会导致烟气中NH_(3)浓度激增。氨的掺混情况也会对烟气中NO_(x)浓度产生影响,当氨喷入速度与一次风速差越大,物料之间混合越不均匀,烟气中NO_(x)浓度越低,相较于等速喷氨烟气中NO_(x)浓度可下降200mg/m^(3)。结果可知,生物质大比例掺氨燃烧无显著氨逃逸,有望通过调节喷氨方式(尤其是氨喷入速度)降低烟气中NO_(x)浓度,是一种有潜力的火电机组减碳技术路线。

Coal-fired boilers are one of the major sources for CO_(2) emission in China.Burning ammonia and biomass as the carbon-free alternative fuels in the coal-fired boiler is an effective way to achieve the goal of“carbon peak and carbon neutrality”in China.To explore the feasibility of co-combustion ammonia with other fuels,this paper studied the combustion characteristics,gaseous pollutant and fine particle formation of co-firing biomass(the corn cob powder)with ammonia on the 25kW down-fired furnace at Tsinghua University,under various co-firing ratio(energy ratio 0~40%)and different ammonia injection speeds by adjusting the gas flow and replacing ammonia jet nozzles with different diameters.The results show that,compared with pure biomass combustion,the co-combustion with ammonia will absorb part of the heat for preheating itself,resulting in changes in the temperature distribution of flue gas.Increasing the co-firing ratio of ammonia,the concentration of NO_(x) in the exhaust increases approximately linearly,the concentration of NH_(3) does not increase significantly,and the mass proportion of PM_(1~10) increases.When the co-firing ratio of ammonia is lower than 40%,the concentration of NH_(3) in the exhaust is not higher than 2 mg/m^(3),with no ammonia slip,but the combustion of pure ammonia will lead to a sharp increase in the concentration of NH_(3) in the exhaust.The mixing mode of ammonia will also affect the NO_(x) concentration in the exhaust.When the difference between the ammonia injection speed and the primary air speed is larger,the mixing between materials is more uneven,and the NO_(x) concentration in the flue gas is lower.Compared with the lower speed ammonia injection,the NO_(x) concentration in the flue gas can be reduced by 200 mg/m^(3).Biomass co-combustion with a large proportion of ammonia has no significant ammonia slip,and it is expected to reduce the NO_(x) concentration in the flue gas by adjusting the ammonia injection mode(especially the ammonia injection speed),which is a potential carbon reduction technology route for boilers.