典型高碱煤灰对氨煤混燃中氨氧化反应特性的影响

Effects of high-alkali coal ash on NO_(x)formation characteristicsduring ammonia and coal co-firing process

氨能作为一种零碳燃料,取代部分煤炭混燃可有效降低电厂原有污染物排放,促进燃煤电厂向煤氨混燃电厂的转型。但由于氨能中含氮量过高,导致NO_(x)排放问题备受关注。在复杂的氨煤混燃过程中,有必要探索NO_(x)排放与煤灰之间存在的关联性。燃煤电厂中高碱煤作为一类开发应用前景广阔的煤种,其中高含量的金属氧化物对氨氧化反应的排放特性却鲜有研究。为探讨氨煤混燃过程中不同种类高碱煤灰对氨氧化反应排放特性的影响,通过搭建立式管式炉氨氧化反应试验平台进行变工况分析,对比不同温度下各类煤灰表面NH_(3)转化率及NO生成率两大指标,从试验结果和反应机理2个层面阐述了煤灰中各类金属氧化物对氨氧化反应排放特性的影响。结果表明:煤灰中主要金属氧化物CaO、MgO及Al_(2)O_(3)可促进氨煤混燃过程中煤灰表面气固氨氧化反应的进行,提高NH_(3)转化率。400~600℃,煤灰对NH_(3)转化率的促进作用依次为:HM-2>HM-1>CJ>AKS>EERDS,与煤灰中CaO含量由高到低的排列顺序对应,与MgO排序基本吻合。且这3类金属氧化物均可促进NH_(3)向NO定向转化,以CaO催化效果最显著,其中,Ca含量最高的HM-2对NO生成的选择性相较于空白组而言可提高67.86%。CaO和MgO可促进NH_(3)和NO在催化剂表面氧化,有利于N_(2)O快速产生,使N_(2)O生成温度提前,而Na_(2)O和Fe_(2)O_(3)的存在则抑制NH_(3)氧化,促进NH_(3)还原NO。

Ammonia can be used as a zero-carbon fuel to replace part of coal for co-firing process,which can effectively reduce the original pollutant emissions of power plants and promote the transformation of coal-fired power plants to coal and ammonia co-firing power plants.However,due to the high nitrogen content in ammonia,the problem of NO_(x)emission has attracted much attention.In the complex coal and ammonia co-firing process,the correlation between NO_(x)emissions and coal ash is also worthy of further exploration and analysis.High-alkali coal in coal-fired power plants is a kind of coal with broad development prospects,but the emission characteristics of high-content metal oxides on ammonia oxidation reaction are rarely studied.In order to explore the influence of different kinds of high-alkali coal ash on the emission characteristics of ammonia oxidation reaction during the coal and ammonia co-firing process,an ammonia oxidation reaction test platform was built to analyze the variable working conditions,and the two indexes of NH_(3)conversion rate and NO generation rate on the surface of various types of coal ash at different temperatures were compared.The specific influence of various metal oxides in coal ash on the emission characteristics of ammonia oxidation reaction was expounded from two aspects of test results and reaction mechanism.The results show that the main metal oxides CaO,MgO and Al_(2)O_(3)in coal ash can promote the gas-solid ammonia oxidation reaction on the surface of coal ash during the coal and ammonia co-firing process,and improve the NH_(3)conversion rate.At 400-600℃,the promoting effect of coal ash on the conversion rate of NH_(3)is as follows:HM-2>HM-1>CJ>AKS>EERDS,which corresponds to the order of CaO content in coal ash from high to low,which is basically consistent with the order of MgO.In addition,the above three kinds of metal oxides can promote the directional conversion of NH_(3)to NO,and the catalytic effect of CaO is the most significant.Among them,the selectivity of HM-2 with the highest Ca content to NO formation can be increased by 67.86%compared with the pure gas phase ammonia oxidation reaction.CaO and MgO can promote the oxidation of NH_(3)and NO on the catalyst surface,which is conducive to the rapid production of N_(2)O the advance of N_(2)O formation temperature.However,the presence of Na_(2)O and Fe_(2)O_(3)has an inhibitory effect on the oxidation reaction of NH_(3),and it has excellent performance in promoting the reduction of NO by NH_(3).Among them,the mechanism of Na_(2)O and Fe_(2)O_(3)promoting NO reduction is not the same.