氨作为零碳燃料和良好的储氢介质,近年来引起广泛关注。未来在燃煤电厂掺烧零碳燃料是碳减排的重要途径。在空气深度分级模式下,对氨煤掺烧进行了数值模拟,讨论了煤燃烧区域不同过量空气系数α工况下炉内的温度场、组分浓度场及NOx排放情况,而各工况总的过量空气系数均维持在1.2。模拟了4个燃烧工况(α=0.696、0.840、0.912、0.996)。对温度场的统计结果表明,随α降低,煤粉燃烧第1阶段的着火位置提前,但形成的高温火焰长度缩短,喷氨口附近的温度更低。在α=0.696工况下,可明显区分出煤粉火焰和氨燃烧火焰。随α提高,二者界限逐渐模糊。α降低有助于在氨燃料喷入上游形成一个较长的还原区,因此氨发生氧化反应的概率降低。但随α降低,炉内燃尽情况降低,CO排放浓度、飞灰含碳量及氨逃逸量提高。炉内NOx浓度统计结果表明,随α降低,NOx排放水平显著降低。进一步对炉内H2浓度进行统计,发现α=0.696工况下,炉内最高H2体积分数可达2%,这意味着该工况下氨的分解反应显著增强。由于氨的消耗反应是3个总反应竞争的结果,因此分解反应的增强使氨直接参与氧化的反应减弱。而H2生成的增加也进一步提高了NOx被还原的几率,使炉内NOx排放水平进一步降低。总之,在实际煤粉炉掺氨运行工况下,可通过空气深度分级的方法,调控氨燃烧区域的温度、氧气浓度,实现低NOx排放。

Recently, ammonia has garnered significant attentionaround the world as an effective zero-carbon fuel and hydrogen storage medium. To reduce carbon emissions in coal - fired power plants, the use of zero - carbon fuel blends shows great promise. Investigatesthe combustion behavior of ammonia coal co-firing under the deep-air staging mode. Specifically, the temperature field, component concentration field, and nitrogen oxide emission in the furnace at varying α coefficient conditions are investigated, while maintaining the totalexcess air coefficient at 1.2. The study analyzes four cases with α coefficients equal to 0.696, 0.840, 0.912, and 0.996 respectively. Thetemperature field reveals that as the α coefficient decreases, the ignition position of the first stage of pulverized coal combustion advances.However, the length of the high-temperature flame formed is shortened, and the temperature near the ammonia injection port is notablylower. When α = 0.696, the pulverized coal flame and ammonia combustion flame are distinctly separate, but as α improves, the boundarybetween the two gradually becomes blurred. Decreasing the α coefficient forms a longer reduction zone upstream of ammonia fuel injection,leading to a lower oxygen concentration of ammonia fuel at the moment of injection, hence reducing the probability of ammonia oxidationpath. However, as the α decreases, there is a corresponding decrease in burnout in the furnace,which includes CO emissions concentration, fly ash carbon content, and ammonia escape. However, the influence is very limited in this simulation. Statistical analysis ofNOx concentration in the furnace showed that NOx emissions significantly decreased as α decreased. Furthermore, the highest H2 concentration in the furnace reached 2% under α = 0.696, led to a significant enhancement of ammonia decomposition reaction. Since the consumption reaction of ammonia depends on three global reactions, improved decomposition reaction can reduce the direct participation inoxidation for ammonia. Increased H2 production also enhances the possibility of nitrogen oxide reduction, leading to further decreases inNOx emissions. Ultimately, utilizing the air depth classification method can optimize the temperature and oxygen concentration within theammonia combustion area, contributing to achieve the low NOx emissions in the furnace.

0 引言

1 模拟对象与方法

   1.1 模拟系统

   1.2 计算模型

2 模拟结果分析

   2.1 空气分级对温度分布的影响

   2.2 空气分级对组分分布的影响

   2.3 空气分级对NOx排放的影响

3 结论