我国是以燃煤发电为主的国家，为减少燃煤电厂CO₂排放，发展替代燃煤的低碳燃料及相应的燃烧技术十分迫切。与氢气相比，氨的储存和运输成本低，也更加安全可靠，是一种更具发展潜力的能源载体和载氢低碳燃料。以氨替代部分燃煤，采用氨与煤在锅炉中混合燃烧的方式，是现阶段降低燃煤机组CO₂排放一个现实可行的技术选择。为在工业尺度燃煤锅炉验证氨煤混合燃烧技术的可行性，设计搭建了世界最大容量的40 MWth燃煤锅炉氨煤混合燃烧试验系统，包括全尺度氨煤混燃燃烧器和氨气供应系统，并在此试验台实现了0～25%混氨比例（按热值）的氨煤混合燃烧试验。结果表明，在所有混氨比例下锅炉皆具有良好的稳燃与燃尽性能，且氨煤混燃条件下煤粉的燃尽优于纯燃煤工况；通过分级燃烧，在高混氨比例下可实现锅炉NO_x排放低于燃煤工况。然而，燃尽风率大于20%后，进一步增加燃尽风率对降低NO_x排放效果不显著，但会显著增大锅炉的CO排放和飞灰含碳量，影响锅炉效率。因此，燃煤锅炉氨煤混合燃烧存在最优燃尽风率，使锅炉NO_x排放与燃尽均处于较优水平。锅炉运行氧量对NO_x排放和NH₃燃尽有显著影响，随运行氧量降低，锅炉NO_x排放显著下降，而NH₃排放快速上升；存在一个锅炉最佳运行氧量区间，在此区间内锅炉NO_x与NH₃排放皆可保持在较低水平。工业尺度试验研究验证了燃煤锅炉氨煤混合燃烧技术的可行性，发现了影响锅炉燃尽与NO_x排放的关键影响因素，为我国燃煤机组实现大幅度CO₂减排提供了一条极具潜力的技术发展方向。

China is a country dominated by coal-fired power generation. In order to reduce the CO2 emissions of coal-fired power plants,it is important to develop low-carbon alternative fuels and corresponding combustion technologies. Compared with hydrogen,ammonia has considerably lower storage and transportation costs,and is safer and more reliable. Thus,it is considered as a better energy carrier and carbon-free fuel. It is a more practical and feasible technical route to reduce CO2 emission of coal-fired boilers at this stage by replacing part of pulverized coal with ammonia and cofiring coal with ammonia in the boiler. In order to examine the technical feasibility of ammonia cofiring in coal-fired boilers,the world′s largest 40 MWth ammonia-coal cofiring test facility equipped with a full-scale ammonia-coal cofiring burner and ammonia supply system was designed and fabricated, and the cofiring tests of 0-25% ammonia cofiring ratios (calorific value) were conducted on this facility.The results show that the boiler can establish stable ignition and combustion at all ammonia cofiring ratios,and the char burnout of ammonia cofiring cases is better than that of pure coal combustion cases. With air-staging combustion,the boiler NOx emission can be controlled lower than that of coal combustion case at high ammonia cofiring ratios. However,at overfire air rates higher than 20%,the further increase of overfire air rate has no significant effect on the NOx emission,but significantly increase the boiler CO emission and the unburned carbon content in fly ash,and hence,reduce the boiler efficiency. Therefore,there is an optimal overfire air rate at which both the NOx emission and char burnout can be kept at low level. The boiler excess O2 level also has significant impacts on boiler NOx and NH3 emissions. With the decrease of excess O2,the boiler NOx emission decreases significantly,while the NH3 emission increases rapidly. Thus,there is an optimal range of excess O2 within which the boiler NOx and NH3 emissions can be both kept at low level. The industrial scale test in this paper verifies the feasibility of ammonia-coal cofiring technology in coal-fired boilers,reveals the key parameters that affect boiler NOx emission and fuel burnout,and provides a promising technical advancement direction for the coal-fired power plants to achieve signification reduction of CO2 emissions.

0 引言

1 40 MWth氨煤混合燃烧试验系统

   1.1 氨煤混合燃烧系统与供风系统

   1.2 氨燃料供应系统

2 氨煤混合燃烧试验

   2.1 混氨比例的影响

   2.2 锅炉燃尽风率的影响

   2.3 锅炉运行氧量的影响

3 结论