Mechanisms of Ultra-low NOx and High Efficiency De-SOx in CO_2 Recycled Coal Combustion

CO_2再生煤由于其易于回收、极低的NOx排放和高的炉内脱硫效率而具有广阔的应用前景。研究了在CO_2循环煤燃烧中同时还原CO_2/NOx/SOx的可行性，以期开发一种新型的环保燃煤技术。通过实验确定，该系统排出的氮氧化物量减少到传统空气燃烧排出量的四分之一以下。利用循环CO_2对煤与空气燃烧总NO减少的贡献如下：1。炉内CO_2浓度的提高在10%以下效果不显著。2. 燃料氮与再生NO相互作用的影响为10 ~ 50%。3. 还原炉内再生NO的效果占主导地位，达到50-80%。理论仿真也证实了这一结果的有效性。通过实验和模拟，阐明了脱硫的特点和机理。CO_2循环煤燃烧的脱硫效率约为空气中燃烧的3倍，且受CaSO_4分解的影响较小。脱硫效率高的主要原因是：1。烟气再循环导致炉内SO_2浓度过高；2. 高SO_2浓度导致CaSO_4分解减少。CO_2再生煤燃烧是实现CO_2/NOx/SOx同时还原的一种很有前途的系统。

CO_2 recycled coal combustion is promising because of its easy CO_2 recovery, extremely low NOx emission and high in-furnace desulfurization efficiency. The feasibility of simultaneous CO_2/NOx/SOx reduction in CO_2 recycled coal combustion was studied in order to develop a novel environmentally favorable coal combustion technology.It was identified through experiments that the amount of NOx exhausted from the system is reduced to less than about one fourth of that exhausted with conventional air combustion. The contributions to the total NO decrease from coal combustion with air caused by the use of recycled CO_2 are as follows : 1. The effect of an increase of CO_2 concentration in the furnace is not significant below 10%. 2. The effect of interaction between fuel-N and recycled NO is 10-50 %. 3. The effect of a reduction of recycled NO in the furnace is dominant and amounts to 50-80%. Theoretical simulation also confirmed the validity of this result. The characteristics and mechanism of desulfurization were clarified through experiment and modeling. The desulfurization efficiency in CO_2 recycled coal combustion is about three times as high as that with coal combustion in air and does not suffer so much from CaSO_4 decomposition. The high desulfurization efficiency is mainly attributed to : 1. high concentration of SO_2 inside furnace owing to the recirculation of gases ; 2. decrease in CaSO_4 decomposition resulted from high SO_2 concentration. CO_2 recycled coal combustion was identified to be a promising system with which simultaneous reduction of CO_2/NOx/SOx can be realized.