随着国家对燃煤电厂污染物排放要求愈加严格，燃煤电厂几乎都安装了SCR烟气脱硝装置处理烟气中NOx。正常运行的SCR烟气脱硝装置脱硝效率为80%～90%。但在超低排放要求下，部分燃煤机组锅炉SCR运行实际脱硝效率高达95%，导致氨逃逸控制难度急剧增大。综述了国内外燃煤电站锅炉SCR脱硝后飞灰中NH4HSO4的形成与脱除，分析其形成机制以及脱除方法，对其工业应用进行了展望。研究表明粉煤灰对单质氨的吸附能力有限，但烟气中SO3与H2O的存在可促使灰中氨含量升高，NH3、SO3浓度和煤种是影响灰中氨含量的主要因素。粉煤灰脱氨技术按原理可分为加热法、氧化法、水洗法以及加碱法等。204 ℃下，粉煤灰中氨的脱除十分缓慢，处理80 min，氨脱除率小于50%，因而加热法需在260 ℃进行，能耗较高。灰中含水量高于3%时，氨脱除速率很高，但在随后的干燥阶段，灰中含水量降至2%以下后，氨脱除速率迅速下降，同时水洗法会产生额外的废水；氧化法是选取合适的催化剂安装在SCR烟气脱硝装置后、空预器前，选择性将烟气中NH3催化氧化成N2，从而有效除去烟气中逃逸的NH3，减少NH4HSO4生成，降低粉煤灰氨含量，但无法保证氧化剂完全与氨反应，导致残余的氧化剂逃逸。向粉煤灰中加入钙基碱和水并搅拌的氨脱除效果很好，向粉煤灰中加入少量水(～2%)和少量碱(≤2%)，粉煤灰中氨质量分数可降至100 mg/kg以下。由于加入的水很少，后续利用机组脱硫后烟气即可干燥，处理过程中产生的NH3可重新喷入SCR烟气脱硝装置或制氨水。加碱法成本低、效率高，是脱除灰中氨的优良方法。目前飞灰中氨含量仍无行业标准，飞灰中氨对于环境及建材利用的影响仍缺乏工程验证，当前飞灰中氨的脱除仍停留在实验室研究与工业小试阶段。未来需要开展全流程的工程验证以及详细的成本核算，从而实现粉煤灰的资源化利用。

Due to the stricter regulations on the emission of pollutants from coal-fired power plants,all coal-fired power plants have installed denitrification devices (SCR) to remove NOx from flue gas in China. Normally,the denitrification efficiency of SCR facility can be 80%-90%. Under the ultra-low emission restriction,the actual denitrification efficiency of SCR operation of some coal-fired boiler is as high as 95%,which will lead to a sharp increase in the difficulty of ammonia escape control. The formation and removal of ammonia hydrogen sulfate in fly ash after SCR denitration of coal-fired power station boilers at home and abroad were reviewed,its formation mechanism and removal methods were analyzed,and its industrial application was prospected. But it is found that the presence of SO3 and H2O in flue gas can promote the adsorption of ammonia in fly ash. The concentration of NH3 and SO3 and coal grade are the main factors affecting the ammonia adsorption on fly ash. The existing fly ash deamination technologies include heating method,oxidation method,water washing method and alkali addition method. At 204 ℃,the removal of ammonia in fly ash is very slow. After treatment for 80 minutes,the ammonia removal rate is less than 50%. The heating method needs to be carried out at 260 ℃,and the energy consumption is high. When the water content in the ash is higher than 3%,the ammonia removal rate is fast,but in the subsequent drying stage,when the water content in the ash drops below 2%,the ammonia removal rate decreases rapidly,and the water washing method will produce additional wastewater;the oxidation method is to select a suitable catalyst and install it behind the SCR Flue gas denitration device and in front of the air preheater to selectively catalyze and oxidize NH3 in the flue gas into N2,so as to effectively remove the escaping NH3 in the flue gas,reduce the generation of NH4HSO4 and reduce the ammonia content of fly ash,but it can not ensure that the oxidant reacts completely with ammonia,resulting in the escape of residual oxidant. Adding calcium base alkali and water to fly ash and stirring can obtain excellent ammonia removal effect. Adding a small amount of water (～2%) and a small amount of alkali (≤2%) to fly ash can reduce the mass fraction of ammonia in fly ash to less than 100 mg/kg. Due to the small amount of water added,the flue gas can be dried after desulfurization of the subsequent unit,and the NH3 generated in the treatment process can be re injected into the SCR Flue gas denitration device or ammonia water. Alkali addition method has low cost and high efficiency. It is an excellent method to remove ammonia from ash. At present,industry standard regarding the ammonia content in fly ash is not issused. Meanwhile,the effect of ammonia in fly ash on environment and its utilization as construction materials still lacks engineering verification testing. At present,the removal of ammonia in fly ash is still in the stage of laboratory research and industrial pilot test. In the future,the detailed economic analysis is also needed to realize its utilization.

0 引言

1 NH4HSO4的生成

   1.1 选择性催化还原技术

   1.2 前体物

   1.3 NH4HSO4生成影响因素

2 粉煤灰对氨的吸附特性

3 含氨粉煤灰脱氨方法

   3.1 加热法

   3.2 水洗法

   3.3 氧化法

   3.4 加碱法

   3.5 脱附氨处理

4 结语及展望