NO氧化耦合灰钙循环(半干法)脱除试验

NO removal experiment of oxidation coupled ash-calcium recycling( semi dry method)

为实现多污染物协同脱除且避免湿法吸收工艺存在的问题,基于低温氧化脱硝结合灰钙循环脱硫除尘提出一种半干法烟气多污染物一体化脱除工艺。针对该工艺中的NO脱除开展试验研究,采用固定床和液相吸收试验装置,研究低温条件下钙基吸收剂对NOx的吸收特性,在气体快速床工业试验装置上进行脱硝验证。结果表明,在相对湿度40%~60%、O2含量5%、70~80℃条件下,固定床NO2钙基吸收率在20%~30%;在NO2浓度200×10^-6、Ca(OH)2悬浮液浓度1%、O2含量5%、70℃条件下,液相吸收平均脱硝率大于90%。反应温度和相对湿度是影响NO2钙基吸收的关键因素,在试验条件下,反应温度越低、相对湿度越高,钙基吸收剂对NO2的脱除率越高;低浓度范围内NO2初始浓度变化对脱硝效果影响较小。在进口NO浓度231~423 mg/m^3、吸收温度75℃、氧化温度140℃、[O3]/[NO]=0.9~1.8条件下,在工业试验装置上钙基吸收剂对NOx的吸收率为83%~89%,NO氧化率为74%~97%,总脱硝率为66%~87%。氧化率和脱硝率随[O3]/[NO]的增加呈上升趋势,氧化后NO浓度及装置出口NOx浓度则随之减少。因此,在一定范围内[O3]/[NO]越高,脱硝效果越好,但臭氧逃逸也随之增多,实际操作时需根据现场情况选用合理工艺参数。根据脱硝产物红外表征结果,NO2与Ca(OH)2发生中和反应生成硝酸盐、亚硝酸盐。3种方法的脱硝率存在以下规律:湿法(液相吸收)>半干法(气体快速床)>干法(固定床),半干法与湿法接近。结果主要受增湿方式的影响,即液态水的存在及相对量是影响吸收反应的关键因素。这是因为有水分存在条件下,NO2与Ca(OH)2间的反应形式将由气固非均相反应转变为快速离子化反应。因此反应器内水分越多,相对湿度越大,吸收反应速率随之提高,脱硝率也越大。最低NOx排放浓度30 mg/m^3,达到超低排放水平,实现了同一装置多污染物的高效协同脱除。氧化耦合灰钙循环烟气净化技术适用于中小型燃煤烟气治理。

In order to achieve the coordinated removal of multi pollutants and avoid the problems of wet absorption process,a semi dry flue gas multi pollutant integrated removal process was proposed based on the combination of low temperature oxidation denitrification and ash calcium cyclic desulfurization and dust removal.The NO removal experiment on pollutants integration removal process of oxidation coupled ash-calcium cycle was carried out.The calcium absorption characteristics of calcium based absorbers for NOxat low temperature were investigated in fixed bed and liquid-phase experimental device.The de NOxeffect was verified on gas-fast-bed industrial test device.The results show that the absorption rate of NO2 calcium base is 20%-30% in fixed bed,under the conditions of 70-80 ℃,O25%,RH 40%-60%.The average denitrification rate of liquid absorption is more than 90%,at NO2 concentration 200×10^-6,Ca( OH)2 suspension concentration 1%,70 ℃,O2 content of 5%.Reaction temperature and relative humidity are the key factors affecting the absorption of NO2.Under the experimental conditions,the lower the reaction temperature is and the higher the relative humidity is,the higher the removal rate of NO2 by calcium based absorbers is;the change of NO2 initial concentration in the low concentration range has little effect on the denitrification effect.Under the condition of inlet NO concentration 231-423 mg/m^3,absorption reaction temperature75 ℃,oxidation temperature 140 ℃,[O3]/[NO]0.9-1.8,the NOxcalcium absorption rate is 83%-89%,NO oxidation rate 74%-97%,and the total de NOxrate 66%-87%in the industrial test device.The oxidation rate and denitration rate increase with the increase of [O3]/[NO],and the concentration of NO and NOxat the outlet of the device decreases after oxidation.Therefore,in a certain range,the higher [O3]/[NO]is,the better the denitration effect is,but the ozone escape increases. In actual operation,the reasonable process parameters should be selected according to the site conditions.According to the denitration products IR results,NO2 reacts with Ca( OH)2 to form nitrate and nitrite.The de NOxrate of the three methods is as follows: wet method( liquid absorption) > semi dry method( gas fast bed) > dry method( fixed bed),and the gas fast bed is close to liquid-phase.The results are mainly affected by the way of humidification,that is,the existence and relative amount of liquid water are the key factors affecting the absorption reaction. This is because the reaction form between NO2 and Ca( OH)2 will change from gas-solid heterogeneous reaction to rapid ionization reaction in the presence of water.Therefore,the more moisture and relative humidity in the reactor is,the higher the absorption rate and the denitrification rate is.The lowest NOxemission concentration is 30 mg/m^3,reaching the ultra-low emission level.It realized the high-efficiency collaborative removal of multi-pollutants in the same device.The flue gas purification technology with oxidation coupled with ash calcium circulation is suitable for the treatment of small and medium-sized coalfired flue gas,and has a broad application prospect.