氧化法烟气脱硫脱硝废水回收NaNO2工艺

Recovery technology of NaNO2 from flue gas desulfurization and denitration wastewater by an oxidation process

针对氧化法烟气脱硫脱硝废水中含大量亚硝酸盐造成水体污染及有价盐资源浪费问题,回收废水中的NaNO2,提出pH调控除杂-碳碱沉淀脱钙-结晶提纯分离工艺,分别考察了pH值、除钙剂投加方式、浓缩总盐浓度和结晶温度对废水中NaNO2结晶率和纯度的影响。结果表明,pH值和浓缩总盐浓度是影响脱硫脱硝废水中Na NO2结晶率及纯度的主要因素。在除杂pH=11、除钙剂湿投、浓缩总盐浓度70wt%、结晶温度50℃的条件下,NaNO2结晶率大于60%,产品质量达到GB/T 2367-2016标准。

The wastewater from the processes of desulfurization and denitration contained complex components, and the recovery of wastewater was limited by the co-existence of nitrates and nitrites. By now, this type of wastewater was mostly directly discharged after a simple treatment or was sent to the sewage treatment plant for further disposal, leading to series ofenvironmental problems or causing instability of biochemical section in sewage treatment plants. Moreover, the cost of the recovery process will decrease via recovering the nitrogenous valuable salt. In this work, a low-cost process with high efficiency of desulfurization and denitration was developed. There were only nitrite ions as nitrogen-containing anions in the wastewater of desulfurization and denitration. Using steel slag slurry combined with ozone oxidation, this process achieved high desulfurization and denitration rate with accessory ingredient of Na2S2O3. There w ?? ere cations such as Na+, Mg2+, Ca2+, Mn2+, Fe2+, etc. and anions such as NO-2, S2 O2-3, SO2-4, etc. existing in the as-generated wastewater. The water pollution and marketable salt resources waste from wet flue gas desulfurization and denitration via a gas phase oxidation-wet absorption process was mainly solved in this work. A technology of pH adjustment-decalcification via adding sodium carbonate-evaporating crystallization to recovery NaNO2 from wastewater was proposed. The effects of pH, addition methods of sodium carbonate, concentrated total salt concentration, and crystallization temperature on the crystallization rate and purity of NaNO2 were discussed. The results indicated that the crystallization rate and the purity of NaNO2 from desulfurization and denitration wastewater were mainly affected by pH and total concentrated salt concentration. Under the optimal conditions, in which pH was 11, addition method of sodium carbonate was concentrated solution, total concentrated salt concentration was 70 wt%, and crystallization temperature was 50℃, the crystallization rate of NaNO2 was greater than 60%. The products of NaNO2 met the quality requirement of national standard(GB/T 2367-2016).