CAS OpenIR
低温烟气钢渣联合脱硫脱硝过程强化工艺与机理研究
孟子衡
Thesis Advisor李会泉
2020-07-01
Degree Grantor中国科学院大学
Degree Name博士
Degree Discipline化学工艺
Keyword钢渣,脱硫脱硝,H2o2,催化氧化,复合助剂
Abstract

非电行业的烟气温度低(<300°C)、成分复杂,导致传统的SCR脱硝催化剂(300−450 °C)难以直接用于非电烟气NOx的高效脱除。工业固废用于烟气污染物的净化,可以实现多污染物的协同治理。钢渣法脱硫已经实现了工业化稳定运行,脱硫的同时具有一定脱硝效率,但是脱硝率偏低。本文针对低温烟气NOx难以高效脱除和钢渣高值化利用水平低的问题,提出了NO气固相催化氧化-还原性助剂强化NO2吸收的钢渣联合脱硫脱硝整体路线,以钢渣为NO氧化催化剂和脱硫脱硝吸收剂,开展了钢渣脱硝机理分析、钢渣基NO高效催化剂制备、NO2强化吸收助剂开发和尾渣废水的资源化利用等方面的研究,形成了低温烟气钢渣联合脱硫脱硝与资源化利用一体化新工艺。主要研究内容和结论如下:(1)开展了钢渣脱硝机理研究。考察了钢渣在弱酸性条件下的浸出规律,结果表明随着浆液pH值不断降低,Ca2+、Mg2+和Mn2+的浸出浓度不断增加;采用小型鼓泡反应器考察了工艺条件对脱硝率的影响,结果表明增大OR值和SO2浓度,均有利于NOx的脱除,优化条件下脱硫脱硝效率分别达到100%和83.4%;进一步开展了钢渣脱硝机理研究,结果表明Mn2+的存在促进NOx的脱除,液相中Mn2+可以与NO2发生氧化还原反应生成Mn3O4和MnO(OH),从而促进NOx的脱除。在此基础上,得出了钢渣体系下NO2的脱除路径包括:1)NO2的水解反应;2)液相中还原性的Mn2+、S(IV)与NO2的氧化还原反应。(2)开发了用于H2O2氧化NO为NO2等高价态NOx过程的酸化钢渣催化剂,研究了催化剂的制备工艺,得到了优化制备条件为:酸化介质为盐酸,酸化程度为70%;开展了催化剂表征,结果表明酸化钢渣表面富集了Fe物种(FeOSi等)、2−4 nm的多孔C-S-H和SiO2凝胶以及SiOAl等活性位点,催化活性与2−4 nm的多孔C-S-H凝胶的数量有关;开展了催化氧化工艺优化,优化条件下运行36 h表明,NO转化率稳定在90%以上,SO2平均转化率<1.8%;进一步开展了催化机理研究,发现酸化钢渣表面分散Fe(III)的多孔C-S-H和SiO2凝胶(FeOSi)是高催化活性位点,能够催化H2O2产生∙OH和HO2∙/O2∙−,将NO氧化为NO2、HNO3和N2O5。(3)筛选了适用于钙基体系下的低成本NO2强化吸收复合助剂(等摩尔量的硫代硫酸钠和硫酸铵组成),开展了工艺条件优化,优化条件下运行24 h表明,脱硫率100%,脱硝率稳定在78.0%左右;当NO2−浓度达到3.0 mol/L时,脱硝率仍能保持在70.0%以上,表明复合助剂能够耐受高浓度NO2−;进一步开展了复合助剂强化脱硝机理研究,发现复合助剂中的S2O32−、NH4+和钢渣中浸出的Mg2+对NOx的脱除具有协同作用,S2O32−作为还原剂和MgSO30的氧化抑制剂促进了NO2的脱除,NH4+有效抑制了脱硝产物(NO2−)分解为NO和NO2,有利于NOx的脱除。(4)开展了钢渣脱硫脱硝尾渣和废水的资源化利用研究,结果表明尾渣中的f-CaO等含量极低,无安定性问题,以尾渣为原料制备的水泥和免烧砖产品性能均能达到国家标准;废水通过蒸氨-pH调控除杂-碳碱沉淀脱钙-结晶提纯分离工艺,实现了杂质脱除、亚硝酸盐回收以及脱硝助剂循环利用,回收的亚硝酸钠产品纯度达到国家标准。在此基础上,进一步开展了整体工艺设计和经济性核算,结合目前成熟的焦炉烟气低氮燃烧技术可以实现焦炉烟气超低排放。在工业化中试装置中对复合助剂强化脱硝效果进行了验证,结果表明SO2脱除率稳定在99%左右,NOx脱除率稳定在50%左右,进一步验证了复合助剂的可靠性。;The flue gas from non-thermal power industries exhibits low flue gas temperature (<300°C) and complex composition, which limits the utilization of the traditional SCR denitration catalyst (300−450 °C) for NOx removal from the flue gas of non-thermal power industries. Industrial solid waste can be used for the purification of flue gas pollutants, which can achieve the co-processing of multiple pollutants. The wet desulphurization using steel slag has been operated stably in industrial-scale devices, in which a certain amount of denitration efficiency is observed together with desulphurization. However, the denitration efficiency is relatively low. In this dissertation, according to the two problems that NOx from low-temperature flue gas cannot be removed efficiently and the value-added utilization of steel slag is insufficient, an integrated technology of catalytic NO oxidation via gas-solid catalytic reactions combined with NO2 absorption enhanced by reductive additives for simultaneous desulphurization and denitration using steel slag was proposed. In this technology, steel slag was a catalyst for NO oxidation and absorbent for desulphurization and denitration. The mechanism analysis of NOx removal by steel slag, the preparation of steel slag-based catalysts for NO oxidation, the development of additives to enhance NO2 absorption, and the resource reuse of tailings and wastewater from desulphurization and denitration using steel slag were investigated. As a result, a new technology of simultaneous desulphurization and denitration from low-temperature flue gas using steel slag combined with the resource reuse was proposed. The main contents and conclusions are as follows: (1) The mechanism of NOx removal by steel slag was investigated. The leaching behavior of steel slag under weak acid conditions was investigated. Results showed that the leaching concentrations of Ca2+, Mg2+, and Mn2+ increased constantly with the decrease of slurry pH. The effects of reaction conditions on NOx removal in a bubbling reactor were investigated. Results showed that the increases of OR (ratio of NO2 to NOx) and SO2 concentration promoted NOx removal, and 100% SO2 removal efficiency and 83.4% NOx removal efficiency under the optimal condition were obtained. The mechanism of NOx removal by steel slag was investigated. Results showed that the existence of Mn2+ promoted NOx removal, and Mn2+ in liquid phase could react with NO2 and produced Mn3O4 and MnO(OH), thereby enhancing NOx removal. Based on the above results, the route of NO2 removal in a steel slag system could be summarized as follows: 1) The hydrolysis reaction of NO2; 2) The redox reactions of NO2 with the reducing Mn2+ and S(IV) in liquid phase. (2) Acidized steel slag catalysts for catalyzing H2O2 to oxidize NO into NO2 or other high-valence NOx were developed. The preparation conditions of catalysts were investigated, and the optimal preparation condition (acid type: HCl solution, acidification degree: 70%) was obtained. The catalyst was characterized, and results showed that the active sites including Fe species (FeOSi et. al.), porous C-S-H and SiO2 gels with 2−4 nm pore, and SiOAl were enriched on acidized steel slag, and the catalytic activity of acidized steel slag was related to the number of the porous C-S-H gels with 2−4 nm pore. The catalytic oxidation conditions were optimized, and within 36-h test, NO conversion of >90% and average SO2 conversion of<1.8% under the optimal condition were obtained. Mechanism study indicated that Fe(III) effectively dispersed into porous C-S-H and SiO2 gels was the highly active site, and the produced ∙OH and HO2∙/O2∙− could oxidize NO into NO2, HNO3, and N2O5. (3) Low-cost compound additives (consisting of the equal molar of sodium thiosulfate and ammonium sulfate) to enhance NO2 absorption were screened, which could be used for wet Ca-based desulphurization systems. Reaction conditions were optimized, and within 24-h test, 100% SO2 removal efficiency and 78.0% NOx removal efficiency under the optimal condition were obtained. When NO2− concentration was 3.0 mol/L, NOx removal efficiency was kept at >70.0%, indicating that the compound additive could tolerate high NO2− concentrations. Mechanisms of the compound additive to enhance denitration were investigated. Results indicated that S2O32− and NH4+ in the compound additive and Mg2+ leached from steel slag had a synergistic effect for NOx removal, in which S2O32− acted as a reducing agent and an oxidation inhibitor of MgSO30 enhanced NO2 removal. NH4+ inhibited the denitration product (NO2−) from decomposing into NO and NO2, thereby accelerating NOx removal. (4) The resource reuse of the tailings and wastewater from the desulphurization and denitration using steel slag was investigated. Results indicated that the content of f-CaO in the tailings was very low, and there was no stability problem of the tailings. As a result, the performance of the cement and baking-free brick products prepared with the tailings as raw materials could meet the national standards. A technology of ammonia distillation-pH adjustment-precipitation-crystallization was proposed to achieve impurities removal, nitrite recovery and recycling of denitration additives, and the purity of the recovered sodium nitrite product reached the national standard. Based on the above results, the technological design and economic calculation of the integrated technology were further carried out, and this technology combined with the current mature low-nitrogen combustion technology of coke oven flue gas could achieve the ultra-low emission of coke oven flue gas. In the industrial plant, the denitration performance of the compound additive was verified. Results showed that SO2 and NOx removal efficiencies were stable at about 99% and 50%, respectively, and the reliability of the compound additive was further verified. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/49702
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
孟子衡. 低温烟气钢渣联合脱硫脱硝过程强化工艺与机理研究[D]. 中国科学院大学,2020.
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