改性生物质焦脱硝及协同钙基循环脱碳的机理研究

Recently, China has simultaneously suffered from the most serious NOx contamination and greenhouse effect from CO2 emission in the world. Our country is facing the double challenges of environmental protection and fulfilling the obligations of carbon emission reduction. To solve the problems such as more complex system, and higher investment and operation cost caused by flue gas disposing separately, an innovative idea which has a practical prospect of high efficiency and economy, is proposed to combine the calcium looping (Ca-L) and char-NO (CARBONOx) technologies using biochar to realize the synergistic removal of NOx and CO2 from coal combustion flue gas. Through the combination of experiment study, theoretical analysis and modeling methods, the proposed project will systematically investigate the ways and the mechanisms of improving the reactivity and selectivity of the biochar reaction with NO. Effects of the biomass type, pyrolysis temperature, nitrogen adding quantity, and oxygen concentration on the denitration performance of modified biochar will be studied thoroughly. Experimental research will be conducted to investigate the characteristics and trends involved in synergistic removal of NOx and CO2 in the carbonation reaction atmosphere to develop the technical system of synergistic removal from coal combustion flue gas. Synergistic mechanisms of CaO-CO2 and modified biochar-NO under the effects of the reaction temperature, flue gas concentrations, and cycling number will be revealed. A kinetic reaction model will be established to obtain the optimum conditions for simultaneous removal of NOx and CO2 with high efficiency and low coats. The outcome of this proposed project is anticipated to provide a sound theoretical basis and valuable guidance for greenhouse gas reduction and at the same time to reduce air pollution.

我国是世界最大的NOx污染国和CO2排放国，面临着保护环境与履行碳减排任务的双重压力。针对污染物排放单独治理造成的系统复杂、投资和运行成本高等问题，本项目提出在钙基循环（Ca-L）工艺的碳酸化反应器中应用改性生物质焦异相还原NO（CARBONOx）技术来实现燃煤电厂高效经济联合脱硝脱碳。采用实验研究、理论分析与建模相结合的方法，探明提高生物质焦还原NO的反应活性和选择性的方法和机理，获得生物质种类、制焦温度、渗氮量和氧气浓度等因素对改性生物质焦脱硝性能的影响规律。研究Ca-L/CARBONOx工艺中改性生物质焦脱硝和CaO脱碳的协同反应机制，建立协同脱硝脱碳的反应动力学模型，揭示反应温度、烟气成分、循环次数等因素对改性生物质焦脱硝和CaO脱碳的协同作用规律。高效率、低成本、同步地解决燃煤烟气的NOx和CO2排放问题，为我国防治大气污染和温室气体减排提供重要的理论基础和科学依据。

我国面临保护环境与双碳目标的双重压力，针对污染物单独治理系统复杂、投资和运行成本高等问题，项目提出在钙基循环（Ca-L）的碳酸化反应器中应用改性生物质焦异相还原NO（CARBONOx）技术来实现燃煤电厂高效经济联合脱硝脱碳。主要研究成果包括：（1）分别用椰壳、花生壳、杉木、榆木、竹子和市政污泥制焦，研究发现，焦-NO异相还原可分为动力学控制区和扩散控制区。由松柏醇和芥子醇衍生单元组成的木质素将在焦表面形成更多的含氧官能团和羟基。动力学控制区中，榆木焦有最高的NO还原率和最强的抗氧化性。松柏醇型木质素成焦孔隙发达，吸附性能好，可改善扩散控制区NO的还原。随着氧气浓度增加，焦表观活化能在NO还原阶段不断增大。氧气在焦-NO反应中，加快动力学控制区的反应速率，而在扩散控制区促进作用受浓度影响。（2）生物质焦经NH3热处理能够有效在焦表面引入N元素，渗氮改性焦-NO反应活性和抗氧化性能有效提高。酸洗脱灰显著优化了焦的孔隙结构，从而增加了焦的氨化作用，引入大量含氮官能团，提升生物质焦的反应活性和选择性。（3）通过醋酸改性的元素调控，提高了钢渣源钙基材料的碳捕集能力和循环稳定性。经介孔材料包覆钛改性的钢渣钙基吸收剂煅烧后形成CaTiO3在其中有间隔作用，有效减少吸收剂在高温下的烧结和融合。（4）应用花生壳焦及其改性焦实现了高效脱硝脱碳，同时减少了CO浓度的排放。氧气浓度的增加会加速焦的消耗，同时C-O2反应生成更多CO2导致CaO吸收压力增大，使得CaO催化作用减弱。渗氮改性能够减少联合脱硝脱碳过程中CO的释放。随着氧气浓度的增加，改性焦联合脱硝脱碳的优势愈发明显。随着钙循环次数增加，CaO发生烧结，其对焦还原NO的催化作用减弱，脱硝性能降低。CaO对酸洗渗氮焦还原NO几乎没有催化作用，改性焦的脱硝性能基本不受钙循环次数的影响。（5）碳酸化反应器内生物质焦和CaO两种燃料密度不同，且易出现流化分层。项目提出了基于希尔伯特-黄变换（HHT法）的混合/分离识别方法。