Knowledge Management System Of Institute of process engineering,CAS
|Thesis Advisor||余剑, 吴昊|
本文以工业硫酸锰为前驱体，通过沉淀、洗涤、挤出、煅烧步骤批量制备了高活性颗粒状低温MnOx脱硝催化剂（Φ5×30 mm），并探索其在低硫高湿烟气及含硫低湿烟气两种烟气环境的脱硝应用。首先在天然气冷热电三联供（CCPH）的高含水低含硫烟气开展应用示范，在入口NOx浓度850 – 1000 mg/m³、床层温度145 - 175 °C、空速4405 h-1工况条件下，脱硝率达到87.88 – 97.47%，连续运行1180 h后脱硝效率有约3%的微弱衰减。对长周期运行后催化剂进行取样，进行XRD, BET、SEM和XPS表征及活性测试。结果表明：该催化剂在高湿烟气长时间运行中发生了一定程度的晶型转变，颗粒烧结、尺寸变大、比表面积降低及化学吸附氧减少，导致其脱硝活性降低。针对结构劣化导致的活性衰减，从材料合成出发，制备复合氧化物CeaMnbOx催化剂及其水热、高温劣化样品，并对其进行活性评价及表征。结果表明：氧化铈掺杂可一定程度上降低劣化样品的活性衰减，阻止高温、高湿环境下催化剂发生晶型转变、比表面积降低及化学吸附氧减少等结构劣化，改善了催化剂结构的热稳定性与水热稳定性。因此该锰基催化剂仍在130 - 200 °C低硫环境下具有良好的脱硝应用前景。鉴于颗粒MnOx在含硫烟气中的易失活特性，固定床工艺下虽然可以通过降低空速、选择低SO2浓度烟气等操作延长工作时间，却始终无法实现长周期的脱硝应用。以模拟流化床、多层床实验参数为基础,保持进料速率5 g/min、空速2125 h-1，温度160 °C，考察500 ppm SO2的烟气中颗粒MnOx在四级多层流化床反应器（MSFB）的同时脱硫脱硝性能。结果表明：运行至稳定的24 h内顶层NO转化率和SO2脱除率维持95%以上，而I - IV层的NO转化率和SO2脱除率逐层下降。各层催化剂取样表征结果表明颗粒自上而下流经反应器时其表面活性Mn物种不断被SO2消耗，生成的硫酸盐不断沉积；同时其比表面积、氧化性不断下降直至底层催化剂完全失活。而硫化失活催化剂经氨洗涤-再生催化剂表面硫酸盐消失，新暴露的内层MnOx的氧化性、价态、脱硝活性皆恢复到新鲜催化剂的水平，因此可实现MnOx持续脱硝脱硫-水洗再生的循环利用。;In this paper, industrial low-temperature MnOx granular catalyst (Φ 5 × 30mm) with high activity was successfully prepared with manganese sulfate as precursor, by serial operations of precipitation, washing, extrusion and calcination, to explore its low-temperature denitration application in two different typical flue gas conditions, with high H2O vapor content but little sulfur or a few sulfur but no H2O vapor included.The produced industrial catalyst was firstly applied in the denitration purification of flue gas from Cold, hot & electric triple supply (CCHP) system on the conditions of 850-1000 mg/m3 inlet NOx and 145-175 °C. The NO conversion can achieve to 87.88 – 97.47% under the GHSV of 4405 h-1 and 3% decline of denitration efficiency was observed after use for 1080 hour. The laboratory test also confirmed the reduced activity for the used sample. Moreover, XRD, BET, SEM and XPS results found the crystal transition, sintered particle, gincreased particle size, decreased surface area and reduced chemisorption oxygen for the used MnOx sample, which accounted for the observed decline of denitration efficiency after long term use on the industrial conditions. To deal with the decline of denitration efficiency from the structural degradation, the CeaMnbOx catalyst and samples treated by hydrothermal degradation and high temperature calcination seperately were prepared. And then the characterizations and SCR activities of the fresh and degradatd catalysts were evaluated. It indicated that CeO2 doping can to some extent reduce the activity decline for degraded samples, prevent structural degradations, i.e. crystal transformation, decreased specific surface area and reduced chemisorption oxygen, and improve the structural thermal and hydrothermal stability. Therefore, the Mn-based catalyst still has a good prospect in 130 - 200 ° C low-sulfur flue gas denitration application.Regarding the deactivation of MnOx particles in sulfur-containing flue gas in fixed bed process, although it can be prolonged by lowering space velocity or SO2 concentration of flue gas. Based on the simulated fluidized bed and multi-layer bed , the simultaneous removal of NO and SO2 by MnOx particles was operated in 500 ppm SO2 included flue gas at a four-layer MSFB reactor with a feed of 5g/min, 2125 h-1 and 160 ° C. It showed that the NO conversion and SO2 removal of the top layer maintained above 95% within 24 hours after operation to stability, while the NO conversion and SO2 removal both decreased layer by layer as MnOx particles go through the reator from top to bottom. Further, charactions for samples in different layers demonstrated that the active Mn species from top consumed and the toxic sulfur species-MnSO4 increased, the specific surface area and the oxidizability reduced for layers until the catalyst get to the bottom and completely deactivated. As for the regenaration of deactivated MnOx, the sulfates on surface disappeared and the oxidation ability, valence and NO activity of the newly exposed MnOx recovered to the same as fresh catalyst after ammonia washing. We can deduced that the recycling of MnOx catalyst could be realized in a circle of continuous denitrification with desulfurization and ammonia -washing regeneration.
|张霄玲. 低温锰系催化剂制备及烟气脱硫脱硝性能研究[D]. 中国科学院大学,2020.|
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