富氧燃烧烟气净化工艺研究进展

随着工业的快速发展,化石燃料消耗与日俱增,造成了大量温室气体CO₂的排放,全球气候变化形势不容乐观。为了减少CO₂排放,需要对高浓度CO₂进行捕获、利用与封存,而富氧燃烧技术能有效实现碳捕集,是目前最具潜力的碳减排技术之一。富氧燃烧过程中,SO_x、NO_x、Hg等污染物以及惰性气体的存在不利于碳的捕集与封存。烟气中各成分浓度会对管道运输、地质储存和提高采收率(EOR)产生影响,介绍了烟气中CO₂及各种杂质浓度的不同标准,系统综述了国内外脱硫、脱硝、脱汞和惰性气体脱除以及联合脱除技术的研究进展。脱硫部分除介绍传统脱硫技术外,重点描述了富氧燃烧烟气中CO₂气氛对SO_x脱除的影响以及加压条件下SO₂的转化与去除。发现CO₂气氛下SO₂的吸收速率相比N2气氛有所降低,且SO₂吸收过程中临界pH发生变化。脱硝部分重点描述了氧化吸收法脱硝技术以及加压条件下NO的氧化机理,并对高压下NO的氧化动力学进行阐述。随着压力的增加,NO氧化速率常数呈先下降后上升的趋势,且证明了反应器压力对液体夹带率的影响比较显著。总结了Hg脱除技术中不同烟气成分对Hg氧化的影响,HCl与Cl2起到了明显的促进作用。对活性炭进行改性,增加孔结构比表面积以及吸附剂表面的活性位点,提高Hg的脱除效率。介绍了惰性气体的净化技术,主要采用变压吸附方法来吸附和解吸附,降低了CO₂气流中惰性气体去除的成本,实现一部分惰性气体再次循环回到锅炉中,提高CO₂的捕获。重点讨论了在烟气压缩液化系统中的联合脱除技术,有效利用压缩过程条件将SO_x、NO_x、Hg分别以硫酸、硝酸、Hg(NO₃)₂形式协同去除,随着压力的增加,SO_x与NO_x去除效率提高,有利于SO₄^-2、NO₃^-、HADS和HAMS(N-S化合物)的生成,同时也导致了N2O生成量增多。证明了Hg与NO₂是气相反应,提出了高压下NO₂与Hg反应产物的不确定性。简单介绍了低温碳捕集技术,有潜力取代洗涤器和其他烟气处理方法,但目前还缺乏可行性的研究。未来需对不同压力下NO氧化速率常数的变化趋势进行解释,高压下NO_x与SO_x联合脱除的产物以及NO₂与Hg的反应产物进行分析。

Research and development on the purification technology for oxy-fuel combustion flue gas

With the rapid development of industry,the consumption of fossil fuels is increasing with each passing day,resulting in a large amount of greenhouse gas CO₂ emissions.The situation for global climate change is not optimistic.In order to reduce the emission of CO₂,it is necessary to capture,utilize and store the high concentration of CO₂.Oxy-fuel combustion technology can effectively achieve car?bon capture,which is considered as one of the most potential carbon emission reduction technologies.In the process of oxy-fuel combus?tion,the existence of pollutants(including SO_x,NO_x and Hg)and inert gas is not conducive to carbon capture and storage.Since the con?centration of various components in flue gas will affect pipeline transportation,geological storage,and enhanced oil recovery(EOR),the dif?ferent standards of CO₂ and various impurities concentration in flue gas were introduced firstly,and the research progress of desulfurization,denitrification,mercury removal,inert gas removal,and combined removal technologies at home and abroad was systematically reviewed.In addition to the introduction of traditional desulfurization technology,the influence of CO₂ atmosphere in oxy-fuel combustion flue gas on SO_x removal and the conversion and removal of SO₂ under pressure were mainly described.It is found that the absorption rate of SO₂ in CO₂ atmosphere is lower than that in N2 atmosphere,and the critical pH changes during the absorption process.In the denitration section,the denitration technology by oxidation absorption method and the oxidation mechanism of NO under high pressure were mainly described,and the oxidation kinetics of NO under high pressure was described.With the increase of pressure,the NO oxidation rate constant first de?creases and then increases,which is proved that the effect of reactor pressure on liquid entrainment rate is significant.The effects of differ?ent flue gas components on Hg oxidation in Hg removal technology were summarized.HCl and Cl2 play a significant role in promoting Hg oxidation.The activated carbon is modified to increase the specific surface area of pore structure and the active sites on the surface of ad?sorbent,so as to improve the removal efficiency of Hg.In this paper,the purification technology of inert gas was introduced.Pressure swing adsorption method is mainly used to adsorb and desorb,which reduces the cost of inert gas removal in CO₂ gas flow,realizes a part of in?ert gas recycling back to the boiler,and improves CO₂ capture.The combined removal technology in the flue gas compression liquefaction system is mainly discussed,which effectively uses the compression process conditions to remove SO_x,NO_x and Hg in the form of sulfuric acid,nitric acid and Hg(NO₃)₂.With the increase of pressure,the removal efficiency of SO_x and NO_x increases,which is conducive to the formation of SO₄^-2,NO₃^-,HADS and HAMS(N-S compounds),and also leads to the increase of N2O production.It is proved that the reac?tion of Hg with NO₂ is a gas phase reaction,and the uncertainty of the product of the reaction of NO₂ with Hg under high pressure is pro?posed.The low temperature carbon capture technology is briefly introduced,which has the potential to replace the scrubber and other flue gas treatment methods,but there is still a lack of feasibility research.In the future,it is necessary to explain the change trend of NO oxidation rate constant under different pressures,analyze the products of NO_x and SO_x combined removal and the reaction products of NO₂ and Hg under high pressure.