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类型 基础研究 预答辩日期 2017-12-05
开始(开题)日期 2015-03-18 论文结束日期 2017-09-20
地点 动力楼420 论文选题来源 国家自然科学基金项目     论文字数 9.5 (万字)
题目 基于燃煤湿法脱硫净烟气环境的膜法 捕集CO2及其失效特性研究
主题词 CO2捕集,膜法,燃煤烟气,膜污染
摘要 由CO2引起的温室效应已成为全球性的焦点,在众多工业CO2排放源中,燃煤电厂对CO2排放的贡献最大,其中,膜法是实现燃煤电厂CO2减排的有效手段之一。膜法CO2捕集装置适于安装在湿法脱硫系统后,然而,现有研究大多以CO2/N2模拟烟气为研究对象,涉及在实际燃煤湿法脱硫净烟气环境中考察膜捕集CO2性能及运行情况的研究相对欠缺。实际燃煤脱硫净烟气中除CO2、N2外,还含有SOx、NOx、水汽等共存气态组分和微量的固体细颗粒物组分,这些气固杂质会对膜分离/吸收CO2捕集性能、稳定运行等造成影响,但是,其影响规律和机理尚不明确。因此,本文从宏观性能和微观机理两个尺度,围绕实际燃煤湿法脱硫净烟气CO2膜法捕集过程中烟气细颗粒与气态共存组分对CO2膜捕集性能及膜材料的影响特性展开了较全面的研究。主要工作有以下几方面: 本文利用膜分离模拟实验台和热态燃煤湿法脱硫试验台考察了SO2、SO3、水汽、SOx与水汽共存及石膏细颗粒等杂质组分对聚酰亚胺(PI)中空纤维膜CO2分离性能的影响规律,并综合利用场发射扫描电镜(FESEM)、能谱分析(EDS)、原子力显微镜(AFM)、傅里叶红外光谱(FTIR)等手段探究气固杂质对膜分离性能和微观结构的影响机理。研究发现:较低浓度的SO2单独存在时,由于其浓度远低于CO2的浓度,基本不会对膜分离CO2性能产生影响;在相对湿度为85~90%的环境中,PI膜的CO2/N2分离因子略有上升,而CO2渗透速率则逐渐下降,总体上水汽存在不利于PI膜分离CO2,但该影响是可逆的。与水汽单独作用相比,水汽与SO2或SO3共存时,PI膜的CO2分离性能下降更加显著,在水汽/SO3共存环境中实验运行50 h后,PI膜的CO2分离性能下降了约75%,膜材质基本失效。烟气中细颗粒组分对PI中空纤维膜CO2分离的影响特性主要表现为:细颗粒在PI膜表面大量沉积,破坏了PI膜表面形貌,减小有效膜分离面积,最终对PI中空纤维膜分离性能造成不可逆的破坏;在燃煤热态CO2捕集实验中发现,虽然SO2、SO3、水汽、细颗粒等气态和固态杂质组分含量低于模拟烟气的情况,但是多种复杂气固杂质的叠加作用,使PI分离膜在运行10 d后,CO2/N2分离因子与CO2渗透速率分别下降了约90%和45%;且实验后的PI膜受到严重污染,表面附着的滤饼层颗粒中含有Al、Si、Mg、Ca、S、O等元素。 针对燃煤烟气的膜吸收CO2技术,分别在模拟烟气和燃煤湿法脱硫实际烟气环境中进行了长时间的膜吸收CO2实验研究,研究了气态共存组分和细颗粒物对膜吸收CO2的影响规律及对膜和膜微结构的影响特性。首先考察了SO2对聚丙烯(PP)、聚四氟乙烯(PTFE)、聚偏氟乙烯(PVDF)三种典型的平板膜材质CO2膜吸收的影响。结果表明:PDVF膜受SO2影响最为明显,PP和PTFE较弱;采用PP中空纤维膜系统地研究了SOx、NO、水汽等单组份或多种组分共存对其CO2膜吸收性能的影响规律,研究发现:SO2、NO单独存在时,CO2膜吸收性能几乎不受影响,然而,水汽单独存在会降低PP中空纤维膜的CO2脱除率,且RH越大影响越显著,但是该影响是可逆的,水汽/SO2、水汽/SO3共存都会加剧PP中空纤维膜吸收CO2性能恶化,但是水汽/SO2实验后,膜材质本身并未遭到破坏,且接触角的下降可通过N2反吹消除,而水汽/SO3共存导致PP膜材质机械强度和疏水性能遭到破坏,造成不可逆的膜污染。烟气中共存细颗粒会导致PP中空纤维膜的CO2脱除性能显著下降,膜组件入口和PP膜丝表面都沉积了大量飞灰颗粒,在水汽共存情况下,CO2脱除率加速下降,且颗粒沉积更加明显,并在膜组件入口形成比较致密的滤饼层,明显减小气-膜有效接触面积,对膜吸收性能和膜形貌结构都造成不可逆的影响;利用D50=11 μm的细颗粒和D50=27 μm的粗颗粒考察颗粒粒度影响时发现,细颗粒使PP膜CO2吸收性能下降更显著,并且在膜表面沉积情况更加明显;此外,含颗粒的模拟烟气采用气体管程流动时,PP中空纤维膜受颗粒污染的程度较弱,且CO2脱除率更高。在实际热态燃煤湿法脱硫净烟气环境中进行10 d的烟气接触实验,结果表明:由于水汽、SOx气体组分与颗粒的共同作用,PP中空纤维膜的CO2吸收性能显著下降,膜微结构遭到严重破坏,细颗粒物在膜表面粘附地更加致密,并且细颗粒会进入膜孔,直接阻塞传质通道。 在颗粒物-膜污染影响实验的基础上,综合利用原子力显微技术和扫描电子显微技术,制备了SiO2、石膏颗粒探针,以微米级球形SiO2颗粒模拟飞灰颗粒,在微观尺度上研究了单个SiO2颗粒与玻璃、硅晶片、PP膜、PVDF膜及颗粒-颗粒间的粘附力作用,分别考察了接触面粗糙度、相对湿度、颗粒物性对粘附力的影响。研究发现:在干燥条件下,接触面纳米级的表面粗糙度对微米颗粒的粘附力影响较小,SiO2颗粒在粗糙度不同的普通玻璃、硅晶片、PVDF膜、PP膜上的的临界粘附力由大到小为:硅晶片>普通玻璃>PP≥PVDF,但是粘附力处于同一数量级。环境相对湿度对颗粒粘附作用的影响较为明显,飞灰和石膏两种颗粒与膜之间的临界粘附力以及颗粒-颗粒间的临界粘附力都随RH的升高逐渐增加;此外,干燥条件下,颗粒-颗粒的临界粘附力与颗粒-膜表面的临界粘附力大小并未观测到明显差异;然而当RH高于65%后,颗粒-颗粒间的临界粘附力超过颗粒-膜间的粘附力,且其增长速度对RH的依懒性更大,颗粒-颗粒的粘附作用是导致大量颗粒沉积的主要因素,对膜污染的贡献最大。另外,发现石膏颗粒-PP膜及石膏颗粒-颗粒间的粘附力作用大于SiO2颗粒-PP膜及飞灰颗粒-颗粒间的粘附力。结合经典力模型分析了微米颗粒与界面的粘附力种类和作用方式,并采用Matlab对颗粒与界面间的范德华力、静电力、毛细力进行了数值模拟;结果表明:颗粒所受各种力的大小顺序为:FL>Fvdw>Fe,在干燥环境下,范德华力对颗粒粘附力贡献最大,对其粘附沉积起主导作用,而在潮湿环境下,毛细力远大于范德华力成为影响颗粒粘附的主导因素。 在水汽-膜污染实验的基础上,结合新颖的分子筐吸附剂(molecular basket sorbent, MBS),研究了不同Si载体(SBA-15、TUD-1、HS-5)及PEG添加剂对MBS捕集CO2的影响。研究发现:负载PEI之后样品的孔参数对CO2吸附量则起到关键作用,具有3-D孔结构的MBS比2-D的MBS表现出更高的CO2吸附量和氨基利用率;在30~95 oC的吸附温度范围内,PEI/HS-5始终表现出最好的CO2吸附性能。此外,吸附剂的温度依赖性与PEI负载层数直接相关,PEI负载层越多,CO2的扩散传质阻力越大,温度依赖性越强;添加PEG可有效缓解扩散传质阻力并提高氨基利用率,从而有效提高三种Si基MBS的CO2捕集性能。该研究结果可为CO2混合基质膜的制备和改性提供参考数据。
英文题目 ?CO2 CAPTURE BY MEMBRANE PROCESS FROM COAL-FIRED WET DESULFURIZED FLUE GAS AND THE FAILURE MECHANISM
英文主题词 CO2 capture,membrane process, coal-fired flue gas, membrane fouling
英文摘要 Greenhouse effect caused by CO2 has become the global focus. Among numerous industrial CO2 emission sources, coal-fired power plant contributes the most amount of CO2. Membrane process is an effective method for CO2 capture from power plant. Generally, the membrane equipment for CO2 capture are suitable to installed downstream of wet flue gas desulfurization (WFGD) system. However, most of the existing studies are based on the simulated flue gas containing CO2/N2 only, and the researches that involve the performance and the operation of membrane for CO2 capture at actual WFGD conditions are relatively defective. The composition of desulfurized flue gas is complex containing a large of impurity such as fine particles, water vapor, SO2, except N2 and CO2. The fine particles and coexistent gaseous components in the flue gas may severely impact the performance of membrane or even to destroy membrane material. So far, there is little known specifically of the effect of impurity components and the influence mechanism. Therefore, this thesis focuses on effects of coexistent gaseous components and fine particles on membrane separation/adsorption properties and membrane materials under the condition of actual WFGD conditions. The systematic studies were conducted from the perspective of macro performance and micro mechanism. Effects of the coexistent gaseous components including SO2、SO3、water vapor、SOx/H2O and gypsum fine particles on the CO2 separation performance of polyimide (PI) hollow fiber membrane were investigated over membrane separation simulated test-bed and thermal WFGD simulated test-bed. Influence mechanism of gaseous and particles impurities on membrane properties and micro-structure were studied by using FESEM、EDS、AFM、FTIR. The results indicate that the individual present of low concentration of SO2 almost has no effect on the membrane separation for CO2; at high RH conditions (85~90%), the CO2/N2 selectivity increased slightly, while the permeation rate decreased gradually. The water vapor showed negative and reversible effect on PI membrane separation for CO2 on the whole. Compared with the case of the individual presence of water vapor, the coexistent of SO2/H2O and SO3/H2O, the CO2 separation performance of PI membrane decreased more significantly. PI membrane became basically failure after operated 50 h under the coexistent of SO3/H2O. Fine particle could deposit on the surface of PI membrane and decreased the gas-membrane contact area then bring the irreversible destruction to the separation performance. During the process of CO2 capture from the actual coal-fired WFGD flue gas, the PI separation properties for CO2 capture still show a significant decrease, although the concentrations of coexistent gaseous components and fine particles were much lower than the case of simulated flue gas. The CO2/N2 selectivity and the permeation rate reduced by ca. 90% and 45% due to the serious membrane fouling induced by the superimposed influence. The cake layer contained Al, Si, Mg, Ca, S, O, et al. Long-term membrane adsorption for CO2 capture was conducted both over membrane adsorption simulated test-bed and thermal WFGD simulated test-bed. Influences of the coexistent gaseous components and fly-ash fine particles on the membrane adsorption performance for CO2 capture were investigated. Firstly, the sorption studies of SO2 on Polypropylene (PP), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) showed that PVDF was affected by SO2 more obvious than PP and PTFE. The effect of SOx、water vapor、SOx/H2O and NO/H2O on CO2 adsorption performance were comprehensively studied by using PP hollow fiber membrane. The results showed that the membrane adsorption for CO2 was not be impacted by the individual exists of SO2 and NO. However, the individual exists of water vapor reduced the properties of PP hollow fiber membrane for CO2 capture. And the influence became more significant with the increase of RH. Moreover, effect of water vapor was reversible. The coexistent of SO2/H2O and SO3/H2O would accelerate the performance deterioration of PP hollow fiber membrane. The influence of SO2/H2O on contact angle of membrane could be eliminated by blowing N2, while the destruction of mechanical strength and hydrophobic properties caused by SO3/H2O was permanent. The deposition of fine particles on the inlet of PP membrane module formed cake-layer, which became more significant with the presence of water vapor. The fine particles with particle size of D50=11 μm and D50=27 μm were introduced into the simulated flue gas to study the effect of particles sized. It was found that the adsorption performance decreased more with presence of particles with D50=11 μm. And particle with smaller size deposited more distinctly. Furthermore, In addition, higher CO2 removal efficiency and less reduction were obtained under the tube side flow scheme. 10 days experiment was conduct under actual WFGD conditions, PP membrane adsorption properties for CO2 capture still show a significant decrease. In addition, fine fly ash particles were observed not only adhering to the surface of the membrane but also entering into and blocking the membrane pores. On the basis of the influence of particulate-membrane fouling, to fully understand the mechanism of membrane fouling, a quantitative study of the adhesion force of particle on membrane surface was investigated by atomic force microscopy (AFM). The adhesion force of a single particle with flat glass, silicon wafer, PP (polypropylene) membrane, and inter-particles were measured. The influence of surface roughness, relative humidity (RH) and particle properties on the adhesion behavior were investigated. The results showed no obvious difference of adhesion force was obtained between the four substrates which has different surface roughness. And the surface roughness of flat substrate has slight effect on the adhesion force of the micrometer scale particle on flat surface at dry condition, while measured adhesion forces show obvious RH dependent for fly-ash and gypsum particles. Additionally, at dry conditions, the adhesion force of inter-particles also shows no obvious quantitative difference. The adhesion force of inter-particles increased more higher with the RH than that on membrane when RH higher than 65%, which indicates the adhesion between micrometer scale particles can accelerate the deposition of particles on membrane and contributes the most to membrane fouling in industry atmosphere. The adhesion force of gypsum particle was obtained larger than fly-ash particle. Van der Waals force, electrostatic force, capillary force between particle and membrane were calculated through classical force model. The results indicate: FL > Fvdw > Fe. In a dry environment, van der Waals force play a critical role in the particles adhesion force, while capillary force become dominated at wet conditions. Based on the water vapor-membrane fouling experiment, combined with novel molecular basket sorbent (MBS), the influences of silica support(SBA-15、TUD-1、HS-5) and PEG additive on the sorption performance of molecular basket sorbent (MBS) for CO2 capture. The results suggest that the pore properties of a support including 3D pore structure, pore size and the pore volume may not be directly related to the CO2 sorption performance of MBS sample. Instead, the pore properties of PEI-modified samples including 3D pore structure, pore size and the pore volume may play a more important role in the CO2 sorption capacity. MBS with 3D pore structure exhibits higher CO2 sorption capacity and amine efficiency than those with 2D-structured support. Among the sorbents studied, fumed silica (HS-5) based MBS showed the highest CO2 sorption capacity at the temperature range of 30 to 95 °C. It was found that the temperature dependence is directly related to the PEI surface coverage layers. The more PEI surface coverage layers, the higher diffusion barrier for CO2 and the stronger temperature dependence of CO2 capacity. Adding PEG could greatly promote the CO2 sorption capacity and improve amine efficiency of all MBS, most likely by effectively alleviating the diffusion barrier within PEI bulk layers through the inter-molecular interaction between PEI and PEG. The results may provide reference data for mixed matrix membrane preparation and modified.
学术讨论
主办单位时间地点报告人报告主题
东南大学杨林军课题组 2014.5.6 热能所一楼会议室 张琳 膜吸收CO2实验初步测试
东南大学杨林军课题组 2014.9.2 热能所一楼会议室 张琳 气固杂质对膜捕集CO2长期影响
东南大学杨林军课题组 2015.3.17 热能所一楼会议室 张琳 颗粒物与膜材料相互作用力研究
东南大学杨林军课题组 2015.9.6 热能所一楼会议室 张琳 颗粒膜污染的AFM研究
Penn State EMS 研究所 2016.5.20 Penn State EMS building 张琳 Effect of SiO2 Supports on MBS for CO2 sorption
Penn State EMS 研究所 2016.9.7 Penn State EMS building 张琳 Effect of PEG on MBS for CO2 sorption
东南大学杨林军课题组 2016.12.5 礼西楼309 张琳 膜捕集CO2模拟试验台重建和补充实验
东南大学杨林军课题组 2017.4.24 礼西楼309 张琳 膜吸收CO2膜润湿长期实验
     
学术会议
会议名称时间地点本人报告本人报告题目
中科院上海高等研究院 2017.7.17-21 上海 CO2 capture over molecular basket sorbents: Effects of support and PEG additive
新加坡国立大学 2015.7.5-9 新加坡 CO2 capture using hollow fiber membrane after WFGD
清华大学 2015.7.19-22 北京
浙江大学 2014.9.20-22 浙江 杭州
     
代表作
论文名称
Membrane gas absorption for CO2 capture from flue gas containing fine particles and gaseous contamin
SO2对膜吸收法捕集烟气中CO2的影响研究
Fouling of Impurities in Desulfurized Flue Gas on Hollow Fiber Membrane Absorption for CO2 Capture
Hollow Fiber Membrane Separation Process in the Presence of Gaseous and Particle Impurities for Post
PI中空纤维膜分离模拟燃煤脱硫烟气中的CO2
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
仲兆平 正高 教授 博导 东南大学
荆肇乾 正高 教授 博导 南京林业大学
宋海亮 正高 教授 博导 南京师范大学
余冉 正高 教授 博导 东南大学
陆勇 副高 副研究员 博导 东南大学
李先宁 正高 教授 博导 东南大学
      
答辩秘书信息
姓名职称工作单位备注
王沛 其他 讲师 东南大学