烟气中水蒸气对钙基吸收剂碳酸化的影响特性

在循环煅烧/碳酸化反应系统上考察煅烧气氛和碳酸化气氛中水蒸气含量以及CO₂分压对钙基吸收剂成型颗粒碳酸化的影响,通过对钙基吸收剂微观结构分析(扫描电镜、氮吸附分析)以理解水蒸气影响碳酸化特性的机理。结果表明,煅烧气氛和碳酸化气氛中的水蒸气均可提高钙基吸收剂的碳酸化转化率,水蒸气含量分别为10%和5%时,吸收剂的碳酸化性能较好;水蒸气在碳酸化气氛中对高铝水泥改性吸收剂的改善作用较石灰石显著。煅烧气氛中的CO₂分压越高,烧结现象越严重,降低钙基吸收剂的捕集效率;碳酸化气氛CO₂分压提高,有利于提高钙基吸收剂的碳酸化转化率。烟气中水蒸气丰富了吸收剂的微观孔隙,使得吸收剂捕集CO₂性能得到改善。     

间歇氯化对电石渣循环捕集CO_2性能的影响

提出在碳酸化气氛中间歇加入HCl(间歇氯化)提高电石渣在循环煅烧/碳酸化反应中捕集CO_2性能的新思路。在双固定床反应器上,在不同循环次数加入HCl、碳酸化温度、CO_2/HCl体积比等条件下,研究HCl间歇加入对电石渣循环碳酸化特性的影响。结果表明,在循环煅烧/碳酸化反应中间歇加入HCl使电石渣间歇氯化能提高其循环捕集CO_2性能。在前N次循环碳酸化时加入0.1%HCl,当N=4时能使电石渣获得最优CO_2捕集性能,第10个循环时的CO_2吸收量比无HCl时提高了51%。HCl与Ca CO3发生氯化反应,破坏致密产物层对CO_2扩散的阻碍,提高了电石渣的碳酸化转化率。在碳酸化气氛加入HCl时,最佳碳酸化温度仍为700℃。随CO_2/HCl体积比增大,HCl对电石渣捕集CO_2性能的促进作用减弱。     

利用蛭石增强石灰石对CO2的循环捕集效率

天然石灰石经高温煅烧分解后所得CaO可以作为捕集CO2的吸收剂,用来捕集水泥、煤电等工业烟气中的CO2.但是由于烧结现象导致钙基吸收剂的循环碳酸化率在多次循环之后会发生迅速衰减,基于此,我们提出利用具有天然纳米片层结构的蛭石对石灰石颗粒表面进行修饰改性,以便提高石灰石颗粒的抗烧结能力及其循环捕集CO2的能力.利用TGA以及SEM对蛭石改性的石灰石进行了表征.试验结果表明:蛭石对石灰石改性有效果,当其添加量为1 wt％时,可以使石灰石的第一次循环碳酸化率提高8.21％.     

失活钙基吸收剂环境中自活化机理

将经历多次循环后失活的钙基吸收剂置于环境中吸水自活化,通过XRD分析了自活化过程吸收剂物相演变规律,在双固定床反应器系统上分析了吸水率对失活钙基吸收剂循环捕集CO₂性能的影响规律, 通过SEM和N₂吸附分析了自活化提高钙基吸收剂循环碳酸化转化率的机理。结果表明：失活钙基吸收剂首先吸收环境中水分生成Ca(OH)₂,当吸水率达到100%后继续吸水生成Ca(OH)₂?2H₂O,自活化极限为170%;自活化可以提高失活钙基吸收剂循环碳酸化转化率,自活化后钙基吸收剂循环捕集CO₂性能与吸水率呈线性比例关系,重复自活化可再次提高吸收剂循环碳酸化转化率;自活化过程中,失活钙基吸收剂颗粒表面重新生成孔隙,比孔容和比表面积增加,有利于吸收剂中CO₂的扩散,因此自活化后钙基吸收剂循环捕集CO₂性能提高。     

凹凸棒石改性钙基吸收剂循环碳酸化特性的试验分析

钙基吸收剂在较高的温度下可有效的循环捕集烟气中的较低浓度的CO2,通过升温释放出高浓度的CO2.但其弊端在于随着CO2释放/吸附的不断进行,吸收剂的烧结现象严重,CO2的吸收效率也显著的下降,若仅采用钙基材料作为CO2捕集剂,需不断的投入新鲜的吸收剂,消耗量较大.本论文以水泥工业为背景,研究其烟气中CO2的捕集,并采用一维结构的凹凸棒对吸收剂进行表面修饰处理,来缓解吸收剂的烧结现象,以提升CO2的吸收效率.试验结果表明:凹凸棒石物理吸附CO2的量对钙基吸收剂碳酸化率的提高有一定的贡献,但此贡献要小于吸收剂抗烧结性能的提高所带来的贡献;凹凸棒石对颗粒粒径较大的吸收剂的改性效果较好;不改变钙基吸收剂的粒径,当将提纯凹凸棒石的粒径减小时,其改性效果进一步提高.     

基于钙基吸收剂循环煅烧/碳酸化反应捕集CO2的试验

利用钙基吸收剂循环煅烧/碳酸化反应(CCCR)吸收CO2是一种新型、廉价、有效的CO2捕集方法.采用热重分析仪研究了吸收剂的矿物组成、颗粒粒径、煅烧温度和碳酸化温度对CCCR快速反应阶段吸收剂循环碳酸化率(XN)的影响.结果表明:吸收剂的碳酸化反应由快速化学反应控制阶段、过渡阶段和缓慢产物层扩散控制阶段组成;白云石具有良好的抗烧结能力,白云石的XN高于石灰石;随着颗粒粒径的增大,吸收剂的XN逐渐降低;当煅烧温度超过950℃时,随着循环反应次数的增加,吸收剂的XN严重降低;吸收剂在725℃碳酸化温度时的XN最高.     

基于钙基吸收剂吸收CO2的研究进展

综述了钙基吸收剂煅烧/碳酸化循环吸收CO2的国内外研究状况.从反应条件对碳酸化反应的影响、改善钙基吸收剂吸收CO2的性能、钙基吸收剂循环热稳定性的方法以及碳酸化反应动力学特性这4个方面进行分析,认为碳酸化反应主要分为化学反应控制和产物层扩散2个阶段,指出CO2分压和吸收剂的颗粒粒径决定着碳酸化反应温度和CO2的脱除效率...     

钾基CO2吸收剂的碳酸化反应特性

对钾基CO2吸收剂的碳酸化反应机理进行研究.利用热重分析、XRD、扫描电镜和氮吸附仪进行试验.结果表明:分析纯碳酸钾的组分为K2CO3·1.5H2O,碳酸化反应速率缓慢;先将分析纯碳酸钾样品脱除结晶水后再进行碳酸化反应时,K2CO3与气氛中的水蒸气迅速生成K2CO3·1.5H2O,不利于碳酸化反应的进行;由KHCO3分解产生的K2CO3却表现出优越的碳酸化反应性能,20 min内转化率高达85%以上,经过多次循环试验后吸收剂仍保持很高的活性.从微观角度分析了两种改性钾基CO2吸收剂碳酸化反应机理差异的原因,通过拟合计算得到了这3种钾基吸收剂的碳酸化反应速率常数,为干法K2CO3/KHCO3循环脱除CO2的研究提供了一定的基础数据.     

利用凹凸棒改性石灰石增强CO2循环捕集效率

石灰石作为天然的CO2吸收剂,可有效的捕集烟气中的CO2,但随着循环反应次数的增加,石灰石颗粒表面会发生严重的烧结,使其酸化率迅速发生衰减.本文中利用自然界储量丰富的凹凸棒石对石灰石颗粒进行改性来减缓这一现象的发生,从而提高其CO2的循环捕集效率.凹凸棒石具有的天然纳米纤维状结构可有效的减少石灰石颗粒之间的相互接触,延缓石灰石的烧结团聚现象,从而提高其碳酸化率.实验结果表明:凹凸棒石原矿和提纯后的凹凸棒石均可作为添加剂提高石灰石对CO2的捕集效率,其中经过提纯处理后的凹凸棒石的改性效果最好;通过比较凹凸棒石改性前后的钙基吸收剂经过多次CO2捕集循环后的颗粒微观形貌的变化,可以发现经过凹凸棒石改性后的石灰石颗粒表面仍留有较多的孔道,使其抗烧结能力得到大幅的提高.     

Cl含量对钙基吸收剂微观结构以及动力学性能的影响

通过浸渍法向分析纯CaCO₃中添加Cl,在双固定床反应器系统和热重分析仪上研究了其对钙基吸收剂循环捕集CO₂性能的影响,利用离子反应模型对添加Cl后吸收剂化学反应控制阶段进行动力学分析。结果显示：Cl对钙基吸收剂循环捕集CO₂性能具有不利影响。当Cl/Ca摩尔比大于0.25%后,随Cl/Ca摩尔比增加,化学反应控制阶段反应速率和持续时间均减小,导致在该阶段最终碳酸化转化率降低。对添加Cl前后吸收剂孔隙分布特性进行分析发现,添加Cl导致煅烧后吸收剂烧结加剧,比表面积降低,10~120nm范围内孔分布减少,导致CO₂在吸收剂内部扩散阻力增加,同时能与CO₂反应的CaO量减少,这是导致吸收剂化学反应控制阶段碳酸化反应速度较慢、最终碳酸化转化率较低的主要原因。鉴于Cl的不利影响,在选择钙基材料作为CO₂吸收剂或合成高活性复合吸收剂时,应避免吸收剂中Cl含量过高。     

Economical assessment of competitive enhanced limestones for CO2 capture cycles in power plants

CO₂ capture systems based on the carbonation/calcination loop have gained rapid interest due to promising carbonator CO₂ capture efficiency, low sorbent cost and no flue gases treatment is required before entering the system. These features together result in a competitively low cost CO₂ capture system. Among the key variables that influence the performance of these systems and their integration with power plants, the carbonation conversion of the sorbent and the heat requirement at calciner are the most relevant. Both variables are mainly influenced by CaO/CO₂ ratio and make-up flow of solids. New sorbents are under development to reduce the decay of their carbonation conversion with cycles. The aim of this study is to assess the competitiveness of new limestones with enhanced sorption behaviour applied to carbonation/calcination cycle integrated with a power plant, compared to raw limestone. The existence of an upper limit for the maximum average capture capacity of CaO has been considered. Above this limit, improving sorbent capture capacity does not lead to the corresponding increase in capture efficiency and, thus, reduction of CO₂ avoided cost is not observed. Simulations calculate the maximum price for enhanced sorbents to achieve a reduction in CO₂ removal cost under different process conditions (solid circulation and make-up flow). The present study may be used as an assessment tool of new sorbents to understand what prices would be competitive compare with raw limestone in the CO₂ looping capture systems.     

The maximum capture efficiency of CO2 using a carbonation/calcination cycle of CaO/CaCO3

The use of natural calcium carbonates as regenerable CO₂ sorbents in industrial processes is limited by the rapid decay of the carbonation conversion with the number of cycles carbonation/calcination. However, new processes are emerging to capture CO₂ using these cycles, that can take advantage of the intrinsic benefits of high temperature separations in energy systems. This work presents an analysis of a general carbonation/calcination cycle to capture CO₂, incorporating a fresh feed of sorbent to compensate for the decay in activity during sorbent re-cycling. A general design equation for the maximum CO₂ capture efficiency is obtained by incorporating to the cycle mass balances a simple but realistic equation to estimate the decay in sorbent activity with the number of cycles.     

NO removal performance of CO in carbonation stage of calcium looping for CO2 capture

Calcium looping realizes CO2 capture via the cyclic calcination/carbonation of CaO.The combustion of fuel supplies energy for the calciner.It is unavoidable that some unburned char in the calciner flows into the carbonator,generating CO due to the hypoxic atmosphere in the carbonator.CO can reduce NO in the flue gases from coal-fired power plants.In this work,NO removal performance of CO in the carbonation stage of calcium looping for CO2 capture was investigated in a bubbling fluidized bed reactor.The effects of carbonation temperature,CO concentration,CO2 capture,type of CaO,number of CO2 capture cycles and presence of char on NO removal by CO in carbonation stage of calcium looping were discussed.CaO possesses an efficient catalytic effect on NO removal by CO.High temperature and high CO concen-tration lead to high NO removal efficiency of CO in the presence of CaO.Taking account of better NO removal and CO2 capture,the optimal carbonation temperature is 650 ℃.The carbonation of CaO reduces the catalytic activity of CaO for NO removal by CO due to the formation of CaCO3.Besides,the catalytic performance of CaO on NO removal by CO gradually decreases with the number of CO2 capture cycles.This is because the sintering of CaO leads to the fusion of CaO grains and blockage of pores in CaO,hin-dering the diffusion of NO and CO.The high CaO content and porous structure of calcium-based sorbents are beneficial for NO removal by CO.The presence of char promotes NO removal by CO in the carbonator.CO2/NO removal efficiencies can reach above 90％.The efficient simultaneous NO and CO2 removal by CO and CaO in the carbonation step of the calcium looping seems promising.     

Enhancement of CO2 capture and microstructure evolution of the spent calcium-based sorbent by the self-reactivation process

The effect of self-reactivation on the CO_2 capture capacity of the spent calcium based sorbent was investigated in a dual-fixed bed reactor.The sampled sorbents from the dual-fixed bed reactor were sent for XRD,SEM and N_2 adsorption analysis to explain the self-reactivation mechanism.The results show that the CaO in the spent sorbent discharged from the calciner absorbs the vapor in the air to form Ca(OH)_2 and further Ca(OH)_2·2 H_2 O under environmental conditions,during which process the CO_2 capture capacity of the spent sorbent can be self-reactivated.The microstructure of the spent sorbent is improved by the self-reactivation process,resulting in more porous microstructure,higher BET surface area and pore volume.Compared with the calcined spent sorbent that has experienced 20 cycles,the pore volume and BET surface area are increased by 6.69 times and 56.3% after self-reactivation when φ=170%.The improved microstructure makes it easier for the CO_2 diffusion and carbonation reaction in the sorbent.Therefore,the CO_2 capture capacity of the spent sorbent is enhanced by self-reactivation process.A self-reactivation process coupled with calcium looping process was proposed to reuse the discharged spent calcium based sorbent from the calciner.Higher average carbonation conversion and CO_2 capture efficiency can be achieved when self-reactivated spent sorbent is used as supplementary sorbent in the calciner rather than fresh CaCO_3 under the same conditions.     

不同钙基吸附剂捕集CO2后的硫酸化反应特性研究

钙基吸附剂进行多次CO₂捕集后,碳酸化效率会大幅衰减,此时的吸附剂能否高效脱硫利用是值得重点关注的问题。鉴于此,筛选了高性能合成钙基吸附剂和天然石灰石吸附剂,通过热重分析仪分析对比其在多循环CO₂捕集后的碳酸化和硫酸化反应性能,采用微粒模型研究其硫酸化反应动力学特征。结果发现,高性能合成钙基吸附剂的碳酸化反应速率和CO₂吸附能力明显高于石灰石吸附剂。在长达500循环的CO₂捕集试验后,高性能合成钙基吸附剂的CO₂吸附能力比石灰石高10倍以上,其SO₂吸附能力相较于石灰石提升约40%。经历多次CO₂捕集反应循环后,2种吸附剂的硫酸化能力均有提升:其中,石灰石吸附剂的提升幅度更大,硫酸化转化率从26%提升到35%,而高性能合成钙基吸附剂的硫酸化转化率则从38%提升到43%。通过微粒模型计算发现,2种吸附剂的硫酸化反应均是与SO₂浓度相关的一级反应,多循环捕集CO₂反应后,石灰石吸附剂的硫酸化反应活化能下降接近30%,而高性能合成钙基吸附剂的硫酸化反应活化能只下降了5%。研究结果说明2种不同钙基吸附剂在进行循环CO₂捕集后,脱硫能力得到了不同程度的提高,且均可以较好地应用于SO₂的脱除。     

Enhancement of Ca‐Based Sorbent Multicyclic Behavior in Ca Looping Process for CO2 Separation

The Ca‐based sorbent looping cycle represents an innovative way of CO₂ capture for power plants. However, the CO₂ capture capacity of the Ca‐based sorbent decays sharply with calcination/carbonation cycle number increasing. In order to improve the CO₂ capture capacity of the sorbent in the Ca looping cycle, limestone was modified with acetic acid solution. The cyclic carbonation behaviors of the modified and original limestones were investigated in a twin fixed‐bed reactor system. The modified limestone possesses better cyclic carbonation kinetics than the original limestone at each cycle. The modified limestone carbonated at 640–660 °C achieves the optimum carbonation conversion. The acetic acid modification improves the long‐term performance of limestone, resulting in directly measured conversion as high as 0.4 after 100 cycles, while the original limestone remains at a conversion of less than 0.1 at the same reaction conditions. Both the pore volume and pore area distributions of the calcines derived from the modified limestone are better than those derived from the original limestone. The CO₂ partial pressure for carbonation has greater effect on conversion of the original limestone than on that of the modified sorbent because of the difference in their pore structure characteristics. The carbonation conversion of the original limestone decreases with the increase in particle size, while the change in particle size of the modified sorbent has no clear effect on cyclic carbonation behavior.     

CO2 Capture Using CaO Modified with Ethanol/Water Solution during Cyclic Calcination/Carbonation

The calcium‐based sorbent cyclic calcination/carbonation reaction is an effective technique for capturing CO₂ from combustion processes. The CO₂ capture capacity for CaO modified with ethanol/water solution was investigated over long‐term calcination/carbonation cycles. In addition, the SEM micrographs and pore structure for the calcined sorbents were analyzed. The carbonation conversion for CaO modified with ethanol/water solution is greater than that for CaO hydrated with distilled water and is much higher than that for calcined limestone. Modified CaO achieves the highest conversion for carbonation at the range of 650–700 °C. Higher values of ethanol concentration in solution result in higher carbonation conversion for modified CaO, and lead to better anti‐sintering performance. After calcination, the specific surface area and pore volume for modified CaO are higher than those for hydrated CaO, and are much greater than those for calcined limestone. The ethanol molecule enhances H₂O molecule affinity and penetrability to CaO in the hydration reaction so that the pores in CaO modified are obviously expanded after calcination. CaO modified with ethanol/water solution can act as a new and promising type of calcium‐based regenerable CO₂ sorbent for industrial applications.     

CO2 capture by double metal modified CaO-based sorbents from pyrolysis gases

High-temperature pyrolysis technology can effectively solve the problem of municipal solid waste pollution. However, the pyrolysis gas contains a large amount of CO₂, which would adversely affect the subsequent utilization. To address this problem, a novel method of co-precipitation modification with Ca, Mg and Zr metals was proposed to improve the CO₂ capture performance. X-ray diffraction (XRD) patterns and energy dispersive X-ray spectroscopy analysis showed that the two inert supports MgO and CaZrO₃ were uniformly distributed in the modified calcium-based sorbents. In addition, the XRD results indicated that CaZrO₃ was produced by the reaction of ZrO₂ and CaO at high temperatures. The effects of doping ratios, adsorption temperature, calcination temperature, CO₂ concentration and calcination atmosphere on the adsorption capacity and cycle stability of the modified calcium-based sorbent were studied. The modified calcium-based sorbent achieved the best CO₂ capture performance when the doping ratio was 10:1:1 with carbonation at 700 ℃ under 20% CO₂/80% N₂ atmosphere and calcination at 900 ℃ under 100% N₂ atmosphere. After ten cycles, the average carbonation conversion rate of Ca-10 sorbent was 72%. Finally, the modified calcium-based sorbents successfully reduced the CO₂ concentration of the pyrolysis gas from 37% to 5%.     

Modified CaO-based sorbent looping cycle for CO2 mitigation

CaO-based sorbent looping cycle, i.e. cyclic calcination/carbonation, is one of the most interesting technologies for CO₂ capture during coal combustion and gasification processes. In order to improve the durability of limestone during the multiple calcination/carbonation cycles, modified limestone with acetic acid solution was proposed as an CO₂ sorbent. The cyclic carbonation conversions of modified limestone and original one were investigated in a twin fixed bed reactor system. The modified limestone shows the optimum carbonation conversion at the carbonation temperature of 650 °C and achieves a conversion of 0.5 after 20 cycles. The original limestone exhibits the maximum carbonation conversion of 0.15 after 20 cycles. Conversion of the modified limestone decreases slightly as the calcination temperature increases from 920 °C to 1100 °C with the number of cycles, while conversion of the original one displays a sharp decay at the same reaction conditions. The durability of the modified limestone is significantly better than the original one during the multiple cycles because mean grain size of CaO derived from the modified limestone is lower than that from the original one at the same reaction conditions. The calcined modified limestone shows higher surface area and pore volume than the calcined original one with the number of cycles, and pore size distribution of the modified limestone is superior to the original one after the same number of calcinations.