【作者】 徐冬；

【导师】 翟玉春； Paul Webley；

【作者基本信息】 东北大学 ， 冶金物理化学， 2011， 博士

【摘要】 过量二氧化碳气体排放所引发的温室效应已经成为严重的世界问题。如何减缓二氧化碳的排放量引起人们极大的关注,已经成为目前及未来人类保护环境、保护地球的重要工作。变压吸附分离提纯工业废气中CO2的技术具有吸附剂使用周期长、工艺流程简单、自动化程度高、环境效益好、无污染产生等优点。活性炭和沸石是最常用的变压吸附捕集CO2的吸附剂。与活性炭相比,13X沸石在干燥进气条件下对二氧化碳具有更高的吸附能力。但是13X具有超强的亲水性,水分子会污染13X而使其失去活性。而实际从电厂中排出的废气中仍含有一部分饱和水蒸气在室温条件下不能被除去。如果处理二氧化碳之前通过增加干燥塔等设备来除去电厂废气中的饱和水蒸气,将会增加操作成本,降低变压吸附技术的优越性。因而本研究采用两种不同方法在分离C02的同时解决水蒸气的问题。一种方法采用多层变压吸附工艺在吸附床内装有至少两种吸附剂,前层吸附剂用来吸附水蒸气,而主吸附剂用来吸附C02；另外一种方法是应用疏水性活性炭材料分离高湿废气中的CO2。本研究利用试验与模拟相结合的方式设计了不同变压吸附工艺。测定了CO2、N2及H20在各种吸附剂上的等温吸附曲线,通过吸附平衡探讨了不同吸附剂在分离C02和除水方面的优缺点。结果表明,13X沸石和LiX沸石因为其较大的C02吸附量和较高的对C02/N2的吸附选择性,是良好的吸附分离C02的吸附剂材料。而H20在BASF Sorbeads WS、F200舌性氧化铝和活性炭纤维上的等温吸附曲线表明这三种材料都非常适合真空变压吸附截留废气中的水蒸气。最后,不同气体在活性炭上的单组分等温吸附曲线和CO2/H2O的双组分等温曲线表明活性炭不仅可以分离C02,而且H20也很容易被解吸下来。H2O/CO2单、双组分在双层VSA及活性炭吸附床中的穿透曲线显示,C02在多种吸附剂上的的吸附速率都远快于H20的吸附速率,而温度变化曲线表明H20在吸附剂材料上的吸附释放的热量远大于CO2吸附释放的热量。在多层变压吸附分离C02的工艺中,利用MINSA软件模拟了以Sorbead和F200为前层吸附剂,以13X为主吸附剂的循环操作过程。LBET方程被用来拟合了水蒸气在F200上的吸附等温线,而CDS和CMMS方程被用来拟合了水蒸气在Sorbead上的吸附等温线。结果显示,两种吸附剂都可以成功截留住水蒸气而保护13X主吸附层。本工艺采用九步循环操作步骤使浓度为12%的CO2浓缩至纯度最高达91%,CO2的回收率也可达80%。简单的单床三步试验装置测试了不同吸附剂材料的性能及多层VSA的可行性。结果表明,LiX三层实验可以提高CO2的回收率和产率。而ACF三层VSA实验中,水蒸气峰面在吸附床的位置低于其他两种实验条件下水蒸气的峰面。简单的三步实验过程可以使CO2的纯度最高达68%,回收率最高为81%。最后,把13X+Sorbead双层VSA试验应用在三床半工业化装置中测定了吸附床内的压力、温度变化,水蒸气和CO2的浓度分布以及各操作参数对CO2分离效果的影响。分别采用六步和九步循环操作步骤进一步提高了CO2的分离纯度。结果显示,解吸压力、进气流速和Sorbead与13X的体积比为三个最重要的影响分离效果和H2O分布的操作参数。6步循环操作可以使进气浓度为12%的CO2纯度达到72.3%,回收率超过85%,而9步VSA实验操作中可以得到96.1%的CO2,回收率为80.5%。以活性炭为吸附剂的CO2-VSA工艺探讨了水蒸气对CO2分离效果的影响。结果表明,H2O的存在几乎不影响活性炭对CO2的分离效果。与13X相比,活性炭对CO2解吸压力要求不高,但是由于活性炭对CO2/N2选择性不高,三床六步实验可以得到纯度为57.2%的CO2,回收率为68%。本研究最后设计了双级VSA工艺。第一级工艺以活性炭为吸附剂,第二级工艺以13X为吸附剂。在不需要增加冲洗等复杂操作步骤的情况下不但解决了工业废气中的水蒸气问题,而且获得了纯度为大于99%的CO2,并且CO2回收率可以高达90%以上,满足了碳的捕获与存储的要求,具有很好的工业应用前景。更多还原

【Abstract】 An increasing concern about controlling carbon dioxide emissions to curb the global warming has been proposed by scientists and it is critical for humanbeing to develop feasible technologies to mitigate the issues of greenhouse gases. CO2capture by adsorption based technology has great potential in CO2capture area due to their system simplicity and low operational&capital costs and much progress has been made in this technology in the recent years.Among various adsorbents, activated carbon (AC) and13X zeolite are the most popular and traditional commercial candidates that can be applied in CO2-VSA system.13X is the better adsorbent for the bulk CO2capture from dry flue gas, due to its favorable isotherm shape and equilibrium selectivity. However, since water adsorption is much stronger than CO2adsorption on13X zeolite, the presence of water vapor can largely displace CO2and reduce the adsorption capacity. Most of the post-combustion carbon capture projects deal with highly humid flue gases in the real industrial plant containing5-10%saturated water vapor. Conventional approaches using a pre-treatment/drying apparatus to remove moisture from post-combustion flue gas would considerably increase the overall capture cost, which is already the dominant portion of the overall carbon capture and storage (CCS) cost. Thus in order to solve the water issues simultaneously, two methods are applied in this study. One of them is multiple-layering VSA using at least two different adsorbents to capture H2O and CO2separately. Another method is to use the hydrophobic material, activated carbon for CO2capture from wet flue gas. Both simulation analysis and experimental work were envisaged to achieve a systematic result.CO2, N2and H2O adsorption isotherms onto different adsorbents were shown the advantage and disadvantage of those materials in VSA. Results indicated that due to the relative large CO2adsorption amount and better adsorption selectivity over CO2/N2,13X zeolite and LiX zeolite were good candidates for CO2capture. The H2O isotherms onto BASF Sorbeads WS, F200alumina and ACF illustrated they were very good desiccant for water removel. And the CO2, N2and H2O isotherms on activated carbon showed that AC is not only good at CO2capture but it will be the latest affected by water vapor. Following, both single and binary H2O/CO2breakthrough curves showed faster adsorption kinetics of CO2on all the materials than H2O on different adsorbents. Temperature swing profiles in the adsorption bed indicated that heat released by H2O adsorption was much larger than CO2adsorption.In the multiple-layering CO2-VSA process, the simulator MINSA was firstly explored to simulate two double-layered work choosing Sorbead and F200as protective layer materials individually and13X as main adsorption layer. Results showed that the both of the two pre-layer adsorbents can stop water vapor from further moving into13X zone, therefore protecting the main layer adsorbent13X zeolite. LEBT equations and CDS&CMMS equations were successfully fitted to the H2O isotherms on F200and Sorbead, respectively. The simulated9-step VSA cycles yielded a good CO2purity of91%from original feed CO2concentration of12%, with a good recovery of80%. Then the VSA process work was applied to a single bed3-stpe rig to study the feasibility of three different layering conditions. Results showed that comparing with13X+Sorbead double-layer experiment, the LiX triple-layer experiment can improve the CO2recovery and productivity, however decrease the CO2purity. On the other hand, the ACF triple-layer experiment could shallow the height of pre-layer material placement. But because of the pressure drop caused by ACF cloth, energy consumption was increased and CO2purity was slightly decreased. The simple single bed VSA process can get the result of68%CO2purity and81%CO2recovery. Lastly, the13X+Sorbead double layered VSA process was applied into our pilot-scale3-bed apparatus. The pressure and temperature profiles were tested and H2O distribution inside the adsorption bed was analysized. The6-step and9-step VSA cycles were used to improve CO2purity. Results showed that the evacuation pressure, feed flow rate and ratio of13X to Sorbead were three most important operation parameters in determining CO2capture and water removal. The3-bed VSA process can retain water adsorption in the pre-layer, providing a CO2recovery of85.4%, and a purity of72.3%achievable with6-step cycles at a vacuum pressure of3.5kPa. For a9-step cycle employing product purge, the best CO2recovery and purity were80.5%and96.1%, respectively.The activated carbon based VSA process is to study the feasibility and advantage of CO2 capture from wet flue gas streams along with simultaneously moisture removal. Through experiment and analysis, water vapor hardly influenced the CO2capture performance. The process can be operated under a relatively high vacuum pressure. Due to the relative low adsorption selectivity over CO2/N2, the preliminary results showed that our pilot-scale three bed VSA process using activated carbon as adsorbent could yield a reasonable CO2purity of57%CO2with the recovery of68%. Then base on the pros and cons that AC showed, a two-stage VSA process was investigated employing AC as the first stage material and13X as the second stage material. The simple cycles could largely save the industrial operation cost. The tow-stage technique could not only solve the water issues exiting in real flue gas, but achieve a excellent CO2purity of over99%, with a great CO2recovery of over90%, which will satisfy the requirement of carbon capture and storage. The two stage VSA process has a good potential in industrial application.更多还原