【作者】 李士凤；

【导师】 王金渠； 樊栓狮；

【作者基本信息】 大连理工大学 ， 化学工艺， 2010， 博士

【摘要】 近年来由于温室效应以及气候改变对人类生产生活的影响日益加剧,以CO2为主的温室气体减排逐渐成为人们关注的焦点。目前CO2排放主要来源于化石能源的燃烧,所以CO2减排的首要措施就是捕获和掩埋电厂烟气中的CO2。水合物法捕获CO2是一种新型分离技术,它是利用烟气中CO2和N2生成水合物的相平衡条件的差异,选择性地使CO2和水生成固态的水合物,从而与气相中的N2分离,该技术具有分离效率高、过程简单等优点。目前水合物法气体分离技术通常采用的添加剂为四氢呋喃(THF),但是该技术还处于初始研究阶段,有一些问题有待解决如：苛刻的温度压力条件,低水合反应速率,高能耗等。本文分别以四丁基溴化铵(TBAB)、四丁基氟化铵(TBAF)以及环戊烷(CP)为添加剂,测定了TBAB和TBAF存在时CO2以及模拟电厂烟气(CO2/N2)生成水合物的相平衡条件,考察TBAB、TBAF以及环戊烷存在下CO2/N2生成水合物的动力学特性以及CO2分离性能,为开发高效快速、低能耗水合物法捕获烟气中CO2工艺技术提供理论依据。采用恒容压力搜索法测量了TBAB以及TBAF存在条件下,CO2以及模拟电厂烟气(CO2/N2)与水生成水合物的相平衡条件,结果发现TBAB、TBAC以及TBAF均能明显降低水合物生成条件,并且随着溶液浓度由0.293 mol%增大到0.617 mol%,水合物相平衡稳定区域随之被扩大。在相同浓度下,TBAF对于CO2和CO2/N2生成水合物的促进作用要强于TBAB和THF。在温度为4.5℃,TBAB、TBAF存在条件下,研究模拟电厂烟气(CO2/N2)生成水合物过程的动力学特性,考察进料压力、气液体积比、TBAB浓度和原料气中CO2浓度等因素对水合反应过程的影响。发现进料压力越高、原料气中CO2浓度越大、TBAB浓、度越高、气液体积比越低则水合反应过程的推动力就越大,体系压力降低的速度也就越快。分别计算和比较了两种添加剂存在时的水合反应速率常数和水合反应器空速。TBAB以及TBAF存在时,水合反应最高速率常数分别为2.82×10-7 mol2/(s·J)和8.26×10-7mol2/(s·J),反应器最大空速分别为25.96 h-1和14.36 h-1。分别以TBAB和TBAF作为促进剂,在系统温度为4.5℃,进料烟气中CO2浓度为16.60 mol%时,进行水合物法捕获模拟烟气中CO2的实验。考察进料压力、反应温度、TBAB或TBAF溶液浓度、进料气中CO2浓度等对CO2分离性能的影响。结果表明在TBAB和TBAF存在时的最大CO2分离因子分别为9.65和36.98。在TBAB存在时通过三级水合分离,在中等压力下将CO2由16.60 mol%浓缩至90.15 mol%,并且可以添加少量丙酮或甲醇来提高CO2分离性能。在TBAF存在时只需两级水合分离就可以在较低压力下,将CO2由16.60 mmol%浓缩至90.40 mol%,并且可以通过提高TBAF溶液浓度使得水合分离在常温(20.1℃)下进行。本文还对另一种添加剂环戊烷存在下的水合法捕获CO2进行实验研究。采用环戊烷和水直接混合以及预先生成水包环戊烷乳化液两种方式,考察了温度为8.1℃,水合物法捕获模拟电厂烟气中CO2过程的水合反应速率和分离性能。通过水合物生成过程放热造成的温升大小来表征水合物生成速率快慢,发现环戊烷存在时水合物生成速率要明显快于未乳化时。环戊烷乳化后的CO2分离因子均小于相同条件下环戊烷未乳化情况下的CO2分离因子。对TBAF存在下水合物法捕获模拟电厂烟气中CO2的二级水合物分离过程的经济性进行分析,估算了过程中各阶段的能耗,并和文献中膜分离以及单乙醇胺(MEA)吸收过程能耗进行比较。通过Aspen流程模拟结合计算得知对于1000 MW电厂捕获CO2的能耗成本为0.57 kW·h/kg-CO2即2.05 MJ/kg-CO2。水合物法捕获模拟烟气中CO2的能耗主要是烟气压缩所产生的,压缩能耗占整个过程能耗的66.3%,与文献中膜分离以及MEA吸收过程能耗相比较,发现水合物法捕获模拟烟气中CO2的能耗略高于膜分离法,比MEA吸收法低。更多还原

【Abstract】 There are increasing concerns for greenhouse gas recently, especially for carbon dioxide emissions mitigation of the influence of global warming and climate change on human activities. The emissions of carbon dioxide primarily result from the combustion of fossil fuels and the main approach for CO2 emissions is carbon capture and sequestration. Hydrate-based capture of CO2 is a new separation technology, which is based on the differences of hydrate phase equilibrium conditions of CO2 and N2 and selectively engaged CO2 into the cages of hydrate. The technology is of high efficiency, simpleness and conveniency and so on. However, hydrate-based technology with. THF as promoter is being at the initial stage, thus there are many problems need to be investigated, such as rigorous temperature and pressure, low reaction rate and high energy consumption. In this study, tetra-n-butyl ammonium bromide (TBAB), tetra-n-butyl ammonium fluoride (TBAF) and cyclopentane were chosen as additives for hydrate formation. The phase equilibrium conditions of CO2, simulate flue gas (CO2/N2) hydrate were determined with TBAB and TBAF, respectively. The dynamics character and separation efficiency of CO2/N2 mixture hydrate were investigated with TBAB, TBAF and cyclopentane for developing high efficient and low energy consumption hydrate-based capture of CO2.The dynamics character of simulate flue gas (CO2/N2) hydrate were studied with TBAB or TBAF at 4.5℃, such as, the effects of the feed pressure, gas liquid volume ratio, TBAB aqueous concentration and CO2 concentration in the feed on the hydrate formation. The higher feed pressure, CO2 or TBAB aqueous concentration, or the lower gas liquid volume ratio were set, the bigger driving force of hydrate formation and the rate of pressure drop could be reached. The hydrate rate constant and space velocity of reactor were calculated and compared with TBAB and TBAF, respectively. The hydrate formation rate constant reached the maximum of 2.82×10-7 mol2/(s·J) with TBAB while it was 8.26×10-7 mol2/(s·J) with TBAF, and the maximal space velocity of hydrate reactor was 14.36 h’1 with TBAB while it was 25.96 h-1 with TBAF.The process of CO2 capture from simulate flue gas (CO2/N2) by formation of TBAB and TBAF hydrate were studied at 4.5℃, and the effects of the feed pressure, temperature, TBAB or TBAF concentration and CO2 concentration in the feed on the CO2 separation efficiency were also investigated. The results showed that the maximum of CO2 separation factor was 9.65 with TBAB and that was 36.98 with TBAF. CO2 could be enriched from 16.60 mol% to-90.15 mol% under the medium feed pressure by three stages hydrate formation process with TBAB, meanwhile CO2 separation factor could be increased with the addition of a little methanol or acetone. CO2 could be enriched from 16.60 mol% to 90.40 mol% under the low feed pressure by only two stages hydrate formation process with TBAF. The process of CO2 capture,via hydrate formation could be carried out at ambient temperature (20.1℃) by increasing the TBAF aqueous concentration.The CO2 capture via hydrate formation with cyclopentane as an additive was also studied. The hydrate formation rate and separation efficiency were investigated at 8.1℃in the presence of the mixture of cyclopentane and water or cyclopentane in water emulsion. The hydrate formation rate was represented by the temperature rise due to the exothermic nature of the hydrate formation. It was found that the hydrate formation rates with cyclopentane in water emulsion were at greater rates than those without emulsion. While CO2 separation factors with cyclopentane in water emulsion were lower than those without emulsion under the same conditions.The economic analysis of CO2 capture from simulate flue gas via two stages TBAF hydrate formation was made. The energy consumption of CO2 capture was estimated and was compared with those for membrane separation and monoethanolamine (MEA) absorption. Based on Aspen flowsheeting simulation and estimation, as for a 1000 MW power plant the energy consumption of capture of CO2 via hydrate was 0.57 kW-h/(kg-CO2) or 2.05 MJ/(kg-CO2). The energy consumption of CO2 capture was mainly caused by the compression process which was 66.3% of entire process. Then the results were compared with two conventional separation processes:MEA amine based absorption separation and membrane separation processes. It was concluded that hydrate separation technology is competitive comparing with the chemical absorption for CO2 capture.更多还原