CaO循环吸收CO2的实验研究

对CaO与CO2的循环反应特性进行实验研究,分析了影响CaO转化率的因素及CaO转化率随循环次数的变化趋势,实验结果表明：CaO转化率随温度和CO2体积分数的增加而增加,颗粒粒径对其影响较大;CaO转化率随循环次数的增加而降低,在循环次数达到一定值后,CaO转化率降低到某一值后不再发生较大的变化,在不同温度下,CaO转化率随循环次数的增加而降低的趋势有所不同。     

固体CaO颗粒吸收CO2特性分析

随着温室效应对全球气候的影响越来越显著,世界上将有更多国家关注温室气体的排放问题.温室气体中CO2的排放量最大,被认为是引起全球变暖的主要原因,有在短期内改变气候的可能.现今许多国家都在研究减排与隔离CO2的措施,希望能够开发一种高效、低成本的CO2吸收技术.相对于其它的吸收剂,CaO具有高吸附量、低制备成本、较长循环使用寿命及良好抗磨特性而成为优选的高温CO2脱除剂,CaO循环吸收CO2技术在工业操作中也较为简单.主要通过分析煅烧/吸收温度、添加剂、CaO颗粒内部孔结构和分布以及烟气中其它主要成分对CaO吸收性能的影响,为CaO吸收CO2性能的改善提供一定的理论基础.     

水蒸气对CaO颗粒脱硫反应转化率的影响

用固定的SO2浓度和干空气、湿空气为载气,对4种CaO样品进行了系列TGA实验研究,结果表明,模拟烟气中含有水蒸气时,水蒸气能够提高CaO颗粒脱硫反应中的转化率．随着反应温度的提高,CaO转化率的相对提高幅度逐渐降低,而绝对提高幅度却逐步增加．模拟烟气中没有包含CO2、NOx等成分,回避了碳酸盐反应和硝酸盐反应对实验结果的干扰．由于CaO样品的性质覆盖了分析纯CaO和工业级石灰,水蒸气对于CaO转化率的提高作用对工业级石灰的烟气脱硫反应有一定参考价值．     

CaO在生物质定向气化条件下的高温CO_2吸收特性

生物质定向气化可以制备富氢燃气和一定化学当量比的合成气(用于合成醇、醚等),同时有效地减少温室气体排放,是一种可持续的清洁能源转化技术。文章基于生物质定向气化这一背景,结合实际工业生产,采用TG/DTA系统对生物质定向气化条件下CaO吸收CO2的特性进行了研究。实验结果表明:升温速率由10℃/min增加到50℃/min,CaO变温吸收CO2的反应都在800℃左右达到吸收与煅烧平衡,且CaO转化率随升温速率增大而减小;CaO转化率和质量变化速率随CO2浓度增加而增大,根据反应平衡时CO2浓度与温度的关系拟合出CO2平衡分压公式为RCO2,eq=1.16×108exp-21!399/T";CaO恒温吸收CO2的最终转化率随吸收温度的升高先增加后减小,生物质定向气化中CaO吸收CO2的最佳温度为700~750℃;循环吸收实验中CaO转化率随循环次数增加而减小。     

CaO与CO2循环反应动力学特性

为分析CaO与CO2循环反应过程动力学参数的变化规律,利用缩核模型对CaO与CO2的循环反应特性进行了研究.结果表明:CaO与CO2的化学反应速率常数在590~743℃为一常数;化学反应速率常数和产物层扩散系数随循环次数的增加而降低,温度对二者的降低规律有一定的影响;由产物层扩散阶段所引起的活性降低主要发生在前几次循环内,化学反应动力学控制阶段的活性降低是引起CaO整体转化率降低的主要因素.     

CaO/SiO2对微晶玻璃析晶行为的影响

借助XRD,DTA和IR等分析手段,研究了CaO/SiO2对微晶玻璃析晶行为的影响。结果表明:随着CaO/SiO2的增加,微晶玻璃的晶体形态由片状向条状转变,晶体尺寸减小;晶相为透辉石和钙铁辉石;在900～1 100 cm 1内,微晶玻璃的吸收带向低频方向移动,且不断有新的谱带出现,与透辉石和钙铁辉石的谱带具有相似的结构。     

SO_2气体在微孔CaO脱硫剂颗粒内的Knudsen扩散

从稀薄气体效应出发,通过对SO2气体分子在CaO脱硫剂颗粒内微尺度孔隙中气体动力学扩散机制的描述,对有效扩散系数进行了修正,建立了基于团聚体概念的Knudsen扩散数学模型,利用误差函数进行求解和简化,得到其函数关系.模拟分析显示:SO2气体分子通过Knudsen扩散向颗粒一级气孔、二级气孔内渗透时,分形孔隙和较大的一级气孔孔隙率都能增大气体向内扩散的阻力,促使径向SO2浓度分布梯度增加.结果表明,分析气体在CaO颗粒内扩散时,忽略气固化学反应等因素而只考虑Knudsen扩散是可行的.     

基于SWMM模型的渗渠LID措施补偿机理研究

针对低影响开发(LID)措施可有效削减洪峰流量和污染负荷,对降低洪涝灾害风险、保护生态环境具有重要作用,但其补偿机理尚不明确的问题,基于SWMM模型,采用控制变量法分别计算了不同大小的渗渠LID措施和相应透水率。结果表明,渗渠LID措施的补偿效果随渗渠LID措施的增大而增大,且渗渠LID措施大小与透水率之间存在定量补偿关系,可确定其补偿效果,为渗渠LID的布设提供了依据,也为LID措施的进一步发展提供了一种新思路。     

CaO和MgO复合催化神木煤焦-CO_2气化的特性研究

利用常压等温CO_2气化的方法,研究了单组分CaO、MgO及CaO/MgO不同复合配比对神木煤焦催化气化的反应特性影响。结果表明:分别添加单组分催化剂CaO和MgO后,煤焦的气化反应活性得到了明显增强,并且CaO的催化作用要强于MgO;2种单组分催化剂添加量存在一个最优值,且均为15%,此时催化强度分别是原煤焦的5.67和2.37倍,当催化剂添加量超过这个最优值后,催化剂对气化的催化作用开始减弱;添加10%的不同CaO/MgO配比的复合催化剂,其催化效果明显强于相同含量的2种单组分,且900℃时存在一个最佳配比比例4:1,最佳配比下,催化强度是原煤焦的5.32倍,是添加10%CaO的1.69倍,是添加10%MgO的2.83倍。Takarada法计算了复合催化剂各工况下的反应性指数R,更直接地反映出了不同配比的复合催化剂对煤焦气化的影响。用未反应核收缩模型能够很好地描述煤焦-CO_2的气化反应过程;添加单组分催化剂煤焦的活化能相比原煤焦变化不大,而添加复合催化剂煤焦的活化能有一定程度的升高。     

烟煤煤焦等温CO2气化动力学模型研究

在建立的化学反应动力学控制实验条件下利用自建固定床实验台研究了烟煤煤焦等温CO2气化反应特性。采用均相模型、未反应收缩核模型和修正体积模型计算得到气化反应活化能分别为147.7kJ/mol、102.9kJ/mol和155.5kJ/mol。利用等转化率法避开反应机理函数的选择,计算得到反应活化能为144.1～166.0kJ/mol。通过比对不同模型相关系数大小以及与等转化率法计算所得活化能范围符合程度相结合的方法,确定均相模型和修正体积模型为最佳动力学模型;根据修正体积模型中经验常数b≈1,可认为修正体积模型与均相模型为同一模型。因此确定烟煤煤焦CO2气化反应最佳动力学模型为均相反应模型。     

CO2 capture using mesocellular siliceous foam (MCF)-supported CaO

CaO is a promising material as an alternative CO₂ capture material which can be used at high temperature. However, CaO sinters to form large particles under long-term high temperature conditions, resulting in a rapid decrease of its surface area and the capacity of CO₂ capture. Incorporating CaO into inert materials is a promising strategy to enhance the performance of CO₂ capture. This work investigated a novel composite material called mesocellular siliceous foam (MCF)-supported CaO to enhance the stability and capacity of CaO-based materials for CO₂ capture. The crystal structure, surface morphology and porosity property of the developed composite materials were investigated. Thermogravimetric measurements were carried out to study the cyclic CO₂ capture performance of the MCF-supported CaO composites. The results showed that a part of CaO reacted with the silica wall, and the formation of Ca₂SiO₄ within the MCF framework limited the presence of CaO in the mesopores, thus inhibited the sintering of CaO. The sample of MCF-3CaO exhibited a better performance of CO₂ capture and long-term stability, compared with the materials prepared with lower CaO loading. This work contributes to the development of high temperature CO₂ capture adsorbents, which can be applied for decarbonizing major industrials e.g. power plant.     

Toluene steam reforming properties of CaO based synthetic sorbents for biomass gasification process

Biomass gasification process generates undesired Topping Atmosphere Residue (TAR), removable by catalytic steam reforming. The use of a CO₂-sorbent powder inside the reactor bed can minimize the content of carbon dioxide and carbon monoxide by enhancing the water gas shift (WGS) reaction, offering a fuel gas rich of H₂. The present study addresses the practical feasibility of such concepts, using toluene as a representative TAR and a hybrid compound Ni/CaO–Ca₁₂Al₁₄O₃₃ as reactor bed material, simultaneously acting as reforming catalyst and CO₂ sorbent. In fact, the CaO is the effective sorbent, whereas the Ca₁₂Al₁₄O₃₃ is a support for both the CaO and the active metallic Ni particles. A different synthesis route with respect to the literature has been developed for the production of the Ni/CaO–Ca₁₂Al₁₄O₃₃ and a total of three different bed reactor powders have been tested and compared: (i) a mixture of olivine and commercial nickel catalyst, (ii) a mixture of CaO–Ca₁₂Al₁₄O₃₃ and commercial nickel catalyst, and (iii) the Ni/CaO–Ca₁₂Al₁₄O₃₃ combined catalyst and sorbent. The best performances have been observed in the latter, with toluene conversion close to 99%, and the volume fraction of hydrogen in the gas over 95%. During multi-cycle tests, the synthetic Ni/CaO–Ca₁₂Al₁₄O₃₃ combined catalyst and sorbent exhibited superior resistance to carbon deposition and stability in toluene conversion compared to the other bed materials that suffer from decreased conversion efficiency after few cycles.     

A density functional theory study of the adsorption of Hg and HgCl2 on a CaO(001) surface

The adsorption of mercury and mercury chloride on a CaO(001) surface was investigated by the density functional theory (DFT) by using Ca₉O₉ cluster embedded in an electrostatic field represented by 178 point charges at the crystal CaO lattice positions. For the mercury molecular axis normal to the surface, the mercury can only coordinate to the O²⁻ anion and has a very weak binding energy of 19.649 kJ/mol. When the mercury chloride molecular axis is vertical to the surface, the Cl atom coordinates to the Ca²⁻ cation and has a binding energy of 23.699 kJ/mol. When the mercury chloride molecular axis is parallel to the surface, the Hg atom coordinates to the O²⁻ anion and has a binding energy of 87.829 kJ/mol, which means that the parallel geometry is more stable than the vertical one. The present calculations show that CaO injection could substantially reduce gaseous mercury chloride, but have no apparent effect on the mercury, which is compatible with the available experimental results. This research will provide valuable information for optimizing and selecting a sorbent for the trace element in flue gas. Translated from Proceeding of the CSEE, 2005, 25(13): 101–104 [译自: 中国电机工程学报]     

烟气中水分对循环流化床受热面上CaO碳酸化特性的影响

为探讨循环流化床炉内受热面上飞灰的沉积特性,在热重分析仪上对有无水分条件下CaO在受热面上的碳酸化特性进行了研究,得到CaO的碳酸化反应速率和最终转化率.结果表明:水分对CaO的碳酸化进程有很大影响;当模拟烟气中存在水分时,CaO呈现出更快的碳酸化反应速率和更高的转化率,且随着温度的降低(由700℃降低到400℃),碳酸化反应得以改善的程度更加明显;温度越低,水分在CaO碳酸化反应中所起的作用越重要.最后,对该现象的反应机理进行了讨论.     

钙基吸收剂循环煅烧/碳酸化中烧结现象及改进措施

钙基吸收剂循环煅烧/碳酸化是现阶段CO2减排中最有发展前景的方法之一。但该方法存在的问题是钙基吸收剂循环捕捉CO2的能力随着循环反应次数的增加迅速下降。这主要是由于高温煅烧产物CaO在煅烧阶段发生烧结,导致空隙率降低,从而抑制了CO2通过这些孔隙扩散与CaO进行碳酸化反应。对烧结现象的机制及影响烧结程度的因素进行了分析,同时总结了国内外对改善抗烧结性能,提高钙离子活性的研究成果,为研究钙基吸收剂循环煅烧/碳酸化提供了理论及实验室条件下的支持。