流化床锅炉内石灰石同时煅烧/硫化反应中煅烧动力学特性

采用恒温热重实验台研究了循环流化床内石灰石同时煅烧硫化反应中煅烧反应与硫化反应的相互作用。当煅烧环境中存在SO₂时,煅烧反应与硫化反应同时发生,并在颗粒中生成CaSO₄。与纯煅烧工况相比,在含有SO₂的气氛中煅烧石灰石时,颗粒的质量下降速率降低,而煅烧终质量升高。SO₂的存在能够降低石灰石的煅烧速率,而且在0～0.3%的范围内,SO₂浓度越高,煅烧越慢。对该现象提出以下机理：当煅烧过程中存在SO₂时,SO₂会与正在煅烧的石灰石颗粒的CaO层发生硫化反应生成CaSO₄,所生成的CaSO₄会堵塞颗粒的孔隙,增加CO₂的扩散阻力,进而减慢煅烧反应速率。对煅烧产物孔结构的测试和计算表明在同时煅烧硫化中部分孔隙被堵塞、封闭,孔内CO₂有效扩散系数下降,证明所提出的机理能够合理解释SO₂对石灰石煅烧的减缓作用。随着粒径由0.4～0.45 mm减小到0.2～0.25 mm,无论反应环境是否存在SO₂,石灰石的煅烧速率均加快。温度对煅烧速率有明显的影响,850℃下SO₂对石灰石煅烧速率的减缓程度大于880℃,这可能是由于880℃下CaSO₄对颗粒孔隙的堵塞作用下降导致的。     

H2O和SO2对CFB内石灰石同时煅烧/硫化反应中煅烧动力学的协同作用

采用自制恒温热重分析仪,研究了CFB工况下石灰石同时煅烧/硫化反应中H₂O和SO₂对石灰石煅烧动力学和孔结构的协同作用。煅烧环境中的H₂O能够促进石灰石的分解,但SO₂会减慢石灰石分解速度,且测试发现SO₂使煅烧后颗粒的孔容积下降,分解反应的效率因子减小。基于此提出SO₂减缓煅烧反应的机理：高温下,石灰石颗粒外层首先分解并生成多孔CaO层,其中的孔隙作为内部CaCO₃分解产生CO₂的外扩散通道,当煅烧气氛中含有SO₂时,颗粒的CaO层与SO₂反应生成CaSO₄,堵塞了CaO中的孔隙,增加了CO₂扩散的阻力,从而减缓了其分解速度。当石灰石在含有15% H₂O和0.3% SO₂的环境中分解时,其分解速度比不含二者的环境下快,而比含15% H₂O但不含SO₂的环境下慢,说明H₂O和SO₂对改变石灰石分解的速度有协同效应,但15% H₂O的作用比0.3% SO₂的作用更大。对效率因子的计算表明,该现象可能由于石灰石煅烧反应的速度控制步骤中本征反应速度的影响比扩散阻力的作用更大,而H₂O能够直接加速煅烧反应的本征速度。温度、粒径等均能够影响石灰石同时煅烧/硫化反应的中的煅烧速度。H₂O还能够促进CaO的烧结,并且H₂O和SO₂在降低石灰石煅烧产物的孔面积和孔容积上具有叠加效应。     

O2/CO2气氛下多种碳基随机孔模型的建立

传统随机孔模型基于简单一步反应建立,不适用于处理O₂/CO₂气氛下焦炭颗粒复杂气固反应。针对此问题,基于焦炭本身具有多种碳基的特点,以及焦炭颗粒在O₂/CO₂气氛下燃烧的特性,建立复杂气固反应下的多种碳基随机孔模型和孔隙结构模型。模拟直径为100 μm的焦炭颗粒在O₂/CO₂气氛下燃烧的过程,使用FORTRAN语言自主编程计算并分析结果。研究表明,燃烧初期颗粒呈现竞争效应,孔隙内部气体浓度产生剧烈波动。波动的生成原因是化学反应与物理扩散之间的竞争,可以通过增加环境氧浓度和减小焦炭颗粒粒径来改善。所提出的多种碳基随机孔模型对于表征O₂/CO₂气氛下焦炭颗粒的燃烧特性有着良好的适应性。     

Effect of the flowing gases of steam and CO2 on the texture and catalytic activity for methane combustion of MgO powders

In this work, the MgO powders was prepared by the precipitation method with carbonate following calcination at 1200 °C, and then the obtained MgO powders was treated under the flowing gaseous mixture of steam and CO₂. The variations of textural properties and activity for methane combustion of the MgO sample were investigated. The sample was characterized by N₂ adsorption isotherm, TEM, XRD, and TG-DTA. The results showed that the treatment temperature and the CO concentration have a significant influence on the textural properties of the MgO sample. After run at 700 °C for 24 h under the flowing gaseous mixture of steam/CO₂/N₂ (CO₂/N₂ = 15/85 volume ratio), the maximum pore sizes varied and the pore volumes increased obviously; and remarkably, the surface area of the MgO sample increased from 37.9 to 80.1 m² g⁻¹. It was proposed that during the process, the disaggregation and rearrangement of the particles have occurred, leading to the obvious variations of the textural properties of the sample. As a result, the treated MgO sample showed a higher activity for methane combustion than the original one.     

循环流化床锅炉内石灰石同时煅烧/硫化反应模型研究

循环流化床锅炉内石灰石分解、脱硫发生的是同时煅烧/硫化反应。建立了石灰石同时煅烧/硫化反应的随机孔模型,综合考虑石灰石的分解、烧结和硫化,且CaO硫化反应基于CaSO₄产物层固态离子扩散模式。模型计算结果与实验测试结果吻合良好,并采用该模型研究了同时煅烧/硫化反应的特性。石灰石的同时煅烧/硫化反应包含连续的质量下降阶段和质量上升阶段,且质量最低点随着SO₂浓度的增加而升高。石灰石颗粒的煅烧反应发生在颗粒的壳层内,煅烧反应更符合区域反应模型而不是均相反应或缩核反应模型。煅烧环境中的SO₂与CaO层反应生成CaSO₄,导致CaO层内孔径和孔隙率减小,CO₂外扩散阻力增大,从而导致煅烧反应减慢。颗粒硫化反应速度随时间减慢,主要是颗粒内SO₂耗尽导致的,颗粒外层不断积累的CaSO₄减小了SO₂扩散通道,增加了SO₂孔内扩散阻力,使颗粒内SO₂耗尽区不断增大,颗粒的硫化反应速度不断下降。     

CHARACTERISTICS OF THE REVERSIBLE REACTION BETWEEN CO2(g) AND CALCINED DOLOMITE

The noncatalytic gas-solid reaction between calcined dolomite and CO₂(g) has been studied in an electrobalance reactor as a function of temperature, pressure, and reactive gas composition. Multicycle tests consisting of as many as ten complete calcination-carbonation cycles were carried out to obtain information on sorbent durability. Surface area, pore volume, and pore size distribution measurements were made to supplement the reaction studies. This reaction is of interest both as a model for studying (he importance of structural property changes in gas-solid reactions, and as the basis for a possible process for the high temperature separation of CO₂ from gas streams.

Calcined dolomite is a superior sorbent to calcined CaCO₃ in that larger fractional conversions of CaO and improved multicycle durability are possible. With CaO obtained from CaCO₃, the first-cycle fractional recarbonation was limited to about 0.80, a value which decreased by 15 to 20% in each subsequent cycle. In contrast, the first-cycle fractional recarbonation of CaO in calcined dolomite was typically 0.90 to 0.95, and this value decreased by only 1 to 2% in each subsequent cycle. These advantages are atlributed to the “excess” pore volume created by the original decomposition of MgCO₃ in dolomite, and by a reduction in the rate of CaCO₃ sintering in the presence of MgO.     

同时煅烧硫化反应中石灰石微观孔结构演变特性

采用自制恒温热重实验装置,测试了石灰石同时煅烧硫化反应的煅烧动力学特性和颗粒孔结构演变特性,探讨了孔结构演变机理。当煅烧环境中存在SO₂时,石灰石颗粒煅烧的同时发生硫化反应。煅烧环境中SO₂的存在降低了石灰石煅烧速率。与纯煅烧相比,同时煅烧硫化反应的比表面积和比孔容增长均较慢,比表面积和比孔容分布曲线均较低,且在反应后期直径2～8 nm内小孔的比表面积和比孔容随时间降低。提出了描述石灰石同时煅烧硫化反应过程中微观孔结构演变的模型：石灰石颗粒的煅烧由颗粒的表面向内进行,在煅烧前期（0～75 s）,少量CaSO₄在CaO表面生成,小部分孔隙被CaSO₄堵塞,CaSO₄对煅烧速率和孔结构的影响较小;在煅烧中期（75～225 s）,CaSO₄厚度和覆盖面积不断增加,堵塞孔体积增加,CO₂的扩散阻力增加,导致石灰石的煅烧速率下降;煅烧后期（225～300 s）,由于CaSO₄的不断积累,孔隙堵塞加剧,且堵塞主要发生在小孔上。对煅烧过程堵塞孔体积的计算表明,在煅烧前期和中期孔堵塞现象已经发生,在反应后期孔堵塞体积快速增加。     

PREDICTION OF MEMBRANE SEPARATION CHARACTERISTICS BY PORE DISTRIBUTION MEASUREMENTS AND SURFACE FORCE-PORE FLOW MODEL

Pore size distribution of polyamide thin film composite reverse osmosis membranes and a cellulosic ultrafiltration membrane were obtained from vapor adsorption data of CO₂ and N₂ gases. The surface: force-pore flow model previously reported in the literature was utilized in this work. The pore distribution data were further used with solutes separation data at a particular pressure to obtain the values of solute-solvent-membrane wall forces involved. The interaction parameters were obtained by the simultaneous solution of the ordinary differential equations describing the model using the software package COLSYS. From the knowledge of the pore distribution data and the interactions forces, the solutes separation data (for nonionized organics and sodium chloride) were predicted over a wide range of pressures and showed excellent agreement with experimental separation data.     

钙循环捕集CO2后CaO的水合/脱水热化学储热性能

提出了基于CaO的钙循环捕集CO₂与CaO/Ca(OH)₂体系热化学储热耦合新工艺，在双固定床反应器上，研究了循环捕集CO₂中煅烧条件和碳酸化条件对CaO储热性能的影响，探究CaO循环捕集CO₂过程和循环水合/脱水储热过程的相互作用。研究表明，多次循环碳酸化/煅烧捕集CO₂后CaO仍具有较高储热性能，10次循环捕集CO₂后再经10次储热循环，CaO水合转化率可达0.66mol/mol。与苛刻煅烧条件相比，温和煅烧条件下经历多次循环捕集CO₂后CaO的储热性能更高。在碳酸化气氛中加入水蒸气对经历多次循环捕集CO₂后CaO储热性能的影响不大。钙循环捕集CO₂过程和水合/脱水循环储热过程能够相互促进。该工艺有望同时实现CO₂捕集和储热，具有一定的应用前景。     

SURFACE AREA AND PORE SIZE CHANGES DURING SINTERING OF CALCIUM OXIDE PARTICLES

Changes in surface area and pore size during the sintering of CaO samples between 0·71 to 1 mm, were studied. Typical operating conditions in fluidized bed combustors (temperature between 973 and 1173  K and CO₂ concentrations up to 15%) were chosen. The longest sintering time was 90min. The decrease in the surface area with sintering time was described using an empirical equation deduced from the German-Munir model. Surface area reduction and increase in pore size was strongly affected by the presence of CO₂. Shrinkage of the CaO particles was not observed during sintering. The pore volume and porosity remain unaffected by sintering. A qualitative model, based on SEM microphotographs, for describing the sintering process was proposed.     

氨水吸收CO2的吸收热预测模型

基于e-NRTL模型,利用Aspen Plus软件建立了氨水吸收CO₂的吸收热预测模型,验证了NH₃-CO₂-H₂O体系的汽液平衡、液相组成形态并与前人的实验数据做了对比,进而结合负载CO₂的氨水溶液中各离子及分子的变化特征,对CO₂吸收过程的反应热随着CO₂负载量的变化规律进行了预测并与已发表的数据进行了比较。结果表明,该吸收热模型能够准确地实现氨水吸收CO₂过程中汽液平衡、液相反应以及吸收热的计算。氨水吸收CO₂的反应热主要受H₂O的电离、NH₃的电离、NH₂COO^-的生成与水解、CO₂的溶解等反应过程的影响,H₂O的电离过程受NH₃的电离过程的抑制,对于总吸收热的贡献最大, NH₂COO^-的反应则随着CO₂负载量的增加先放热再吸热。随着温度的升高,总吸收热有所降低,当温度为80℃时,在较低的CO₂负载区间[0.2～0.5 mol CO₂·(mol NH₃)^-1],总吸收热约为70.5 kJ·(mol CO₂)^-1。     

焙烧温度对MnZnOx物化性质及催化性能的影响

采用湿化学共沉淀法制备了MnZnO_x固溶结构催化剂,考察了焙烧温度对催化剂物化性质和催化性能的影响。采用X射线衍射（XRD）、X射线光电子能谱（XPS）、N₂吸附-脱附、CO₂-TPD（程序升温脱附）及H₂-TPR（程序升温还原）等手段对不同焙烧温度下催化剂物化性质进行了分析表征。结果表明,焙烧温度对MnZnO_x晶相组成、孔结构性质、二氧化碳吸附特性及表面氧空位浓度等物化性质影响较大。500 ℃焙烧条件下制得的MnZnO_x催化剂形成了具有丰富的表面氧空位、较大的二氧化碳吸附量和介孔孔容且溶质组分分散均匀的固溶结构。在反应压力为3.0 MPa、反应空速（GHSV）为14 400 mL/（g·h）、V（氢气）∶V（二氧化碳）∶V（氮气）=72∶24∶4条件下,MnZnO_x催化剂于380 ℃表现出优异的催化性能,甲醇选择性为86.1%、二氧化碳转化率为16.0%、甲醇时空产率（STY）达0.68 g_MeOH /（h·g_cat）。     

煤焦在气化合成气中高温气化反应特性

在固定床管式炉反应器中进行了煤焦在H₂O、CO₂、H₂和CO混合气氛中气化特性的实验研究,考察了反应温度、原料气组成和加煤量对产物气组成以及碳转化率的影响。实验结果表明,在各实验条件下,合成气与煤焦反应后CO流量均增加最多,H₂少量增加。煤焦与CO₂的反应受到明显抑制。混合气体通过与煤焦反应可以提高有效气（CO+H₂）的含量,实验条件下反应出口气体中有效气浓度比反应结束时最多提高3.3个百分点。反应速率受气化剂之间的竞争和气化产物的抑制作用较为明显,在1100℃和1300℃时,煤焦在相同气化剂流量的合成气中的最高反应速率分别只有在纯气化剂（水蒸气或CO₂）中最高反应速率的49%和69%。受到多种气体组分之间的相互影响,气体在孔道里的扩散和吸附对反应影响更加显著,随机孔模型可以较好地拟合此类反应,而不考虑孔结构的均相模型和缩芯模型拟合度较差。     

HIGH TEMPERATURE CAPTURE OF CARBON DIOXIDE: CHARACTERISTICS OF THE REVERSIBLE REACTION BETWEEN CaO(s) and CO2(g)

The reversible reaction between CaO(s) and CO₂(g) may ultimately find application in a high temperature process to control CO₂ emissions from advanced power generation processes. At appropriate temperature and pressure combinations, CO₂(g) is removed from the gas phase and captured as CaC₃(s). At higher temperature and/or lower pressure, the reaction is reversed to produce a gas stream having high CO₂(g) concentration suitable for use or ultimate disposal. Both the calcination and carbonation reactions have been studied in an electrobalance reactor as a function of temperature, pressure, and gas composition. Multicycle tests have provided preliminary information on sorbent durability. Solid structural property characteristics have been measured as a supplement to the reaction studies.

Rapid and complete calcination of CaCO₃ can be achieved at temperatures as low as 750°C under one atmosphere of N2. Higher pressure reduces the calcination rate while the presence of CO₂ in the calcination atmosphere requires the use of higher temperature. Mild calcination conditions produce a CaO product which is most reactive during the carbonation phase. Carbonation is characterized by a rapid initial reaction rate followed by an abrupt transition to a quite slow rate. Significant reduction in CO₂ capacity between the first and second carbonation cycles, ranging from 15% under favorable reaction conditions to more than 30% at severe conditions, was found. However, the capacity loss tended to moderate as the number of cycles increased.     

Characteristics of reactivity and structures of palm kernel shell (PKS) biochar during CO2/H2O mixture gasification

Palm kernel shell (PKS) biochars with different levels of carbon conversion were initially prepared using a tube furnace, after which the reactivity of each sample was assessed with a thermogravimetric analyzer under a CO₂ atmosphere. The pore structure and carbon ordering of each biochar also examined, employing a surface area analyzer and a Raman spectroscopy. Thermogravimetric results showed that the gasification index R_s of the PKS biochar decreased from 0.0305 min^-1 at carbon conversion (x)=20% to 0.0278 min^-1 at x=40%. The expansion of micropores was the dominant process during the pore structure evolution, ad mesopores with sizes ranging from 6 to 20, 48 to 50 nm were primarily generated during gasification under a CO₂/H₂O mixture. The proportion of amorphous carbon in the PKS biochar decreased significantly as x increased, suggesting that the proportion of ordered carbon was increased during the CO₂/H₂O mixed gasification. A significantly reduced total reaction time was observed when employing a CO₂/intermittent H₂O process along with an 83.46% reduction in the steam feed, compared with the amount required using a CO₂/H₂O atmosphere.     

Coupling the porous conditional moment closure with the random pore model: applications to gasification and CO2 capture

Gasification of coal or biomass with in situ CO₂ capture simultaneously allows production of clean hydrogen at relatively low cost and reduced emission of CO₂ into the atmosphere. Clearly, this technology has a great potential for a future carbon constrained economy. Therefore, the development of a comprehensive, physically-based gasifier model is important. The sub-models that describe reactive transport processes in coal particles as well as in particles of CO₂ sorbent material are among the key sub-models, which provide a necessary input for an overall gasifier model. Both coal and sorbent are materials that have complicated pore structures. The porous conditional moment closure (PCMC) model proves to be adequate for modeling reactive transport through porous media with fixed pore structure. Consumption of coal in the heterogeneous gasification reaction, however, widens the pores and reduces the surface area available for this reaction. At the same time, formation of a carbonate layer narrows the pores in the sorbent material and reduces the reaction rate of CO₂ sorption. In both cases the pore structures are affected. Such changes are not taken into account in the existing PCMC model. In this study, we obtain the parameters of the diffusive tracer distribution based on the pore size distribution given by the widely applied random pore model (RPM), while coupling PCMC with RPM. Such coupling allows taking into account changes in pore structure caused by heterogeneous reactions and thus improves the accuracy of these key sub-models.     

高温煤焦气化反应的Langmuir-Hinshelwood动力学模型

应用基于吸附和脱附原理的Langmuir-Hinshelwood （L-H） 动力学模型来描述煤焦在H₂O和CO₂混合气氛下的气化反应时,存在单独活性位和相同活性位两个相互矛盾的假设。在管式炉实验装置内考察了在不同气化温度和气化剂分压的条件下,内蒙煤焦（NMJ）与H₂O和CO₂的气化反应特性,获得了NMJ-H₂O 和NMJ-CO₂反应的L-H动力学模型,同时考察了H₂、CO对煤焦气化反应的抑制作用,并探究了NMJ在H₂O和CO₂混合气氛下的气化反应机理。研究结果表明：NMJ-H₂O以及NMJ-CO₂反应的活化能分别为214.78 kJ·mol^-1和145.96 kJ·mol^-1。H₂对NMJ-H₂O以及CO对NMJ-CO₂的反应存在明显的抑制作用,且CO的抑制作用随反应温度的降低而愈加明显。基于L-H动力学模型计算得到的反应速率曲线与实验结果十分吻合。对于NMJ在H₂O和CO₂混合气氛下的气化反应,基于相同活性位假设的L-H模型的反应速率预测值与实验结果吻合,更加适用于NMJ在混合气氛下的气化反应机理。     

基于CO2循环的低碳高效白云石煅烧新工艺

白云石是一种广泛应用的冶金、建材和化工原料。针对白云石煅烧过程中CO₂排放严重等问题,构建了基于CO₂循环载热与资源化回收的白云石低碳煅烧竖窑新工艺。通过白云石（CaCO₃·MgCO₃）煅烧过程的Gibbs自由能变计算,发现提高煅烧温度（50~100 K）可有效克服CO₂对反应的抑制作用;通过纯CO₂环境中CaCO₃分解过程的热重实验分析,验证了CO₂循环煅烧白云石煅烧的可行性;通过化学反应动力学计算,解析了全CO₂组分环境下CO₂压力对CaCO₃·MgCO₃高温分解过程的影响,并发现提高CO₂压力可促进气固传热,从而提升分解速率和改善矿料分解均匀性;对CO₂循环煅烧工艺系统能-质平衡计算表明：该工艺理论能耗仅为140 kg/(t 煅白),且煅烧过程的CO₂排放降低70%以上,环境效益显著。     

Atomistic simulations for adsorption and separation of flue gas in MFI zeolite and MFI/MCM-41 micro/mesoporous composite

Adsorption of pure CO₂ and N₂ and separation of CO₂/N₂ mixture in MFI zeolite and MFI/MCM-41 micro/mesoporous composite have been studied by using atomistic simulations. Fully atomistic models of MFI and MFI/MCM-41 are constructed and characterized. A bimodal pore size distribution is observed in MFI/MCM-41 from simulated small- and broad-angle X-ray diffraction patterns. The density of MFI/MCM-41 is lower than MFI, while its free volume and specific surface area are greater than MFI due to the presence of mesopores. CO₂ is preferentially adsorbed than N₂, and thus, the loading and isosteric heat of CO₂ are greater than N₂ in both MFI and MFI/MCM-41. CO₂ isotherm in MFI/MCM-41 is similar to that in MFI at low pressures, but resembles that in MCM-41 at high pressures. N₂ shows similar amount of loading in MFI, MCM-41 and MFI/MCM-41. The selectivity of CO₂ over N₂ in the three adsorbents decreases in the order of MFI>MFI/MCM-41>MCM-41. With increasing pressure, the selectivity increases in MFI and MFI/MCM-41, but decreases in MCM-41. The self-diffusivity of CO₂ and N₂ in MFI decreases as loading increases, while in MFI/MCM-41, it first increases and then drops.     

二氧化碳浓度对石灰石分解反应动力学的影响

基于石灰石热重-差示扫描量热（TG-DSC）分析结果,分别在不同浓度的二氧化碳（二氧化碳与空气的混合气）气氛下对石灰石进行热分解特性研究。TG和DSC分析结果表明,碳酸钙分解是吸热反应,反应温度范围为750~950 ℃;提高升温速率,反应进程加快,TG曲线向高温区移动,DSC曲线吸热峰和吸热面积明显增大;反应气氛中二氧化碳浓度提高,TG曲线稍微向高温区移动,反应起始温度相同,反应终止温度相差约20 ℃。在高浓度二氧化碳气氛下,石灰石分解遵循随机成核和随后生长模型。此研究结果可为进一步优化石灰石煅烧工艺以及煅烧炉的设计提供理论支持。