Modification of CaO-based sorbents prepared from calcium acetate for CO_2 capture at high temperature

CaO-based sorbent is considered to be a promising candidate for capturing CO_2 at high temperature. However,the adsorption capacity of CaO decreases sharply with the increase of the carbonation/calcination cycles. In this study, CaO was derived from calcium acetate(CaAc_2), which was doped with different elements(Mg, Al,Ce, Zr and La) to improve the cyclic stability. The carbonation conversion and cyclic stability of sorbents were tested by thermogravimetric analyzer(TGA). The sorbents were characterized by N_2 isothermal adsorption measurements, scanning electron microscopy(SEM) and X-ray diffraction(XRD). The results showed that the cyclic stabilities of all modified sorbents were improved by doping elements, while the carbonation conversions of sorbents in the 1st cycle were not increased by doping different elements. After 22 cycles, the cyclic stabilities of CaO–Al, CaO–Ce and CaO–La were above 96.2%. After 110 cycles, the cyclic stability of CaO–Al was still as high as 87.1%. Furthermore, the carbonation conversion was closely related to the critical time and specific surface area.

Effect of pre-calcination for modified CaO-based sorbents on multiple carbonation/calcination cycles

In the present work,the effect of pre-calcination on carbonation conversion and cyclic stability of modi fied CaObased sorbent was investigated by thermogravimetric analyzer(TGA).The modi fied CaO-based sorbents with CaAc_2 as precursor were respectively doped with different elements(Mg,Al,Ce,Zr and La).The speci fic surface area,pore volume and pore size distribution were tested by N_2 isothermal adsorption measurements.The phase compositions of sorbents were characterized by X-ray diffraction(XRD).The results showed that the cyclic stabilities of the sorbents were improved by pre-calcination.The pre-calcination was conducted at 900°C for 5 h in air by the muf fle furnace.With pre-calcination,the cyclic stabilities of sorbents could be as high as 96% after 22 cycles,such as CaO-Al,CaO-Ce and CaO-La.After contact with air,the carbonation conversions of spent sorbents with pre-calcination suddenly increased by about one-sixth due to the change of channel structure by hydration.Both the cyclic stability of sorbent and the durability of reactivation were related to the structural stability of sample,especially the stability of mesopores between 2 nm and 5.5 nm.The present work also provided an easy and low-cost method for reactivating the spent CaO-based sorbents.

EFFECTS OF TEMPERING TEMPERATURE AND TIME ON SHEAR MODULUS OF Fe-Mn BASED ALLOYS

Effects of the tempering temperature and time on the shear modulus of Fe-Mn based alloys have been studied.The results show that(ΔG/G)-Tcurves of tempered alloys containing Cr and Ti have two extreme values—maximum and minimum,and that the curves of tem- pered alloys containing Cr,Ni,W and C only have a maximum value.This is the reason that Ni,W and C decrease the transformation point T_N of the antiferromagnetism.The ΔG_λ ef- feet increases gradually with the rise of tempering temperature or with the increase of tem- pering time.

Relations between the Lattice Parameter and the Stability of Austenite against ε Martensite for the Fe-Mn Based Alloys

The influences of lattice parameter of austenite, the electron concentration, the yield strength of parent phase on γ→ε martensite start temperature Ms in the Fe-Mn alloys containing C, Al, Ge and Si have been experimentally investigated. The results show that the lattice parameter of austenite is more important than the electron concentration and the yield strength of parent phase in governing the γ→ε martensitic transformation in Fe-Mn based alloys. A relation between the Ms and lattice parameter of austenite in Fe-Mn based alloys is suggested. The elements Mn, C, Al, Ge, which increase the lattice parameter of austenite lower the Ms; while the element Si, which decreases the lattice parameter increases the MS. The depressing effect of antiferromagnetic transition on the γ→ε martensitic transformation may be related to the increase of lattice parameter due to the positive magnetostriction during the antiferromagnetic transition.

Research on improvement in Zn-based sorbent for hot gas desulfurization

Two Zn-based sorbents, L-991 and L-992 used for hot gas desulfurization (HGD) were introduced. Zn/Ti ratio of the two sorbent was 1:1 and 2:3 resptively and a certain proportion of Cu and Mn metal oxide were added into L-992, which provided better performance than L-991 in aspects of suitable work temperature, sulfur capacity and agglomeration on the surface of sorbent particles. The evaluation tests were done on both sorbents include multi cycles tests. ARD and SEM analysis were done on fresh and post tests sorbent. During continuous sulfidation/regeneration, the H2S concentra- tion can be reduced from about 10 g/m3 to less than 20 mg/m3, the H2S removal effi- ciency >99 %.

失活石灰石自活化增强循环捕集CO_(2)特性

钙循环工艺是一种低成本高效率捕集CO_(2)技术,运行过程需不断补充新鲜吸收剂并排出失活吸收剂,实现失活钙基吸收剂原位资源化利用具有重要意义。为研究颗粒状石灰石失活后自活化特性,运用双固定床反应器制备了失活石灰石,分析了自活化后石灰石碳酸化转化率随循环次数的变化规律,采用XRD、SEM、N_(2)吸附等分析测试手段探究了自活化提高失活石灰石循环捕集CO_(2)性能机理。结果表明,失活石灰石置于环境中可吸收空气中水分生成Ca(OH)_(2),吸水率φ达100%后,继续吸水生成氢氧化钙水合物,极限吸水率为130%。不同程度自活化后的石灰石循环捕集CO_(2)性能均有不同程度提高,随吸水率变化呈线性升高趋势。与分析纯CaCO3相比,失活石灰石对吸水率变化更敏感,随吸水率升高其循环捕集CO_(2)性能提高更快。吸水率为130%时,自活化后石灰石循环捕集CO_(2)性能甚至优于新鲜石灰石。微观结构分析结果显示:新鲜石灰石因高温烧结而失活过程中,CaO晶粒尺寸由41.9 nm长大至72.2 nm,孔隙结构发生坍塌阻塞,比孔容和比表面积显著降低。经过自活化,煅烧后的石灰石中CaO晶粒尺寸降低,原本密实的表面重新生成孔隙结构;吸水率为130%时,晶粒尺寸降至35.1 nm,比孔容和比表面积分别恢复至新鲜石灰石的70.5%和107.6%,特别是10~100 nm孔隙得以再生,因此失活石灰石循环捕集CO_(2)性能恢复。虽然自活化过程会加剧失活石灰石颗粒磨损速率,但吸水率100%的自活化石灰石磨损导致直径每小时减小量仅为颗粒直径的0.55%。综上所述,自活化后的失活石灰石完全可替代新鲜石灰石,作为补充钙基吸收剂用于钙循环捕集CO_(2)。

焙烧温度对Fe-Mn基吸附剂中高温煤气脱硫性能的影响及其作用机理

对优选出的Fe/Mn摩尔比为7∶3的7F3M系列复合氧化物吸附剂进行孔结构特性和活性组分形态的表征及其还原、硫化性能的考察,主要研究焙烧温度对吸附剂比表面积、孔体积和活性组分存在形态及其含量的影响,并与不同焙烧温度制得的吸附剂在不同空速和硫化温度下的脱硫行为进行关联。结果表明:焙烧温度升高,吸附剂比表面积和孔容逐渐增大,600℃时达到最大值;继续升高焙烧温度,吸附剂表面会因烧结而使其比表面积和孔容急剧下降;吸附剂的还原性随焙烧温度的升高而降低,这直接影响吸附剂中活性组分铁和锰的存在形态;吸附剂在脱硫反应过程中的活性组分也与其硫化反应的温度有关,硫化温度越高,铁锰各形态活性组分的化学反应能力越低,吸附剂中Fe3O4的含量在硫化反应过程中起主要作用。600℃焙烧制得的7F3M600吸附剂在2 000 h-1,500℃下具有最佳的脱硫行为,其脱硫效率高于99%的稳定运行时间大于30 h,硫容最大可达45.56 gS/100 g吸附剂。

Desulfurization kinetics of ZnO sorbent loaded on semi-coke support for hot coal gas

Zn-based sorbent （Z20SC） prepared through semi-coke support in 20 wt% zinc nitrate solution by high-pressure impregnation presents an excellent desulfurization capacity in hot coal gas,in which H2 S can not be nearly detected in the outlet gas before 20 h breakthrough time.The effects of the main operational conditions and the particle size of Z20SC sorbent on its desulfurization performances sorbent were investigated in a fixed-bed reactor and the desulfurization kinetics of Z20SC sorbent removing H2 S from hot coal gas was calculated based on experimental data.Results showed that the conversion of Z20SC sorbent desulfurization reaction increased with the decrease of the particle size of the sorbent and the increases of gas volumetric flow rate,reaction temperature and H 2 S content in inlet gas.Z20SC sorbent obtained from hydrothermal synthesis by high-pressure impregnation possessed much larger surface area and pore volume than semi-coke support,and they were significantly reduced after the desulfurization reaction.The equivalent grain model was reasonably used to analyze experimental data,in which k s=4.382×10-3 exp（-8.270×103/RgT） and Dep=1.262×10-4exp（1.522×104/RgT）.It suggests that the desulfurization reaction of the Z20SC sorbent is mainly controlled by the chemical reaction in the initial stage and later by the diffusion through the reacted sorbent layer.

HCl Dry Removal with Modified Ca-Based Sorbents at Moderate to High Temperatures

Modified Ca-based sorbents were obtained by adding sodium alkali into Ca(OH)2 and CaCO3. Reactive properties of modified Ca-based sorbents with acidic gases were investigated through reacting with gaseous HC1 at 450--760℃, and SEM and XRD technologies were adopted to get information on the reaction mechanism. Experimental data showed that HC1 dry removal efficiencies increased with temperature before 700℃ for all of the investigated sorbents, and there existed improved sorbents that corresponded to the highest removal efficiencies under the similar conditions. SEM photographs exhibited morphology difference between original and improved sorbents both before and after the reaction; and displayed that improved sorbents formed more porous product layers than original sorbents especially at higher temperature when product sintering became heavier, which is favorable to HC1 dry removal. XRD analysis showed that (1) improved Ca(OH)2 and CaCO3 were less crystalline than original lime and limestone; (2) the reaction product species of improved Ca(OH)2 changed with reaction temperature,while for original Ca(OH)2 the same product species appeared for all of the teated temperatures; and (3) for improved CaCO3, the only product at lower temperatures was CaCl2.2H20 and more product species were produced when temperature was higher than 650℃,but no CaCl2.Ca(OH)2.H2O formed at 700℃, while for the case of original CaCO3, the undesired CaCl2.Ca(OH)2.H2O appeared at 700℃. Presently, reaction temperature interval of 650--700℃ is recommended for improved Ca(OH)2 to get the highest efficiency, for improved CaCO3 reaction at higher temperature deserves further investigation to make a good choice.

基于CFD的钠基干法脱硫反应器的研究优化

本文采用CFD技术并结合DPM模型计算了钠基干法脱硫反应器(SDS)运行时小苏打颗粒的扩散状态。通过在不同场景下拾取反应器中4个截面的颗粒分布形态判断其均匀程度,研究出扰流板的合理布置方式,以确保反应器的脱硫效率。研究结果显示,在反应器前端布置3级扰流板对颗粒流进行扰流,可使其在反应器内尽早地均匀扩散。该场景下小苏打颗粒从开始喷射至反应器出口,停留时间约2.5 s,烟气与小苏打粉末在反应器内均匀混合且有足够的反应时间,有效的保证了该反应器的脱硫效率。

Effects of steam on CO2 absorption ability of calcium-based sorbent modified by peanut husk ash

The CO_2 absorption ability of synthetic calcium-based sorbent modified by peanut husk ash (PHA) was tested by Thermal Gravimetric Analyzer (TGA), and the effects of steam and calcination temperature were investigated. The PHA composition was analyzed by X-Ray Fluorescence (XRF), the apparent morphology was characterized by scanning electron microscope (SEM), and the phases of the sorbent before and after calcination were examined by X-ray diffraction (XRD). The addition of PHA effectively improved the cyclic stability of the calcium-based sorbent. The optimal molar ratio of SiO_2 in PHA to CaO was around 0.07. Steam had positive effect on keeping porosity of the sorbent at the chemical reaction stage, and improved its CO_2 absorption ability. Steam also reduced the diffusion resistance of the product layer, and depressed the influence of high temperature calcination. It was also found that the steam hydration after calcination was an effective way to recover the absorption ability of the sorbent, while the hydration duration of 10 min was enough.

固定床PVC燃烧脱氯的机理和试验

研究垃圾组分PVC在焚烧过程中HCl的排放和脱除特性的实验在准等温、电加热的水平石英管反应器中进行 .随着床温从 70 0℃升高到 90 0℃ ,HCl的转化率从 82 5%平缓增加到 88 3% ,而过量空气系数的增加促使部分HCl转化为Cl2 ( 1 9%～ 4 5% )的形式存在 .钙基吸收剂CaCO3,Ca(OH) 2 ,Ca(CH3COO) 2 对HCl的脱除效率高达 68%～ 79% ,而镁基吸收剂的脱氯效率却低于 3% .小的吸收剂粒径、高的Ca/Cl比会促进脱氯效率的提高 ;烟气中CO2 和H2 O对脱氯效率的影响与它们在反应平衡中所起作用有关 .高温下燃烧固氯机理反应的平衡常数的计算不仅诠释了实验结果 ,而且提供了脱氯吸收剂选择的依据 .

钙基类吸附剂脱除烟气中气态汞的试验研究

用恒温水浴中汞渗透管的汞蒸气发生装置和其他烟气主要气体成分模拟烟气条件，在小型固定床试验台上开展钙基类物质作为吸附剂脱除单质汞的试验研究。结果表明，无SO2时，两种钙基吸附剂以及飞灰和熟石灰混合物对单质汞的吸附效率不高；当SO2存在时，对单质汞的脱除效率可增加15％-20％，30min时吸附量可增加50％以上，且吸附在较高温度下更有利。其原因在于SO2同钙基吸附剂之间的化学反应，在钙基物质表面产生了活性区域，有利于提高对Hg^0的捕捉效率，化学吸附起到了促进吸附的作用。

钙基吸收剂脱硫反应特性的研究

本文对两种钙基吸收剂——ＣａＯ和Ｃａ（ＯＨ）２的脱硫反应机理进行了试验研究。对两者的反应活性进行了比较，并就一些因素（包括吸收剂粒径、脱硫反应温度、Ｆｅ２Ｏ３、ＮａＣｌ、Ｖ２Ｏ５和ＺｎＯ等添加剂等）对脱硫活性的影响作了研究，所得结论对脱硫反应的优化。

钙基吸收剂循环煅烧/碳酸化法捕集CO_2的研究进展

控制和减缓化石能源燃烧所排放的CO2对于缓解全球变暖和温室效应具有重要意义。作为一种燃烧后CO2捕集技术,采用钙基吸收剂循环煅烧/碳酸化(cyclic calcination/carbonation reaction,CCCR)法捕集烟气中CO2的技术因其相对于胺吸收法有一定的经济性而受到关注。在对钙基吸收剂CCCR法的基本概念与特点介绍的基础上,对其中3个重要的研究内容与存在问题,即反应动力学、吸收剂循环转化率与吸收剂的改性以及双流化反应器的研究现状进行综述分析,指出应研究气固反应临界产物层的形成与生长规律,研制高循环反应活性、稳定性和机械强度且价廉及环境友好的吸收剂,开展钙基吸收剂CCCR法综合特性、与燃煤电厂系统组合与优化方案及其技术经济分析。

新型钡基高温燃烧固硫剂的研究与应用

The desulfurization technology during coal combustion in furnace has been a competitive choice for middle and small industrial boilers to meet the environmental protection requirements,with the advantage of low cost and convenient operation.The ordinary calcium-based sorbents such as limestone and calcium carbide residue have low desulfurization efficiency during coal combustion because of CaSO 4 decomposition.The sulphation product BaSO 4 which don’t decompose until 1580?℃ has much better thermal stability than CaSO 4 which rapidly decompose at about 1300?℃.A new type of barium-based sorbent with high desulfurization efficiency was developed.ZCS intelligent sulfur determination analyzer was used to study sulfur capture mechanism during the high temperature combustion process of coal.In addition the dynamic sulfur capture process of the mixture of barium-based sorbent and calcium-based sorbent was studied in detail.Industrial grate furnace experiment revealed that the desulfurization efficiency of barium-based sorbents could reach 35.5%, which is higher than 13.88% of calcium-based sorbent.It implied that the desulfurization effect of barium salt was much better than calcium salt during coal combustion at about 1200～1300?℃.

高CO_2浓度下钙基吸收剂脱硫的实验研究

本文进行了高ＣＯ２浓度下钙基吸收剂脱硫的实验研究。结果表明，高浓度ＣＯ２下钙基吸收剂的脱硫效率随脱硫时间的变化与空气条件下显著不同。孔隙结构分析及热重分析等手段表明高ＣＯ２浓度主要影响了钙基吸收剂的煅烧分解过程，形成了有利于脱硫反应的孔隙结构。实验结果还表明提高温度有利于改善高浓度ＣＯ２气氛下钙基吸收剂煅烧后孔隙结构，在适当的脱硫时间内，高温下高浓度ＣＯ２气氛比空气气氛更有利于炉内喷钙脱硫。

钾钠盐类对钙基CO_2吸附剂循环碳酸化的影响

钙基CO2吸附剂如石灰石在循环煅烧/碳酸化过程中随着循环次数的增加碳酸化转化率迅速衰减,这对CO2的捕捉极为不利。该文在常压煅烧/碳酸化反应器系统上研究KCl、K2CO3、NaCl和Na2CO3作为添加剂对CaCO3循环碳酸化特性的影响。结果表明,在初始循环时,钾钠盐类的添加造成CaCO3碳酸化转化率的明显衰减,但随着循环次数的增加,添加剂使CaCO3转化率下降缓慢,反而高于原CaCO3转化率。钾盐较钠盐对CaCO3循环捕捉CO2能力有更好的促进作用,钾/钠氯化物比钾/钠碳酸盐效果更好。在CaCO3中添加质量比为0.5%～0.6%的KCl,碳酸化温度在680～700℃时,吸附剂能取得最高的循环碳酸化转化率,经20次循环反应后转化率可达0.44,而在相同条件下原CaCO3转化率仅为0.21。KCl对CaCO3碳酸化的影响包括两方面。一方面,KCl虽然在初始循环时使CaCO3煅烧后的比表面积和比孔容减小,但在长期的循环中能够使它们保持稳定;另一方面,KCl能增加反应中碳酸化产物层的缺陷浓度,有可能增大未反应Ca离子通过产物层的扩散率。因此添加了KCl的CaCO3能够在长期煅烧/碳酸化循环中保持良好的碳酸化性能。

O_2/CO_2方式下钙基吸收剂在脱硫过程中微观结构变化的研究

本文研究了 Ｏ２／ＣＯ２方式下钙基吸收剂在脱硫过程中微观结构的变化。研究结果表明，不同浓度的 ＣＯ２对孔隙结构的影响完全不同；且提高温度有利于改善高浓度ＣＯ２气氛下钙基吸收剂煅烧后的孔隙结构，较之空气气氛，高浓度ＣＯ２气氛更有利于高温下炉内喷钙脱硫。