NO removal performance of CO in carbonation stage of calcium looping for CO2 capture

Calcium looping realizes CO2 capture via the cyclic calcination/carbonation of CaO.The combustion of fuel supplies energy for the calciner.It is unavoidable that some unburned char in the calciner flows into the carbonator,generating CO due to the hypoxic atmosphere in the carbonator.CO can reduce NO in the flue gases from coal-fired power plants.In this work,NO removal performance of CO in the carbonation stage of calcium looping for CO2 capture was investigated in a bubbling fluidized bed reactor.The effects of carbonation temperature,CO concentration,CO2 capture,type of CaO,number of CO2 capture cycles and presence of char on NO removal by CO in carbonation stage of calcium looping were discussed.CaO possesses an efficient catalytic effect on NO removal by CO.High temperature and high CO concen-tration lead to high NO removal efficiency of CO in the presence of CaO.Taking account of better NO removal and CO2 capture,the optimal carbonation temperature is 650 ℃.The carbonation of CaO reduces the catalytic activity of CaO for NO removal by CO due to the formation of CaCO3.Besides,the catalytic performance of CaO on NO removal by CO gradually decreases with the number of CO2 capture cycles.This is because the sintering of CaO leads to the fusion of CaO grains and blockage of pores in CaO,hin-dering the diffusion of NO and CO.The high CaO content and porous structure of calcium-based sorbents are beneficial for NO removal by CO.The presence of char promotes NO removal by CO in the carbonator.CO2/NO removal efficiencies can reach above 90％.The efficient simultaneous NO and CO2 removal by CO and CaO in the carbonation step of the calcium looping seems promising.     

电石水解制备复合钙基吸附剂及其循环吸附CO2的特性

利用电石水解制乙炔工艺制备新型电石渣CaO/Ca12Al14O33复合钙基吸附剂,考察了Ca12Al14O33含量、碳酸化和煅烧再生温度对CaO转化率和多循环吸附CO2的影响,并与分析纯CaCO3和传统电石渣进行了比较,对其表面形貌、比表面积和孔结构进行了分析. 结果表明,新型复合钙基吸附剂在多循环煅烧/碳酸化过程中具有较好的多循环吸附CO2的性能. Ca12Al14O33有效减缓了吸附剂烧结现象. 20次循环后,自制电石渣吸附剂的CaO转化率仍保持在48%以上.     

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。     

Effect of different organic compounds on the preparation of CaO-based CO2 sorbents derived from wet mixing combustion synthesis

CaO based sorbents have great potential for commercial use to capture CO_2 of power plants. In the demand of producing sorbents with better cyclic performance, CaO-based sorbents derived from different kinds of calcium precursors, containing calcium carbonate(CC-CaO), calcium gluconate monohydrate(CG-CaO), calcium citrate(CCi-CaO) and calcium acetate monohydrate(CA-CaO), were tested cyclically and compared using simultaneous thermal analyzer(STA). And further study was conducted on the sorbents modified with citric acid monohydrate and 50% gluconic acid solution by wet mixing combustion synthesis. The modified sorbents showed better performance and higher pore parameters as well as porous microstructure with more organic acid added. After 20 cycles of carbonation and calcination, the C2CCi8(CaO: citric acid = 2:8 by mass ratio) and C2G8(CaO: gluconic acid = 2:8 by mass ratio) sorbent possess CO_2 capture capacity of 0.45 g·g~(-1)(g CO_2 per g sorbents) and 0.52 g·g~(-1) respectively. The citric acid was more effective for modification than gluconic acid for extended 50 cycles. Furthermore, good linear relationship between CaO conversion and specific surface area as well as pore volume were determined, of which the specific surface area showed closer correlation with CaO conversion.     

Sulfation Rates of Particles in Calcium Looping Reactors

The sulfation reaction rate of CaO particles in three reactors comprising a post‐combustion calcium looping system is discussed: a combustion chamber generating flue gases, a carbonator reactor to capture CO₂ and SO₂, and an oxy‐fired calciner to regenerate the CO₂ sorbent. Due to its strong impact on the pore size distribution of CaO particles, the number of carbonation/calcination cycles arises as a new important variable to understand sulfation phenomena. Sulfation patterns change as a result of particle cycling, becoming more homogeneous with higher number of cycles. Experimental results from thermogravimetric tests demonstrate that high sulfation rates can be measured under all conditions tested, indicating that the calcium looping systems will be extremely efficient in SO₂ capture.     

Preparation and Application of the Sol-Gel Combustion Synthesis-Made CaO/CaZrO3 Sorbent for Cyclic CO2 Capture Through the Severe Calcination Condition

abstract Calcium looping method has been considered as one of the efficient options to capture CO2 in the combustion flue gas. CaO-based sorbent is the basis for application of calcium looping and shou...     

Enhancement of CO2 capture and microstructure evolution of the spent calcium-based sorbent by the self-reactivation process

The effect of self-reactivation on the CO_2 capture capacity of the spent calcium based sorbent was investigated in a dual-fixed bed reactor.The sampled sorbents from the dual-fixed bed reactor were sent for XRD,SEM and N_2 adsorption analysis to explain the self-reactivation mechanism.The results show that the CaO in the spent sorbent discharged from the calciner absorbs the vapor in the air to form Ca(OH)_2 and further Ca(OH)_2·2 H_2 O under environmental conditions,during which process the CO_2 capture capacity of the spent sorbent can be self-reactivated.The microstructure of the spent sorbent is improved by the self-reactivation process,resulting in more porous microstructure,higher BET surface area and pore volume.Compared with the calcined spent sorbent that has experienced 20 cycles,the pore volume and BET surface area are increased by 6.69 times and 56.3% after self-reactivation when φ=170%.The improved microstructure makes it easier for the CO_2 diffusion and carbonation reaction in the sorbent.Therefore,the CO_2 capture capacity of the spent sorbent is enhanced by self-reactivation process.A self-reactivation process coupled with calcium looping process was proposed to reuse the discharged spent calcium based sorbent from the calciner.Higher average carbonation conversion and CO_2 capture efficiency can be achieved when self-reactivated spent sorbent is used as supplementary sorbent in the calciner rather than fresh CaCO_3 under the same conditions.     

钢渣及电石渣与废弃混凝土固化储存CO_2基本参数研究

对钢渣、电石渣、废弃混凝土等固体废弃物碳酸化固化储存温室气体二氧化碳(CO2)进行研究。实验从固体废弃物颗粒粒径、水分添加量等因素,考察碳酸化固化储存二氧化碳(CO2)的效果,并利用XRD、FTIR和SEM对反应机理进行分析。结果表明,固体废弃物颗粒粒径越小,二氧化碳(CO2)固化效率越高。水分添加量过低或过高均不利于碳酸化反应的进行,适宜的水分添加量为4kg/kg。XRD和FTIR分析表明,固体废弃物中的大量的CH、硅酸三钙(C3S)和氧化钙(CaO)转化为碳酸钙(CaCO3),以达到固化储存二氧化碳(CO2)的效果。SEM实验结果表明,经碳酸化处理后固体废弃物颗粒表面生成颗粒状的晶体物质。电石渣,钢渣及废弃混凝土对二氧化碳(CO2)固化效率分别为81%,76%和49%;每千克电石渣,钢渣及废弃混凝土分别可以固化二氧化碳(CO2)气体0.094kg,0.088kg及0.057kg。     

循环捕集CO2后煅烧石灰石的硫化特性

ZEC(zero emission coal)系统中,粗煤气进入碳酸化/重整炉前需先脱除H₂S,提出利用经过多次碳酸化/煅烧捕集CO₂循环的煅烧石灰石(CaO)脱除H₂S,并研究循环碳酸化/煅烧次数、硫化温度、H₂S浓度和微观结构对循环CaO硫化特性的影响。结果表明,多次循环碳酸化/煅烧捕集CO₂后CaO仍具有较高H₂S吸收性能。前20次循环,CaO硫化转化率随循环次数增加迅速降低;20次循环后,CaO硫化转化率缓慢下降。硫化120 min后,未循环CaO的硫化转化率接近100%,而经历1、20和100次循环后CaO的硫化转化率分别为94%、81%和74%。H₂S浓度对循环CaO硫化性能影响较大。硫化温度(800～1000℃)对循环CaO的硫化性能影响较小,最佳硫化温度为900℃。随循环次数增加,CaO颗粒发生高温烧结,导致比表面积降低和20～150 nm内孔隙减少,而这是与H₂S吸收密切相关的孔隙,导致CaO硫化转化率降低。     

Calcium looping heat storage performance and mechanical property of CaO-based pellets under fluidization

The CaO-based pellets were fabricated using extrusion-spheronization method for calcium looping thermochemical heat storage under the fluidization. The effects of adhesive, biomass-based pore-forming agent, binder and particle size on the heat storage performance and mechanical property of the CaO-based pellets were investigated in a bubbling fluidized bed reactor. The addition of 2%(mass)polyvinylpyrrolidone as an adhesive not only helps granulate, but also improves the heat storage capacity of the pellets. All biomass-templated CaO-based pellets display higher heat storage capacity than biomass-free pellets, indicating that the biomass-based pore-forming agent is beneficial for heat storage under the fluidization. Especially, bagasse-templated pellets show the highest heat storage conversion of 0.61 after 10 cycles. Moreover, Al_2 O_3 as a binder for the pellets helps obtain high mechanical strength.The CaO-based pellets doped with 10%(mass) bagasse and 5%(mass) Al_2 O_3 reach the highest heat storage density of 1621 kJ·kg~(-1) after 30 cycles and the highest crushing strength of 4.98 N. The microstructure of the bagasse-templated pellets appears more porous than that of biomass-free pellets. The bagassetemplated CaO-based pellets doped with Al_2 O_3 seem promising for thermochemical heat storage under the fluidization, owing to the enhanced heat storage capacity, excellent mechanical strength, and simplicity of the synthesis procedure.     

The calcium looping cycle for CO2 capture from power generation, cement manufacture and hydrogen production

Calcium looping is a CO₂ capture scheme using solid CaO-based sorbents to remove CO₂ from flue gases, e.g., from a power plant, producing a concentrated stream of CO₂ (∼95%) suitable for storage. The scheme exploits the reversible gas-solid reaction between CO₂ and CaO(s) to form CaCO₃(s). Calcium looping has a number of advantages compared to closer-to-market capture schemes, including: the use of circulating fluidised bed reactors—a mature technology at large scale; sorbent derived from cheap, abundant and environmentally benign limestone and dolomite precursors; and the relatively small efficiency penalty that it imposes on the power/industrial process (i.e., estimated at 6-8 percentage points, compared to 9.5-12.5 from amine-based post-combustion capture). A further advantage is the synergy with cement manufacture, which potentially allows for decarbonisation of both cement manufacture and power production. In addition, a number of advanced applications offer the potential for significant cost reductions in the production of hydrogen from fossil fuels coupled with CO₂ capture. The range of applications of calcium looping are discussed here, including the progress made towards demonstrating this technology as a viable post-combustion capture technology using small-pilot scale rigs, and the early progress towards a 2 MW scale demonstrator.     

CO2 mineralization of carbide slag for the production of light calcium carbonates

The production of polyvinyl chloride by calcium carbide method is a typical chemical process with high coal consumption, leading to massive flue gas and carbide slag emissions. Currently, the carbide slag with high CaO content is usually stacked in residue field, easily draining away with the rain and corroding the soil. In this work, we coupled the treatment of flue gas and carbide slag to propose a facile CO₂ mineralization route to prepare light calcium carbonate. And the route feasibility was comprehensively evaluated via experiments and simulation. Through experimental investigation, the Ca²⁺ leaching and mineralization reaction parameters were determined. Based on the experiment, a process was built and optimized through Aspen Plus, and the energy was integrated to obtain the overall process energy and material consumption. Finally, the net CO₂ emission reduction rate of the entire process through the life-cycle assessment method was analyzed. Moreover, the relationship between the parameters and the CO₂ emission life-cycle assessment was established. The final optimization results showed that the mineralization process required 1154.69 kW·h·(t CO₂)^-1 of energy (including heat energy of 979.32 kW·h·(t CO₂)^-1 and electrical energy of 175.37 kW·h·(t CO₂)^-1), and the net CO₂ emission reduction rate was 35.8%. The light CaCO₃ product can be sold as a high value-added product. According to preliminary economic analysis, the profit of mineralizing can reach more than 2,100 CNY·(t CO₂)^-1.     

间歇氯化对电石渣循环捕集CO2性能的影响

提出在碳酸化气氛中间歇加入HCl（间歇氯化）提高电石渣在循环煅烧/碳酸化反应中捕集CO₂性能的新思路。在双固定床反应器上,在不同循环次数加入HCl、碳酸化温度、CO₂/HCl体积比等条件下,研究HCl间歇加入对电石渣循环碳酸化特性的影响。结果表明,在循环煅烧/碳酸化反应中间歇加入HCl使电石渣间歇氯化能提高其循环捕集CO₂性能。在前N次循环碳酸化时加入0.1% HCl,当N=4时能使电石渣获得最优CO₂捕集性能,第10个循环时的CO₂吸收量比无HCl时提高了51%。HCl与CaCO₃发生氯化反应,破坏致密产物层对CO₂扩散的阻碍,提高了电石渣的碳酸化转化率。在碳酸化气氛加入HCl时,最佳碳酸化温度仍为700℃。随CO₂/HCl体积比增大,HCl对电石渣捕集CO₂性能的促进作用减弱。     

Stabilized Performance of Al‐Decorated and Al/Mg Co‐Decorated Spray‐Dried CaO‐Based CO2 Sorbents

The sharp loss‐in‐capacity in CO₂ capture as a result of sintering is a major drawback for CaO‐based sorbents used in the calcium looping process. The decoration of inert supports effectively stabilizes the cyclic CO₂ capture performance of CaO‐based sorbents via sintering mitigation. A range of Al‐decorated and Al/Mg co‐decorated CaO‐based sorbents were synthesized via an easily scaled‐up spray‐drying route. The decoration of Al‐based and Al/Mg‐based supports efficiently enhanced the cyclic CO₂ capture capability of CaO‐based sorbents under severe testing conditions. The CO₂ capture capacity losses of Al‐decorated and Al/Mg co‐decorated CaO‐based sorbents were alleviated, representing more stable CO₂ capture performance. The stabilized CO₂ capture performance is mainly attributed to the formation of Ca₁₂Al₁₄O₃₃, MgAl₂O₄, and MgO that act as the skeleton structures to mitigate the sintering of CaCO₃ during carbonation/calcination cycles.     

干排电石渣热分解特性的研究

试验研究了模拟烟气下影响干排电石渣分解的几种因素。结果表明：气氛对电石渣的分解过程影响较大,当有CO2存在时电石渣先合成为CaCO3再分解为CaO,在纯N2条件下电石渣分两步分解为CaO。电石渣的粒度和升温速率会影响具体分解温度但不改变分解过程。     

Ca-based sorbent looping combustion for CO2 capture in pilot-scale dual fluidized beds

To demonstrate process feasibility of in situ CO₂ capture from combustion of fossil fuels using Ca-based sorbent looping technology, a flexible atmospheric dual fluidized bed combustion system has been constructed. Both reactors have an ID of 100 mm and can be operated at up to 1000 °C at atmospheric pressure. This paper presents preliminary results for a variety of operating conditions, including sorbent looping rate, flue gas stream volume, CaO/CO₂ ratio and combustion mode for supplying heat to the sorbent regenerator, including oxy-fuel combustion of biomass and coal with flue gas recirculation to achieve high-concentration CO₂ in the off-gas. It is the authors' belief that this study is the first demonstration of this technology using a pilot-scale dual fluidized bed system, with continuous sorbent looping for in situ CO₂ capture, albeit at atmospheric pressure. A multi-cycle test was conducted and a high CO₂ capture efficiency (> 90%) was achieved for the first several cycles, which decreased to a still acceptable level (> 75%) even after more than 25 cycles. The cyclic sorbent was sampled on-line and showed general agreement with the features observed using a lab-scale thermogravimetric analysis (TGA) apparatus. CO₂ capture efficiency decreased with increasing number of sorbent looping cycles as expected, and sorbent attrition was found to be another significant factor to be limiting sorbent performance.     

Polygeneration of hydrogen and power based on coal gasification integrated with a dual chemical looping process: Thermodynamic investigation

This paper assesses, from a thermodynamic perspective, the conversion of coal to power and hydrogen through gasification simultaneously with a dual chemical looping processes, namely chemical looping air separation (CLAS) and water–gas shift with calcium looping CO₂ absorption (WGS-CaL). CLAS offers an advantage over other mature technologies in that it can significantly reduce its capital cost. WGS-CaL is an efficient method for hydrogen production and CO₂ capture. The three major factors, oxygen to coal (O/C), steam to coal (S/C) and CaO to coal (Ca/C) were analyzed. Moreover, the comparisons of this suggested process and the traditional processes including integrated gasification combined cycle (IGCC), integrated gasification combined cycle with carbon capture and storage (IGCC-CCS) and integrated gasification combined cycle with calcium-based chemical looping (IGCC-CaL) were discussed. And, the exergy destruction analysis of this suggested process has also been calculated.     

蒸汽活化钙基吸收剂联合脱碳脱硫特性

利用管式炉（TF）、蒸汽发生器和热重分析仪（TGA）研究了钙基吸收剂联合脱碳脱硫以及水合特性,并通过N2吸附实验对不同烧结程度以及水合前后样品的孔隙结构进行了测量。结果表明,无水合时,40次碳化循环后的样品碳化活性降至18%,但仍具有44%的硫化活性,比新鲜剂仅低4%,说明脱碳失效剂仍是良好的脱硫剂。碳循环失效剂经蒸汽活化后其碳化活性可提高至68%左右,且具有与新鲜剂类似的活性下降规律。每两次碳化循环后进行一次蒸汽活化,可使样品保持65%的平均转化率。蒸汽活化后吸收剂硫化率可提高至80%,远高于新鲜剂,由电镜扫描实验发现这是由于水合时颗粒产生了大的裂缝和破碎,提供了大量产物可自由生长的外表面积。不考虑颗粒磨损,利用钙基吸收剂先循环脱碳再蒸汽活化最后脱硫是一项联合脱除烟气中CO₂和SO₂的新方法。     

二氧化碳捕集技术及应用分析

分析了CO2捕集技术及现状。CO2捕集是CCS的关键技术单元之一,针对不同的CO2气源,国内外研究开发了多种技术。许多CO2捕集技术已经工业化,其中燃烧后烟气中CO2的捕集技术主要是以一乙醇胺(MEA)为基础的胺法;燃烧前的CO2捕集技术主要应用于IGCC电厂,一般需要对煤气中CO进行部分变换,变换后脱碳可采用成熟技术,如Selexol(NHD)等。富氧燃烧则是在中试成功的基础上,进行更大规模的工业示范。国内外大型煤制油化工项目主要采用低温甲醇洗脱除CO2,如果设置CO2产品塔,则可以获得体积分数98%以上的CO2。天然气脱碳主要采用MDEA技术。另外还有低温法、PSA、膜分离等CO2捕集技术及化学链燃烧等一些正在研发的技术。     

镁负载CaO基吸附剂捕集CO2性能及抗烧结机理

复合钙基吸附剂制备成本过高是限制其工业化应用的主要瓶颈问题。本文以不可溶的CaCO₃和Ca(OH)₂作为钙源,通过燃烧合成法制备钙镁复合吸附剂,在双固定床反应器上研究了其循环捕集CO₂性能。结果显示：制备得到的钙镁复合吸附剂具有更发达的孔隙结构,吸附剂表面Ca和Mg分散均匀,MgO均匀分布于CaO晶粒之间,有效提高了钙镁复合吸附剂的抗烧结特性,因此钙镁复合吸附剂循环反应过程中具有高捕集CO₂活性。以Ca(OH)₂作为钙源时,燃烧合成过程中Ca和Mg均匀同时析出,分散更加均匀,有效避免了CaCO₃作为钙源时Mg的团聚问题,因此得到的钙镁复合吸附剂循环捕集CO₂性能最优。最佳的Ca/Mg摩尔比为(8∶2)~(7.5∶2.5)。本研究以不可溶钙源制备得到高活性钙镁复合吸附剂,有效控制了吸附剂成本,具有更好的工程应用前景。