废弃咖啡渣化学链气化反应特性

利用溶胶-凝胶法制备了以Fe₂O₃为活性组分,天然凹凸棒土(ATP)为惰性载体,KNO₃修饰的Fe4ATP6K1铁基复合载氧体。在高温流化床中考察了反应温度、水蒸气流量和O/C摩尔比对咖啡渣化学链气化过程的影响。结果表明,与以石英砂为床料的咖啡渣气化相比,以Fe4ATP6K1载氧体为床料的咖啡渣化学链气化对应的碳转化率由71.38%提高到86.25%。咖啡渣化学链气化的较优操作条件为:反应温度900℃、水蒸气量0.23 g·min^-1、O/C摩尔比1;在此操作条件下,合成气产量达到1.30 m³·kg^-1,氢气产量达到83.79 g·kg^-1,氢气的平均浓度达到52.75%。通过X射线衍射(XRD)、扫描电镜-能谱(SEM-EDS)对900℃反应前后的Fe4ATP6K1进行表征,发现Fe相、K相、Si相可以发生相互作用,K以KFeSi₃O₈的形式存在于载氧体中,并且K在反应过程中有少量流失。20次氧化/还原过程中,铁基复合载氧体Fe4ATP6K1表现出较好的循环性能,碳转化率和冷煤气效率均保持在75%以上,各气体的平均浓度较稳定。     

化学链气化中准东煤灰对CaSO4载氧体改性及其作用机理

以CaSO₄为载氧体，采用机械混合法制备了将军庙煤灰修饰的CaSO₄-Ash复合载氧体。借助TG-MS考察复合载氧体CaSO₄-Ash与将军庙煤的化学链气化反应特性，并对将军庙煤灰改性CaSO₄载氧体的作用机理进行了研究。结果表明：将军庙煤灰对CaSO₄载氧体有一定的改性作用。900℃时，与纯CaSO₄载氧体相比，CaSO₄-Ash复合载氧体表现出良好的反应活性和稳定性，CaSO₄-Ash复合载氧体化学链气化产生的CO量明显增多，产率也更加稳定。X射线衍射分析表明，CaSO₄-Ash复合载氧体中存在少量的Ca₂Fe₂O₅和Fe₂O₃，它们附着在CaSO₄表面，作为CaSO₄晶格氧传输的中介，起到促进CaSO₄晶格氧迁移...     

Co-Fe2O3[104]铁基载氧体优化体系作用下褐煤化学链燃烧特性

前期研究发现高弥勒指数晶面载氧体Fe₂O₃[104]具有高的化学链燃烧反应特性,且Co对煤及其热解中间产物具有催化气化和催化转化作用。通过正交实验优化制备Co-Fe₂O₃[104]/Al₂O₃载氧体体系结构,开展Co-Fe₂O₃[104]/Al₂O₃与褐煤的化学链燃烧,揭示载氧体与褐煤发生化学链燃烧的特性。结果表明:形貌控制制备的高弥勒指数晶面铁基载氧体Co-Fe₂O₃[104]/Al₂O₃(质量分数10%)促进了褐煤化学链燃烧过程中氧的迁移速率以及载氧体的还原程度,进而显著提高了载氧体与褐煤化学链燃烧的反应速率及反应效率。进一步通过CO多循环化学链燃烧反应、XRD和TEM表征了Co-Fe₂O₃[104]/Al₂O₃(10%)的可再生性及反应稳定性。     

Mg修饰Fe/Al载氧体煤化学链制氢

目前化学链过程常用的Fe₂O₃/Al₂O₃载氧体会形成FeAl₂O₄,因热力学限制很难与水反应制氢。为了抑制FeAl₂O₄的形成,本文向Fe/Al载氧体中添加Mg,在固定床上进行煤化学链制氢（CLHG）,深入分析Mg的作用机理并探究其对实验结果的影响。XRD结果表明,Mg质量分数从1%增加到26.5%时,MgAl₂O₄特征峰增强,FeAl₂O₄特征峰逐渐消失,说明Mg减弱了Fe和Al之间的相互作用。SEM显示Mg添加后载氧体颗粒减小,耐烧结性能优异。对比不同煤/载氧体质量比的实验,质量比为0.5/15时碳转化率和产氢量最高。在不同Mg含量的载氧体中,Fe40Mg20Al40具备最好的反应性能,碳转化率和产氢量为81.75%和1.7182L/g,比Fe40Al60分别增加10.2%和58.5%。Fe40Mg20Al40经10次循环,表面仅有轻微烧结,碳转化率和产氢量均在78%和1.52L/g以上,循环性能良好。添加Mg可以有效抑制FeAl₂O₄的生成,显著增强蒸汽氧化过程的反应活性,大幅提高氢气产量,十分适用于煤化学链制氢。     

基于CoFe2O4载氧体的生物质化学链气化反应特性

在热重分析仪和固定床反应器上对基于CoFe₂O₄载氧体的生物质化学链气化反应特性进行了研究，考察了载氧体与生物质质量比、水蒸气、反应温度对生物质化学链气化反应特性的影响，同时也对载氧体的循环反应性能进行了研究。通过XRD及SEM对新制备的和反应后的载氧体进行了表征。热重结果表明：CoFe₂O₄能够提供晶格氧，有效促进生物质气化。当CoFe₂O₄与生物质质量比为0.8，水蒸气体积分数为50%，温度为900 ℃时，气化反应效果最好。5次循环反应后，仍能获得较高品质的合成气，载氧体能够循环再生且未出现明显烧结团聚。     

化学链燃烧过程Fe2O3/Al2O3载氧体表面CH4反应：ReaxFF-MD模拟

借助ReaxFF-MD方法,对化学链燃烧过程Al₂O₃负载Fe₂O₃载氧体（Fe₂O₃/Al₂O₃）表面CH₄反应过程模拟,探究Al₂O₃惰性载体对Fe₂O₃-CH₄体系燃烧过程的调控机制。研究发现添加Al₂O₃惰性载体改变了化学链燃烧过程中Fe₂O₃载氧体反应性和Fe₂O₃/Al₂O₃-CH₄反应体系的热力学和动力学行为。主要是促进了Fe₂O₃载氧体表面CH₄氧化,并对CH₄反应过程、中间体、产物及其反应速率和放热量等均具有显著促进和调控作用。原因在于Al₂O₃惰性载体对Fe₂O₃活性相中晶格氧的活化作用促进了晶格氧的迁移-扩散-释放。添加惰性载体增强了Fe₂O₃载氧体在化学链燃烧过程晶格氧释放速率和释放量,有利于CH₄氧化燃烧向合成气的高效、清洁转化,强化了化学链燃烧过程,满足当前能源高效转化和碳减排目标。     

化学链燃烧过程Fe2O3/Al2O3载氧体表面CH4反应：ReaxFF-MD模拟

借助ReaxFF-MD方法,对化学链燃烧过程Al₂O₃负载Fe₂O₃载氧体（Fe₂O₃/Al₂O₃）表面CH₄反应过程模拟,探究Al₂O₃惰性载体对Fe₂O₃-CH₄体系燃烧过程的调控机制。研究发现添加Al₂O₃惰性载体改变了化学链燃烧过程中Fe₂O₃载氧体反应性和Fe₂O₃/Al₂O₃-CH₄反应体系的热力学和动力学行为。主要是促进了Fe₂O₃载氧体表面CH₄氧化,并对CH₄反应过程、中间体、产物及其反应速率和放热量等均具有显著促进和调控作用。原因在于Al₂O₃惰性载体对Fe₂O₃活性相中晶格氧的活化作用促进了晶格氧的迁移-扩散-释放。添加惰性载体增强了Fe₂O₃载氧体在化学链燃烧过程晶格氧释放速率和释放量,有利于CH₄氧化燃烧向合成气的高效、清洁转化,强化了化学链燃烧过程,满足当前能源高效转化和碳减排目标。     

废弃活性炭化学链气化制富氢合成气

以废弃活性炭为原料,以Fe4ATP6复合载氧体为载氧体,在间歇高温流化床中考察了废弃活性炭化学链气化制富氢合成气反应的较优条件及复合载氧体的循环反应特性。结果表明,Fe4ATP6复合载氧体具有提供晶格氧及催化气化的双重作用,显著提高了碳转化率,促进了废弃活性炭气化过程,反应活性良好。废弃活性炭化学链气化制富氢合成气的优化反应条件：900℃、水蒸气流量为0.25 g·min^-1、OC/C比为1。在上述条件下,碳转化率达92.15%,合成气产量达1.20 L·g^-1,其中H₂产量为1.09 L·g^-1,平均浓度为55.30%。10次循环实验表明Fe4ATP6复合载氧体的反应活性略有降低,通过SEM、XRD分析载氧体的表面形貌、物质组成发现,载氧体反应后结构变化较大,粒径减小,生成了无反应活性的硅酸铁。     

CaSO4载氧体在煤气化化学链燃烧中的脱汞

为了研究载氧体在煤气化化学链燃烧中的脱汞机理,选择CaSO₄载氧体作为研究对象,900℃的反应温度下,在还原反应器中通入CO₂气体和水蒸气作为气化介质进行实验。结果表明：以CaSO₄作为载氧体的煤气化化学链燃烧中,CaSO₄载氧体本身促进Hg⁰的氧化,但CaSO₄分解产生的SO₂抑制Hg⁰的氧化。CaSO₄促进煤气化化学链燃烧产生S单质,会进一步与Hg⁰反应生成多种复杂的HgS_n,降低了烟气中Hg⁰含量,提高了脱汞效率。同时CaSO₄载氧体在还原-氧化的循环反应中具有良好的循环特性,是一种优良的化学链载氧体。     

以CeO2为载体的Fe基载氧体与CO反应机理模拟

化学链燃烧技术是一种新型的近“零碳”排放燃烧技术,载氧体在化学链燃烧反应过程中发挥着载氧和传热的双重作用。以活性催化组分为载体,通过调谐微观结构提高Fe基载氧体的反应性能是目前化学链领域的研究热点之一。基于密度泛函理论,以CeO₂为活性催化载体,对Fe基载氧体进行催化调谐。通过优化构建组合物模型,系统分析了组合物模型中Fe₂O₃团簇不同点位吸附CO的态密度、吸附能、差分电荷密度和活化能等电子结构特性参数。研究结果表明,Fe₂O₃团簇的电子向CeO₂(111)表面转移,Fe₂O₃团簇的吸附能为-3.92 eV,Fe₂O₃团簇与CeO₂(111)表面稳定结合;态密度(DOS)分析发现负载后的Fe₂O₃团簇p和d轨道在-8～0 eV电子向费米能级方向迁移,表明吸附作用增强。Fe₂O     

Hydrogen production in fluidized bed by chemical-looping cycle

To investigate the feasibility of a chemical-looping hydrogen generation system, we investigated the reduction and water splitting reaction characteristics for three mediators and two reducing gas in a bubbling fluidized bed reactor (0.02 m I.D.). For three oxygen carrier particles (NiO/bentonite, Fe₂O₃/bentonite, (NiO:Fe₂O₃)/bentonite), hydrogen was used as a reduction gas and water was used as an oxidation gas. For (NiO: Fe₂O₃)/bentonite particle, carbon monoxide, which is the main component in the syngas from coal or heavy residue, was used as a reducing gas to check reactivity for the carbon containing fuels and carbon deposition characteristics. Based on the reactivity tests, (NiO: Fe₂O₃)/bentonite particle was selected as the best mediator for the chemical-looping hydrogen generation system to achieve stable continuous operation. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Catalytic steam gasification of Yallourn coal using sodium hydridotetracarbonyl ferrate

Catalytic steam gasification of Yallourn coal using sodium hydridotetracarbonyl ferrate was carried out in a semi-flow-type fixed-bed reactor at 873 and 973 K at atmospheric and high pressures. With Na[HFe(CO)₄] (Fe 1.67 wt%, Na 0.68 wt%), the steam gasification of the coal was more highly promoted than with Na₂CO₃ (Na 2.17%) and the coal was almost completely burnt out. The gasification rate decreased with increasing carbon burnoff with or without catalyst at 873 K, but increased in the presence of the catalyst at 973 K. Under pressurized steam (0.4 MPa), the catalyst exhibited higher activity. The char, obtained from Yallourn coal under argon at 823 K for 2 h, gasified under steam partial pressures of 0.4 and 0.8 MPa behaved the same as the original coal and no increase in gasification rate with steam pressure was observed. X-ray diffraction analysis showed that Na[HFe(CO)₄] was converted to Fe₃O₄ and Na₂CO₃ during the reaction.     

Reduction and oxidation properties of Fe2O3/ZrO2 oxygen carrier for hydrogen production

Fe₂O₃ is a promising oxygen carrier for hydrogen production in the chemical-looping process. A set of kinetic studies on reduction with CH₄, CO and H₂ respectively, oxidation with water and oxygen containing Ar for chemical-looping hydrogen production was conducted. Fe₂O₃ (20 wt.%)/ZrO₂ was prepared by a co-precipitation method. The main variables in the TGA (thermogravimetric analyzer) experiment were temperatures and gas concentrations. The reaction kinetics parameters were estimated based on the experimental data. In the reduction by CH₄, CO and H₂, the reaction rate changed near FeO. Changes in the reaction rate due to phase transformation were observed at low temperature and low gas concentration during the reduction by CH₄, but the phenomenon was not remarkable for the reduction by CO and H₂. The reduction rate achieved using CO and H₂ was relatively faster than achieved using CH₄. The Hancock and Sharp method of comparing the kinetics of isothermal solid-state reactions was applied. A phase boundary controlled model (contacting sphere) was applied to the reduction of Fe₂O₃ to FeO by CH₄, and a different phase boundary controlled model (contacting infinite slab) was fit well to the reduction of FeO to Fe by CH₄. The reduction of Fe₂O₃ to Fe by CO and H₂ can be described by the former phase boundary controlled model (contacting sphere). This phase boundary controlled model (contacting sphere) also fit well for the oxidation of Fe to Fe₃O₄ by water and FeO to Fe₂O₃ by oxygen containing Ar. These kinetics data could be used to design chemical-looping hydrogen production systems.     

Multicycle investigation of a sol‐gel‐derived Fe2O3/ATP oxygen carrier for coal chemical looping combustion

Fe‐based oxygen‐carrier particles with attapulgite (ATP) as a support material for coal chemical looping combustion (CLC) have been prepared using a sol‐gel approach. The multiredox characteristics of the prepared Fe4ATP6 (Fe₂O₃ to ATP mass ratio of 40:60) were experimentally examined in a batch fluidized bed reactor at 900°C. The experimental results indicated that the synergistic reactions between ATP and Fe₂O₃ increased the coal conversion. Fe4ATP6 exhibited high reactivity, particularly for low‐rank coals, in the CLC process. The improved pore structure and surface area were responsible for the high reactivity of Fe4ATP6. In 60 redox cycles, H₂ was mainly generated in the outlet gas as the carbon conversion efficiency had reached 95%, and both the coal combustion efficiency and CO₂ capture efficiency were greater than 95%. © 2015 American Institute of Chemical Engineers AIChE J, 62: 996–1006, 2016     

The use of ilmenite as an oxygen carrier in chemical-looping combustion

The feasibility of using ilmenite as oxygen carrier in chemical-looping combustion has been investigated. It was found that ilmenite is an attractive and inexpensive oxygen carrier for chemical-looping combustion. A laboratory fluidized-bed reactor system, simulating chemical-looping combustion by exposing the sample to alternating reducing and oxidizing conditions, was used to investigate the reactivity. During the reducing phase, 15 g of ilmenite with a particle size of 125–180 μm was exposed to a flow of 450 mL_n/min of either methane or syngas (50% CO, 50% H₂) and during the oxidizing phase to a flow of 1000 mL_n/min of 5% O₂ in nitrogen. The ilmenite particles showed no decrease in reactivity in the laboratory experiments after 37 cycles of oxidation and reduction. Equilibrium calculations indicate that the reduced ilmenite is in the form FeTiO₃ and the oxidized carrier is in the form Fe₂TiO₅ + TiO₂. The theoretical oxygen transfer capacity between these oxidation states is 5%. The same oxygen transfer capacity was obtained in the laboratory experiments with syngas. Equilibrium calculations indicate that ilmenite should be able to give high conversion of the gases with the equilibrium ratios CO/(CO₂ + CO) and H₂/(H₂O + H₂) of 0.0006 and 0.0004, respectively. Laboratory experiments suggest a similar ratio for CO. The equilibrium calculations give a reaction enthalpy of the overall oxidation that is 11% higher than for the oxidation of methane per kmol of oxygen. Thus, the reduction from Fe₂TiO₅ + TiO₂ to FeTiO₃ with methane is endothermic, but less endothermic compared to NiO/Ni and Fe₂O₃/Fe₃O₄, and almost similar to Mn₃O₄/MnO.     

In situ gasification and CO2 separation using chemical looping with a Cu-based oxygen carrier: Performance with bituminous coals

This paper is concerned with the chemical looping combustion of coal in a technique whereby the fuel is gasified in situ using CO₂ in the presence of a batch of supported copper oxide (the “oxygen carrier”) in a single reactor. As the metal oxide becomes depleted, the feed of fuel is discontinued, the inventory of fuel is reduced by further gasification and then the contents are re-oxidised by the admission of air to the reactor, to begin the cycle again. A catalyst support, impregnated with a saturated solution of copper and aluminium nitrates, acted as a durable oxygen carrier over numerous cycles of reduction and oxidation, using air as the oxidant. Two bituminous coals (Taldinskaya, Russia, and Illinois No. 5, USA) were investigated and compared with a lignite (Hambach, Germany). The lignite was highly reactive and was gasified completely by 15 mol% CO₂ in N₂ at 1203 K and 1 bar, so that there was no build up of char in the bed. The bituminous coals produced chars much less reactive than the lignite char, so that there was a steady accumulation of char in the bed with number of cycles, with the degree of accumulation being dependent on the reactivity of the char. Since the kinetics of gasification by CO₂ of the chars from either bituminous coal were slow, their rates were controlled by intrinsic chemical kinetics and were not affected by the ability of the oxygen carrier to alter the rates of external mass transfer when gasification is rapid. However, it is likely that rates of gasification in the presence of the carrier are still larger than in its absence, owing to the overall lower [CO] present in the bulk of the fluidised bed during chemical looping. At the temperature used, the carrier was cycling between Cu and Cu₂O, since CuO is only stable if the partial pressure of O₂ exceeds 0.03 bar at 1203 K. The CuO decomposes to Cu₂O and O₂ relatively rapidly at these temperatures, once the oxygen concentration is effectively zero. It was impossible to ascertain in our experiments whether the oxygen so generated, after the switching of the air for nitrogen before the start of the succeeding cycle of gasification, made any substantial difference to the reactivity of the char present in the bed. The rate of oxidation of the carrier was found to be much more rapid than the rate of oxidation of the inventory of char. This allows a preferential oxidation of the carrier and most likely accounts for why progressively less CO and CO₂ is produced during successive cycles with short periods of oxidation: the increasingly reduced carrier reacts more rapidly than the char. There was no obvious impact from the sulphur contained in the fuels, but longer-term testing is needed. No agglomeration between the carrier particles and the ash was observed, despite the high temperatures during oxidation.     

Fe2O3/粉煤灰载氧体化学链燃烧实验与机理研究

提出了一种以粉煤灰为载体制备的新型铁基载氧体。采用同步热重分析仪、小型流化床以及DFT分别研究了新型载氧体的活性与热稳定性,发泡剂含量与反应温度以及粉煤灰主要组分之间的协同作用对新型载氧体性能的影响。研究结果表明,新型载氧体在以CO为燃料的化学链系统中具有较高的活性;新型载氧体较大的孔隙率以及粉煤灰多组分间的协同作用促使850℃下发泡剂含量为10.0%(质量)的新型铁基载氧体的最大转化率(84.9%)比Fe₂O₃/Al₂O₃的最大转化率(54.3%)高30%,且新型铁基载氧体在30个循环测试中表现出良好的热稳定性。载体制备采用的发泡剂含量以及反应温度对新型铁基载氧体性能影响很大,适当的发泡剂含量(约10%(质量))可提高新型载氧体性能。此外,高温下会造成载氧体的烧结现象。最后,采用密度泛函理论(DFT)研究了粉煤灰与载氧体之间的界面作用以及协同氧化CO的电子特性。计算结果表明,粉煤灰和Fe₂O₃之间的界面电荷转移使Fe₂O₃为电正性,促使CO在表面的相互作用,载体和活性组分之间的协同作用降低了载氧体与CO前线轨道能量差,进而促进了CO与Fe₂O₃的反应。     

The use of petroleum coke as fuel in chemical-looping combustion

Chemical-looping combustion is a novel technique used for CO₂ separation that previously has been demonstrated for gaseous fuel. This work demonstrates the feasibility of using solid fuel (petroleum coke) in chemical-looping combustion (CLC). Here, the reaction between the oxygen carrier and solid fuel occurs via the gasification intermediates, primarily CO and H₂. A laboratory fluidized-bed reactor system for solid fuel, simulating a CLC-system by exposing oxygen-carrying particles to alternating reducing and oxidizing conditions, has been developed. In each reducing period, 0.2 g of petroleum coke was added to 20 g of oxygen carrier composed of 60% active material of Fe₂O₃ and 40% inert MgAl₂O₄. The effect of steam and SO₂ concentration in the fluidizing gas was investigated as well as effect of temperature. The rate of reaction was found to be highly dependent on the steam and SO₂ concentration as well as the temperature. Also shown was that the presence of a metal oxide enhances the gasification of petroleum coke. A preliminary estimation of the oxygen carrier inventory needed in a real CLC system showed that it would be below 2000 kg/MW_th.