Assessment of chemical looping-based conceptual designs for high efficient hydrogen and power co-generation applied to gasification processes

Carbon capture and storage (CCS) technologies are expected to play a significant role in the coming decades for curbing the greenhouse gas emissions and to ensure a sustainable development of power generation and other energy-intensive industrial sectors. Chemical looping systems are very promising options for intrinsically capture CO₂ with lower cost and energy penalties. Gasification offers significant advantages compared with other technologies in term of lower energy and cost penalties for carbon capture, utilization of wide range of fuels, poly-generation capability, plant flexibility, lower environmental impact, etc.     

A comparative simulation study of power generation plants involving chemical looping combustion systems

This work presents a simulation study on both energy and economics of power generation plants with inherent CO₂ capture based on chemical looping combustion technologies. Combustion systems considered include a conventional chemical looping system and two extended three-reactor alternatives (exCLC and CLC3) for simultaneous hydrogen production. The power generation cycles include a combined cycle with steam injected gas turbines, a humid air turbine cycle and a simple steam cycle. Two oxygen carriers are considered in our study, iron and nickel. We further analyze the effect of the pressure reaction and the turbine inlet temperature on the plant efficiency. Results show that plant efficiencies as high as 54% are achieved by the chemical looping based systems with competitive costs. That value is well above the efficiency of 46% obtained by a conventional natural gas combined cycle system under the same conditions and simulation assumptions.     

Hydrogen enrichment of fuels using a novel miniaturised chemical looping steam reformer

Experiments were conducted on the Fe₃O₄/FeO metal oxide system under pure methane and pure steam environments in a thermogravimetric analyser (TGA) and a prototype-miniaturised micro-reactor. Experimental results show that during a typical fuel oxidation step the concentration of methane in the product gas stream gradually decreases while Fe₃O₄ is being reduced to FeO. However, on or about a fractional conversion of 60% the slope of the CH₄ plot sharply increases due to catalytic effects of FeO on methane decomposition. Similarly, the H₂ plot associated with steam reforming step picks up rapidly and reaches a maximum of 98% at a fractional conversion of 30%. The conversion times of steam and fuel in the micro-reactor were generally shorter than conversion times obtained in the TGA system. The experimental results provided two vital pieces of information: (i) the chemical looping steam reforming cycle is technically viable, and (ii) the performance of the process at micro-scales needs to be further understood before high throughput miniaturised reformers could be designed and built.     

化学链空分联合化学链制氢的煤制甲醇过程参数优化与分析

我国能源结构决定了以煤为主的甲醇生产路线。传统煤制甲醇过程主要存在过程能量效率低、CO₂捕集能耗高等问题。本文提出了一种化学链空分联合化学链制氢的煤制甲醇新过程,以降低能耗、二氧化碳排放及提高能源效率。化学链空分技术的集成可以替代传统煤制甲醇过程的空气分离单元,并在一定程度上降低能耗。化学链制氢技术的集成,一方面可以替代水煤气变换装置,并且可以极大程度降低二氧化碳捕集能耗;另一方面,化学链制氢技术还可生产用于调整合成气氢与碳比的氢。本文对新过程的核心单元进行了参数优化以及全流程的模拟,基于模拟对新过程的性能进行了分析,结果表明新过程与传统的煤制甲醇过程相比,空分和二氧化碳捕集能耗分别降低了41%和89%。同时,新过程的能量效率提高了18%,二氧化碳排放量降低了45%。     

Simulation and thermodynamic analysis of chemical looping reforming and CO2 enhanced chemical looping reforming

The production of hydrogen from methane via two chemical looping reforming (CLR) processes was simulated and thermodynamically analysed, one process being the conventional CLR process, the other being a CO₂ sorption enhanced process. The aim of the work was to identify suitable operating conditions for obtaining an optimum hydrogen gas purity and yield, whilst operating auto-thermally, at atmospheric pressure and with no carbon formation. In both simulations, the reactors were simulated using the Gibbs minimisation technique. NiO was used as the oxygen storing species, whilst CaO was used as the CO₂ adsorbent.     

Syngas and a separate nitrogen/argon stream via chemical looping reforming - A 140 kW pilot plant study

A dual circulating fluidized bed pilot plant was operated in chemical looping reforming conditions at a scale of 140 kW fuel power with natural gas as fuel. A nickel-based oxygen carrier was used as bed material. The pilot plant is equipped with an adjustable cooling system. Three experimental campaigns have been carried out at 747 °C (1020 K), 798 °C (1071 K) and 903 °C (1176 K), respectively. In each campaign, the global stoichiometric air/fuel ratio was varied step-wise between 1.1 and the minimum value possible to keep the desired operating temperature when the cooling is finally switched off. The results show that the fuel reactor exhaust gas approaches thermodynamic equilibrium. The residual amount of methane left decreases with increasing fuel reactor temperature. Further, the oxygen in the air reactor can be completely absorbed by the solids as soon as the air reactor operating temperature is higher than 900 °C (1173 K). Even though no steam was added to the natural gas feed no carbon formation was found for global excess air ratios larger than 0.4.     

Experimental and mechanistic study on chemical looping combustion of caking coal

Under high-temperature batch fluidized bed conditions and by employing Juye coal as the raw material,the present study determined the effects of the bed material,temperature,OC/C ratio,steam flow and oxygen carrier cycle on the chemical looping combustion of coal.In addition,the variations taking place in the surface functional groups of coal under different reaction times were investigated,and the varia-tions achieved by the gas released under the pyrolysis and combustion of Juye coal were analyzed.As revealed from the results,the carbon conversion ratio and rate were elevated significantly,and the vol-ume fraction of the outlet CO2 remained more than 92％ under the oxygen carriers.The optimized reac-tion conditions to achieve the chemical looping combustion of Juye coal consisted of a temperature of 900℃,an OC/C ratio of 2,as well as a steam flow rate of 0.5 g·min-1.When the coal was undergoing the chemical looping combustion,volatiles primarily originated from the pyrolysis of aliphatic-CH3 and-CH2,and CO and H2 were largely generated from the gasification of aromatic carbon.In the CLC process,H2O and CO2 began to separate out at 270 ℃,CH4 and tar began to precipitate at 370 ℃,and the amount of CO2 was continuously elevated with the rise of the temperature.     

Oxygen carriers for chemical looping combustion of solid fuels

A thermal analyzer-differential scanning calorimeter-mass spectrometer (TG-DSC-MS) was used to study oxygen carriers (OC) for their potential use for the application of chemical looping combustion (CLC) to solid fuels. Reaction rates, changes in reaction rates with repeated oxidation-reductions, exothermic heats during oxidation, and the effect of changing reduction gas compositions were studied. Oxidation rates were greater than reduction rates and reaction rates were reproducible through multiple oxidation-reduction cycles except where agglomeration occurred with powders. Iron oxide (Fe₂O₃ powder) and iron-based catalysts were found suitable for CLC of solid fuels having rapid reduction rates which increased with higher reducing gas concentrations. Fe₂O₃ powder was used to oxidize a high carbon coal char in an inert gas removing 88% of the carbon from the char. Other properties such as cost and durability indicated iron oxide OCs potential use for CLC of solid fuels.     

化学链合成氨技术研究进展及展望

氨气不仅是重要的化工原料和良好的氢载体,其可以作为无碳燃料的属性也引起了广泛关注。低能耗高效率的合成氨工艺是实现氨作为燃料应用的关键。阐述了合成氨工艺的发展历程,概述了以Haber-Bosch工艺为基础的多相催化和光、电等外场力驱动的合成氨工艺的新发展,重点介绍了化学链合成氨的最新研究成果,并对其研究方向进行展望。传统Haber-Bosch工艺苛刻的反应条件以及热力学和动力学之间的矛盾,促使科研工作者一直努力探索可持续的环境友好型合成氨技术。随着催化科学和表面科学的进步,人们对合成氨的反应机理和催化剂的物化性质有了更深入的认识,这为开发“绿色”合成氨工艺提供了有价值的参考信息,如要提高过渡金属催化合成氨性能,须尽量规避表面物种吸附能间的线性关系。另外,以可再生能源为能量来源的光、电催化合成氨,借助外场作用可以有效影响反应速率和机理。化学链技术的发展为合成氨工艺提供了新思路,将合成氨过程解耦为吸氮和释氮产氨2个或多个分步反应,可较好地缓解合成氨热力学和动力学矛盾,规避反应物竞争吸附。同时,各分步反应可分别优化,使整个化学链合成氨工艺达到最佳反应效果。未来采用太阳能聚热供能以及以生物质炭为碳源,并对化学链合成氨工艺进行经济性分析反馈指导工艺流程的优化,可降低碳基化学链制氨工艺的成本和能耗。     

Layered Mg-Al spinel supported Ce-Fe-Zr-O oxygen carriers for chemical looping reforming

A series of layered Mg-Al spinel supported Ce-Fe-Zr-O oxygen carriers were prepared for co-production of syngas and pure hydrogen via chemical looping steam reforming (CLSR). The presence of magnesium-aluminum layered double oxides (MgAl-LDO) significantly increases the specific surface area of the mixed oxides, reduces the particle size of CeO₂-based solid solution and promotes the dispersion of free Fe₂O₃. When reacting with methane, MgAl-LDO supported oxygen carrier shows much lower temperature for methane oxidation than the pure Ce-Fe-Zr-O sample, indicating enhanced low-temperature reactivity. Among different Ce-Fe-Zr-O(x)/MgAl-LDO samples, the Ce-Fe-Zr-O(40 wt%)/MgAl-LDO sample shows the best performance for the selective oxidation of methane to syngas and the H₂ production by water splitting. After a long period of high temperature redox experiment, the Ce-Fe-Zr-O(40 wt%)/MgAl-LDO oxygen carrier still shows high activity for syngas generation. The comparison on the morphology of the fresh and cycled oxygen carriers indicates that the Mg-Al spinel support still forms a stable skeleton structure with high dispersion of active components on the surface after the long-term cycling, which contributes to excellent redox stability of the Ce-Fe-Zr-O(40 wt%)/MgAl-LDO oxygen carrier.     

Thermodynamic study of combining chemical looping combustion and combined reforming of propane

Existing energy generation technologies emit CO₂ gas and are posing a serious problem of global warming and climate change. The thermodynamic feasibility of a new process scheme combining chemical looping combustion (CLC) and combined reforming (CR) of propane (LPG) is studied in this paper. The study of CLC of propane with CaSO₄ as oxygen carrier shows thermodynamic feasibility in temperature range (400-782.95 °C) at 1 bar pressure. The CO₂ generated in the CLC can be used for combined reforming of propane in an autothermal way within the temperature range (400-1000 °C) at 1 bar pressure to generate syngas of ratio 3.0 (above 600 °C) which is extremely desirable for petrochemical manufacture. The process scheme generates (a) huge thermal energy in CLC that can be used for various processes, (b) pure N₂ and syngas rich streams can be used for petrochemical manufacture and (c) takes care of the expensive CO₂ separation from flue gas stream and CO₂ sequestration. The thermoneutral temperature (TNP) of 702.12 °C yielding maximum syngas of 5.98 mol per mole propane fed, of syngas ratio 1.73 with negligible methane and carbon formation was identified as the best condition for the CR reactor operation. The process can be used for different fuels and oxygen carriers.     

Experimental investigation of some metal oxides for chemical looping combustion in a fluidized bed reactor

Chemical looping combustion (CLC) is the process in which metal oxides, rather than air or pure oxygen, supply the oxygen required for combustion. In this process, different gaseous fuels can be burnt with the inherent separation of CO₂. The feasibility of the CLC system depends greatly on the selection of appropriate metal oxides as oxygen carriers (OC). In this study, NiO-NiAl₂O₄, Cu_0.95Fe_1.05AlO₄, and CuO-Cu_0.95Fe_1.05AlO₄ were tested experimentally in a fluidized bed reactor as a function of oxidation-reduction cycles, temperature, bed inventory and superficial gas velocity. The results showed that flue gases with a CO₂ concentration as high as 97% can be obtained. The flue gases should be suitable for transport and storage after clean-up and purification. With an increase in the bed inventory or a decrease in superficial gas velocity, the flue gas characteristics improved i.e. more CO₂ and fewer secondary components or less unreacted fuel were obtained. Carbon formation could occur during the reduction phase but it decreased with an increase in temperature and inventory and could be completely avoided by mixing steam with the fuel. The reactivity of NiO/NiAl₂O₄ was higher than the Cu- and Fe-based oxygen carriers. Increasing the CuO fraction in the oxygen carrier led to defluidization of the bed during the reduction and oxidation phases.     

制氢工艺能量分析

本文用过程模拟法对以轻烃为原料的制氢工艺作了能量分析。计算表明在H_2O/C较低,转化温度较高及原料轻质化的条件下,可以获得较低的能耗。     

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.     

Ammonia/hydrogen mixtures in an SI-engine: Engine performance and analysis of a proposed fuel system

In recent years there has been increasing focus on using metal ammine complexes for ammonia storage. In this paper a fuel system for ammonia fuelled internal combustion engines using metal ammine complexes as ammonia storage is analyzed. The use of ammonia/hydrogen mixtures as an SI-engine fuel is investigated in the same context. Ammonia and hydrogen were introduced into the intake manifold of a CFR-engine. Series of experiments with varying excess air ratio and different ammonia to hydrogen ratios was conducted. This showed that a fuel mixture with 10 vol.% hydrogen performs best with respect to efficiency and power. A comparison with gasoline was made, which showed efficiencies and power increased due to the possibility of a higher compression ratio. The system analysis showed that it is possible to cover a major part of the necessary heat using the exhaust heat. It is proposed to reduce the high NO_x emissions using SCR as exhaust after treatment.     

抽氢气及合成气工艺在合成氨装置的应用

介绍了抽氢气、合成气装置的工艺路线,技术特点,运行情况。该工艺在30万t／a年合成氨装置上的应用为国内首创,7．0MPa甲烷化工艺的工业化应用亦为国内首创。     

A comparative study of reaction models applied for chemical looping combustion

Kinetic models applicable for chemical looping combustion in conjunction with relevant experimental studies investigating carrier material kinetics are reviewed. Based on a selection of experimental investigations from literature, where both data at different temperature levels and different gaseous reactant compositions are provided, a broad range of commonly used kinetic models is reviewed. The reaction rate as function of the degree of conversion is addressed which is important if kinetic models are applied within simulations on chemical looping combustion like particle based methods, multiphase CFD-approaches or macroscopic models. Results obtained indicate that most of the models tend to fail towards higher degrees of conversion where reaction rate is rapidly declining. As an alternative to commonly used models, several empirical models are proposed for the conversion rate. The new models perform well and might lead to improved large scale simulations.     

基于化学链燃烧的吸收剂引导的焦炉煤气水蒸气重整制氢过程模拟

建立了基于化学链燃烧供能的吸收剂引导的焦炉煤气水蒸气重整制氢系统,该系统包含吸收剂引导的焦炉煤气重整反应器（SECOGSR）、燃料反应器和空气反应器。该系统能产生高纯H₂［93.23%（mol）］,仅通过冷凝即可实现CO₂的捕获,分离能耗低。采用Aspen Plus软件对吸收剂引导的焦炉煤气重整制氢过程进行了模拟,得到优化的反应条件为：温度650℃,压力1.5 MPa,Ca/C=1,H₂O/C=4。并对系统进行了模拟,以NiO/Y₂O₃/ZrO₂(0.73/0.022/0.248,摩尔比）为化学链燃烧的载氧体和载能体,在满足反应器自热平衡和系统吸放热平衡的基础上,重整1mol焦炉煤气,燃料反应器和空气反应器所需的焦炉煤气、空气及载氧体NiO/Y₂O₃/ZrO₂的量分别为0.139、0.648、3.11 mol。该系统消耗1 mol焦炉煤气的产H₂量为1.30 mol,捕获的CO₂的量为0.355 mol。     

基于化学链制氧的煤气化集成系统工艺参数分析

利用化学链制氧（chemical looping air separation,CLAS）取代传统空气分离制氧技术,提出了基于化学链制氧的煤气化集成系统。以Mn2O3/Mn3O4为氧载体,依据Gibbs自由能最小化原理,利用Aspen Plus对该集成系统进行模拟研究。结果表明,当还原温度高于840℃时,还原程度和粗煤气温度不随还原温度增加而发生明显变化,H2、CO和CH4流量及含量变化趋势较平缓,冷煤气效率为80%左右;随CO2循环比增大,水蒸气用量逐渐减少,粗煤气中H2流量和含量降低,CO流量和含量升高,CH4流量和含量基本不变,冷煤气效率升高,粗煤气温度降低。气化压力变化对粗煤气中H2、CO和CH4流量和含量无明显影响,气化压力升高会降低冷煤气效率,提高粗煤气温度。     

Ca-and Mg-rich waste as high active carrier for chemical looping gasification of biomass

Chemical looping gasification (CLG) is a promising technology for high-quality syngas production.One key issue to successful CLG is the selection of high-performance oxygen carrier.In this study,several Ca-and Mg-rich steelmaking wastes from steel industry,such as blast furnace slag (BF slag),blast furnace dust (BF dust) and Linz-Donawitz converter slag (LD slag),were used as oxygen carriers in chemical loop-ing gasification of biomass.The results showed that the reducibility of Ca-and Mg-rich waste,especially LD slag and BF dust,was superior to that of hematite.Considering long-term operation,the cyclic stability of steelmaking waste was tested.BF dust showed a poor stability,while the other carrier (hematite,BF slag or LD slag) presented an excellent stability during multiple redox cycles in spite of partial sintering and agglomeration.Moreover,the effects of supply oxygen coefficient (O/B ratio) and reaction tempera-ture on CLG of biomass were investigated.The results revealed that Ca-and Mg-rich waste exhibited a higher syngas production compared to hematite.The higher performance could be attributed to the improved reduction rate of Fe2O3 and gasification rate of biomass by Ca or Mg in steelmaking waste.In addition,LD slag exhibited the higher gas value at the O/B ratio of 1 at 900 ℃.As a consequence,LD slag was an appropriate oxygen carrier for CLG of biomass in terms of perfect reducibility,superior cyclic stability and high reactivity.