The calcium looping cycle for large-scale CO2 capture

The reversible reaction between CaO and CO₂ is an extremely promising method of removing CO₂ from the exhaust of a power station, generating a pure stream of CO₂ ready for geological sequestration. The technology has attracted a great deal of attention recently, owing to a number of its advantages: the relatively small efficiency penalty which it imposes upon a power station (estimated at 6–8 percentage points, including compression of the CO₂); its potential use in large-scale circulating fluidised beds (a mature technology, as opposed to the vastly upscaled solvent scrubbing towers which would be required for amine scrubbing); its excellent opportunity for integration with cement manufacture (potentially decarbonising both industries) and its extremely cheap sorbent (crushed limestone).     

Assessment of calcium-based chemical looping options for gasification power plants

This paper evaluates various calcium-based chemical looping concepts to be applied in Integrated Gasification Combined Cycle (IGCC) plants for decarbonised energy vectors poly-generation (with emphasis on power generation and hydrogen and power co-generation). Two calcium-based chemical looping configurations were analysed. The first concept is based on post-combustion capture using the flue gases resulted from the power block (combined cycle gas turbine). The second concept is based on pre-combustion capture, the calcium-based chemical looping systems being used simultaneous to capture carbon dioxide (by sorbent enhanced water gas shift) and to concentrate the syngas energy in the form of hydrogen-rich gas.     

Investigation of hydrogen and power co-generation based on direct coal chemical looping systems

This paper evaluates hydrogen and power co-generation based on direct coal chemical looping systems with total decarbonization of the fossil fuel. As an illustrative example, an iron-based chemical looping system was assessed in various plant configurations. The designs generate 300–450 MW net electricity with flexible hydrogen output in the range of 0–200 MW_th (LHV). The capacity of evaluated plant concepts to have a flexible hydrogen output is an important aspect for integration in modern energy conversion systems. The carbon capture rate of evaluated concepts is almost total (>99%). The paper presents in details evaluated plant configurations, operational aspects as well as mass and energy integration issues. For comparison reason, a syngas-based chemical looping concept and Selexol^®-based pre-combustion capture configuration were also presented. Direct coal chemical looping configuration has significant advantages compared with syngas-based looping systems as well as solvent-based carbon capture configurations, the more important being higher energy efficiency, lower (or even zero) oxygen consumption and lower plant complexity. The results showed a clear increase of overall energy efficiency in comparison to the benchmark cases.     

Evaluation of syngas-based chemical looping applications for hydrogen and power co-generation with CCS

This paper evaluates hydrogen and power co-generation based on coal-gasification fitted with an iron-based chemical looping system for carbon capture and storage (CCS). The paper assess in details the whole hydrogen and power co-production chain based on coal gasification. Investigated plant concepts of syngas-based chemical looping generate about 350–450 MW net electricity with a flexible output of 0–200 MW_th hydrogen (based on lower heating value) with an almost total decarbonisation rate of the coal used.     

Techno-economic and environmental performances of glycerol reforming for hydrogen and power production with low carbon dioxide emissions

This paper is evaluating from the conceptual design, thermal integration, techno-economic and environmental performances points of view the hydrogen and power generation using glycerol (as a biodiesel by-product) reforming processes at industrial scale with and without carbon capture. The evaluated hydrogen plant concepts produced 100,000 Nm³/h hydrogen (equivalent to 300 MW_th) with negligible net power output for export. The power plant concepts generated about 500 MW net power output. Hydrogen and power co-generation was also assessed. The CO₂ capture concepts used alkanolamine-based gas–liquid absorption. The CO₂ capture rate of the carbon capture unit is at least 90%, the carbon capture rate of the overall reforming process being at least 70%. Similar designs without carbon capture have been developed to quantify the energy and cost penalties for carbon capture. The various glycerol reforming cases were modelled and simulated to produce the mass & energy balances for quantification of key plant performance indicators (e.g. fuel consumption, energy efficiency, ancillary energy consumption, specific CO₂ emissions, capital and operational costs, production costs, cash flow analysis etc.). The evaluations show that glycerol reforming is promising concept for high energy efficiency processes with low CO₂ emissions.     

Evaluation of iron based chemical looping for hydrogen and electricity co-production by gasification process with carbon capture and storage

Integrated Gasification Combined Cycle (IGCC) is one of power generation technologies having the highest potential for carbon capture with low penalties in efficiency and cost. Syngas produced by gasification can be decarbonised using chemical looping methods in which an oxygen carrier (usually a metallic oxide) is recycled between the syngas oxidation reactor (fuel reactor) and the chemical agent oxidation reactor (steam reactor). In this way, the resulted carbon dioxide is inherently separated from the other products of combustion and the syngas energy is transferred to an almost pure hydrogen stream suitable to be used not only for power generation but also for transport sector (PEM fuel cells).     

Investigation on gasification performance of sewage sludge using chemical looping gasification with iron ore oxygen carrier

Chemical looping gasification (CLG), with inherent characteristic of low pollutant emissions can realize the treatment and disposal principle of sewage sludge of harmlessness, reduction, stabilization and reutilization. This work attempted to investigate the feasibility of CLG of sewage sludge with hematite oxygen carrier. The role of hematite in CLG was firstly determined and it was used as gasification agent to provide the required oxygen for sludge conversion. Subsequently, the effect of various operating parameters on sludge CLG was discussed. An optimal mass ratio of sludge to hematite oxygen carrier was determined at 0.33 to achieve the high-efficient conversion of sludge. The reaction temperature of sludge gasification was set at 900 °C to avoid the excessive reduction of hematite. Suitable steam content was assigned to at 19.52%, where the sludge conversion attained the maximum. Ash deposited caused the decrease of specific surface area of hematite, but the accumulated mineral elements in sludge ash can improve the reactivity of oxygen carrier. Additionally, the ash accumulation also can prolong the gas mean residence time. Hence, the sludge conversion showed a slight uptrend with the cycle numbers. The phosphorus element of sludge was formed of CaH₂P₂O₇ and CaHPO₄ during the CLG. Although some sludge ash deposited on the surface of hematite particles, the new compounds were not observed in the reacted oxygen carrier. Additionally, sludge ash has a relatively high resistance trend for bed agglomeration and deposit formation due to the high content of Ca/Al elements. Consequently, the accumulation of sludge ash only reveals physical effects rather than chemical effects on the hematite particles. Thus, it is easy to separate the sludge ash from hematite particles according to the differences in density and size.     

Hydrogen production from fossil fuels with carbon capture and storage based on chemical looping systems

This paper analyzes innovative processes for producing hydrogen from fossil fuels conversion (natural gas, coal, lignite) based on chemical looping techniques, allowing intrinsic CO₂ capture. This paper evaluates in details the iron-based chemical looping system used for hydrogen production in conjunction with natural gas and syngas produced from coal and lignite gasification. The paper assesses the potential applications of natural gas and syngas chemical looping combustion systems to generate hydrogen. Investigated plant concepts with natural gas and syngas-based chemical looping method produce 500 MW hydrogen (based on lower heating value) covering ancillary power consumption with an almost total decarbonisation rate of the fossil fuels used.The paper presents in details the plant concepts and the methodology used to evaluate the performances using critical design factors like: gasifier feeding system (various fuel transport gases), heat and power integration analysis, potential ways to increase the overall energy efficiency (e.g. steam integration of chemical looping unit into the combined cycle), hydrogen and carbon dioxide quality specifications considering the use of hydrogen in transport (fuel cells) and carbon dioxide storage in geological formation or used for EOR.     

Performance of hydrogen and power co-generation system based on chemical looping hydrogen generation of coal

An integrated hydrogen and power co-generation system based on slurry-feed coal gasification and chemical looping hydrogen generation (CLH) was proposed with Shenhua coal as fuel and Fe₂O₃/MgAl₂O₄ as an oxygen carrier. The sensitivity analyses of the main units of the system were carried out respectively to optimize the parameters. The syngas can be converted completely in the fuel reactor, and both of the fuel reactor and steam reactor can maintain heat balance. The purity of hydrogen produced after water condensation is 100%. The energy and exergy analyses of the proposed system were studied. Pinch technology was adopted to get a reasonable design of the heat transfer network, and it is found pinch point appears at the hot side temperature of 224.7 °C. At the given status of the proposed system, the hydrogen yield is 1040.11 kg·h⁻¹ and the CO₂ capture rate is 94.56%. At the same time, its energy and exergy efficiencies are 46.21% and 47.22%, respectively. According to exergy analysis, the degree of exergy destruction is ranked. The gasifier unit has the most serious exergy destruction, followed by chemical looping hydrogen generation unit and the heat recovery steam generator unit.     

Expert opinions on carbon dioxide capture and storage—A framing of uncertainties and possibilities

There are many uncertainties and knowledge gaps regarding the development of carbon dioxide capture and storage (CCS)—e.g., when it comes to costs, life-cycle effects, storage capacity and permanence. In spite of these uncertainties and barriers, the CCS research community is generally very optimistic regarding CCS’ development. The discrepancy between the uncertainties and the optimism is the point of departure in this study, which is based on interviews with 24 CCS experts. The aim is to analyse experts’ framings of CCS with focus on two key aspects: (i) the function and potential of CCS and (ii) uncertainties. The optimism among the CCS experts is tentatively explained. The interpretative flexibility of CCS is claimed to be an essential explanation for the optimism. CCS is promoted from a wide variety of perspectives, e.g., solidarity and peace, bridge to a sustainable energy system, sustaining the modern lifestyle and compatibility with the fossil fuel lock-in. Awareness of the uncertainties and potential over-optimism is warranted within policy and decision making as they often rely on scientific forecasts and experts’ judgements.     

Assessing innovation in emerging energy technologies: Socio-technical dynamics of carbon capture and storage (CCS) and enhanced geothermal systems (EGS) in the USA

This study applies a socio-technical systems perspective to explore innovation dynamics of two emerging energy technologies with potential to reduce greenhouse gas emissions from electrical power generation in the United States: carbon capture and storage (CCS) and enhanced geothermal systems (EGS). The goal of the study is to inform sustainability science theory and energy policy deliberations by examining how social and political dynamics are shaping the struggle for resources by these two emerging, not-yet-widely commercializable socio-technical systems. This characterization of socio-technical dynamics of CCS and EGS innovation includes examining the perceived technical, environmental, and financial risks and benefits of each system, as well as the discourses and actor networks through which the competition for resources – particularly public resources – is being waged. CCS and EGS were selected for the study because they vary considerably with respect to their social, technical, and environmental implications and risks, are unproven at scale and uncertain with respect to cost, feasibility, and life-cycle environmental impacts. By assessing the two technologies in parallel, the study highlights important social and political dimensions of energy technology innovation in order to inform theory and suggest new approaches to policy analysis.     

Evaluation of power generation schemes based on hydrogen-fuelled combined cycle with carbon capture and storage (CCS)

IGCC is a power generation technology in which the solid feedstock is partially oxidized to produce syngas. In a modified IGCC design for carbon capture, there are several technological options which are evaluated in this paper. The first two options involve pre-combustion arrangements in which syngas is processed, either by shift conversion or chemical looping, to maximise the hydrogen level and to concentrate the carbon species as CO₂. After CO₂ capture by gas-liquid absorption or chemical looping, the hydrogen-rich gas is used for power generation. The third capture option is based on post-combustion arrangement using chemical absorption.Investigated coal-based IGCC case studies produce 400-500 MW net power with more than 90% carbon capture rate. Principal focus of the paper is concentrated on evaluation of key performance indicators for investigated carbon capture options, the influence of various gasifiers on carbon capture process, optimisation of energy efficiency by heat and power integration, quality specification of captured CO₂. The capture option with minimal energy penalty is based on chemical looping, followed by pre-combustion and post-combustion.     

Carbon capture and storage

Carbon capture and storage (CCS) covers a broad range of technologies that are being developed to allow carbon dioxide (CO₂) emissions from fossil fuel use at large point sources to be transported to safe geological storage, rather than being emitted to the atmosphere. Some key enabling contributions from technology development that could help to facilitate the widespread commercial deployment of CCS are expected to include cost reductions for CO₂ capture technology and improved techniques for monitoring stored CO₂. It is important, however, to realise that CCS will always require additional energy compared to projects without CCS, so will not be used unless project operators see an appropriate value for reducing CO₂ emissions from their operations or legislation is introduced that requires CCS to be used. Possible key advances for CO₂ capture technology over the next 50 years, which are expected to arise from an eventual adoption of CCS as standard practice for all large stationary fossil fuel installations, are also identified. These include continued incremental improvements (e.g. many potential solvent developments) as well as possible step-changes, such as ion transfer membranes for oxygen production for integrated gasifier combined cycle and oxyfuel plants.     

Techno-economic appraisal of fossil-fuelled power generation systems with carbon dioxide capture and storage

Carbon capture and storage (CCS) facilities coupled to power plants provide a climate change mitigation strategy that potentially permits the continued use of fossil fuels whilst reducing the carbon dioxide (CO₂) emissions. This process involves three basic stages: capture and compression of CO₂ from power stations, transport of CO₂, and storage away from the atmosphere for hundreds to thousands of years. Potential routes for the capture, transport and storage of CO₂ from United Kingdom (UK) power plants are examined. Six indicative options are evaluated, based on ‘Pulverised Coal’, ‘Natural Gas Combined Cycle’, and ‘Integrated (coal) Gasification Combined Cycle’ power stations. Chemical and physical CO₂ absorption capture techniques are employed with realistic transport possibilities to ‘Enhanced Oil Recovery’ sites or depleted gas fields in the North Sea. The selected options are quantitatively assessed against well-established economic and energy-related criteria. Results show that CO₂ capture can reduce emissions by over 90%. However, this will reduce the efficiency of the power plants concerned, incurring energy penalties between 14 and 30% compared to reference plants without capture. Costs of capture, transport and storage are concatenated to show that the whole CCS chain ‘cost of electricity’ (COE) rises by 27-142% depending on the option adopted. This is a significant cost increase, although calculations show that the average ‘cost of CO₂ captured’ is £15/tCO₂ in 2005 prices [the current base year for official UK producer price indices]. If potential governmental carbon penalties were introduced at this level, then the COE would equate to the same as the reference plant, and make CCS a viable option to help mitigate large-scale climate change.     

Design and comparisons of three biomass based hydrogen generation systems with chemical looping process

The technology of hydrogen generation from biomass has attracted more and more attentions nowadays. In this work, three biomass-based chemical looping hydrogen generation systems, Systems A, B and C, are comprehensively studied. System A is mainly composed of biomass hydrogasification, methane reformation and the calcium-looping based CO₂ absorption. System B is mainly composed of biomass steam gasification and Fe₂O₃/FeO-looping based hydrogen generation circulation. System C is mainly composed of biomass steam gasification and Fe₃O₄/FeO-looping based hydrogen generation circulation. The three systems are modeled and their characteristics are analyzed and compared thermodynamically. System A has the highest cold gas efficiency (CGE) which is 72%; System B has the lowest CGE of 54% but it can generate additional nitrogen as byproduct; System C has the highest hydrogen generation ratio and its CGE is moderate and is 60%. The carbon dioxide sequestration rates of the three systems are all above 90%.     

Techno-economical evaluations of decarbonized hydrogen production based on direct biogas conversion using thermo-chemical looping cycles

Hydrogen production by biogas conversion represent a promising solution for reduction of fossil CO₂ emissions. In this work, a detailed techno-economic analysis was performed for decarbonized hydrogen production based on biogas conversion using calcium and chemical looping cycles. All evaluated concepts generate 100,000 Nm³/h high purity hydrogen. As reference cases, the biogas steam reforming design without decarbonization and with CO₂ capture by gas-liquid chemical absorption were also considered. The results show that iron-based chemical looping design has higher energy efficiency compared with the gas-liquid absorption case by 2.3 net percentage points as well as a superior carbon capture rate (99% vs. 65%). The calcium looping case shows a lower efficiency than chemical scrubbing, with about 2.5 net percentage points, but the carbon capture rate is higher (95% vs. 65%). The hydrogen production cost increases with decarbonization, the calcium looping shows the most favourable situation (37.14 €/MWh) compared to the non-capture steam reforming case (33 €/MWh) and MDEA and iron looping cases (about 42 €/MWh). The calcium looping case has the lowest CO₂ avoidance cost (10 €/t) followed by iron looping (20 €/t) and MDEA (31 €/t) cases.     

Making carbon dioxide sequestration feasible: Toward federal regulation of CO2 sequestration pipelines

As the United States moves closer to a national climate change policy, it will have to focus on a variety of factors affecting the manner in which the country moves toward a future with a substantially lower carbon footprint. In addition to encouraging renewable energy, smart grid, clean fuels and other technologies, the United States will need to make substantial infrastructure investments in a variety of industries. Among the significant contributors to the current carbon footprint in the United States is the use of coal as a major fuel for the generation of electricity. One of the most important technologies that the United States can employ to reduce its carbon footprint is to sequester the carbon dioxide (“CO₂”) from coal-fired power plants. This article focuses on the legal and policy issues surrounding a critical piece of the necessary sequestration infrastructure: CO₂ pipelines that will carry CO₂ from where it is removed from fuel or waste gas streams to where it will be sequestered. Ultimately, this article recommends developing a federally regulated CO₂ pipeline program to foster the implementation of carbon sequestration technology.     

Techno-economic and environmental evaluations of large scale gasification-based CCS project in Romania

Gasification is a promising technology in terms of reducing carbon capture energy and cost penalties as well as for multi-fuel multi-product operation capability. The paper evaluates two carbon capture options in terms of main techno-economic indicators. The first option involves pre-combustion capture, the syngas being catalytically shifted to convert carbon species into CO₂ and H₂. Gas–liquid absorption is used for separate H₂S and CO₂ capture, then clean gas is used for power generation. The second capture option is based on post-combustion capture using chemical absorption. The most promising gasifiers were evaluated in a CCS design.     

Study of the crystal structure effect and mechanism during chemical looping gasification of coal

Chemical looping gasification (CLG) of coal, in which oxygen is provided to coal by oxygen carriers directly, is a clean and efficient way to generate syngas. Thermo-gravimetric analysis (TGA) of lignite char with oxygen carriers was conducted in this work, and the experimental results indicated that the oxygen carriers, Ti_0·5Mn_0·5Fe₂O₄, MnFe₂O₄, FeTiO₃ and Fe₂TiO₄, had a positive effect on CLG of lignite char. The effect of these oxygen carriers was discussed in the perspective of the crystal structure. XPS experiment was performed and the spectra of O 1s revealed the effect of different element on reactivity of spinel-based oxygen carriers. Five kinetic models, including Uniform Reaction (UR), Integrated Model (IM), Modified Random Pore Model (MRPM), Random Pore Model (RPM) and Modified Volumetric Model (MVM), were employed for revealing the reaction mechanism. MRPM had the highest correlation coefficient for each oxygen carrier, which means the introduction of the oxygen carriers effectively increases the active site of the reaction surface.     

High quality product gas from biomass steam gasification combined with torrefaction and carbon dioxide capture processes

Gasification is currently recognized as a mature technology to convert biomass into useful and versatile product gas for further energy and fuel applications. However, there are some remaining problems relating to the process operation and process efficiency due to inherent properties of biomass feedstock such as high moisture content, low energy density and high oxygen content. Strategies to improve the efficiency of biomass gasification as well as the quality of product gas are thus required. For this purpose, a combined process of torrefaction, gasification, and carbon dioxide capture is developed and simulated in a commercial simulator to investigate the performance of a biomass gasification coupled with a pre-treatment and a post-treatment processes. The results show that the quality of product gas is enhanced when combining gasification with a torrefaction and a CO₂ capture processes. The heating value of the product gas and the cold gas efficiency are both increased with additional torrefaction. The CO₂ capture process using monoethanolamine offers a CO₂ removal efficiency of about 83% and consequently increase the product gas heating value up to 27%.