Oxyfuel concept development

Abstract

The reduction of greenhouse gas emissions and replacement of fossil fuels by renewable energy sources are important national and international targets. Oxyfuel (oxygen combustion technology) is one of the most promising technologies enabling carbon capture and storage from flue gases. The aim of oxyfuel concept development is to study different oxygen production technologies, combustion processes, CO₂ capture methods and integrate those to optimised concept. The goal is to create technical readiness for demonstration of oxygen combustion by using state of the art knowledge, experiments, modelling and simulation. Demonstration plan for oxygen combustion for an existing power plant(s) in Finland will be prepared. Main results will be an evaluation of oxygen combustion business potential for implementation in existing and new power plants, and improvement of competitiveness of Finnish companies in energy sector by developing CO₂ free power production technologies.

Before oxygen combustion can be demonstrated in full scale, small scale testing and model development must be done. Material exposure conditions in oxygen combustion will differ from any present day environment. Current high temperature steel grades have not been developed or tested for such aggressive conditions. VTT (Technical Research Centre of Finland) has in Jyväskylä unique small scale combustors applicable for oxygen combustion research.     

A review of recent developments in carbon capture utilizing oxy‐fuel combustion in conventional and ion transport membrane systems

Fossil fuels provide a significant fraction of the global energy resources, and this is likely to remain so for several decades. Carbon dioxide (CO₂) emissions have been correlated with climate change, and carbon capture is essential to enable the continuing use of fossil fuels while reducing the emissions of CO₂ into the atmosphere thereby mitigating global climate changes. Among the proposed methods of CO₂ capture, oxyfuel combustion technology provides a promising option, which is applicable to power generation systems. This technology is based on combustion with pure oxygen (O₂) instead of air, resulting in flue gas that consists mainly of CO₂ and water (H₂O), that latter can be separated easily via condensation, while removing other contaminants leaving pure CO₂ for storage. However, fuel combustion in pure O₂ results in intolerably high combustion temperatures. In order to provide the dilution effect of the absent nitrogen (N₂) and to moderate the furnace/combustor temperatures, part of the flue gas is recycled back into the combustion chamber. An efficient source of O₂ is required to make oxy‐combustion a competitive CO₂ capture technology. Conventional O₂ production utilizing the cryogenic distillation process is energetically expensive. Ceramic membranes made from mixed ion‐electronic conducting oxides have received increasing attention because of their potential to mitigate the cost of O₂ production, thus helping to promote these clean energy technologies. Some effort has also been expended in using these membranes to improve the performance of the O₂ separation processes by combining air separation and high‐temperature oxidation into a single chamber. This paper provides a review of the performance of combustors utilizing oxy‐fuel combustion process, materials utilized in ion‐transport membranes and the integration of such reactors in power cycles. The review is focused on carbon capture potential, developments of oxyfuel applications and O₂ separation and combustion in membrane reactors. The recent developments in oxyfuel power cycles are discussed focusing on the main concepts of manipulating exergy flows within each cycle and the reported thermal efficiencies. Copyright © 2010 John Wiley & Sons, Ltd.     

Post combustion CO2 capture by carbon fibre monolithic adsorbents

As generation of carbon dioxide (CO₂) greenhouse gas is inherent in the combustion of fossil fuels, effective capture of CO₂ from industrial and commercial operations is viewed as an important strategy which has the potential to achieve a significant reduction in atmospheric CO₂ levels. At present, there are three basic capture methods, i.e. post combustion capture, pre-combustion capture and oxy-fuel combustion. In pre-combustion, the fossil fuel is reacted with air or oxygen and is partially oxidized to form CO and H₂. Then it is reacted with steam to produce a mixture of CO₂ and more H₂. The H₂ can be used as fuel and the carbon dioxide is removed before combustion takes place. Oxy-combustion is when oxygen is used for combustion instead of air, which results in a flue gas that consists mainly of pure CO₂ and is potentially suitable for storage. In post combustion capture, CO₂ is captured from the flue gas obtained after the combustion of fossil fuel. The post combustion capture (PCC) method eliminates the need for substantial modifications to existing combustion processes and facilities; hence, it provides a means for near-term CO₂ capture for new and existing stationary fossil fuel-fired power plants.This paper briefly reviews CO₂ capture methods, classifies existing and emerging post combustion CO₂ capture technologies and compares their features. The paper goes on to investigate relevant studies on carbon fibre composite adsorbents for CO₂ capture, and discusses fabrication parameters of the adsorbents and their CO₂ adsorption performance in detail. The paper then addresses possible future system configurations of this process for commercial applications.Finally, while there are many inherent attractive features of flow-through channelled carbon fibre monolithic adsorbents with very high CO₂ adsorption capabilities, further work is required for them to be fully evaluated for their potential for large scale CO₂ capture from fossil fuel-fired power stations.     

Oxy-fuel combustion technology for coal-fired power generation

The awareness of the increase in greenhouse gas emissions has resulted in the development of new technologies with lower emissions and technologies that can accommodate capture and sequestration of carbon dioxide. For existing coal-fired combustion plants there are two main options for CO₂ capture: removal of nitrogen from flue gases or removal of nitrogen from air before combustion to obtain a gas stream ready for geo-sequestration. In oxy-fuel combustion, fuel is combusted in pure oxygen rather than air. This technology recycles flue gas back into the furnace to control temperature and makeup the volume of the missing N₂ to ensure there is sufficient gas to maintain the temperature and heat flux profiles in the boiler. A further advantage of the technology revealed in pilot-scale tests is substantially reduced NO_x emissions. For coal-fired combustion, the technology was suggested in the eighties, however, recent developments have led to a renewed interest in the technology. This paper provides a comprehensive review of research that has been undertaken, gives the status of the technology development and assessments providing comparisons with other power generation options, and suggests research needs.     

CO2 chemical conversion to useful products: An engineering insight to the latest advances toward sustainability

In the fossil‐fuel‐based economies, current remedies for the CO₂ reduction from large‐scale energy consumers (e.g. power stations and cement works) mainly rely on carbon capture and storage, having three proposed generic solutions: post‐combustion capture, pre‐combustion capture, and oxy fuel combustion. All the aforementioned approaches are based on various physical and chemical phenomena including absorption, adsorption, and cryogenic capture of CO₂. The purified carbon dioxide is sent for the physical storage options afterwards, using the earth as a gigantic reservoir with unknown long‐term environmental impacts as well as possible hazards associated with that. Consequently, the ultimate solution for the CO₂ sequestration is the chemical transformation of this stable molecule to useful products such as fuels (through, for example, Fischer–Tropsch chemistry) or polymers (through successive copolymerization and chain growth). This sustainably reduces carbon emissions, taking full advantage of CO₂‐derived chemical commodities, so‐called carbon capture and conversion. Nevertheless, the surface chemistry of CO₂ reduction is a challenge due to the presence of large energy barriers, requiring noticeable catalysis. This work aims to review the most recent advances in this concept selectively (CO₂ conversion to fuels and CO₂ copolymerization) with chemical engineering approach in terms of both materials and process design. Some of the most promising studies are expanded in detail, concluding with the necessity of subsidizing more research on CO₂ conversion technologies considering the growing global concerns on carbon management. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermogravimetric analysis and process simulation of oxy‐fuel combustion of blended fuels including oil shale,semicoke, and biomass

Oxy‐fuel (OF) combustion is considered as one of the promising carbon capture and storage technologies for reducing CO₂ emissions from power plants. In the current work, the thermal behaviour of Estonian oil shale (EOS) and its semicoke (SC), pine saw dust, and their blends were studied comparatively under model air (21%O₂/79%Ar) and OF (30%O₂/70%CO₂) conditions using thermogravimetric analysis. Mass spectrometry analysis was applied to monitor the evolved gases. The effect of SC and pine saw dust addition on different combustion stages was analysed using kinetic analysis methods. In addition, different co‐firing cases were simulated using the ASPEN PLUS V8.6 (APV86) software tool to evaluate the effects of blending EOS with different biomass fuels of low and high moisture contents. The specific boiler temperatures of each simulated case with the same adjusted thermal fuel input were calculated while applying the operation conditions of air and OF combustion. According to the experiment and process simulation results, the low heating value and high carbonate content of SC brings along endothermic decomposition of carbonates, which negatively affects the heat balance during the conventional co‐combustion of EOS with SC. Instead, firing of EOS with SC and biomass in OF process can be an effective solution to reduce the environmental impact in terms of the reduction of CO₂ emissions and ash. Furthermore, the sensible heat from SC can positively affect the energy balance of the system as the endothermic effect of decomposition of CaCO₃ (for both EOS and SC) can be avoided in OF combustion.     

System study of carbon dioxide (CO2) capture in bio-based motor fuel production

A number of different technologies for producing renewable motor fuels have been studied; some effects of applying carbon dioxide (CO₂) capture to the production of renewable motor fuels are described in this paper. Some of the technologies studied are well suited for CO₂ capture. However, it is shown that the advantages with CO₂ capture for these technologies are not enough to offset their shortcomings described in previous studies, which show that the largest CO₂ reduction from biomass in Sweden may be achieved by producing fuel pellets for coal substitution or using the biomass in combined heat and power plants. A conclusion of the present paper is that even with CO₂ capture added to the respective technology, it is inefficient to use renewable resources for motor fuel production if the aim is to achieve as high CO₂ emission reduction as possible per input of biomass. Therefore, the large Swedish subsidies of the production of motor fuels appear sub-optimal, also when the possibility of CO₂ capture is considered. Nevertheless, incorporating CO₂ capture in the production of renewable motor fuels from biomass might be a cost-effective way of reducing CO₂ emissions.     

Progress in Chemical-Looping Combustion and Reforming technologies

This work is a comprehensive review of the Chemical-Looping Combustion (CLC) and Chemical-Looping Reforming (CLR) processes reporting the main advances in these technologies up to 2010. These processes are based on the transfer of the oxygen from air to the fuel by means of a solid oxygen-carrier avoiding direct contact between fuel and air for different final purposes. CLC has arisen during last years as a very promising combustion technology for power plants and industrial applications with inherent CO₂ capture which avoids the energetic penalty present in other competing technologies. CLR uses the chemical looping cycles for H₂ production with additional advantages if CO₂ capture is also considered.     

Materials challenges in CO2 capture and storage

Abstract

To achieve deep reductions in CO₂ emission from power generation, technologies for CO₂ capture and storage are required to complement other approaches such as improved fuel use efficiency, the switch to low carbon fuels, and the use of renewable and nuclear energy. Three main options currently exist for CO₂ capture: removal of CO₂ from the flue gas; removal of carbon from the fuel before combustion; and oxyfuel combustion systems that have CO₂ and water, which can be separated by condensation, as principal combustion products. On the transport and storage side, the materials issues arise from corrosion and may be solved by drying and purification of the CO₂ stream. On the capture side, there are few specific issues regarding the materials used in technologies such as chemical absorption of CO₂ in an appropriate solvent (usually amines). The high temperature membranes used to separate oxygen from nitrogen in oxyfuel combustion systems raise materials issues in relation to ionic conduction, thermal and mechanical stability and lifetime when integrated in boilers, fluidised beds and gas turbine systems. The performance of systems integrating ceramic oxygen separating membranes is largely dependant on operating temperature, so the behaviour of these materials at ever higher temperatures is a real technical challenge. Membranes can also be used instead of chemical absorption for the separation of CO₂ and hydrogen in fuel de-carbonisation.     

CO2 capture and separation technologies for end-of-pipe applications – A review

Carbon capture from point source emissions has been recognized as one of several strategies necessary for mitigating unfettered release of greenhouse gases (GHGs) into the atmosphere. To keep GHGs at manageable levels, large decreases in CO₂ emissions through capturing and separation will be required. This article reviews the possible CO₂ capture and separation technologies for end-of-pipe applications. The three main CO₂ capture technologies discussed include post-combustion, pre-combustion and oxyfuel combustion techniques. Various separation techniques, such as chemical absorption, physical absorption, physical adsorption, cryogenics, membrane technology, membranes in conjunction with chemical absorption and chemical-looping combustion (CLC) are also thoroughly discussed. Future directions are suggested for application by oil and gas industry. Sequestration methods, such as geological, mineral carbonation techniques, and ocean dump are not covered in this review.     

Direct air capture from demonstration to commercialization stage: A bibliometric analysis

Concerns related to increasing CO₂ emission and its effects on global warming and climate change have been increased with increasing the global consumption of fossil fuels. One solution to respond to this challenge is the development and utilization of carbon capturing and storage technologies. Among different carbon capturing technologies, direct air capture (DAC) reduces CO₂ emissions from air. While the technology readiness level (TRL) of DAC is in the demonstration stage, identifying the commercialization research gaps and possible opportunities can help with diffusion and adoption of the technology. This research uses a knowledge discovery in research databases, based on bibliometric analysis and data mining, to understand DAC research and development's current status and future. Then, we identify the critical areas of the research gap for commercialization. The bibliometric analysis results show that DAC has not yet reached its maturity level compared with other carbon capture technologies (CCTs). However, there are different opportunities for the development of this technology. The results indicate that (a) new systematic designs, improvement in nano-catalysts, increase in the capturing capacity, (b) economic and investment improvements in combination with the environmental assessment of the optimized DAC technology, (c) assessment of future prospects, (d) integration with alternative energy supply sources especially renewable energy to respond to the required energy and process integration with current carbon emitted processes, (e) technology demonstration and readiness assessment, and (f) policy and uncertainty analysis of the market are the key areas that should be investigated for the success of this technology in the competitive market.     

Frontiers in combustion techniques and burner designs for emissions control and CO2 capture: A review

The use of fossil fuel is expected to increase significantly by midcentury because of the large rise in the world energy demand despite the effective integration of renewable energies in the energy production sector. This increase, alongside with the development of stricter emission regulations, forced the manufacturers of combustion systems, especially gas turbines, to develop novel combustion techniques for the control of NO_x and CO₂ emissions, the latter being a greenhouse gas responsible for more than 60% to the global warming problem. The present review addresses different burner designs and combustion techniques for clean power production in gas turbines. Combustion and emission characteristics, flame instabilities, and solution techniques are presented, such as lean premixed air‐fuel (LPM) and premixed oxy‐fuel combustion techniques, and the combustor performance is compared for both cases. The fuel flexibility approach is also reviewed, as one of the combustion techniques for controlling emissions and reducing flame instabilities, focusing on the hydrogen‐enrichment and the integrated fuel‐flexible premixed oxy‐combustion approaches. State‐of‐the‐art burner designs for gas turbine combustion applications are reviewed in this study, including stagnation point reverse flow (SPRF) burner, dry low NO_x (DLN) and dry low‐emission (DLE) burners, EnVironmental burners (including EV, AEV, and SEV burners), perforated plate (PP) burner, and micromixer (MM) burner. Special emphasis is made on the MM combustor technology, as one of the most recent advances in gas turbines for stable premixed flame operation with wide turndown and effective control of NO_x emissions. Since the generation of pure oxygen is prerequisite to oxy‐combustion, oxygen‐separation membranes became of immense importance either for air separation for clean oxy‐combustion applications or for conversion/splitting of the effluent CO₂ into useful chemical and energy products. The different carbon‐capture technologies, along with the most recent carbon‐utilization approaches towards CO₂ emissions control, are also reviewed.     

Fireside issues in advanced power generation systems

Abstract

The traditional trend towards the development and use of power plants with ever increasing efficiencies is now being coupled to the use of a wider range of fuels and technologies designed to minimise CO₂ emissions. Alternative solid fuels such as biomass and waste products, which can be classified as CO₂ neutral, are being used alone or cofired with fossil fuels. The cofiring of biomass and coal is currently the most efficient and effective method for using biomass to generate power. CO₂ capture technologies include systems for either precombustion or postcombustion CO₂ removal. Gasification of fuels (using either oxygen or steam as the oxidant) produces a gas that can be conditioned to enable precombustion CO₂ removal. Post-combustion CO₂ capture can be carried out using either solid or aqueous sorbent processes. Oxy firing of fuels is a technology that would enable more efficient post-combustion CO₂ capture. The various combinations of new fuels, novel technologies and higher temperature component operating conditions are producing challenging operating environments for components. Deposition, erosion and corrosion issues for hot gas path components in these advanced power generating systems, which are potentially life limiting, are reviewed. Reduction in heat transfer owing to high rates of deposition can significantly reduce heat transfer and increase the need for component cleaning. Depending on the system, component parts can include various heat exchangers, gas cleaning systems and gas turbines.     

Solar thermal hybrids for combustion power plant: A growing opportunity

The development of technologies to hybridise concentrating solar thermal energy (CST) and combustion technologies, is driven by the potential to provide both cost-effective CO₂ mitigation and firm supply. Hybridisation, which involves combining the two energy sources within a single plant, offers these benefits over the stand-alone counterparts through the use of shared infrastructure and increased efficiency. In the near-term, hybrids between solar and fossil fuelled systems without carbon capture offer potential to lower the use of fossil fuels, while in the longer term they offer potential for low-cost carbon-neutral or carbon-negative energy. The integration of CST into CO₂ capture technologies such as oxy-fuel combustion and chemical looping combustion is potentially attractive because the same components can be used for both CO₂ capture and the storage of solar energy, to reduce total infrastructure and cost. The use of these hybrids with biomass and/or renewable fuels, offers the additional potential for carbon-negative energy with relatively low cost. In addition to reviewing these technologies, we propose a methodology for classifying solar-combustion hybrid technologies and assess the progress and challenges of each. Particular attention is paid to “direct hybrids”, which harness the two energy sources in a common solar receiver or reactor to reduce total infrastructure and losses.     

Green hydrogen-based E-fuels (E-methane,E-methanol,E-ammonia) to support clean energy transition: A literature review

Renewable power-to-fuel (PtF) is a key technology for the transition towards fossil-free energy systems. The production of carbon neutral synthetic fuels is primarily driven by the need to decouple the energy sector from fossil fuels dependance which are the main source of environmental issues. Hydrogen (H₂) produced from water electrolysis powered by renewable electricity and direct carbon dioxide (CO₂) captured from the flue gas generated by power plants, industry, transportation, and biogas production from anaerobic digestion, are used to convert electricity into carbon-neutral synthetic fuels. These fuels function as effective energy carriers that can be stored, transported, and used in other energy sectors (transport and industry). In addition, the PtF concept is an energy transformation that is capable of providing services for the balancing of the electricity grid thanks to its adaptable operation and long-term storage capacities for renewable energy surplus. As a consequence, it helps to potentially decarbonize the energy sector by reducing the carbon footprint and GHG emissions. This paper gives an overview on recent advances of renewable PtF technology for the e-production of three main hydrogen-based synthetic fuels that could substitute fossil fuels such as power-to-methane (PtCH₄), power-to-methanol (PtCH₃OH) and power-to-ammonia (PtNH₃). The first objective is to thoroughly define in a clear manner the framework which includes the PtF technologies. Attention is given to green H₂ production by water electrolysis, carbon capture & storage (CCS), CO₂ hydrogenation, Sabatier, and Haber Bosch processes. The second objective is to gather and classify some existing projects which deal with this technology depending on the e-fuel produced (energy input, conversion process, efficiency, fuel produced, and application). Furthermore, the challenges and future prospects of achieving sustainable large-scale PtF applications are discussed.     

Biomass integrated gasification combined cogeneration with or without CO2 capture – A comparative thermodynamic study

Fossil fuels presently cater to majority of energy demand of the world. However, due to the climate change problem capture of CO₂ emitted from the use of fossil fuels is emerging as a necessity. Alternately, developing technology with CO₂ neutral fuels may reduce green house gas emission. Possible even better solution may be combining both of these options, i.e., employing CO₂ capture process for energy efficient system using CO₂ neutral fuels, say biomass. In this paper, such cogeneration system with CO₂ capture using amine solution has been proposed. Thermodynamic modeling for the detail process has been implemented using ASPEN Plus^®. Comparative study of performance relative to a similar base case plant without carbon capture has been presented. Results show post combustion CO₂ capture process is better than pre-combustion CO₂ capture process for such plants with net negative CO₂ emission. Also degree of CO₂ capture has to be optimized on the basis of the overall performance of the plant as higher CO₂ capture affects thermodynamic and economic performance of the plant, specifically beyond certain value. In a net CO₂ negative emission plant extent of CO₂ capture is quite flexible and may be decided for optimum performance.     

Capturing and using CO2 as feedstock with chemical looping and hydrothermal technologies

Chemical looping technology for capturing and hydrothermal processes for conversion of carbon are discussed with focused and critical assessments. The fluidized and stationary reactor systems using solid, including biomass, and gaseous fuels are considered in chemical looping combustion, gasification, and reforming processes. Sustainability is emphasized generally in energy technology and in two chemical looping simulation case studies using coal and natural gas. Conversion of captured carbon to formic acid, methanol, and other chemicals is also discussed in circulating and stationary reactors in hydrothermal processes. This review provides analyses of the major chemical looping technologies for CO₂ capture and hydrothermal processes for carbon conversion so that the appropriate clean energy technology can be selected for a particular process. Combined chemical looping and hydrothermal processes may be feasible and sustainable in carbon capture and conversion and may lead to clean energy technologies using coal, natural gas, and biomass. Copyright © 2014 John Wiley & Sons, Ltd.     

Recent progress and remaining challenges in post-combustion CO2 capture using metal-organic frameworks (MOFs)

The emissions of carbon dioxide (CO₂) and other greenhouse gases from rapidly growing industries and households are of great concern. These emissions cause problems like global warming and climate change. Although various technologies can be used to decline the alarming levels of greenhouse gases, CO₂ capturing is deemed more cost-effective. The metal-organic frameworks (MOFs) are proving to be effective adsorbent material for CO₂ capture due to their microporous structure. MOFs exhibit varying extents of chemical and thermal stabilities; hence, distinct MOFs can be selected for applications based on the working environment. In this article, thermal, chemical, mechanical, and hydrothermal stabilities of MOFs and adsorption mechanisms of CO₂ capture in MOFs were overviewed. Also, the approaches for enhancing the adsorption capacity and efficacy of MOFs were discussed. Moreover, the utilization of MOFs to improve the separation efficacy of mixed matrix membranes (MMMs) is also discussed. Furthermore, as the conversion of CO₂ to fuels and other useful products is a viable next step to CO₂ capture, therefore, recent progress in the utilization of MOFs as catalysts for CO₂ conversion was also briefly discussed. Present work attempts to link the chemistry of MOFs to process economics for post-combustion CO₂ capture.     

Efficiency enhancement of pressurized oxy‐coal power plant with heat integration

The oxy‐coal combustion with carbon dioxide capture and sequestration is among the promising clean coal technologies for reducing CO₂ emissions. Because most of oxy‐coal power plants need to cope with energy penalties from air separation and CO₂ compressor units, the pressurized combustion is added to reduce the electricity demand for the CCS system, and the waste heat of the pressurized flue gas is recovered by the heat integration technique to increase the power generation from steam turbines. Finally, the efficiency enhancement of a 100 MW_e‐scale power plant is successfully validated by Aspen Plus simulation. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of coal characteristics to performance of a highly efficient thermal power generation system based on pressurized oxy‐fuel combustion

Because of its fuel flexibility and high efficiency, pressurized oxy‐fuel combustion has recently emerged as a promising approach for efficient carbon capture and storage. One of the important options to design the pressurized oxy‐combustion is to determine method of coal (or other solid fuels) feeding: dry feeding or wet (coal slurry) feeding as well as grade of coals. The main aim of this research is to investigate effects of coal characteristics including wet or dry feeding on the performance of thermal power plant based on the pressurized oxy‐combustion with CO₂ capture versus atmospheric oxy‐combustion. A commercial process simulation tool (gCCS: the general carbon capture and storage) was used to simulate and analyze an advanced ultra‐supercritical(A‐USC) coal power plant under pressurized and atmospheric oxy‐fuel conditions. The design concept is based on using pure oxygen as an oxidant in a pressurized system to maximize the heat recovery through process integration and to reduce the efficiency penalty because of compression and purification units. The results indicate that the pressurized case efficiency at 30 bars was greater than the atmospheric oxy‐fuel combustion (base line case) by 6.02% when using lignite coal firing. Similarly, efficiency improvements in the case of subbituminous and bituminous coals were around 3% and 2.61%, respectively. The purity of CO₂ increased from 53.4% to 94% after compression and purification. In addition, the study observed the effects of coal‐water slurry using bituminous coal under atmospheric conditions, determining that the net plant efficiency decreased by 3.7% when the water content in the slurry increased from 11.12% to 54%. Copyright © 2016 John Wiley & Sons, Ltd.