Fuel cells for carbon capture and power generation: Simulation studies

The decarbonization of hydrocarbons is explored in this work as a method to produce hydrogen and mitigate carbon dioxide (CO₂) emissions. An integrated process for power generation and carbon capture based on a hydrocarbon fueled-decarbonization unit was proposed and simulated. Ethane and propane were used as fuels and subjected to the thermal decomposition (decarbonization) process. The system is also composed of a carbon fuel cell (CFC) and hydrogen fuel cell (HFC) for the production of power and a pure CO₂ stream that is ready for sequestration. The HFC is a high-temperature proton exchange membrane fuel cell operating at 200 °C. Simulations were performed using ASPEN HYSYS V.10 for the entire process including the CFC and HFC being operated at various operating temperatures (200–800 °C). The power output from the CFC and the HFC as well as the overall process efficiency were calculated. The model incorporates an energy recovery system by adopting a counter-current shell and tube heat exchangers and a turbine. The water produced from the fuel cell system can be utilized in the plant to recover the heat from the furnace. The results showed a 100% carbon capture with a nominal plant capacity of 108 MWe produced when propane fuel was fed to the decarbonizer. The CFC theoretical efficiency is 100% and the practical efficiency was taken as 70% when all internal polarizations were considered. The results showed that, in the case of propane, the CFC power output was 89 MWe when the CFC operated at 650 °C, and the HFC power output was around 45 MWe at 200 °C with an overall actual plant efficiency of 35% and 100% carbon capture. Sensitivity analysis recommends a hydrocarbon fuel cost of 0.011 $/kW as the most feasible option. The results reported here on the decarbonization of hydrocarbon fuels are promising toward the direct production of hydrogen with full carbon dioxide sequestration at a potentially lower cost especially in rural areas. The overall actual efficiencies are very competitive to those of conventional power plants operated without carbon capture.     

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.     

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.     

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.     

关于核燃料技术经济性的探讨

从宏观和微观角度对核燃料的技术经济性进行评价分析.核燃料热值高,比化石燃料产出净能高3～4倍.核燃料(核电)拥有巨大的温室气体减排潜力,燃烧时不排放二氧化硫、氮氧化物,不产生烟尘、煤渣,是节能减排效果非常好的清洁能源.据IPCC的研究,在各种发电技术中,石油的温室气体排放量为600～1200g二氧化碳当量/(kW.h),煤、褐煤为800—1800g二氧化碳当量/(kW.h),而核电的排放量平均值仅为10g二氧化碳当量/(kW.h).至2030年,可再生能源发电和核电可减排温室气体近60×108t二氧化碳当量,其中核电约占1/3.核燃料资源丰富,可循环利用、实现增殖,从而扩大了核燃料资源.现有天然铀热中子堆可用百年;快中子堆可提高铀资源利用率60倍以上,可用千年;聚变核燃料氘可供人类使用百亿年,且无放射性.可见,核能是化石能源最有前途的替代能源.同时,核燃料能量密度高,体积/小,所需运力少,价格稳定,供应可靠.核电的投资成本分别高出煤电、气电约50％和140％,而发电总成本煤电、气电仍比核电高出约30％,根本原因是核燃料费用低,只占发电总成本的23％.核电的燃料成本优势除弥补了自身投资成本高的缺点以外,还形成了发电总成本低的竞争优势.     

Potential of molten carbonate fuel cells to enhance the performance of CHP plants in sewage treatment facilities

In spite of its slow commercial deployment, fuel cells are amongst the most efficient and environmentally friendly electric power generators. The case of Molten Carbonate Fuel Cells is even more interesting since, in addition to these features that are common to all fuel cells, these systems can be used as active carbon capture devices due to their capability to migrate carbon dioxide from one electrode (cathode) to another (anode). In this context, this work presents the operation of a fuel cell of this type coupled to a combined heat and power plant based on gas reciprocating engines as typically used in wastewater treatment plants. The biogas produced in the water sludge digestion process is burnt in the reciprocating engines, whose exhaust gases are mixed with air and blown into the fuel cell cathode. The carbon dioxide contained in this stream is conveyed in the form of carbonate ions (CO₃⁼) through the electrolyte to the anode where it reacts with the hydrogen fuel, being released as carbon dioxide. The exhaust gases from the anode comprise carbon dioxide, water steam and a small fraction of unspent hydrogen fuel. The combustion of the latter species with pure oxygen followed by a cooling process permits separating a gaseous stream of pure carbon dioxide from a liquid stream of water.     

Design of a solar hydrogen refuelling station following the development of the first Croatian fuel cell powered bicycle to boost hydrogen urban mobility

Hydrogen refuelling stations are important for achieving sustainable hydrogen economy in low carbon transport and fuel cell electric vehicles. The solution presented in this paper provides us with a technology for producing carbon dioxide free hydrogen, which is an approach that goes beyond the existing large-scale hydrogen production technologies that use fossil fuel reforming. Hence, the main goal of this work was to design a hydrogen refuelling station to secure the autonomy of a hydrogen powered bicycle. The bicycle hydrogen system is equipped with a proton exchange membrane fuel cell stack of 300 W, a DC/DC converter, and a metal hydride storage tank of 350 NL of hydrogen. The hydrogen power system was made of readily available commercial components. The hydrogen station was designed as an off-grid system in which the installed proton exchange membrane electrolyzer is supplied with electric energy by direct conversion using photovoltaic cells. With the hydrogen flow rate of 2000 cc min⁻¹ the hydrogen station is expected to supply at least 5 bicycles to be used in 20 km long city tourist routes.     

The extraction,conversion and use of energy resources: future challenge to materials technology

Abstract

The growing shortage of all types of fossil fuels, and concerns about global warming are beginning to have a major impact on the power generation and transport sectors. Renewable energy, in conjunction with energy conservation measures such as cogeneration, and the use of biofuels and hydrogen in transport will help extend fossil fuel resources, but there is real need to find and exploit new coal, oil, and gas reserves. Materials technology must play its part in these new developments. Future fossil fuel generating plants will have to capture the carbon dioxide produced, and to compensate for the parasitic power losses this implies, this will require conventional plants to operate at very high temperatures. Likely targets for the strength of advanced austenitics are postulated, and the need to carry out R&D into type IV cracking, dissimilar metal weld issues, and steam side oxidation is emphasised.     

Natural gas usage as a heat source for integrated SMR and thermochemical hydrogen production technologies

This paper investigates various usages of natural gas (NG) as an energy source for different hydrogen production technologies. A comparison is made between the different methods of hydrogen production, based on the total amount of natural gas needed to produce a specific quantity of hydrogen, carbon dioxide emissions per mole of hydrogen produced, water requirements per mole of hydrogen produced, and a cost sensitivity analysis that takes into account the fuel cost, carbon dioxide capture cost and a carbon tax. The methods examined are the copper–chlorine (Cu–Cl) thermochemical cycle, steam methane reforming (SMR) and a modified sulfur–iodine (S–I) thermochemical cycle. Also, an integrated Cu–Cl/SMR plant is examined to show the unique advantages of modifying existing SMR plants with new hydrogen production technology. The analysis shows that the thermochemical Cu–Cl cycle out-performs the other conventional methods with respect to fuel requirements, carbon dioxide emissions and total cost of production.     

Alkaline falling-film fuel cell A breakthrough in technology and cost

The work described in this paper was oriented towards fuel cells for practical applications, but mainly presents data obtained using half-cells. The economic significance of these data is discussed, together with the technical concept of fuel cell power stations and for transportation applications. The proposed fuel cell with generate power at much lower costs than conventional power plants, and a zero-emission vehicle with fuel cells will operate at lower fuel cost than a car with an internal combustion engine. The simple falling-film process leads to high power densities (6 kW/l) and low cost. The details given are valid for the use of hydrogen produced from fossil energy sources. Concentrated CO₂, a byproduct of this technology can be stored in discussed oil and gas fields at a very low cost to avoid global warming. Thus, this ‘down-to-earth’ hydrogen technology is a free from CO₂ emissions as solar-hydrogen technology.     

Performance modelling of a carbon dioxide removal system for power plants

In this paper, a carbon dioxide removal and liquefaction system, which separates carbon dioxide from the flue gases of conventional power plants, was modelled. The system is based on an amine chemical absorption stripping system, followed by a liquefaction unit to treat the removed CO₂ for transportation and storage. The effect of the main parameters on the absorption and stripping columns is presented. The main constraints set for the model are a capture efficiency of 90% and the use of an aqueous solution with a maximum 30% amine content by weight. The goal of this study is to remove the CO₂ with minimum energy requirements for the process when it is integrated in a fossil fuel fired power plant. Results of the simulation are compared to experimental and literature data from feasibility studies and existing plants.

The power plant to which the removal system is connected is a 320 MW steam power plant with steam reheat and 8 feedwater heaters. Two different fossil fuels were considered: coal and natural gas. The effect of the modifications necessary to integrate the CO₂ removal system in the power plant is also studied.

The capital cost of the removal and liquefaction system is estimated, and its influence on the cost of generated electricity is calculated.     

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.     

Optimal sizing of photovoltaic systems based green hydrogen refueling stations case study Oman

Green hydrogen reduces carbon dioxide emission, advances the dependency on fossil fuels and improves the economy of the energy sector, especially in developing countries. Hydrogen is required for the green transportation sector and many other industrial applications. However, the high cost of green hydrogen production reduces the fast development of renewable energy projects based on hydrogen production. So, sizing by optimization is required to determine the optimum solutions for green hydrogen production. In this context, this paper aims to analyze three methods that can be developed and implemented for the production of green hydrogen for refueling stations using photovoltaic (PV) systems. Techno-economic models are adopted to calculate the Levelized Hydrogen Cost (LHC) for the PV grid-connected system, stand-alone PV system with batteries, and stand-alone PV system with fuel cells. The photovoltaic systems based green hydrogen refueling stations are optimized using Homer software. The optimization results of the Net Profit Cost (NPC), and the LHC permit the comparison of the three cases and the selection of the optimal solution. The analysis has shown that a 3 MWp grid-connected PV system represents a promising green hydrogen production at an LHC of 5.5 €/kg. The system produces 58 615 kg of green hydrogen per year reducing carbon dioxide emission by 8209 kg per year. The LHC in the stand-alone PV system with batteries, and stand-alone PV system with fuel cells are 5.74 €/kg and 7.38 €/kg, respectively.     

A fossil-fuel based recipe for clean energy

A zero-emission process of hydrogen production from fossil fuel through a system of reactions involving hydroxide, carbon, CO, CO₂ and water is described here. It provides for a complete sequestration of carbon (CO₂ and CO) from coal/natural-gas burning plants. The CO and or CO₂ produced in coal or natural gas burning power plants and the heat may be used for producing hydrogen. Economically hydrogen production cost is less than the current price of fossil-fuel produced hydrogen with the added benefit of carbon sequestration. The reduced cost of the hydrogen may aid in making a hydrogen fueled automobile economically viable.     

Use of lower grade coals in IGCC plants with carbon capture for the co-production of hydrogen and electricity

This paper investigates the potential use of lower grade coals in an IGCC-CCS plant that generates electricity and produces hydrogen simultaneously with carbon dioxide capture and storage. The paper underlines one of the main advantages of gasification technology, namely the possibility to process lower grade coals, which are more widely available than the high-grade coals normally used in European power plants. Based on a proposed plant concept that generates about 400 MW net electricity with a flexible output of 0–50 MW_th hydrogen and a carbon capture rate of at least 90%, the paper develops fuel selection criteria for coal fluxing and blending of various types of coal for optimizing plant performance e.g. oxygen consumption, hydrogen production potential, specific syngas energy production per tonne of oxygen consumed, etc. These performance indicators were calculated for a number of case studies through process flow simulations. The main conclusion is that blending of coal types of higher and lower grade is more beneficial in terms of operation and cost performance than fluxing high-grade coals.     

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.     

The effects of changes in the UK energy demand and environmental legislation on atmospheric pollution by carbon dioxide

It has been demonstrated that the combustion of fossil fuel accounts for 97% of the carbon dioxide generated in the UK. The demand for primary energy over the 1970–1994 period has only marginally increased, however the demand for natural gas which has a significantly lower carbon content per unit of energy than other fuels accounts largely for the lowering of carbon dioxide emissions. The enactment UK/EU Environmental Legislation coupled with World Agreements accounts for a significant lowering of carbon dioxide emissions over this period. Future predictions suggest that a further downturn in carbon dioxide emissions will take place over the 1990–2000 period, followed by a pronounced increase over the 2000–2020 period. The expansion of the use of CCGT and/or the introduction of the IGCC and the SUPC in the power generating sector provides an opportunity for a further reduction in carbon dioxide 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).     

The energy and environmental implications of UK more electric transition pathways: A whole systems perspective

Electricity generation contributes a large proportion of the total greenhouse gas emissions in the United Kingdom (UK), due to the predominant use of fossil fuel (coal and natural gas) inputs. Indeed, the various power sector technologies [fossil fuel plants with and without carbon capture and storage (CCS), nuclear power stations, and renewable energy technologies (available on a large and small {or domestic} scale)] all involve differing environmental impacts and other risks. Three transition pathways for a more electric future out to 2050 have therefore been evaluated in terms of their life-cycle energy and environmental performance within a broader sustainability framework. An integrated approach is used here to assess the impact of such pathways, employing both energy analysis and environmental life-cycle assessment (LCA), applied on a ‘whole systems’ basis: from ‘cradle-to-gate’. The present study highlights the significance of ‘upstream emissions’, in contrast to power plant operational or ‘stack’ emissions, and their (technological and policy) implications. Upstream environmental burdens arise from the need to expend energy resources in order to deliver, for example, fuel to a power station. They include the energy requirements for extraction, processing/refining, transport, and fabrication, as well as methane leakage that occurs in coal mining activities – a major cotribution – and from natural gas pipelines. The impact of upstream emissions on the carbon performance of various low carbon electricity generators [such as large-scale combined heat and power (CHP) plant and CCS] and the pathways distinguish the present findings from those of other UK analysts. It suggests that CCS is likely to deliver only a 70% reduction in carbon emissions on a whole system basis, in contrast to the normal presumption of a 90% reduction. Similar results applied to other power generators.     

Effective use of hydrogen sulfide and natural gas resources available in the Black Sea for hydrogen economy

In this article, we propose a novel system to effectively deploy an integrated fuel processing system for hydrogen sulfide and natural gas resources available in the Black Sea to be used for a quick transition to the hydrogen economy. In this regard, the proposed system utilizes offshore wind and offshore photovoltaic power plants to meet the electricity demand of the electrolyzer. A PEM electrolyzer unit generates hydrogen from hydrogen sulfide that is available in the Black Sea deep water. The generated hydrogen and sulfur gas from hydrogen sulfide are stored in high-pressure tanks for later use. Hydrogen is blended with natural gas, and the blend is utilized for industrial and residential applications. The investigated system is modeled with the Aspen Plus software, and hydrogen production, blending, and combustion processes are analyzed accordingly. With the hydrogen addition up to 20% in the blend, the carbon dioxide emissions of combustion decrease from 14.7 kmol/h to 11.7 kmol/h, when the annual cost of natural gas is reduced from 9 billion $ to 8.3 billion $. The energy and exergy efficiencies for the combustion process are increased from 84% to 97% and from 62% to 72%, respectively by a 20% by volume hydrogen addition into natural gas.