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Solar Upgrading of Fuels for Generation of Electricity
Abstract
This paper presents a novel process comprising solar upgrading of hydrocarbons by steam reforming in solar specific receiver-reactors and utilizing the upgraded, hydrogen- rich fuel in high efficiency conversion systems, such as gas turbines or fuel cells. In comparison to conventionally heated processes about 30% fuel can be saved with respect to the same specific output. Such processes can be used in small scale as a stand-alone system for off-grid markets as well as in large scale to be operated in connection with conventional combined-cycle plants. The complete reforming process will be demonstrated in the SOLASYS project, supported by the European Commission in the JOULE/THERMIE framework. The project has been started in June 1998. The SOLASYS plant is designed for 300 kW(el) output, it consists of the solar field, the solar reformer and a gas turbine, adjusted to operate with the reformed gas. The SOLASYS plant will be operated at the experimental solar test facility of the Weizmann Institute of Science in Israel. Start-up of the pilot plant is scheduled in April 2001. The midterm goal is to replace fossil fuels by renewable or non-conventional feedstock in order to increase the share of renewable energy and to establish processes with only minor or no CO2 emission. Examples might be upgrading of bio-gas from municipal solid waste as well as upgrading of weak gas resources.
... The catalyst-coated absorber, a porous medium ( Figure 2-34 (c)) or tubes ( Figure 2-34 (d)), exposed to a solar radiative flux, absorbs the thermal energy and a feed gas composition flows through the absorber to receive the heat required for the chemical reaction [273]. Both directlyirradiated designs (including receiver with a catalytic porous absorber and receiver with particle additives) and indirectly-irradiated tubular receivers can be used as a receiver reactor. ...
... When the feed was CO2/CH4 mixture, the endothermic chemical reaction took place within the catalysed absorber, hence a significant reduction in the temperature [276,277]. Within 1987 to 1991, a project named "Catalytically (SOLASYS)" project [273,281] employed a high-temperature receiver reactor, similar to the high-temperature volumetric SOLGATE receiver (REFOS) [66], to operate within 900 to 1000˚C for the CO2 reforming. The feed was a mixture of CH4/CO2/H2O/H2 with an inlet temperature at around 480˚C and a pressure of 10 bar. ...
... The feed was a mixture of CH4/CO2/H2O/H2 with an inlet temperature at around 480˚C and a pressure of 10 bar. Results showed a product gas outlet temperature of around 800˚C with methane conversion of 83.7% and overall receiver efficiency of 93.5% [273]. The performance of a receiver reactor cluster, like the SOLGATE receiver cluster [66], was assessed in a subsequent project (which was commenced in 2014) called "Solar Steam Reforming (SOLREF)" [281,282]. ...
... The receiver reactor model is primarily a pressurised gas-phase receiver acting as a reactor. The catalyst-coated absorber, a porous medium (Fig. 34(c)) or tubes (Fig. 34(d)), exposed to a solar radiative flux, absorbs the thermal energy and a feed gas composition flows through the absorber to receive the heat required for the chemical reaction [266]. Both directly-irradiated designs (including receiver with a catalytic porous absorber and receiver with particle additives) and indirectly-irradiated tubular receivers can be used as a receiver reactor. ...
... Within 1987-1991, a project named "Catalytically Enhanced Solar Absorption Receiver (CAESAR)", designed ceramic foam absorbers coated by a rhodium catalyst used in a volumetric receiver reactor for the CO 2 reforming of methane ( Fig. 35(d)) [271][272][273]. In 1998, the "Novel Solar Assisted Fuel Driven Power System (SOLASYS)" project [266,274] employed a high-temperature receiver reactor, similar to the high-temperature volumetric SOLGATE receiver (REFOS) [57], to operate within 900-1000°C for the CO 2 reforming. The feed was a mixture of CH 4 /CO 2 /H 2 O/H 2 with an inlet temperature at around 480°C and a pressure of 10 bar. ...
... The feed was a mixture of CH 4 /CO 2 /H 2 O/H 2 with an inlet temperature at around 480°C and a pressure of 10 bar. Results showed a product gas outlet temperature of around 800°C with methane conversion of 83.7% and overall receiver efficiency of 93.5% [266]. The performance of a receiver reactor cluster, like the SOL-GATE receiver cluster [57], was assessed in a subsequent project (which was commenced in 2014) called "Solar Steam Reforming (SOLREF)" [274,275]. ...
Gas-phase solar receivers use atmospheric or pressurised gas as their heat transfer fluid (HTF). The ideal gas-phase receiver would provide high thermal efficiency and high HTF outlet temperature with low pressure drop and low capital cost. In practice, these four objectives are hard to achieve simultaneously since it is difficult to (cost-effectively) overcome the intrinsically poor heat transfer performance between the solid absorber and the gaseous HTF. Thus, this review provides an in-depth look at the recent progress towards solving this challenge of pressurised gas-phase receivers to identify the remaining knowledge/research gaps. In general, gas-phase receivers can be classified as direct or indirect solar absorbers and by the type of heat transfer enhancement (HTE) employed to address the poor absorber-to-HTF heat transfer rate. The present review suggests the receiver designs that show the most promise for further improvement from each of the active, passive and compound HTE methods. This study also finds that there is a need for more proof-of-concept tests for these receiver designs, since the number of studies which include real prototypes operating under real weather conditions is limited. Based on a review of successful prototyping research, this review suggests proper prototyping procedures for high-temperature receivers. Overall, the authors believe the present study presents an up-to-date, comprehensive review of the progress on gas-phase receivers, along with some meaningful, specific guidance on the necessary next steps in their development. This is significant because gas-phase receivers represent the best near-term solution for pushing solar systems to higher temperatures, enabling integration with advanced/combined cycles and solar thermochemical reactors with endothermic chemical reactions at high temperature (e.g. mineral processes and solar fuels).
... The most common reforming processes used in solar systems are steam or CO 2 (dry) reforming. The key reactions for the two processes (steam and dry reforming, respectively) are shown below for the case of methane [16]: ...
... Most often, the water-gas shift reaction occurs in conjunction with the reforming reactions. The water-gas shift reaction is shown below [16]: ...
... Further work on a solar dry reformer system similar to the CAESAR project was done in the SOLASYS project [16]. A schematic of the solar reformer is shown in Fig. 13. ...
Because of the increasing demand for energy and the associated rise in greenhouse gas emissions, there is much interest in the use of renewable sources such as solar energy in electricity and fuels generation. One problem with solar energy, however, is that it is difficult to economically convert the radiation into usable energy at the desired locations and times, both daily and seasonally. One method to overcome this space-time intermittency is through the production of chemical fuels. In particular, solar reforming is a promising method for producing chemical fuels by reforming and/or water/carbon dioxide splitting. In this paper, a review of solar reforming systems is presented, as well as a comparison between these systems and a discussion on areas for potential innovation including chemical looping and membrane reactors. Moreover, a brief overview of catalysis in the context of reforming is presented.
... [116] Die Reformierung mit direkt bestrahlten Receivern/Reaktoren aus poröser Keramik realisierten erstmals das DLR und SANDIA in den USA. [117][118][119] ...
Wasserstoff hat das Potenzial, der zentrale Baustein für eine Energiewirtschaft mit massiv reduzierten Treibhausgasemissionen zu sein. Er bietet Antworten auf bisher ungelöste Fragen der Energiewende, insbesondere in den Bereichen Transport und Langzeitspeicherung. Wasserstoff ermöglicht es außerdem industrielle Prozesse emissionsfrei zu gestalten, bei denen dies auf andere Art kaum realisierbar wäre. Aufgrund seiner vielfältigen Einsatzmöglichkeiten über die Sektorengrenzen hinaus lassen sich zudem Synergiepotenziale nutzen, die die Wasserstoffwirtschaft mit voranschreitendem Ausbau der erforderlichen Infrastruktur zunehmend auch ökonomisch attraktiv machen. Hilfreich wird in diesem Zusammenhang eine langfristige Investitionssicherheit für Importinfrastruktur und lokale Verteilinfrastrukturen sein. Es gibt eine Vielzahl von Verfahren zur Herstellung von Wasserstoff. Diese unterscheiden sich sowohl in den eingesetzten Prozessen und Komponenten zur Stoffumwandlung als auch in den verwendeten Energie- und Materialquellen. Dadurch ergeben sich unterschiedliche Produktionskosten und mit der Produktion verbundene stark variierende Treibhausgasemissionen. Da angesichts der Erreichung von Klimaschutzzielen die graue Produktion von Wasserstoff nicht zielführend ist, sind die blauen und vor allem die grünen Verfahren zu betrachten und vergleichend zu bewerten. Der weitere Einsatz von blauen Methoden wird entscheidend davon abhängen, wie schnell und effizient CCS-Optionen großskalig zur Verfügung stehen werden und inwiefern eine dauerhafte Speicherung im Untergrund garantiert werden kann. Dies vorausgesetzt, bieten auch blaue Technologien in einem Übergangszeitraum Potenzial für eine kostengünstige, großskalige Produktion von emissionsreduziertem bzw. -freiem Wasserstoff. Langfristig wird sich allerdings die grüne Herstellung von Wasserstoff durchsetzen müssen, um Wasserstoff als universalen Energieträger eines CO2-neutralen Energiesystems zu etablieren. Dass dies großskalig technisch möglich und ökonomisch attraktiv sein kann, zeigt die Analyse der verfügbaren und sich in der Entwicklung befindlichen Technologien. Eine essentielle Voraussetzung für den Erfolg der grünen Herstellungsmethoden wird die ausreichende und kostengünstige Verfügbarkeit von erneuerbaren Energiequellen sein. Hier sind vor allem Sonne und Wind, aber auch Biomasse, Wasserkraft und Geothermie zu nennen. Als einer der Hauptstränge für die Wasserstoffproduktion in Deutschland, teils auch in Europa, wird häufig die Nutzung von Überschussstrom aus intermittierenden erneuerbaren Energiequellen in Elektrolyseanlagen genannt. Hierbei ist jedoch zu beachten, dass die Wasserstoffgestehungskosten stark vom jährlichen Ausnutzungsgrad der Umwandlungsanlagen abhängen und daher ein Anlagenbetrieb mit höheren Volllaststunden vorteilhaft ist. Auch ist zukünftig mit der Nutzung von Überschussleistungen durch andere flexible Verbraucher (zum Beispiel Power-to-Heat) zu rechnen. Für eine großskalige grüne Wasserstoffproduktion ist daher ein massiver zusätzlicher Ausbau von Anlagen zur Erzeugung von erneuerbarem Strom erforderlich. Nichtsdestotrotz können flexibel ausgelegte Wasserstoff-Produktionsanlagen prinzipiell auch anteilig erneuerbaren Überschussstrom nutzen und so sowohl zur besseren Integration fluktuierender Erzeugungsleistungen als auch zur Stabilisierung der Stromnetze beitragen. Das Potenzial der erneuerbaren Energien ist in Deutschland aufgrund der Ressourcen sowie angesichts des beanspruchbaren Platzangebots beschränkt. Ebenso ist bei einem massiven weiteren Ausbau von insbesondere Windkraftanlagen mit zunehmenden Akzeptanzrisiken zu rechnen, was die derzeitige Krise der Windkraft eindrücklich zeigt. Vor diesem Hintergrund erscheint vor allem die großskalige, zentrale Produktion von Wasserstoff in Ländern mit großem Angebot an erneuerbaren Energiequellen sowie an geeigneten und verfügbaren Flächen attraktiv. Als wichtiger Aspekt für die zukünftige Versorgungssicherheit müssen in diesem Zusammenhang unter anderem geopolitische Aspekte beachtet werden. Für eine importbasierte Wasserstoffwirtschaft scheinen technologische Lösungen für die Speicherung und den Transport in Größe und Kosten kein Hindernis zu sein. Daher stellt diese Option eine zumindest aus techno-ökonomischer Sicht attraktive und zentrale Komponente dar.
... 12. Volumetric (windowed, fixed media) receivers are a highly efficient method of solar capture. Radiation is transmitted through a quartz glass window to allow direct heating of the reaction (Tamme et al., 2001). 13. ...
Australia has a wealth of both renewable and fossil energy resources. It also has strong and economically significant energy export relationships with other countries, exporting coal and liquefied natural gas. As the world transitions to lower carbon sources for its primary energy consumption, Australia is ideally placed to provide the next generation of traded energy commodities – which will be produced from renewable energy, in part or in full.
The Concentrating Solar Fuels (CSF) Roadmap study was established by the Australian Solar Institute, the predecessor of the Australian Renewable Energy Agency (ARENA), to identify what Australia needs to do to become a world leader in this area. The key milestone outcomes of the project were reports that detailed the:
– Australian context for solar fuels and state of the art for solar technologies
– evaluation and ranking of solar fuel technologies in consultation with industry
– techno-economic analysis and commercial assessment
– roadmap and strategic recommendations for solar hybrid fuel technology options and
opportunities suitable for Australia, including the research required to expand Australia’s
capability base at that time.
... By using the results, we predict that at DNI 800 W/m 2 and reaction temperature of 400°C, the solar conversion efficiency is about 31.9% when the process is integrated with the combined cycle. This is much higher than the SSMR-CC (solar steamreforming methane, 800°C) about 28.4% [51]. It may be due to that the required low temperature can provide a possibility for lowering down the solar radiation loss, thereby bringing higher solar utilization efficiency. ...
... [27]. Within the successor project SOLASYS between the Weizmann Institute of Science (WIS) in Israel and DLR, receivers were developed for a power input of up to 300 kW th [28,29]. Eventually, within the project SOLREF, an advanced and more compact and cost-effective volumetric receiver/reformer was designed to operate at higher power, pressure, and temperature levels (400 kW th , 950°C, 15 bar, respectively) resulting in higher efficiency. ...
This chapter reviews the conversion of solar energy to various fuels through the use of thermochemical processes. The chapter begins with an overview of solar thermal technologies capable of providing the necessary energy at appropriate temperatures, before summarizing the sometimes bewildering range of process options. As many hundreds of potential cycles have been proposed over the years, the chapter will necessarily focus on groups of reaction schemes with common characteristics. It will also endeavor to provide the reader with an up-to-date summary of research and demonstration activities around the world, along with a summary of some of the priorities for further work.
... By using the results, we predict that at DNI 800 W/m 2 and reaction temperature of 400°C, the solar conversion efficiency is about 31.9% when the process is integrated with the combined cycle. This is much higher than the SSMR-CC (solar steamreforming methane, 800°C) about 28.4% [51]. It may be due to that the required low temperature can provide a possibility for lowering down the solar radiation loss, thereby bringing higher solar utilization efficiency. ...
... Schematic of solar syngas fired power plant (adapted from[163]). (Acronyms: C -compressor, GT -gas turbine). ...
This paper reviews the hybrid power generation technologies of concentrated solar power (CSP) and other renewable and non-renewable resources such as biomass, wind, geothermal, coal, and natural gas. The technologies have been categorized into high, medium, and low-renewable hybrids based on their renewable energy component. The high-renewable hybrids report the least specific CO2 emissions (< 100 kg/MWh), followed by the medium (< 200 kg/MWh) and low-renewable hybrids (> 200 kg/MWh). The hybrids have been compared based on their plant characteristics and performance metrics using data from the literature and of actual hybrid power plants. The low-renewable hybrids such as ISCC, solar-Brayton, and solar-aided coal Rankine power systems are technologically mature and offer superior performance over the high and medium-renewable hybrids. The medium renewable hybrids such as solar plants with natural gas backup offer high solar share but suffer mostly from low efficiency and high cost that hinders their market penetration. The high-renewable hybrids such as CSP-wind, CSP-biomass, and CSP-geothermal have minimum negative impact on the environment. However, several parameters such as energy efficiency, solar-to-electricity efficiency, capacity factor, and cost effectiveness need to improve for these systems to be competitive.
... Elysia and Mitsos [25] performed an analysis of a 14 combined cycle integrated with solar reforming, and the results indicated that the maximum solar 15 share could reach 20.5% with a thermal efficiency of 47.6%. Tamme et al. [26] used a solar specific 16 receiver-reactor to upgrade fuel in gas turbine systems. The shortcoming of SRGT system is that the 17 solar share is limited to 25%-30% depending on the process conditions. ...
There is insufficient literature about solarized gas turbines that achieved high efficiency and solar share simultaneously. It is because the outlet temperature of a solar receiver is always much lower than a combustor and it is difficult to design a high-efficiency exhaust-heat recovery system except for a complicated Rankine cycle. A solar-assisted chemically recuperated gas turbine system is proposed and expected to achieve a good performance by combining with two-stage fuel-steam reforming. The first stage is a low-temperature reformer, recovering exhaust gas heat, and the second stage is a high-temperature one, absorbing concentrated solar radiation. Thermodynamic analyses and comparisons are conducted. This system is expected to have a competitive thermal efficiency of 47.7%, which is 10.6 percentage points higher than that of a solarized gas turbine system without reformers. Meanwhile, it has a solar share of 75.0%, which is 12.8 percentage points higher than that of a solarized gas turbine system with a low-temperature reformer. In the viewpoint of energy level, the two-stage fuel reforming upgrades low-level thermal energy of the turbine exhaust and solar receiver into high-level chemical energy, reducing exergy destruction. The relative upgrade of energy level is 38.2% for turbine exhaust and 17.4% for solar thermal energy.
... Thermo-chemical energy storage systems have also been researched and developed for use with solar thermal systems. These range from systems that produce usable fuels such as hydrogen and syngas by feedstock dissociation, using concentrated solar radiation [65][66][67][68][69][70][71][72] to multilevel sorption based "thermal battery" cascaded storage systems [73][74][75][76][77][78][79][80][81]. Thermochemical energy storage systems are therefore promising either for producing "green substitute fuels" or for serving as thermal battery systems, being especially useful when scavenging waste heat from industrial processes. ...
... Now a days there is an increasing demand for use of solar energy for the production of chemical fuels. Solar methane reforming has been demonstrated on a pilot scale in various research laboratories (Tamme et al. 2001;Sugarmen et al. 2004;Steinfeld, Zurich, and Palumbo 2001;Spiewak, Tyner, and Langnickel 1993). On the broad basis, solar reactors are classified into two types: directly and indirectly heated reactors. ...
Hydrogen does not occur in the elemental form in nature. Currently about 95% of hydrogen is produced from hydrocarbons-the most economic route to make hydrogen. The remaining supply of hydrogen (~5%) is met by electrolysis of water-the most abundant source of hydrogen. In view of the accelerated depletion of the fossil fuels and the CO2-induced global warming, the humanity has to find a new and renewable source of hydrogen. A thermochemical route of hydrogen (H2) production employs heat or a combination of heat and O2/water to extract hydrogen bound to a fuel or water.
... Despite the challenges, this concept has been proved feasible. In the projects SOLASYS and SOLREF, a consortium of DLR and WIS, as well as other partners, constructed and tested receiver-reactors with catalytically active foam successfully [38,39]. WIS successfully constructed and operated a receiver-reactor with their previously developed porcupine receiver [40]. of receiver-reactors are 15 bar [9]. ...
Methanol production via solar reforming of methane
... [126][127][128]. The reactor uses an Al 2 O 3 or SiC reticulate porous ceramic structure, supporting the γ-Al 2 O 3 washcoat and rhodium catalyst and acting as both the radiation absorber and reaction site. ...
Concentrated solar energy has numerous potential applications besides electricity production as a source of high-temperature process heat. This chapter aims at providing an overview of applications other than electricity generation, with focus on H2/CO production, material processing and chemical commodity production, and other thermal processes. Material, process, and reactor developments are discussed alongside advances in thermodynamics, kinetics, and thermal transport.
... Despite the challenges, this concept has been proved feasible. In the projects SOLASYS and SOLREF, a consortium of DLR and WIS, as well as other partners, constructed and tested receiver-reactors with catalytically active foam successfully [38,39]. WIS successfully constructed and operated a receiver-reactor with their previously developed porcupine receiver [40]. of receiver-reactors are 15 bar [9]. ...
Open Access Link: https://index.ub.rwth-aachen.de/TouchPointClient_touchpoint/singleHit.do?methodToCall=showHit&curPos=1&identifier=2_SOLR_SERVER_128302904
Abstract:
In the present work, a solar reforming process for production of methanol was investigated.
Withthis process, it is possible to reduce the greenhouse-gas emissions associated with the
production of methanol significantly in the near-term future. This would be a significant
step in the development of a more sustainable chemical industry. Furthermore, methanol
can be applied as a fuel. Thus, methanol can contribute to a more climate friendly energy
supply, if it is produced via solar reforming. First of all, the overall reforming process was de
veloped based on the concept of indirectly heated solar reforming. One central aspect of this was
to make use of the waste-heat streams. As a consequence a large fraction of the off heat is converted into electricity in a water steam cycle, because no other demand exists for this heat. Furthermore, the off-gas
stream of the methanol synthesis is partly used for additional electricity production.
The developed process uses solar energy and natural gas to produce methanol and
electricity. The ratio between the different streams can be changed by parameter variation.
An optimization of the process with conventional criteria such as energy- or exergy - balances
is therefore not possible. Thus, a new evaluation criterion was developed. This criterion is based on the target to reduce fossil fuels reduction and the associated greenhouse-gas emissions.
Based on this evaluation criterion, the process was optimized by parameter variation. The
results show that the process has the potential to make more efficient use of solar energy
than is the case for sole production of electricity. A subsequent economic investigation
showed that the developed process can in theory be competitive with conventional solar
energy utilization. However, in practice support mechanism, as they exist for solar electricity
production, would have to be implemented for solar production of chemical feedstocks.
... Solar thermochemical process is based on the use of concentrated solar energy for driving an endothermic chemical transformation. More recently, considerable attention has been attracted toward solar thermochemical processes [1,2] . So far, most of solar thermochemical processes focus on the utilization of solar heat at above 800°C under a fixed solar radiation, solar heat at 150-300°C has not been paid more attention. ...
In our previous research, we ever proposed a solar-driven methanol decomposition system by using solar heat at temperature around 300°C for producing solar fuel to generate power. The system performance at solar radiation from 100∼400W/m2 was poor, the daily average solar to electricity efficiency was only 14∼16% due to varied solar radiation. Here, in contrast to the ‘individual’ methanol decomposition system, we proposed a ‘synergetic’ system which use the methanol steam reforming and methanol decomposition together to match the varied solar radiation. Exergy destruction of solar fuel combustion is disclosed. In addition, the inherent reason of reducing the exergy destruction was also disclosed by using the concept of the energy level. As a result, the daily average exergy destruction in the ‘synergetic’ system is 9% lower than the ‘individual’ system, the daily average solar to electricity efficiency reaches 19%, which is 3∼5 percentage points higher, leading to the increase of average work output and providing the possibility of reducing the size of solar field. The results here would provide an approach to improve the poor performance of solar thermochemical power system at varied solar radiation conditions.
... Solar energy is a promising clean energy source that is of great economic and technological importance. Typically, one of three conversion pathways are followed in converting solar energy to usable energy: (a) direct electrical power through photovoltaics, (b) solarthermal electric power generation, or (c) chemical processing and production of hydrogen or other fuels [3,4,5,6]. The present work is motivated from the perspective of trying to address important technological challenges that could enable efficient solar thermo-chemical processing of clean fuels using biomass products (CO 2 , CH 4 ). ...
This study investigates use of solar thermochemical processing of clean fuels using biomass products (in particular CH 4 , H 2 O). To address technological feasibility of a microchannel-based solar receiver/reactor, a combined numerical and experimental study of methane-steam reforming is carried out on a single microchannel with Palladium-deposited channel walls and heat input to facilitate endothermic heterogeneous reactions producing syngas. A simple one-dimensional model solving steady state species mass fraction, energy, and overall conservation of mass equations is developed, calibrated and validated against concurrent experimental data [1, 2]. Methane-steam reforming is modeled by three reduced-order reactions occurring on the reactor walls. The effects of the total heat input, heat flux profile, and inlet flow rate on production of hydrogen are investigated to assess the effectiveness of the microchannel configuration for production of hydrogen. A coupled shape-constrained optimization and Monte-Carlo radiative heat transfer model is developed to design a receiver shape that can yield a desired heat flux distribution on the channel walls for improved yield of hydrogen.
... For natural-gas fired power plants, the methane-steam reforming generally requires above 800 o C with Ni-based catalyst to obtain high methane conversion. Tamme presented a high temperature (>1000 o C) solar hybrid system comprising solar upgrading of methane by steam reforming in solar specific receiver-reactors and utilizing the upgraded H 2 -rich fuel in advanced gas-steam combined cycles [4]. In comparison to a conventional CC system, about 30% of fuel can be saved. ...
Based on the principle of cascade utilization of multiple energy resources, a novel concept for gas-steam combined cycle integrated with solar thermo-chemical conversion and CO 2 capture, named low CO 2 emission hybrid Solar CC power plant (LEHSOLCC), has been proposed and analysed. The hybrid power system uses methane as its input fuel. The collected solar heat at 550 o C is applied to provide heat for the endothermic methane reformation. The reforming reaction is integrated with a hydrogen separation membrane, which continuously withdraws hydrogen from the reaction zone and enables the chemical equilibrium to shift towards the product side. The pure H 2 , collected in permeate side, fuel a topping Brayton cycle, and the exhaust drives a triple-pressure reheat Rankine bottoming cycle to produce additional power. The produced syngas in retentate zone is enriched with CO 2 (81.8%v) and thus can be suitable to be processed with precombustion decarbonization. In the proposed power system, the low level solar heat is first converted to syngas chemical exergy via reforming, and then released as high-temperature thermal energy in an advanced combined cycle system for power generation, thus achieving its high-efficiency heat-power conversion. To reduce the exergy destruction, special attention is paid to the thermal match of the internal heat recuperation, as well as to the thermo-chemical match between the solar heat and the reforming process. The system is thermodynamically simulated using the ASPEN PLUS code. The results show that with 91% CO 2 captured, the specific CO 2 emission is 25 g/kWh. Exergy efficiency of 58% and thermal efficiency of 51.6% can be obtained. CO 2 capture brings about 8.4%-points thermal efficiency penalty compared with a gas-steam combined cycle system at the same technical level without CO 2 capture, but exergy efficiency remains the same level as the reference system. Fossil fuel saving ratio of 31.2% is achievable with a solar thermal share of 28.2%, and the net solar-to-electric efficiency, based on the gross solar heat incident on the collector, is about 36.4% compared with the same gas-steam combined cycle system with equivalent CO 2 removal rate by way of post-combustion decarbonization.
... As a matter of fact the first examples of such "structured" solar chemistry reactors can be traced back in 1990 when such reactors based on ceramic foams were the first structured reactors to be tested in solar chemistry applications for the solar-aided CO 2 methane reforming [12]. Thereafter reactors based on either foams [13][14][15][16] or honeycombs [17,18] have been regularly employed to perform solar-aided reactions. ...
Based on the characteristics of the oxide redox pair system
Co3O4/CoO as a thermochemical heat storage medium and the advantages of porous ceramic structures like honeycombs and foams in heat exchange applications, the idea of employing such ceramic structures coated with or manufactured entirely from a redox material like Co3O4, has been implemented. Thermo-Gravimetric Analysis (TGA) experiments have demonstrated that laboratory-scale Co3O4-coated, redox-inert ceramic foams and honeycombs exhibited repeatable, cyclic reduction-oxidation operation within the temperature range 800-1000oC, employing all the redox material incorporated, even at loading levels exceeding 100 wt% loading percentages. To further improve the volumetric heat storage capacity, monolithic porous ceramic foams made entirely of Co3O4 were
manufactured, together with analogous pellets. Such porous
structures were also capable of cyclic reduction–oxidation,
exploiting the entire amount of Co3O4 used in their
manufacture. In this perspective, “open” porous structures like the ones of ceramic foams seem to have significant Advantages in addressing problems associated with cyclic expansioncontraction that could be detrimental to structural integrity.
The high-temperature heat produced through concentrated solar irradiation facilities can be exploited to cover partially or totally the enthalpy needs of endothermal reactions of significant industrial importance and scale like methane reforming. This so-called solar thermal methane reforming can serve as a “bridge technology” based initially on fossil fuels with a lower environmental impact, in the transition toward a fully renewable energy/fuels-based economy. This work presents the current development of solar thermal-aided methane reforming, including concepts and endeavors that have recently emerged such as new, allothermally heated reformers and hybrid redox looping schemes. The focus is on the concentrated solar energy-relevant aspects of the specific technology, i.e., on reactor and heat exchanger concepts employed to couple it effectively to the thermochemistry requirements of the various methane reforming process schemes. Areas where future work on this topic should be focused on in conjunction with current and future societal/environmental requirements are proposed and barriers that can possibly hinder such commercialization efforts are identified.
Thermochemical energy storage (TCES) is considered the third fundamental method of heat storage, along with sensible and latent heat storage. TCES concepts use reversible reactions to store energy in chemical bonds. During discharge, heat is recovered through the reversal reaction. In the endothermic charging process, a material dissociates into components that can be stored at ambient temperature, which is a unique property of TCES. This chapter introduces the technical variants of TCES and presents the state of the art of this storage technology.
In this paper, a novel solar thermochemical volumetric receiver/reactor with nanofluid is proposed. Thermal and chemical performance analyses of the volumetric receiver/reactor are numerically investigated and compared with those of the conventional surface receiver/reactor. A two-dimensional axisymmetric heat and mass transfer model coupled with reaction kinetics is developed to predict the temperature distribution and reactant conversion ratio. The effects of particle characteristics including size and volume fraction and solar irradiation intensity are discussed. The results indicate that for the nanofluid with a volume fraction greater than 0.005, an optical path depth of 0.015 m is sufficient to absorb almost 100% of the incident solar energy. The volume weighted average temperature of the volumetric receiver/reactor with a volume fraction of 0.05 and particle diameter of 10 nm can reach 506.0 K which is about 8.8 K higher than that of the surface receiver/reactor leading to a 5.2% increase of the outlet methanol conversion ratio from 56.9% to 62.1% under a typical operating condition. The methanol conversion ratio increases with the reduction of nanoparticle size and the increment of the volume fraction and solar irradiation intensity. The thermochemical efficiency has a maximum value of 48.9% when solar irradiation intensity is 600 W/m².
Intermittent nature of solar energy and solution strategies for steam methane reforming reaction powered by concentrated solar energy over Ni/mullite and Pd/CeO 2 /mullite catalysts were demonstrated. The solar concentration was achieved using a parabolic mirror with a 70 cm, delivering concentrated solar flux onto a focal area that is approximately 3 cm in diameter. The solar field tests conducted on monolithic catalyst support structures were compared with the laboratory scale measurements on powdered catalysts. Despite the fluctuations in solar irradiation, CH 4 conversions higher than 90% could be obtained. Coke deposition was observed over the 15%Ni/Mullite monolith. On the 1%Pd/20%CeO 2 /Mullite monolith, the oxidative nature of the catalyst resulted in oxidation reactions with local temperatures exceeding 1700 °C, inferred through the melting point of mullite. Numerical simulations revealed temperature gradients as large as 500 °C, over the refractory monoliths.
In this study, thermal performance and optical properties of MAX phase materials subjected to high concentrated flux are characterized. A new indoor facility is developed that allows for investigation of the independent effect of irradiance and temperature on the thermal performance of the material. Two MAX namely, Titanium Aluminum Carbide (Ti2AlC) and Chromium Aluminum Carbide (Cr2AlC) are examined in this study. Both materials are exposed to high concentrated homogenized flux in the range of 527.2 kWm⁻² – 917 kWm⁻² for 1000 s and 3000 s using a high flux solar simulator while their temperatures are maintained at 60 °C ± 5 °C via water-cooled heat flux gage. Materials’ surface characterization before and after irradiation is carried out using X-ray diffraction, scanning electron microscopy and X-ray fluorescence analysis. It is found that both materials have excellent resistance to high concentrated flux, but that Ti2AlC shows higher light scattering due to the oxidation of its surface. It is also found that the variations in the optical properties over time do not depend on the selected incident flux level. The thermal performance of Ti2AlC and Cr2AlC was found to varies in the 0.56 – 0.68 and 0.60 – 0.67 range, respectively, for selected flux levels. Flux transmission performance of both materials is not affected by exposure to high concentrated flux.
At present, practically all industrial production of hydrogen either directly or indirectly (e.g., through electricity generation) relies on fossil fuels (mostly, natural gas and coal) and, according to many projections, this trend will continue in the foreseeable future. As a result, hydrogen plants are and will remain a major source of CO2 emissions to the atmosphere, with potentially adverse consequences to our planet's ecosphere and climate. In view of these negative trends, there is an urgent need to substantially reduce or even completely eliminate CO2 emissions from fossil fuel-based hydrogen production processes in order to underscore environmental advantages of hydrogen as an ecologically clean fuel. The main technological approaches to low to near-zero CO2 production of hydrogen from fossil fuels can be classified into three main groups: (1) coupling hydrogen plants with CO2 capture and storage systems, (2) dissociation of hydrocarbons to hydrogen and carbon, and (3) integrating hydrogen production processes with non-carbon energy sources such as nuclear and solar energy. The objective of this paper is to overview and analyze the current status of existing and emerging technological options and solutions to drastically reducing the amount of CO2 emissions from fossil fuel-based hydrogen manufacturing plants. A near-to-mid term outlook for low to near-zero CO2 hydrogen production from fossil fuels in the light of new technological trends is examined in this paper.
Hybridizing solar energy and coal-fired steam power plant is one of most attractive approaches of cost-efficient solar electricity in the present. By using the concentrated solar heat at around 300 oC to replace the bleed steam of the turbine for preheating feed-water of coal-fired steam cycle, higher solar-to-power efficiency is possibly achieved in that the conversion of solar to power can utilize higher-temperature steam cycle. In this paper, with the aid of exergy methodology, we derive expressions of the conversion of solar energy into power for such kind of solar hybrid plant, especially an explicit correlation is obtained for explaining solar-to-power efficiency. By using the derived expressions, we examine a typical hybrid solar system with 330 MW coal-fired power plant and evaluate thermal performance of solar-to-power. In addition, the influences of key operation parameters on the solar thermal performance are disclosed such as solar irradiation, incident angle and turbine load. The results obtained here would be expected to provide a possibility for designing and evaluating practical hybrid solar and coal-fired power plant.
This paper is a proposal and analysis of a novel low-CO2 emission solar hybrid combined cycle power system, which is based on solar-driven methane reforming. Nearly full methane conversion is achieved at a mild temperature (∼550 °C) using a methane reforming reactor integrated with a hydrogen separation membrane, enabling the solar thermal energy collected at middle temperature to be applied as the reaction heat in methane reforming, thereby converting the solar heat to chemical energy of the produced syngas. The membrane reactor also offers the advantage of continuously withdrawing hydrogen from the reaction zone, which is then burned at high temperature for power generation in the proposed advanced combined cycle system. The CO2-enriched gas concentrated at the end of the reaction zone is processed through pre-combustion decarbonization. It was shown that system thermal efficiency of 51.6% can be obtained, which is 2.2%-points higher than that of a referenced gas-steam combined cycle system with post-combustion decarbonization (CC-Post) at an equal CO2 removal ratio and no solar assistance. Fossil fuel saving ratio of 31.2% is achieved with a solar thermal share of 28.2%. Exergy analysis indicates that the main contributors for efficiency improvements are the reduced exergy destructions in the combustion and CO2 separation processes. The hybrid system has an exergy efficiency of 58% with 91% CO2 capture, which is 10%-points higher than that of a comparable CC-Post system. A preliminary economic analysis predicts that levelized electricity cost and payback period for the system are found to be 0.062 /(ton CO2), which is 42.5% lower than that for a CC-Post system. The proposed system hybridization approach simultaneously achieves the dual-purpose of high-efficiency solar heat conversion and low-energy penalty CO2 capture.
Solar-assisted hybrid power generation systems integrated with thermochemical fuel conversion are of increasing interest because they offer efficient use of lower temperature solar heat, with the important associated advantages of lower emissions, reduction of use of depletable fuels, production of easily storable fuel to alleviate the variability of solar heat, and relatively low cost of the use of lower temperature solar components. This paper examines economic performance of two previously proposed and analyzed thermochemical hybridized power generation systems: SOLRGT that incorporates reforming of methane, and SOLRMCC that incorporates methanol decomposition, both of which use low temperature solar heat (at ∼220 °C) to help convert the methane or methanol input to syngas, which is then burned for power generation. The solar heat is used “indirectly” in the methane reforming process, to vaporize the needed water for it, while it is used directly in the methanol decomposition process since methanol decomposition requires lower temperatures than methane reforming. This analysis resulted in an equation for each power system for determining the conditions under which the hybrid systems will have a lower levelized electricity cost, and how it will change as a function of the fuel price, carbon tax rate, and the cost of the collection equipment needed for the additional heat source.
As demand for energy continues to rise, the concern over the increase in emissions grows, prompting much interest in using renewable energy resources such as solar energy. However, there are numerous issues with using solar energy including intermittency and the need for storage. A potential solution is the concept of hybrid solar-fossil fuel power generation. Previous work has shown that utilizing solar reforming in conventional power cycles has higher performance compared to other integration methods. In this thesis, a two level analysis of a hybrid redox redox cycle is performed. First, a system analysis of a hybrid cycle utilizing steam redox reforming is presented. Important cycle design and operation parameters such as the oxidation temperature and reformer operating pressure are identified and their effect on both the reformer and cycle performance is discussed. Simulation results show that increasing oxidation temperature can improve reformer and cycle efficiency. Also shown is that increasing the amount of reforming water leads to a higher reformer efficiency, but can be detrimental to cycle efficiency depending on how the reforming water is utilized. Next, a system analysis for a CO2 redox reforming hybrid cycle and comparison of cycle and reformer performance between a CO 2 redox reformer and steam redox reformer hybrid cycle are presented. Similar to the steam redox system, results show that increasing the oxidation temperature or the amount of reforming CO2 leads to higher reformer and cycle efficiencies. In addition, the comparison between the CO2 and steam redox reformer hybrid cycles shows that the CO2 cycle has the potential to have better overall performance.Based on the system analysis, a reformer level analysis is also performed. A novel receiver reactor concept for a solar steam redox reformer is presented, and a computational model is developed to assess its performance. The receiver-reactor consists of a dumbbell shape absorber system that has two distinct absorbers. This absorber system setup allows for the switching between reduction and oxidation steps without having to constantly change inlet streams to the reactor and is designed such that the inlet connections do not interfere with the solar window. In addition, at any point in time only one solar absorber is irradiated by the solar energy (during the reduction step). Simulation results show that the receiver-reactor strongly absorbs the solar radiation and most of the radiative heat transfer occurs in the front half of the reactor. Moreover, results show that higher conductivity absorber materials are more suitable for long term reactor operation. A sensitivity analysis is also performed for the solar steam redox reformer with respect to different performance metrics. Important parameters include channel size, inlet temperature, and reformer pressure. Moreover, a strategy for reactor design based on performance as well as integration with the power cycle is discussed.
Interest in using renewable energy sources like solar energy for power production has grown because of the concern over CO2 emissions. One method of implementing solar energy for large scale power production is using hybrid solar fossil fuel power generation systems. Solar reforming has been shown to be a promising integration method with steam redox reforming to raise the chemical energy of the fuel. In this article, a sensitivity analysis for a solar steam redox reformer (proposed in Sheu and Ghoniem, 2016) with respect to different performance metrics is presented. Results show that the channel cross section, inlet gas temperature, and reformer pressure have the largest effect on the reactor performance. Furthermore, the analysis shows that the reduction kinetics can have a large effect on the calculated reactor performance and should be considered carefully. A reactor sizing analysis was also performed and results show that complete conversion can be achieved with a reasonable reactor size and that there is a tradeoff between conversion and cost/solar utilization efficiency. Moreover, a strategy for reactor design based on maximizing stand-alone performance as well as integration with a power cycle is discussed.
Virtually all hydrogen produced today is sourced from fossil fuels, with the principal method employed being the catalytic reforming of methane (CH4 , the principal component of natural gas and other gaseous fuels) [1]. Two different reactions can be distinguished in the methane reforming process: steam methane reforming (SMR) and C02 (or dry) methane reforming (DMR), represented by Eqs. (8.1) and (8.2) respectively: CH4 + H20 ~ 3 H2 +COD.H~98 K = +206 kJ 11101-I(8.1) CH,1 + C02 ~ 2 H2 + 2 CO; D.H~98 K = +247 kJ mol- 1; (8.2) Both reactions are highly endothermic, and are, thus, favored by high temperatures; industrial reforming processes are carried out between · 800 and 1000 °C [1 ]. The required energy is supplied by combustion of additional natural gas and process waste gas from the downstream hydrogen purification step. The share of natural gas consumed as fuel varies from 3% to 20% of the total plant's natural gas consumption [2]. The reaction gas product mixture is known as Synthesis gas (syngas): a gas mixture that contains varying amounts of CO and H2 whose exothermic conversion into fuel and other products has long been commercially practiced, for example, via the Fischer-Tropsch technology [3]. In fact hydrogen and syngas are the basic raw materials to produce synthetic liquid fuels (SLFs) and chemicals via industrially available processes.
Virtually all hydrogen produced today is sourced from
fossil fuels, with the principal method employed being
the catalytic and highly endothermic steam reforming of
methane (CH4, the principal component of natural gas
and other gaseous fuels such as coal seam gas). While this
is likely to remain the technology of choice for some
time, hydrogen is regarded as a clean fuel of the future
and will need to be produced entirely from energy
sources with zero greenhouse gas emissions.
As a transitional strategy, considerable effort is being
spent on developing a hybrid hydrogen technology in
which concentrated solar thermal energy is used to
provide the heat for the high-temperature endothermic
steam–methane reforming reaction. In doing so, solar
energy is embodied thermochemically in the product
hydrogen. This overcomes many of the limitations of
solar energy, enabling it to be stored at ambient conditions,
transported from the point of collection to where
it is required, and used outside daylight hours. Such a
transitional technology is considered by many to be an
essential stepping stone from current practice to a truly
renewable-based hydrogen economy.
This article outlines the steam reforming process for
hydrogen production, summarizes the key thermochemistry
and thermodynamics of the steam–methane
reforming reaction, reviews the past and current work
being done to integrate solar thermal energy into the
steam reforming process, and identifies where future
work on this topic should be focused. Emphasis is placed
on producing hydrogen with carbon monoxide levels low
enough for it to be used in proton-exchange membrane
(PEM) fuel cells.
Virtually all hydrogen used today is produced from fossil fuels, primarily through the highly energy intensive steam reforming of methane, the principal component of natural gas. While this is likely to remain the technology of choice for some time, the role of hydrogen as a clean fuel of the future is predicated on new production routes with low or zero greenhouse gas emissions.
Solar thermal reforming of natural gas is regarded as a promising transitional technology to produce hydrogen with reduced carbon intensity. In this process, the reforming reaction is carried out using thermal energy supplied from concentrated solar energy rather than the combustion of fossil fuels. Besides reducing the carbon intensity of the product hydrogen, the process provides a viable means for storage of solar energy in the chemical bonds of a transportable product, overcoming many of the limitations of solar energy.
This article summarizes the key thermochemistry and thermodynamics of conventional methane reforming, and addresses the issue of how solar energy can be used to drive the process. Various reactor concepts are reviewed and discussed, and past and current research activities are reviewed to identify where future work on this topic should be focused.
Based on the principle of cascade utilization of multiple energy resources, a gas-steam combined cycle power system integrated with solar thermo-chemical fuel conversion and CO2 capture has been proposed and analyzed. The collected solar heat at 550°C drives the endothermic methane reforming and is converted to the produced syngas chemical exergy, and then released as high-temperature thermal energy via combustion for power generation, achieving its high-efficiency heat-power conversion. The reforming reaction is integrated with a Pd-based hydrogen separation membrane, which continuously withdraws hydrogen from the reaction zone and enables nearly full methane conversion. The CO2 enriched gas being concentrated in the retentate zone is collected and processed with pre-combustion decarbonization. The results from preliminary economic analysis show that the cost of electricity is 0.062 $/kWh, 11.4% lower than that in the reference system with the same methane input and CO2 removal ratio, and payback period is 10 years.
This paper reviews development in the field of solar thermochemical processing by considering experimental demonstrations, reactor technology development, thermodynamic, economic and life cycle analyses. The review then builds on these aspects and compares various solar thermochemical processes. Solar upgrading of carbon feed has been demonstrated on pilot scale. It is observed that for the thermochemical cycles, only iron and ceria based redox pair have been demonstrated on pilot scale. For industrial applications, solar thermochemical production of zinc, upgrading of landfill gas and organic waste have been demonstrated on pilot scale. However, long term performance data of these pilot plants is not reported in literature.
Thermodynamic comparison reveals that the processes involving upgrading of carbon feed have energy and exergy efficiency at 50–90% and 46–48% respectively. Multistep thermochemical cycles operating at 900–1200 K have energy efficiency of 34–38%. Metal oxide redox pair based thermochemical cycles operating at 1900–2300 K have energy and exergy efficiencies of 12–32% and 20–36% respectively. Methane reforming and lime production processes have chemical efficiencies of 55% and 35% respectively and have demonstrated better performance than other solar thermochemical processes. A few processes like solar gasification of solid carbon feed have demonstrated lower chemical efficiency of around 10% even at pilot scale. The hydrogen production cost for solar upgrading of fossil fuels is estimated at 3.21–6.10/kg and CSP driven electrolysis at 3.15–10.23$/kg. It is observed that there is limited actual data and significant uncertainty in cost. Under these circumstances, it is recommended that initial screening of processes be done by net energy, material and life cycle analysis.
Two novel hybrid combined cycle power systems that use solar heat and methanol, and integrate CO2 capture, are proposed and analyzed, one based on solar-driven methanol decomposition and the other on solar-driven methanol reforming. The high methanol conversion rates at relatively low temperatures offer the advantage of using the solar heat at only 200–300 °C to drive the syngas production by endothermic methanol conversions and its conversion to chemical energy. Pre-combustion decarbonization is employed to produce CO2-free fuel from the fully converted syngas, which is then burned to produce heat at the high temperature for power generation in the proposed advanced combined cycle systems. To improve efficiency, the systems’ configurations were based on the principle of cascade use of multiple heat sources of different temperatures. The thermodynamic performance of the hybrid power systems at its design point is simulated and evaluated. The results show that the hybrid systems can attain an exergy efficiency of about 55%, and specific CO2 emissions as low as 34 g/kW h. Compared to a gas/steam combined cycle with flue gas CO2 capture, the proposed solar-assisted system CO2 emissions are 36.8% lower, and a fossil fuel saving ratio of ∼30% is achievable with a solar thermal share of ∼20%. The system integration predicts high efficiency conversion of solar heat and low-energy-penalty CO2 capture, with the additional advantage that solar heat is at relatively low temperature where its collection is cheaper and simpler. The systems’ components are robust and in common use, and the proposed hybridization approach can be also used with similar benefits by replacing the solar heat input with other low heat sources, and the system integration achieves the dual-purpose of clean use of fossil fuel and high-efficiency conversion of solar heat at the same time.
In solar reforming, the heating value of natural gas is increased by utilization of concentrated solar radiation. Hence, it is a process for storing solar energy in a stable and transportable form that also permits further conversion into liquid fuels like methanol. The feasibility of solar reforming is proved. However, its overall process efficiency potential has not been studied systematically. In this work, an indirectly heated solar reforming process with air as heat transfer fluid is designed and modelled to produce syngas suitable for subsequent methanol synthesis. For provision of solar high temperature heat, an open volumetric receiver is implemented into the process model and the overall performance is investigated. Results show the paramount significance of the air return ratio of the receiver and its ability to achieve high efficiencies at temperatures above 850 °C. For realistic air return ratios, design point process efficiencies of 19 % can be achieved, for an increased air return ratio, values up to 23 % are feasible. The determined corresponding annual efficiencies are 12 % and 14 % respectively. Considering its relative technical simplicity this makes indirectly heated solar reforming a promising technology to overcome the current limitations of solar energy in the medium term.
The interest in hybrid power production facilities, based on the integration of renewable resources and conventional fossil fuels, is rapidly rising. The question of what fraction of the electricity produced in such facilities is to be considered as produced from the renewable resources is still being debated. We show that the conventional Fossil-Centered-Solar-Share method and the Exergy-based method lead to unfair allocations that may result in unfair access to subsidies granted to renewable electricity. We propose a more balanced Single-Resource-Separate-Production-Reference (SRSPR) allocation method based on prescribed reference partial primary energy factors chosen by some authority to represent reference efficiencies of non-hybrid power production from the same renewable and fossil resources used by the hybrid facility. We then show that as hybridization gains higher fractions of the local energy market, the SRSPR method may still result in somewhat unfair allocations leading to local market distortions. To overcome this drawback, we formulate a more consistent Self-Tuned-Average-Local-Productions-Reference (STALPR) allocation method whereby the electricity allocation fractions are based on the average partial primary energy factors of the actual energy portfolio of the local area that includes the hybrid plant itself. Results are illustrated with reference to a solar-integrated combined cycle facility.
There has been much interest in the use of renewable resources for power generation as the world's energy demand and the concern over the rise in emissions increases. In the near term, however, renewable sources such as solar energy are expected to provide a small fraction of the world's energy demand due to intermittancy and storage problems. A potential solution is the use of hybrid solar-fossil fuel power generation. Previous work has shown the potential of steam redox reforming for hybridization. However, this type of reforming requires some water consumption (which may be infeasible in certain locations) as not all the water can be recovered through recycling. An alternative is to utilize dry (or CO2) redox reforming. In this paper, a system analysis for a CO2 redox reforming hybrid cycle and comparison of cycle and reformer performance between a CO2 redox reformer and steam redox reformer hybrid cycle are presented. The effect of important operating parameters such as pressure, amount of reforming CO2, and the oxidation temperature on the reformer and cycle performance are discussed. Simulation results show that increasing the oxidation temperature or the amount of reforming CO2 leads to higher reformer and cycle efficiencies. In addition, the comparison between the CO2 and steam redox reformer hybrid cycles shows that the CO2 cycle has the potential to have better overall performance.
Hydrogen production plays a very important role in the development of hydrogen economy.Hydrogen gas production through solar energy which is abundant, clean and renewable is one of the promising hydrogen production approaches. This article overviews the available technologies for hydrogen generation using solar energy as main source.Photochemical, electrochemical and thermochemical processes for producing hydrogen with solar energy are analyzed from a technological environmental and economical point of view. It is concluded that developments of improved processes for hydrogen production via solar resource are likely to continue in order to reach competitive hydrogen production costs. Hybrid thermochemical processes where hydrocarbons are exclusively used as chemical reactants for the production of syngas and the concentrated solar radiation is used as a heat source represent one of the most promising alternatives: they combine conventional and renewable energy representing a proper transition towards a solar hydrogen economy.
Based on the principle of cascade utilization of multiple energy resources, a gas-steam combined cycle power system integrated with solar thermo-chemical fuel conversion and CO2 capture has been proposed and analyzed. The collected solar heat at 550 °C drives the endothermic methane reforming and is converted to the produced syngas chemical exergy, and then released as high-temperature thermal energy via combustion for power generation, achieving its high-efficiency heat-power conversion. The reforming reaction is integrated with a hydrogen separation membrane, which continuously withdraws hydrogen from the reaction zone and enables nearly full methane conversion. The CO2 enriched gas being concentrated in the retentate zone is collected and processed with pre-combustion decarbonization.The system is thermodynamically simulated using the ASPEN PLUS code. The results show that with 91% CO2 captured, the specific CO2 emission is 25 g/kWh. An exergy efficiency of 58% and thermal efficiency of 51.6% can be obtained. A fossil fuel saving ratio of 31.2% is achievable with a solar thermal share of 28.2%, and the net solar-to-electricity efficiency based on the gross solar heat incident on the collector is about 36.4% compared with the same gas-steam combined cycle system with an equal CO2 removal ratio obtained by post-combustion decarbonization.
Molten salt, a solar thermal energy storing medium, shows excellent dual function as reaction medium for biomass gasification due to its high heat transfer performance and significant catalytic activity. Enhancement of CO2 gasification by Ni/Al2O3 catalyst was investigated in molten eutectic carbonate salt using cellulose powder as a model biomass and three candidates of biomass wastes including sawdust, chopstick, and newspaper. Compared to the case of only molten salt, adding 7%wt of Ni/Al2O3 catalyst could increase yield of syngas from CO2 gasification of the tested biomasses by 28, 17, 23, and 18%, respectively. The peak rate of CO production was shifted to ~100 K lower temperature while H2 yield increased by at least 300%. The experimental results revealed that the enhancement remain valid for more complex feedstock besides cellulose. Though the catalyst was very active for H2 production, it could enhance CO production via accelerating C-C bond cleavage. The Ni/Al2O3 catalyst is shown to be an effective catalyst to accelerate CO2 gasification of biomass in high-temperature molten salt. In addition, the oxide precipitate from dissociation of the salt at high temperatures was restored by the use of CO2.
A novel solar hybrid power generation system with near zero CO2 emission (ZE-SOLRGT) has been proposed in the previous work, which is based on a GRAZ-like cycle integrating methane-steam reforming, solar-driven steam generation and CO2 capture. Solar heat assistance increases power output and reduces fossil fuel consumption. Besides near zero CO2 emission with oxy-fuel combustion and cascade recuperation of turbine exhaust heat, the system is featured with indirect upgrading of low-mid temperature solar heat and its high efficiency heat-to-power conversion. A performance analysis of ZE-SOLRGT cycle has been carried out using ASPEN PLUS code to explore the effects of key parameters on system performances. It is concluded that similar to 54% exergy efficiency can be attained with similar to 100% CO2 capture. The net solar-to-electricity efficiency can reach up to 34.7% in the base case. Steam-to-methane molar ratio of 2-3 is suitable for system performance improvement. High system efficiency can be obtained as the HPT pressure ratio is in the range of 15-18. The system integration achieves the complementary utilization of fossil fuel and solar heat, as well as their high-efficiency conversion into electricity.
Solar radiation is an abundant and environmentally friendly energy source. However, its capture and effective utilization is one of the most difficult challenges faced by modern science today. An effective way to capture solar energy is to convert it to chemical energy using concentrated solar power. Methane, the main component of natural gas, is poised to become a leading feedstock in the near term due to recent developments in shale gas extraction. Solar to chemical conversion of energy can be achieved by reforming methane into synthesis gas in a single, highly endothermic catalytic process when reacted with steam or carbon dioxide. This review highlights different aspects of solar thermal reforming of natural gas, including thermodynamics, challenges related to catalyst activity and stability and reactor design. Equilibrium limitations of steam and dry methane reforming are discussed in detail with respect to solar thermal reforming. Recent developments in methane reforming catalysis are critically reviewed in a broad scope, addressing catalyst deactivation drawbacks and focusing on alternative catalysts. The potential of the low-temperature solar methane steam reforming and the related technological challenges are discussed, including catalyst requirements. Future directions are also outlined.
Steam reforming of methane is a candidate process for converting concentrated high-temperature solar heat to chemical fuels because it is a high-temperature, highly endothermic process. We developed a tubular reformer system using novel double-walled reactor tubes with molten-salt thermal storage for solar reforming to produce hydrogen or synthetic gas (CO + H-2) from a gas mixture of methane and steam using concentrated solar radiation as an energy source. The high heat capacity and large latent heat (heat of solidification) of the molten salt circumvents rapid temperature changes in the reactor tubes at high temperatures under fluctuating insolation. In this paper, we focused on under intermittent heating-cooling mode, the steam reforming performance of double-walled reactor tubes with Na2CO3/MgO composite thermal storage in comparison to pure Na2CO3 thermal storage. A heating mode using an electric furnace simulates reactor startup in the morning and reheating of the reactor by concentrated solar radiation after brief periods of cloud passage. The intermittent heating-cooling mode simulates fluctuating incident solar radiation during cyclic short-term cloud passage. The temperature variations of the catalyst and storage material, methane conversion, and higher heating value power of the reformed gas were examined for the double-walled reactor tubes and a single-wall (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).
The CO2CH4 reforming-methanation chemical cycle provides an attractive means of transporting solar energy to a central station in accord with the Solchem concept. A number of receiver elements (chemical reactors) have been tested in the laboratory in an effort to optimize the catalyst parameters and the catalyst-reactor configuration. These tests led to the design and fabrication of both prototype and full scale production model Solchem receivers which were operated successfully at the White Sands Solar Furnace. The development of energy delivery methanation reactors is proceeding along with the design of both laboratory and field-model closed-loop Solchem systems.
Concentrated solar radiation has been used to heat air in a volumetric receiver device. Such a receiver, using a wire mesh arrangement placed in the focal zone, can also be used for carrying out a chemical reaction where the catalyst is heated directly by the concentrated solar beam without any intermediary heat transfer fluid. The advantage of such a concept is that the highest temperature of the whole system is at the reaction site and not on the wall of the reactor or in the heat transfer fluid. Thus, higher conversion efficiencies will be obtained. Moreover, as the reaction site is directly irradiated by a very intense solar flux, photochemically enhanced reactions may result under certain conditions. The disadvantage of the approach is the difficulty in insuring uniform insolation and temperature distribution throughout the catalyst surface. Another problem is that a transparent window is required to seal off the reactants from the environment; this may complicate scaling up of the process. In this communication the authors report the results of preliminary experiments demonstrating that catalysed chemical reactions can be carried out by direct solar irradiation of the catalyst.
The objective of the Closed Loop Efficiency Analysis (CLEA) Project at Sandia National Laboratories is to develop the data base, the calculational tools, and the operational experience necessary for the design of cost-effective energy transport systems based on reversible chemical reactions. A series of experiments and analyses have been carried out to explore the effects of catalyst selection, starting composition, reactor temperature, system pressure, and water recycle on the operation and the efficiency of an energy transport system based on the reversible carbon dioxide reforming of methane. Both the experiments in the CLEA laboratory facility and the analyses indicate that the carbon dioxide/methane thermochemical energy transport system can be operated in a stable, closed-loop mode and that the system can be started up and shut down, as it must be daily in a solar applications, without triggering either catastrophic instabilities or carbon deposition. 11 refs., 8 figs., 3 tabs.
Solar reforming of methane with CO2 was demonstrated successfully with a direct absorption receiver/reactor on a parabolic dish capable of 150 kW solar power. The reactor, a volumetric absorber, consisted of a reticulated porous alumina foam disk coated with rhodium catalyst. The system was operated during both steady-state and solar transient (cloud passage) conditions. The total solar power absorbed reached values up to 97 kW and the maximum methane conversion was almost 70 %. Receiver effiviencies ranged up to 85 & and chemical efficiencies peaked at 54 %.
The layout and the design of a volumetric receiver/reactor are described. This receiver will be operated as part of a closed thermochemical storage and transportation system at a solar tower test facility in Israel. Methane reforming with CO2 was chosen as the energy absorbing reaction. The receiver is designed for a power level of 280kW, a methane conversion level of 80% and an operating pressure of 2.5barabs. In front of the receiver, a secondary concentrator will be installed. The receiver aperture is covered by a domed quartz window. The directly irradiated volumetric absorber is made of highly porous ceramic foam. Insulation and support structures are made from ceramic fibre materials. Results of lab experiments with samples of the ceramic foam are presented, providing information on properties of the absorber (i.e. thermal shock resistance, solar absorptivity, various catalytic aspects).
A joint US/Federal Republic of Germany (FRG) project has successfully tested a unique solar-driven chemical reactor in the Catalytically Enhanced Solar Absorption Receiver (CAESAR) experiment. The CAESAR test was a proof-of-concept demonstration of carbon-dioxide reforming of methane in a commercial-scale, solar, volumetric receiver/reactor on a parabolic dish concentrator. The CAESAR design, test facility and instrumentation, thermal and chemical tests, and analysis of test results are presented in detail. Numerical models for the absorber and the receiver are developed and predicted performance is compared with test data. Post test analyses to assess the structural condition of the absorber and the effectiveness of the rhodium catalyst are presented. Unresolved technical issues are identified and future development efforts are recommended.
Rhodium supported on γ-Al2O3 was an effective catalyst for reforming methane with carbon dioxide at low ratios of CO2/CH4. Unlike other metals tested, no carbon deposited on the catalyst in the temperature range 600–800°C. Kinetic experiments on a 0.5 wt.-% Rh/Al2O3 catalyst gave rate equations for the reforming and shift reactions. A model was constructed for conversion in a pellet by incorporating both the reverse reaction and the effect of external and internal diffusion. This model, when tested with the data from a pellet string reactor, gave very good agreement with conversions and product distributions. External diffusion was negligible but internal effectiveness factors were about 0.3 or more. The model was expanded to a large-scale packed bed with appropriate heat transfer parameters. Adjustable factors were determined by matching measured temperature profiles from pilot unit experiments. The catalyst later performed successfully in a solar receiver/reactor and shows potential for conventional processing.
The Weizmann Institute of Science 480 kW Reformer System, IEA SSPS Task V
- I Spiewak
- M Epstein
Overture to CLEA: The Closed Loop Efficiency Analysis Project
- J D Fish
Catalytic Ceramic Foam Supports for Solar Receivers
- J T Richardson