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US DOE aids development of carbon capture technologies
FEATURE
US DOE aids development of carbon capture technologies This feature summarises some of the work that the US Department of Energy (DOE) is doing to help fund and contribute to the development of carbon capture technologies. It briefly looks at a membrane system which, according to its developers Membrane Technology and Research Inc, successfully captures 90% of carbon dioxide from flue gas, and describes novel composite membranes for carbon capture, utilisation and storage, that are currently under development at Ohio State University. A promising post-combustion membrane technology that can separate and capture 90% of the carbon dioxide (CO2) from a pulverised coal plant has been successfully demonstrated and has been approved by the US Department of Energy (DOE) to advance to a larger-scale field test. In an $18.75-million project funded by the American Recovery and Reinvestment Act of 2009, Membrane Technology and Research Inc (MTR) and its partners tested the Polaris membrane system, which uses a CO2-selective polymeric membrane material and module to capture CO2 from a plant’s flue gas.
Challenging Post-combustion separation and capture of CO2 is challenging because of the low pressure and diluted concentration of CO2 in the waste ÃÌÀi>ÆÊÌÀ>ViÊ«ÕÀÌiÃÊÊÌ iÊvÕiÊ}>ÃÊÌ >ÌÊ>vviVÌÊ ÀiÛ>Ê«ÀViÃÃiÃÆÊ>`ÊÌ iÊ>ÕÌÊvÊiiÀ}ÞÊ required for CO2 capture and compression. Because the Polaris membranes are 10 times more permeable to CO2 than conventional materials (reducing the membrane area required), and use a slipstream of combustion air as a sweep gas, the system has great potential for reduced energy requirements, reasonable capture costs and greater efficiencies for postcombustion capture – all important factors for retrofitting existing coal-based plants.
Capturing more than 90% of CO2 Demonstrating and further validating this innovative, cost-effective membrane CO2 separation process at the 1-MW equivalent (MWe) pilot scale is expected to be a major step towards meeting DOE’s programme goals of capturing more than 90% of CO2 from flue gas, with less than a 35% increase in the cost of electricity. Consequently, MTR will now begin fabricat8
Membrane Technology
ing a 1-MW system capable of meeting this goal from a 20-ton-per-day slipstream of coalfired flue gas. The 1-MW system will be tested at DOE’s National Carbon Capture Center (NCCC) based in Wilsonville, Alabama, beginning in 2013. The Post-Combustion Carbon Capture Center at the NCCC enables testing and integration of advanced CO2-capture technologies, at scale, using flue gas from Alabama Power’s Gaston power plant Unit 5 – an 880-MW supercritical pulverised coal unit. Data generated in a six-month field test of the 1-MW system will be used by MTR to develop a preliminary 20-MW full-scale commercial design in cooperation with the firm’s partners, Vectren and WorleyParsons. In addition to MTR, other collaborators on the three-year project include Babcock & Wilcox Co, Electric Power Research Institute and Southern Co. The objectives of the project – part of the DOE’s Clean Coal Research Program portfolio – include reducing the capital cost, footprint and energy penalty for CO2 capture in conventional coal-fired power plants, compared with existing commercial systems.
Mitigating climate change In a project funded by the US DOE’s Office of Fossil Energy (FE), researchers at Ohio State University have developed what they claim is a ground-breaking new hybrid membrane that combines the separation performance of inorganic membranes with the cost-effectiveness of polymer membranes. The breakthrough technology has vast commercial potential for use at coal-fired power plants with carbon capture, utilisation and storage (CCUS), a key element in national efforts to mitigate climate change.
Carbon capture programme Before the CO2, generated at a power plant, can be securely stored or put to beneficial use, it first must be separated from the flue gas stream. Unfortunately, the energy cost of current separation technologies is too high to make rapid commercial deployment of CCUS technologies feasible. To overcome this barrier, high-performance membrane separation is a focus of FE’s Carbon Capture Program, under which the Ohio State project is managed. The programme supports the DOE goal of cost-effective deployment of CCUS technologies within 10 years to position the USA as a leader in the global, clean energy race.
Energy efficient To illustrate how membranes are more energy efficient than other separation methods, scientists sometimes use a familiar substance – sea water. Pure water can be obtained by boiling the sea water and condensing the salt-free vapour, but boiling requires heat, which means using energy. Alternatively, membrane processes for separating salt from water do not require heat, making them more cost-effective and environment-friendly. Separating CO2 from flue gas is similar. Energy is still required for pre-separation and post-separation processes, such as compressing the gas, but for the key process of separating the CO2, new membrane technologies pioneered by FE’s National Energy Technology Laboratory (NETL) and its research partners are designed to eliminate most of the energy costs.
Hybrid membrane Polymer membranes are mass produced and are cost-effective, while inorganic membranes are expensive to produce, but exhibit much better performance. Ohio State’s new hybrid membrane consists of a thin, inorganic zeolite Y layer sandwiched between an inorganic intermediate and a polymer cover. These three layers sit atop a polymer support, which, in turn, rests on a woven backing.
November 2012
RESEARCH TRENDS NETL project manager José Figueroa, commented: ‘Combining inorganic and organic membrane materials in a hybrid configuration is a breakthrough that could potentially lower costs associated with clean coal technologies.’ Ohio State researchers say that they realised a first prototype by combining new nanotechnology characterisation and fabrication methods with advanced manufacturing techniques. In the laboratory, they were able to slash the zeolite Y growth-rate from 8 h to less than 15 min and reduce ceramic processing time from
RESEARCH TRENDS Membrane bio-fouling and scaling in a FO membrane bioreactor The forward osmosis (FO) membrane bioreactor (FOMBR) has received much attention recently. Because of the high rejection nature of FO membranes, the biomass, dissolved organic and inorganic compounds retained in the bioreactor could cause membrane fouling by multiple mechanisms. In this study, a 45% permeate flux decrease was observed in a well controlled FOMBR equipped with a submerged hollow-fibre FO membrane module, using a configuration in which the active layer is facing the draw solution (AL-DS). A series of characterisations were performed to explore membrane fouling mechanisms in the FOMBR. It was found that a bio-fouling layer covered the substrate surface of the FO membrane with a combined structure of bacterial clusters and extracellular polymeric substances (EPS), which contributed to a 72% drop in the membrane mass transfer coefficient (Km) and about a 10% increase in hydraulic resistance. The inorganic fouling was caused by Ca, Mg, Al, Si, Fe and P that contributed 60% of the total hydraulic resistance of the fouled membrane and reduced the Km by around 34%. These results suggest that in this application the FO fouling is governed by the coupled influences of bio-film formation and inorganic scaling. When the configuration was reversed, with the active layer facing the feed solution (ALFS), a negligible flux decline was obtained by applying intermittent tap-water flushing to the membrane surface, which suggests that the AL-FS orientation is favourable for FOMBR operation. An effective strategy
November 2012
{ÎÊ ÊÌÊÓäÊ]ÊÀiÃÕÌ}ÊÊÀ}>VÉÀ}>VÊ membrane development within one hour. They have also achieved adhesion of the inorganic intermediate layer onto a polymer support. The team, which has emphasised the membrane’s broader separation applications in its reports, received funding for the project in October 2011, and presented its first results at the NETL Carbon Capture and Storage meeting, which was held in July, 2012. The promising results follow the previous success the team had in making continuous,
intact inorganic layers on polymer supports and developing new membrane-production techniques.
for controlling fouling is to prevent internal scaling and over-growth of bio-film on the membrane surface. J. Zhang, W.L.C. Loong, S. Chou, C. Tang, R. Wang and A.G. Fane: J. of Membrane Science 403–404 8–14 (1 June 2012). http://dx.doi.org/10.1016/j.memsci.2012.01.032
improvement in resistance against compaction, compared with neat membranes. Furthermore, the tensile strength of the membranes at the 2 wt% MWCNTs loading increased by over 97%, compared with that of the neat ones. S. Majeed, D. Fierro, K. Buhr, J. Wind, B. Du, A. Boschetti-de-Fierro and V. Abetz: J. of Membrane Science 403–404 101–109 (1 June 2012). http://dx.doi.org/10.1016/j.memsci.2012.02.029
Multi-walled carbon nano-tubes mixed polyacrylonitrile UF membranes In this study, hydroxyl functionalised multiwalled carbon nano-tubes (MWCNTs) were blended with polyacrylonitrile (PAN) to prepare ultrafiltration (UF) membranes using the phase inversion process. Three different concentrations of MWCNTs were used in the PAN – 0.5 wt%, 1 wt% and 2 wt%. The water flux of the membranes increased by 63% at the 0.5 wt% loading of MWCNTs, compared with the neat PAN membranes. The water flux decreased upon a further increase in the concentration of MWCNTs, but at 2 wt% loading it was still higher than that of the pure PAN membranes. The surface hydrophilic properties of the membranes was enhanced following the addition of MWCNTs, as observed by contact angle measurements. The enhanced hydrophilic properties might have an impact on the improved water flux. All the membranes showed a molecular weight VÕÌÊvvÊ 7 "®ÊvÊ>««ÀÝ>ÌiÞÊxäÊ}É mol. Surface pore size analysis by scanning electron microscopy (SEM) showed no significant difference in the mean pore size of the nano-composite membranes, compared with that of the neat membranes. The cross-section morphology was influenced by the introduction of MWCNTs – fewer, but enlarged macro-voids were observed, which was particularly prominent at a loading of 2 wt% MWCNTs. The membranes containing 2 wt% MWCNTs showed a 36%
Contacts: US Department of Energy, 1000 Independence Avenue SW, Washington, DC 20585, USA. Tel: +1 202 586 5000, www.fossil.energy.gov Membrane Technology and Research Inc, 39630 Eureka Drive, Newark, CA 94560, USA. Tel: +1 650 328 2228, www.mtrinc.com
Anti-fouling membranes prepared by electro-spinning polylactic acid containing biocidal nano-particles The authors of this study prepared nonwoven electro-spun polylactic acid (PLA) membranes containing functionalised sepiolite fibrillar particles (5 wt%). Biocidal activity was achieved by functionalising sepiolite fibres with Ag (26 wt%) and Cu (26 wt%), which were embedded in the fibre surface. Sepiolite particles were negatively charged in all cases – with zeta potential in the range of -15 mV to -37 mV – increasing their negative charge with pH. The membranes were bio-fouled in a cross-flow filtration device using model biofoulants, cultures of Saccharomyces cerevisiae (pH 4.5) and Pseudomonas putida (pH 7.5), which were pumped across the membrane vÀÊÓ{É{nÊ °Ê/ iÊ>ÃÃiÃÃiÌÊvÊ>VÌÛiÊ biomass was performed by measuring the concentration of adenosine-5’-triphosphate (ATP) in the used membranes. The results showed a significant decrease in the amount of surface ATP for PLA loaded with Ag and Cu functionalised sepiolite. The effect was particularly intense for Ag-sepiolite in contact with Saccharomyces cerevisiae, where the reduction amounted to 85% compared with neat PLA (control). This was attributed to the differences in ion availability as a function of pH and to the presence of chloride
Membrane Technology
9
US DOE aids development of carbon capture technologies This feature summarises some of the work that the US Department of Energy (DOE) is doing to help fund and contribute to the development of carbon capture technologies. It briefly looks at a membrane system which, according to its developers Membrane Technology and Research Inc, successfully captures 90% of carbon dioxide from flue gas, and describes novel composite membranes for carbon capture, utilisation and storage, that are currently under development at Ohio State University. A promising post-combustion membrane technology that can separate and capture 90% of the carbon dioxide (CO2) from a pulverised coal plant has been successfully demonstrated and has been approved by the US Department of Energy (DOE) to advance to a larger-scale field test. In an $18.75-million project funded by the American Recovery and Reinvestment Act of 2009, Membrane Technology and Research Inc (MTR) and its partners tested the Polaris membrane system, which uses a CO2-selective polymeric membrane material and module to capture CO2 from a plant’s flue gas.
Challenging Post-combustion separation and capture of CO2 is challenging because of the low pressure and diluted concentration of CO2 in the waste ÃÌÀi>ÆÊÌÀ>ViÊ«ÕÀÌiÃÊÊÌ iÊvÕiÊ}>ÃÊÌ >ÌÊ>vviVÌÊ ÀiÛ>Ê«ÀViÃÃiÃÆÊ>`ÊÌ iÊ>ÕÌÊvÊiiÀ}ÞÊ required for CO2 capture and compression. Because the Polaris membranes are 10 times more permeable to CO2 than conventional materials (reducing the membrane area required), and use a slipstream of combustion air as a sweep gas, the system has great potential for reduced energy requirements, reasonable capture costs and greater efficiencies for postcombustion capture – all important factors for retrofitting existing coal-based plants.
Capturing more than 90% of CO2 Demonstrating and further validating this innovative, cost-effective membrane CO2 separation process at the 1-MW equivalent (MWe) pilot scale is expected to be a major step towards meeting DOE’s programme goals of capturing more than 90% of CO2 from flue gas, with less than a 35% increase in the cost of electricity. Consequently, MTR will now begin fabricat8
Membrane Technology
ing a 1-MW system capable of meeting this goal from a 20-ton-per-day slipstream of coalfired flue gas. The 1-MW system will be tested at DOE’s National Carbon Capture Center (NCCC) based in Wilsonville, Alabama, beginning in 2013. The Post-Combustion Carbon Capture Center at the NCCC enables testing and integration of advanced CO2-capture technologies, at scale, using flue gas from Alabama Power’s Gaston power plant Unit 5 – an 880-MW supercritical pulverised coal unit. Data generated in a six-month field test of the 1-MW system will be used by MTR to develop a preliminary 20-MW full-scale commercial design in cooperation with the firm’s partners, Vectren and WorleyParsons. In addition to MTR, other collaborators on the three-year project include Babcock & Wilcox Co, Electric Power Research Institute and Southern Co. The objectives of the project – part of the DOE’s Clean Coal Research Program portfolio – include reducing the capital cost, footprint and energy penalty for CO2 capture in conventional coal-fired power plants, compared with existing commercial systems.
Mitigating climate change In a project funded by the US DOE’s Office of Fossil Energy (FE), researchers at Ohio State University have developed what they claim is a ground-breaking new hybrid membrane that combines the separation performance of inorganic membranes with the cost-effectiveness of polymer membranes. The breakthrough technology has vast commercial potential for use at coal-fired power plants with carbon capture, utilisation and storage (CCUS), a key element in national efforts to mitigate climate change.
Carbon capture programme Before the CO2, generated at a power plant, can be securely stored or put to beneficial use, it first must be separated from the flue gas stream. Unfortunately, the energy cost of current separation technologies is too high to make rapid commercial deployment of CCUS technologies feasible. To overcome this barrier, high-performance membrane separation is a focus of FE’s Carbon Capture Program, under which the Ohio State project is managed. The programme supports the DOE goal of cost-effective deployment of CCUS technologies within 10 years to position the USA as a leader in the global, clean energy race.
Energy efficient To illustrate how membranes are more energy efficient than other separation methods, scientists sometimes use a familiar substance – sea water. Pure water can be obtained by boiling the sea water and condensing the salt-free vapour, but boiling requires heat, which means using energy. Alternatively, membrane processes for separating salt from water do not require heat, making them more cost-effective and environment-friendly. Separating CO2 from flue gas is similar. Energy is still required for pre-separation and post-separation processes, such as compressing the gas, but for the key process of separating the CO2, new membrane technologies pioneered by FE’s National Energy Technology Laboratory (NETL) and its research partners are designed to eliminate most of the energy costs.
Hybrid membrane Polymer membranes are mass produced and are cost-effective, while inorganic membranes are expensive to produce, but exhibit much better performance. Ohio State’s new hybrid membrane consists of a thin, inorganic zeolite Y layer sandwiched between an inorganic intermediate and a polymer cover. These three layers sit atop a polymer support, which, in turn, rests on a woven backing.
November 2012
RESEARCH TRENDS NETL project manager José Figueroa, commented: ‘Combining inorganic and organic membrane materials in a hybrid configuration is a breakthrough that could potentially lower costs associated with clean coal technologies.’ Ohio State researchers say that they realised a first prototype by combining new nanotechnology characterisation and fabrication methods with advanced manufacturing techniques. In the laboratory, they were able to slash the zeolite Y growth-rate from 8 h to less than 15 min and reduce ceramic processing time from
RESEARCH TRENDS Membrane bio-fouling and scaling in a FO membrane bioreactor The forward osmosis (FO) membrane bioreactor (FOMBR) has received much attention recently. Because of the high rejection nature of FO membranes, the biomass, dissolved organic and inorganic compounds retained in the bioreactor could cause membrane fouling by multiple mechanisms. In this study, a 45% permeate flux decrease was observed in a well controlled FOMBR equipped with a submerged hollow-fibre FO membrane module, using a configuration in which the active layer is facing the draw solution (AL-DS). A series of characterisations were performed to explore membrane fouling mechanisms in the FOMBR. It was found that a bio-fouling layer covered the substrate surface of the FO membrane with a combined structure of bacterial clusters and extracellular polymeric substances (EPS), which contributed to a 72% drop in the membrane mass transfer coefficient (Km) and about a 10% increase in hydraulic resistance. The inorganic fouling was caused by Ca, Mg, Al, Si, Fe and P that contributed 60% of the total hydraulic resistance of the fouled membrane and reduced the Km by around 34%. These results suggest that in this application the FO fouling is governed by the coupled influences of bio-film formation and inorganic scaling. When the configuration was reversed, with the active layer facing the feed solution (ALFS), a negligible flux decline was obtained by applying intermittent tap-water flushing to the membrane surface, which suggests that the AL-FS orientation is favourable for FOMBR operation. An effective strategy
November 2012
{ÎÊ ÊÌÊÓäÊ]ÊÀiÃÕÌ}ÊÊÀ}>VÉÀ}>VÊ membrane development within one hour. They have also achieved adhesion of the inorganic intermediate layer onto a polymer support. The team, which has emphasised the membrane’s broader separation applications in its reports, received funding for the project in October 2011, and presented its first results at the NETL Carbon Capture and Storage meeting, which was held in July, 2012. The promising results follow the previous success the team had in making continuous,
intact inorganic layers on polymer supports and developing new membrane-production techniques.
for controlling fouling is to prevent internal scaling and over-growth of bio-film on the membrane surface. J. Zhang, W.L.C. Loong, S. Chou, C. Tang, R. Wang and A.G. Fane: J. of Membrane Science 403–404 8–14 (1 June 2012). http://dx.doi.org/10.1016/j.memsci.2012.01.032
improvement in resistance against compaction, compared with neat membranes. Furthermore, the tensile strength of the membranes at the 2 wt% MWCNTs loading increased by over 97%, compared with that of the neat ones. S. Majeed, D. Fierro, K. Buhr, J. Wind, B. Du, A. Boschetti-de-Fierro and V. Abetz: J. of Membrane Science 403–404 101–109 (1 June 2012). http://dx.doi.org/10.1016/j.memsci.2012.02.029
Multi-walled carbon nano-tubes mixed polyacrylonitrile UF membranes In this study, hydroxyl functionalised multiwalled carbon nano-tubes (MWCNTs) were blended with polyacrylonitrile (PAN) to prepare ultrafiltration (UF) membranes using the phase inversion process. Three different concentrations of MWCNTs were used in the PAN – 0.5 wt%, 1 wt% and 2 wt%. The water flux of the membranes increased by 63% at the 0.5 wt% loading of MWCNTs, compared with the neat PAN membranes. The water flux decreased upon a further increase in the concentration of MWCNTs, but at 2 wt% loading it was still higher than that of the pure PAN membranes. The surface hydrophilic properties of the membranes was enhanced following the addition of MWCNTs, as observed by contact angle measurements. The enhanced hydrophilic properties might have an impact on the improved water flux. All the membranes showed a molecular weight VÕÌÊvvÊ 7 "®ÊvÊ>««ÀÝ>ÌiÞÊxäÊ}É mol. Surface pore size analysis by scanning electron microscopy (SEM) showed no significant difference in the mean pore size of the nano-composite membranes, compared with that of the neat membranes. The cross-section morphology was influenced by the introduction of MWCNTs – fewer, but enlarged macro-voids were observed, which was particularly prominent at a loading of 2 wt% MWCNTs. The membranes containing 2 wt% MWCNTs showed a 36%
Contacts: US Department of Energy, 1000 Independence Avenue SW, Washington, DC 20585, USA. Tel: +1 202 586 5000, www.fossil.energy.gov Membrane Technology and Research Inc, 39630 Eureka Drive, Newark, CA 94560, USA. Tel: +1 650 328 2228, www.mtrinc.com
Anti-fouling membranes prepared by electro-spinning polylactic acid containing biocidal nano-particles The authors of this study prepared nonwoven electro-spun polylactic acid (PLA) membranes containing functionalised sepiolite fibrillar particles (5 wt%). Biocidal activity was achieved by functionalising sepiolite fibres with Ag (26 wt%) and Cu (26 wt%), which were embedded in the fibre surface. Sepiolite particles were negatively charged in all cases – with zeta potential in the range of -15 mV to -37 mV – increasing their negative charge with pH. The membranes were bio-fouled in a cross-flow filtration device using model biofoulants, cultures of Saccharomyces cerevisiae (pH 4.5) and Pseudomonas putida (pH 7.5), which were pumped across the membrane vÀÊÓ{É{nÊ °Ê/ iÊ>ÃÃiÃÃiÌÊvÊ>VÌÛiÊ biomass was performed by measuring the concentration of adenosine-5’-triphosphate (ATP) in the used membranes. The results showed a significant decrease in the amount of surface ATP for PLA loaded with Ag and Cu functionalised sepiolite. The effect was particularly intense for Ag-sepiolite in contact with Saccharomyces cerevisiae, where the reduction amounted to 85% compared with neat PLA (control). This was attributed to the differences in ion availability as a function of pH and to the presence of chloride
Membrane Technology
9