PartagerICR2011 highlights: carbon capture and storage (CCS) perspectives
During ICR2011, a complete session was devoted to carbon capture and storage (CCS).
Berstad et al.(1) stressed that according to IEA, out of the targeted global annual CO2 emissions reductions – 50% by 2050 compared to 2005 levels –, CO2 CCS from power generation and industry is estimated being about 19% of the mitigation potential. Nekså et al. (2) gave an overview of current and possible application of refrigeration technologies within CCS and pointed out challenges encountered.
During ICR2011, a complete session was devoted to carbon capture and storage (CCS).
Berstad et al.(1) stressed that according to IEA, out of the targeted global annual CO2 emissions reductions – 50% by 2050 compared to 2005 levels –, CO2 CCS from power generation and industry is estimated being about 19% of the mitigation potential. Nekså et al. (2) gave an overview of current and possible application of refrigeration technologies within CCS and pointed out challenges encountered.
A major challenge in realising CCS is the related parasitic power consumption and costs. Current baseline technology for capture from coal based power production typically may reduce net power yield by about 25%, corresponding to a 12 %-points reduction in plant efficiency. The power is required mainly for CO2 capture and the compression for the subsequent transport.
A tremendous RD&D effort has therefore been initiated in order to increase efficiency and reduce
costs. As an example, the objective set by the EU-project DECARBit is to “contribute to improved and morecost efficient solutions aiming at zero-emission pre-combustion power plants by 2020 with a capture cost of less than 15 €/ton CO2”. Refrigeration technologies may play an important role in meeting the overall objective of the ongoing effort, both in increasing energy efficiency and reducing costs.
A wide range of CO2 capture technologies is currently being developed for short-, mid- and long-term deployment. Examples are: chemical solvents, physical solvents, solid sorbents, membranes and low-temperature/cryogenic separation.
The main CO2 capture routes within power production can be divided into post-combustion, precombustion and oxy-combustion, including chemical looping combustion. Capture from industrial point sources may often be compared to the boundary conditions of post-combustion capture.
Post-combustion capture from power production is associated with capture from flue gases containing relatively low concentrations of CO2 at pressures close to atmospheric. The most commonly considered capture technology for post-combustion capture is chemical absorption using amines which is considered commercially available but several of the amines have however undesirable environmental effects. The most commonly evaluated low temperature technique for atmospheric flue gas is freezing out the CO2 from the flue gas at atmospheric pressure, often denoted anti-sublimation. A big challenge for capture from flue gases at atmospheric pressure is the relatively low temperatures required before CO2 will undergo a phase change from gas to solid form, i.e. antisublimation. For pure CO2 the freeze-out will occur at -73°C. In flue gas as a mixture with other components, however, temperatures below -100°C may be required in order to transfer a sufficient part of the CO2 to solid form.
Pre-combustion capture is related to capture of the CO2 before combustion. H2 from a shifted synthesis gas is used as fuel in a gas turbine. The syngas is produced by gasification of coal or reforming of natural gas. Gasification and oxygen blown reformers require oxygen from an air separation unit (ASU) as input. The conventional technology for air separation utilizes cryogenic separation. Alternative technologies under consideration are membranes and possibly adsorption. Cryogenic separation involves distillation and related auxiliary cooling duties. Separation of CO2 from the shifted synthesis gas is the other process step where refrigeration technologies may be utilized in pre-combustion capture. Commonly considered technology for the capture in an integrated gasification combined cycle is physical sorbents, however low temperature distillation concepts show very promising possibilities for reducing the specific power required for the capture and compression of CO2. An important advantage of capturing at low temperature is that the CO2 is captured in liquid form. The subsequent pressurisation to transport pressure may therefore be performed by pumping, rather than energy consuming compression of gaseous CO2.
In oxy-combustion, fuel is burnt with oxygen instead of air. In this way high CO2 concentrations in the flue gas can be obtained. After condensing out the water content in the flue gas, CO2 is captured from the remaining flue gas mixture, mainly CO2 and non-condensable gases, before pressurization for transport in a compression and purification unit (CPU). The oxygen used in the fuel combustion is produced in an ASU. Low-temperature technologies are viable options for the ASU and for the CO2 purification of the CPU.
Nekså et al. conclude that by adaption of improvement possibilities given by increased component efficiencies, better integration and gains made possible due to plant scale-up, it should be possible to retain and possibly improve the strong position of refrigeration technologies. Several important RD&D tasks are still to be done in order to realise CCS in a cost efficient way.
(1) Potential for low-temperature concepts in different CCS applications, Berstad et al.
(2) Overview of current and possible applications for refrigeration technologies within CCS, Nekså et al.
Berstad et al.(1) stressed that according to IEA, out of the targeted global annual CO2 emissions reductions – 50% by 2050 compared to 2005 levels –, CO2 CCS from power generation and industry is estimated being about 19% of the mitigation potential. Nekså et al. (2) gave an overview of current and possible application of refrigeration technologies within CCS and pointed out challenges encountered.
A major challenge in realising CCS is the related parasitic power consumption and costs. Current baseline technology for capture from coal based power production typically may reduce net power yield by about 25%, corresponding to a 12 %-points reduction in plant efficiency. The power is required mainly for CO2 capture and the compression for the subsequent transport.
A tremendous RD&D effort has therefore been initiated in order to increase efficiency and reduce
costs. As an example, the objective set by the EU-project DECARBit is to “contribute to improved and morecost efficient solutions aiming at zero-emission pre-combustion power plants by 2020 with a capture cost of less than 15 €/ton CO2”. Refrigeration technologies may play an important role in meeting the overall objective of the ongoing effort, both in increasing energy efficiency and reducing costs.
A wide range of CO2 capture technologies is currently being developed for short-, mid- and long-term deployment. Examples are: chemical solvents, physical solvents, solid sorbents, membranes and low-temperature/cryogenic separation.
The main CO2 capture routes within power production can be divided into post-combustion, precombustion and oxy-combustion, including chemical looping combustion. Capture from industrial point sources may often be compared to the boundary conditions of post-combustion capture.
Post-combustion capture from power production is associated with capture from flue gases containing relatively low concentrations of CO2 at pressures close to atmospheric. The most commonly considered capture technology for post-combustion capture is chemical absorption using amines which is considered commercially available but several of the amines have however undesirable environmental effects. The most commonly evaluated low temperature technique for atmospheric flue gas is freezing out the CO2 from the flue gas at atmospheric pressure, often denoted anti-sublimation. A big challenge for capture from flue gases at atmospheric pressure is the relatively low temperatures required before CO2 will undergo a phase change from gas to solid form, i.e. antisublimation. For pure CO2 the freeze-out will occur at -73°C. In flue gas as a mixture with other components, however, temperatures below -100°C may be required in order to transfer a sufficient part of the CO2 to solid form.
Pre-combustion capture is related to capture of the CO2 before combustion. H2 from a shifted synthesis gas is used as fuel in a gas turbine. The syngas is produced by gasification of coal or reforming of natural gas. Gasification and oxygen blown reformers require oxygen from an air separation unit (ASU) as input. The conventional technology for air separation utilizes cryogenic separation. Alternative technologies under consideration are membranes and possibly adsorption. Cryogenic separation involves distillation and related auxiliary cooling duties. Separation of CO2 from the shifted synthesis gas is the other process step where refrigeration technologies may be utilized in pre-combustion capture. Commonly considered technology for the capture in an integrated gasification combined cycle is physical sorbents, however low temperature distillation concepts show very promising possibilities for reducing the specific power required for the capture and compression of CO2. An important advantage of capturing at low temperature is that the CO2 is captured in liquid form. The subsequent pressurisation to transport pressure may therefore be performed by pumping, rather than energy consuming compression of gaseous CO2.
In oxy-combustion, fuel is burnt with oxygen instead of air. In this way high CO2 concentrations in the flue gas can be obtained. After condensing out the water content in the flue gas, CO2 is captured from the remaining flue gas mixture, mainly CO2 and non-condensable gases, before pressurization for transport in a compression and purification unit (CPU). The oxygen used in the fuel combustion is produced in an ASU. Low-temperature technologies are viable options for the ASU and for the CO2 purification of the CPU.
Nekså et al. conclude that by adaption of improvement possibilities given by increased component efficiencies, better integration and gains made possible due to plant scale-up, it should be possible to retain and possibly improve the strong position of refrigeration technologies. Several important RD&D tasks are still to be done in order to realise CCS in a cost efficient way.
(1) Potential for low-temperature concepts in different CCS applications, Berstad et al.
(2) Overview of current and possible applications for refrigeration technologies within CCS, Nekså et al.