Thermodynamic analysis of low-temperature carbon dioxide and sulfur dioxide capture from coal-burning power plants

Abstract

We discuss the possibility of capturing carbon dioxide from the flue gas of a coal-fired electrical power plant by cryogenically desublimating the carbon dioxide and then preparing it for transport in a pipeline to a sequestration site. Various other means have been proposed to accomplish the same goal. The problem discussed here is to estimate the "energy penalty" or "parasitic energy loss,' defined as the fraction of electrical output that will be needed to provide the refrigeration and that will then not be deliverable. We compute the energy loss (7.9-9.2% at 1 atm) based on perfect Carnot efficiency and estimate the achievable parasitic energy loss (22-26% at 1 atm) by incorporating the published coefficient of performance values for appropriately sized refrigeration or liquefaction cycles at the relevant temperatures. The analyses at 1 atm represent a starting point for future analyses using elevated pressures.

A preliminary investigation of cryogenic CO2 capture utilizing a reverse Brayton Cycle

“…In summary, modifying the process described by Swanson et al [14] by simply increasing the flue gas pressure increases the associated energy penalty. However, a pressurized flow stream provides the potential for energy recovery by expansion through a turbine.…”

“…Except that properties of CO 2 and SO 2 below their respective triple points are determined as described in Swanson et al [14] . The simulation incorporates three primary features: 1) accurate thermodynamic and transport properties for each of the flue gas components 2) the compression and expansion processes for the gas mixture, and 3) heat exchanger design calculations.…”

“…In the recent work by Swanson et al [14] ., the possibility of capturing the pollutants (including CO 2 , NO x , SO x ) from the flue gas of a coal-fired power plant by cryogenic de-sublimation was analyzed from a thermodynamics perspective. The computed energy penalty for an ideal refrigeration cycle cooling a 1 atm effluent is found to be 7.9~9.2% based on the Carnot efficiency for the ideal refrigerator.…”

“…The computed energy penalty for an ideal refrigeration cycle cooling a 1 atm effluent is found to be 7.9~9.2% based on the Carnot efficiency for the ideal refrigerator. Using a reasonable figure of merit (34% of Carnot) associated with real industrial refrigeration systems operating at the same conditions, results in an estimated energy penalty of about 22~26% [14] . As reflected in the phase diagram of CO 2 , the sublimation temperature increases as the pressure increases, and the refrigeration energy could be expected to decrease if the pressure of the flue gas is increased.…”

“…In order to capture 90% of the CO 2 , in the gas mixture into its liquid form, the process consumes about 0.395 MJ per kg of CO 2 with a resulting CO 2 purity of over 99% [13] . The advantages of cryogenic CO 2 capture techniques, as readily recognizable from the above examples, are: (1) the energy penalty of solvent regeneration and generated pressure drop can be neglected [4][5][6][7][8][9][10][11][12][13] ; (2) CO 2 can be captured in the liquid or solid phase, enabling compression without the huge energy consumption associated with gaseous compression, and providing a convenient means for storage and transport [4][5][6] ; (3) the compression, expansion and refrigeration technologies in the cryogenic CO 2 capture system are all relatively mature industrial processes, and can be easily utilized on an industrial-scale [10,13] ; (4) various refrigeration byproducts will be produced in some systems, such as high purity N 2 , and these can reduce the operation cost of the plant [14] . Nevertheless, to extract CO 2 from the other components in the flue gas (typically as N 2 , CO 2 , H 2 O, NO x , SO x ), a very low-temperature is required, resulting in the following problems [4][5][6][7][8][9][10][11][12][13] : (1) a large amount of energy is consumed for the refrigeration, leading to a high energy penalty for capture, and the process covers a large range of operating conditions from normal to supercritical states; (2) in the anti-sublimation processes, CO 2 will be frozen on the cold surfaces of the flow channels or heat exchangers, potentially causing several operational problems, such as plugging; (3) for the pre-combustion power plant and the oxy-fuel power plant, a large amount of additional energy is consumed in the hydrogen production or air separation unit; (4) acidic gas, such as NO x , SO x , may damage the devices, and shorten their operational life time.…”