Post-combustion capture technology uses scrubbers to remove carbon dioxide (CO2) from the existing emissions using a solvent to absorb the CO2 from the gas. The captured CO2 is then heated to release a stream of pure CO2. Then the solvent is reused after the CO2 is extracted.
Constraints for retrofitting (adding the technology onto existing plants) with post-combustion technology include age, size, and space constraints (MIT, 2009). Old plants will likely not have the required sulfur dioxide (SO2) and nitrogen oxide (NOx) controls necessary for post combustion capture (MIT, 2009). The solvent will degrade in the presence of any SO2 or NOx, so these must be removed prior to CO2 removal with the help of other processes (Simbeck & Roekpooritat, 2009). Also, older plants will retire sooner, so retrofitting is undesirable (Simbeck & Roekpooritat, 2009). Additionally, the space required to retrofit a typical plant is approximately 6 acres (MIT, 2009). Issues with the existing plant layout may prevent retrofits from being the most cost-effective solution, and if a power plant has a low efficiency, the efficiency losses could make it uneconomical to maintain (MIT, 2009). There are other constraints that are minor in comparison to these.
CO2 Reduction: (Simbeck, 2009a)
Adding post-combustion capture technology to add to existing plants (retrofit) could reduce CO2 emissions by 86.3%.
Building new plants with post-combustion capture technology could reduce CO2 emissions by 89.5%.
Advantages: (Herzog, 2009)
- Implementation of post-combustion capture does not require deconstruction of existing plants.
- Malfunctions do not affect plant operations and post-combustion capture equipment may be turned off if necessary for maintenance purposes.
- Start up costs are high (Simbeck, 2009b).
- Post-combustion capture has not yet been demonstrated on a large scale (MIT, 2009).
- The toxicity of the amine based solvents currently used is in question because some amine based solvents are known to be toxic to humans (MIT, 2009).
Efficiency Losses: (Simbeck, 2009a)
- With this technology, a retrofitted plant's efficiency will decrease from 33.6% to 24.7%.
- With this technology, a new plant's efficiency will decrease from 33.6% to 30.9%.
Cost Estimates: (Simbeck, 2009a).
- $528 million to retrofit an average 500MWe plant
- $1,765 million to build an average 500MWe plant