Capture and storage of carbondioxide (CO
2) from fossil fuel fired power plants is drawing increasing interest as a potential method for the control of greenhouse gas emissions. An optimization and technical parameter study for a CO
2 capture process of the flue gas of a commercial gas power plant, based on absorption/desorption process with different solvents, using Aspen Plus has been performed. The optimization has the aim of reducing the energy requirement for solvent regeneration (which is high in a CO
2 sequestration by absorption and later desorption) and also the reflux ratio needed. The simulations have been carried out using the ASPEN PLUS process simulation software for CO
2 compositions in the flue gas. ASPEN PLUS optimizes the absorber in terms of the minimum height of the absorber, minimum solvent loading, packing segments that is required to get more capture efficiency with proper packing properties that are in built within the software. The simulations considered the flue gas from a 600 MW coal-fired power plant with a flue gas mass flow rate of 577 kg/s with a CO
2 mass fraction of 15%. The simulations have been carried out for an MEA-based absorption/desorption system (Kohl, 1997) and for various compositions of piperazine-promoted potassium carbonate (K
2CO
3/PZ) mixtures (Cullinane, 2005) which are more environmentally friendly than mono ethanolamine (MEA)-based systems. The desorber pressure has also been varied to reduce the overall heat duty of the stripper (desorber) system. The principal features of the computed absorption system are summarized in Table 1. It can be seen that for the same capture rate of CO
2 coming from the same power plant, the K
2CO
3/PZ with the desorber operating at 3 bar gives a significant reduction (~25%) of the reboiler heat duty. The size of the absorbption/ desorption is also reduced with the K
2CO
3-based system.
Table 1. Comparison of the principal features of the CO2 absorption system based on MEA and PZ-doped K2CO3
| Feature |
MEA based System |
K2CO3/PZ system |
|
|
|
|
|
| Solvent concentration (wt%) |
30 |
22.1/13.8 |
| CO2 capture rate (%) |
90 |
90 |
|
|
|
|
|
| Desorber pressure (bar) |
2.1 |
3.0 |
|
|
|
|
|
| Reboiler temperature (oC) |
128 |
125 |
|
|
|
|
|
| Solvent flow rate (m3 /tCO2 ) |
27.8 |
74.4 |
|
|
|
|
|
| Reboiler heat duty (GJ/t CO2) |
3.3 |
2.4 |
|
|
|
|
|
| Absorber Column height (m) |
18 |
12 |
|
|
|
|
|
| Absorber column diameter(m) |
11 |
12.7 |
|
|
|
|
|
