In this work, plantwide control of an absorption/stripping CO 2 capture process using monoethanol-amine was investigated using dynamic simulation. In this system, CO 2 removal ratio is influenced by operating variables such as lean solvent rate and lean solvent loading, which is in-turn determined by reboiler duty in the stripper. Moreover, we found that the long-term stability of the system cannot be achieved unless the water balance is properly maintained. Hence the following control structure was proposed. In this scheme, the CO 2 removal target is guaranteed using the lean solvent feed rate to the top of the absorber column. The overall water inventory was maintained by controlling the liquid level in the reboiler of the stripping column using makeup water. In order to operate the process with an appropriate lean solvent loading, the temperature at the bottom of stripper is controlled by the reboiler duty. This control structure was tested by disturbances involving inlet flue gas flow, CO 2 concentrations, and H 2 O concentrations as well as changes in removal targets. Dynamic simulations showed that the system can achieve removal targets and stabilize quickly while keeping optimum lean loading constant. To ensure minimum energy consumption, optimizing control can be carried out by adjusting the set point of the reboiler temperature.

About 20% power output penalties will be incurred for implementing CO 2 capture from power plant. This loss can be partially compensated by flexible operation of capture plant. However, daily large variations of liquid and gas flows may cause operation problems to packed columns. Control schemes were proposed to improve the flexibility of power output without causing substantial hydraulic disturbances in capture plant is presented. Simulations were implemented using ASPEN Plus. In varying lean solvent flow strategy, the flow rate of recycling solvent was manipulated to control the CO 2 capture rate. The liquid flow of the absorber and gas flow of the stripper will vary substantially. In an alternative strategy, the lean solvent loading will be varied. Variation of gas throughput in the stripper is avoided by recycling part of CO 2 vapor to stripper. This strategy provided more stable hydraulics condition in both columns and is recommended for flexible operation.

Amine scrubbing is the most mature CO2 capture technology for fossil fuel power plants, but the energy use for CO2 regeneration and compression will be 20 to 25% of the power plant output. The objective of this work is to develop alternative stripper configurations that reduce the energy use of CO2 capture. The advanced stripper configurations were modeled and optimized using Aspen Plus. Total equivalent work was used as an indicator of overall energy performance accounting for reboiler duty, compression work, and pump work. The rich exchanger bypass recovers stripping steam heat by using an exchanger. To get better energy performance, this strategy was applied to advanced configurations including a reboiler-based stripper, an interheated stripper, and a flash stripper. Both 9 m monoethanolamine (MEA) and 8 m piperazine (PZ) were investigated. The best energy performance was obtained from the stripper with a warm rich bypass and a rich exchanger bypass, which provides 10% less equivalent work for PZ and 6% less for MEA compared to the simple stripper. A flash stripper with a warm rich bypass and rich exchanger bypass uses 9% less energy with PZ and 5% less with MEA. With the warm rich bypass and rich exchanger bypass, MEA can provide 8% less equivalent work at 135 °C with acceptable thermal degradation.

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