## 2 Dynamic Model Configuration for the CO2 Capture Process  
This section presents the dynamic model of an MEA-based post-combustion CO2 capture plant for a 1 MWe power plant, which is used as the simulation platform in this study. All of the process modules are developed using the gCCS toolkit, which can provide high-fidelity models for the MEA-based CO2 capture process. The gCCS, developed by the process systems enterprise (PSE, London, UK) company, is professional software used in studying the dynamics of amine-based post-combustion CO2 capture processes [36]. The process topology in gCCS is presented in Figure 1, which describes the major processes within the MEA-based post-combustion CO2 capture system. Before decarbonization, the flue gas from the power plant is firstly desulphurized and denitrified. The treated flue gas is then cooled to 305-315 K before entering the bottom of the absorber. The flue gas and lean MEA are introduced counter currently into the absorber such that the CO2 can be sufficiently removed. After that the flue gas, mainly consisting of water and nitrogen, is emitted to the atmosphere, and the lean MEA becomes rich MEA. After the absorption reaction in the absorber, the rich solvent is further heated in a cross-heat exchanger by the hot lean MEA from the reboiler. Thereafter, the rich MEA enters the stripper and releases a part of the captured CO2. In the stripper, the energy required for releasing the CO2 is provided by the high temperature gas from the reboiler. Finally the rich MEA is sent to the reboiler and heated up to 380-390 K by the steam extracted at the crossover pipe between the intermediate and low pressure steam turbine in the power plant [15]. In this way, the remaining captured CO2 is released. The released gas from stripper is condensed in the condenser to obtain pure CO2 gas. The CO2 capture plant in this paper is designed for a 1 MWe coal fired power plant, which can generate as much as 0.13 kg/s flue gas with 25.2 wt % CO2 content at the 100% load condition. The established capture plant model is valid when the power plant operates between 40% and 100% load. The gCCS models of absorber and stripper column are developed based on the two-film theory, while the reboiler and the condenser models are developed using the lumped parameters approach. In the gCCS models, the following assumptions are made:  
1. All the chemical reactions are in equilibrium state. 2. The pressure drop along the column is linear. 3. The holdup in the vapor balk and the solvent degradation are neglected. Figure 1: Monoethanolamine (MEA)-based post-combustion CO2 capture plant topology. The phase at the interface between liquid and vapor films attains equilibrium. The bulks, films, and interface of liquid and vapor in the packed columns are shown in Figure 2. The key dynamic equations of the packed column are presented as follows. The mass and energy balance of the liquid bulk can be described using differential equations [2]:  
\[\frac{dM_{i}}{dt}=\frac{-1}{L\cdot A}\frac{\partial F_{t}^{L}}{\partial y}+N_{i }\cdot Sp\cdot\omega\cdot MW_{i} \tag{1}\]  
\[\frac{dU}{dt}=\frac{-1}{L\cdot A}\frac{\partial F_{H}^{L}}{\partial y}+Sp \cdot\omega\cdot\left(H_{liq}^{cond}+H_{liq}^{conv}+H_{abs}\right)+HL \tag{2}\]  
where \(M_{i}\) is the \(i\)-th component hold up, \(L\) and \(A\) are the length and cross-sectional area of column section, \(F_{i}^{L}\) is the liquid component mass flow along the axis of the column, \(N_{i}\) is the molar flux to and from the liquid bulk, \(MW_{i}\) is the molecular weight, \(Sp\) is specific area, \(\omega\) is the wetted area ratio, \(U\) is the energy hold up, \(F_{H}^{L}\) is the energy flow along the axis of column, \(H_{liq}^{cond}\), \(H_{liq}^{conv}\), and \(H_{abs}\) are the heat fluxes of liquid conduction, convection, and chemical reactions at the liquid film-liquid bulk interface, respectively, and \(HL\) is the heat loss to the environment.