Modeling, Simulation and Optimization of Absorption, Membrane and Adsorption-Based CO2 Capture for Variable Feed CO2 Concentration and Feed Flow

Studies on four leading technologies for industrial CO₂ capture are performed. The technologies are MEA-based chemical absorption, multi-stage membrane, pressure swing adsorption (PSA) and vacuum swing adsorption (VSA). Each process is rigorously modeled, optimized, and energy integrated to capture and compress at least 90% of CO₂ from the feed for sequestration, over a range of feed CO₂ compositions and total feed flow rates. Emphasis is given on understanding and quantifying how the cost of CO₂ capture changes with CO₂ feed composition and flow rate of the gas mixtures coming from various chemical, power and heat generation plants. The novel features of this study include:

(i)        variation in feed CO₂ composition (ranging from 1 to 90%) and total feed flow rate (ranging from 0.1 to 10 kmol/s);

(ii)      CO₂ capture coupled with compression to 150 bar;

(iii)    rate-based modeling of the MEA absorption-based CO₂ capture coupled with heat integration;

(iv)    multi-stage superstructure model for CO₂ capture using membranes;

(v)      detailed and grey-box modeling of PSA and VSA alternatives for the adsorption-based CO₂ capture;

(vi)    cost-based comparison between the absorption, membrane, PSA and VSA-based CO₂ capture technologies for different emission scenarios; and

(vii)  explicit expressions for the investment and operating costs as function of feed CO₂ composition and total feed flow rate.

In this talk, we will discuss our approach towards the modeling, simulation and optimization of each of the four technologies. A rigorous simulation-based optimization model is proposed to determine the minimum annualized cost of the MEA-absorption process. The MEA-absorption process is further heat integrated through heat exchanger network optimization. A novel mathematical model is developed for the optimization of multi-stage and multi-component separation of CO₂ using membranes, which can be also used for a range of membrane-based gas separation applications. A 4-step cyclic process with multiple adsorption columns, purging and product recovery at moderate to low vacuum is configured for the PSA and VSA processes. A PDE-based non-isothermal adsorption model is used, which are fully discretized and optimized via a Kriging model.

We will also present a cost-based technology comparison over a range of feed gas compositions and flow rates. This may assist the decision-makers to select the cost-appropriate technology for CO₂ mitigation by taking the diverse emission scenarios into consideration. Furthermore, we will discuss an explicit input-output model for the investment and operating costs for the first time. This would provide a basis towards scaling up a CO₂ capture process, and lay the foundation for (i) process synthesis studies, and (ii) CO₂ supply chain network studies in the carbon management domain.