2021 Annual Meeting
(354m) Targeting the Minimum Cost of Membrane Systems for CO2 Capture
Membrane-based separation processes are considered to be an attractive option for CO2 capture. Recently, many studies have focused on the feasibility of membrane systems (such as using multi-stages, changing operating temperature, and membrane materials). However, there is a lack of systematic methods to evaluate different processes in terms of cost. The reason lies in the highly nonlinear relationship between different equipment variables in the system, which leads the corresponding mathematical model hard to solve. In this paper, we propose a new strategy to efficiently evaluate the minimum cost of different membrane systems while ensuring the model's accuracy. Based on the idea of divide and conquer, we deconstruct a membrane system into two parts: membrane units and a work and heat exchanger network (WHEN) and connect the two parts using operating variables of membranes (temperature, pressure, and area). In this way, we can apply the characteristics of each part to calculate and optimize. For membrane units, the selectivity and permeability, and membrane costs can be determined when the operating variables are fixed, thereby obtaining the flowrates and component concentrations of process streams in the system. For the WHEN, it is an optimization problem to determine its minimum cost, including the capital cost of heat exchangers and pressure equipment and the operating cost of hot/cold utility and electricity. The problem can be solved to globally optimal using our problem-specific algorithm. Therefore, we can determine the whole system's cost for a fixed set of operating variables of membranes. Using a derivative-free algorithm (e.g., genetic algorithm), the optimal operating variables and the corresponding minimum cost of membrane systems can be obtained. Several examples are presented to illustrate our strategy's performance. Compared with previous studies, this work has several contributions to the problem of membrane systems for CO2 capture: (1) We propose a systematic method to evaluate the minimum cost of membrane systems. (2) Membrane unis, pressure equipment, and heat exchanger networks are synthesized simultaneously in the method. (3) The PR-EOS is implemented in the model to ensure the method's accuracy. (4) Membrane temperatures and pressure are variable in the procedure of optimization calculation.