Operational strategy of pre-cooling process of CO2 storage tank in CCS ship transportation using model-based optimization

• Published in: Chemical engineering research & design Vol. 109; pp. 770 - 779
• Main Authors: Lim, Yu Kyung, Lee, Seok Goo, Ko, Minsu, Park, Kunyung, Lee, Jong Min
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2016
• Subjects: CO2 carrier; Model predictive control; Pre-cooling process; CO2 carrier; Model predictive control; Pre-cooling process
• ISSN: 0263-8762
• DOI: 10.1016/j.cherd.2016.03.030

[Display omitted] •A dynamic model of the pre-cooling process of cryogenic CO2 tanks is developed.•Optimal control input sequences are obtained by the linearized MPC.•The terminal penalty is calculated by the modified Lyapunov stability condition.•Input sequences are affected by the value of the terminal penalty. CO2 storage tanks must be cooled before loading cryogenic liquid CO2 to prevent physical and thermal damage to the tank wall. This pre-cooling process gasifies a fraction of the liquid CO2 cargo and injects the resulting gas into the storage tank until the tank reaches the target temperature of 243.15K and pressure of 500kPa. In this paper, we propose a model predictive control approach for optimizing the injection flowrate of CO2 gas to reduce the loss of liquid CO2 cargo and CO2 capturing and compression cost. First, the process is mathematically formulated into a nonlinear multi-input-multi-output (MIMO) gas-phase system in which the injection mass flowrate and the outlet purging mass flowrate of CO2 gas act as control inputs. Then, a finite-horizon linearized model predictive control (MPC) scheme is designed to make the tank system reach the target state within 24h with a maximum cooling rate of −10K/h. A terminal penalty is suboptimally approximated by solving a modified discrete Lyapunov stability condition. The performance of the proposed method in optimizing the pre-cooling process is illustrated with example case studies based on the SIMULINK environment in MATLAB R2015a.