Optimal Capacity Design of Amine-Based Onboard Co2 Capture Systems Considering Flexible Ship Operations

Abstract

The International Maritime Organization has adopted a strategy aiming for net-zero greenhouse gas emissions from international shipping, prompting various mitigation technologies to comply with this strengthened strategy. Carbon capture technologies are increasingly being considered to satisfy the IMO strategy. In particular, amine-based capture technologies, which are emerging as the most mature option, have been proposed for ship applications. However, the conventional design approach for onboard carbon capture systems, which assumes a fixed high engine load (75–100%), does not reflect flexible ship operation in a low engine load range, leading to oversizing and unnecessary capital investment. This study designs MEA-based carbon capture systems with five different capacities (sizes) based on the exhaust gas conditions. The study investigates the off-design performance over the entire engine load range while maintaining the capacity of the capture systems at their design values. To identify the optimal capacity of the capture system, the off-design performance is applied to an actual sailing profile in order to quantify the energy requirement, potential CO2 reduction rate, and capture cost. The results show that smaller systems can reach a similar level of CO2 reduction as other larger systems while reducing capture costs. This means that it is possible to reduce capture costs by decreasing the capture capacity while maintaining the carbon reduction potential. The small capacity capture system also achieves a more competitive CO2 avoidance cost (235 € per tonne) compared to biofuel (304 € per tonne) for a similar CO2 avoidance rate (59%). Thus, this study demonstrates a new approach to the design of amine-based onboard carbon capture systems considering flexible ship operations and presents the potential of the decarbonization technology for shipping industry.

Keywords: Onboard carbon capture, MEA-based CO2 capture process, Off-design performance, Ship engine load profile, Techno-economic assessment