Analyzing the Potential of MCFC-based CO2 Capture and Storage Onboard Seagoing Vessels: A Techno-Economic Assessment

Abstract

Reducing carbon emissions from the naval shipping sector is crucial for lowering global CO2 levels. For complete decarbonization, transitioning to sustainable, non-carbon-based fuels is necessary. However, carbon capture onboard ships is gaining interest as a cost-effective intermediate solution. This thesis investigates the techno-economic potential of Molten Carbonate Fuel Cell (MCFC) based carbon capture (MCFC-OCC) on ships fueled by LNG, MDO, and HFO, building on previous work by Lukas Weimann and Matteo Gazzani. The study evaluates the effectiveness of MCFC-OCC systems in reducing CO2 emissions and their economic feasibility.

The MCFC-OCC system, designed in Aspen, was re-used and a techno-economic model was improved in Matlab, assessing not only an LNG carrier but also a container ship, oil tanker and bulk carrier operating on LNG, MDO, and HFO. The techno-economic feasibility was measured using Key Performance Indicators (KPIs): (equivalent) Carbon Avoidance Rate (eCAR) [%], Cost of Carbon Avoidance (CCA) [$/t], total CAPEX and yearly costs, total size, and deadweight loss. These KPIs were analyzed on both Tank-to-Wake (TtoW) and Well-to-Wake (WtoW) levels, including upstream emissions.

The MCFC-OCC system can produce power, potentially replacing auxiliary engines and removing methane slip from LNG-fueled engines. Effective matching of propulsion power to auxiliary load is crucial to avoid wasted energy. The system was optimized for the MDO case in terms of CAR and CCA by varying operational parameters, including cell voltage.

Results show the CAR and CCA are best for container ships, followed by LNG carriers. Container ships using HFO achieve the highest carbon utilization factor at 75%, with an eCAR (TtoW) of 82.68%. The MDO case, with an eCAR (TtoW) of 80.92%, incurs 17% lower yearly costs, resulting in a CCA of $88.46/t. The LNG case shows an eCAR (TtoW) of 76.29% with the highest CCA at $121.63/t, but could potentially achieve better results with further optimization.

Sensitivity analyses reveal that the LNG case is the least sensitive to fuel price variations, while the HFO case is more sensitive. Variations in MCFC costs and lifetime significantly impact the CCA. The MCFC-OCC system’s sensitivity to auxiliary load variations is more critical. The Paux/Pmain ratios for maximum CAR are 15% for LNG, 35% for MDO, and 39% for HFO. These findings suggest MCFC-OCC systems are particularly beneficial for ships with high auxiliary power demands, like container ships.

The full life cycle (Well-to-Wake) Carbon Avoidance Rate (CAR) decreases by 15-19% in the MCFC-OCC case compared to the Tank-to-Wake case due to higher upstream emissions from increased LNG use. When accounting for CO2 geological storage costs, the Well-to-Wake Cost of Carbon Avoidance (CCA) increases by $20 to $26 per ton.

Several limitations are acknowledged, including assumptions about complete fuel conversion and the need for facilities to handle and store captured CO2. Experimental validation with a pilot plant is necessary for further research, including assessing the impact of pollutants and considering cell degradation.

In conclusion, MCFC-OCC systems present a viable intermediate solution for reducing CO2 emissions in the maritime sector, particularly for ships with high auxiliary loads. Compared to MEA-based carbon capture systems, MCFC-OCC offers advantages by producing power without needing additional heat. This technology could serve as a transitional solution towards sustainable fuels, aligning with global maritime decarbonization goals.