Energy-Transition Options for Offshore Vessels

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 31800, “Energy Transition Options for Offshore Vessels,” by Jeroen Hollebrands, Benny Mestemaker, and Jan Westhoeve, Royal IHC, et al. The paper has not been peer reviewed. _ A future offshore fleet must comply with emissions regulations and policies that will become increasingly stringent. Making the right decisions with regard to emissions-reduction technologies and preparing vessels for future fuel options to keep the vessels compliant over time is, therefore, of great importance. The cable-lay vessels (CLV) used as a basis for the analysis presented in the complete paper are designed to meet such requirements. The authors highlight types of fuels and drive systems and the consequences of different combinations thereof on vessel design and operational profile. Alternative Fuels To Reduce Emissions Several alternative fuels are under consideration to replace fossil fuels currently used in the maritime sector. These include the following: - Liquefied natural gas (LNG) - Methanol - Ammonia - Hydrogen (compressed, liquefied, or in a storage medium) Design Approach for Zero-Emission Vessels The drive system of any zero-emission vessel requires four changes to integrate alternative fuels and prime movers effectively from a system-integration perspective: operational-profile design, electrification, hybridization, and modularization. - The operational profile defines the activities and operational demands of a specific vessel. - Electrification is necessary for the application of novel prime movers such as fuel-cell systems. Most CLVs already are equipped with a diesel electric configuration. - Redundancy of the prime movers leads to more engines online than are necessary. This is where hybridization comes into play because an energy-storage system can be used as a spinning reserve. - Modularization of drive systems provides flexibility to optimize the drive system for each task the work vessel must perform. Prime-Mover Technology for Zero-Emission Vessels The prime movers considered for future maritime application can be divided into internal combustion engines and fuel cells. Fuel cells generally are more efficient than engines and produce fewer emissions because the fuel is oxidized in an electrochemical process and not combusted at higher temperatures. However, fuel cells come at the cost of a slower transient response and have a lower tolerance for fuel impurities. In the complete paper, the following three fuel cell types are stipulated for use in maritime applications: - The low-temperature polymer electrolyte membrane fuel cell (LT-PEMFC) operates at 65–80°C with a high power density and good load-following capabilities but requires high-purity hydrogen because of its sensitivity to carbon monoxide. - The high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) operates at 140–160°C with a better tolerance for fuel purity but with a lower efficiency and a slower startup time and transient response than the LT-PEMFC. - The solid oxide fuel cell (SOFC) operates at relatively high temperatures of 500–1000°C, a trait that enables integration with internal fuel processing and waste-heat recovery. Despite their fuel flexibility and electrical efficiencies up to 65%, SOFC products are still relatively expensive, large, and heavy. In addition, cold starts are slow and load-following is sluggish to prevent thermal overloading and fuel starvation.