Offshore Hydrogen Production Enables Far Offshore Wind Development
The accelerated deployment of renewable wind sources far offshore creates challenges in transporting large amounts of energy. An alternative being considered currently is energy transport through molecules in the form of hydrogen (H2). The objective of the PosHYdon project, the first offshore hydrogen production plant, whose conception and development are detailed in the complete paper, not only is to build up experience with the production of H2 in an offshore environment, but also will be a test platform for innovative power-to-gas (P2G) technologies and integrated systems.
The industry requires the ability to test system concepts in a realistic environment on a pilot-scale size. While several units up to 10 MW are being tested onshore, existing electrolyzer technology to convert power to H2 has not yet been applied offshore. However, many suppliers are developing innovative concepts and are scaling up to larger units. It has been estimated that at least 1 MW of electrolyzer capacity can be placed on an offshore platform with existing technology.
The detailed project aims to realize the first offshore P2G pilot, featuring the following specifications:
Located offshore in the Dutch sector of the North Sea
Minimum total electrolyzer capacity of 1 MW and 200-Nm3/hr production of H2
Proton exchange membrane (PEM) electrolyzer technology
Reverse-osmosis (RO) desalinization technology
Variable renewable power from shore (as a precursor to offshore wind)
Eventually, the offshore pilot is envisioned to perform several functions, including the following:
Demonstrate offshore system integration and the reuse of existing infrastructure
Gather experience with the production of H2 offshore, thereby derisking future developments
Determine the long-term performance of offshore P2G in terms of efficiency, performance degradation, and operational cost
Determine the dynamic load response of electrolyzer technologies
Evaluate the operational, inspection, and maintenance requirements of offshore P2G
Become a test center for P2G technologies offshore
Gain insight into H2 admixing in natural-gas streams and effect on industrial applications
To select a candidate platform for the pilot, the project team proposed technical and economic criteria. Because of limited space on the platform, the size of the electrolyzer was important, but also its weight because the crane on the platform has limitations. A list of the criteria was composed and the criteria were ranked. After platform selection was complete, validation was performed to ensure that no criteria had been overlooked. Tables 1 and 2 of the complete paper provide a list of technical and economic criteria for the selection of the electrolyzer systems for offshore installation.
Design of the Pilot Installation
The design is aimed at an electrolysis-based H2 production system installed on an existing offshore platform (Q13a, operated by Neptune Energy). The hydrogen produced by the electrolyzer will be injected into the two-phase (natural gas and crude oil) production stream from the platform and transported to the nearby P15 platform (operated by TAQA Energy). The natural gas with the blended hydrogen will be separated from the oil on the P15 platform and transported to shore through an export pipeline. The percentage of hydrogen in the natural gas is acceptable for the onshore distribution grid.
Q13a Description. This platform was installed and commissioned in 2013. The design oil flow is 15.000 B/D; design gas flow is 272,000 Nm³/d. At the time of writing, the platform is operating at approximately 30% capacity at a pressure of 30 barg. Q13 is the only platform in the Dutch sector powered from shore through a cable connection. The platform is normally manned and will stay in production until at least 2027.
System Concept Description. Purified water, produced from sea water using RO technology, is used as feedstock in the water-electrolysis process. The main product is H2, which will be injected into the oil and gas export pipeline toward the P15 platform. Stringent regulatory constraints apply to the design and operation of such a system, as well as to the method of hydrogen export.
The pilot system on the Q13A platform will comprise a water-electrolysis system and all the utilities and auxiliary equipment required for this process (i.e., a water-treatment unit; a power-supply system; a heating, ventilating, and air-conditioning unit; and nitrogen for purging). The process consists of the following steps:
Seawater is pumped directly from the sea using a water pump already installed on the Q13A platform.
Seawater is passed through a backwash filter to remove solids.
Demineralized water will accumulate in a buffer vessel, used to balance the intermittent demand from the electrolyzer and avoid frequent cycling of the desalination RO unit.
Demineralized water from the buffer vessel is pumped to the electrolyzer system, which contains a second water-purification unit comprised of a finer RO unit and an ion-exchange unit.
The purified water is now of sufficient quality for water electrolysis using a PEM stack.
Electrolysis essentially consists of the electrolyzer stack, which uses electricity to split water into oxygen and H2; subsequent separation steps; and a cooling system to remove residual heat from the process.
H2 from the electrolyzer is injected into the export oil and gas pipelines.
Nitrogen is stored near the electrolyzer in high-pressure cylinders and available for instrumentation and for purging the system.
In addition to the design and installation of the first electrolyzer to be operated on an offshore platform, a test program outlined in the complete paper is proposed for the demonstration system. This is intended to obtain as much information as possible from the completion of the pilot project, which will support future developments. This work package covers the proposed test strategy for the system, separated into four sections: acceptance/commissioning tests (onshore), demonstration of safety and reliability (on- and offshore), system-flexibility testing (on- and offshore), and long-term monitoring (offshore).
Admixing of H2 With the Hydrocarbon Stream
The Q13a platform has been producing oil and gas since 2013, and the hydrogen will be produced while oil and gas production will continue. Because the PEM electrolyzer will be operating at high pressures of approximately 30 bar, the produced hydrogen stream will commingle with the hydrocarbon stream to the P15 platform. The existing 8-in. pipeline connection between Q13a and P15 is a multiphase flow pipeline that will carry a maximum of 10% H2 in the gas stream at full capacity of the electrolyzer. At the P15 platform, the gas will be separated from the multiphase flow stream and commingled with other natural-gas streams from other reservoirs connected to P15. The H2 content will thereby reduce to approximately 1% at maximum.
Over the long term, the objective is to scale up the technology to a scale relatable to far-offshore wind parks currently under development and planned beyond 2025. These are planned to handle up to 1 GW each, with individual wind turbines of 12-MW power currently under test in Rotterdam.
The next phase in the scaling up of offshore H2 production will be to fit it on an existing offshore installation on the order of 10 MW, assuming the current footprint and weight per MW power. It is expected that the industry will drive the development of electrolyzers toward a smaller footprint and weight-per-MW power, including a capital-expenditure reduction from 1 million Euro/MW toward 300,000 Euro/MW in 2030. This can be realized by standardization and upscaling of the electrolyser stack and optimized balance of the plant.
The maximum power to an H2 unit on an existing offshore installation that has stopped production of oil and gas may be limited to approximately 250 MW in the current estimation of reduction of footprint and weight. The prerequisite for this development is that oil and gas platforms will have to be electrified in the near future to ensure availability of electricity. Ten to fifteen platforms in the Dutch part of the North Sea are currently estimated to be suitable for hydrogen production.
The next step in scaling up toward 1 GW will likely be developed on dedicated offshore hubs (energy islands or floating hubs).
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