Application and Experience of Hydrogen Deoxidizers in Seawater Deoxygenation Systems

Abstract The scope of the research presented in this paper encompasses over 25 years of cumulative experience in employing hydrogen deoxidizers within water deoxygenation process systems. Seawater is injected into the system to strip the O2 from water by means of inert nitrogen gas. In these systems, the nitrogen stripping gas is circulated in a closed loop and regenerated over a chemical catalytic reactor, where a purity of at least 99.995 % is achieved. This paper presents empirical data derived from the operation of these systems. A test system has been purpose-built to leverage several years of experience gained from hydrogen-fueled water deoxygenation in analogous onshore systems, with the aim of making it applicable to a new seawater deoxygenation system. This system is designed to purify a nitrogen stream, which is utilized to remove oxygen from seawater. Consequently, the nitrogen stream initially contains oxygen, and it is reused for the deoxygenation process, necessitating the removal of oxygen. The elimination of oxygen occurs within the hydrogen deoxidizer by introducing hydrogen upstream of a reactor equipped with a palladium catalyst. Hydrogen and oxygen react to produce water. The gas stream is driven by a liquid jet compressor, and the research presents operational procedures encompassing the control of hydrogen levels in the gas stream, control system considerations, safety protocols, and the regulation of other process variables, such as temperature, both upstream and downstream of the reactor. Notably, nitrogen shares similar thermal properties as hydrogen, and the reaction characteristics within such a reactor closely resemble the reaction in deoxo-reactors for deoxygenation hydrogen in Alkaline hydrogen production by electrolysis. Results from hydrogen deoxidizer performance will be presented together with design considerations for generic hydrogen deoxo-reactors. Historically, this process has been driven by methanol offshore, and the paper will explore the feasibility of offshore on-demand hydrogen generation for the deoxo-reaction and evaluate alternatives for the supply of hydrogen such as storage solutions. The novelty of the research is the combination of hydrogen deoxo-reactors with other process streams in combination with the seawater deoxygenation process.