Ocean Thermal Plantships for Co-Production of Ammonia and Desalinated Water

Abstract

Abstract The world's oceans are the largest collector and storage of solar energy and have an enormous potential to supply the growing worldwide demand of ammonia and desalinated water. The general perception is that ocean energy is limited to only topical countries; therefore, the full potential of ocean energy for at-sea production of ammonia as the hydrogen carrier and desalinated water production has not been adequately evaluated. This study presents an updated analysis that shows the technical and economic viability of the ocean thermal plantships. This study is based on a detailed plantship design performed in 1980 by The Johns Hopkins University Applied Physics Laboratory in collaboration with industrial partners. This design has been fitted with an updated power system based on compact heat exchangers that have a proven manufacturability and performance history. The analysis shows promising favorable economics for at-sea production of ammonia and desalinated water by ocean-thermal plantships. In addition to the commodity value of ammonia as fertilizer and chemical feedstock, the potential use of ammonia as the hydrogen delivery systems is further supported by the established surface and ocean transportation systems. Achieving this goal of ammonia-based distributed power generation may take some time; however, there is significant near-term market opportunity for green-ammonia as fertilizer and hydrogen derived from renewable non-carbon sources in petrochemical and refining industries in California and the Gulf of Mexico States. Introduction Conventional petroleum, natural gas, and coal are the primary sources of energy that have underpinned modern civilization. Their continued availability in the projected quantities required and the impacts of emission of greenhouse gases (GHGs) on the environment are issues at the forefront of world concerns. New primary sources of energy are being sought that would significantly reduce the emissions of GHGs. One such primary source that can help supply energy, water, and ammonia fertilizer without GHG emissions is available in the heretofore unexploited thermal gradients of the tropical oceans. Among renewable energy options, ocean thermal energy provides a base-load supply of solar energy. The general perception is that ocean energy is limited to only tropical countries by providing electric power via cable. Therefore, the full potential of ocean energy for at-sea production of ammonia as the hydrogen carrier and desalinated water production has not been adequately evaluated. With the focused R&D by the US Department of Energy (DOE) and the Maritime Administration (MarAd) of Department of Commerce in the 1970's and 1980's, the technical risks and design uncertainties have been reduced to an acceptable level for commercial deployment of Ocean Thermal Energy Conversion (OTEC) plantships. However, due to cheaper fossil energy in 1970's and 1980's, further development of OTEC diminished to low-level developments. The present energy, environmental and economic conditions provide a Window of Opportunity for at-sea OTEC plantships for the co-production of ammonia and fresh water, and therefore, the near-term deployment of multiple OTEC plantships and their associated transport tanker fleets.