Exergy Analysis of Large-Scale Hydrogen Transportation using Several Types of Hydrogen Carriers

Abstract

A method to evaluate the efficiency of hydrogen transportation systems is proposed. Three major types of long-distance hydrogen carrier, organic chemical hydride, ammonia, and liquid hydrogen, are evaluated with the exergy efficiency as a criterion. In addition, exergy loss resulting from gas compression for road haulage is examined. Efficiency is expressed in terms of the ratio of net reserved exergy in the carrier to chemical exergy of hydrogen. The examined carriers would be normally expected to lose around 40 to 50% of exergy during modification processes (hydrogenation, dehydrogenation, and liquefaction) and to lose 2.5 to 10% during long-distance transportation. With the exergy consumption accruing from compression for local delivery and filling included, which comprise another 17% of losses, depending on the type of carrier, around half or more of the chemical exergy is found to be lost in the whole transportation system, based on the current technologies. In order for hydrogen to be an efficient medium as an energy carrier, it is necessary to recover unused exergy generated in the system, which would improve efficiency by 10% to more than 30%.