Thanks to its high gravimetric energy density and ease of transportation, ammonia is one of the best candidates as hydrogen carrier for long distance transfers, thus the demand and adoption of ammonia – in its "green” connotation, to avoid GHG emissions – is expected to rapidly increase in next years.
On large industrial scale, the most convenient and adopted production method is the Haber-Bosch process in which the synthesis of ammonia is obtained combining hydrogen and nitrogen as reagents, at right pressure and temperature, in presence of a catalyst. Green ammonia is obtained through the Haber-Bosch process as well, where the hydrogen is produced in green way, through electrolyzers fed by renewable power.
By switching from gray to green, the Steam Methane Reforming (SMR) process is avoided and, as consequence, the production of synthesis gas to feed the ammonia converter can occur at any pressure level. Without such pressure constraint, the most reasonable scheme appears to be in making synthesis gas at the pressure level of nitrogen coming from air separation unit (typically 7-9 bar). This method would in fact minimize the investment on compression in the front-end, avoiding any nitrogen booster and minimizing – or even eliminate, depending on electrolyzers technology – the investment in hydrogen compressors.
Nevertheless, such approach will move the challenge on the back-end portion of the process, jeopardizing the above benefit: the synthesis gas compression will jump from a traditional pressure ratio of 5-7 to 20-30, requiring additional compression units and relative drivers.
The aim of this paper is to show how an integrated development approach considering mechanical improvements, aerodynamic innovations, and new material validations, has changed the limits on hydrogen and syngas compression, reaching unparalleled pressure ratio capabilities and solving that typical “short-blanket dilemma” to obtain an overall plant optimization.