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Abstract The desalination through humidification-dehumidification (HDH) presents still a high energy-footprint but shows many unique attributes that pushed a recent revival of R&D for decentralized production of water. In this paper, a novel process scheme consisting of a multiple extraction humidification-dehumidification with vapour adsorption (HDHA) and brine recirculation is analysed. It works with bottom brine temperatures below the coldest heat source and direct recirculation. With respect to the common classification, the process can be considered a closed-air closed-water (CACW) HDH. The study of the degrees of freedom and the mathematical model for the sensitivity analysis are presented. Process simulation showed how to increase the performances above the GOR of 10 with multiple extractions. The basic design of a HDHA producing > 30 m3 day− 1 of distilled water, with higher performance (GOR of 7 and a RR of 50%) than the current state-of-the-art, is discussed. Furthermore, the paper reports the process scheme and the mathematical model of the adsorption unit integrated with the HDH, the breakthrough curves and the mass of sorbent needed to carry the novel process. The considerations here presented highlight the key benefits of the new process and bode well for its technological development.

The increasing demand for energy and commodities has led to escalating greenhouse gas emissions, the chief of which is represented by carbon dioxide (CO2). Blue hydrogen (H2), a low-carbon hydrogen produced from natural gas with carbon capture technologies applied, has been suggested as a possible alternative to fossil fuels in processes with hard-to-abate emission sources, including refining, chemical, petrochemical and transport sectors. Due to the recent international directives aimed to combat climate change, even existing hydrogen plants should be retrofitted with carbon capture units. To optimize the process economics of such retrofit, it has been proposed to remove CO2 from the pressure swing adsorption (PSA) tail gas to exploit the relatively high CO2 concentration. This study aimed to design and numerically investigate a vacuum pressure swing adsorption (VPSA) process capable of capturing CO2 from the PSA tail gas of an industrial steam methane reforming (SMR)-based hydrogen plant using NaX zeolite adsorbent. The effect of operating conditions, such as purge-to-feed ratio and desorption pressure, were evaluated in relation to CO2 purity, CO2 recovery, bed productivity and specific energy consumption. We found that conventional cycle configurations, namely a 2-bed, 4-step Skarstrom cycle and a 2-bed, 6-step modified Skarstrom cycle with pressure equalization, were able to concentrate CO2 to a purity greater than 95% with a CO2 recovery of around 77% and 90%, respectively. Therefore, the latter configuration could serve as an efficient process to decarbonize existing hydrogen plants and produce blue H2.