Abstract
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.
Highlights
Because of the constantly rising and unabated greenhouse gas emissions, of which the main constituent is carbon dioxide, the world is experiencing the detrimental effects of climate change
In this study we overcame for the first time the above limitations by designing and numerically investigating a vacuum pressure swing adsorption (VPSA) process capable of capturing CO2 from the pressure swing adsorption (PSA) tail gas of an industrial steam methane reforming (SMR)-based hydrogen plant equipped with a conventional single stage high temperature water gas shift (WGS) reactor
These operating parameters have been extensively evaluated in the literature for CO2 capture processes by VPSA technology [11,12,13,22]
Summary
Because of the constantly rising and unabated greenhouse gas emissions, of which the main constituent is carbon dioxide, the world is experiencing the detrimental effects of climate change. A great deal of research and development has been carried out into low-carbon alternatives to fossil fuels, one of which is represented by hydrogen [2]. Low-carbon hydrogen is useful in decarbonizing sectors with hard-toabate emission sources, such as the refining, chemical and petrochemical industries, and in providing flexible energy across power, heating and transport sectors. Despite its great potential, several challenges need to be solved before hydrogen can be adopted as a common low-carbon energy carrier such as a well-planned synergy among production, transmission, storage and distribution
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