• Energy Research

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.

Water scarcity is a pressing global issue driving the need for efficient and sustainable water reuse and desalination technologies. In the last two decades, humidification–dehumidification (HDH) has emerged as a promising method for small-scale and decentralized systems. This paper presents a comprehensive review of recent scientific literature highlighting key advancements, challenges, and potential future directions of HDH research. Because the HDH process suffers from low heat and mass transfer, as well as thermodynamic limitations due to the mild operating conditions, this work indicates three main strategies for HDH enhancement: (1) Advanced Heat and Mass Transfer Techniques, (2) Integration with Other Technologies, and (3) Optimization of System Operative Conditions. Particularly for advanced HDH systems, the reference GOR values exceed 3, and certain studies have demonstrated the potential to achieve even higher values, approaching 10. In terms of recovery ratio, there appear to be no significant process constraints, as recycling the brine prepared in innovative schemes can surpass values of 50%. Considering electricity costs, the reference range falls between 1 and 3 kWh m–3. Notably, multi-stage processes and system couplings can lead to increased pressure drops and, consequently, higher electricity costs. Although consistent data are lacking, a baseline SEC reference value is approximately 360 kJ kg–1, corresponding to 100 kWh m–3. For comparable SEC data, it is advisable to incorporate both thermal and electric inputs, using a reference power plant efficiency of 0.4 in converting thermal duty to electrical power. When considering the utilization of low-temperature solar and waste heat, the proposed exergy-based comparison of the process is vital; this perspective reveals that a low-carbon HDH desalination domain, with II-law efficiencies surpassing 0.10, can be achieved.

AbstractThis study evaluated different configurations of post-combustion amine processes using 30wt% aqueous MEA solvent. The configurations were compared with respect to total energy consumption including thermal and electrical energy involved in its operation to capture 90% CO2 from an exemplary sub-critical PC-boiler power plant The improved amine processes reported in the literature were analysed and simulated using the Honeywell UniSim process simulator to evaluate their performance and it was suggested that they could be further improved by appropriate modifications. Simultaneous implementation of several improvement methods has been explored in order to reduce further the reboiler heat duty. Several alterations to the base configuration can achieve greater reduction in reboiler duty (or equivalent work) compared to simple modifications based on a single variation. The extent of energy saving must be evaluated carefully through the implementation of appropriate process simulations since we have shown that the overall effect is different from a simple sum of the saving effects estimated individually.

Adsorption refrigeration has become an attractive technology due to the capability to exploit low-grade thermal energy for cooling power generation and the use of environmentally friendly refrigerants. Traditionally, these systems work with pure fluids such as water, ethanol, methanol, and ammonia. Nevertheless, the operating conditions make their commercialization still unfeasible, especially owing to safety and cost issues as a consequence of the working pressures, which are higher or lower than 1 atm. The present work represents the first thermodynamic insight in the use of mixtures for adsorption refrigeration and aims to assess the performance of a binary system of ammonia and ethanol. According to the Gibbs’ phase rule, the addition of a component introduces an additional degree of freedom, which allows to adjust the pressure of the system varying the composition of the mixture. The refrigeration process was simulated with isothermal- isochoric flash calculations to solve the phase equilibria, described by the Peng-Robinson-Stryjek-Vera (PRSV) equation of state for the vapor and liquid phases and by the ideal adsorbed solution theory (IAST) and the multicomponent potential theory of adsorption (MPTA) for the adsorbed phase. In operating condenser and evaporator, pressure levels around atmospheric pressure can be achieved using an ammonia/ethanol mixture with a mole fraction of ethanol in the range of 0.70−0.75. A good agreement in the predictions of the adsorbed phase composition was also reported using the IAST and the MPTA methods.

: Climate change necessitates urgent actions to mitigate carbon dioxide (CO2) emissions from fossil fuel-based energy generation. Among various strategies, the deployment of carbon capture and storage (CCS) solutions are critical for reducing emissions from point sources such as power plants and heavy industries. In this context, cryogenic carbon capture (CCC) via desublimation has emerged as a promising technology. While CCC offers high separation efficiency, minimal downstream compression work, and integration potential with existing industrial processes, challenges such as low operating temperatures and equipment costs persist. Ongoing research aims to address these hurdles in order to optimize the desublimation processes for widespread implementation. This review consolidates diverse literature works, providing insights into the strengths and limitations of CCC technology, including the latest pilot plant scale demonstrations. The transformative potential of CCC is first assessed on a theoretical basis, such as thermodynamic aspects and mass transfer phenomena. Then, recent advancements in the proposed process configurations are critically assessed and compared through key performance indicators. Furthermore, future research directions for this technology are clearly highlighted.

Abstract Ionic liquids (ILs) have emerged as novel sorption materials capable to achieve exceptional water vapour uptake that is attractive for their use in heat transformation technologies. Water sorption equilibria on 2-hydroxyethyl-trimethylammonium acetate or choline acetate ([Cho][OAc]) were measured at eight different temperatures: 298.25, 303.25, 308.35, 318.55, 328.75, 333.85, 344.15 and 349.55 K. Equilibrium measurements were performed with a dynamic vapour sorption (DVS) system. With a relative humidity of around 90% a water uptake larger than 3.5 gW gIL−1 was observed for all the temperatures. The resulting type III isotherms were correlated with the Guggenheim-Anderson-de Boer (GAB) model as well as the Redlich-Kister (RK) excess Gibbs energy model. It was found that both models fit the experimental data with great accuracy and provide an appropriate description of the water sorption equilibria. The regressed parameters of the RK model were also employed to predict excess properties of the binary system. Moreover, a thermodynamic cycle was assessed and compared with sorbent benchmarks, highlighting a performance that makes the choline acetate/water pair a viable option in sorption chiller applications.

It was aimed to derive rigorous momentum and energy balance equations where the change of kinetic energy in both spatial and temporal domains of a fixed-bed adsorption column was newly taken into account. While the effect of kinetic energy on adsorption column dynamics is negligible in most cases, it can become more and more influential with an adsorption column experiencing a huge pressure drop or with the gas velocity changing abruptly with time and along the column. The rigorous momentum and energy balance equations derived in this study have been validated with two limiting cases: (1) an inert gas flow through a packed column with a very high pressure drop and (2) blowdown of an adiabatic empty column. The new energy balance including the kinetic energy effect paves a way for simulating with an improved accuracy a Rapid Pressure Swing Adsorption process that inherently involves a very high pressure drop along the column and requires very high pressure change rates for column blowdown and pressurisation.