The last 60 years has seen unprecedented groundwater extraction and overdraft as well as development of new technologies for water treatment that together drive the advance in intentional groundwater replenishment known as managed aquifer recharge (MAR). This paper is the first known attempt to quantify the volume of MAR at global scale, and to illustrate the advancement of all the major types of MAR and relate these to research and regulatory advancements. Faced with changing climate and rising intensity of climate extremes, MAR is an increasingly important water management strategy, alongside demand management, to maintain, enhance and secure stressed groundwater systems and to protect and improve water quality. During this time, scientific research—on hydraulic design of facilities, tracer studies, managing clogging, recovery efficiency and water quality changes in aquifers—has underpinned practical improvements in MAR and has had broader benefits in hydrogeology. Recharge wells have greatly accelerated recharge, particularly in urban areas and for mine water management. In recent years, research into governance, operating practices, reliability, economics, risk assessment and public acceptance of MAR has been undertaken. Since the 1960s, implementation of MAR has accelerated at a rate of 5%/year, but is not keeping pace with increasing groundwater extraction. Currently, MAR has reached an estimated 10 km3/year, ~2.4% of groundwater extraction in countries reporting MAR (or ~1.0% of global groundwater extraction). MAR is likely to exceed 10% of global extraction, based on experience where MAR is more advanced, to sustain quantity, reliability and quality of water supplies.@en

This paper addresses the uncertainty and variability in techno-economic studies of carbon capture technologies, based on a detailed comparison of the results of different studies on postcombustion CO2 capture with advanced amines, and on an in-depth uncertainty analysis using a combination of sensitivity and pedigree analyses. The results show that despite efforts to harmonize capital cost estimates, the capital cost results of the same PCC carbon capture systems can still show large (65%) differences. This uncertainty may simply be inherent to early stage cost estimates. Amongst the most important causes for the variability shown in this work are differences in equipment sizing methods and purchased equipment cost estimates. This capital cost variability only mildly propagates into the Levelised Cost of Electricity and Cost of CO2 Avoided, more so in case of low power plant utilisation scenarios. To enhance insight into these uncertainties and enable their communication, the paper argues to use in-depth uncertainty evaluation for early stage techno-economic studies. It suggests to complement current practice of sensitivity analysis with pedigree analysis and to combine the results of both analyses in diagnostic diagrams. This may lead to more informed interpretation of the results of techno-economic studies, and helps focus techno-economic research efforts towards the parameters that most influence final performance indicators.@en

Aqueous amino acid salt solutions that precipitate due to CO2 absorption are a relatively novel and promising class of solvents. Although the presence of solids in the process stream requires adequate measures related to slurry handling and crystallization control, precipitation also increases the solvent CO2 capacity and the energy performance of the stripper. By using an additional solid–liquid separation step to concentrate the slurry before it is sent to the stripper, known as the DECAB+ process, the energy performance can be further improved. Most of the current experimental work on these systems focuses on the amino acids taurine, α- and β-alanine, sarcosine, glycine, and proline, neutralized with equimolar amounts of potassium hydroxide. Investigated properties include the CO2 concentration at which precipitation is first observed, which is closely related to the solubility of the amino acid, the composition of the precipitate, and the CO2 absorption rate. The precipitate typically contains pure amino acids and/or bicarbonate, depending on the amino acid solubility. Shortcut process simulations have been used to estimate the energy performance of absorption processes using precipitating amino acids, so far focusing on 4M KOH + taurine (K-tau) and 4M KOH + α-alanine (K-α-ala) solutions. Specific regeneration duties below 2 GJ/ton CO2 seem possible for the DECAB+ process when using K-α-ala and lean vapor compressor (LVC). Compared to a conventional process using 30 wt % monoethanolamine and LVC, this corresponds to a reduction of 35% in the regeneration duty. Future research should focus on more-detailed process simulations, based on a predictive thermodynamic model that consistently describes the vapor–liquid–solid equilibria of the system. Demonstration of the DECAB+ process on a pilot scale is also highly recommended, with a special focus on the crystallization and slurry handling process steps and units@en

This work summarises the results of the design of novel separation processes for CO₂ removal from flue gas based on precipitating amino acid solvents. The processes here described (DECAB, DECAB Plus and pH-swing) use a combination of enhanced CO₂ absorption (based on the Le Chatelier;s principle) and / or enhanced CO₂ desorption (based on pH-shift), which contribute substantially to the reduction of regeneration energy. An evaluation of these processes has been developed based on literature data, thermodynamic principles and experimental data. As solvent example, the potassium salt of taurine was selected. The results show that these processes are environmentally friendly (no emissions to the air, lower ecotoxicity) and have lower energy consumption than conventional MEA. The DECAB Plus process has been identified as the option with lower energy consumption (66% of conventional MEA- ie ca 2.4 GJ/t CO₂). This study has established the potential of precipitating amino acids as an energy effective alternative to alkanol amines. The future work will focus on determining the cost of CO₂ avoidance and investigating other solvents that will further lead to benefits over conventional processes.

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CO₂ capture based on post-combustion capture has the potential to significantly reduce the CO₂ emissions from coal-fired power plants. However, this capture process reduces considerably the energy efficiency of the power plant. To reduce this energy penalty, this paper studies different post-combustion CO₂ capture process configurations combined with different levels of heat integration with the power plant. The cases studied were based on a 1070MW_e power plant connected to a demo size capture plant (250MW_e equivalent - approximately 1.1Mton CO₂ captured/year). The integral evaluation of the energy needed for the capture plant together with the electrical and heat integration with the power plant is a suitable methodology for determining overall power plant efficiency. This approach gives a good overview of the effect of different capture options and integration levels, that cannot be obtained when evaluated independently.

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This work describes the conceptual design of a novel separation process for CO₂ removal from flue gas based on precipitating solvents. The process here described (DECAB) is an enhanced CO₂ absorption based on the Le Chatelier's principle, which states that reaction equilibrium can be shifted by removing one of the constituents in the reaction. A conceptual design of this process has been developed based on literature data, thermodynamic principles and a limited number of experiments. As solvent example, the potassium salt of taurine was selected. The strategy followed is based on the compilation and determination of the key properties and parameters that govern the absorption and regeneration of the solvent. Then, the performance of the process is evaluated with the aid of short cut design methods. Results show that the key advantages of this process are environmental friendliness (no emissions to the air) and low energy consumption related to a lower vapor pressure of the solvent and higher net loading than conventional processes. The design developed allows for future economic evaluation and assessment of options that will further lead to benefits over conventional processes.

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In this work, a perspective is given on the development lines for CO ₂ post-combustion capture technology. Guidelines for cost reductions and suggestions for future research on solvent and process development are presented. By analyzing the post-combustion capture process in this work, it is evident that to achieve significant reduction of the capture process cost, multiple process parameters need to be improved. For future development of CO₂ post-combustion capture process, it would be beneficial to direct the solvent development research towards solvents systems, which have lower reaction enthalpy and higher solvent capacity. A significant improvement can be obtained by the development of solvent systems where the solvent is regenerated at higher pressure. In addition, smart process improvement and integration are required to achieve a reasonable cost reduction. It can be expected that by improving the process design and the solvent, implementation of post combustion capture on larger scale will be possible in the near future.

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Thermo pervaporation (PV) is a pervaporation process that makes use of low quality heat to recover or purify solvents from water. Based on this technology it is possible to integrate the condensation energy for the direct heating of the feed during pervaporation in one single module. This concept was experimentally investigated for the separation of ethanol from a mixture of ethanol-water. It was possible to obtain a heat recovery of 33% (meaning that 33% of the heat transferred to the feed stream is condensation heat) and fluxes up to 0.5 kg/m² h at high ethanol concentration.

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