• Energy Research
• Restricted close
• Embargo close
• chemical engineering close
• US close
• EU close

Abstract To reduce the environmental impact of the industrial sectors, circular strategies should be implemented to purify the effluents and recover raw materials. In this context, a novel integrated methodological approach is proposed to identify the most suitable strategy to improve the sustainability of the water softening industry via the treatment and recycling of the produced wastewater. Different concentration technologies and energy supply systems are compared to find economically feasible and environmentally friendly treatment systems. The investigated chains present the same pre-treatment step (nanofiltration and crystallization) and different concentration technologies: Multi-Effect Distillation (MED), Membrane Distillation (MD) and the coupling of Reverse Osmosis and Membrane Distillation (RO-MD). In the case of electricity supplied by the grid, the MED and the RO-MD chain are economically competitive with the state of the art (Levelized Brine Cost (LBC) between 4 and 6$/m3, lower than the regenerant solution cost, equal to 8$/m3). Moreover, the specific CO2 emissions due to the energy required by the treatment processes (10.8 kgCO2/m3regenerant for the MED chain and 16.7kgCO2/m3regenerant for the RO-MD chain) are lower than those produced by the current system (19.7kgCO2/m3regenerant). Varying the feed flow rate, the MED-chain is more feasible at larger plant sizes for its lower energy demand, while the chain including RO-MD shows lower costs at smaller plant sizes for its lower investment costs. When a photovoltaic-battery system is coupled, both the MED-chain and RO-MD-chain show a CO2 emission reduction of more than 75% with respect to the state of the art. Furthermore, their LBC values are very competitive, especially if the plant is located in a region with high solar potential.

The separation of biogas leads to not only recovery and sequestration of CO2, but also to much greater purification and recovery of value-added CH4 able to be used, for example, to directly feed pipelines for domestic or small plants. In this work, an alternative approach for a preliminary design of separation process based on the use of polymeric membranes is proposed. Two different types of polymeric membranes were taken into account, Hyflon AD60 and Matrimid 5218, the first showing a higher permeability with respect to other membranes but a quite low selectivity (12.9), the second exhibiting a higher selectivity with respect to other membranes (41 and 100) even though a lower permeability. Four possible operation schemes using two different types of membranes in multistage configuration system are analysed as functions of the main design parameters, i.e., pressure ratio and permeation number. The achieved results are compared with certain targets and are also discussed in terms of process metrics, according to the Process Intensification strategy. This latter analysis, coupled with a conventional one, provides an alternative point of view over the evaluation of the plant performance taking into account not only the final characteristics of the streams but also process efficiency, exploitation of raw material and energy, and the footprint occupied by the installation.

This paper introduces a generalized formulation for the entropy production analysis. The use of relations valid under the hypothesis of validity of the principle of detailed balance, that is violated in the remarkable case of irreversible reactions, is avoided by using more general expressions for the entropy generation due to the chemical reactions. As a result, the new formulation is applicable to generate reduced mechanisms involving both irreversible reactions or ad hoc estimated reverse rates.

When designing a concentrating solar power (CSP) system, selection of a proper heat transfer fluid (HTF) material is a key, especially when employed in parabolic trough CSP plants. In particular, the use of low melting mixtures as an alternative to the widely commonly used “solar salt” can increase the CSP manageably and, as a result, several innovative nitrite/nitrate mixtures have been proposed. However, very few thermodynamics data are available for these compounds, especially regarding ternary compositions. One of the most interesting low freezing mixture is prepared with sodium and potassium nitrate together with sodium nitrite. The aim of this work is to investigate the thermodynamics properties of this ternary system, starting from its binary subunits, studying the phase diagram of this compound both experimentally and by a regular solution model. At this purpose, the literature phase diagrams of the binary subsystem were simulated in order to obtain the fitting parameters necessary for the employed semi-predictive tool. Then, the ternary system was modeled and the results showed very good agreement with the experimental points. It is quite interesting to note that both the theoretical and experimental results showed a low melting zone presenting greater sodium nitrate molar fractions with respect to sodium nitrite than previously reported in literature. This would lead to a decrease in the HTF price and an improvement regarding the fluid toxicity.

Residual trapping of carbon dioxide during geological storage – insight gained through a pore-network modeling approach

Abstract The effects of CO2-brine-rock interaction on the physical and macro-mechanical properties of rock have been extensively studied in CO2 sequestration-related research. However, there are few studies focus on mechanochemical effects of the interaction of supercritical CO2 (SC−CO2), water, and rock and its effects on micromechanical properties of sandstone. In this work, we studied the micromechanical mechanism of crack initiation induced by SC−CO2-water saturated sandstone. A micromechanical model including parameters of fracture cohesive strength, friction coefficient, and fracture energy was proposed, which extended the “sliding surface” to include not only the friction, but also the cohesions on the surfaces and the tensile resistance at the crack-tips. To this end, tests of two saturation conditions, water and SC−CO2-water, were conducted on 25 mm diameter by 50 mm length Sichuan sandstone with a porosity of ∼15.57 % for 15 days and 30 days under temperature of 80 ℃ and pressure of 30 MPa. Afterward, samples were subjected to triaxial compression tests with confining pressure up to 24 MPa. The mineralogical alteration and induced crack morphology were examined to better understand the mechanism of mechanochemical coupling on compression failure induced by SC−CO2-water-rock interaction. Experimentally, mineralogical and microstructural changes induced by illite and kaolinite dissolution, weaken the quartz grain contacts in SC−CO2-water saturated sandstone. Compared to water-saturated sandstone, the SC−CO2-water saturated sandstone exhibits a maximum reduction by 18.82 % and 21.21 % in compressive strength and crack initiation stress respectively under unconfined condition. Additionally, reductions of 5%, 50 %, and 37.3 % were observed in friction coefficient, fracture energy, and cohesive strength respectively for SC−CO2-water saturated sandstone. The reductions of these three parameters, especially the fracture energy and cohesive strength, significantly weaken SC−CO2-water saturated sandstone. The results are representative for the partly saturated zone where SC−CO2 is displacing the in-situ pore fluid and could be used to analyze effects of CO2 injection on stability and integrity of storage formation under mechanochemical coupling effects of SC−CO2-water on sandstone.

Abstract The environmental impacts of brine disposal from seawater desalination plants and wastewater treatment plants represent a subject of growing concern; thus, determining the potential applicability of zero liquid discharge (ZLD) for water treatment is crucial. Membrane-based technologies are a potentially attractive strategy that can be used to reach this goal. Recent studies have highlighted that integrating a series of membrane processes is a viable approach to achieving ZLD for industrial use. However, a relatively limited number of reports have been published on the challenging problems encountered with ZLD approaches. Here, we provide a review of membrane processes that may be used in ZLD approaches and describe their problems as well as potential solutions and innovative technologies for improving their performance. Furthermore, the energy consumption of the different approaches is calculated and analyzed because it represents a major contributor to the total cost, and investments in innovative technologies are discussed. Finally, the prospects for membrane-based ZLD and further research are highlighted.