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A new membrane distillation (MD) concept (MemPower) has been developed for the simultaneous production of high-quality water from various aqueous feedstocks with cogeneration of mechanical power (electricity). Driven by low-grade heat (waste, solar, geothermal, etc.) a pressurized distillate can be produced by operating TNO’s Memstill® process at high hydraulic pressures. These pressures are theoretically limited by the liquid entry pressure (LEP) of the membrane. The proof of principle has been shown and is based on the transport of water vapor against a hydraulic pressure gradient. Various commercially available membranes have been evaluated in order to obtain high yields in water flux and power densities. Power densities have been measured which are sufficient to drive the pumps in MD. This allows standalone Memstill® units without electricity consumption to be possible, which are fully driven by waste heat. The application of new incompressible hydrophobic membranes, combining a high permeance with a high LEP, will allow for much higher power densities. Presented at the Conference on Desalination for the Environment: Clean Water and Energy 11–15 May 2014, Limassol, Cyprus

The European KIC-Climate project Water and Energy for Climate Change (WE4CC) aims at the technical demonstration, business case evaluation and implementation of new value chains for the production of high-quality water using low-grade thermal waste energy from cooling water. A typical large-scale waste heat water network is the production of the boiler feed water from surface water using waste heat of temperatures below 60°C from power plants. Two innovative membrane distillation concepts for the production of high-quality water were evaluated for this case in terms of operational conditions, equipment size and costs which are dependent on the available amount of waste heat and its temperature. • Memstill® (partial use of waste heat, by partially cooling down cooling water such that the remaining heat can be reused for other applications, e.g. for the recovery of desiccant solutions) • MD-HEX, i.e. membrane distillation with an extra integrated heat envelope within the Memstill® module for full use of waste heat which is taken up by the produced water and/or the concentrate. Both Memstill® and MD-HEX behave as a demineralised water (demi-water) producing once-through cooler. Due to the utilisation of waste heat, much less electricity is needed for the production of demi-water relative to other water production technologies. Memstill® also behaves as a waste heat-consuming demi-water producing technology. Thus, significant reductions in cooling water intake, costs and GHG emissions can be achieved. © 2014 Balaban Desalination Publications. All rights reserved.

The European KIC-Climate project Water and Energy for Climate Change (WE4CC) aims at the technical demonstration, business case evaluation and implementation of new value chains for the production of high-quality water using low-grade thermal waste energy from cooling water. A typical large-scale waste heat water network is the production of the boiler feed water from surface water using waste heat of temperatures below 60°C from power plants. Two innovative membrane distillation concepts for the production of high-quality water were evaluated for this case in terms of operational conditions, equipment size and costs which are dependent on the available amount of waste heat and its temperature. • Memstill® (partial use of waste heat, by partially cooling down cooling water such that the remaining heat can be reused for other applications, e.g. for the recovery of desiccant solutions) • MD-HEX, i.e. membrane distillation with an extra integrated heat envelope within the Memstill® module for full use of waste heat which is taken up by the produced water and/or the concentrate. Both Memstill® and MD-HEX behave as a demineralised water (demi-water) producing once-through cooler. Due to the utilisation of waste heat, much less electricity is needed for the production of demi-water relative to other water production technologies. Memstill® also behaves as a waste heat-consuming demi-water producing technology. Thus, significant reductions in cooling water intake, costs and GHG emissions can be achieved. © 2014 Balaban Desalination Publications. All rights reserved.

Organic Rankine cycles (ORCs) are an established technology to convert waste heat to electricity. Although several commercial implementations exist, there is still considerable potential for thermo-economic optimization. As such, a novel framework for designing optimized ORC systems is proposed based on a multi-objective optimization scheme in combination with financial appraisal in a post-processing step. The suggested methodology provides the flexibility to quickly assess several economic scenarios and this without the need of knowing the complex design procedure. This novel way of optimizing and interpreting results is applied to a waste heat recovery case. Both the transcritical ORC and subcritical ORC are investigated and compared using the suggested optimization strategy. Keywords: organic Rankine cycle (ORC); thermo-economic; optimization; subcritical; transcritical

Cжиженный природный газ (СПГ) широко используется во многих странах мира как высокоэффективный энергоноситель. При его регазификации можно утилизировать высокий криогенный потенциал для производства холода или работы. Показана возможность регазификации СПГ с производством полезной работы. Рассмотрена схема силовой установки, в которой реализуется цикл Ренкина. В цикле верхним тепловым источником являются отработавшие газы газотурбинной установки (ГТУ). Показано, что при использовании холода СПГ значительно возрастает эффективность силовой установки. В качестве рабочих тел в цикле Ренкина применяются бинарные смеси на основе метана, этана, пропана и бутана. Исследовано влияние состава рабочего тела на эффективность силовой установки при разных температурах нижнего источника. Эффективность производства энергии при утилизации холода СПГ и теплоты отработавших газов ГТУ составляет более 60 %., Liquefaction of natural gas (LNG) is widely used in many countries of the world as a highly effective energy source. With its regasification a high cryogenic potential for production cold or work can be utilized. The possibility of LNG regasification with the production of useful work was demonstrated. A scheme for the power plant in which the Rankine cycle is realized was considered. In a series of upper heat source are exhaust gases gas turbine unit (GTU). It is shown that by using LNG cold significantly increases the efficiency the power plant. As the working media in the Rankine cycle the binary mixtures are used based of methane, ethane, propane and butane. The influence of working medium on the efficiency of the power plant at different temperatures of the lower source is investigated. The efficiency of energy utilization at the cold of LNG and heat exhaust gas of GTU is more than 60 %.

Low-grade heat (LGH) sources, here defined as those below 500 oC, are a group of abundant energy sources available as industrial waste heat, solar thermal, and geothermal which are not used to their full advantages. For example, they are not adequately for conversion to power because of low efficiency energy conversion. The utilization of LGH can become advantageous for achieving to the highest thermal efficiency. Technologies that allow the efficient conversion of low-grade heat into mechanical and electrical power need to be developed. Various studies have been carried out to appraise the potential of using supercritical carbon dioxide (S-CO2) in a closed Brayton cycle using LGH source for power generation. In this study, the objective of research is to perform a thermodynamic analysis on five different configurations of S-CO2 Brayton cycle. Different configurations are examined among which recompression and partial cooling have been found very promising. The main part of this study is focused on carbon dioxide Brayton cycle. CO2 Brayton cycle has wide range of applications such as heat and power generation and in automotive and aircraft industry. Proposed configurations of each carbon dioxide Brayton cycle performance simulation are conducted and subsequently compared with other power cycles utilizing LGH sources. The CO2 transcritical power cycle (CDTPC) utilizing LGH is also studied. The models are developed by using the Engineering Equation Solver (EES) for several different Brayton cycle configurations. The choice was made to pursue Brayton cycle with regeneration configuration for further, due to its simplicity and high efficiency. Keywords: Supercritical CO2 Brayton cycle, transcritical CO2 cycle, simulation, low-grade heat. ÖZ: Burada, 500 oC altında olarak tanımlanan düşük-dereceli ısı kaynakları, tüm avantajları kullanılmayan endüstriyel atık ısı, güneş enerjisi ve jeotermal gibi mevcut bol enerji kaynaklarından bir gruptur. Ancak, düşük enerji dönüşümü verimliliğinden dolayı bu kaynaklardan az yararlanılıyor. Düşük-dereceli ısı kullanımı birçok nedenden dolayı avantajlıdır. Düşük-dereceli ısının mekanik ve elektrik güç haline verimli dönüşümünü sağlayan teknolojileri geliştirmek oldukça önemlidir. Süper kritik karbon dioksitin, düşük-dereceli ısı kaynaklı kapalı Brayton çevriminin güç üretimide kullanım potansiyelini değerlendirmek için çeşitli çalışmalar gerçekleştirilmiştir. Bu çalışmadaki araştırmanın amacı beş farklı konfigürasyonda süper kritik karbon dioksit Brayton çevriminin termodinamik analizini gerçekleştirmektir. Farklı konfigürasyonlar incelendi ve bunlar arasında tekrar sıkıştırma ve kısmi soğutma çok umut verici bulundu. Bu çalışmanın ana kısmı, karbon dioksit Brayton çevrimine odaklanmıştır. Karbon dioksit Brayton çevrimi geniş uygulama yelpazesine sahiptir, örneğin ısı ve güç üretimi, otomotiv ve uçak sanayisi. Önerilen karbon dioksit Brayton çevrimi konfigürasyonlarının performans simülasyonu yapıldı ve diğer düşük dereceli ısı kullanan güç çevrimleri ile karşılaştırıldı. Düşük-dereceli ısı kaynağı kullanan CO2 transkritik güç çevrimi ayrıca incelendi. Engineering Equation Solver yazılımı kullanılarak farklı konfigürasyonlardaki Brayton çevriminin modelleri geliştirildi. Rejenaratörlü basit Brayton çevriminin sadeliği ve yüksek verimliliği nedeniyle daha fazla takip edilmesi gerektiği seçimi yapıldı. Anahtar kelimeler: Süper kritik CO2 Brayton çevrimi, transkritik CO2 çevrimi, simülasyon, Düşük-dereceli ısı Master of Science in Mechanical Engineering. Thesis (M.S.)--Eastern Mediterranean University, Faculty of Engineering, Dept. of Mechanical Engineering, 2014. Supervisor: Prof. Dr. Fuat Egelioğlu.

A thermally powered circulator based on a two-phase thermofluidic oscillator was constructed and operated successfully as a replacement for a central heating hot water circulator coupled to a domestic gas-fired boiler. During regular operation the thermally powered circulator demonstrated a pumped flow-rate that decreased monotonically as the head applied across it increased. A maximum measured flow-rate of 850 L/h was achieved at zero head, and a maximum head of 8.4 mH2O was attained at near-stalling (zero flow-rate) conditions. In agreement with previous modelling studies of the technology, increased inertia in the load line seems to lead to improved circulator performance. Further, the oscillating circulator exhibited an operational frequency between 0.24 and 0.33 Hz, which was mostly determined by the circulator configuration. The pumping capacity was strongly affected by the oscillating liquid amplitudes in the power cylinder that defined the positive displacement amplitudes of the liquid piston into and out of the hot water circuit. The best circulator configuration was associated with lower operation frequencies and relatively large ratios of suction to discharge displacement.

This paper begins with an overview of the current supply and demand characteristics of primary energy for the provision of heat and power in the UK. This is followed by a brief review of a variety of solutions that are being proposed towards the establishment of a sustainable energy landscape, including clean coal, wind and solar energy. The discussion extends to the economics and performance of various renewable energy systems in comparison to fossil fuel equivalents. Placed in this context, the study then focuses specifically on the role of pumped heat, combined heat and power (CHP) schemes, and options for the recovery and conversion of waste heat into useful work, all of which have a potential to contribute towards the creation of a ‘high-efficiency sustainable energy future’. It is concluded that although the problem is complex, the relative costs of competing technologies are not prohibitive, but comparable, leading to an inability to make a decisive choice and delaying progress. CHP and pumped heat are found to be similar in terms of overall efficiency, with the load factor (heat-to-power demand ratio) being of critical importance. Various waste heat conversion systems are also found to be similar in terms of the important indicator of power per unit cost.

International audience; A deep-freezing process has been designed and experimented to cool a cold box down to about −30 °C using only low-grade heat produced by simple flat plate solar collectors operating at 70 °C. The original process involves two cascaded thermochemical systems using BaCl2 salt reacting with ammonia. It works discontinuously, with one day phase of regeneration at high pressure and one night phase of cold production at low pressure. A global dynamic model allows the simulation of the different system components functioning depending on the hourly weather conditions. It takes into account the transient periods and shows the temperature changes of the components, the chemical reactions in the system and its performances. This system will cover the cooling needs of a 560 L cold box at −20 °C during the 3 sunniest months of the year and provide more than 60% of the total yearly cooling needs of this box for the weather conditions of Perpignan (South of France). The prototype is expected to show a system coefficient of performance (COP) of about 0.07 over the 10 sunniest months of the year, and a net solar COP of 0.05, taking into account the collectors efficiencies.

Traveling-wave thermoacoustic electric generator is promising in solar power generation and energy recovering due to its high efficiency, high reliability, and capability of utilizing low-grade heat. A traveling-wave thermoacoustic electric generator composed of a thermoacoustic engine and two linear alternators is designed and constructed. Output electric power and thermal-to-electric efficiency of the system are studied under different working conditions. Experimental results show that the load resistance should be optimized to achieve a good performance. A maximum electric power of 473.6 W and a maximum thermal-to-electric efficiency of 14.5% are achieved by optimizing the load resistances, respectively. Further improvements are expected by increasing the working pressure and optimizing the acoustic coupling between the linear alternators and the thermoacoustic engine.

The RED Heat Engine operates as a closed-loop RED system, where limited amounts of artificial saline solutions are used as working fluids. The solutions exiting from the RED unit are regenerated by means of a separation step, which uses low-temperature heat as its energy source. Essentially the system converts low-grade heat to electricity. There are two main alternative regeneration strategies: (i) extract solvent from the high salinity solution and move it to the low salinity solution or (ii) extract salt from the low salinity solution and move it to the high salinity solution. In this thesis are considered the Multi-effect distillation (MED) and the Membrane Distillation (MD) under the solvent extraction strategy, while the use of thermolytic salts with distillation and absorption columns are considered for the solute extraction option. This thesis studied the RED Heat Engine perspectives in terms of: • the sources that can provide the heat necessary for running the system, indicating the characteristics that the system should have to match the market requirements • the life-cycle impacts, providing evidence for the environmental credentials of the technology, compared to alternative electricity supply options, and providing direction to system designs with the minimum environmental impacts. • economic performance, improving the understanding of the factors that affect it, including the design options, operational choices as well as the development over time of the key components in terms of performance and cost

Our society is undergoing a progressive change about the life style and habits. The world population is continuously increasing with 7.6 billion of human beings in 2018, resulting in an increasingly demand of resources in terms of food, water and energy. The exploitation of the planet resources since the first Industrial Revolution, results today in an unsustainable condition, which requires fundamental changes. In particular, in the energy sector the adoption of fossil fuels as the main energy source for human beings’ activities resulted in a strong impact on our planet, leading to climate changes and environmental pollution. Nowadays these aspects have induced society to a substantial challenge to find new sustainable energy sources for the future of human civilization. Low-grade thermal energy, derived from industrial or geothermal sources, represents an interesting resource for energy production. Indeed, huge amounts of low-grade thermal energy are available. Considering the industrial sector an amount ranging between 20-50% of the energetic input of industrial plants, are lost every day, in the form of hot gasses and liquid streams. However, the recovery and re-use of low-grade thermal energy or waste heat is limited due to the lack of efficient technologies for converting low-temperature heat sources into electrical power. Recently, Salinity Gradient Power Heat Engines (SGP-HEs) have been proposed as a viable process for the recovery of low-grade heat. In particular, this PhD thesis focuses on the analysis of Reverse Electrodialysis Heat Engines (RED-HEs), contributing to the activities of the European project “RED-Heat-to-Power” funded by the European Union’s Horizon 2020 Research and Innovation Programme (www.red-heat-to-power.eu). The aim of the project is to study and develop the first prototypes for the conversion of low-grade heat into electricity through a reverse electrodialysis (RED) unit. A reverse electrodialysis heat engine consists of two main units: (i) a power generation unit based on the reverse electrodialysis process, where the salinity gradient between two salt solutions is exploited to produce electricity, and (ii) a regeneration unit where low-grade heat is used to restore the salinity gradient of the reverse electrodialysis solutions exiting from the power generation unit. The restoring of the two solutions can be achieved by means of different strategies, e.g. solvent extraction and salt extraction, as summarized in the following. (a) In solvent extraction, the salt exchanged within the reverse electrodialysis unit is integrated by adding a part of the exhausted dilute stream to the exhausted concentrate stream, then, the resulting solution is fed to the regenerative unit where solvent is recovered by a thermal separation process (e.g. multi-effect distillation, membrane distillation) and transferred to the dilute solution. (b) In salt extraction, the exhausted dilute solution is fed to the regenerative unit where the salt is recovered by using low-grade heat as an energy source and transferred again to the concentrate solution. Rebalancing of the solvent is eventually carried-out to restore the solvent amount in the two streams. The main objective of this thesis is to provide a proof of the ground-breaking concept of a reverse electrodialysis heat engine, demonstrating the technological readiness level of such technology at a lab-scale prototype level. To this aim, both configuration, solvent and salt extraction reverse electrodialysis heat engines were investigated. The first part of this PhD thesis was dedicated to the development of a mathematical model for the RED process, based on a multi-scale modelling approach, considering two different scales of description: (i) a lower-scale model, describing the main phenomena involved in a single repeating unit (cell pair) and (ii) a higher-scale model related to the whole system, including all cell pairs and the relevant interconnections. The mathematical model was validated against experimental results and integrated with exergy analysis tools useful to evaluate the main causes and location of irreversibility sources. Ad hoc experimental campaigns were carried out in order to characterize the behaviour of different salt-water solutions, membrane properties and the operability of lab-scale units. In particular, a purposely-developed test rig was built in order to evaluate the osmotic and activity coefficients of salt-solutions from vapour pressure measurements, then used to determine novel data for caesium and potassium acetate salt solutions. This activity was performed at the University of Edinburgh, during a period abroad of six months. Furthermore, several experimental results on lab-scale reverse electrodialysis unit were carried out in order to provide membrane properties and experimental results for the mathematical model validation. In the case of solvent extraction strategies, validated mathematical models were developed for a reverse electrodialysis heat engine implementing either membrane distillation or multi-effect distillation as regeneration unit. These activities were performed in collaboration with the “Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT)” of Almeria. Finally, an exergy analysis at component level was performed for the integrated RED-MED HE, analysing the impact of the main operating conditions and membranes properties on the exergy efficiency of the system and identifing the main irreversibility sources. In the case of salt extraction strategies, thermolytic salts were selected and studied as working solutions of the RED-HE. Solutions of thermolytic salts have the peculiarity that their ions dissolved in water undergo a degradation process into gaseous species when the temperature is increased over a certain limit. Then, the dissolved thermolytic salt can be removed nearly completely from the solution by means of a thermal desorption process. The stripped gaseous species can be dissolved again in the aqueous solutions through an absorption step, resulting in an aqueous solution consisting of the very same ions of the thermolytic salt. Experimental test-rigs were designed, built and tested to investigate the stripping process of thermolytic salts. Mathematical models were developed in ASPEN Plus® and validated by comparison with experimental results. The model was also used to perform a sensitivity analysis and investigate the performance of the whole regeneration unit, including also the absorption process. Then, a mathematical model of a RED-HE fed by thermolytic salts was developed by coupling the ASPEN Plus® process model for the regeneration unit to the RED process model and used to perform sensitivity analyses. Finally, all the knowledge gained by theoretical and experimental works have made possible the design, construction and operation of the first world prototype of the thermolytic RED HE, demonstrating for the first time the feasibility of the process. The present thesis has been organised in order to cover the main aspects of the RED process and describe the aforementioned objectives. Chapter 1 introduces the concept of salinity gradient power (SGP) and related SGP-HEs, describing the SGP-HE concept and analysing the state of the art of the technology. Section I - Reverse Electrodialysis process Chapter 2 presents an overview of the reverse electrodialysis process, describing the technological fundamentals, experimental tests and modelling. Chapter 3 reports an original exergy analysis of the RED unit and the potential applications of the process in real environments. Chapter 4 presents the analysis on the influence of salt-solution properties on the RED-HE performance, reporting novel osmotic and activity coefficients for potassium acetate and caesium acetate water solutions. Section II - Solvent Extraction: RED with evaporative regeneration unit Chapter 5 and Chapter 6 are dedicated to the solvent extraction reverse electrodialysis heat engine. In particular, Chapter 5 reports the simplified mathematical models used to evaluate preliminary performances of (i) theoretical SGP unit fed by different salt solutions, (ii) RED-MED HE and (iii) RED-MD HE fed by NaCl solutions. Chapter 6 describes the advanced RED-MED-HE model developed to perform exergy analysis on the integrated system. Section III - Salt Extraction: Thermolytic salts Chapter 7 and Chapter 8 reports the analysis on thermolytic salts. In particular, Chapter 7 is focused on the regeneration unit of thermolytic salts presenting mathematical models and experimental assessments. Chapter 8 presents the first operating thermolytic RED heat engine (t-RED HE) and a perspective analysis based a validated process model for the t-RED HE.