Many countries worldwide experience water shortages on a daily basis and this water crisis is expected to increase even more in the near future due to limited fresh water resources. Alternative sources of fresh water such as desalinated seawater are becoming an attractive option for many developing countries. Although various desalination technologies exist today, interest in multi-effect distillation (MED) is growing rapidly worldwide. Today various energy power sources are utilized in MED plants, but the use of nuclear power as a clean and effective heat source for the MED process seems to be gaining interest. Implementation of HTGR technology, such as the Pebble Bed Modular Reactor being developed in South Africa is ideal for MED desalination purposes. In these types of reactors high temperature water is available as waste heat as opposed to high temperature steam from conventional steam power plants. Currently conventional MED plants utilize steam as the process heat source, to drive the MED process. In this study a system simulation model was developed in the computer language C++. It evaluates different MED process flow configurations in order to identify an optimum MED plant configuration for both water and steam as process heat source. Simulation results indicate that a steam-heat-source (SHS) MED plant produces approximately 25-30% more product water than a water-heat-source (WHS) MED plant while utilizing less plant stages. Plant layout and economics are impacted by the available process heat source. Results also indicate that a parallel feed configuration (PFC), which incorporates preheating of feed water, seems to be the optimum process flow configuration type for both the SHS and WHS type plants. Product water costs for optimized SHS and WHS MED plants were also compared. Various system parameters influence plant performance, but the serie effect temperature difference seems to be the most influential parameter in terms of water production. Preheating of feed water increases production levels up to 30%. Results from the C++ model have been compared to results calculated with MEE-TVC, a desalination system design program and were generally in good agreement. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2008.

This work introduces a systematic seawater reverse osmosis (SWRO) membrane network synthesis approach, based on the coordinated use of process superstructure representations and global optimization. The approach makes use of superstructure formulations that are capable of extracting a globally optimal design as a performance target, by taking into consideration desired process conditions and constraints that are typically associated with reverse osmosis systems. Thermodynamic insights are employed to develop lean network representations so that any underperforming solutions can be eliminated a priori. This essentially results in considerable improvement of the overall search speed, compared to previously reported attempts. In addition, the approach enables the extraction of structurally different design alternatives. In doing so, distinct membrane network design classes were established by partitioning the search space, based on network size and connectivity. As a result, corresponding lean superstructures were then systematically generated, which capture all structural and operational variants within each design class. The overall purpose is thus to enable the extraction of multiple distinct optimal designs, through global optimization. This mainly helps provide design engineers with a better understanding of the design space and trade-offs between performance and complexity. The approach is illustrated by means of a numerical example, and the results obtained were compared to previously related work. As anticipated, the proposed approach consistently delivered the globally optimal solutions, as well as alternative efficient design candidates attributed to different design classes, with reduced CPU times. This work further capitalizes on the developed representation, by accounting for detailed water quality information, within the SWRO desalination network optimization problem. The superstructures were modified to incorporate models that capture the performance of common membrane elements, as predicted by commercially available simulator tools, e.g. ROSA (Dow) and IMSDesign (Hydranautics). These models allow tracing of individual components throughout the system. Design decisions that are supported by superstructure optimization include network size and connectivity, flow rates, pressures, and post treatment requirements. Moreover, a detailed economic assessment capturing all the significant capital and operating costs associated in SWRO processes, including intake, pre and post treatment has also been accounted for. These modifications were then illustrated using a case study involving four seawater qualities, with salinities ranging from 35 to 45 ppt. The results highlight the dependency of optimal designs on the feed water quality involved, as well as on specified permeate requirements.

Heat exchanger fouling is the deposition of material onto the heat transfer surface causing a reduction in thermal efficiency. A study using Computational Fluid Dynamics (CFD) was conducted to increase understanding of key aspects of fouling in desalination processes. Fouling is a complex phenomenon and therefore this numerical model was developed in stages. Each stage required a critical assessment of each fouling process in order to design physical models to describe the process???s intricate kinetic and thermodynamic behaviour. The completed physical models were incorporated into the simulations through employing extra transport equations, and coding additional subroutines depicting the behaviour of the aqueous phase involved in the fouling phenomena prominent in crystalline streams. The research objectives of creating a CFD model to predict fouling behaviour and assess the influence of key operating parameters were achieved. The completed model of the key crystallisation fouling processes monitors the temporal variation of the fouling resistance. The fouling rates predicted from these results revealed that the numerical model satisfactorily reproduced the phenomenon observed experimentally. Inspection of the CFD results at a local level indicated that the interface temperature was the most influential operating parameter. The research also examined the likelihood that the crystallisation and particulate fouling mechanisms coexist. It was found that the distribution of velocity increased the likelihood of the particulate phase forming within the boundary layer, thus emphasizing the importance of differentiating between behaviour within the bulk and the boundary layer. These numerical results also implied that the probability of this composite fouling was greater in turbulent flow. Finally, supersaturation was confirmed as the key parameter when precipitation occurred within the bulk/boundary layer. This investigation demonstrated the advantages of using CFD to assess heat exchanger fouling. It produced additional physical models which when incorporated into the CFD code adequately modeled key aspects of the crystallisation and particulate fouling mechanisms. These innovative modelling ideas should encourage extensive use of CFD in future fouling investigations. It is recommended that further work include detailed experimental data to assist in defining the key kinetic and thermodynamic parameters to extend the scope of the required physical models.

Η εξάντληση των ορυκτών καυσίμων και το ενδεχόμενο ενεργειακό αδιέξοδο σε συνδυασμό με τη δυνατότητα παραγωγής ενέργειας από ανεξάντλητες πηγές χωρίς επιβάρυνση στο περιβάλλον έχουν οδηγήσει τους τομείς έρευνας προς τις ανανεώσιμες πηγές ενέργειας. Ένα άλλο μεγάλο πρόβλημα είναι αυτό της εξάντλησης του νερού. Έτσι έχει αναπτυχθεί η έρευνα για την αξιοποίηση των αλμυρών ή υφάλμυρων αποθεμάτων νερού της Γης μέσω της τεχνολογίας αφαλάτωσης. Στην εργασία αυτή παρουσιάζεται ο σχεδιασμός και η οικονομική αξιολόγηση ενός συστήματος αφαλάτωσης το οποίο τροφοδοτείται απο υβριδικό σύστημα φωτοβολταϊκών πλαισίων και ανεμογεννητριών. Για τη διαστασιολόγηση χρησιμοποιήθηκαν γενετικοί αλγόριθμοι οι οποίοι αποτελούν εργαλεία επίλυσης προβλημάτων βελτιστοποίησης. / The depletion of mineral fuels and the potential future energy issues, conbined with the ability to produce energy from alternative sources of practically infinite capacity without causing environmental damage, has driven research towards exploring renewable energy sources. A major issue is also the issue of water depletion, driving research towards the development of desalination technologies that use seawater or brackish water. In this thesis we explore the potential and we perform the economic evaluation of a desalination system, which is powered by a hybrid system of photovoltaics and wind turbines. The parameters of the proposed implementation are optimized using genetic algorithms.

abstract: Scarcity of potable water is one of the major problems faced in the world today. Majority of this problem can be solved if technology is developed to obtain potable water from brackish or saline water. The present desalination methods face challenges such as high costs in terms of energy consumption and infrastructure, physical size of the system, requirement of membrane and high pressure systems and hence have been facing various issues in implementation of the same. This research provides a new low pressure, low energy, portable method to desalinate water without the need for separation membranes, heat or chemical reactions. This method is energy efficient, cost effective, compact, environment friendly and suitable for portable desalination units. This technology, named as Polyphase Alternating current Bi-Ionic Propulsion System (PACBIPS) makes use of polyphase alternating current source to create a gradient in salt concentration. The gradient in salt concentration is achieved due to the creation of a traveling wave which attracts anions on its positive peak (crests) and cations on its negative peak (troughs) and travels along a central pipe thereby flushing the ions down. Another method of PACBIPS is based on Helmholtz capacitor which involves the formation of an electric double layer between the electrode and electrolyte consisting of equal and opposite ions which can be approximated as a capacitor. Charging and discharging this capacitor helps adsorb the ions onto a carbon electrode which has high surface area and electrical conductivity. This desalinates seawater and provides pure water. Mathematical modeling, analysis and implementation of the two methods have been presented in this work. The effects of zeta potential, electric field screening, electric mobility on desalination have been discussed. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2014

Submitted by Lucienne Costa (lucienneferreira@ufcg.edu.br) on 2018-04-10T17:36:57Z No. of bitstreams: 1 RODRIGO VIEIRA ALVES - TESE (PPGEQ) 2017.pdf: 4663584 bytes, checksum: 1fbfe2df3144935946e63d14cdcc7ade (MD5) / Made available in DSpace on 2018-04-10T17:36:57Z (GMT). No. of bitstreams: 1 RODRIGO VIEIRA ALVES - TESE (PPGEQ) 2017.pdf: 4663584 bytes, checksum: 1fbfe2df3144935946e63d14cdcc7ade (MD5) Previous issue date: 2017-08-31 / Capes / O processo de dessalinização de águas salobras vem sendo uma das alternativas de obtenção de água potável, para beneficiar as comunidades difusas da região do semiárido. Dentro dessa conceituação foram implantados dois sistemas de dessalinização para produção de água potável: um na comunidade de Uruçu da Cidade de São João do Cariri, e outro na Escola Macário Zulmiro do distrito de Santa Luzia, da Cidade de Picuí, ambos no Estado da Paraíba. O aproveitamento dos concentrados gerados durante o processo de dessalinização dos sistemas foram estudados para produção de alface, através de sistemas hidropônicos de fluxo laminar de nutrientes. O objetivo desse trabalho foi avaliar os parâmetros de crescimento, níveis de nitrato, aspectos sensoriais e dos custos de produção de alface hidropônica com uso do concentrado. Foram realizados experimentos a partir do concentrado (1) com níveis de tratamentos de (0,1; 2,3; 4,4; 6,2 e 8,4) mS.cm-1 e com o concentrado (2), nos níveis de (0,1; 1,1; 2,1; 3,1 e 4,1) mS.cm-1 para o cultivo das alfaces crespa “crocante” e americana “gloriosa”. O delineamento experimental foi inteiramente ao acaso, com três repetições. Observou-se que o desenvolvimento das duas alfaces estudadas, dependeram dos níveis da condutividade elétrica de cada concentrado. O consumo hídrico das plantas foi reduzido em 7,53% e 8,89% para alface crespa e americana cultivadas com o concentrado (1) e 1,60% e 4,03 para o concentrado (2), por incremento unitário de condutividade elétrica, respectivamente. Foi observado com os resultados dos parâmetros de crescimento, que a alface crespa apresentou maior tolerância ao excesso de sais do concentrado, quando cultivadas com os tratamentos do concentrado (1), principalmente nos tratamentos 6,2 e 8,4 mS.cm-1, observadas pelas reduções lineares do número de folhas, massa fresca da parte aérea, massa seca da parte aérea, umidade, massa seca das raízes, massa do caule e área foliar. As reduções dos parâmetros de crescimento foram menores ao utilizar o concentrado (2) e os dois tipos de alface foram tolerantes aos níveis dos tratamentos. Com relação as concentrações de nitrato, foram encontrados resultados variando entre 694,5 e 1.982,0 mg.kg-1 nas alfaces crespa e americana, os quais estão de acordo, com o valor máximo permissível (3.500 mg.kg-1) da regulamentação europeia 1881/2006, das quais, a alface americana acumulou mais nitrato do que a crespa. Nos experimentos com o concentrado (1), os atributos cor, sabor, crocância e impressão global foram afetados com o excesso de sais nos experimentos com alface americana, enquanto para alface crespa, foram afetados a cor, sabor e impressão global. Ao utilizar o concentrado (2), nenhum parâmetro foi afetado para o experimento com alface crespa. A preferência de compras foi acima de 90% para a alface crespa cultivada com o concentrado (2). Os resultados das estimativas dos custos mostraram um investimento de R$114.663,00 na implantação dos sistemas hidropônico e de dessalinização, retorno sobre investimento em aproximadamente 4 anos, custos de produção da alface de R$ 0,30 por planta e custos para produção da água de R$ 1,47 por m³. / The process of desalination of brackish water has been one of the alternatives for obtaining potable water to benefit the diffuse communities in the semi-arid region. Two desalination systems for potable water production were implemented: one in the community of Uruçu in the city of São João do Carirí and another in the School Macário Zulmiro in the district of Santa Luzia in the city of Picuí, both in the state of Paraíba. The utilization of the concentrates generated during the desalination process of the systems were studied for lettuce production through hydroponic laminar flow systems of nutrients. The objective of this work was to evaluate growth parameters, nitrate levels, sensory aspects and production costs of hydroponic lettuce using concentrate. Experiments were performed from the concentrate (1) with treatments levels of (0.1; 2.3; 4.4; 6.2 and 8.4) mS.cm-1 and with the concentrate (2), in the (0.1, 1.1, 2.1, 3.1 and 4.1) mS.cm-1 levels for the cultivation of crisp "crocante" and american "gloriosa" lettuce. The experimental design was completely randomized, with three replicates. It was observed that the development of the two lettuces studied depended on the electrical conductivity levels of each concentrate. The water consumption of the plants was reduced by 7.53% and 8.89% for crisp and American lettuce cultivated with concentrate (1) and 1.60% and 4.03 for concentrate (2), per unit increment of conductivity respectively. It was observed with the results of the growth parameters that the crispy lettuce presented higher tolerance to the excess salts of the concentrate when cultivated with the treatments of the concentrate (1), mainly in the treatments 6,2 and 8,4 mS.cm-1, Observed by linear reductions of leaf number, fresh shoot mass, shoot dry mass, moisture, dry mass of roots, stem mass and leaf area. The reductions of the growth parameters were lower when using the concentrate (2) and the two types of lettuce were tolerant to the levels of the treatments. Regarding the nitrate concentrations, results ranging from 694.5 to 982.0 mg.kg-1 were found in crisp and american lettuce, which are in agree with the maximum permissible value (3,500 mg.kg-1) of the regulation European seed 1881/2006 and american lettuce accumulated more nitrate than crisp. In the experiments with concentrate (1), the attributes color, flavor, crispness and overall impression were affected with the excess salts in the experiments with American lettuce, while for crisp lettuce, the color, flavor and overall impression were affected. When using the concentrate (2), no parameter was affected for the experiment with crisp lettuce. The purchase preference was above 90% for the crisp lettuce grown with the concentrate (2). The results of the cost estimates showed an investment of R$ 114,663.00 in the implementation of hydroponic and desalination systems, return on investment in approximately four years, lettuce production costs of R$ 0.30 per plant and costs for water production of R$ 1.47 per m³.

abstract: Just for a moment! Imagine you live in Arizona without air-conditioning systems! Air-conditioning and refrigeration systems are one of the most crucial systems in anyone’s house and car these days. Energy resources are becoming more scarce and expensive. Most of the currently used refrigerants have brought an international concern about global warming. The search for more efficient cooling/refrigeration systems with environmental friendly refrigerants has become more and more important so as to reduce greenhouse gas emissions and ensure sustainable and affordable energy systems. The most widely used air-conditioning and refrigeration system, based on the vapor compression cycle, is driven by converting electricity into mechanical work which is a high quality type of energy. However, these systems can instead be possibly driven by heat, be made solid-state (i.e., thermoelectric cooling), consist entirely of a gaseous working fluid (i.e., reverse Brayton cycle), etc. This research explores several thermally driven cooling systems in order to understand and further overcome some of the major drawbacks associated with their performance as well as their high capital costs. In the second chapter, we investigate the opportunities for integrating single- and double-stage ammonia-water (NH3–H2O) absorption refrigeration systems with multi-effect distillation (MED) via cascade of rejected heat for large-scale plants. Similarly, in the third chapter, we explore a new polygeneration cooling-power cycle’s performance based on Rankine, reverse Brayton, ejector, and liquid desiccant cycles to produce power, cooling, and possibly fresh water for various configurations. Different configurations are considered from an energy perspective and are compared to stand-alone systems. In the last chapter, a new simple, inexpensive, scalable, environmentally friendly cooling system based on an adsorption heat pump system and evacuated tube solar collector is experimentally and theoretically studied. The system is destined as a small-scale system to harness solar radiation to provide a cooling effect directly in one system. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2018

O desenvolvimento de fontes alternativas de energia, com o intuito de diminuir a poluição gerada pela queima de combustíveis fósseis, tem estimulado cientistas a procurar novos meios de converter e armazenar energia. Adicionalmente, mudanças climáticas e o crescimento populacional têm gerado uma preocupação crescente com relação à escassez de água. Atualmente, cerca de 3% do consumo global de energia elétrica é referente ao tratamento de águas residuais oriundas de zonas urbanas. A humanidade precisa encontrar meios de usar água limpa e potável de forma mais eficiente. O armazenamento de energia durante o tratamento de águas residuais pode encorajar a preservação ambiental, e desta forma, contribuir para um crescimento mais sustentável, pois pode tornar-se rentável para as indústrias que geram e tratam estes resíduos. Uma estratégia é a utilização de gradientes iônicos e, então, convertê-los em energia elétrica. Pesquisas têm sido realizadas com sistemas contendo soluções eletrolíticas, com diferentes concentrações, e utilizando ciclos eletroquímicos para produzir trabalho elétrico. Neste contexto, são propostos sistemas eletroquímicos, chamados máquinas ácido-base foto-assistidas, que possibilitam a conversão, e o armazenamento, de energia elétrica durante a neutralização de soluções ácidas mediante irradiação de luz UV. Configurações alternativas destes dispositivos permitem, também, a dessalinização de soluções salinas com a possibilidade de recuperar parte da energia utilizada no procedimento. O princípio operacional destes sistemas baseia-se na variação entrópica, oriunda da mudança nas atividades de prótons e íons alcalinos, como também, na conversão de energia eletromagnética em energia elétrica. Através de experimentos de prova de conceito, foi possível obter 108 kJ por mol de íon eletroinserido, valor que corresponde a 10,8 kJ dm-3 de solução ácida neutralizada. / The development of alternative energy sources to mitigate the pollution generated by fossil fuel combustion has stimulated the search for new ways to convert and to harvest energy. Climate change, pollution, and population growth have raised concern about water scarcity. Nowadays, about 3% of the global electricity is consumed by municipal wastewater treatment plants. Humankind has to find the means to use clean and potable water more effectively. One strategy to harvest energy is to employ an ionic gradient and then convert it into electrical energy. Researchers have recently tested systems that apply electrolytic solutions containing different salt concentrations to deliver work after electrochemical cycles. Energy harvesting during wastewater treatment should encourage environmental preservation and contribute to sustainable growth. In this context, electrochemical systems are proposed, so-called photo-assisted acid-base machines, which promote energy conversion and harvesting during acidic solution neutralization under UV irradiation. Also, alternative configurations of these systems allow the desalination of salt solutions with regain of part of the used energy. Operating principle of these machines is based upon entropic variation, associated with proton and alkali ion activity changes, and in the conversion of the electromagnetic energy into electrical energy. Proof-of-concept experiments provided 108 kJ per mol of electroinserted ion, which corresponds to 10.8 kJ dm-3 of neutralized acid solution.

In this PhD thesis, seawater desalination by Membrane Distillation (MD) has been explored from the perspective of process and membrane. Regarding the process, an innovative, energy efficient, and environmentally friendly Zero Thermal Input Membrane Distillation (ZTIMD) process was proposed. ZTIMD uses thermal energy stored in seawater, which makes the process sustainable by being independent of the external sources of thermal energy, which is one of the major contributors to the cost and energy consumption of conventional MD desalination processes. Economic feasibility study was carried out for the ZTIMD process, and it was demonstrated that drinking water could be produced with a cost of $0.28/m3, which is approximately half of the cost of conventional desalination processes. Regarding the membrane, novel MD membranes were developed through incorporation of nanomaterials in polyvinylidene fluoride (PVDF). Different nanomaterials including superhydrophobic SiO2, amine modified hydrophilic SiO2, CuO, and CaCO3 were used for this purpose. It was shown that membrane structure and consequently its performance could be affected by the nanoparticle properties, concentration, presence of backing material, PVDF blend ratio, and penetration time. In a best membrane developed in this work, almost 2500% increase was observed in the Vacuum Membrane Distillation (VMD) flux over that of the neat PVDF membrane at a feed temperature of 27.5 °C and vacuum pressure of 1.2 kPa, when 7.0 wt.% hydrophilic SiO2 nanoparticles were added into a PVDF membrane supported with Non-Woven Fabric (NWF) polyester. The membrane possessed near perfect selectivity.

In this thesis I aim to query the Ecological Modernisation vision of green growth by focusing on the emblematic case of desalination technology as the solution to the threat of water scarcity. I focus the study on a drought crisis, which resulted in the adoption of desalination in the Eden District Municipality (EDM) of South Africa. Focusing on the towns of Sedgefield and Knysna, in the Knysna Local Municipality (KLM) of the EDM, I ask the questions of ‘what, how, by whom, why and to what end was desalination adopted?’. This interrogation is characterised by two movements, firstly tracing the process and mechanism through which this consensus was manufactured; and secondly countering this by examining the underlying metabolic relations constituting crisis and solution. The research was carried out over a period of 11 months, from October 2011 to August 2012, during which I undertook 91 semi-structured interviews, extensive document analysis and participant observation. The theoretical strands drawn upon are a blending of post political theory, to inform an analysis of the techno-managerial orientation of consensus manufacture; and a Marxian relational ontology, to examine what is produced and foreclosed by the logic. This project is undertaken in five parts. Firstly, I show that the dominant representation of 'drought crisis' insisted upon the indisputability of drought as a threat posed by an externalised nature. Next, in examining the metabolism of drought I counter this narrative by showing the drought crisis to be a socio-natural assemblage, rather than an externalised threatening nature. This is a vital finding, showing that the support for the adoption of desalination technology as a necessary response to 'nature's crisis', pivoted on the maintenance of an ideological fiction, obscuring the relational 'becoming' of drought. In the third chapter, moving on to an examination of the solution, it emerges that an essential aspect of the solidification of consensus was the employment of exceptional disaster and environmental legislation which had the effect of neutralising drought as 'nature's crisis' and desalinationas the indisputable solution. Enabling the urgent release of disaster funding to ensure water security for economic growth. This chapter also argues that the maintenance of the dominant crisis narrative produced an opportunity for the desalination industry, by treating 'nature' as a direct accumulation strategy. In the remaining two empirical chapters I evaluate the 'promise' of the desalination techno-fix. Through focusing on the conditionality placed on disaster funding and how this impacted on project assembly, resulting in problems and costs emerging out of the desalination solution from the outset. Fundamentally, it is argued that, rather than being external to, these problems are intrinsically connected to the mechanisms and logic through which consensus emerged in the first place. To clarify, through the preceding chapters it was shown that the basis for the 'disaster funding' release was an insistence on 'nature's crisis', as an ideological fiction. These remaining chapters show that this had the effect of placing limitations on what was spent on, when, and how much. Thereby informing project assembly, with these constraints resulting in problems emerging out of the solution. In sum, the thesis concludes that the adopted E.M. logic was a false promise that served to intensify the penetration of nature by capital, resulting in a deeper movement into crisis by moving the problems around as opposed to resolving them.