Grootvlei Power Station’s thermal efficiency had been on a steady declining trend since it was re-commissioned in 2008, which had tremendous financial implications to the company at the time of writing. The main contributory factor to the thermal efficiency losses was identified to be the condenser backpressure losses that the station was experiencing. This loss was responsible for approximately 17% of the total efficiency losses. Therefore an investigation was conducted to determine the potential impact of the condenser backpressure loss on the thermal efficiency and the financial implications thereof. The deliverables were to determine the cause of the condenser backpressure loss and propose possible resolutions, to quantify the financial effect and to produce a cost benefit analysis in order to justify certain corrective actions. Grootvlei Power Station is one of the older power stations in South Africa and it was used as the first testing facility for dry-cooling in South Africa. It consists of six 200MW units, two of which are dry-cooled units. In 1990 it was mothballed and due to rising power demands in South Africa, it was re-commissioned in 2008. Thermal efficiency has been playing a great role due to the power constraints and therefore it was deemed necessary to conduct this study. The approach that was used was one of experimental and quantitative research and analyses, incorporating deductive reasoning in order to test various hypotheses of factors that could have been contributing to the backpressure losses. In order to do so, a logic diagram was designed which could be used to aid in the identification of possible causes of the condenser backpressure losses. The logic diagram was able to identify whether the problem had to do with the cooling tower or the condenser. It was able to identify which area on the condenser was defective i.e. whether the pumps were not performing, or whether the air ejectors were not performing. It was also able to indicate whether the inefficiency was due to air ingress or fouling. Alongside the logic diagram, a condenser efficiency analysis was used in order to strengthen and improve on the investigation. This analysis was able to identify whether the condenser was experiencing fouling conditions, air ingress, passing valves or low cooling water flow. After the investigation commenced, it was decided to focus on the two largest contributing units since the largest contributor was a dry-cooled unit and the second largest contributor was a wet-cooled unit, thus some comparison between the units was incorporated. The condenser efficiency analysis on Unit 3 (wet-cooled unit) indicated a low cooling water flow, fouling as well as air ingress. The logic diagram indicated poor cooling tower performance, high air ingress as well as fouling. Further tests and analyses as well as visual inspections confirmed these phenomena and condenser fouling was identified to be the largest contributor to the backpressure loss on this unit. The condenser efficiency analysis on Unit 6 indicated that air was entering the condenser. The logic diagram indicated that a segment of the backpressure loss was due to poor cooling tower performance. Inspection of the cooling tower indicated damage and leaks. A cooling tower performance test was conducted and the result of the test indicated that the tower was in need of cleaning. Further analyses according to the logic diagram indicated that the condenser was experiencing air ingress which concurred with the condenser efficiency analysis. A helium test, condensate extraction pump pressure test as well as a flood test was conducted on this unit and various air in-leakage points were identified. The financial implications of the backpressure losses were investigated and found to be costing millions each month. The condenser backpressure loss was contributing more than 2% to the thermal efficiency loss. The cost benefit analysis indicated that the cost of cleaning the condenser on Unit 3 would be made up within six months and a return on investment of 16,6% was calculated. The cost benefit analysis motivates for extended outage times for the purpose of cleaning the condensers from a financial perspective. Therefore, it was recommended to clean the condenser on Unit 3 and fix all known defects on the unit as well as on Unit 6. The cooling towers were recommended to be refurbished. Further investigation was recommended to determine the feasibility of installing an online cleaning system on the wet-cooled units’ condensers such as a Taprogge system. Alternative investigation methods were suggested such as smoke stick analyses for air ingress determination. It was also recommended to review the maintenance strategies that were being used since many of the defects were found to be maintenance related. If the identified problem areas are attended to, the condenser backpressure loss will decrease and the condensers transfer heat more efficiently which will lead to financial gains for Grootvlei Power Station as well as efficiency gains, plant reliability and availability gains. / MIng (Development and Management Engineering), North-West University, Potchefstroom Campus, 2015

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The meteorological conditions at Eskom’s Majuba Power Station are measured, evaluated and trended in this dissertation. The results are used to evaluate the current natural draught wet-cooling tower (NDWCT) design- and performance test specifications and to compare these to the original design- and performance test specifications. The evaluation reveals that the design parameters for the NDWCTs at Majuba Power Station, a cooling system that was originally designed optimally, could have been determined differently and arguably more accurately by using the wet-bulb temperature (Tawb) as the main design variable instead of the dry-bulb temperature (Ta). A new technique to determine optimal NDWCT design and performance test conditions is consequently proposed. In order to satisfy the atmospheric conditions required for a successful NDWCT performance test, it is also proposed that the tests be undertaken between 12:00 and 14:00 during Summer. It is found that the NDWCT inlet Tawb, measured at specific heights, does not compare well to the far-field Tawb measured at the same heights when a Tawb accuracy of 0.1 K is required. It is proposed that a more representative far-field Tawb measuring height of 10 m should be used in future NDWCT designs as the NDWCT design temperature reference height. The industry-standard reference height should, however, still be used during temperature profile calculations. A parametric study of the water-steam cycle and wet-cooling system at Majuba indicates that during full load conditions, the generated output (Pst) is primarily dependent on the condenser saturation pressure (pc). The latter is reliant on Tawb, the temperature lapse rate (LRT) that is represented by the temperature profile exponent (bT), the main cooling water flow rate (mcw), atmospheric pressure (pa), and wind speed (VW). Using historical plant data relatively simple methods, enabling the quick and effective determination of these relationships, are proposed. The plant-specific and atmospheric parameters required for these analyses are also tabulated. Two NDWCT effectiveness models, one mathematical (Kröger, 1998) and one statistical artificial neural network (ANN) model are presented and evaluated. ANNs, which are not often used to evaluate NDWCT effectiveness, provide accurate NDWCT temperature approach results within 0.5 K of measured values for varying dependent variables. This motivates that an ANN, if set up and used correctly, can be an effective condition-monitoring tool and can be used to improve the accuracy of more empirical NDWCT performance models. The one-dimensional mathematical effectiveness model provides accurate results under NDWCT design conditions. The dependency of Majuba’s NDWCT to the rain zone mean drop diameter (dd) is evaluated by means of the one-dimensional mathematical model. A reduction in dd from 0.0052 m to 0.0029 m can reduce the NDWCT re-cooled water temperature (Tcwo) so that the rated pc is reduced by 0.15 kPa, which relates to a combined financial saving during peak and off-peak periods of R1.576M in 2013 and R1.851M in 2016. Similar improvements can result in higher savings at other wet-cooled stations in the Eskom fleet due to less optimally-designed wet-cooling systems. The proposed techniques should be considered in future economic evaluations of wet-cooling system improvements at different power stations. / AFRIKAANSE OPSOMMING: Die meteorologiese toestande by Eskom se Majuba-kragstasie is deur die navorser gemeet en -evalueer. Die resultate word gebruik om die Natuurlike-trek, Nat koeltoring (NTNKT) se ontwerp- en werkverrigting toetsspesifikasies te evalueer en vergelyk met die oorspronklike toetsspesifikasies. Die resultate dui daarop dat die ontwerpsparameters vir die NTNKTs by Majuba-kragstasie, ‘n verkoelings-sisteem wat aanvanklik optimaal ontwerp is, op ‘n ander, selfs meer akkurate manier bepaal kon word deur die natbol-temperatuur (Tawb) te gebruik as die hoof-ontwerpsparameter inplaas van die droëbol temperatuur (Ta).’n Nuwe tegniek wat gebruik kan word om akkurate NTNKT ontwerp- en werkverrigting toetsspesifikasies te bepaal word voorgestel. Die tydperk vir die mees optimale atmosferiese toestande, wanneer NTNKT-toetse uitgevoer moet word, word vasgestel as tussen 12:00 en 14:00 tydens Somermaande. Dit word bewys, vir ’n Tawb akkuraatheid van 0.1 K, dat die NTNKT inlaat-Tawb, gemeet by verskillende hoogtes, nie vergelykbaar is met Tawb wat ver van die NTNKT af op dieselfde hoogtes gemeet word nie. ’n Meer aanvaarbare hoogte van 10 m word voorgestel as die NTNKT ontwerpstemperatuur verwysingshoogte vir toekomstige NTNKT ontwerpe wanneer die Tawb ver van die NTNKT af meet word. Die industrie-standaard temperatuur verwysingshoogte moet wel steeds gebruik word tydens temperatuur-profielberekeninge. ’n Parametriese studie van die turbine se water-stoom siklus en die nat-verkoelingstelsel by Majuba dui daarop dat die generator se uitset (Pst) hoofsaaklik afhanklik is van die kondensator se druk (pc) gedurende vol-vrag toestande. Druk (pc) is weer afhanklik van Tawb, die temperatuur vervaltempo (LRT) wat voorgestel word deur die temperatuur profiel eksponent (bT), die verkoelingswater-vloeitempo (mcw), atmosferiese druk (pa) en windspoed (VW). Deur die gebruik van historiese data word redelike eenvoudige metodes voorgestel om dié verhoudings doeltreffend te bepaal. Die atmosferiese- en stasie-spesifieke parameters wat benodig word vir dié ontleding is ook getabuleer. Twee modelle vir NTNKT-effektiweit, ’n wiskundige (gebaseer op Kröger, 1998) en statistiese kunsmatige neurale-netwerk (KNN) model, word aangebied en geëvalueer. KNNe, wat nie gereeld gebruik word om NTNKTe se effektiwiteit te evalueer nie, lewer akkurate NTNKT temperatuur-benadering resultate binne 0.5 K van die gemete resultate vir wisselende afhanklike parameters. Dié resultate motiveer dat ’n KNN wat korrek opgestel is doeltreffend gebruik kan word om die toestand van NTNKTs te bepaal en om die akkuraatheid van ander NTNKT-modelle te verbeter. Die eendimensionele, wiskundige model lewer akkurate resultate onder NTNKT ontwerpspesifikasies. ’n Wiskundige NTNKT-model word gebruik om die afhanklikheid van Majubakragstasie se NTNKTe tot die reënsone druppelgrootte (dd) te bereken. 'n Vermindering in dd van 0,0052 tot 0,0029 m kan die NTNKT se afgekoelde watertemperatuur (Tcwo), van só 'n aard verlaag dat pc verminder met 0,15 kPa. Só kan ’n gesamentlike vol- en gedeeltelike vrag finansiële besparing van R1.576M in 2013 en R1.851M in 2016 behaal word. Soortgelyke verbeterings aan verkoelingstelsels sal lei tot meer en hoër besparings by ander Eskom nat-verkoelde stasies. Dié tegnieke moet in ag geneem word tydens toekomstige ekonomiese evaluasies van verbeterings tot nat-verkoelingstelsels by ander kragstasies.

Thesis (PhD) -- University of Stellenbosch, 2010. / ENGLISH ABSTRACT: In the design of a modern natural draught wet-cooling tower (NDWCT), structural and performance characteristics must be considered. Air flow distortions and resistances must be minimised to achieve optimal cooling which requires that the cooling towers must be modelled two-dimensionally and ultimately threedimensionally to be optimised. CFD models in literature are found to be limited to counterflow cooling towers packed with film fill, which is porous in one direction only and generally has a high pressure drop, as well as purely crossflow cooling towers packed with splash fill. This simplifies the analysis considerably as the effects of flow separation at the air inlet are minimised and fill performance is determined using the method of analysis originally employed to determine the fill performance characteristics from test data. Many counterflow cooling towers are, however, packed with trickle and splash fills which have anisotropic flow resistances, which means the fills are porous in all flow directions and thus air flow can be oblique through the fill, particularly near the cooling tower air inlet. This provides a challenge since available fill test facilities and subsequently fill performance characteristics are limited to purely counter- and crossflow configuration. In this thesis, a CFD model is developed to predict the performance of NDWCTs with any type of spray, fill and rain zone configuration, using the commercial code FLUENT®. This model can be used to investigate the effects of different: atmospheric temperature and humidity profiles, air inlet and outlet geometries, air inlet heights, rain zone drop size distributions, spray zone performance characteristics, variations in radial water loading and fill depth, and fill configurations or combinations on cooling tower performance, for optimisation purposes. Furthermore the effects of damage or removal of fill in annular sections and boiler flue gas discharge in the centre of the tower can be investigated. The CFD modelling of NDWCTs presents various options and challenges, which needed to be understood and evaluated systematically prior to the development of a CFD model for a complete cooling tower. The main areas that were investigated are: spray and rain zone performance modelling by means of an Euler-Lagrangian model; modelling of air flow patterns and flow losses; modelling of fill performance for oblique air flow; modelling of air pressure and temperature profiles outside and inside the cooling tower. The final CFD results for the NDWCT are validated by means of corresponding one-dimensional computational model data and it is found that the performance of typical NDWCTs can be enhanced significantly by including protruding platforms or roundings at the air inlet, reducing the mean drop size in the rain zone, radially varying the fill depth and reducing the air inlet height. / AFRIKAANSE OPSOMMING: By die ontwerp van ‘n moderne natuurlike trek nat koeltoring (NTNK), moet strukturele en werkverrigtings eienskappe in ag geneem word. Wanverdeelde lugvloei en vloeiweerstande moet geminimaliseer word om optimale verkoeling te bewerkstellig, wat vereis dat die koeltorings twee-dimensioneel en uiteindelik driedimensioneel gemodelleer moet word om hulle te kan optimeer. Dit is gevind dat berekeningsvloeidinamika (BVD of “CFD” in engels) modelle in die literatuur, beperk is tot teenvloei koeltorings gepak met film tipe pakking, wat net in een vloeirigting poreus is en boonop gewoonlik ook ‘n hoë drukval het, sowel as suiwer dwarsvloei koeltorings met spatpakking. Hierdie vergemaklik die analise aansienlik omdat die effekte van vloeiwegbreking by die luginlaat verklein word en die pakking se werkverrigtingsvermoë bereken kan word met die analise metode wat oorspronklik gebruik is om die pakkingseienskappe vanaf toets data te bepaal. Baie teenvloei koeltorings het egter drup- (“trickle”) of spatpakkings met anisotropiese vloeiweerstand, wat beteken dat die pakking poreus is in alle vloeirigtings en dat die lug dus skuins deur die pakking kan vloei, veral naby die koeltoring se lug inlaat. Hierdie verskaf ‘n uitdaging aangesien beskikbare pakking toetsfasiliteite, en dus ook pakking karakteristieke, beperk is tot suiwer teenvloei en dwarsvloei konfigurasie. ‘n BVD model word in hierdie tesis ontwikkel wat die werkverrigtingsvermoë van NTNK’s kan voorspel vir enige sproei, pakking en reënsone konfigurasie deur van die kommersiële sagteware FLUENT® gebruik te maak. Hierdie model kan gebruik word om die effekte van verskillende: atmosferiese temperatuur- en humiditeitsprofiele, lug inlaat en uitlaat geometrië, lug inlaat hoogtes, reënsone druppelgrootteverdelings, sproeisone werkverrigtingskarakteristieke, variasie in radiale waterbelading en pakking hoogte, en pakking konfigurasies of kombinasies op koeltoringvermoë te ondersoek vir optimerings doeleindes. Verder kan die effekte van beskadiging of verwydering van pakking in annulêre segmente, en insluiting van ‘n stoomketel skoorsteen in die middel van die toring ondersoek word. Die BVD modellering van NTNK bied verskeie moontlikhede en uitdagings, wat eers verstaan en sistematies ondersoek moes word, voordat ‘n BVD model van ‘n algehele NTNK ontwikkel kon word. Die hoof areas wat ondersoek is, is: sproeien reënsone modellering mbv ‘n Euler-Lagrange model; modellering van lugvloeipatrone en vloeiverliese; modellering van pakking verrigting vir skuins lugvloeie; modellering van lugdruk- en temperatuurprofiele buite en binne in die koeltoring. Die BVD resultate word mbv van data van ‘n ooreenstemmende eendimensionele berekeningsmodel bevestig en dit is bevind dat die werkverrigting van ‘n tipiese NTNK beduidend verbeter kan word deur: platforms wat uitstaan of rondings by die luginlaat te installeer, die duppelgrootte in die reënsone te verklein, die pakkingshoogte radiaal te verander, en die luginlaathoogte te verlaag.

Orientador: Pedro Magalhães Sobrinho / Resumo: A pesquisa desenvolvida visa a otimização do consumo de energia elétrica de torres de resfriamento a parir do controle de acionamento dos respectivos ventiladores e bombas de circulação, além da melhoria na instrução de trabalho dos operadores, os quais frequentemente são responsáveis pela gestão da temperatura e geralmente utilizam meios manuais para manter o processo estável. O método empregado consiste em avaliar três cenários com uma equipe multidisciplinar e, respeitando a limitação técnica e o ponto de vista de cada uma das áreas, desenvolver, validar e implementar soluções de eficiência energética e térmica de rápida configuração e com retornos mensuráveis. As alterações nas construções mecânicas dos equipamentos não são consideradas e as soluções propostas têm a automação e alteração nas instruções de operação como fontes de melhoria. O requisito básico para a implementação do método é a existência de um sistema de automação, nos casos avaliados, um Sistema Digital de Controle Distribuído (SDCD), os quais contemplam os sinais de instrumentos de medição instalados em campo e realizam o acionamento dos ventiladores e bombas nos modos manual e automático. Os resultados obtidos são controles eficientes para utilização dos ventiladores e bombas de circulação, levando em conta a possibilidade de economia de energia elétrica, diminuição das chances de um eventual desgaste mecânico natural e estabelecimento mais preciso das temperaturas de processo. Os resultados alcançados e... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The developed research aims electrical energy’s consumption optimization on cooling towers through fans and circulation pumps actuating controls, besides improvements on operators instructions forms that are the responsibles for temperature management and frequently use manual mode to keep the process estability. The used method consists in a multidisciplinar team assessment in three scenarios and, based on each area technical’s limitation, develop, validate and implement themal and energy eficient solutions with fast implementation and measurable results. It was not evaluated equipment’s mechanical improvement and the expected proposal were based on automation and operators instructions. The basic requirements for the method was the existance of a DCS (Distributed Control System) that was already in place in the evaluated scenarios. The DCS already manages the measurements from the installed instruments and acts fans and circulating pumps in manual and automatic mode. As results, it was developed eficient controls on fans and circulating pumps, electrical energy savings, reducing chances of natural mechanical detrition and optimize the process’ temperatures. The results evaluated on energy efficiency were promising without operation losses, saving up to 50% on fans usage and in extreme cases, avoiding the usage of circulating pumps. The implemented proposals had a low cost investment and relevant results where payback was less than one month. / Mestre

Les légionelles sont un enjeu de santé publique majeur car ces bactéries sont responsables des cas de légionellose, parfois mortels. Les tours aéroréfrigérantes (TAR) peuvent être incriminées car pouvant potentiellement émettre des aérosols contaminés. Un traitement de désinfection de ces eaux est donc nécessaire. Cependant les techniques actuelles conduisent très souvent à des injections importantes de réactifs induisant des rejets écotoxiques dans l'environnement qu'il est nécessaire de limiter. L'application du traitement d'oxydation avancée H2O2/UV – considéré comme innovant pour ce domaine et dont l'impact environnemental est limité (décomposition du peroxyde d'hydrogène en eau et oxygène, peu de production de composés toxiques) – a prouvé son efficacité de désinfection à la fois au sein d'un pilote de laboratoire sur une eau reconstituée, chargée en microorganismes et matière organique, mais aussi lors du traitement de l'eau d'une TAR du secteur tertiaire. Les ultraviolets ont été appliqués de manière continue (10 à 22 J.cm-2 sur le pilote ; 2 à 7 J.cm-2 sur la TAR) avec le maintien d'un résiduel constant en peroxyde d'hydrogène (10 à 50 mg.L-1 sur le pilote ; 3 à 10 mg.L-1 sur la TAR). Sur le pilote de laboratoire, le traitement H2O2/UV a montré une efficacité supérieure à l'application des UV ou du peroxyde d'hydrogène seul. Des abattements plus importants sur les paramètres microbiologiques de l'eau et des biofilms (ATP, bactéries cultivables et totales) et une modification profonde de la matière organique (minéralisation) ont pu être observés. Il a ainsi été conservé les avantages de chaque technique (désinfection reconnue des UV et action bactéricide de H2O2), tout en limitant leurs inconvénients (absence de rémanence des UV, fortes concentrations nécessaires en H2O2) grâce à la génération de radicaux hydroxyles pouvant agir sur les microorganismes et la matière organique. L'étude sur une TAR a confirmé ces résultats et a montré de bonnes performances de désinfection en comparaison avec celles obtenues pour le dioxyde de chlore. Cependant, lors les phases d'optimisation des essais, une adaptation des bactéries au peroxyde d'hydrogène a été observée indiquant la nécessité d'un contrôle régulier de cet oxydant afin de maintenir un résiduel conséquent et d'éviter la mise en place d'une dérive du système. De plus, il a été montré que le traitement n'a eu qu'une faible action sur les produits de conditionnement de l'eau (antitartre, anticorrosion). Une rapide évaluation économique a permis de placer le couplage H2O2/UV dans le même ordre de grandeur que les traitements habituels. / Legionella is a major public health issue as they are responsible for Legionnaires' disease, which can be fatal. Cooling towers are often incriminated because of their potential emission of contaminated aerosols. A disinfection process for treating water is then necessary. However, current techniques often need high concentrations of chemical products which lead to ecotoxic releases into the environment. UV-H2O2 is an advanced oxidation process with a limited environmental impact (hydrogen peroxide decomposition into oxygen and water, low production of toxic compounds). It was shown that this method is an effective technique of disinfection both in a laboratory pilot on water charged with microorganisms and organic matter, and in the water treatment of a cooling tower (service sector). UV irradiation was applied continuously (10 – 22 J.cm-2 on the pilot; 2 – 7 J.cm-2 on the cooling tower) with a constant residual of hydrogen peroxide (10 to 50 mg.L-1 on the pilot; 3 to 10 mg.L-1 on the cooling tower). On the laboratory pilot, UV-H2O2 showed a higher efficacy than UV or hydrogen peroxide treatments applied alone. A more important reduction of microbiological parameters in water and biofilms (ATP, heterotrophic plate and total bacteria counts) and a deep change in organic matter (mineralization) were observed. The advantages of each process (both well-known UV disinfection and bactericidal action of H2O2) were selected by limiting their disadvantages (no residual with UV, need for high concentrations of H2O2) through the generation of hydroxyl radicals, acting on microorganisms and organic matter. The study on a cooling tower confirmed these results and showed good disinfection performances compared with those obtained for chlorine dioxide. However, the optimization phases of the treatment highlighted a bacterial adaptation to hydrogen peroxide. A monitoring of this oxidant is required in order to maintain a residual, and therefore to avoid a drift of the system. Besides, UV-H2O2 showed little effect on scale and corrosion inhibitors. A rapid economic assessment allowed to placing UV-H2O2 in the same order of magnitude as usual treatments.

Indiana University-Purdue University Indianapolis (IUPUI) / The following thesis looks into modeling a chilled water system equipped with variable speed drives on different piece of equipment and optimization of system setpoints to achieve energy savings. The research was done by collecting data from a case-study and developing a system of component models that could be linked to simulate the overall system operation.

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2003. / The thermal performance prediction of wet-cooling towers is critically analyzed and refined. Natural draft counterflow towers and mechanical draft counterflow and crossflow towers are considered. The Merkel, Poppe and e-NTU heat and mass transfer methods of analysis are derived from first principles, as these methods form the cornerstone of wet-cooling tower performance evaluation. The critical differences between these methods, when applied to fill performance analyses and cooling tower performance evaluations, are highlighted. The reasons for these differences are discussed with the aid of psychrometric charts. A new extended empirical relation for the loss coefficient of fills is proposed where the viscous and form drag effects are accounted for as well as the buoyancy, momentum and fill height effects. The empirical equation for the transfer characteristic of fills is extended to include the effects of fill height and the inlet water temperature. Empirical equations to predict the temperature inversion profile, height of the temperature inversion and the height from which air is drawn into the cooling tower are developed. The influence of temperature and humidity inversions on the performance of wet-cooling towers is subsequently investigated. A comprehensive analytical computer program is developed to predict and optimize the performance of wet-cooling towers. Computer programs are also developed to generate cooling tower performance curves, analyze fill performance test data and plot psychrometric charts.

Neste trabalho, foi estudado o desempenho de um sistema constituído de torres de resfriamento e a sua integração em uma planta industrial de hidrogenação de butadieno. Caracterizou-se o desempenho das torres de resfriamento com base em um modelo fenomenológico, cujos parâmetros foram obtidos a partir da medição de variáveis operacionais reais. O processo de hidrogenação foi configurado em um simulador de processos, sendo o caso base estabelecido nas condições de projeto. Elaborou-se um módulo específico referente às torres de resfriamento, que foi integrado ao processo configurado no simulador. Em seguida, analisaram-se as interações das condições operacionais da torre de resfriamento no desempenho do processo industrial. / In the present work, the performance of a system composed of a cooling tower integrated in butadiene hydrogenation plant was studied. An experimental investigation was made to characterize the cooling towers based on a phenomenological model and in real process conditions. The hydrogenation process was configured on a process simulator and design specifications were considered as base case. A cooling tower module was developed and integrated to the process simulator. The interaction of the cooling tower system and the plant operation was investigated.

O segmento industrial é um grande usuário de água e, na maior parte das situações, está localizado junto a aglomerações urbanas, caracterizando situação de dificuldade na obtenção deste recurso para as suas operações. As fontes de água estão cada vez mais saturadas e os processos de tratamento mais sofisticados. O objetivo deste estudo foi avaliar a viabilidade técnico-econômica da implantação do tratamento eletromagnético para água de resfriamento em indústrias químicas, substituindo ou complementando o tratamento químico convencional. O texto descreve inicialmente os fundamentos do tratamento de água baseado na aplicação de campo eletromagnético e, em seguida, os efeitos do uso dessa tecnologia sobre custos anuais de resfriamento em um caso típico da indústria química. Neste estudo foi dada ênfase ao efeito sobre os custos anuais da menor adição de produtos químicos, redução na vazão de purga e de reposição de água, além da redução na frequência de limpeza dos equipamentos e redução da carga poluente nos efluentes líquidos. O estudo foi aplicado a uma torre de resfriamento industrial, para a qual foi elaborado um modelo matemático considerando as taxas de consumo e especificações de água de resfriamento, além de parâmetros do processo de tratamento de água convencional e eletromagnético. São apresentados resultados de um estudo de sensibilidade para diferentes cenários, em que são identificados os fatores com maior efeito sobre os custos. Além disso, na aplicação ao sistema proposto, são estimadas condições ótimas de operação, considerando os ciclos de concentração para os quais pode haver maior redução de custos. Utilizando-se o tratamento eletromagnético para a água de resfriamento, há uma economia significativa, pois o número de paradas para a manutenção dos equipamentos pode ser reduzido. Dessa forma, o produto final do trabalho constitui-se em uma estrutura de cálculo voltada à estimação de custo do tratamento físico de água de resfriamento, o qual pode ser aplicado a diferentes cenários e condições de operação industrial. / The industrial sector is a major water user and in most situations is located next to urban areas, in a situation of increasing difficulty in collecting and treating water resources for its operations. The water sources are becoming more saturated and thus demanding more sophisticated treatment processes. The aim of this study was to evaluate the technical and economic feasibility of the implementation of electromagnetic treatment of cooling water in chemical industries, thus replacing or complementing the conventional chemical treatment. The text initially describes the principles of the physical process for water treatment based on the application of an electromagnetic field, and then focuses on the effects of the use of this technology on the annual costs of cooling in a typical case of the chemical industry. The study is focused on the effects of the electromagnetic treatment on the annual cost of cooling in view of the reduced consumption of chemicals, as well as reduction in purge flow and water replacement, reduced frequency of equipment cleaning, and reduction of pollution load caused by wastewater. The study results were applied to an industrial cooling tower for which a mathematical model was developed by considering consumption rates and cooling water specifications, as well as parameters of the electromagnetic and conventional water treatment processes. A sensitivity study was carried out for different scenarios, in which the most important factors affecting the annual cost are identified, and optimal process conditions are estimated for maximum concentration cycles. The study shows that the use of electromagnetic treatment for cooling water results in significant savings due to the reduced number of maintenance periods. The final product of this study is a calculation structure for cost estimation related to the physical treatment of cooling water, which can be applied to different scenarios and industrial operation conditions.

Zur Kühlung von Prozessströmen kommen aufgrund hoher Leistungsdichten häufig Verdunstungskühltürme zum Einsatz. Um die Übertragungsfläche für Wärme und Stoff zu vergrößern, werden in diesen Kühltürmen Struktureinbauten integriert. Die Weiterentwicklung von Kühlturmeinbauten und die Untersuchung der den Kühlprozess beeinflussenden Faktoren erfolgt empirisch, was eine Vielzahl von Versuchen notwendig macht. Eine numerische Simulation des Kühlprozesses kann diese Messungen unterstützen und so helfen eine Vielzahl an Versuchen einzusparen. Des Weiteren können bei versuchsbegleitender Simulation mit einem geeigneten Modell weitere Untersuchungen durchgeführt und Erkenntnisse gewonnen werden, die bei Messungen am Versuchskühlturm verborgen bleiben. In dieser Arbeit werden zwei Ansätze der numerischen Simulation eines Verdunstungskühlturms betrachtet. Es werden eine CFD-Simulation und ein vereinfachtes Modellkonzept hinsichtlich der Anwendbarkeit auf diese Problemstellung untersucht. Schwerpunkt der vorliegenden Arbeit ist die methodische Entwicklung eines solchen vereinfachten mathematischen Modells. Dieses beruht auf der physikalisch deterministischen Beschreibung der im Kühlturm ablaufenden Prozesse der Wärme- und Stoffübertragung unter Berücksichtigung des Stoffverhaltens. Aufgrund der Nichtlinearität des Stoffverhaltens und der erforderlichen Inkrementierung des Berechnungsgebiets ist ein methodisches Vorgehen erforderlich, um die Erstellung der Modellgleichungen und deren Lösung überhaupt realisieren zu können. Hierfür wird auf allgemeine Methoden der gleichungsorientierten Simulation technischer Systeme zurückgegriffen. Das entwickelte Modellkonzept wird für die Modellierung und Simulation eines Versuchskühlturms angewandt. Mit den so ermittelten Messdaten wird das Modell kalibriert und validiert. Es zeigt sich, dass mit dem erstellten Modell quantitativ und qualitativ valide Ergebnisse erzielt werden können. / Due to the high power density, the cooling of process streams is often done bei evaporative cooling towers. To enlarge the exchange area for the heat and mass transfer, these cooling towers contain integrated structural fills. The future development of cooling tower fills and the research regarding the cooling process and its influencing parameters will be carried out empirically, resulting in a large number of required experiments. A numeric simulation of the cooling process can support theses measurements and reduce the vast number of needed experiments. Furthermore, with the use of test-related simulations and adapted models, it will be possible to gain knowledge and do research in areas which are omitted during regular measurements on cooling towers. In this study it is looked to two different approaches of numeric simulation of a evaporative cooling tower. There will be an examination of a CFD-Simulation and a simplified model concept regarding their respective applicability for this problem. This work is focussed on the systematic developement of such simplified mathematical models, based on the physical deterministic description of the occurring processes of heat and mass transfer in cooling towers considering the stock behaviour. Due to the non-linearity of the stock behaviour and the required incrementation of the calculation area, a systematic approach is needed to model equations and their respective solutions. For this purpose it is necessary to access general techniques of equation-based simulations of technological systems. The developed model concept will be applied for the modelation and simulation of an experimental cooling tower. The model will be calibrated and validated with data from this experimental tower. It shows, that the results from this model are qualitatively and quantitatevily valid.