Water distribution system pipes span thousands of miles and form a significant part of the total infrastructure of the country. Rehabilitation of this underground infrastructure is one of the biggest challenges currently facing the water industry. Water main deterioration is twofold: the main itself loses strength over time and breaks; also, there is degradation of water quality and hydraulic capacity due to build of material within a main. The increasing repair and damage costs and degrading services demand that a deteriorating water main be replaced at an optimal time instead of continuing to repair it. In addition, expanding business districts, indirect costs, and interruptions including protected areas, waterways and roadways require examination of trenchless technologies for pipe installation. In this thesis a new threshold break rate criterion for the optimal replacement of pipes is provided. As opposed to the traditional present worth cost (PWC) criterion, the derived method uses the equivalent uniform annualized cost (EUAC). It is shown the EUAC based threshold break rate subsumes the PWC based threshold break rate. In addition, practicing engineers need a user-friendly decision support system to aid in the optimal pipeline replacement process. They also need a task-by-task cost evaluation in a project. As a part of this thesis a comprehensive decision support system that includes both technology selection knowledge base and cost evaluation spreadsheet program within a graphical user interface framework is developed. Numerical examples illustrating the theoretical derivations are also included. / Master of Science

As the importance of water use in the power generation sector increases across the nation, the ability to obtain and analyze real power plant data is pivotal in understanding the water energy nexus. The Navajo Generating Station in Arizona and the Browns Ferry Nuclear Plant in Alabama are examples of where water shortages have threatened the operation of power generators. The availability of freshwater in the United States is beginning to dictate how and where new power plants are constructed. The purpose of this study is to provide and analyze cooling system parameters using 2008 data provided by the Energy Information Administration. Additionally, the cost of water saved among different categories of power plants is calculated. In general, the conditions which cause cooling systems to withdraw less water are not necessarily the more expensive conditions, and vice versa. While not all the variability in the cost of cooling systems is being accounted for, the results from this study prove that nameplate capacity, capacity factor, age of power plant, and region affect the costs of installed cooling systems. This study also indicates that it would be most cost effective for once-through cooling systems to be replaced with recirculating- pond instead of recirculating- tower systems. The implications of this study are that as power plant owner's struggle in balancing cost with water dependence, several parameters must first be considered in the decision-making process. / Master of Science

A destilação é um processo de separação com uma alta demanda de energia, razão pela qual, através de diferentes épocas tem sido estudadas diferentes configurações. O problema da separação de misturas multicomponente pode envolver sequências de colunas de destilação convencionais. Neste caso, surge um problema combinatório a fim de projetar a sequência mais econômica de separação. Por outro lado, em anos recentes têm sido proposto o uso de equipamentos alternativos, sendo as colunas com paredes divididas uma opção bastante estudada que se caracterizam pela integração de 2 seções de colunas compartilhando um único condensador e um único refervedor. Estes equipamentos propõem diminuir o custo total de processo de separação de misturas multicomponentes. Neste trabalho apresenta-se um estudo econômico da separação de três misturas ternárias de Benzeno, Tolueno, P-xileno, comparando os projetos ótimos de sequências convencionais e de colunas de paredes divididas. Inicialmente, são definidas as variáveis de projeto para cada configuração por meio de uma análise de graus de liberdade. O dimensionamento é realizado inicialmente com o método não rigoroso de valor de fronteira. Finalmente, as sequências diretas e indiretas e as colunas de parede divididas são projetadas usando modelos rigorosos, baseados no método de ponto de bolha, programação matemática para resolver os problemas de otimização do Custo Total Anualizado TAC com variáveis contínuas e enumeração exaustiva para tratar o problema combinatório. São obtidos projetos ótimos para uma alimentação com três composições diferentes. A sequência indireta forneceu o melhor resultado para a alimentação rica no componente mais pesado (-58,35%) e no componente intermediário (-45,98%). Já a sequência direta foi a melhor quando a alimentação é rica em componente leve (-33,36%). A coluna com parede dividida teve o pior desempenho em todos os três casos estudados. / Distillation is a high-energy demand separation process, for that reason, alternative configurations have been studied through the ages. The separation problem of multicomponent mixtures may involve a sequence of conventional distillation columns. In this case, a combinatorial problem arises in order to design the most economical separation sequence. On the other hand, in recent years the use of alternative devices has been proposed. One of those options is the divided wall column, which is extensively studied, and is characterized by the integration of two column sections sharing a single condenser and a single reboiler. This equipment is sought to decrease the total cost of the separation process for multicomponent mixtures. This work presents an economic study for the separation of three ternary mixtures of benzene, toluene and p-xylene, comparing the optimum design of conventional sequences and divided wall columns. Initially, the design variables are defined for each configuration through a degrees of freedom analysis. The sizing is initially performed with the boundary value shortcut method. Then, the direct and indirect sequences, and divided wall columns are designed using rigorous models based on the bubble point method. Mathematical programming is used for solving the optimization problems of minimization of the total annualized cost (TAC) with continuous variables and exhaustive enumeration to handle the combinatorial issue. Optimal designs for three feeds with different compositions are obtained. The indirect sequence provided the best result for the feed rich in the heaviest component (-58.35 %) and in the intermediate component (-45.98 %). The direct sequence result was the best when the feed composition is rich in lighter component (-33.36 %). The divided wall column had the worst performance in all three cases studied.

A destilação é um processo de separação com uma alta demanda de energia, razão pela qual, através de diferentes épocas tem sido estudadas diferentes configurações. O problema da separação de misturas multicomponente pode envolver sequências de colunas de destilação convencionais. Neste caso, surge um problema combinatório a fim de projetar a sequência mais econômica de separação. Por outro lado, em anos recentes têm sido proposto o uso de equipamentos alternativos, sendo as colunas com paredes divididas uma opção bastante estudada que se caracterizam pela integração de 2 seções de colunas compartilhando um único condensador e um único refervedor. Estes equipamentos propõem diminuir o custo total de processo de separação de misturas multicomponentes. Neste trabalho apresenta-se um estudo econômico da separação de três misturas ternárias de Benzeno, Tolueno, P-xileno, comparando os projetos ótimos de sequências convencionais e de colunas de paredes divididas. Inicialmente, são definidas as variáveis de projeto para cada configuração por meio de uma análise de graus de liberdade. O dimensionamento é realizado inicialmente com o método não rigoroso de valor de fronteira. Finalmente, as sequências diretas e indiretas e as colunas de parede divididas são projetadas usando modelos rigorosos, baseados no método de ponto de bolha, programação matemática para resolver os problemas de otimização do Custo Total Anualizado TAC com variáveis contínuas e enumeração exaustiva para tratar o problema combinatório. São obtidos projetos ótimos para uma alimentação com três composições diferentes. A sequência indireta forneceu o melhor resultado para a alimentação rica no componente mais pesado (-58,35%) e no componente intermediário (-45,98%). Já a sequência direta foi a melhor quando a alimentação é rica em componente leve (-33,36%). A coluna com parede dividida teve o pior desempenho em todos os três casos estudados. / Distillation is a high-energy demand separation process, for that reason, alternative configurations have been studied through the ages. The separation problem of multicomponent mixtures may involve a sequence of conventional distillation columns. In this case, a combinatorial problem arises in order to design the most economical separation sequence. On the other hand, in recent years the use of alternative devices has been proposed. One of those options is the divided wall column, which is extensively studied, and is characterized by the integration of two column sections sharing a single condenser and a single reboiler. This equipment is sought to decrease the total cost of the separation process for multicomponent mixtures. This work presents an economic study for the separation of three ternary mixtures of benzene, toluene and p-xylene, comparing the optimum design of conventional sequences and divided wall columns. Initially, the design variables are defined for each configuration through a degrees of freedom analysis. The sizing is initially performed with the boundary value shortcut method. Then, the direct and indirect sequences, and divided wall columns are designed using rigorous models based on the bubble point method. Mathematical programming is used for solving the optimization problems of minimization of the total annualized cost (TAC) with continuous variables and exhaustive enumeration to handle the combinatorial issue. Optimal designs for three feeds with different compositions are obtained. The indirect sequence provided the best result for the feed rich in the heaviest component (-58.35 %) and in the intermediate component (-45.98 %). The direct sequence result was the best when the feed composition is rich in lighter component (-33.36 %). The divided wall column had the worst performance in all three cases studied.