Optimization of cooling water systems.

• Ano de defesa: 2022
• Autor(a) principal: Levy, Ana Lucia Lisbona
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade do Estado do Rio de Janeiro; Centro de Tecnologia e Ciências::Instituto de Química; Brasil; UERJ; Programa de Pós-Graduação em Engenharia Química
• Palavras-chave em Português: Optimization; Cooling water system; Cooling water tower; Heat exchangers; Água; Otimização; Sistema de água de resfriamento; Torre de água de resfriamento; Trocadores de calor; ENGENHARIAS::ENGENHARIA QUIMICA::OPERACOES INDUSTRIAIS E EQUIPAMENTOS PARA ENGENHARIA QUIMICA
• Link de acesso: http://www.bdtd.uerj.br/handle/1/20117

Cooling water systems are widely used in chemical, petrochemical, refinery and power plant industries. In a typical configuration, they consist of a cooling tower, a pumping system, heat exchangers, and interconnection piping among these elements. The literature about the design of these systems is dominated by nonlinear mathematical programming solutions and metaheuristic methods. However, these approaches are associated with important limitations, e.g. the convergence of nonlinear mathematical programming algorithms may be difficult and metaheuristic methods cannot guarantee global optimality. Therefore, this thesis proposes a set of design procedures that avoid the limitations of the literature approaches. The first analyzed problem corresponds to the optimization of the design of the hydraulic system of the cooling water distribution network together with the thermal design of the heat exchangers. The use of appropriate mathematical techniques allows the formulation of the problem as an integer linear programming problem (ILP). The results obtained showed that the proposed design approach presents solutions with lower total annualized cost than traditional procedures usually employed in the engineering practice. The second problem corresponds to an extension of the previous problem, where the temperatures of the cooling water leaving the heat exchangers become optimization variables. Due to its complexity and number of variables, this problem needs to be solved with a more specialized approach, encompassing Set Trimming and a recursive mixed-integer linear programming (MILP) problem. The results obtained showed that the iterative method showed a cost improvement of 5.2% in relation to the simpler model with a fixed flow rate distribution. The third problem presents the optimization of the cooling tower considering as optimization discrete variables the height of the filling, the type of filling, the number of towers and the area of the tower. This problem is solved using Set Trimming and Smart Enumeration. The fourth problem integrates all the previous problems in a unique task. The resultant analysis involves the design of all elements of the system, encompassing cooling tower, pump, pipe network, and heat exchangers. This problem is solved using a set of different techniques including conventional enumeration, Set Trimming, Smart Enumeration, and a recursive MILP. The results showed that a cooling water system with the lowest annualized total cost was selected and that the cost variations for the cooling tower were more significant than for the cooling water network. The solution proposed for these problems are unprecedented. In addition, they will help the industry to design lower cost cooling water systems. Due to the magnitude of the cooling services in a process plant, cost reductions in this type of system can be associated with a significant impact in financial terms.