Uma abordagem matricial para modelagem e simulação de redes de trocadores de calor com aplicações para o gerenciamento da deposição

Abstract

A Heat Exchanger Network (HEN) can be defined as a group of heat exchangers interconnected aiming to reduce the energy demand of a system, being widely used in the process industries. However, a HEN is subject to fouling, which causes a decrease on the thermal effectiveness of heat exchangers. This phenomenon is provoked by the accumulation of undesirable materials on thermal surface. In order to compensate the reduction of thermal effectiveness caused by fouling, it becomes necessary to increase the utility consumption. Thus, there is an increase of the operation costs, as maintenance costs. It is estimated that the costs associated to fouling reach billions of dollars annually. Facing this problem, several researches have investigated methods to prevent fouling and/or how to manage HEN operations. Studies involve since optimization of individual heat exchangers, simulation and fouling monitoring, until cleaning schedule optimization of HENs. The present work proposes a HEN simulation model, applied to fouling management. Consequently, it was developed a set of integrated computational codes, which involve a HEN stationary simulation, a pseudo-stationary simulation of HEN behavior related to fouling, a parameter estimation procedure for diagnosing fouling problems and an operational optimization procedure of this sort of system. Related to the stationary simulator, the HEN model is formulated using a matrix approach and the mass and energy balances are solved as linear equation systems. Focusing on optimization, it redistributes the HEN flows in order to improve the heat exchangers thermal efficiency, for example, searching for the HEN flows that maximize the inlet furnace stream temperature in crude distillation units. The algorithm was implemented to some literature examples and on a problem of a real refinery. All results show to be promising, which suggests that the proposal of this work may be an interesting approach for operations involving HENs