Thesis (M.Eng.)--Chulalongkorn University, 2007

In all chemical plants using heat exchangers, fouling of heat transfer surfaces is a major problem because it increase energy consumption resulting in economic losses. Thus, the regular cleaning of fouled units is implemented to reduce this losses. In this work, the simulations of heat exchanger in a case of single unit and also in network are performed based on linear and asymptotic fouling models. The effect of various model parameters on a variations with time of outlet temperature of hot and cold stream, heat transfer coefficient and heat transfer rate is investigated. In addition, the problem of optimal cleaning schedule of heat exchangers based on time discretisation approach is formulated. The formulated optimization problem minimizes the summation of operating cost with subject to various operating conditions constraints. The optimized variables are logical variables decided whether a heat exchanger should be cleaned in each time period specified. Moreover, we also develop a new technique to handle a very large number of logical variables occurred in the problem formulated. Our technique can efficiently solve the problem while obtain a better solution compared with the traditional method.