A risk based heat exchanger analysis subject to fouling. Part II : Economics of heat exchangers cleaning

Fouling is one of the major uncertainties associated with the operation and maintenance of heat exchangers in the power and process industries. The decision regarding periodic maintenance (cleaning) to meet the target performance level is generally based on both thermal and economic behavior of the process. In this paper, we present a cost model, which includes the risk level and the scatter parameter of random fouling growth models. Four models, namely linear, power law, falling rate and asymptotic fouling growth are integrated in the model. The non-dimensional cost function Γ as a function of reduced time t/M is examined by considering the dimensionless cost parameters γ1, γ2 and γ3, representing additional fuel cost, antifoulant cost and miscellaneous costs, respectively. These dimensionless cost elements are examined for a heat exchanger that is used in a crude oil preheat train. The results are presented in terms of risk level p and scatter parameter α for the underlying fouling models. Furthermore, a simplified closed-form solution is also obtained to study the optimal cycle time, representing minimum cost of operation and maintenance of heat exchangers.

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