Fouling in phosphoric acid concentration is a persistent operational problem that compromises energy recovery in this process. Progress is hampered by the lack of quantitative knowledge of fouling dynamic effects on heat exchanger transfer. The object of this work is an experimental determination of the thermal fouling resistance in the tubular heat exchanger of phosphoric acid preheated installed in phosphoric acid concentration process. By measuring the inlet and outlet temperatures of phosphoric acid, steam temperature, suction and discharge pressure of the pump and acid density measurement, the overall heat transfer coefficient has been determined. The determination of the overall heat transfer coefficient with clean and fouled surfaces, allowed calculating the fouling resistance. The results from the heat exchanger studies showed that the fouling resistance increased with time and presented an asymptotic evolution in compliant with the proposed model by Kern and Seaton, with the existence of fluctuation. The poorly cleaned heat exchanger implied the absence of the induction period and caused, consequently, high values of the fouling resistance in a relatively short-time period.

In typical heat exchanger design methods it is generally assumed that the overall heat transfer coecient is constant and uniform; however, the heat transfer coecients on the hot and cold sides of the heat exchanger may vary with times. In this work, a large number of operating parameters were collected for three types of heat exchangers, namely stainless-steel tubular and two graphite blocks from dierent suppliers (A and B), in an industrial phosphoric acid concentration unit over a period of two years. An experimental study performed to determine both the overall heat transfer coecients in the clean state and the overall heat transfer coecients at time t. A statistical approach was proposed to determine the overall heat transfer coecients in the clean state as well as the retain cycles. The overall heat transfer coecients were evaluated at dierent times. Our results show that the overall heat transfer coecients decreased exponentially with the time and reach a minimum value ranging between 1419 to 2406 W m −2 K −1 according to the type of heat exchanger.

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