Diaz-Bejarano E., Pelloja G., Coletti F., Macchietto S., 2015, Heat Exchanger Bypass Control to Mitigate the Cost of Fouling in Refinery Preheat Trains, Chemical Engineering Transactions, 43, 2119-2124.
Heat exchangers in refineries are usually designed with oversized exchange area to compensate for the gradual loss in thermal performance due to fouling. The control of bypasses during the initial stages of operation (clean conditions) represents a common strategy. This work focuses on the simulation of a preheat train heat exchanger undergoing fouling, equipped with a control of tube-side bypass, and subject to thermal and hydraulic limits. An advanced dynamic model of heat exchangers undergoing fouling, capable to accurately capture both the thermal and hydraulic impact of fouling, is used to simulate the behavior of the exchanger. The study explores the use of bypasses to counter not only thermal over-performance during initial stages of operation, but also to avoid (or minimize) throughput reduction when the maximum allowable pressure drop is reached in late stages of operation. Dynamic simulations of the system, including models for bypass control and cost evaluation, are run to find the optimal time profiles of bypass opening that minimize the total cost associated with the gradual loss of performance. The results demonstrate the potential application of these strategies to guarantee operation within both thermal and hydraulic limits and prolong operation time.
