Mitigation of Fouling in Crude Preheat Trains by Simultaneous Dynamic Optimization of Flow Rate and Velocity Distribution

Crude oil fouling has been researched for decades, whereas optimization methods proposed to mitigate the effect of fouling on heat exchanger network performance are not many. For preheat trains with multi parallel branches, flow rate redistribution (change split ratios) is a valid mean for fouling mitigation, but related works ignored the consideration of significant power and pump cost associated with pressure drop caused by fouling. Crude velocity is correlated with fouling, so that detailed modification of heat exchanger can be considered to change velocity to further correlate heat transfer, pressure drop, and fouling. A time discretization method is proposed in this paper for fouling mitigation of heat exchanger network by dynamic optimization of velocity distribution through two ways. Simulated annealing algorithm is used to solve the model. Fouling rate in heat exchanger affected by wall temperature and velocity can in turn decrease wall temperature and increase velocity, which corresponds to a dynamic process. To describe the dynamic behaviour of optimization problem, the whole operational time horizon is divided into several time intervals and adjacent intervals are linked by fouling resistance. The flow split ratios both for cold and hot streams are changed with time. The objective function is represented by minimum annual total cost for preheat train. The main optimization constraints are composed of mass and energy balances and bounds for fluid velocity. A simple preheat train is used to illustrate the utilization of the optimization method. The optimization results present better heat exchanger network performance compared to the base case.