Conference Dates

July 1-6, 2007

First Page



Fouling in preheat networks of crude distillation units (CDU) plays an important role in energy consumption. In this work a procedure to monitor the performance of the heat exchanger network (HEN) and to optimize the cleaning strategies is presented. The procedure is based on a rigorous simulation of the HEN using Hysys (from Aspen Technology). The simulation is used to estimate the service overall heat transfer coefficient with real operational data acquired from the unit’s Plant Information System (PI). The clean overall heat transfer coefficient is calculated for each one of the individual heat exchangers with a rigorous simulation using TASC (rigorous heat exchanger simulator also from Aspen Technology), embedded into Hysys. A comparison between the service and clean overall heat transfer coefficients provides the actual performance for each individual heat exchanger and for the complete HEN. The first step is to collect the HEN operative data from the Plant Information System and to perform an ad-hoc preprocessing of each individual exchanger data (i.e., feed and product inlet and outlet temperatures and flow rates) in order to identify stable periods from which the mentioned calculations will be performed. As the feed/products flow rates and unit operating conditions are constantly changing, the steady intervals detection is a very important task because calculations performed with data of unstable operation time intervals could be erroneous and produce non-sense results. The overall procedure is managed from an Excel environment, which performs the needed calls to PI and Hysys/TASC simulators in order to calculate each exchanger fouling and HEN overall performance under the actual fouling situation. Excel also commands the evaluation of the cleaning policies economics, searching between several pre-defined cleaning alternatives. Results of the above mentioned methodology applied to a complex feed preheat HEN of the Topping IV CDU of REPSOL YPF Luján de Cuyo Refinery, Argentina, are presented.