Development of Heat Exchanger Fouling Model and Preventive Maintenance Diagnostic Tool

Abstract

The Crude Preheat Train (CPT) is a set of large heat exchangers which recover the waste heat from product streams back to preheat the crude oil. The overall heat transfer coefficient in these heat exchangers may be significantly reduced due to fouling. One of the major impacts of fouling in CPT operation is the reduced heat transfer efficiency. The objective of this paper is to develop a predictive model using statistical methods which can a priori predict the rate of the fouling and the decrease in heat transfer efficiency in a heat exchanger in a crude preheat train. This predictive model will then be integrated into a preventive maintenance diagnostic tool to plan the cleaning of the heat exchanger to remove the fouling and bring back the heat exchanger efficiency to their peak values. The fouling model was developed using historical plant operating data and is based on Neural Network. Results show that the predictive model is able to predict the shell and tube outlet temperatures with excellent accuracy, where the Root Mean Square Error (RMSE) obtained is less than 1%, correlation coefficient R2 of approximately 0.98 and Correct Directional Change (CDC) values of more than 90%. A preliminary case study shows promising indication that the predictive model may be integrated into a preventive maintenance scheduling for the heat exchanger cleaning.

A Model-Based Method for Visualization, Monitoring, and Diagnosis of Fouling in Heat Exchangers

“…In Figure 2(a), the hydraulic limit (HL), indicated by the vertical line, was set at 5 times the value of the clean pressure drops (as recommended in ref. 19 ), whilst the thermal limit (TL), indicated by the horizontal line, was set to a minimum thermal performance of 30% of the clean one, as recommended by Zabiri et al 57 .…”

“…Useful limit lines refer to minimum acceptable performance and may be operational constraints (e.g., maximum allowable pressure drop) or design targets (e.g., minimum heat duty). In Figure a, the hydraulic limit (HL), indicated by the vertical line, was set at 5 times the value of the clean pressure drops (as recommended in ref ), while the thermal limit (TL), indicated by the horizontal line, was set to a minimum thermal performance of 30% of the clean one, as recommended by Zabiri et al These limits are typically set by engineering personnel. By comparing the location and evolution of the TH-line relative to the TL and HL, one can immediately obtain useful insights into the dominant impact of fouling (hydraulic or thermal).…”

Joint economic optimization of heat exchanger design and maintenance policy

“…While the discussion of fouling phenomena is beyond the scope of this paper the interested reader can consult a large number of literature works on this subject [44][45][46][47][48][49][50][51].…”