Real Time Fouling Diagnosis And Heat Exchanger Performance

CATEGORY: HEAT EXCHANGERS
ECI Symposium Series, Volume RP2: Proceedings of 6th International Conference on Heat Exchanger Fouling and Cleaning - Challenges and Opportunities, Kloster Irsee, Germany, June 5 - 10, 2005
Real Time Fouling Diagnosis And Heat Exchanger Performance
Fábio dos Santos Liporace1 and Sérgio Gregório de Oliveira2
1 Petrobras R&D Center (CENPES), Basic Engineering, Process Automation and Optimization (EB/AOT) CEP: 21949-900, Rio de Janeiro, RJ, Brazil, E-mail: liporace@petrobras.com.br
2 Petrobras R&D Center (CENPES), Basic Engineering, Process Automation and Optimization (EB/AOT) CEP: 21949-900, Rio de Janeiro, RJ, Brazil, sgregorio@petrobras.com.br
ABSTRACT
The issue of fouling in preheat trains of crude oil distillation units in Petrobras' refineries is a major concern, especially now, as heavier Brazilian crudes with higher asphaltene content are being refined. As the efficiency of the preheat train plays an important role in the energy consumption of a distillation unit, its performance must be tracked as precisely as possible in order to identify operational problems. This work describes an on-line heat exchanger performance evaluation system based on rigorous simulation of the equipment in order to predict both the operational and clean overall heat transfer coefficient.
A real time comparison between these two values indicates the actual performance of the heat exchanger and of the preheat train. The use of a rigorous process simulator (Petrox from Petrobras) together with a rigorous calculation of the global heat transfer coefficient (using the program Xist from HTRI) allows one to consider aspects that are not usually taken into account in this kind of evaluation. These aspects include crude vaporization after the desalters, variations of crude and products composition with the distillation unit run. The system is being implemented at the biggest Petrobras refinery (360 000 bpd), in a 25 heat exchanger preheat train.
Introduction
This paper aims to present the methodology used by Petrobras to work on the third scale. A computational tool, using C++, has been developed to infer, on a real time basis, the thermal efficiency of each heat exchanger (measured by the fouling factor, for instance) as well as of the whole preheat train. This tool can help to choose which pieces of equipment should be removed for cleaning (Smaïli et al., 2001; O'Donnell et al., 2001) and also to help the crude unit operator to make decisions regarding the preheat operation so he can maximize the heat recovery from it. Also, the actual fouling factors that are being measured can be used by Cenpes (Petrobras R&D Center, in Rio de Janeiro, Brazil) heat exchanger design team in order to improve their design. Currently, in most cases, those factors are taken from tables presented by TEMA and do not always represent the reality regarding time dependency, crude and process stream composition and so forth.
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