July 1-6, 2007
In a time that crude oil prices are constantly higher than US$ 60 per barrel, low fouling heat exchangers can reduce total fouling cost in all crude oil preheat trains in the world with a throughput of 74 Mn bpd by 90%. For 2006, this is a reduction from approximately US$ 11 Bn to US$ 1.3 Bn and a saving on annual fouling cost of US$ 9.7 Bn. Besides this saving on fouling cost, substantial additional savings can be realized on energy by a more ‘energy efficient’ design of the crude oil preheat train. The advantages of the low fouling exchanger have been achieved by novel, although already proven, heat transfer mechanisms for both the tube-side and the shell-side of the exchanger. The tube-side applies the circulation of solid particles, which ensures ‘zero-fouling’ in the tubes in combination with very high heat transfer film coefficients, whereas the shell-side applies Grid baffles also responsible for an excellent film coefficient and a low fouling factor. Combination of above technologies in one heat exchanger realizes clean overall heat transfer coefficients or k-values, which are approximately 200% higher than in conventional heat exchangers, while the fouling rates or fouling factors in low fouling exchangers can be reduced to less than 5% of values generally applied in conventional heat exchangers. The influence of these excellent results on additional pumping power requirements are marginal. Low fouling exchangers are also characterized by their very compact design and vertical lay-out, which characteristics are responsible for a low weight and small plot area. Another advantage of the low fouling exchangers is the possibility to vary the crude oil throughput from 100% to less than 30% without losing its excellent heat transfer performance. In spite of the low fouling design, it is still possible that the shell-side might suffer from a slow build-up of fouling deposits. To avoid this, the low fouling heat exchanger can be designed in such a way that the bundle can be removed from the shell and sufficient distance between the tube rows allow for mechanical (hydro-blasting) cleaning using the standard available equipment. As to investment cost of low fouling crude oil preheat trains versus savings, it should be mentioned that at crude oil prices of US$ 60 /barrel, the low fouling crude oil preheat train with a 100% back-up in low fouling heat transfer surface shows a ‘Return Of Capital’ (ROC) of approximately 6 months. If the existing conventional heat exchangers are used as back-up, then the ROC becomes less than 4 months. In the case of an ‘energy efficient’ design and higher crude oil prices, these ROC’s drop to less than 5 months and even less than 3 months respectively. However, if only the most problematic sections of the existing problematic crude oil preheat train are replaced by low fouling heat exchangers, the ROC’s for these investments are further reduced and might come close to 2 months. The conclusion is new crude oil preheat trains should be equipped with these low fouling exchangers and existing crude oil preheat trains or sections of these trains containing conventional heat exchangers, should be modified by replacing the conventional heat exchangers with low fouling exchangers.
D.G. Klaren, E.F. de Boer, and D.W. Sullivan, "LOW FOULING CRUDE OIL PREHEATERS: SCRAP YOUR EXISTING CONVENTIONAL CRUDE OIL PREHEATERS, REPLACE THEM BY LOW FOULING HEAT EXCHANGERS AND SAVE MONEY" in "Heat Exchanger Fouling and Cleaning VII", Hans Müller-Steinhagen, Institute of Technical Thermodynamics, German Aerospace Centre (DLR) and Institute for Thermodynamics and Thermal Engineering, University of Stuttgart, Germany; M. Reza Malayeri, University of Stuttgart, Germany; A. Paul Watkinson, The University of British Columbia, Canada Eds, ECI Symposium Series, (2007). http://dc.engconfintl.org/heatexchanger2007/34