Tranter International faced an unusual challenge when asked to supply heat exchangers for Eni’s field FPSO offshore Nigeria.
The field’s crude has a waxing point of 37 ºC (98.6 ºF), well above the usual temperature of 30 ºC (86 ºF). This meant the wall temperature of the heat transfer plates had to be maintained at a temperature of 37 ºC or more to prevent wax build-up fouling.
One of several FPSO heat exchangers supplied by Tranter. Its latest delivery is Eni’sOyo production ship off Nigeria.
Normally the two media between which the heat is transferred flow in opposite directions to facilitate efficient heat exchange. For Oyo, however, the decision was taken to use a co-current flow, flow in the same direction, to maintain the wall temperature at the required level at the expense of some loss of efficiency, explains areas sales manager for oil and gas, Stefan Gavelin.
Heat transfer is a function of pressure drop – in this case, the application of Tranter’s patented asymmetrical plate technology allowed the maximum permitted pressure drop, regaining some of the efficiency lost through use of co-current flow. Through providing high shear rates on both sides, asymmetrical plates also prevent the build-up of fouling layers.
Another benefit of this technology is that it allows the overall heat transfer surface to be reduced, compared with symmetrical plates. Also, the asymmetric plates are made of a high-cost titanium alloy, which is resistant to the corrosive effect of sea water coolant.
The solution was embodied in two GX-51 heat exchangers, Tranter’s plant in Vänersborg near Gothenburg, where most of its offshore orders are manufactured. Through its Singapore office, Tranter is also well connected with the Far East yards where many FPSOs are built or converted. For the Oyo delivery, the customer was Eni’s FPSO contractor, Bumi Armada Berhad.
For more information, contact Stefan Gavelin, Tranter International. Tel +46 8442 4998, fax +46 8 442 4980.[email protected], www.tranter.com
