Integrated separator/heat exchanger

Typical Prosperpack system configuration.

Framatome subsidiaries Proser and Packinox have teamed up to develop a compact heat exchanger/separator named Proserpack. Integration of these modules is claimed to offer a reduction in overall weight as well as in the number of connecting pipes.

The system is suited particularly for gas cooling to aid condensate recovery or for dew point control in applications where mechanical refrigeration or turbo-expanders are used. Norsk Hydro has become the first buyer, for its Oseberg Field expansion project in the Norwegian CS.

The shell and tube version of Proserpack combines two Packinox, explosion-formed plate, heat exchangers with an integrated Proser separator. The plate design offers higher efficiency and low pressure drop, in turn improving heat recovery with a reduced expansion ratio or refrigeration load.

The compact design and low weight (180 tons for the shell and tube solution) reduces the overall footprint, allowing additional capex cost savings. Maintenance costs are also said to be low.

Chief characteristics of the expander inlet heat exchanger are:

Hot side, 706122 kg/hr; temperature in/out +22 degrees C/-10.6 degrees C
Cold side, 710640 kg/hr; temperature in/out -29.2 degrees C/-16 degrees C; heat transfer duty - 21343 kW. For the expander inlet cooler:
Hot side, 96289 kg/hr: temperature in/out 22 degrees C/-5.7 degrees C
Cold side 78951 kg/hr; temperature in/out -16.8 degrees C/+16 degrees C; heat transfer duty 2428 kW.

Bongkot

In a separate development, Proser is supplying gas treatment (dehydration) units for Phase 3 of Total Thailand's Bongkot, which will push gas production up from 11 MMcm to 17 MMcm daily. Proser also supplied units for the two earlier expansion phases. To date Proser has supplied 10 such systems in the Far East, with end-users including Shell, Petronas, Unocal and Pertamina.

Synthetic ropes-suction anchors offer strong FPSO mooring options

Taut leg mooring using suction anchors in combination with synthetic fibers is becoming a serious option for floating production units, following full-scale tests at sea.

Suction Pile Technology (SPT) has proposed using suction anchors for mooring FPSOs in deep water. A strong candidate for the mooring lines could be DSM's Dyneema rope which is both lightweight and sturdy.

Vertically loaded anchors are an accepted solution. "But handling these anchors may be difficult due to the force needed to stabilize them at the appropriate soil penetration," says SPT's general manager Ton Geul.

"Anchors with a loading capacity of 500 to 1,000 tons should be installed by tugs with 200-250 bollard pull. The costs of mobilizing such tugs are relatively high and with regard to the large number of FPSOs to be installed in the coming years, one might even expect a shortage of tugs at certain times."

The use of suction anchors is a proven technology. SPT has installed numerous such moorings inshore as well as offshore for platform applications. The vertical loading capacity can be extremely high and sufficient for applications such as FPSOs and TLPs.

The simple installation procedure is well known. A typical advantage of suction anchors over other mooring systems is the simplicity with which they can be removed. Pumping air under the anchors allows them to float and they can be towed to shore or other locations by small tugs.

The Dyneema rope, designed by DSM High Performance Fibers, proved superior to polyester rope during tests by Saga Petroleum off Norway in 280 meters of water. The rope has a specific weight slightly less than one and has thus virtually zero weight in water, whatever the length. The DSM fiber is 10-15 times stronger than steel and also stronger than polyester on a weight and diameter basis. The rope also appeared to meet criteria for withstanding very high loads that can occur during severe storms.