52
LNG
INDUSTRY
SEPTEMBER
2016
can be welded in full length onshore, transported offshore,
upended and connected to the FLNG hull.
Installation from the FLNG vessel is facilitated by
connecting the flanged riser joints while the riser is supported
in a spider at ship deck. The lifting and lowering height will be
dictated by the selected riser joint length. Heading control is
assumed for the riser installation, either by using the vessel
heading control system (if applicable), or by connecting tugs
to the stern of the vessel.
The plan is to install the risers outside of the monsoon
season to avoid strong currents and severe wave conditions.
Installation in the monsoon season remains feasible, but
should be avoided due to increased risk of stop in operation
and waiting on weather.
If forecasted or measured environmental conditions
exceed a specified level, the installation will enter into a safe
condition within 3 hours. In the safe condition, the partly
assembled riser will survive an event with return period of
10 years. Heading control is not required for the safe condition.
The described installation method is based on established
industry solutions and technology.
Preventing marine growth
Cooling water intake systems make use of hypochlorite
to prevent marine growth in water intake risers, sea chest
compartments, seawater pumps, seawater piping and heat
exchangers for gas cooling. Hypochlorite can be injected into the
seawater at the 500mdeep intake, or at the inlet to the sea chest
compartment. However, marine growth is dependent on solar
light (a considerable reduction inmarine life is observed close to
the solar light limit). Deeper intake risers will be environmentally
beneficial due to the substantially reduced need for use of
hypochlorite.
Conclusion
Aker Solutions’ new deep cooling water intake solution for FLNG
can help to increase the efficiency of offshore LNG processing.
Reducing cooling water temperature by 15 – 20°C has significant
efficiency gains in a large FLNG development. The efficiency
improvements are complemented by a design that eliminates the
need for separate installation vessels, reducing field development
costs. Use of deepwater intake risers also decreases the need
for hypochlorite use in operation, adding an environmental
benefit. The concept is based on extending the use of well-known
technology. While some further technology qualification is
necessary, the company’s deep cooling water intake solution is
ready for front end engineering and design (FEED) application on
relevant FLNG developments.
References
1. PEK, B. and VAN DER VELDE, H., ‘A High Capacity
Floating LNG Design’, 17
th
International Conference &
Exhibition on Liquefied Natural Gas, Houston, Texas, US,
(April 2013), pp. 16
–
19.
2. NEERAAS, B. O. and PETTERSEN, J., ‘Technical Innovation
for Floating LNG’, 3
rd
Trondheim Gas Technology
Conference, (4
–
5 June 2014).
Figure 5.
Riser installation – top end with flexible hang-off
assembly.
Figure 4.
Riser installation – mounting of standard joints with
vortex induced vibration (VIV) strakes.
