SEPTEMBER
2014
LNG
INDUSTRY
49
increased with the groovy fin technology and only a few
fins were distorted, whereas the conventional fins were
damaged.
Savings for end users
The performance increase of the ACHE should be evaluated
depending on the service it is used for. The following
example is for a condenser with an internal fluid that is
to be condensed at a temperature of 60°C by air at 30°C.
Typically in a pure component condenser, 25% of the
thermal resistance is due to the internal two phase flow
heat exchange between the fluid and the tube, 5% is due
to the conduction of the heat inside the tube material, and
70% is due to the convective heat exchange (HE) between
the fin and the air. The total resistance is the sum of these
three factors.
Increasing the air side heat transfer coefficient by 25%
allows a reduction of the total resistance by 17.5%,
meaning an increase of the global HE by 17.5%. However,
because the heat transfer is enhanced, the air side
temperature at the outlet of the ACHE is slightly
decreased. Thus, the mean logarithmic temperature
difference (ΔTLM) is reduced. Considering the example of
the condenser, calculations show that the ΔTLM is reduced
by 10%. Directly, this means that the total heat transfer
enhancement can be up to 15% for the condenser service.
In the case that no performance increase is required on the
service, the use of the groovy fin can result in a saving of
up to 15% on the plot area, through substantial savings on
the finned surface installed. This saving on the plot has a
direct impact on the total cost of the plant. It is not only
the cost of an ACHE that will impact on the Capex, as
there are many additional costs that are linked to
structure, piping, civil work and cabling. As previously
mentioned, the performance increase is estimated for a
given operating point on the fan system. Reducing the
number of items through the use of groovy fins also
directly impacts the operating costs. Fewer fans have to
be installed, which directly impacts on the plant’s power
consumption. A saving of 15% on the total heat exchanger
surface directly results in a saving on the power
consumption by the same amount. However, if the focus is
to reduce the power consumption without changing the
heat exchanger surfaces, these savings can reach up to
40%. It is also important to note that when the quantity of
fans on the equipment can be reduced less maintenance is
necessary.
Finned tube type
GEA groovy fins have been primarily developed for an
embedded finned tube type. However, many applications,
in particular LNG plants, require finned tube technology
that protects the steel tubes from the external environment
and the corrosive atmosphere. In order to answer this need,
GEA developed a bimetallic wrapped finned tube in parallel
to the groovy fin. The technology simply consists of a bare
tube recovered by a thin aluminium envelope, into which
the fins are embedded. The groovy fin is fully compatible
and can be integrated with this new wrapped bimetallic
finned tube. Another advantage is that the contact between
the bare tube and the external aluminium envelop is
excellent, due to the magnetoforming process used to
press the aluminium to the tube. This technology is reliable
as it shows no air gap and no deterioration of contact along
the product life cycle.
Technology in action
The first bundles equipped with GEA groovy fins were
deployed in 2009. Since then, over 1000 tube bundles have
been delivered using the groovy technology, mostly in gas
condensing. Groovy cooling technology is well suited to
usage in the LNG industry.
As previously mentioned, it is most efficient when the air
side heat transfer coefficient is preponderant, as with gas
coolers and condensers. Considering the example of an LNG
train of 128 tube bundles of propane condenser, measuring
211 m long, the use of groovy technology would result in a
train of 120 tube bundles measuring 174 m long, 37 m less, a
17% plot reduction for the pipe rack and minus 8 tube bundles.
The reduction of the pipe rack length is all the more
important as it accounts for 50 - 75% of the total cost of air
coolers.
Conclusion
The GEA groovy cooling technology is a solution for the
ACHE performance issue, allowing substantial savings on
plot area and life cycle cost. The solution is also applicable
for debottlenecking issues, while generating interest in the
revamping market.
Figure 4.
Fouling test result on a small scale prototype.
Figure 5.
Comparison of pressure drop with groovy and
standard fin during fouling test.
