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Oilfield Technology
August
2015
Any contaminants in the air will adversely affect the operating
efficiency, fuel consumption and availability of the gas turbine. Add
salt aerosols into themix and the risk of hot end or cold end erosion
significantly increases. Therefore, the air filtration system is a crucial
element in a turbine package.
Notall filtersarecreatedequal
Most standards and specifications for filtration systems for rotating
machinery have been derived and adapted fromthose used to specify
filters in theHVAC business. However, because gas turbines drawmuch
more air at comparatively higher rates than anHVAC system, filters need to
be stronger andmore robust.
Earlier HVAC standards relied heavily on the filtrationmedia having
electrostatic properties. These propertiesmade reaching a high efficiency
rating relatively easy. In the highmoisture, salty environments found in
many oil and gas applications, however, these properties are short-lived
and the efficiency of the filter quickly deteriorates. The resulting poor
performance of the filtration system leaves valuable, critical rotating
machinery exposed and vulnerable to contaminate damage, reduced
efficiency and risk of early failure.
Newer standards, suchas filtration classification standardEN779:2012,
focus onaminimumefficiency level withneutralisedmedia that takes the
effect of any electrostatic properties out of the testing criteria. As thewhole
systemof classifying filters has improved tobetter accommodate the needs
of the operators andgive a true representationof filter efficiency, systems
are less prone to rapiddegradationand there ismuch greater confidence
thatmachinery is protectedas it shouldbe. Neutralisation can substantially
change a filter’s rating. It is consideredbest practice toneutralise the full
filter andnot just themedia for truest results.
The newest revision to the EN1822 filtration classification standard
for ratings of E10 to E12, which covers the category of efficiency particulate
air (EPA) filters, accommodates different ways of defining efficiencymore
suited to the needs of the oil and gas industry, but it still does notmanage
thewhole story. In relatively easy environmental conditions that are fairly
unchangeable, such as a dry, sandy desert area; there is a high level of
confidence in performance against a test rating. In an application based in
an area such as theNorth Sea, however, the situation is very different. Here
a filtration systemneeds tomanage seamists, salt aerosol, hydrocarbons
andwidely fluctuating conditions.
Standard filter ratings are based on efficiency, particle size and
pressure drop, but do not considermoisture. When a particulate ismixed
withwater it fundamentally becomesmuch harder tomanage in a system.
Moisture can swell captured contaminants, increasing pressure loss and
creating blockages. If moisture is allowed to pass through the filter it will
also carry contaminantswith it, whichmakes the turbine vulnerable to
increased fouling, damage and corrosion.
The use of newermaterials such as
PTFEmembranes can enhance filtration
performance. However, thesematerials
have proved unsuitable for some harsh
environments especially the demanding
operating conditions in the upstreamoil
and gas sector. What is required for these
types of challenging conditions are filters
that are EPA rated, with proven hydrophobic
performance, mechanically and thermally
robust, capable of capturing salt aerosols
and that provide sufficient dust holding
capacity tomeet operatormaintenance
schedules.
Superior filtrationtechnology
offersmorerobust
performance
High levels of small particulates in the
formof sand, dust and shot-debris from
drilling, salt aerosols in offshore and
coastal locations, and harshweather
conditions all threaten the performance
and health of a gas turbine. To combat this
and ensure reliable performance tomeet
an offshore operator’s needs, the testing
Figure 1.
ThealtairODSYvCell filter combinesmicroglass technology
withextendeddepth tokeepmediavelocity constantwhileavoidingany
systempressure loss increases. This ensures that the filter house remains
compactwhilegreatlyextending final filter life. This technology isavailable
in12 in., 17 in. and24 in. depths to fit any standard filter house size.
Figure 2.
The altair ODSY vCell filter is designed to fit a range of newand retrofit filter house systems and
is constructed towithstand extremely challenging operating environments to keepgas turbines running
in topperformance.
