Page 70 - Industrial Plant 2015

turbine in order to minimize the effects fouling on the
performance of the gas turbine. However, the most
effective type of cleaning is on-crank washing, which
requires that the engine is shut down. This results in a
lower availability of the engine, and, associated with
this, may cause the cost of lost production.
Pressure Loss
The pressure loss across the inlet filtration system also
have a significant effect on the cost of operation. An
increase in the pressure loss across the filtration
system leads to reduced power output from the gas
turbine and an increased heat rate. The cost of these
effects is included in the LCC analysis as 1. a pressure
drop value per stage and filter in operation and 2.
Pressure drop for the housing itself including cooling/
heating and silencers.
Failure / Event Cost
Not included in the LCC software analysis is the cost
associated with a failure or event that occurs due to the
inlet filtration system or inlet air quality. This could be a of 99.5% of MPPS (Most Penetrating Particle Size), an
failure of a gas turbine blade or other interior parts
which occurred due to corrosion from poor inlet air
quality. These costs are often included based on past
experience with the gas turbine or other filtration
systems and should favorably be added to the total
cost of operation.
How to optimize the filtration
system
In line with tougher environmental as well as
operational requirements there is a clear trend that
operators are requesting higher grades of filtration
efficiency in order to achieve better protection of
their gas turbines and longer operational cycles. It’s
Fig. 3 - Three stage
Air Inlet System
Industrial Plants - May 2015
68
more and more frequent that operators are asking
for 1 up to even 3 years long cycles between
shutdowns. This means that gas turbine air intakes
need to enter the HEPA (High Efficiency Particulate
Air filter) world, a world previously normally seen in
surgery theatres, sensitive labs, nuclear power
plants etc. This puts high requirement not only on
the filter system design but also on the construction
and the air tightness of the system. Even a small
leak will move the system back to the F-world.
In line with tougher environmental
as well as operational requirements
there is a clear trend that operators
are requesting higher grades of
filtration efficiency in order to achieve
better protection of their gas turbines
and longer operational cycles.
With standard filters, E12/H13 needs a 3-stage system
to provide long enough filter life. With new deep type
filters the same grade of filtration can be achieved in a
2-stage filtration system. Remember, with an efficiency
E12 “takes it all”. With a system in EPA- or HEPA-class
it’s possible to achieve intervals between shutdowns of
1 year and above.
An typical offshore CamGT Inlet filtration system
(figure 3) consists of:
• Stage 1: (optional) weather hoods as first stage
arrest snow and large water droplets;
• Stage 2: vertical droplet separator with a vane
profile design for keeping pressure loss and noise
levels to a minimum;
• Stage 3: prefilter / coalescer. Normally a bagfilter
with large surface for long life and low pressure
drop. The prefiltration stage captures coarse