Gas Turbine Handbook : Principles and Practices

Gas Turbine Inlet Treatment 117
water to wet the evaporative cooler pads. In this case, the DI water
would break down the bond in the evaporative cooler pads and the
filter (assuming that the filters are downstream of the cooling flow)
and reduce them to a mush-like substance. On the other hand, using
water with a high calcium (C a
) or calcium carbonate (C a
CO 3
) content
would result in calcium deposits throughout the compressor and the
cooling passages of the turbine.
Also, contaminant particle size varies within each area. For
example, in a desert environment 50% of the contaminant consists of
particles smaller than 1.5 microns (μm). The following details the size
of contaminant and the major components:
>5.0 μm dust, rain, fog, chemicals, minerals and metals
1-2 μm dust, salts, fog, soot, chemicals, minerals and metals
0.3-0.5 μm hydrocarbon emissions, smog.
INLET AIR FILTERS
Filter types and configurations should be selected on the basis
of the environment in which they are expected to operate, the
amount of maintenance available, and the degree of protection expected.
Inertial Separators are available with and without dust
removal capability (Figure 8-1). They are useful in areas where
there is a significant level of contaminants above 25 microns. Prefilters
provide a similar function as the inertial separator and their
initial cost is considerably lower. Intermediate Filters, with and
without viscous coating, help to extend the life of the high efficiency
filter. Intermediate filters must be capable of capturing 30% or more
of the target micron size of the problematic contamination in the
environment. High Efficiency Filters must be capable of capturing
in excess of 95% of the problematic contamination down to 1.0
micron. Prefilters, intermediate filters, and high efficiency filters are
commonly available in the barrier or pad type configuration. These
are usually 24 inch × 24 inch square with depths ranging from 6
inches to 24 inches (Figure 8-2). This configuration lends itself to
stacked filters. That is the intermediate filter and the high efficiency
filter elements may be mounted back to back. This is convenient and
economical.