Gas Turbine Handbook : Principles and Practices

Gas Turbine Inlet Treatment 121
buildup on the compressor blades and stators, or the turbine blades
and nozzles during an inspection of the gas turbine (boroscope or
physical teardown).
The mere presence of a filter is no guarantee that the required
filtration is being achieved. To ensure full filter efficiency, the following
items must be checked:
• The filter elements have been properly installed.
• The correct type of filter media has been installed.
• The filter element is being properly maintained.
• The inlet plenum is being properly maintained.
• The operating environment has not changed since the unit was
installed.
A decrease in gas turbine power output, a decrease in compressor
efficiency, or an increase in the frequency of cleaning the gas
turbine compressor are all signs that the filter system is not functioning
properly. Filters become more efficient as they load up with contaminants.
The dust laden filter is significantly more effective than a
new (unloaded) filter. However, as the dust load increases so does the
pressure drop across the filter and this adversely affects gas turbine
performance and power output. Therefore, the operator must determine
the amount of power degradation his operation can “tolerate,”
and allow the filters to load to that level. Too frequent cleaning of the
self-clean filter will reduce its efficiency and could possibly damage
the filter element.
Once a filter system has been installed the operator or maintenance
personnel have the task of maintaining or even improving the
filter system. For the barrier type filter configuration there are new,
more efficient, filter elements in the same 24-inch × 24-inch size that
will fit into the existing rack. If prefilters were not part of the initial
design, they can be added with a simple, inexpensive, modification to
the main filter rack. Considering the cannister type filter, a prefilter
wrap can be installed after the target differential pressure is reached.
This will extend the time at this level of efficiency. Operators should
establish a target filter differential pressure based on their operating
requirements, and they should allow the filter to load to that differential
pressure target. For most installations it is advisable to rely
solely on the automated mechanism to clean the filters when the tar-