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and environmental costs; • Failure / Event Cost: unplanned stops and repair
• stopping a gas turbine for offline compressor due to parts wear out and/or accidents.
washing and/or filter change out means in many Purchase Price / Initial Cost
cases stop of production / revenue;
• fouling and erosion of turbine blades may also The purchase price occurs in the first year of the LCC
cause imbalance and vibrations, resulting in higher analysis. It is the cost to purchase and install the inlet
stress on components and consequently filtration system. Once these costs are established,
destruction of vital parts. Starting and stopping they are brought back to the net present value.
the turbine for cleaning lead to thermal stress of
components that may shorten the life of the Maintenance Cost
engine and lead to unnecessary maintenance
stops; The maintenance cost includes the cost of filter
• gas turbines exposed to fine dust, humidity and/or replacement and disposal. It is a recurring cost that
salt and are faced with high risks of serious should be included in each year that the cost is
breakdowns caused by hot gas corrosion, cooling acquired. This cost is calculated based on estimated
hole plugging etc.; again potentially very high filter change out frequencies, cost of filters, labor cost
costs for loss of production and equipment. for maintenance per hour.
How to evaluate the filtration Availability / Reliability of Gas Turbine
system
The availability/reliability of a gas turbine impacts the
Most operators know there is more to filtration than the cost due to the lost production and revenue due to
actual filter cost. Shipping, installation and lost shutdown of the engine. The loss of revenues is based
production during filter replacement are obvious and on average value of output (electricity, oil, gas or other
easily accounted for. But when it comes to the indirect unit for revenue), the service cycles and the estimated
costs associated with fouling, such as lower MW life time of the filter (filter change-out can either be
output and downtime for water washing or the cost of based on the final pressure drop or scheduled operating
higher pressure drop, making a full evaluation is not as hours).
straight forward. If the engine is not used 100% of the time, for example,
When selecting a filtration system, one must decide the because it is a standby or peaking unit, the cost of lost
level of protection the system should achieve. This revenues must be adjusted accordingly.
includes the particle filtration efficiency, the particle size
to be filtered, the filter replacement cycles, what rate of Gas turbine degradation and
degradation is acceptable for the gas turbine, the compressor washing
required availability of the gas turbine, what type of
washing scheme will be used (online, offline, or a Gas turbine degradation is perhaps the most
combination of both), and initial cost of the filtration important cost in the analysis. This is often the cost
system. The cost impact of each of the items mentioned which drives the analysis to favor one filtration
is quantified to compare different filtration system system option over another. The cost a fouled
options. The main parameters for evaluating the inlet
system are: Gas turbine degradation is perhaps
• Purchase Price / Initial Cost: initial investment for the most important cost in the
the complete Air Inlet System; analysis. This is often the cost which
• Maintenance Cost: cost of replacement filters and drives the analysis to favor one
labor cost for filter replacement and disposal; filtration system option over another
• Availability / Reliability of Gas Turbine: downtime
engine is calculated based on the reduced power
for complete offline water washes and downtime output and increased heat rate due to the lost
during filter replacement; engine efficiency. The change in fuel cost is
• Turbine degradation and compressor washing: calculated based on the fuel consumption in relation
gas turbine degradation, performance loss (% to the change of efficiency and the price of fuel.
per kPa, heat rate, heat rate increase % per Compressor cleaning is often performed in a gas
kPa);
• Pressure Loss: costs related to pressure drop
across other components as a sum of power
output loss and fuel cost increase;
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