The cost of clean air

The cost of fouling

When electricity is generated by gas turbines, the fuel cost typically represents 60% of the electricity selling price. Meanwhile, environmental requirements continue to increase. This is why many operators are now looking for better filtration systems to avoid fouling and keeping fuel consumption at a minimum.

The effect of fouling

Axial compressor fouling is primarily caused by airborne submicron particles. Fouling changes the shape of both rotating and stationary vanes and results in a reduction of both mass flow and pressure ratio generated by the compressor. The net result of fouling is a reduction of power output and an increase in heat rate for a given combustor outlet temperature. Conversely, if an engine is not running at its temperature limit, a fouled engine has to run hotter to produce a given output.

A secondary effect of fouling is an increase in airfoil temperatures in the high pressure turbine, as fouling in the internal vane and blade cooling passages reduces heat transfer effectiveness and ultimately reduces the life of the hot section. The costs of fouling far exceed the cost of eliminating it, but since capital costs tend to weigh heavily in equipment purchase decisions, many gas turbines are equipped with inadequate inlet air filtration and the operator ends up paying many times more in extra operating costs.

Extended service intervals

Many operators are now looking at possibilities to operate their gas turbines for longer periods of 2-3 years without shutdowns. Keeping the engine clean by preventing small particles from entering the air inlet system is one important step towards achieving this target. It means taking gas turbine filtration systems from the now typical medium efficiency technology to clean room technology or HEPA filtration. By going from the typical F8 grade to H12, penetration is dramatically reduced. For example, penetration on 0.4 micron particles is reduced from typically 25% for a F8 filter to less than 0.5% in a H12 filter – a huge improvement which cuts fouling dramatically. 


In conclusion:

The cost of fouling far exceed the cost of eliminating it

 

Read more about: Life-cycle cost of filtration

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