All around the world, shockwaves from constantly high oil and gas prices and electricity rates are being felt in the budgets of power producers and customers. When electricity is generated by gas turbine the fuel cost represents typically 60percent of the electricity selling price.

In addition environmental requirements continue to increase. This is why operators around the world are looking for better filtration systems as a mean to avoid fouling and keep fuel consumption at a minimum. 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 be weighed heavy 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.

Many operators are now looking at possibilities to operate their gas turbines for longer periods, two-three years, without shutdowns. Keeping the engine clean by preventing small particles from entering the air inlet system is one important step to achieve this target.

It means taking gas turbine filtration systems from the now typical medium efficiency technology to the ‘clean room’ technology or HEPA filtration. By going from the typical F8 grade to H12, penetration is dramatically reduced.

For example, penetration on 0.4micron particles is reduced from typically 25percent for a F8 filter to less than 0.5percent in a H12 filter. A huge improvement which cuts fouling dramatically. Camfil Farr Power Systems has developed a Life Cycle Cost (LCC) program that allows operators to assess how different filtration solutions affect the total cost of operating a gas turbine. The

LCC-GT software can be used to optimise an intake system for a specific gas turbine taking into account the variables including engine performance characteristics, airborne contaminations, filter efficiency, pressure drop, filter dust holding capacity and life, filter and fuel prices, the value of engine output, downtime costs for filter changes and off-line engine cleaning, labour cost for filter maintenance and filter disposal costs.

Camfil Farr Power Systems AB is based in Boras, Sweden. www.camfilfarr.com