Canadian Manufacturing

Washington firm says its experimenting with methods to improve turbine efficiency

ClearSign blade-cooling concept involves electrically charging both hot gas cloud and turbine blades

SEATTLE, Wash.—Emissions control technology firm ClearSign Combustion Corp. says it has successfully demonstrated an experimental concept for cooling turbine blades.

Turbine efficiency is limited by the capacity of turbine blades and metal structures within the turbine to withstand high levels of sustained heat loading without suffering structural damage, the company says.

In order to minimize mechanical stresses on the blades, turbines are designed so that hot combustion gases are cooled to well below their peak temperature before coming in contact with the rotor blades.

Since the mechanical output of a turbine derives directly from the expansion of the gas as temperature is increased, cooling the hot inlet gases, while necessary to protect the blades, has the consequence of severely limiting turbine efficiency.

Currently, turbine designers employ “film-cooling” techniques to deliver cooling air to the blades in order to reduce heat buildup.

However, shear forces from the high-speed rotation of the blades quickly pull this cooling air away.

The ClearSign blade-cooling concept involves electrically charging both the hot gas cloud and the turbine blades so that the hot gases are pushed away and cooling air is sandwiched between the charged blade and the gas cloud.

The boundary layer of cool air effectively insulates the blade to reduce heat loading.

“If the blades can be cooled you’re going to see a gain in efficiency,” ClearSign CEO Rick Rutkowski said in a statement. “The economic value of effective blade cooling is enormous since it translates directly into fuel savings for both jet engines and power generators.

“A gain of just one per cent in efficiency is seen by industry experts as being very significant (and) we believe that it may be possible to realize gains of as much as a few per cent in energy efficiency if we can sufficiently cool the blade surfaces.”

According to ClearSign, the combined annual market for both land-based natural gas turbines for power generation and jet engines for civil aviation is in excess of $40-billion.

ClearSign, quoting the Congressional Research Service, says the use of gas turbines accounted for 19 per cent of energy production in 1989, increased to 39 per cent in 2008, and is projected to continue the trend over the next two decades.

The market for aircraft jet engines is also projected to experience significant growth.

General Electric, which accounts for approximately 50 per cent of the global market, projects its current installed base of 26,000 engines will increase to over 45,000 by 2020.

Depending upon its size, a gas turbine running in single cycle mode can range from as little as 20 per cent to as much as 45 per cent efficiency, according to ClearSign.

According to the Company, cooler turbine blades should also lengthen the life of the equipment by reducing metal fatigue and “creep,” which together eventually lead to failure of costly parts like turbine blades and guide vanes.

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