DRY ICE BLASTING ON HEAVY DUTY GAS TURBINES
Ashwin S Narayanan @ Preva Icetech SB
The Gas Turbine
Gas turbines use the hot gas produced by burning a fuel to drive a turbine. They are also called combustion turbines or combustion gas turbines. The main components of a gas turbine are an air compressor, several combustors (also called burners) and a turbine. The air compressor compresses the inlet air (raises its pressure). Fuel is mixed with the high pressure air in burners and burnt in special chambers called combustors. The hot pressurised gas coming out of the combustors is at very high temperature (up to 1350 C). This gas then passes through a turbine, giving the turbine energy to spin and do work, such as turn a generator to produce electricity.
Maintenance
The gas turbine has several categories of maintenance. These Maintenance are scheduled based on operation hours (EOH). Most of the components at the hot section are changed at 8000 EOH intervals by stages. However, during every 40,000 hours, the gas turbine will be scheduled to a major overhaul which last about 20 to 30 days. During this time, removal of contamination and cleaning works will take up 5 to 7 days of their schedule. For this, the use of cryogenic cleaning is much effective to remove contamination from the components. Components which can be cleaned with Dry Ice Cleaning 1. 2. 3. 4. 5. 6. Compressor Blades Compressor Casings Seals Heavy duty Bolts & Dowels Gears (Gearbox) Auxiliary Components
Compressor Blades
The Compressor blades is divided in 2 parts: Stationary Blades (attached to the casings) Rotating Blades (attached to the Rotor Body)
Types of contamination usually found - fowling, soot, hardened carbon, oil & rust. The contamination on the blades can cause power augmentation. Although online cleaning with detergent is done regularly, the last stages of the blades suffers from heavy deposit of dirt. Turbine Blades
Compressor Blades (Rotating) Bearing Housing & Seals
Compressor Blades (Stationary/Casing)
Bearing Seals & Casings
Casing Types of Contamination usually found - fowling, soot, hardened carbon, oil & rust. Bearing Housing and Seals Types of Contamination usually found heavy carbon deposit, oil and grease.
Compressor top half casing
Bearing Housing
Photo shows before & after of labyrinth seals on bearing. The grooves are difficult to clean by hand and with dry ice, it takes less than 15 minutes.
Before
Photo shows before & after of compressor blade. Please note the fowling. Traditional ways to remove fowling is by using scotch pads and thinners. This method takes approx 4 5 days to clean the blades. Dry ice will remove the hardened carbon content and dirt. As for rust, it will only remove the hard face on the material. Will not give the surface the cosmetic finishing, since dry ice cleaning is non abrasive.
After
Compressor Rotor Blades Before
Compressor Rotor Blades After
BLASTING EFFECTS
1 2
1. Kinetic effect: Dry ice pellets make impact on the layer provoking fractures
Thermal effect: dry ice penetrates and generates a sudden local temperature decrease on both the dirt layer and the substrate. The different materials contract unequally so that the adherence between them diminishes. The layer cracks even more and begins to loosen off the substrate 4
Sublimation: after making impact, the dry ice turns into gas, expanding its volume by a factor of 800. The expansion acts as an explosion that detaches completely the layer from the substrate.
The substrate remains clean and completely intact.
THE PROCES DRY ICE BLASTING
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MACHINE PRINCIPLE
Dry ice is dosed in through the air current
Dry ice is filled into the machine manually or automatically by use of the auto-fill system or autodirectly connecting the IceMaker PR150 to the machine
Dry ice is led by the air current out through the blasting hose The compressed air is connected
The gun can be operated manually or by use of a robot for automatic blasting
The coating is cleaned with dry ice
THE PROCES DRY ICE BLASTING
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BLASTING GUNS WITH FLAT NOZZLES
PRODUCTS
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EFFECTS OF ICE SPLITTER
PRODUCTS
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Cleaning with Dry Ice
Compressor Blades The operator needs to be advised on the type of blades he is cleaning. There are coated blades and un-coated steel blades. On coated blades, its much easier to remove the contamination; however, the operator needs to be advised to use non aggressive cleaning method of cleaning. Coated blades Nozzle to use: Pressure @ Ice Flow Rate: Uncoated Steel Blades Nozzle to use: Pressure @ Ice Flow Rate: Turbine Casing. The casings are divided on to 2. Top half and bottom half. The top half is usually removed during any major maintenance work and the bottom half stays in place. Once the rotors are removed, this will expose the bottom half which most rectification and maintenance done in-situ. Since cleaning is a part of any major maintenance, dry ice cleaning is excellent to be included on their routine shutdown. Use same combination as blades. Ice Splitter + 50mm Flat or 8mm round nozzle 8 10 bar @ 30-40kg/hr Ice Splitter + 50mm Flat or 8mm round nozzle 6-7 bar @ 30kg/hr
Thank You
