DRY ICE BLASTING ON HEAVY DUTY GAS

TURBINES

Ashwin S Narayanan @ Preva Icetech SB

The Gas TurbineGas 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 scheduledbased on operation hours (EOH). Most of the components at the hot section are changedat 8000 EOH intervals by stages. However, during every 40,000 hours, the gas turbinewill 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 fromthe components.

Components which can be cleaned with Dry Ice Cleaning

1. Compressor Blades2. Compressor Casings3. Seals4. Heavy duty Bolts & Dowels5. Gears (Gearbox)6. Auxiliary Components

Compressor BladesThe 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.

Bearing Housing & Seals

Compressor Blades (Rotating)

Compressor Blades (Stationary/Casing)

Turbine Blades

Bearing Seals & CasingsCasing

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

After

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.

Compressor Rotor Blades -

Before

Compressor Rotor Blades -

After

WWW.ICETECH.DK

1 2

3 4

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

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.

BLASTING EFFECTS

THE PROCES THE PROCES –– DRY ICE BLASTINGDRY ICE BLASTING

WWW.ICETECH.DK

DryDry iceice is is doseddosed in in throughthrough thethe air air currentcurrent

DryDry iceice is is filledfilled intointo thethemachinemachine manuallymanually ororautomaticallyautomatically by by useuse ofofthethe autoauto--fillfill system system orordirectlydirectly connectingconnecting thetheIceMakerIceMaker PR150 to PR150 to thethemachinemachine

TheThe compressedcompressed air air is is connectedconnected

DryDry iceice is led by is led by thethe air air currentcurrent out out throughthrough thetheblastingblasting hosehose

TheThe coating is coating is cleanedcleaned withwith drydry iceiceTheThe gungun cancan bebe operatedoperated manuallymanually

oror by by useuse ofof a robot for a robot for automaticautomaticblastingblasting

MACHINE PRINCIPLE

THE PROCES THE PROCES –– DRY ICE BLASTINGDRY ICE BLASTING

WWW.ICETECH.DK

BLASTING GUNS WITH FLAT NOZZLESBLASTING GUNS WITH FLAT NOZZLES

PRODUCTS PRODUCTS

WWW.ICETECH.DK

EFFECTS OF EFFECTS OF ICE SPLITTERICE SPLITTER

PRODUCTS PRODUCTS

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, it’s 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: Ice Splitter + 50mm Flat or 8mm round nozzle

Pressure @ Ice Flow Rate: 6-7 bar @ 30kg/hr

Uncoated Steel Blades

Nozzle to use: Ice Splitter + 50mm Flat or 8mm round nozzle

Pressure @ Ice Flow Rate: 8 – 10 bar @ 30-40kg/hr

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.

Thank You