Figure 21-8. Effect of cleaning on po.er output.
However， in a regenerative unit they can deposit in the regenerator. Some regenerator burnouts have been attributed to these deposits. In steam sys-tems they will probably plug up traps throughout the system.
During discussions about abrasivecleaning， the possibility of causinglabyrinth damage is always raised. In fact， these apprehensions have provengroundless. No one knowswhy， but it could be that the particles are too bigto enter the clearance space. On a centrifugal compressor， a typical radialclearance on the interstage shaft labyrinth is 0.008inches， as compared to aparticle size of 0.060 inches. The eye labyrinth has a much greater clearance， but an abrasive particle would have to make an unguided 1800 turn to reach it. It is unlikely that a particle would do so.
How are the abrasives introduced into the machine? With air compressors， the abrasive can be thrown into the open suction. If the suction or point ofinjection ispressurized， the abrasives can be introduced with a blow pot. An eductor should be used to put the abrasive leaving the blow pot into a fluidized state before introducing it to the main gas stream. A good starting point for the injection rate is 0.1 weight percent of gas flow.
Solvent cleaning is a much more delicate technique than the brute force of abrasion. Inreality， there will almost always be some abrasive action involved. The idea is to dissolve the deposit in a solvent. The solution must then be removed from the system before the solute is redeposited. Each solvent-cleaning application presents different problems. Two methods are outlined:
1. .ater wash. This method is used to remove deposits. Distilled water is sprayed into the air inlet at a specified rate and engine speed. This speed is normally at a reduced rpm so that the water will not flash into steam in the compressor and therefore become ineffective on the latter stages or diffuser.
2. .etergent wash. This method is used to remove oil and oil-like depos-its. A mixture of solvent detergent and water is sprayed into the inlet while the gas turbine is being rotated by the starter. The unit is allowed to remain idle for a period of time to allow the solution to dissolve and loosen the deposits. The procedure is then repeated except that distilled water is used to flush the deposits off the com-pressor and out the combustor drains..
.ot-Section Maintenance
Combustion chambers can be removed if integrally arranged with theturbine， or they can be minutely inspected for cracks or burned areas with aborescope. Short， individual cracks are not uncommon and need noimmediate attention. However， if the cracks are grouped such that their continuance or the beginning of another crack could cause the loss of apiece of metal， then a repair should be made. Cracks of this nature normally can be welded with a type of welding rod recommended by the manufac-turer， depending on the kind of metal involved. Burned or warped areas in combustion chambers or baskets can be cut out and new sections welded.However， burned areas should be studied with regard to location， pattern， or repetition in all chambers to determine the cause of the burning.
Individual burned areas may indicate a dirty or faulty fuel burner nozzle or misalignment of the combustion chamber. Similar burned areas in various chambers may indicate abnormally high firing temperatures during starting due to excessive fuel use. They may also be the result of ""slugs"" of liquidsentering with the fuelgas， excessively rapidstarts， or overloading of the
. Solvent wash of the hot section requires the unit to be brought down to idle speed. The metal temperatures in the unit should be around 200 0F. To achieve this temperature in a reasonabletime， the unit can be run on the starter rotor. For a largeturbine， the entire wash cycle will take about 16-20 hours.
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