A METHOD AND DEVICE FOR CLEANING AN AXIAL COMPRESSOR

This invention regards a method of cleaning compressor blades in an axial compressor. More particularly, it regards a method in which fluid jet-shaping nozzles are moved into a compressor stage through an opening in the compressor casing, pressurized fluid being sprayed through the nozzles against the blades while the compressor rotates relatively slowly about its rotor axis. The invention also comprises a device for implementing the method.

Although the invention is aimed especially at an axial compressor it may advantageously be adapted for an axial turbine, and the invention also includes these. However, the following only refers to axial compressors.

According to prior art, axial compressors are cleaned of e.g. salt or other undesirable materials by spraying a detergent into the compressor inlet while the rotor is rotated by the starting motor. In the case of a gas turbine the detergent is then drawn into the axial compressor and on through the turbine, and out at the discharge side of the turbine.

The detergent may be injected into the compressor air intake, as described in e.g. US patent no. 6 073 637, or through bores in the compressor casing between the rows of blades in the compressor, as shown in e.g. US patent application no. 2003/0133789.

Experience has shown that the injected detergent will quite quickly be flung to the periphery of the rotor. Therefore, only the first of the typically ten to sixteen rows of blades (stages) in an axial compressor, or those located nearest to the points of injection, will receive an approximately uniform distribution of detergent, while the blades further to the rear will only see a slight effect of the detergent.

This type of cleaning process is supposed to work by dissolving deposits and then transporting these to the outlet of the machine. The detergent flow has only a minimal mechanical effect on the blade surfaces.

Subsequent inspections have shown that only the first three to four rows of blades achieve satisfactory cleaning through use of this method, as the deposits removed from the first few rows of blades also tend to be deposited on the rows of blades located further to the rear.

As mentioned above, the detergent flows out of the machine along with a flushing medium and a significant amount of air. This only allows a certain amount of the detergent to be recovered, and thus it will flow to a nearby drain system or another undesirable recipient such as a municipal sewage system.

In order to overcome the environmentally concerns associated

with such a method, this type of detergent must satisfy- relatively strict environmental requirements, essentially preventing the use of effective detergents.

The object of the invention is to remedy or reduce at least one of the drawbacks of prior art.

The object is achieved in accordance with the invention, by the characteristics stated in the description below and in the following claims .

Cleaning of an axial compressor or an axial turbine is performed by adding detergent via apertures in the compressor or turbine casing, the detergent being sprayed against the compressor or turbine blades under pressure, whereby the jet of detergent effects mechanical cleaning of the surface of the blade .

The pressure of the cleaning nozzles may vary between a few tens of bar up to several hundred bar.

During this cleaning operation, the compressor is rotated in the opposite direction of the normal rotating direction. By so doing, dissolved contaminants will not be transported further on to a connected turbine but flows out of the axial compressor at the inlet of the axial compressor.

A low rotation speed will cause that each blade passes its respective cleaning nozzle at a relatively low speed, thus contributing to a thorough cleaning of the blade.

Advantageously the detergent is collected after use, by means

of e.g. a mantle enclosing the compressor inlet.

Advantageously the detergent and entrained air is directed to a separator in which the detergent is separated from the air.

Generally, recovering the detergent, e.g. through filtration, and then reusing it will prove profitable.

The method of the invention allows the blades to be subjected to both chemical and mechanical cleaning, thereby achieving significantly improved cleaning results compared with prior art. Due to the relatively slow rotation of the compressor in the opposite direction of the normal operating direction, the detergent is mixed only with a moderate amount of air, and the detergent is also transported to the compressor inlet, all of which makes it easy to collect and recover the detergent .

The following describes a non-limiting example of a preferred method and embodiment illustrated in the accompanying drawings, in which:

Fig. 1 shows an axial compressor in which it is provided cleaning nozzles connected to a cleaning aggregate; and

Fig. 2 shows the location of the cleaning nozzles relative to the rows of blades in the axial compressor.

In the drawings, reference number 1 denotes an axial compressor comprising a rotor 2 and a casing 4 (compressor casing) . A plurality of rotor blades 6 are distributed in a

row about the rotor 2, forming, in a manner that is known per se, together with a plurality of stator vanes 8 distributed in a row internally of the casing 4, a compressor stage 10, see Figure 2. A plurality of compressor stages 10 are provided one after the other in the longitudinal direction of the axial compressor 1.

The casing 4 is provided with an opening, typically an inspection window 12, at each row of stator vanes 8. The inspection windows 12 are arranged primarily to allow the probe of a borescope (not shown) to be inserted into the casing 4 for inspection of the rotor blades 6.

To clean the rotor blades 6, a nozzle tube 14 is moved in through the inspection window 12 , towards the rotor 2 in each compressor stage 10. The nozzle tube 14 is provided with cleaning nozzles 16 designed so as to ensure that jets 18 of detergent from the cleaning nozzles 16 cover the longitudinal extent of the corresponding rotor blade 6, see Figure 2.

A nozzle tube 14 may be connected to other nozzle tubes 14 to form an array 20 of nozzles. The array 20 of nozzles is connected to a supply pipe 22 via an array valve 24.

The number of arrays 20 of nozzles is adapted for the axial compressor in question.

The supply pipe 22 receives a sequential supply of detergent and rinse water from a feed pump 26. In this example of a preferred embodiment the feed pump 26 is part of a cleaning aggregate 28.

The cleaning aggregate 28 comprises a carriage 30 provided with an air/liquid separator 32, a first receptacle 34 for used detergent and rinse water, a cleaning unit 36 of a type that is known per se, for used detergent, comprising filters (not shown) , a second receptacle 38 for detergent and a third receptacle 40 for rinse water.

The feed pump 26 receives detergent via a detergent pipe 42 and a detergent valve 44, and rinse water via a rinse water pipe 46 and a rinse water valve 48.

Used detergent and rinse water is passed to the air/liquid separator 32 by a blower 50 and a tubing connection 52 from a mantel 54 covering the inlet to the compressor 1.

The separated air is evacuated from the air/liquid separator 32 via an outlet 56, while liquid flows into the first receptacle 34.

The cleaning aggregate 28 is supplied with the required power via a control system (not shown) which also controls the array valves 24 plus the detergent valve 44 and the rinse water valve 48.

To clean the blades 6 and vanes 8 of the axial compressor 1, the nozzle, arrays 20, which must be adapted for the axial compressor 1 in question, must first be placed in the inspection windows 12. By so doing, the nozzle tubes 14 are arranged in a gap between two stator vanes 8, with their respective cleaning nozzles 16 directed at the adjacent rotor blade 6.

The mantle 54 is sealingly mounted about the compressor 1 inlet.

The rotor 2 is then slowly rotated in a manner that is known per se, in the opposite direction of the normal rotating direction, by means of equipment commonly used to rotate the rotor 2 during inspection. This equipment is well known to a person skilled in the art and will not be described in any greater detail.

Pressurized detergent is pumped to the array valves 24 while the rotor 2 is rotated as described. The array valves are opened one after the other in order to achieve efficient cleaning of the blades 6 and vanes 8, and also to ensure that any loosened deposits are transported out of the axial compressor 1. When the cleaning is complete, the detergent valve 44 is closed, and then the rinse water valve 48 is opened. The array valves 24 are again controlled in a certain sequence to achieve optimum flushing of the axial compressor 1.

Detergent, rinse water and entrained air all flow to the air/liquid separator 32 via the blower 50 and the tubing connection 52, in which separator 32 the liquid collects in the first receptacle 34.

This means that the amount of detergent discharged through the outlet 56 is negligible.

In another embodiment (not shown) the nozzle tube 14 is connected directly to the supply pipe 22 to allow the use of a low capacity feed pump 26. In this case the compressor stages 10 are cleaned sequentially.

Naturally, purification of used detergent may be performed in a separate installation (not shown) .