GB2484337A

GB2484337A - A compressor washing apparatus and associated nozzle for a gas turbine engine

Info

Publication number: GB2484337A
Application number: GB201016963A
Authority: GB
Inventors: Uyioghosa Leonard Igie; Pericles Pilidis; Paul Lambart; Ken Ramsden; Shuo Shi
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-10-08
Filing date: 2010-10-08
Publication date: 2012-04-11
Also published as: GB201016963D0

Abstract

A compressor washing arrangement comprising a nozzle 4, the washing arrangement using bleed air 9 from the compressor in the washing process. The bleed air from the compressor preferably atomises the washing liquid before it is sprayed 6 into the compressor. The nozzle used preferably has an outlet designed to emit the washing liquid at an angle towards the blades 3, 7, 8. The nozzle may have a liquid channel within, surrounded by a bleed air channel (see figure 5). During use, the bleed air forces the washing liquid through the nozzle outlet. Ideally, the wash nozzle does not protrude from the surfaces 5 that bound the compressor working fluid. A plurality of nozzles may be provided, and the nozzles may be linked to a common pipe ring. This compressor cleaning arrangement is intended for use while a gas turbine engine is online / operational, and it sprays 6 high pressure atomised washing liquid and air into the compressor intake.

Description

An Installation of Compressor Wash Apparatus and Nozzles for Gas Turbine Engines

Background

Gas turbine engines are susceptible to compressor fouling, which may be accompanied by erosion and corrosion. Fouling is the deposition and accretion of particles on compressor blades, which emanate from ambient air. This leads to an alteration in the aerodynamic shape of the compressor blade through increase in surface roughness, which results in a reduction of blade-to-blade pitch distance. The consequence of this is a reduced mass flow and pressure ratio that consequently reduces power output and thermal efficiency. An attainment of the lost power and efficiency leads to a requirement for an increased fuel burn with the possibility of elevated exhaust gas temperatures that risk infringing OEM warranties. The reduction of turbine blade creep life due to prolonged high firing temperature is a detrimental effect as well as the increased NOx emission that occurs.

Compressor washing includes a passive and active approach often regarded as off-line and on-line cleaning respectively. The former is normally conducted during a major overhaul, which may infer that it is an opportunist practice as opposed to the latter which operates in real time during engine run. Experience from gas turbine operations provides the individual advantages of both methods; however a complimentary regime of both methods is regarded most beneficial. This is because the major objective for off-line washing is to clean a dirty compressor while on-line washing is used to keep a compressor relatively clean to maintain perform ance.

There are currently different washing installations such as Patent US-5868860 that discloses a method in which nozzles are attached to pipes that are further connected to a ring pipe hanging on the propeller hub end. The supply of wash liquid from the main supply feeder is made possible by the connection of an intermediary hose to the circular pipe/nozzle distribution. In this method, the nozzle piping is elongated from the fan blades towards the guide vanes into the compressor. The discussed patent also discloses another method in which the piping is clipped to the nacelle for support with a similar nozzle/pipe extension around the fan, for an aircraft without a fan blade.

Other methods for compressor washing may include nozzles protruding from the inlet duct walls, at a distance away from the compressor blades as provided in Patent WO- 2005/02811 9-Al. The patent also reveals a nozzle designs with one and more than one orifice per nozzle that claims to improve the local concentration of atomised wash droplets.

The invention revealed here encompasses a method that operates farther into the compressor, with nozzle concepts which meets the technical confrontation of such an implementation that is not possible in most existing nozzles.

I

Statement of Invention

One of the objects of this invention is a compressor wash arrangement with nozzles at a proximity to the compressor blades, allowing for enhanced wash coverage and droplet penetration that is applicable to off-line and on-line washing. The invention also embodies two novel nozzle concepts of a liquid only and pressurised bleed air assisted means of injection for an internally inclined orifice channel. The nozzle arrangement shown in Figure 1 and 2 relate to both nozzle concepts, consisting of any number of nozzles whose configuration: 1. preserves the kinetic energy of atom ised wash liquid for effective blade impact due to its proximity to the blades.

2. enhances the potential for wash liquid to travel farther down the compressor end, that aid rare-stage washing when a non-high temperature carrier liquid is injected and optimises it when the opposite is the case.

3. effectively makes best use of desired mean droplets sizes that can penetrate the boundary layer around the blade. In conventional arrangements large droplets are usually thrown away towards the casing by centrifugal forces while small droplets often lack the kinetic energy to be effective. With R-MC's technique devised to provide a wider range of mid-size droplets, this relatively short distance between nozzle and blade rnaximises the use of droplets.

4. avoids the interference between nozzle and air flow which often leads to unwanted turbulence that reduces the quality of air supply, since the nozzle does not protrude the compressor casing.

5. significantly improves the overall washing of the compressor blades due to the placement of nozzles around the compressor casing periphery. In addition, allows for a more precise impact on the compressor blade especially at the front stages, minimising waste of wash liquid.

The liquid only nozzle concept ensures a consistent discharge and rapid response to changes of wash liquid flow rate that negates flow related instabilities. The capability to spray directly towards the front blades in the direction of the flow assist in preserving the effective droplet size before impacting the front blades. This is made possible by the internally inclined orifice channel and orifice.

On the other hand the pressurised bleed air assisted nozzle concept incorporates the characteristics of the former, together with a section that allows the kinetic energy of pressurised air to shatter the wash liquid for atom isation. This generally reduces the demand for high pressure on wash liquid that often requires more pump mechanical effort relative to air. Fressurising air as stated requires less work/power consumption on an external feed pump due to its significantly less density. This in turn reduces the delay between wash and rinse from the pump.

In this concept, the compressed bleed air has a pressure up to 3bar at the time of entry into the external pump to be further pressurised. This also leads to a further reduction in the pump mechanical work. The importance of this second stage pressurisation is that bleed pressure may be insufficient to atomise the wash liquid. This design is also accompanied by a greater degree of freedom to control wash liquid and bleed air flow rate, as well as droplet size.

The nozzle body for both concepts are considered to be made of chemical and corrosion resistant materials which may be fabricated from casting techniques or axial machining of the material piece. The ellipse orifice of the nozzle can be bored by drilling, as in the case of adopting machining.

Drawings The depiction of the nozzle arrangement combined with the nozzle concept includes the figures attached: 1. Annulus view of a compressor with nozzle embedded inside the casing, for which the nozzle does not protrude the casing.

2. Periphery of a compressor installed with nozzles.

3. Depicted exterior view of nozzle design with atomised droplet spray.

4. Cross-sectional view of the liquid only concept, spray angle and penetration.

5. Cross-sectional view of the pressurised bleed air assisted nozzle.

The Figure 1 portrays the annulus view of a compressor during operation. Ambient air flows via the inlet 1 as the shaft 2 rotates the rotor blade 3. The fixed nozzle body 4 in the embedded casing 5 squirts the wash liquid or water 6 towards the Variable Inlet Guide Vanes (VIGV) 7, rotor 3 and stator 8. The connecting pipe 9 to the nozzle 4 is an imprecise illustration which would normally be channelled to a pressure feed pump.

Figure 2 illustrates a peripheral view of the compressor with nozzle 4 in the casing 5 which may support any amount of nozzle 4 depending on the engine size. In a typical operation with nozzle 4 installed, the spray or atomisation of wash liquid is activated by the increasing pressure from a feed pump via the pipe 9. In the case of the pressurised bleed air concept, pipe 9 represents both the liquid and air channel. The compressor air is bled simultaneously with discharge of wash liquid.

Figure 3 is an exterior view of the nozzle 4 applicable to both nozzle concepts of Figure 4 and 5. The upper section could be a thread section 10 which allows for convenient attachment to a feed pipe while the lower section 11 would normally be implanted into the compressor casing.

Figure 4 is the cross-sectional view of the liquid only nozzle. The representative description illustrates the internal volume 12 of the nozzle with an orifice 13, whose diameter is dO and spray angle is oO. When the wash liquid 6 is pumped into the internal volume 12, the orifice diameter dO causes the spray angle cO. This angle oO is also a function of the internal orifice channel 14 as well as the external feed pump pressure. For optimum performance of the nozzle for a bespoke solution, the spray penetration distance has to show relationship to the nozzle distance dl (from the nozzle centre line to the VIGV leading edge, at least). The spray penetration is dependent on the liquid and compressor air flow densities, their temperatures, the orifice diameter dO, time after atomisation, aspect ratios (length/diameter) of nozzle and orifice. With an increasing aspect ratio, the penetration distance increases, however the divergence height hO reduces. Obtaining a good balance between divergence height hO and penetration distance (or dl) is hence desirable; because as the difference between average height hi of the front blades 7, 3, 8 and divergence height hO becomes small, the coverage area increases.

Figure 5 demonstrates the procedure involved in the pressurised bleed air concept. The pressurised bleed air as described in the statement of invention is fed into the sections 15 of the nozzle. The wash liquid 6 is then introduced into section 12 after which on arrival at the first inner orifice 16 the wash liquid is shattered by the air pressure. The bleed air leaves no option for the atom ised liquid but to flow through the inner orifice channel 14 where it is further atomised, escaping the outer orifice 13.

Claims

Claims 1. A method of compressor washing in which any number of the said nozzles in subsequent claims are embedded inside the compressor and installed around the periphery of the compressor, at any defined distance separating each nozzle.
2. A method of compressor washing according to claim 1, in which the nozzles are placed within the proximity of the VIGV, determined by nozzle spray angle and penetration depth.
3. A nozzle design applicable to claim 1 and 2, in which the internal channel leading to the outer orifice is projected at an angle, fitted to either side of the nozzle, as well as any mechanism for the said nozzle that provides a spray angle preferably between 0 to 100° with the effect of compressor drift air taken into account.
4. A nozzle design according to claim 3, for the liquid only design, for which the wash liquid pressure range between 2 to lOObar.
5. A nozzle design targeted towards compressor washing, in which bleed air is part of the atomisation/wash process.
6. A nozzle design which includes the use of bleed air to atomise the wash liquid, that is applicable to claims 1 to 3, whose air blast pressure is typically around the range stated in claim 4, however applicable to extremely high pressures, depending nozzle size, fluid viscosity and density.
7. A nozzle design according to claim 6 for which the wash liquid pressure is below that stated in claim 4 for any given similar operation and for which the wash fluid in the said nozzle, undergoes re-atomisation through the inner and then the outer orifice, or any one of the two.
S. A method and nozzle design according to the preceding claims, for which the nozzle does not interfere with the compressor air flow and having a capability of scaling any parts to provide design flexibility.