WO2020043541A1

WO2020043541A1 - Method for operating a gas turbine

Info

Publication number: WO2020043541A1
Application number: PCT/EP2019/072201
Authority: WO
Inventors: Johannes Döhnert; Sarah GÄRTLEIN; Andreas Heilos; Francis Ladru; Thorsten Schulz
Original assignee: Siemens Aktiengesellschaft
Priority date: 2018-08-30
Filing date: 2019-08-20
Publication date: 2020-03-05
Also published as: DE102018214752A1

Abstract

The invention relates to a method for operating a gas turbine (100) comprising a rotor (103) with a plurality of rotor blades (120) and a housing (138), at least some of the rotor blades (120) being coated with a hard material, and an abradable coating being applied to the housing (138) in the region of the rotor blades (120), and there being a gap (n) between the rotor (103) and the housing (138), characterised in that the gas turbine (100): - is started up, - is operated at full load for at least 15 minutes, - is slowed down and kept in rotation at a low frequency without firing for several hours, and then speeded up again. This allows operation of the gas turbine (100) which is particularly protective of the coated tips of the rotor blades (120) by deliberately causing the rotor blades (120) to brush against the still intact coating.

Description

Process for operating a gas turbine

The invention relates to a method for operating a gas turbine comprising a rotor with a plurality of rotor blades and a housing, wherein at least the tips of the rotor blades are coated with a hard material and an abradable layer is attached to the housing in the region of the rotor blades, and wherein between the Rotor and the housing a gap is formed. The invention further relates to a control device for performing such methods and a gas turbine with such a control device.

In every turbomachine, especially a gas turbine, there are radial gaps in the flow channel between the rotating components (usually the rotor blades, hereinafter also referred to as rotor blades) and the housing. This gap leads to pressure losses which reduce the efficiency of the process. The gaps in the design of the gas turbine are therefore chosen to be as small as possible.

The size of the column changes during operation of the gas turbine. There are many reasons for this, for example different heating or cooling speeds of the housing and blades (especially in transient operation), deformation of the shaft bearings when heating, ovality or uneven deformation of the housing when heating due to asymmetrical cooling air supply or asymmetrical housing design, uneven aging (creep) of the components, etc. This leads to the rotor blades rubbing against the housing, in particular during transient operation of the gas turbine. The rotor blades are shortened as a result, so that larger gaps and thus greater losses occur in the subsequent full-load operation. For example, a system for predicting turbine friction is known from US Pat. No. 8,682,563 B2.

To ensure maximum gas turbine efficiency, it is crucial to keep the gap between the rotating and static components as small as possible during operation. In the case of a conical flow channel, one possibility for this, after transient phases have passed, in which the gaps at the blade tips narrow as much as possible, is the rotor in stationary high-load operation, e.g. to move axially with a hydraulic system. If the rotor is moved against the direction of flow, the gaps are reduced.

A method for minimizing an adjustable gap between a rotor blade and a housing of a turbine is known from WO 2014/016153 A1. By moving the rotor and housing against each other, the gap between the rotor and the housing is to be minimized in a simple manner. For this purpose, an output signal is sent to the runner

and / or the structure-borne noise monitoring system assigned as a measure of the size of the gap and thus used for setting a minimum gap.

A grindable seal is attached to the turbine housing, which is also referred to as the abradable layer. On strip seals or layers for the rotor blades of gas turbines, which are arranged on the inner wall of the turbine housing, are designed as honeycomb structure seals (also called "honeycomb seal") or as porous, ceramic coatings. The blade tip is cut into the grindable seal without substantial wear or substantial damage to the coating or the blade tip.

In order to avoid removal of the material at the tip of the rotor blade, it is already known from the prior art to cover the ends or tips of the blades with a ceramic see covering or with hard material particles or with abrasive particles to armor. In particular, cubic boron nitride is used as the hard material coating. Such a coating device is shown, for example, in DE 44 36 186 C2. However, it is problematic that the cubic boron nitride has only a limited service life of several hundred hours at the operating temperatures (> 1100 ° C) of a gas turbine.

The invention has for its object to enable a particularly gentle operation of the gas turbine for the coated tips of the rotor blade.

The object is achieved by a method for operating a gas turbine comprising a rotor with a plurality of rotor blades and a housing, wherein at least some of the rotor blades are coated with a hard material and a stripping layer is attached to the housing in the region of the rotor blades, and wherein between a gap is formed in the rotor and the housing, the gas turbine being:

- is started,

- is operated at full load for at least 15 minutes,

- is shut down and kept rotating at low frequency for several hours without firing, and

- is started up again.

Additionally or alternatively, the object is achieved according to the invention by a further method for operating a gas turbine comprising a rotor with a plurality of rotor blades and a housing, wherein at least the tips of the rotor blades are coated with a hard material and on the housing in the region of the rotor blades AbstreifSchicht is attached, and wherein a gap is formed between the rotor and the housing, wherein

- the gas turbine is started,

the gas turbine is operated at full load until the gas turbine is completely warmed up, an optional gap optimization in which there is an axial offset of the rotor and / or the housing is switched on,

- The gas turbine is relieved at part load and operated at least one hour at part load.

In addition, the object is achieved according to the invention by a control device for carrying out the method or methods described above.

The object is finally achieved according to the invention by a gas turbine with such a control device.

The parts and preferred embodiments listed below with respect to the method can be analogously transferred to the control device and the gas turbine.

It is known from studies in which phases of transient operation and at which position the blade tips are brushed. The invention is based on the idea of deliberately provoking the rubbing, in particular establishing the rubbing in the first operating hours of the gas turbine as a standard. The main advantage is that the coating, e.g. contains cubic bornite trit, is still intact and can therefore be rubbed into the abradable layer without shortening the tip of the blade. It is not mandatory for all rotor blades to be coated with hard material particles, but at least 10% of the rotor blades have a hard material coating per stage. In the case of the coated rotor blades, it is also sufficient if only the tips have the coating.

The rubbing occurs in particular in two operating states. The invention aims to drive these two operating states selectively through different operating modes. In the first case, the gas turbine is started up as usual and operated for several minutes or hours (depending on the turbine type between 15 minutes and 100 hours) at full load.

If the gas turbine is then shut down and continues to rotate without firing for several hours, preferably up to 24 hours, but up to a maximum of 30 hours, a natural convection occurs due to the very low speeds at low speed. This leads to a vertical temperature gradient in the diameter of the gas turbine and consequently to a deformation of the standing housing parts. This deformation causes a smaller, radial turbine gap in at least one place. The gap is closed continuously, so that the gaps have a minimum value about 10 hours after the gas turbine has been shut down, so the gas turbine rotates in this state for several hours, in particular up to 24 hours.

If the gas turbine is started again in such a state, there is a strong rubbing in the area of the reduced gap or the reduced gap. This operating state is targeted according to independent claim 1. This guarantees rubbing in with coated blade tips, so that later, when the coating is no longer intact, the blade tips do not shorten, this operating state should be set again.

According to a preferred embodiment, the gas turbine is operated between 8 hours and 12 hours at full load. This ensures that the gas turbine is completely heated.

According to a further preferred embodiment variant, the gas turbine is not fired (ie in a so-called “turning gear” operating mode in which the gas turbine, for example an external electric motor or the generator is kept in rotation) at a frequency between 0.5 Hz and 5 Hz operated to induce natural convection, which cal temperature gradients and thus ultimately leads to grazing.

The second case or operating state relates to rubbing against a different position. In particular, due to an uneven supply of cooling air, which leads to a temperature gradient in the circumferential direction during operation, and a non-optimal centering of the rotor to the housing above the bearing star, there is a three-dimensional deviation of the turbine radial gaps. In order to enforce this streaking, the gas turbine is relieved from a warmed-up full-load operation in accordance with independent method claim 4 and then relieved for one hour at part load, i.e. in particular with a load shedding of at least 10%, with activated gap optimization, if this is present, operated. Relief from the fully warmed-up full-load operation is preferably carried out to a minimally achievable or permissible partial load for the gap optimization.

In order to provoke the brushing with the coated tips of the rotor blade as early as possible, namely as long as the coating of the blade tips is safely in an intact state, the first start of the gas turbine in both methods is preferably startup of the gas turbine. When commissioning, operation is also understood after the rotor blades have been replaced as part of maintenance work.

For the same reasons, the method or methods described above are preferably carried out within the first 200 operating hours. However, provoking the rubbing as early as possible is more efficient and advantageous, which is why the rubbing in accordance with the above-described method is specifically brought about within the first 100 operating hours.

The focus of both operating methods according to the invention is on the planned touching during commissioning. The pre Part of this is that the blade tips no longer shorten and the hot gaps in operation are smaller. This results in lower gap losses and a higher efficiency of the gas turbine. In addition, blade tip corrosion is reduced. In the prior art, the protective layer of the rotor blade was damaged when it was touched, so that increased aging / damage (hot gas corrosion) was caused at these points. However, since according to the invention the brushing takes place with an intact coating, this is no longer the case. Due to the hard material coating, which contains boron nitride in particular, the blade tips are protected when they are touched, thus ensuring a longer service life for the rotor blades.

Embodiments of the invention will be explained in more detail with reference to a drawing. Show here:

1 shows a gas turbine in longitudinal section,

2 shows the sequence of a first method according to the invention for provoking the grinding in,

and

3 shows the sequence of a second method according to the invention for provoking the grinding in.

The same reference symbols have the same meaning in the different figures.

1 shows a turbine 100, here a gas turbine, in a partial longitudinal section. The gas turbine 100 has a rotor 103 which is rotatably mounted about an axis of rotation 102 (axial direction). Along the rotor 103, a suction housing 104, a compressor 105, an annular combustion chamber 106 with a plurality of coaxially arranged burners 107, a turbine 108 and an exhaust gas housing 109 follow one another.

The annular combustion chamber 106 communicates with an annular hot gas channel 111. There, for example, four turbine stages 112 connected in series form the turbine 108. Each Turbine stage 112 is formed from two blade rings. Seen in the flow direction of a working medium 113, in the hot gas duct 111 a row of guide vanes 130 is followed by a row formed from rotor blades or rotor blades 120. The tips of the blades 120 have a hard material coating made of cubic boron nitride.

The guide vanes 130 are fastened to the housing 138, whereas the rotor blades 120 are attached to the rotor 103. A generator or egg machine (not shown) is coupled to the rotor 103.

During operation of the gas turbine 100, the compressor 105 sucks air 135 through the suction housing 104 and seals it. The compressed air provided at the turbine-side end of the compressor 105 is led to the burners 107 and mixed there with a fuel. The mixture is then burned to form the working medium 113 in the combustion chamber 106. From there, the working medium 113 flows along the hot gas channel 111 past the guide vanes 130 and the rotor blades 120. The working medium 113 relaxes in a pulse-transmitting manner on the rotor blades 120, so that the rotor blades 120 drive the rotor 103 and the latter the working machine coupled to it Generator.

In the exemplary embodiment shown, the rotor 103 is axially displaceable along the axis 102, but hydraulic gap optimization is not absolutely necessary for carrying out the method according to the invention, but rather has a supporting effect and is merely optional. Due to the taper of the rotor 103 and the housing 138 to one another, an axial displacement of the rotor 103 or the housing 138 reduces or increases the gap d between the rotor 103, in particular the rotor blade ends, and the housing 138. The axial displacement takes place hydraulically.

Due to the uneven thermal expansion of the various turbine components, there are reductions of the radial gap d and thus for brushing the tips of the rotor blades 120 on the housing 138. The housing 138 has a brushing layer in the contact area, which is not shown in more detail here.

According to a first operating method, it is provided to control the gas turbine 100 in such a way that a targeted grazing of the rotor blades 120 is caused. The procedure is shown in FIG 2. 2 shows a rotational frequency f of the turbine 100 over time t. In the period from to to ti when the gas turbine 100 is started up, the gas turbine 100 is first started up. If a full load of 50 Hz is reached in this exemplary embodiment, the gas turbine 100 is operated between ti and t ₂ for at least 15 minutes, but preferably for several hours, in particular between 8 and 12 hours, under full load.

At t ₂ , the gas turbine 100 is shut down, while it continues to rotate in the "turning gear" operating mode without firing. It is important that the housing parts are still well warmed. This operating mode lasts, for example, 8 hours, but it can also last up to 24 hours. The gas turbine 100 is started up again from t ₃ until it has reached full load again at ts, where the brushing takes place at time t _4. It is not necessary to reach full load when starting up again, the decisive factor is primary a quick start, for example with an increase of 10% of the maximum output per minute. At time t ₄ , the coating of the rotor blades 120 is still intact, so grinding marks are left in the abradable layer. This ensures that even if there is a later When the gap d between the rotor 103 and the housing 138 n is closed, the blade tips are not damaged at this point.

A second operating method for the gas turbine 100 can be seen from FIG. 3. 3 shows the development of the gas turbine load P over time t. The aim here is to touch in a different position than in the operating procedure to force according to FIG 2. In order to achieve this, the gas turbine 100 is started up (possibly at a variable speed) and operated at full load from ti until the gas turbine 100 is completely warmed up. Depending on the size, the gas turbine takes up to 10 hours to fully warm up. Then, between t ₂ and t _4, the gas turbine 100 is quickly relieved at a maximum permissible rate or at least 30% of this rate. If the gas turbine 100 has a gap optimization, the gap optimization is activated during this maneuver. Under these conditions, the gas turbine 100 is operated for at least one hour from t ₄ . Finally, the gas turbine can be run up to full load again and the hydraulic gap optimization can be switched off.

Both methods can be used in succession on the same gas turbine 100 during commissioning.

Claims

claims

1. A method for operating a gas turbine (100) comprising a rotor (103) with a plurality of rotor blades (120) and a housing (138), at least some of the rotor blades (120) being coated with a hard material and on the housing (138) in the area of the rotor blades (120) there is an abradable layer, and a gap (d) is formed between the rotor (103) and the housing (138),

characterized in that the gas turbine (100):

is started

is operated at full load for at least 15 minutes, is shut down and is kept rotating for several hours without firing at a low frequency and is started up again.

2. The method according to any one of claims 1,

characterized in that the gas turbine (100) is operated between 8 hours and 12 hours at full load.

3. The method according to any one of claims 1 or 2,

characterized in that the gas turbine (100) is operated without firing at a frequency between 0.5 Hz and 5 Hz.

4. A method for operating a gas turbine (100) comprising a rotor (103) with a plurality of rotor blades (120) and a housing (138), at least the tips of the rotor blades (120) being coated with a hard material and on the housing (138 ) an abradable layer is applied in the area of the rotor blades (120), and a gap (d) is formed between the rotor (103) and the housing (138),

characterized in that:

the gas turbine (100) is started the gas turbine (100) is operated at base load until the gas turbine is completely warmed up,

optionally a gap optimization, in which an axial displacement of the rotor (103) and / or the housing (138) follows, is switched on,

the gas turbine (100) is relieved at part load and is operated at least one hour at part load.

5. The method according to claim 4,

characterized in that the relief follows a minimally achievable partial load for the gap optimization.

6. The method according to any one of the preceding claims,

which is carried out when the gas turbine (100) is started up.

7. The method according to any one of the preceding claims,

which is carried out within the first 200 operating hours.

8. Control device for performing the method according to one of the preceding claims.

9. gas turbine (100) with a control device according to claim 8.