EP0790466A2 - Method for quick switching from premix to diffusion burning modes in the combustion chamber of a gas fuelled gas turbine - Google Patents

Abstract

The method involves initiating one changeover criterion for changing from premix to diffusion mode if timely detection of a transient process which could lead to premix flame extinction occurs or the initiation of a second changeover criterion if timely detection occurs of a premix flame extinction. The first and second criteria involve transferring to changeover logic the displacement (Z) of the valve in the fuel feed line and the pressure in the combustion chamber(s) respectively. The drive logic (8) continually checks the input values against the entered criteria. If a criterion is fulfilled, the drive logic passes a drive signal to the servovalve (7) of a rapid changeover valve (3) in the combustion gas feed line.

Description

The invention relates to a method and a device for rapid switching from premixing mode to diffusion mode in gas turbines with at least one combustion chamber with simultaneous control of the diffusion and premixing control valves in the fuel gas supply lines, i. H. Opening of the diffusion gas path and simultaneous closing of the premix gas path of a burner with rapid load reduction and extinguishing of the premix flame.

When NO _x-poor operation of gas turbines with one or more combustion chambers also are fuel gas and air in a mixing system, a premix burner, mixed as homogeneously as possible. In this way, zones of stoichiometric combustion with correspondingly high temperatures are avoided in the flame and the formation of NO _{x is} largely prevented.

Such a burner can be operated both in the so-called diffusion and in the premix mode. In diffusion mode, there are also zones with stoichiometric combustion and thus high temperature in the flame, which lead to NO _x formation. When the gas turbine starts, the burner works as a diffusion burner and, as soon as the gas turbine has reached a certain output, is switched over to operation as a premix burner. The premix flame is stabilized by a small pilot flame. Gas turbines are used, for example, to drive pipeline compressors and generators.

In the event of sudden load reductions (compressor pumps, generator load cut-off, etc.), the fuel gas control valve closes very quickly to prevent the turbine speed from increasing.

This means that the fuel supply is drastically reduced while the gas generator air quantity remains virtually the same, as a result of which the air-fuel ratio increases and the mixture becomes even leaner.

If this happens in diffusion mode, i. H. with a diffusion flame, this is not critical since the flame does not go out. In premix mode, however, the flame, which is already lean per se, can extinguish when the mixture becomes even leaner and then ignite again in an uncontrolled manner.

The reignition occurs either through the pilot gas flame still burning or through hot parts in the combustion chamber or in the hot gas area of the gas turbine. This reignition takes place in an uncontrolled manner and takes the form of a deflagration or detonation.

From DE 32 41 162 a premix burner with an integrated diffusion burner is known, the premix burner having a premixing chamber delimited at the downstream end by a flame holder, into which a main fuel nozzle opens and wherein the diffusion burner has a pilot fuel nozzle. The entire supply of the combustion air takes place via a feed device which opens into the premixing chamber.

A fuel control device regulates the fuel supply in such a way that a pure diffusion burner operation occurs after starting, then a diffusion burner and premix burner operation and a premix burner operation in the upper load range.

The fuel control device, to which a load signal is applied, regulates the flow through the fuel control valve via corresponding control lines.

So-called two-way valves are used as fuel control valves, which limit the fuel supply between a min. and max. Control the flow rate. Control devices that enable a quick switchover in unstable operation are not arranged here.

A method is also known in which the combustion chamber and burner in the event of load jumps or load shedding, the gas turbine working as a generator drive, switches from premixing to diffusion operation. The speed gradient of the gas turbine is used to identify these transient operating processes. If this criterion detects a load jump, the diffusion control valves are opened and the premixing control valves are closed at the same time. The valve operating time is 5 seconds. In the event of a load shedding, the pilot gas quantity is increased via a 2/2 way valve with a positioning time of approx. 150 ms and a so-called quick changeover is carried out.

• eine erloschene Vormischflamme im Vormischbetrieb rückzündet und damit die Gefahr einer Verpuffung oder Detonation besteht und
• daß während der gleichzeitigen Umschaltung der Stellventile auf die Flammen kein Einfluß genommen werden kann. Die Vormischflamme kann innerhalb dieser Zeit trotz Erhöhung der Stützwirkung durch die Pilotflamme verlöschen, rückzünden oder eine Verpuffung hervorrufen.

A disadvantage of this control method is that

• an extinguished premix flame ignites in the premix mode and there is a risk of deflagration or detonation and
• that no influence can be exerted on the flames during the simultaneous switching of the control valves. The premixing flame can extinguish, reignite or deflagrate within this time despite the increase in the support effect from the pilot flame cause.

The object of the invention is to provide a control method for a rapid switchover from premixing to diffusion operation in order to prevent fuel deflagrations and detonations in the combustion chamber or in the hot gas area during premixing operation, combined with an uncontrolled reignition of the premixing flame.

The problem is solved in the manner as specified in claims 1 and 3. The respective subclaims represent an advantageous embodiment of the invention.

In order to avoid pressure surges due to deflagrations and instabilities of the premixing flame, rapid changeover valves according to the invention are installed in the premixing gas line with a connection to the diffusion gas burner, which upon detection of such a process - extinguishing of the premixing flame or upon occurrence of a fault which can lead to extinguishing of the premixing flame - switches from premixing mode to diffusion mode within approx. 100 ms so that an uncontrolled re-ignition of the premixing flame is excluded.

• das Brenngasregelventil schnell um einen gewissen Betrag schließt,
• oder ein schneller Druckabfall um einen gewissen Betrag im Inneren des Flammrohres zu verzeichnen ist,
• oder die optische, schnelle Flammenüberwachung ein Verlöschen der Vormischflamme meldet.

For the detection or detection of this flame instability and triggering the quick switchover, three switchover criteria were determined and their effectiveness tested. These switchover criteria trigger a quick switchover, if

• the fuel gas control valve closes quickly by a certain amount,
• or there is a rapid drop in pressure by a certain amount inside the flame tube,
• or the optical, fast flame monitoring signals that the premix flame has gone out.

By arranging an extremely fast switching 3/2-way valve in the fuel gas supply line to the combustion chamber (s), the amount of fuel gas to be burned can be passed from the premix gas supply line to the diffusion gas line and thus to the diffusion burner within approx. 100 ms.

An embodiment of the invention is explained using two schematic control schemes.

Fig. 1

ein Regelverfahren für zwei Brennkammern mit je einem Brenner,

Fig. 2

ein Regelschema der Ansteuerlogik einer Schnellumschaltung.

Show it:

Fig. 1

a control procedure for two combustion chambers with one burner each,

Fig. 2

a control diagram of the control logic of a quick changeover.

1 shows the control method according to the invention, including the associated devices for operating a gas turbine with two burners (11, 12) on the combustion chambers (9, 10). The combustion chambers (9, 10) are designed in the upper part as a flame tube (17) and in the lower part as a mixing tube (18) with the inlet manifold (19) for the supply of compressor or combustion air. Fuel gas is fed to the burners (11, 12) via a fuel gas supply line (13). A pilot gas line (14) branches off in front of the fuel gas control valve (1) with the displacement sensor (Z) (4), in which the fuel supply is regulated by a pilot gas control valve (2).

The fuel gas supply line (13) branches after the fuel gas control valve (1, 4) into fuel supply lines for both combustion chambers (9, 10). By installing a quick changeover valve (3) with servo valves V ₁ , V ₂ (7) in the branching fuel supply lines (13), the fuel supply to the diffusion gas line (15) and the premix gas line (16) is controlled.

The combustion chambers (9, 10) are monitored in the area of the flame tube (17) by pressure measuring devices P ₁ , P ₂ (5) and by an optical flame monitor B ₁ , B ₂ (6).

The displacement sensor or displacement transducer (Z) (4), the monitoring devices (5) for pressure measurement P ₁ , P ₂ , the monitoring devices for optical flame monitoring B ₁ , B ₂ (6) and the servo valves (Z) (7) Quick changeover valves (3) are wired with control logic for quick changeover (8).

Fig. 2 shows the structure of the control logic of a rapid changeover (8) which contains a total of three changeover criteria from premixing to diffusion operation in the case of two burners. Additional switching criteria can be added if required.

Switching criterion 20 is the path measurement (Z) (4) of the fuel gas valve (1), switchover criterion 21 is the pressure measurement P ₁ , P ₂ (5) in the flame tube (17) and switchover criterion 22 is the optical flame monitoring B ₁ , B ₂ (6) in the flame tube (17) of the combustion chamber (9, 10).

The control logic of the quick changeover (8) immediately after evaluating the entered measurement results for the changeover criteria 20 and 21 or for all three changeover criteria 20, 21 and 22 causes a parallel Control of the servo valves V ₁ , V ₂ (7) for the quick changeover valves (3), which divert the fuel gas quantity from the premix gas line (16) into the diffusion gas line (15) within approx. 100 ms.

List of reference numbers:

1

Fuel gas control valve

2nd

Pilot gas control valve

3rd

Quick changeover valve

4th

Displacement transducer, displacement measurement

5

Pressure measurement combustion chamber P ₁ , P ₂

6

Optical flame monitoring of the combustion chamber B ₁ , B ₂

7

Servo valves V ₁ , V ₂

8th

Control logic of quick changeover valves

9

Combustion chamber 1

10th

Combustion chamber 2

11

Burner 1

12th

Burner 2

13

Fuel gas supply line

14

Pilot gas line

15

Diffusion gas line

16

Premix gas line

17th

Flame tube

18th

Mixing tube

19th

Compressor air intake manifold

20th

Switching criterion "distance measurement of fuel gas control valve"

21

Switching criterion "pressure measurement"

22

Switching criterion "flame monitoring"

Claims (7)

Process for rapid switching from premix operation to diffusion operation in gas turbines with at least one combustion chamber and with simultaneous activation of the diffusion and premix control valve in the fuel gas supply lines, ie opening of the diffusion gas path and simultaneous closing of the premix gas path of the burner with rapid load reduction and extinguishing of the premix flame,
characterized, that when an early detection of a transient process that could lead to the extinction of a premix flame, the switching criterion 20 and when an early recognition of the extinction of a premix flame, the switching criterion 21 initiates the switching from the premix mode to the diffusion mode, for which purpose the distance measurement (Z) of the fuel gas control valve in the fuel gas supply line and, in the case of switchover criterion 21, the pressure measurement (P) in the combustion chamber (s) are continuously transmitted to a control logic for rapid switchover, that the control logic for a rapid changeover continuously checks the input measured values by means of the inputted criteria and, when the switchover criterion 20 or the switchover criterion 21 is met, a control signal to the Servo valve (V) transmits a quick changeover valve in the fuel gas supply line, whereby the fuel supply in the premix gas line to the burner (s) is abruptly interrupted and the diffusion gas line to the burner (s) is immediately supplied with fuel gas. Method according to claim 1,
characterized, that in addition the switching criterion 22 for switching from the premixing mode to the diffusion mode is continuously transmitted by an optical flame monitor (B) at the output of the (r) burner (r) in the flame tube to a control logic for quick switching and that the control logic also constantly checks these input measured values together with the measured values of the switchover criteria 20 and 21 and, when the switchover criterion 22 is met, also transmits a control signal to the servo valve (V) of the quick changeover valve of the fuel gas supply line. Device for carrying out the method for rapid switching from the premix mode to the diffusion mode of a combustion chamber of a gas turbine according to claims 1-2,
characterized, that in the fuel gas supply line (13) after the fuel gas control valve (1) with the displacement sensor (Z) (4) per burner (11, 12, n) a quick changeover valve (3) with servo valve (V) (7) is used, which with the Burner (11, 12, n) is connected by a diffusion gas line (15) and by a premix gas line (16). Device according to claim 3,
characterized, that devices for pressure measurement (P) (5) and for optical flame monitoring (B) (6) are arranged on the combustion chamber (9, 10, n). Device according to claims 3 and 4,
characterized, that a control logic for quick switching (8) with the displacement sensor (Z) (4) for the fuel gas control valve (1), with the pressure measuring devices (P) (5) and the devices for optical flame monitoring (B) (6) on the combustion chamber ( 9, 10, n) and the servo valves (V) (7) of the quick changeover valves (3). Device according to claims 3 to 5,
characterized, that the control logic for quick changeover (8) has a switchover criterion 20 for the displacement transducer (Z) (4) of the fuel gas control valve (1) and a switchover criterion 21 for the pressure measurement (P) (5) and a parallel control of the servo valves (V) (7) the quick changeover valves (3). Device according to claims 3 to 6,
characterized, that the control logic for quick switching (8) has a switching criterion 22 for optical flame monitoring (B) (6) and a control of the servo valves (V) (7) of the quick switching valves (3).

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