EP2151629A2

EP2151629A2 - Method for determining the location of burners in an annular combustion chamber of a gas turbine

Info

Publication number: EP2151629A2
Application number: EP09167518A
Authority: EP
Inventors: Federico Bonzani; Lorena Della Fiore; Carlo Piana
Original assignee: Ansaldo Energia SpA
Current assignee: Ansaldo Energia SpA
Priority date: 2008-08-08
Filing date: 2009-08-07
Publication date: 2010-02-10
Anticipated expiration: 2029-08-07
Also published as: IT1391245B1; ITMI20081514A1; EP2151629A3; EP2151629B1; EP2151629A8

Abstract

A method for determining the location of burners (6, 7) in an annular combustion chamber (1) of a gas turbine envisages:
detecting flow rates (Q_Pi, Q_PXi) of a plurality of burners (6, 7);
calculating an average flow rate (Q_PM, Q_PXM) of the detected flow rates (Q_Pi, Q_PXi);
calculating a deviation (ΔQ_Pi, ΔQ_PXi) of each detected flow rate (Q_Pi, Q_PXi) from the average of the flow rates (Q_PM, Q_PXM); and
associating at least one of a plurality of seats (2) of the annular combustion chamber (1), that arranged along a circular path, to at least one burner (6, 7) on the basis of the calculated deviations (ΔQ_Pi, ΔQ_PXi).

Description

The present invention relates to a method for determining the location of burners in an annular combustion chamber of a gas turbine.
The ever-increasing needs to reduce the environmental impact determined by power stations have directed the sector of combustion in high-power gas turbines towards the use of combustion chambers structured according to the so-called "lean-premix" technology. Said technology substantially envisages having an annular combustion chamber comprising a plurality of burner assemblies set at the same distance apart from one another, each of which comprises a premix burner, also referred to as primary burner, and a pilot burner, also referred to as secondary burner. The premix burner is supplied with an air-fuel mixture, with marked excess of air, for the purpose of generating a flame such as to guarantee a uniform temperature range and avoid possible temperature peaks that may lead to high emissions of NO_x at the exhaust.
The pilot burner is instead supplied with fuel and stabilizes the flame generated by the premix burner.
This type of combustion chambers is affected, however, by phenomena of thermo-acoustic instability, commonly designated by the term "humming", which are determined by the fluctuation of the parameters of the fluids present in the combustion chamber. These phenomena of thermo-acoustic instability constitute in the long run a danger for the structure of the combustion chamber itself.
Combustion chambers are known that have a system of injection differentiated for each premix burner and/or pilot burner for reducing the phenomena of thermo-acoustic instability. Also known are combustion chambers having flow deflectors designed to deflect the flow at output from the premix burner in such a way as to reduce the phenomena of thermo-acoustic instability.
These combustion chambers, however, are unable to meet the ever-increasing needs of minimization of the phenomena of thermo-acoustic instability.
An aim of the present invention is to provide a method for determining the location of burners of an annular combustion chamber of a gas turbine that will be able to overcome the drawbacks of the known art highlighted herein; in particular, an aim of the invention is to provide a method for determining the location of the burners of an annular combustion chamber of a gas turbine that will be able to minimize the phenomena of thermo-acoustic instability.
In accordance with the above aims, the present invention regards a method for determining the location of burners in an annular combustion chamber of a gas turbine comprising the steps of:

detecting flow rates of a plurality of burners;
calculating an average flow rate of the detected flow rates;
calculating a deviation of each detected flow rate from the average flow rate;
associating at least one of a plurality of seats of the annular combustion chamber arranged along a circular path with at least one burner on the basis of the deviations calculated.

Further characteristics and advantages of the present invention will emerge clearly from the ensuing description of a non-limiting example of embodiment thereof, with reference to the figures of the annexed drawings, wherein:

Figure 1 is a schematic view, with parts represented in sectional view and parts removed for reasons of clarity, of an annular combustion chamber without burners;
Figure 2 is a cross-sectional view, with parts removed for reasons of clarity, of a burner assembly;
Figure 3 is a diagram that illustrates schematically the flow rates of the premix burners as a function of the position of the premix burners within the combustion chamber;
Figure 4 is a schematic view, with parts removed for reasons of clarity, of an annular combustion chamber provided with burners; and
Figure 5 is a diagram that illustrates schematically the flow rates of the pilot burners as a function of the position of the pilot burners within the combustion chamber.

Designated by the reference number 1 in Figure 1 is an annular combustion chamber for a gas turbine (not illustrated for reasons of simplicity in the attached figures).
The combustion chamber 1 extends along a longitudinal axis A and comprises a plurality of seats 2, each of which is designed to be engaged by a burner assembly 3 (Figure 2). The seats 2 are arranged along a circular path in the proximity of a peripheral edge 5 of the combustion chamber 1. In the non-limiting example described and illustrated herein, the seats 2 and the burner assemblies 3 are twenty-four.
With reference to Figure 2, each burner assembly 3 extends along an axis B and comprises a pilot burner 6 set along the axis B and supplied with fuel, and a premix burner 7 set substantially around the pilot burner 6 and supplied with an air-fuel mixture.
The premix burner 7 can be of the type provided with a cylindrical outlet element 9, commonly referred to as "cylindrical burner outlet" (and hereinafter referred to as "CBO element") or else of the type without said CBO element 9. The CBO element 9 is substantially a prolongation of the outlet channel of the premix burner 7 and is designed to stabilize the flame generated by the premix burner 7.
In the non-limiting example described herein, four of the twenty-four premix burners 7 are without the CBO element 9, whilst the remaining premix burners are of the type provided with the CBO element 9.
The location of the premix burners 7 and of the pilot burners 6 in the seats 2 of the combustion chamber 1 is made in accordance with the method according to the present invention.
The method envisages determining the location of the premix burners 7 and subsequently determining the location of the pilot burners 6 in the combustion chamber 1.
For determining location of the premix burners 7, the method according to the present invention envisages:

detecting the flow rates Q_PXi of all the premix burners 7 by means of experimental tests that we shall describe in detail hereinafter;
calculating an average flow rate Q_PXM of the detected flow rates Q_PXi (see the dashed and dotted line of the diagram of Figure 3) excluding from the calculation of the average the flow rates Q_PXi of the premix burners 7 without the CBO element 9;
calculating a deviation ΔQ_PXi of each flow rate Q_PXi detected from the average flow rate Q_PXM;
replacing the premix burners 7 having a deviation ΔQ_PXi greater than a given threshold value S_PX, preferably equal to 5%, with new premix burners having a deviation ΔQ_PXi lower than said threshold value S_PX ; and
associating a seat 2 of the combustion chamber 1 to each premix burner 7 on the basis of the respective deviation ΔQ_PXi calculated.

With reference to Figures 3 and 4, the step of associating a seat 2 of the combustion chamber 1 to each premix burner 7 comprises the steps of:

associating a first number of first premix burners 7a (Figure 4) having deviation ΔQ_PXi (plotted with a solid line in the diagram of Figure 3) lower than the deviations of the remaining premix burners 7b (Figure 4) to respective first seats 2a (Figure 4) of the consecutive combustion chamber 1 along the circular path (indicated in the diagram of Figure 3 with the positions 1-6); the first premix burners 7a (Figure 4) are of the type provided with the CBO element 9; in the non-limiting example described and illustrated herein, the first number of first premix burners 7a is six; and
associating the remaining premix burners 7b (Figure 4) to the remaining seats 2b (Figure 4) of the combustion chamber 1 (indicated in the diagram of Figure 3 with the positions 7-24), alternating remaining premix burners 7b with positive deviation ΔQ_PXi and remaining premix burners 7b with negative deviation ΔQ_PXi along the circular path (plotted with a solid line in the diagram of Figure 3); in particular, the method envisages associating the premix burners 7b of the type provided with the CBO element 9 to the remaining seats 2b subsequent to the first seats 2a and consecutive along the circular path (indicated in the diagram of Figure 3 with the positions 7-20) and finally associating the premix burners 7b of the type without the CBO element 9 to the remaining consecutive seats 2b along the circular path (indicated in the diagram of Figure 3 with the positions 20-24).

For determining location of the pilot burners 6, the method according to the present invention envisages:

detecting the flow rates Q_Pi of all the pilot burners 6 by means of experimental tests that we shall describe in greater detail hereinafter;
calculating an average flow rate Q_PM of the detected flow rates Q_Pi (see the dashed and dotted line of the diagram of Figure 5);
calculating a deviation ΔQ_Pi of each flow rate Q_Pi detected from the average flow rate Q_PM;
replacing the pilot burners 6 having a deviation ΔQ_Pi greater than a given threshold value S_P, preferably 3%, with new pilot burners having a deviation ΔQ_Pi lower than said threshold value Sp; and
associating a seat 2 of the combustion chamber 1 to each pilot burner 6 on the basis of the respective deviation ΔQ_Pi calculated.

In particular, the step of associating a seat 2 of the combustion chamber 1 to each pilot burner 6 comprises the steps of:

associating a first number of first pilot burners 6a (Figure 4) having deviation ΔQ_Pi (plotted with a solid line in the diagram of Figure 5) lower than the deviations of the remaining pilot burners 6b to the seats 2a of the consecutive combustion chamber 1 along the circular path (indicated in the diagram of Figure 5 with the positions 1-6); in the non-limiting example described and illustrated herein the first number of first pilot burners 6a is six; and
associating the remaining pilot burners 6b (Figure 4) to the remaining seats 2b of the combustion chamber 1 (indicated in the diagram of Figure 5 with the positions 7-24), alternating remaining pilot burners 6b with positive deviation ΔQ_Pi and remaining pilot burners 6b with negative deviation ΔQ_Pi along the circular path (plotted with a solid line in the diagram of Figure 5) so that one and the same seat 2b will house a premix burner 7b and a pilot burner 6b having deviations ΔQ_Pi, ΔQ_PXi of the same sign (plotted with a solid line in the diagrams of Figures 3 and 5); in particular, in associating the remaining pilot burners 6b to the remaining seats 2b the aim is substantially to follow as much as possible the same evolution of the flow rates Q_PXi of the remaining premix burners 7b.

As already specified above, the flow rates Q_Pi of all the pilot burners 6 and the flow rates Q_PXi of all the premix burners 7 are detected experimentally. In particular, each pilot burner 6 and each premix burner 7 is connected to a device (not illustrated) comprising an air-supply circuit, in which pressurized air flows, connected to the inlet of the gas line of the burner under test via a purposely provided pipe, and a computer. The flow rate is acquired continuously through a flow-meter set in a section of the air-supply circuit substantially at the inlet of the burner under test. If the value of the flow rate acquired remains constant for approximately thirty seconds, the value of the flow rate is stored by the computer. The value of flow rate is calculated in such a way as to render the tests independent of variations of pressure and/or temperature. To render the measurement independent of the variations of ambient pressure, the supply circuit is supplied with air at a supply pressure p such that the ratio between the supply pressure p and the atmospheric pressure p_a expressed in mbar, is:

p/p_a = 1.150 ± 0.001 for the premix burner 7;
p/p_a = 2.000 ± 0.001 for the pilot burners 6;
where the values of supply pressure p and p_a are detected around the area of detection of the flow rates.

To render the value of flow rates detected independent of the value of ambient temperature, the flow rate detected is appropriately normalized with respect to the ambient temperature (measured in degrees Kelvin) and consequently is measured in m³/s·K^1/2.
The method according to the present invention presents the following advantages.
In the first place, the application of the method according to the present invention determines a reduction of the thermo-acoustic instability of the combustion chamber 1.
The method according to the present invention, in fact, determines both for the premix burners 7 and for the pilot burners 6 the best configuration for generating a temperature range that limits the propagation of the thermo-acoustic waves generated by the phenomenon of humming previously described. Furthermore, the uniformity of evolution between the flow rates Q_PXi of the premix burners and the flow rates Q_Pi of the pilot burners enables maximum limitation of the NOx emissions produced at exhaust.
In addition, the method according to the present invention is based exclusively upon the measurement of the effective flow rates Q_PXi and Q_Pi, i.e., affected by the machining tolerances, of the premix burners 7 and pilot burners 6, preventing any need to intervene with mechanical modifications on the premix burners 7 and/or pilot burners 6 and without intervening on the control device of the combustion chamber 1.
A further advantage is represented by the possibility of using premix burners 7 and pilot burners 6 having a deviation ΔQ_PXi, ΔQ_Pi that is substantially wide (up to 5%), which otherwise would have to be rejected in so far as not compliant with the specifications normally considered in the known art.
Finally, it is evident that modifications and variations may be made to the method described herein, without thereby departing from the scope of the annexed claims.

Claims

Method for determining the arrangement of burners (6,7) in an annular combustion chamber (1) of a gas turbine comprising the steps of:
- detecting flow rates (Q_Pi, Q_PXi) of a plurality of burners (6, 7) ;

- calculating an average flow rate (Q_PM, Q_PXM) of the detected flow rates (Q_Pi, Q_PXi);

- calculating a deviation (ΔQ_Pi, ΔQ_PXi) of each detected flow rate (Q_Pi, Q_PXi) from the average flow rate (Q_PM, Q_PXM) ;

- associating at least one of a plurality of seats (2) of the combustion chamber (1), that are arranged along a circular path, with at least one burner (6, 7) on the basis of the calculated deviations (ΔQ_Pi, ΔQ_PXi).
Method according to Claim 1, characterized in that the step of associating comprises the steps of:
- associating a first number of first burners (6a, 7a), having deviation (ΔQ_Pi, ΔQ_PXi) lower than the deviations of the remaining burners (6b, 7b), with respective first seats (2a) of the combustion chamber (1), consecutive along the circular path;

- associating the remaining burners (6b, 7b) with the remaining seats (2b) of the combustion chamber (1).
Method according to Claim 2, characterized in that the step of assigning the remaining burners (6b, 7b) comprises the step of alternating along the circular path remaining burners (6b, 7b) having positive deviation (ΔQ_Pi, ΔQ_PXi) and remaining burners (6b, 7b) having negative deviation (ΔQ_Pi, ΔQ_PXi).
Method according to Claim 3, characterized in that the burners (6, 7) comprise pilot burners (6).
Method according to Claim 3 or 4, characterized in that the burners (6, 7) comprise premix burners (7).
Method according to Claim 3, characterized in that the burners (6, 7) comprise pilot burners (6) and premix burners (7); the step of associating the remaining burners (6b, 7b) comprising the step of associating to the same seat of the remaining seats (2b) a pilot burner (6b) and a premix burner (7b) from the remaining burners (6b, 7b) with deviation (ΔQ_Pi, ΔQ_PXi) having the same sign.
Method according to Claim 6, characterized in that the first burners (7a) are premix burners provided with a CBO element (9).
Method according to Claim 6 or 7, characterized in that the remaining burners (6b, 7b) comprise a first group of premix burners (7b) provided with a CBO element (9) and a second group of premix burners (7b) without the CBO element (9) .
Method according to Claim 8, characterized in that the step of associating the remaining burners (6b, 7b) comprises the steps of:
- associating the first group of premix burners (7b) with respective second seats of the remaining seats (2b), arranged consecutive to the first seats (2a) along the circular path;

- associating the second group of premix burners (7b) with respective third seats of the remaining seats (2b), arranged consecutive to the second seats along the circular path.
Method according to Claims 8 or 9, characterized in that the step of calculating an average flow rate (Q_PXM) of the detected flow rates (Q_PXi) comprise calculating an average flow rate of the detected flow rates (Q_PXi) of the premix burners provided with the CBO element (9).
Method according to anyone of the previous Claims, characterized by comprising the step of replacing burners (6, 7) having deviation (ΔQ_Pi, ΔQ_PXi) greater than a given threshold (S_P, S_PX) with new burners having deviation lower than said given threshold (S_P, S_PX).