EP1621811A1 - Operating Method for a Combustion Apparatus - Google Patents

Abstract

A power station gas turbine engine has a burner chamber (1) with a number of flame burners (2). Fuel to the burner is regulated in accordance with a target pressure that is proportional to the pulse pressure (P). The mixture is enriched on reaching a predetermined target pressure.

Description

Technical area

The present invention relates to a method for operating a furnace with multi-burner system for hot gas production, in particular gas turbine, preferably a power plant.

State of the art

A furnace, e.g. a gas turbine, usually has a combustion chamber with a plurality of burners. Furthermore, a fuel supply system is provided on a regular basis, with the help of which the burners are supplied with fuel.

In view of ever stricter regulations on limit values for pollutant emissions to be observed, an attempt is made to operate the burners as lean as possible, that is, with a significant excess of oxidant, usually air. In particular, lean operation can significantly reduce the generation of particularly harmful NOx emissions. By lean combustion, the combustion reaction is simultaneously approximated to its lean extinction limit. For minimal pollutant emissions, it is therefore attempted to operate the gas turbine or its combustion chamber as close as possible to the lean extinction limit. In a conventional operating method, the fuel supply must be adjusted depending on various boundary conditions. Usually considered boundary conditions are, for example, the ambient temperature, the relative humidity, the current air mass flow, in particular the degree of contamination of a combustion chamber upstream of the compressor depends on the switching position ("on" or "off") of a fuel and / or Luftvorwärmeinrichtung, the composition of the currently used fuel and so on. Particularly complex is the control of the fuel supply system, if the considered boundary conditions vary. For example, the ambient temperature and / or the fuel composition will usually change over a gas turbine operating day. Since the individual boundary conditions have different effects on the stability of the combustion process, it is not always possible to find a setting for the fuel supply, which enables stable operation of the individual burners close to the lean extinction limit. In order nevertheless to be able to ensure proper operation of the gas turbine, which has the highest priority in particular in a power plant for generating electricity, it is regularly accepted that the combustion chamber is operated at a safe distance with respect to the lean extinction limit, in which case the larger resulting inevitably Pollutant emissions must also be taken into account.

Presentation of the invention

This is where the present invention begins. The invention, as characterized in the claims, deals with the problem of providing for an operating method of the type mentioned in an improved embodiment, which in particular simplifies safe operation of the combustion chamber near the lean extinction limit or only possible. Preferably, a hitherto required safety distance to the lean extinction limit should be reduced.

According to the invention, this problem is solved by the subject matter of the independent claim. Advantageous embodiments are the subject of the dependent claims.

The invention is based on the general idea of controlling the fuel supply to the burners of the combustion chamber as a function of pressure pulsations occurring in the combustion chamber. This means that the pressure pulsations occurring in the combustion chamber serve as a reference variable for the regulation of the fuel supply to the burners. The invention uses the knowledge that the pressure pulsations increase as the combustion process approaches the lean extinction limit. Of particular importance in this case, however, is the surprising finding that the intensity or amplitude of the pressure pulsations at certain characteristic frequencies correlates with the distance between the combustion process and the associated lean extinction limit, essentially independently of the combustion process and / or the lean extinction limit Boundary conditions, such as ambient temperature, fuel composition and humidity. This means that a change in the boundary conditions, which leads, for example, to an increase in the distance of the currently running combustion process to the lean extinction limit, is accompanied by a decrease in the pressure pulsations that occur.

The pressure pulsations can be detected in a conventional manner, which allows a comparison between a measured actual value and a predetermined or adjustable setpoint value and, depending on this setpoint-actual comparison of the pressure pulsations, enables a corresponding adaptation of the fuel supply. As a result of this feedback via the pressure pulsations, a closed control loop is provided for supplying the burner with fuel. The operation of the gas turbine or the fuel supply of the burner is extremely simplified by the operating method according to the invention, since by taking into account the intensity or amplitude of the pressure pulsations already mentioned above several boundary conditions, which determine the distance between the combustion process and the lean extinction limit in the Be taken into account automatically, without them to be explicitly monitored and / or integrated into the scheme. It is obvious that by the operating method of the invention, the effort to operate the gas turbine significantly reduced. Furthermore, the combustion chamber can be operated safely and yet very close to the lean extinction limit by a corresponding selection of setpoint values for the pressure pulsations.

Of particular advantage in the operating method according to the invention is also the fact that a modern combustion chamber is already regularly equipped with a sensor for monitoring the pressure pulsations, so that for operating the gas turbine according to the invention can be accessed on this sensor and accordingly no additional costs for instrumentalization or Realization of the operating method according to the invention arise.

According to a particularly advantageous embodiment, upon reaching a predetermined or adjustable maximum value for the pressure pulsations, the fuel supply to at least one burner of the combustion chamber can be enriched by a predetermined value. The maximum value of the pressure pulsations can be determined empirically, for example, and defines the smallest distance to the lean extinction limit, at which still a stable operation of the combustion chamber can be ensured. The specification of a specific value by which the fuel supply to the respective burner is to be greased if necessary, thereby enabling a rapid response of the control and thus compliance with the smallest possible distance between pulsation and pulsation setpoint.

In another embodiment, upon reaching a predetermined or adjustable minimum value for the pressure pulsations, the fuel supply to at least one burner may be reduced to a predetermined value. In this embodiment, a maximum distance between the combustion reaction and the lean extinction limit is defined for the operation of the combustion chamber, which should not be exceeded. This measure ensures that the lowest possible distance to the lean extinction limit is always maintained, which leads to low pollutant emissions.

With the maximum value and the minimum value for the pressure pulsations, a pulsation window is defined for the operation of the combustion chamber, in which the burners of the combustion chamber are operated and which ensures a sufficient, but very small distance from the lean extinction limit and at the same time compliance with low limit values for the pollutant emissions ,

Other important features and advantages of the operating method according to the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the drawings.

Brief description of the drawings

Fig. 1

ein Diagramm, in dem die Verläufe von Druckpulsationen und Schadstoffemissionen über einem Brennstoff/Oxidator-Verhältnis aufgetragen sind,

Fig. 2

eine schaltplanartige Prinzipdarstellung einer Brennkammer,

Fig. 3

eine Darstellung wie in Fig. 2, jedoch bei einer anderen Ausführungsform.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components. Show, in each case schematically,

Fig. 1

a diagram in which the courses of pressure pulsations and pollutant emissions are plotted against a fuel / oxidizer ratio,

Fig. 2

a circuit diagram-like schematic representation of a combustion chamber,

Fig. 3

a representation as in Fig. 2, but in another embodiment.

Ways to carry out the invention

2, a combustion chamber 1 of a firing system, not shown otherwise, is equipped with a plurality of burners 2, whereby a multi-burner system is formed. The burners 2 are arranged on an inlet side of, for example, an annular combustion chamber 3 of the combustion chamber 1. at a gas turbine, in particular a power plant, designed firing system is located upstream of the combustion chamber 1 usually a compressor not shown here, while downstream of the combustion chamber 1, the actual, not shown here turbine is arranged.

The burners 2 are divided into two groups, namely a main group and a subgroup. The burners 2 of the main group are symbolized here by full circles and are referred to below as the main burner 4. In contrast, the burners 2 of the subgroup are symbolized by empty circles and are also referred to below as secondary burners 5. Usually, the main burners 4 are operated fatter than the auxiliary burners 5. Accordingly, the main burners 4 regularly have a greater distance to the lean extinction limit of the combustion reaction than the auxiliary burners 5. Due to the given exponential relationship between NO _x and combustion temperature produce the main burner 4 significantly more NO _x than the auxiliary burner 5. In contrast to the representation chosen here is the In any case, the main burners 4 have a significantly greater influence on the combustion reaction in the combustion chamber 3 than the auxiliary burners 5. An equal number of burners in both groups could therefore, for example, by a different dimensioning of the main burner. 4 and the auxiliary burner 5 are achieved with respect to different mass flow rates.

For supplying the burner 2 with fuel, a fuel supply system 6 is provided which supplies the burners 2 with a total fuel flow 7 via a corresponding overall line. This total fuel flow is thereby split by the fuel supply system 6 into a main fuel stream 8 assigned to the main burners of the main group and a secondary fuel stream 9 assigned to the auxiliary burners 5 of the subgroup. Corresponding distribution devices are not shown here. The individual burners 2 are supplied with fuel from the fuel supply system 6 via corresponding individual lines with individual fuel streams 10. It can also be between here the main burners 4 associated Hauptbrennstoffeinzelströmen 11 and the secondary burners associated Nebenbrennstoffeinzelströmen 12 are distinguished.

Furthermore, a control device 13 is provided, which is coupled to the actuation of the fuel supply system 6 with this and which is also connected to at least one pulsation sensor 14 for measuring pressure pulsations in the combustion chamber 1 and in the combustion chamber 3. Furthermore, the control device 13 is connected to at least one emission sensor 15, with the aid of pollutant emissions in the exhaust gases of the combustion chamber 1 or downstream of the turbine can be detected.

According to the invention, the gas turbine is operated such that the fuel supply to the burners 2 is controlled at least for the maintenance of a stationary or quasi-stationary operation of the gas turbine as a function of pressure pulsations occurring in the combustion chamber 1.

For a better understanding of the control concept according to the invention, reference is made to FIG. 1, whose abscissa represents the mass ratio of fuel to oxidizer, which is generally designated λ. On the ordinate intensity and the amplitudes of the pressure pulsations P and on the other hand the mass fractions of the pollutant emissions E in the exhaust gas of the combustion chamber 1 are plotted. The diagram of FIG. 1 includes a solid line a pulsation curve P _(λ) and a dashed line an emission curve E _(λ) , each depending on the fuel / oxidizer mass ratio λ. It can be seen here that the pulsation profile P _{(λ) increases} from left to right, ie with increasing leaning of the fuel / oxidizer ratio λ, while in contrast the emission profile E _(λ) decreases with increasing leaning, ie from left to right ,

The diagram according to FIG. 1 also contains a maximum value for pressure pulsations P _max , which defines a limit value for maximum permissible pressure pulsations P, and a minimum value for pressure pulsations P _min , which defines a limit value for minimum permissible pressure pulsations P. Furthermore, a maximum value for pollutant emissions E _{max is also} entered here, which defines a maximum permissible limit value for the pollutant emissions. Finally, the diagram plots a lean extinction limit λ _{L of} the fuel / oxidizer ratio λ, which represents such a lean fuel / oxidizer ratio λ that the extinguishment of the combustion reaction must be expected. Finally, a minimum value for pollutant emissions E _{min is} entered.

With the aid of the operating method according to the invention, the gas turbine or its combustion chamber 1 can now be operated very close to the lean extinguishing limit λ _L , ie at very low pollutant emissions E and yet comparatively safe, ie stable. By using a fast-reacting control, the operation of the gas turbine near the lean extinction limit is much safer compared to a conventional control. For this purpose, the intensity or the amplitude of the pressure pulsations occurring in the combustion chamber 1 is determined via the at least one pulsation sensor 14 and compared with at least one, in particular empirically determined, pulsation setpoint P _soll . The pressure pulsations P thus form the reference variable of the closed loop constructed here. Depending on the control deviation, the fuel supply of the burner 2 is then adapted. Since the Oxidatorzufuhr, so from the compressor (not shown) coming airflow is generally constant, the change in the fuel supply to the fuel / oxidizer ratio λ affects. On the basis of the dependence of the pressure pulsations P on the fuel / oxidizer ratio λ explained with reference to FIG. 1, the change in the fuel supply also leads to a corresponding change in the pressure pulsations P. Here the control circuit closes.

Preferably, the control of the fuel supply is performed so that adjusts a proportional control with respect to the pulsation setpoint P _soll . Preferably, the control should be performed in the manner of a PI controller. The pulsation setpoint P _{soll is} expediently selected so that it is as close as possible to the pulsation _maximum value P _max .

According to a preferred embodiment, the operating method according to the invention operates so that upon reaching the maximum value of the pressure pulsations P _max or when exceeding the setpoint P _{soll of} the pressure pulsation P, the fuel supply to one or more burners 2 is enriched, in particular by a predetermined value. This means that the current operating point then moves from the desired pulsation value P _soll or from the point of intersection between the pressure pulsation curve P _(λ) and the pulsation axial value P _max along the pulsation curve P _(λ) to the left, ie towards enrichment. Since the pressure pulsations P in the pulsation _maximum value P _{max have} a predetermined minimum distance to the lean extinction limit λ _L , enrichment of the fuel supply enriches the distance to the lean extinction limit λ _L (to the left).

Furthermore, the operating method can be designed such that when the _minimum pulsation value P _{min is reached} or when the pulsation setpoint P _soll falls _, the fuel supply to at least one of the burners 2 is reduced, in particular by a predetermined value. This has the consequence that the current operating state then migrates from the pulsation setpoint P _setpoint or from the intersection between the _minimum pulsation value P _min and the pulsation curve P _(λ) to the right, ie in the direction of leaning along the pulsation curve P _(λ) . With the help of the Pulsationsminimalwerts P _min while a maximum distance to the lean extinction limit λ _{L is} defined, which should not be exceeded to ensure low pollutant emissions E. As is apparent from Fig. 1, the Pulsationsminimalwert P _{min is} suitably chosen so that in this area is about the emission _maximum value E _max .

With the aid of the pulsation _maximum value P _max and the _minimum pulsation value P _min , an operating window F is thus defined for the operation of the combustion chamber 1 as a function of the pressure pulsations P. In this operating window F, the combustion chamber 1 can be operated safely, that is to say stably, wherein always the smallest possible, but sufficient, distance from the lean extinction limit λ _L can be ensured. Furthermore, it is also achieved that the pollutant emissions E always move between the maximum value of the pollutant emissions E _max and the minimum value of the pollutant emissions E _min .

Optionally, monitoring of the pollutant emissions E can additionally be carried out for monitoring the pressure pulsations P. The fuel supply to at least one of the burners 2 can then also be regulated as a function of the pollutant emissions E. It is intended in particular to a scheme in which the fuel supply is at least one burner 2 emaciated when the pollutant emissions E reach the emission _maximum value E _max . As a result of the emaciation, the operating state moves from the point of intersection between emission _maximum value E _max and emission curve E _(λ) to the right, that is to say in the direction of leaning along the course of emission E _(λ) .

Since the emission _maximum value E _max and the pulsation _minimum value P _{min are} expediently assigned to the same fuel / oxidant ratio λ, the monitoring of the lower limit of the operating window F can be carried out optionally with reference to the emission _maximum value E _max or the _minimum pulsation value P _min . However, since the absolute value of the pulsation _minimum value P _{min is} comparatively small, measurement errors can occur, so that the monitoring of the pollutant emissions E under certain boundary conditions can lead to more accurate results. However, preference is given to a cumulative application of the two reference variables, wherein the fuel supply is always emaciated when at least one of the two reference variables reaches its respective limit value, ie either the emission _maximum value E _max or the _minimum pulsation value P _min .

The combination of the two control methods can also cover the case that the relationship between the pollutant emissions E and the pressure pulsations P changes during the course of the operation of the gas turbine.

For enriching and for leaning the fuel supply of the burner 2, the total fuel flow 7 can in principle be increased or decreased accordingly. In particular, the fuel supply of all burners 2 is substantially evenly emaciated or enriched. By changing the total fuel flow 7, however, the power of the gas turbine changes, which is not desirable in every case. Rather, a gas turbine should be operated regularly with constant load. Therefore, an embodiment is preferred in which, in order to reduce the pressure pulsations, the fuel supply to the main burners 4 is enriched, while the fuel supply to the auxiliary burners 5 is emaciated. The enrichment of the main burner 4 and the emaciation of the auxiliary burner 5 is carried out so that the total fuel flow 7 remains constant. This is achieved by a corresponding different division of the total fuel flow 7 to the main fuel stream 8 and the secondary fuel stream 9. Since the combustion process in the combustion chamber 3 is dominated by the main burners 4 and thus essentially defined by them and therefore the auxiliary burners 5 e.g. due to their smaller number and / or due to their smaller size less affect the combustion process than the main burner 4, the effects of the enrichment of the main burner 4 outweigh so that the pressure pulsations decrease.

Additionally or alternatively, depending on the degree of enrichment, at least one of the auxiliary burners 5 can also be switched off and the main burners 4 can at the same time be enriched so far that the total fuel flow 7 remains constant. This measure also leads to a reduction of the pressure pulsations. The above-described alternatively or cumulatively applicable measures for reducing the pressure pulsations P can be used within the scope of the operating method according to the invention be used to increase the distance to the lean erase limit λ _L again on reaching the Pulsationsmaximalwerts P _max .

To increase the pressure pulsations P or to lower the pollutant emissions E can then proceed in a corresponding manner. For example, for this purpose, the fuel supply to the main burners 4 is emaciated, while the fuel supply to the secondary burners 5 is enriched, with leaning and enrichment are coordinated so that the total fuel flow 7 remains constant. If at least one of the auxiliary burners 5 is switched off when the minimum pulsation value P _min or upon reaching the maximum emission value E _max, at least one of the auxiliary burners 5 can additionally or alternatively be connected to the measure described above, while at the same time the fuel supply to the main burners 4 is reduced is that in turn the total fuel flow 7 remains constant.

The fuel individual streams 10 can be supplied to the individual burners 2 via individual lines. It is also possible for the Hauptbrennstoffeinzelströme 11 and 12 for the Nebenbrunstoffeinszelströme separate common supply lines, in particular ring lines to provide, from which individual supply lines to the main burners 4 and zur Nebenbrennern 5 branch off.

In the embodiment shown in FIG. 2, the individual burners 2, that is to say the main burners 4 and the auxiliary burners 5, are assigned to the same burner stage. It is also possible to assign the main burner 4 and the secondary burner 5 different burner stages. The main group of burners 2 then forms a main stage, while the subgroup of burners 2 forms a secondary stage. For example, the main stage may be a premix stage of a premix burner, while the secondary stage is a pilot stage, which may be formed, for example, in the form of a lance in the premix burner. Accordingly, FIG. 3 shows by way of example a premix burner whose premix stage forms the main burner 4 and whose pilot stage forms the auxiliary burner 5. The combustion chamber 1 usually has several such Vormischbrenner, whereby a multi-burner system is present. The auxiliary burner 5 of the pilot stage generates a pilot flame 16, which essentially serves to stabilize the flame front. In contrast, the main burner 4 produces the premix stage of a premix flame 17. While the premix flame 17 usually leads to relatively low pollutant emissions E and generates comparatively high pressure pulsations P, the pilot flame 16 causes higher pollutant emissions E with simultaneously lower pressure pulsations P.

The control concept described above can now be readily applied to the multi-stage burner principle shown here, in order to be able to safely operate the combustion chamber 1 as close as possible to the lean extinction limit λ _L.

LIST OF REFERENCE NUMBERS

1

combustion chamber

2

burner

3

combustion chamber

4

main burner

5

Afterburner

6

Fuel supply system

7

Overall fuel flow

8th

Fuel main stream

9

Fuel bypass

10

Individual fuel power

11

Main fuel single stream

12

In addition to individual fuel power

13

control device

14

Pulsationssensor

15

emission sensor

16

pilot flame

17

premixed

P

pressure pulsation

P _(λ)

Pulsationsverlauf

P _max

Maximum value for the pressure pulsations

P _min

Minimum value for the pressure pulsations

e

Emissions

E _(λ)

emission course

E _max

Maximum value for pollutant emissions

E _min

Minimum value for pollutant emissions

λ

Fuel / oxidizer ratio

λ _L

lean limit of extinction

F

operating window

Claims (12)

Method for operating a firing installation with a multi-burner system for producing hot gas, in particular a gas turbine, preferably a power plant, - wherein the furnace has a combustion chamber (1) with a plurality of burners (2), - In which the fuel supply to at least one burner (2) for stationary operation of the furnace in response to in the combustion chamber (1) occurring pressure pulsations (P) is controlled. That the regulation of the fuel supply with respect to an adjustable or predetermined setpoint (P _set) Method according to claim 1, characterized in that the pressure pulsations (P) is proportional. The method of claim 1 or 2, characterized in that _(to P) upon reaching a predetermined or adjustable maximum value (P _max) for the pressure pulsations (P) or exceeds the target value of the pressure pulsations (P) the fuel supply to at least one burner (2 ) is greased. Method according to one of claims 1 to 3, characterized in that _(to P) upon reaching a predetermined or adjustable minimum value (P _min) for the pressure pulsations (P) or when it falls below the target value of the pressure pulsations (P) the fuel supply to at least one burner (2) emaciated. Method according to one of claims 1 to 4, characterized in that the fuel supply to at least one burner (2) also in response to in the exhaust gases of the combustion chamber (2) occurring pollutant emissions (E) is controlled. A method according to claim 5, characterized in that upon reaching a predetermined or adjustable maximum value (E _max ) for the pollutant emissions (E), the fuel supply to at least one burner (2) is emaciated by a predetermined value. Method according to one of claims 1 to 6, characterized in that the combustion chamber (1) has a plurality of burners (2) to which a fuel supply system (6) supplies a single fuel stream (10), all fuel individual streams (10) together forming a total fuel flow (7), - That the burner (2) in a main group with several main burners (4) and a subgroup with several auxiliary burners (5) are divided. A method according to claim 7, characterized in that on reaching the maximum value (P _max ) for the pressure pulsations (P) the fuel supply to the main burners (4) enriched and the fuel supply to the auxiliary burners (5) is so emaciated that the total fuel flow (7 ) remains constant. A method according to claim 7 or 8, characterized in that when reaching the maximum value (P _max ) for the pressure pulsations (P) at least one of the auxiliary burners (5) turned off and the fuel supply to the main burners (4) is so far enriched that the total fuel flow (7) remains constant. Method according to one of claims 7 to 9, characterized in that on reaching the minimum value (P _min ) for the pressure pulsations (P) and / or upon reaching the maximum value (E _max ) for the pollutant emissions (E), the fuel supply to the main burners ( 4) and the fuel supply to the auxiliary burners (5) is so enriched that the total fuel flow (7) remains constant. Method according to one of claims 7 to 10, characterized in that upon reaching the minimum value (P _min ) for the pressure pulsations (P) and / or at Achieving the maximum value (E _max ) for the pollutant emissions (E) of at least one of the auxiliary burners (5) switched on and the fuel supply to the main burners (4) is so far emaciated that the total fuel flow (7) remains constant. Method according to one of claims 7 to 11, characterized - That the main burner (4) and the secondary burner (5) are assigned to the same burner stage, or - That the main burner (4) and the secondary burner (5) of different fuel levels, such as a premixing stage and a pilot stage, are assigned.

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