EP2118569A1

EP2118569A1 - Method for operating a firing system

Info

Publication number: EP2118569A1
Application number: EP08701682A
Authority: EP
Inventors: Daniel Hofmann
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2007-02-06
Filing date: 2008-02-06
Publication date: 2009-11-18
Also published as: RU2009133372A; EP1956294A1; US20100024430A1; CN101606021A; WO2008095948A1

Abstract

The invention relates to a method for operating a firing system (12) with a combustion chamber (20), in which a fuel is preheated and is supplied in the preheated state for combustion in the combustion chamber (20). To achieve a high operating efficiency of the firing system (12) in part-load operation, it is proposed that the preheating temperature of the fuel is set in dependence on a variable obtained from the combustion, in particular a load of the firing system (12).

Description

description

Method for operating a furnace

The invention relates to a method for operating a

Furnace with a combustion chamber in which a fuel is preheated and preheated combustion is fed into the combustion chamber.

In a firing system is gaseous or liquid

Fuel is supplied to a burner in a combustion chamber and burned there to heat a working fluid, which is then available for the performance of labor. For example, in a gas turbine, ambient air in a compressor is compressed to a high pressure, mixed with fuel gas in a combustion chamber, and then burned. The resulting from the combustion, under very high pressure hot exhaust gas is directed to a turbine, which is driven by a relaxation of the exhaust gas. The shaft of the turbine is connected to the shaft of a generator for generating electrical energy.

Since a gas turbine produces a high waste heat, it is particularly effectively used in conjunction with a steam turbine in a combined process in which the waste heat generated by the gas turbine is used for operation of the steam turbine. A gas turbine plant and a steam turbine plant are hereby fused to form a power plant unit with an overall efficiency.

To improve the efficiency of the gas turbine or the power plant unit, it is known, for example from EP 0 918 151 Bl, to preheat the fuel before combustion. For this purpose, heat is taken from a process step in which the resulting deterioration in efficiency is less than the achieved efficiency improvement by the fuel preheating. As the efficiency deterioration increases with the temperature of the withdrawn preheat medium, the overall efficiency improvement decreases with increasing preheat temperature.

It is the object of the present invention to provide a furnace and a method for operating a furnace, with which a high degree of operating efficiency can be achieved.

The object directed to the method is achieved by a method of the type mentioned, in which, according to the invention, the preheating temperature of the fuel is set as a function of a quantity resulting from the combustion. It can also be made at a partial load operation of the furnace an efficiency-oriented preheating.

The invention is based on the consideration that the maximum preheating temperature of the fuel is specified by stability criteria of the combustion. The fuel can only be heated as far as a stable combustion is ensured with it. To determine the optimum preheating temperature, the stability criteria for the base load, in which the furnace is usually operated, are determined and the preheating of the fuel is adjusted accordingly.

The invention is based on the further consideration that power plants - due to the ever-increasing flexibility of the electricity market - to a greater extent a variable power output is required. At a

Firing system, it is therefore becoming increasingly important to work in part-load operation with a good preheating temperature in terms of efficiency. Since the stability of the combustion is also dependent on the instantaneous power or load of the furnace, consideration of the power in the adjustment of the preheating temperature can be used to the efficiency of the preheating in wide load ranges of the furnace optimize.

In this way, by an operation-dependent adjustment of the preheating temperature of the efficiency of the furnace can be kept high in other modes than a base load operation.

Here, the amount resulting from the combustion may be the power or load of the furnace, which increases with the strength of the combustion. Since the load or power is usually determined regularly, the control of the preheating temperature on the load offers. The power here is an absolute value, which can be measured for example by means of a force or determined by means of electrical variables on a generator. The load is an equivalent but relative size, which is based on the conditions currently prevailing, e.g. Type of fuel, air humidity, etc., obtainable achievable power.

In a rotary machine, the quantity resulting from the combustion may be the speed of a component driven by the combustion. In particular, the size of the current size, with a timely offset of up to 1 minute is possible, whereby the fuel is already preheated briefly, for example, in terms of a reduction in load more of the load reduction more. The size is in this case no nominal size of the furnace but a directly or indirectly resulting from the combustion size, which is determined for example from a measured value.

The furnace is advantageously a gas turbine plant with a gas turbine. A gas and steam turbine plant is conceivable or a steam power plant. The operation of the furnace is expediently a different from a starting operation of the furnace regular operation. The fuel is expediently gaseous or liquid. In an advantageous embodiment of the invention, the preheating temperature of the fuel is set higher at a partial load of the furnace than at a base load. At a partial load, combustion is still stable at a higher fuel temperature than at full load or base load of the furnace. Thus, the preheating temperature can be raised at a partial load and thereby the efficiency of the furnace at the partial load can be raised.

In a further advantageous embodiment of the invention, the preheating temperature of the fuel is adjusted as a function of a flame stability in the combustion chamber. In this way, the preheating temperature in the direction of a high efficiency, for example, can always be set so that the combustion is just stable. The quantity resulting from the combustion may in this case be the flame stability or a pressure fluctuation in the combustion chamber, which as such or e.g. can be measured as the hum of the combustion chamber.

If a heat source is available with which the fuel can be preheated to a high temperature with only a slight loss of efficiency, a maximum possible preheating temperature is always advantageous. Therefore, in a further advantageous variant of the invention, the preheating temperature of the fuel is basically set to a maximum possible value while maintaining a predetermined flame stability. "Basically" in this context can always be a regular operation, always an operation that is unchanged in time, or always another operation that is free from operating irregularities.

In a flexible use of the firing system, this is often started and shut down depending on the current energy requirements. Since starting up is a longer process, it is advantageous to work with high efficiency already when starting up to be able to. The operation-dependent setting of the preheating temperature according to the invention is also applicable to starting processes, so that it is proposed as a further variant of the invention that the fuel is already heated when starting the furnace and combustion resulting size is a size of a starting parameter of the furnace. The size may be a system temperature or - especially in a gas turbine - a speed of the rotor.

Flame stability depends on a number of parameters, such as air pressure, humidity, stiffness of the fuel supply, flow conditions in the combustion chamber, etc. Depending on the current flame stability, the fuel may be more or less preheated. Good preheating can be achieved in this complex system of parameters if the preheating temperature of the fuel is preset in a first step as a function of a stored assignment and fine-tuned in a second step by means of a measurement result. The deposited allocation can link the resulting from the combustion quantity - for example, the current performance of the system - with a preheating temperature, so that from this a preliminary preheating temperature results, is set to the default. By measuring another parameter - for example, a flame stability by measuring a pressure fluctuation - the preheating temperature can be further improved in terms of efficiency.

The object directed to the furnace is achieved by a firing plant of the type mentioned in the introduction, which according to the invention comprises a control means for adjusting the preheating temperature of the fuel as a function of a quantity resulting from the combustion. The preheating temperature can be adjusted for operational reasons and it is possible to achieve a high efficiency of the firing system in various operating modes. The control means may be a control unit with a corresponding control program containing, for example, a stored assignment of one or more operating parameters of the furnace to preheat temperatures. The

Fuel feed is an operational fuel-carrying means which may include one or more conduits.

In an advantageous development of the invention, the heating means has at least two heat exchangers arranged in the fuel feed, which are connected to heating stages of different operating temperatures. Heat can be extracted both from a relatively cool heat transfer medium with only a slight loss of efficiency and, in addition, heat from a warmer heat transfer medium to further heat the fuel to a high and efficient temperature. The heating stages may be in a high-, medium- or low-pressure preheater, for example in the form of heat exchangers, in an exhaust gas duct of a gas turbine or as a cooling element in the system, for example for cooling turbine blades.

In an alternative and inexpensive embodiment of the invention, the heating means comprises only one

Heat exchanger, which is flowed through during operation with hot preheating medium.

Advantageously, the heat exchangers are arranged serially in the fuel supply. Thus, the fuel can first be heated by a heat exchanger and then reheated by the second heat exchanger. If the heat exchanger connected to the cooler heating stage is arranged in the fuel flow in front of the heat exchanger connected to the warmer heating stage, then the heating energy of the warmer rear heat exchanger can be limited to a reheating of the fuel, whereby a small heat loss of the warmer heating stage is connected. In an alternative embodiment of the invention, the heat exchangers are arranged in parallel in the fuel supply, whereby a high degree of flexibility in the selection of the heat supply to the fuel can be achieved.

Advantageously, the BrennstoffZuführung comprises at least two parallel, each a partial fuel flow to one of the heat exchanger leading lines, the fuel partial flows through the lines after the

Heat exchangers are combined. Depending on the preheating temperature, the fuel streams can be distributed, so that the heating heat from, above all, the cooler heat exchanger is as fully usable. The control means can divide the partial streams to achieve the desired fuel temperature in terms of quantity on the two lines.

An efficiency loss by the preheating can be kept low, if the control means is provided, primarily the one associated with the cooler heating stage

Utilize heat exchanger and use the other heat exchanger for further heating of the fuel. As further heating can be seen in this case an additional heating on the heating by the cooler heat exchanger addition. In a serial arrangement, the warmer

Heat exchangers are used to further increase the temperature of the heated fuel, and in a parallel arrangement for higher heating of a partial flow.

In particular, in an operating method such that the

Preheat temperature of the fuel is preset in a first step depending on a stored assignment and is fine adjusted in a second step using a measurement result, it is advantageous if the control means is designed self-learning with respect to the control of the preheating temperature, that is provided with a corresponding program. Here, for example, the stored assignment by self-learning to the system and / or priority operating modes of the operator are further adapted so that a default becomes more accurate.

The invention will be explained in more detail with reference to exemplary embodiments, which are illustrated in the drawings. Show it :

1 shows a diagram in which the efficiency of a gas turbine plant is plotted as a function of a preheating temperature of the fuel combusted in the gas turbine of the gas turbine plant,

2 shows a diagram in which the efficiency of a combined cycle plant is plotted as a function of a preheating temperature of the fuel taking into account the energy required for the preheating, FIG. 3 shows a combined cycle plant with a heating means for heating

Preheating of fuel, 4 shows a diagram of the fuel supply to a combustion chamber of a gas turbine plant, 5 shows a representation of the heating means for preheating of fuel and

6 shows a representation of an alternative heating means for preheating fuel.

1 shows a diagram in which the efficiency η _G τ of a gas turbine plant of a gas and steam turbine plant (gas and steam turbine plant) as a function of the preheating temperature of the in the combustion chamber of

Gas turbine plant burned fuel is applied. As a starting point, a fuel temperature of 15 ° C is selected, in which the efficiency η _G τ of the gas turbine plant with 100% and the power of the gas turbine plant is also given as 100%. As the preheating temperature of the fuel introduced into the combustion chamber increases, the efficiency η _G τ increases linearly and the power P _{GT of} the gas turbine decreases slightly. At a preheating temperature of the fuel of 300 ⁰ C. An efficiency η _G τ of 101.5% can be achieved, the power P _GT has fallen slightly to 99.8%.

Is the energy required for preheating, which is taken from a working process of the combined cycle plant, in the

Involved efficiency calculation, so there is a dependent of the fuel preheating efficiency η _GU D of the entire CCGT plant, which is shown in FIG. Up to about 125 ° C, the efficiency η _GU D of the CCGT plant increases linearly. At low preheat temperatures, energy can be used for preheating that is not used in the steam turbine process. From a preheating temperature of about 125 ° C usable heat is also used in the steam turbine process for preheating, which is therefore no longer available for the performance of the steam turbine. The power P _{GuD of} the combined cycle power plant therefore decreases increasingly with increasing preheating temperature. Nevertheless, an increase in the efficiency η _GuD of CCGT plant up to preheating temperatures of 300 ⁰ C and more achievable, as long as the combustion in the combustion chamber remains stable.

In Figure 3, a gas and steam plant 2 is shown in a schematic overview. It comprises a steam turbine 4 whose rotor is connected via a shaft 6 to a generator 8. This is in turn connected to the rotor of a gas turbine 10, which is part of a furnace 12. On the exhaust side of the gas turbine 10, a heat recovery steam generator 14 is arranged, which is heated with the exhaust gas of the gas turbine 10. The exhaust gases leave the CCGT 2 via a chimney 16.

The furnace 12 comprises a compressor 18, for

Compressing combustion air, which is supplied to a combustion chamber 20. There it is mixed with preheated fuel and the mixture is burned. Heat for preheating the fuel can be taken from various points of the CCGT plant 2. Thus, compressed combustion air can be passed from the compressor 16 over to the turbine part of the gas turbine 10 and used there for cooling turbine blades. The thus heated air is returned via lines 22 and used to preheat the fuel.

Alternatively or additionally, heat can be taken from the steam system of the combined cycle plant 2, for example from the heat recovery steam generator 14. The heat recovery steam generator 14 comprises a high-pressure stage 24, a medium-pressure stage 26 and a low-pressure stage 28. The hot exhaust gas leaving the gas turbine 10 first flows through the high-pressure stage 24, which is heated the most, then the intermediate pressure stage 26 and finally the low pressure pressure stage 28. Condensate is pumped by means of a condensate pump 30 to a preheater 32, where the condensate is preheated. Before the preheated condensate is led to a low-pressure preheater 34, it can deliver heat to the low-temperature preheating of the fuel in a heating stage 36 designed, for example, as a heat exchanger. Via lines 38 and by a valve 42 controlled by a control means 40, the preheating medium reaches a heat exchanger (not shown in FIG. 2) for transferring the heat to the fuel.

Via a feedwater pump 44, the preheated condensate is also supplied under medium and high pressure to a medium-pressure preheater 46 or a high-pressure preheater 48. Previously, it can deliver heat as a heat transfer medium in a heating stage 50, which is also designed as a heat exchanger, for medium-temperature preheating of the fuel. Optionally, an even hotter heating stage 52 may be provided for the high-temperature preheating of the fuel. The corresponding supply of heat to the fuel is caused by the control means 40 by means of further valves 54, 56. Due to the arrangement of the heating stages 36, 50, 52 in the heat recovery steam generator or in its vicinity, the operating temperatures of the heating stages 36, 50, 52 are different. Depending on the desired preheating temperature of the fuel, heat is removed from the heat carrier only in the coolest heating stage 36 or even in the heating stage 50 or even the heating stage 52.

The heating stages 36, 50, 52, the control unit 40 and the Lines 38 with the valves 42, 54, 56 and the heat exchanger, not shown, for heat transfer to the fuel are part of a heating means 58 for preheating the fuel.

In an alternative that is favorable in terms of investment costs, the heating means on the heat absorption side comprises only a single heat exchanger, for example that of heating stage 50, which extracts heat for all preheating temperatures of the fuel from the heat carrier.

The furnace 12 with the gas turbine 10 and a fuel supply 60 to the combustion chamber 20 is shown in more detail schematically in FIG 4. Combustion air guided to the combustion chamber 20 is preheated in a heat exchanger 62. The fuel is preheated with the heating means 58 shown only schematically in FIG. 4, which on the heat delivery side can comprise one or more heat exchangers 66, 68, 70, 72 (see FIGS. 5 and 6). The fuel preheating is controlled by the control means 40, which detects the temperature of the still unheated fuel via a sensor 74 and the temperature of the preheated fuel via a sensor 76. Flame stability is determined by the control means 40 via another sensor 78 on or in the combustor 20. By means of another

Sensor 80, which may be located at the gas turbine 10 or at another suitable location, the power or load of the furnace 12 and the gas turbine 10 is detected.

As shown in FIG. 5, the heating means 58 is provided with two heat exchangers 66, 68 arranged serially in the fuel feeder 60. Optionally, a third heat exchanger is possible which receives heat from the optional heating stage 52, which however is not shown for the sake of clarity. The flowing in operation in the flow direction 82 fuel first reaches the heat exchanger 66, which is connected to the heating stage 36. The heating stage 36 In turn, the heat carrier of the operating temperature Ti of 130 ° C, namely the preheated condensate, supplied with heat. As a result, the preheating medium in the heating circuit of the heat exchanger 66 is heated to eg 125 ° C. Thereafter, the fuel reaches the heat exchanger 68, which is connected to the heating stage 50 with the higher operating temperature. The heating step 50 is supplied by heat transfer to the warmer operating temperature T ₂ of 210 ⁰ C, which is supplied to the medium-pressure 46 namely the condensate with heat. As a result, the preheating medium in the heating circuit of the heat exchanger 68 is heated to eg 200 ⁰ C. Via sensors 84, 86, the control means 40 respectively determines the temperature of the preheating medium in the two heating circuits of the heating means 58.

An alternative heating means 88 with two mutually parallel heat exchangers 70, 72 is shown in FIG. The following description is essentially limited to the differences from the exemplary embodiment in FIG. 5, with regard to characteristics which remain the same

Functions is referenced. Substantially identical components are basically numbered with the same reference numerals. Each of the heat exchangers 70, 72 is arranged in a separate line 90, 92, which are guided parallel to each other. The fuel flows through one of the

Control means 40 controlled distribution means 94, which divides the Brennstoffström on the two lines 90, 92. After preheating the fuel, the two fuel streams are recombined in a merging zone 96 into a fuel stream at the desired preheat temperature.

During the operation of the CCGT 2, the preheating temperature of the fuel is adjusted depending on a resulting from the combustion size. In a simple variant of the invention, this is the load of the gas turbine 10 or the CCGT 2, which is detected by the control means 40, for example by means of the sensor 80. In this case, the preheating temperature, ie the temperature measured in the sensor 76, with which the fuel reaches the combustion chamber 20, is set higher in a partial load operation of the combined cycle gas turbine 2 or the gas turbine 10 or the firing system 12 than in a base load or full load operation. In a more complex variant of the invention, the preheating temperature is set as a function of a flame stability of the combustion in the combustion chamber 20. Here, the preheating temperature can first be preset based on the load as a function of a stored in the control means 40 assignment, and then fine-adjusted or corrected based on the flame stability. The flame stability is detected by the control means 40, for example, by means of the sensor 78, for example by means of a pressure fluctuation in the combustion chamber 20 or a hum of the combustion chamber 208. In an additional, selectable by operating control program of the control means 40 is the

Preheating in principle adjusted to a maximum possible value while maintaining a predetermined flame stability.

Regardless of the setting of the preheating temperature of the control means 40 primarily associated with the cooler heating stage 36 heat exchanger 66, 70 is used, so that as little as possible hochtemperierter heat carrier cooled and the steam process as little usable heat is withdrawn. Thus, if possible, the fuel is fully or at least as much as possible heated by the cooler heat exchanger 66, 70, and the hotter heat exchanger 68, 72 is only used to further increase the fuel temperature or hotter fuel for admixture through the heat exchanger 70 maximum possible heated fuel to provide. Accordingly, the flows of preheating medium through the heat exchangers 66, 68, and the fuel flows through the heat exchangers 70, 72 are set by the control means 40. Another control program of the control means 40 allows self-learning of the control means 40 in the setting of the preheating temperature. The preheating temperature, which is fine-tuned with the aid of a measuring result, is linked in each case to the prevailing operating parameters of the furnace 12 or the CCGT 2. If, at a later point in time, the same or a similar operating point is reached with regard to the operating parameters, the stored preheating temperature is adjusted and, if necessary, set even finer by further measurements.

In the described method, the fuel can already be preheated when starting up the firing system 12 according to data stored, for example with the aid of a size of a starting parameter of the firing system 12, and / or measurement results, so that a high efficiency of the furnace 12 is achieved quickly.

Claims

claims

A method of operating a combustion plant (12) having a combustion chamber (20) in which a fuel is preheated and fed to combustion in the combustion chamber (20), characterized in that the preheating temperature of the fuel at a partial load of the combustion plant ( 12) is set higher than at a base load.

2. The method according to claim 1, characterized in that the preheating temperature of the fuel is adjusted in dependence on a flame stability in the combustion chamber (20).

3. The method according to claim 1 or 2, characterized in that the preheating temperature of the fuel is basically set to a maximum possible value while maintaining a predetermined flame stability.

4. The method according to any one of the preceding claims, characterized in that the fuel is already heated when starting the furnace (12) and resulting from the combustion size is a size of a starting parameter of the furnace (12).

5. The method according to any one of the preceding claims, characterized in that the preheating temperature of the fuel is preset in a first step in dependence on a stored assignment and fine-adjusted in a second step by means of a measurement result.