EP2372239A2 - Method for operating a steam turbine power plant with fluidized bed combustion - Google Patents

Abstract

The method involves supplying primary air (2a), secondary air (2b) and fluidization air (20) via a separate delivery system. The primary air and/or secondary air are pre-heated before entering into a fluidized bed kettle. The fluidization air is pre-heated using air pre-heaters (11, 18), where warm necessary for heating the fluidization air is extracted from flue gas (3) in multi-stages. The air pre-heaters are operated in series with a boiler feeding water pre-heater, where one of the heaters (11) is designed as a rotary air pre-heater.

Description

The invention relates to a method for operating a steam turbine power plant with a fluidized bed combustion, in particular one with a circulating fluidized bed combustion, in which primary air, secondary air and fluidization air are provided via separate feed systems, wherein the primary air and / or the secondary air are preheated before entering the fluidized bed boiler.

The operation of power plants is usually geared to the objectives of efficiency, security of supply and environmental compatibility. In particular, in power plants fueled with fossil fuels measure to increase efficiency appear particularly suitable to meet this requirement profile. Since a higher power plant efficiency reduces the fuel input at constant power plant output, efficiency-enhancing measures are synonymous with decreasing emissions and a contribution to resource conservation.

The efficiency of a fossil fuel-fired steam generator is significantly dependent on the temperature of the exhaust gas and the type of use of the exhaust heat.

The most effective method of achieving high steam generation efficiency is to utilize exhaust heat by preheating as much combustion air as possible to a high temperature. As a rule, however, the regulated, i. quantitatively detectable amount of combustion air compared to the amount of exhaust gas specifically too low to achieve the desired low exhaust gas temperature.

Basically, steam generators distinguish between dust-fired steam generators and those with fluidized bed combustion. at

For example, in the combustion of lignite, the use of fluidized bed combustors often employs so-called circulating fluidized bed firing, which differs from stationary fluidized bed firing in that the bed material, i. mostly the ashes, are recycled.

When operating dust-fired steam generators, the combustion air preheating is known by means of regenerative air preheater. This is relatively easy there, since the largest part of the combustion air is regulated with a uniform pressure supplied to the steam generator.

Steam boilers with fluidized bed combustion have the disadvantage in comparison to dust-fired steam generators that the controlled supply of combustion air at different pressure levels must be conceived in the steam generator. The secondary air has an overpressure of approx. 100 mbar and ensures complete combustion. The primary air usually has an overpressure of about 200 mbar and is supplied via a nozzle bottom of the circulating fluidized bed combustion. With the fluidizing air, which is supplied at about 500 mbar, the fine-grained inert material (bed material / ash) is usually fluidized.

Even with steam generators with circulating fluidized bed combustion, it is known to preheat or heat the primary and secondary air for the furnace via a regenerative air preheater.

In the known methods, an increase in efficiency along with a reduced fuel consumption is still desirable.

The invention is therefore based on the object to provide a method for operating a steam turbine power plant with a fluidized bed combustion, in which a significant increase in the steam generation efficiency and associated overall system efficiency is achieved with constant energy consumption for supplying the combustion air.

The object is firstly achieved by a method for operating a steam turbine power plant with a fluidized bed combustion, in which primary air, secondary air and fluidization air are provided via separate feed systems, wherein the primary air and / or the secondary air are preheated before entering the fluidized bed boiler , wherein the inventive method is characterized in that in addition a Fluidisierungsluftvorwärmung is provided.

The fluidizing air is used in particular in the circulating fluidized bed combustion to fluidize the fine-grained inert materials (ash / bed material). With the fluidizing air, the components such as fluidized bed cooler, external heat exchangers, ash ash, ash return locks, siphons, ash coolers, etc. are also operated, for which an overpressure of about 500 mbar is usually required. Frequently, separate fluidizing air supply systems with different blowers / compressors are also used.

Surprisingly, it has been found that by an additional preheating of the fluidizing air, i. In addition to the preheating of the primary and secondary air, a significant increase in efficiency can be achieved. Up to now, therefore, one has refrained from preheating in particular because conventional regenerative air preheaters are not usable because of the high overpressure within the fluidizing air systems (about 500 mbar) and the resulting leakage currents. For this reason, in known fluidized bed combustion, the fluidizing air is introduced into the steam generator without preheating.

In a particularly expedient variant of the method according to the invention, it is provided that the preheating of the fluidizing air is decoupled from the preheating of the primary and / or secondary air. This has the particular advantage that the preheating of the fluidizing air is not at the expense of the flue gas inlet temperature of the regenerative air preheater. This would make the hot air temperature of the primary and secondary air unnecessarily reduced, which in turn causes an increasing exhaust gas temperature and a decreasing steam generation efficiency.

In a particularly expedient and advantageous variant of the method of the invention, it is provided that the heat required for the fluidization air preheating is nevertheless decoupled from the flue gas stream.

For this purpose, it can be provided, for example, that the flue gas stream is divided before the energy extraction and guided via parallel flue gas paths. In this way, it is ensured that both the air preheater required for preheating the primary and secondary air and the air preheater required for the preheating of the fluidization air are subjected to the highest possible flue gas temperature and thus the preheating of the fluidizing air is not at the expense of the hot air temperature of the primary and secondary air takes place.

The preheating of the primary air and / or secondary air fed to the fluidized-bed furnace and the fluidizing air are preferably carried out via air preheaters connected in parallel.

In an advantageous embodiment of the method according to the invention, it is provided that the decoupling for the heat required for preheating the fluidizing air takes place from the flue gas path of a boiler feed water preheating.

Expediently, the heat which can be used for the preheating of the fluidizing air is coupled out of the flue gas stream in a multistage manner.

For example, the coupling-out of the heat required for preheating the fluidizing air can take place by means of a plurality of air preheaters connected in series.

These series-connected air preheaters can be operated in series with at least one boiler feedwater pre-heater.

Particularly favorable is a multi-stage preheating of the fluidizing air with a multi-stage boiler feedwater preheating in staggered arrangement, i. the boiler feedwater preheater and fluidization air preheater are alternately connected in series, so that a performance penalty of the boiler feedwater preheaters is avoided as much as possible.

The invention will be explained below with reference to an embodiment shown in the drawings:

Fig. 1

das Verfahrensschema einer Variante eines Dampfturbinenkraftwerks mit herkömmlicher Luftvorwärmung,

Fig. 2

das Verfahrensschema einer ersten Verschaltungsvariante der Fluidisierungsluftvorwärmung gemäß der Erfindung,

Fig. 3

ein Verfahrenschema einer zweiten Verschaltungsvariante der Fluidisierungsluftvorwärmung gemäß der Erfindung und

Fig. 4

ein Verfahrenschema einer dritten Verschaltungsvariante der Fluidisierungsluftvorwärmung gemäß der Erfindung.

Show it:

Fig. 1

the process diagram of a variant of a steam turbine power plant with conventional air preheating,

Fig. 2

the process diagram of a first wiring variant of the Fluidisierungsluftvorwärmung according to the invention,

Fig. 3

a process diagram of a second Verschaltungsvariante the Fluidisierungsluftvorwärmung according to the invention and

Fig. 4

a process diagram of a third Verschaltungsvariante the Fluidisierungsluftvorwärmung according to the invention.

In Fig. 1 Parts of a dry lignite steam turbine power plant are shown schematically, with essentially mass flows of drying vapors 1, combustion air 2 and flue gas 3 are shown for reasons of simplification. The water-steam cycle of the steam turbine power plant is shown only partially and greatly simplified. The FIG. 1 describes an example of a steam turbine power plant for the purpose of reciting the process schemes FIGS. 2 to 4 in a context.

The reference numeral 4 designates the steam generator of the steam turbine power plant. The steam generator 4 is designed as a dry lignite-fired fluidized bed boiler. The mass flow of combustion air 2 in the Steam generator is simplified as a single flow path shown. The steam generator 4 of the steam turbine power plant is designed in particular as a fluidized bed boiler with circulating fluidized bed. A fluidized bed with circulating fluidized bed is basically known and will therefore not be described in detail below. In the steam generator 4, water is evaporated in a manner known per se and expanded in a downstream steam turbine 5. The steam turbine 5 comprises a high-pressure part, a medium-pressure part and a low-pressure part, which are not designated more precisely in the process diagram. The steam turbine 5 drives a generator 6, which in turn feeds electrical energy into a power grid.

The steam turbine 5 is followed by a condenser 7, is condensed in the low-pressure steam.

By means of a boiler feed water pump, the condensate is returned to the steam generator 4.

The steam generator 4 is charged with dry lignite as fuel, which was subjected to indirect drying in a fluidized bed dryer 8. It should be noted at this point that the steam generator 4 does not necessarily have to be charged with dry brown coal as fuel. This variant of the method has been chosen here for illustrative purposes only.

The fluidized-bed dryer 8 is heated with steam from the low-pressure part of the steam turbine 5. Part of the resulting in the drying of brown coal vapor 1 is first dedusted in a dust collector 9 and fed back to the fluidized bed dryer 8 as a fluidizing means with a blower 10. Further partial streams of the vapor 1 are, as will be described below, used to preheat the combustion air 2.

The combustion air 2 is supplied in a known manner to a regenerative air preheater 11, which may be designed, for example, as a rotary vane can. In the regenerative air preheater 11, the combustion air is preheated in countercurrent with the flue gas 3.

A partial flow of the flue gas 3 is guided via a bypass line 12 to the air preheater 11 over. This first passes through a first high-pressure air bypass economizer 13 (HD-Lubeco), and is then passed through a low-pressure air bypass economizer 14 (ND Lubeco), which are connected in series with respect to the flue gas stream 3. The heat content of the flue gas 3 is coupled via the HD Lubeco 13 in the high pressure part of the feedwater circuit, the remaining heat of the flue gas is coupled in the next stage in the low pressure part of the boiler feedwater cycle.

In the flow direction behind the air preheater 11 and the economizers 13, 14 is in the in Fig.1 a further flue gas cooler 15 is provided, which emits its heat load via a water / air preheater 16 provided in the combustion air supply. The flue gas cooler 15 and the water / air preheater 16 communicate with each other via water as the heat transfer medium in a closed circuit.

The combustion air 2 is first preheated in a Brüdenluftvorwärmer 17. The Brüdenluftvorwärmer 17 is acted upon by a partial flow of the vapor from the fluidized bed dryer 8. The Brüdenluftvorwärmer 17 is viewed from the direction of flow of the combustion air 2, the Wasserluftvorwärmer 16 downstream, in which the combustion air is further warmed. The combustion air 2 then flows through the regenerative air preheater 11, where it is heated in countercurrent with the about 360 ° C hot flue gas to about 330 ° C. The flue gas, which enters the air preheater 11 at 360 ° C., can leave it, for example, at about 160 ° C.

While in Fig. 1 the combustion air preheating for the steam generator 4 is shown only greatly simplified, shows Fig. 2 a first variant of combustion air preheating according to the invention. In addition to the aforementioned regenerative air preheater 11, a further air preheater 18 is provided, which is connected in parallel to the air preheater 11. The air preheater 18 is designed as a tube air preheater and is acted upon by a portion of the flue gas 3.

The combustion air 2 in the form of primary air 2a and secondary air 2b is preheated by means of the blower 19 via the regenerative air preheater 11. Parallel to this, the steam generator 4 or the ZWF boiler (circulating fluidized bed combustion) fluidizing air 20 is supplied, which is also heated by the parallel air preheater 18 in countercurrent to the flue gas 3. The flue gas 3 is guided in the region of the air preheater 11 and 18 in two mutually parallel partial streams 3a, 3b.

Basically, the in Fig. 2 illustrated variant of the combustion air preheating without the in Fig. 1 represented air bypass economizer system (feedwater pre-heating by means of the economizer 13 and14) can be realized.

In Fig. 3 an alternative embodiment of the combustion air preheating is shown according to the invention and in combination with the air bypass economizer system according to Fig. 1 , This variant does not represent a plant-technical simplification compared to in Fig. 2 However, in order to reduce the number of flue gas paths, the preheating of the fluidizing air 20 in the flue gas path of the boiler feedwater preheating (air bypass economizer system) can take place.

Basically, the order of switching of parts of the economizer and the air preheater is possible.

Another variant of the combustion air preheating according to the invention is shown in FIG Fig. 4 shown.

There, the preheating of the fluidizing air 20 is provided in two stages by means of the Luftvorwärmers 11 a and the Luftvorwärmers 11 b, which are connected in series. The air preheaters 11a, 11b are arranged in series with the economizers 13 and 14 in series in the flue gas path of the boiler feedwater preheating, to minimize the performance penalty of the HD-Lubecos 15 (high pressure air bypass economizer). The first stage 11b of the air preheater, viewed in the flow direction of the flue gas 3b, is provided at the highest possible flue gas temperature location to raise the temperature of the fluidizing air as much as possible for the purpose of maximizing efficiency.

LIST OF REFERENCE NUMBERS

1

vapors

2

combustion air

2a

primary air

2 B

Secondary air

3

flue gas

3a, b

Flue gas partial flows

4

steam generator

5

steam turbine

6

generator

7

capacitor

8th

Fluidized bed dryer

9

dust collector

10

fan

11

air preheater

12

bypass line

13

ND Lubeco (Low Pressure Air Bypass Economizer)

14

HD-Lubeco (High Pressure Air Bypass Economizer)

15

Flue gas cooler

16

Wasserluftvorwärmer

17

Brüdenluftvorwärmer

18

air preheater

19

fan

20

fluidization

Claims (10)

Method for operating a steam turbine power plant with a fluidized bed combustion, in particular with a circulating fluidized bed, in which primary air, secondary air and fluidization air are provided via separate feed systems, wherein the primary air and / or the secondary air are preheated before entering the fluidized bed boiler, characterized in that additionally Fluidisierungsluftvorwärmung is provided. A method according to claim 1, characterized in that the preheating of the fluidizing air is decoupled from the preheating of the primary and / or secondary air. Method according to one of claims 1 or 2, characterized in that the heat required for the Fluidisierungsluftvorwärmung heat is decoupled from the flue gas stream. A method according to claim 3, characterized in that the flue gas stream is divided before the heat extraction and guided over parallel flue gas paths . Method according to one of claims 1 to 4, characterized in that the preheating of the fluidized bed combustion supplied primary air and / or secondary air and the fluidizing air via parallel connected air preheater takes place. Method according to one of claims 1 to 5, characterized in that the decoupling of the heat required for preheating the fluidizing air from the flue gas path of a boiler feed water preheating takes place. Method according to one of claims 1 to 6, characterized in that the heat required for the preheating of the fluidizing air is coupled in multiple stages from the flue gas stream. Method according to one of claims 6 or 7, characterized in that the decoupling of the heat required for preheating the fluidizing air by means of several series-connected air preheater takes place. A method according to claim 8, characterized in that the air preheaters for preheating the fluidizing air are operated in series with at least one boiler feedwater pre-heater. Method according to one of claims 8 or 9, characterized in that a multi-stage preheating of the fluidizing air is provided with a multi-stage boiler feedwater preheating in staggered arrangement.

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