EP0278357B1 - Device for generating combustion gas for driving a gas turbine - Google Patents

Description

The invention relates to a device according to the preamble of patent claim 1.

Such a device is known as a steam generator from German Offenlegungsschrift 31 32 659. The inlet openings for combustion air of this known device open in the axial direction at the bottom of the shaft into the combustion chamber, in which a fluidized bed is generated with the combustion air and with the fine-grained coal supplied. In this fluidized bed, in which there are also convection heating surfaces of the steam generator, the combustion of the supplied fine-grained coal takes place with a considerable overpressure in relation to the atmosphere.

Fine-grained limestone is also added to the fluidized bed in order to bind the sulfur dioxide produced during combustion. In view of this chemical reaction, the combustion temperature must not be higher than 850 ° C. Therefore, only relatively little nitrogen oxide is generated. The consequence of the low combustion temperature is, however, a low flue gas inlet temperature for a gas turbine connected to the flue gas outlet port of the steam generator.

The invention has for its object to further develop the known device and to enable the flue gas temperature at the flue gas outlet connection to be increased, thereby increasing the efficiency of the power plant in which the device is integrated and nevertheless largely suppressing the formation of nitrogen oxides.

To achieve this object, a device of the type mentioned at the outset has the features of the characterizing part of patent claim 1.

The combustion of the fine-grained coal with the coal dust burner takes place in this device at a combustion temperature higher than 850 ° C, since the sulfur dioxide formed is not integrated during the combustion but only afterwards. The flue gas generated during combustion would be cooled by a convection heating surface within the shaft, but even then the flue gas at the flue gas outlet connection of the device would still have a significantly higher temperature than 850 ° C. The inlet opening for combustion air may be axially directed, but a swirl of the combustion air generated by the arrangement or configuration of the inlet opening for combustion air even causes hot flue gas to be returned to the vicinity of the feed opening for fine-grained coal and thereby ensures the correct ignition of this fine-grained coal despite the short amount of time this coal has in the combustion chamber. Due to the spatial separation of the air nozzle from the inlet opening for combustion air or the additional inlet opening for fine-grained coal from the feed opening for fine-grained coal, the heat release during combustion is evenly distributed in the combustion chamber. In addition, the combustion can take place with a large excess of air and thus with a reduced combustion temperature, so that extensive suppression of nitrogen oxide formation is brought about. Furthermore, the flue gas is mostly already dedusted within the device for generating this flue gas.

The subclaims are directed to advantageous developments of the device according to claim 1.

• FIG 1 zeigt stark schematisiert einen Längsschnitt durch eine erfindungsgemäße Vorrichtung, die als Dampferzeuger ausgebildet ist.
• FIG 2 und FIG 3 zeigen im Längsschnitt bzw. in der Draufsicht eine Einzelheit aus FIG 1.
• FIG 4 und FIG 5 zeigen im Längsschnitt bzw. in der Draufsicht eine Einzelheit einer abgewandelten Vorrichtung nach FIG 1.
• FIG 6 zeigt stark schematisch im Längsschnitt eine weitere Abwandlung der Vorrichtung nach FIG 1.
• FIG 7 zeigt ein stark vereinfachtes Schaltbild eines Kraftwerkes mit einer erfindungsgemäßen als Dampferzeuger ausgebildeten Vorrichtung.
• FIG 8 zeigt stark schematisiert einen Längsschnitt durch eine weitere Vorrichtung gemäß der Erfindung.

The invention and its advantages are explained in more detail with reference to the drawing using exemplary embodiments:

• 1 shows a highly schematic longitudinal section through a device according to the invention, which is designed as a steam generator.
• 2 and 3 show a detail from FIG. 1 in longitudinal section and in plan view.
• 4 and 5 show in longitudinal section and in plan view a detail of a modified device according to FIG. 1.
• 6 shows, in a highly schematic, longitudinal section, a further modification of the device according to FIG. 1.
• 7 shows a greatly simplified circuit diagram of a power plant with a device according to the invention designed as a steam generator.
• 8 shows a highly schematic longitudinal section through a further device according to the invention.

The steam generator according to FIG 1 has a hollow cylindrical housing 2, in which an elongated shaft 3 is arranged coaxially. The shaft wall 4 of this elongated shaft 3 is formed by fin tubes welded to one another in a gastight manner.

The hollow cylindrical housing 2 and the shaft 3 are arranged vertically. At the end of the shaft, which represents the lower end of the shaft 3, the shaft 3 forms a combustion chamber 5, while a flue gas outlet connection 6 is arranged at the other end of the shaft, which represents the upper end of the shaft 3. Between the shaft 3 or the flue gas outlet connection 6 and the hollow cylindrical housing 2 there is an intermediate space 7 in the hollow cylindrical housing 2.

In front of the flue gas outlet connection 6 there are 3 convection heating surfaces 8 which hang from supports 9 within the shaft.

A closing part 10 at the shaft end forming the lower end of the shaft 3 also consists of fin tubes welded to one another in a gastight manner. A feed opening 11 for fine-grained coal is attached to it, which opens into the combustion chamber 5. Furthermore, there is an inlet opening 12 for combustion air at the end part 10, which together with the feed opening 11 for fine-grained coal forms a coal dust burner.

The cross section of the combustion chamber 5 at the shaft end forming the lower end of the shaft 3 has the shape of a circle and widens conically in the direction of the flue gas flow to the flue gas outlet connection 6 to two additional inlet openings 13 for combustion air, which are provided in the shaft wall 4 of the shaft 3.

At a distance from the end part 10, but in the combustion chamber 5 there is also an additional inlet opening 14 for fine-grained coal in the shaft wall 4.

At a distance from the additional inlet openings 13 provided for combustion air and from the additional inlet opening 14 for fine-grained coal in the direction of the flue gas flow to the flue gas outlet connection 6, there are air nozzles 15. They are also arranged in front of the convection heating surfaces 8, seen in the direction of the flue gas flow.

As FIG 2 and FIG 3 show, the feed opening 11 for fine-grained coal opens centrally and axially into the combustion chamber 5. The inlet opening 12 for combustion air surrounds the feed opening 11 for fine-grained coal in a ring shape. This feed opening 12 contains guide vanes 16 which give the combustion air fed into the combustion chamber 5 a swirl.

The additional inlet openings 13 for combustion air in FIG. 1 can open tangentially into the shaft 3 and be directed in such a way that the air supplied through them receives a swirl which has the same direction of rotation as the swirl of the combustion air supplied through the inlet opening 12. One, several or all additional inlet openings 13 can also be directed radially.

The air nozzles 15 are also directed tangentially so that the air supplied through them has a swirl, the direction of rotation of which is equal to the direction of rotation of the combustion air supplied through the inlet opening 12. In addition, these air nozzles 15 are to the end part 10, which is located at the shaft end forming the lower end of the shaft 3, i.e. inclined to the gradation 18 of the shaft wall 4.

Inside the shaft 3 between the air nozzles 15 and the additional inlet openings 13 for combustion air, helically rising guide plates 17 are attached, the spiral direction of which is selected such that they impart a swirl to the flue gas rising from the combustion chamber 5, which has the same direction of rotation as that through the air nozzles 15 supplied air. These guide plates 17 can also consist of fin tubes which are welded together.

Between the air nozzles 15 and the baffles 17, the cross section of the shaft 3, viewed in the direction of the flue gas flow, widens to the flue gas outlet connection 6 to form a step 18 in the shaft wall 4. In this step 18, which is arranged between the additional inlet opening 13 for combustion air and the air nozzles 15 there are ash discharge openings 19, from which ashes fall downward in the direction of arrow 19a into a collecting space 80 and can be discharged to the outside through an ash line 81.

A cylindrical heating surface 20 made of fin tubes welded to one another in a gastight manner also hangs on the support 9 in the shaft 3. This heating surface 20 is located between the additional inlet openings 13 for combustion air and the convection heating surfaces 8 in the middle of the shaft 3, to which it is coaxial.

The space 7 between the shaft wall 4 of the shaft 3 and the inside of the hollow cylindrical housing 2, the air nozzles 15, the inlet opening 12 for combustion air and the feed opening 11 for fine-grained coal are connected to the same air compressor 48 via connecting pipes, while the additional inlet openings 13 for combustion air are on Interspace 7 are connected. In the connecting pipeline 22, which leads to the feed opening 11 for fine-grained coal, a coal supply line 23 opens outside the housing 2 at a point which, seen in the flow direction of the air, is located behind the branching point of the connecting pipeline 22 from the other connecting pipelines.

As FIGS. 4 and 5 show, the inlet opening 12 for combustion air can also open tangentially into the combustion chamber 5. A tangential inlet opening 12 is directed so that the combustion air supplied through it has the same direction of rotation as the combustion air supplied through the supply opening 12 with the guide vanes 16 according to FIGS. 2 and 3.

According to FIG. 6, the feed opening 11 and the additional inlet opening 14 for fine-grained coal are connected to a pipeline 23 with a liquid pump 24, through which a pumpable mixture of water and the fine-grained coal is fed. The inlet opening 12 for combustion air can be designed either in accordance with FIGS. 2 and 3 or in FIGS. 4 and 5.

A mixture of water and fine-grained coal can be introduced particularly easily via the feed opening 11 and the additional inlet opening 14 into the combustion chamber 5 of the steam generator, which is under a considerable excess pressure on the flue gas side. Furthermore, the water evaporating in the combustion chamber 5 reduces and evenens the combustion temperature and thereby contributes to reducing the nitrogen oxide formation.

The cross section of the combustion chamber 5 in the form of a circle or a regular polygon promotes the swirl formation of the combustion air in the combustion chamber 5 through the combustion air supplied through the inlet opening 12 and thus also the ignition of the fine-grained coal supplied through the supply opening 11. The blowing in of a part of the total coal flow fed to the combustion chamber 5 through the additional inlet opening 14, which is located between the additional inlet openings 13 for combustion air and the air nozzles 15, leads to a further reduction in nitrogen oxide formation.

The flue gas rising from the combustion chamber 5 in the shaft 3 is kept away from the inside of the shaft wall 4 both by the combustion air entering tangentially through the additional inlet opening 13 and by the air supplied through the air nozzles 15, which is thereby protected against corrosion by carbon monoxide contained in the flue gas .

The flue gas rising from the combustion chamber 5 is further deflected by the baffles 17 rising in a spiral. This and the air supplied through the air nozzles 15 increase the swirl of the flue gas, so that the ash carried by the flue gas collects near the shaft wall 4 and can to a large extent be discharged through the discharge opening 19. The largely dedusted flue gas flows to the convection heating surfaces 8 and is cooled there. Because of its low dust content, this flue gas not only causes little contamination of the convection heating surfaces 8, but a flue gas deduster connected to the flue gas outlet connection 6 need only have a relatively low separation efficiency.

The transport of the ash carried by the flue gas in the direction of the ash discharge slots 19 can be improved if the air flow supplied through the air nozzles 15 is increased at intervals and the air flow supplied through the additional inlet openings 13 is reduced in the same cycle. The sum of the two air flows advantageously remains approximately constant.

The heating surface 20, which is advantageously cylindrical, is intended to reduce the flue gas temperature in the combustion chamber 5 and thereby simultaneously reduce the nitrogen oxide formation. Their fin tubes are wound helically and welded together gas-tight. It can hang on the supports 9 with its outlet pipes 24. These outlet pipes 24 can also be vertical support pipes for the convection heating surfaces 8.

A high flue gas pressure is aimed for in shaft 3, which shortens the reaction time between the fine-grained coal and the combustion air. As a result, the combustion chamber essentially consisting of the combustion chamber 5 can have a relatively small volume. The heating surface 20 can nevertheless bring about sufficient cooling of the flue gas rising from the combustion chamber 5, so that the ash carried by the flue gas does not melt.

Since all of the air supplied to the steam generators according to FIGS. 1 to 6 comes from the same air compressor 48, the air pressure in the space 7 between the shaft wall 4 and the inside of the hollow cylindrical housing 2 is always greater than the pressure of the flue gas inside the shaft 3. Therefore due to a leak in the shaft wall 4, no flue gas can get out of the shaft 3 into the intermediate space 7.

The shaft can also have the combustion chamber with the end part, the feed opening for fine-grained coal and the inlet opening for combustion air at the end of the shaft, which is the upper end of the shaft, and the flue gas outlet connection at the other, the lower end of the shaft, forming the shaft end, so that the flue gas flows from top to bottom in the shaft.

Otherwise, such a steam generator can be designed in the same way as in Figures 1 to 6, with the exception that the air nozzles are inclined towards the lower end with the flue gas outlet connection and the gradation in the shaft wall is designed such that the discharge openings for ash located there are used for the ashes discharge the bottom end of the shaft.

The combined gas / steam turbine power plant according to FIG. 7 has a steam generator 30 according to FIGS. 1 to 6, which is operated as a continuous steam generator, and a steam turbine with a high pressure part 31 and a medium and low pressure part 32, which are connected to a live steam line 33 coming from the steam generator 30 and which are connected to it an electrical generator 34 is coupled and which drives this generator 34. At the steam generator 30, the supply line 23 for the fine-grained coal and a single connecting pipeline 35 for air are indicated instead of the connecting pipelines shown in FIG.

The medium and low pressure part 32 of the steam turbine is followed by a condenser 36 with a condensate pump 37 which pumps the condensate via a low pressure preheater 38 into a feed water tank 39, which is also effective as a degasser. A feed water pump 40 with downstream feed water high-pressure preheaters 41 and 58 is connected to the feed water tank 39 and lies in the feed water supply line 42 to the high-pressure heating surfaces 43 in the steam generator 30. These high pressure heating surfaces 43 are through the fin tubes of the end part 10, the shaft wall 4, the heating surface 20 and the guide plates 17 and two of the convection heating surfaces 8 of the steam generator according to FIGS. 1 to 6, which represent economiser heating surfaces, evaporator heating surfaces and preheater and final superheater heating surfaces with live steam outlet to the live steam line 33 connected to one another on the water side.

A flue gas discharge line 44, which contains a dust separator 45, is connected to the steam generator 30 or to the flue gas outlet connection 6 of the steam generator according to FIG. This dust separator 45, the walls of which can consist of fin tubes welded to one another in a gas-tight manner for the transmission of flue gas heat to the water-steam circuit of the power plant, is followed by a flue gas turbine 46, the drive unit of both an electric generator 47 and an air compressor 48 in the air supply line 35 Steam generator 30 is. A further air compressor 49 is connected upstream of this air compressor 48 and is used as a drive unit e.g. has an electric motor 50, the speed of which is adjustable. Both air compressors 48 and 49 form the air compression device according to FIG. 1.

A finned tube heat exchanger 52 and the feed water high-pressure preheater 41, both of which are connected in series in the flue gas duct 51, are connected downstream of the flue gas turbine 46 in the flue gas duct 51 leading from the flue gas turbine 46. The steam line 53 carrying the intermediate steam of the high-pressure part 31 of the steam turbine is connected to the steam side of the finned tube heat exchanger 52, which in turn is connected to the feed line 54 to an intermediate superheater heating surface 55 in the steam generator. This reheater heating surface 55 is one of the convection heating surfaces 8 of the steam generator according to FIGS. 1 to 6. A steam discharge line 56 of the reheater heating surface 55 leads to the medium and low pressure part 32 of the steam turbine.

The steam flowing from the high pressure part 31 to the medium and low pressure part 32 of the steam turbine is thus heated in the finned tube heat exchanger 52 before it reaches the reheater heating surface 55 in the steam generator 30 and from there into the medium and low pressure part 32 of the steam turbine. This also increases the efficiency of the power plant shown in FIG. 7.

While the smoke gas turbine 46, which drives the air compressor 48, is operated at a constant speed, the speed of the electric motor 50 driving the air compressor 49 is reduced at part load of the power plant. As a result, the air mass flow delivered by the compressor 49 is reduced, and the air pressure upstream of the air compressor 48 is also lower. This means that the gas pressure in the steam generator 30 or in the shaft 3 of the steam generator according to Figures 1 to 6 also drops, so that the effective air and flue gas speeds in this shaft 3, which are decisive for the dust transport, the combustion process and the ash discharge through the discharge opening 19 are not proportional to the load.

8, in which the same parts have the same reference numerals as in FIGS. 1 to 6, shows a device for generating flue gas, which differs from the device designed as a steam generator according to FIG. 1 in that it does not have any inside the shaft 3 in front of the flue gas outlet connection 6 Has convection heating surfaces and no hanging heating surface coaxial to the shaft 3 in the middle of the shaft 3. The additional inlet opening 14 for fine-grained coal is also not between the baffle 17 and the combustion chamber 5, but between the baffle 17 made of steel or ceramic and the flue gas outlet 6 at approximately the same location as the air nozzles 15. The shaft wall 4 is made of sheet steel.

A smoke gas turbine 46, which drives a first air compressor 48 and an electric generator 47, is connected to the flue gas outlet connection 6 with the interposition of a dust separator 45. The first air compressor 48 is preceded by a second air compressor 49, which has an electric motor 50 with adjustable speed as the drive unit. The air compressors 48 and 49 in FIG. 8 are operated like the corresponding air compressors 48 and 49 in FIG. 7.

The smoke gas turbine 46 is followed by a steam generator 43 on the exhaust gas side, the steam of which can feed a steam turbine (not shown).

The baffle 17 in FIG. 8 can also be formed from tubes welded together and be a convection heating surface, so that the steam generated in the steam generator 43 can be passed through the tubes of the baffle 17 and overheated on the way to the steam turbine (not shown).

Claims (15)

1. A device for generating flue gas for driving a gas turbine, particularly a steam generator or steam superheater, with a closed hollow-cylindrical housing and an elongated stack located inside this housing, the stack wall of which forms an intermediate chamber to the housing and which has at one stack end a combustion chamber, a closing piece and an inlet opening for combustion air, opening into the combustion chamber, and a supply opening for fine-grained coal, and which has at the other stack end a flue-gas outlet pipe which is arranged, with an intermediate space, in an air inlet pipe of the hollow-cylindrical housing,
   characterised in that the supply opening (11) for fine-grained coal and the inlet opening (12) for combustion air form a pulverized coal burner,
   in that in order to produce a twisting motion in the combustion air the inlet opening (12) for combustion air opens tangentially into the combustion chamber (5) or contains guide vanes (16),
   in that an auxiliary inlet opening (13) for combustion air is provided which opens into the combustion chamber (5) in the stack (3),
   in that an auxiliary inlet opening (14) for fine-grained coal is provided in the stack wall (4) at a distance from the closing piece (10) and opening into the combustion chamber (5) in the stack (3),
   in that an air nozzle (15) is fixed in the stack wall at a distance from the auxiliary inlet opening (13) for combustion air, seen in the direction of flow of the flue gas, which opens tangentially into the stack (3) in the direction in which it produces a twist in the air supplied, which has the same direction of rotation as that of the combustion air supplied through the inlet opening (12) for the combustion air, which opens into the stack (3) in the direction of the end of the stack forming a bottom end,
   in that inside the stack (3), between the auxiliary inlet opening (13) for the combustion air and the air nozzle (15) there is arranged a guide plate (17) formed like a spiral, the direction of spiral of which is selected such that the flue gas obtains a twist with the same direction of rotation as the air supplied through the air nozzle (15),
   in that a gradation (18), formed by altering the cross-section of the stack (3), is located in the stack wall (4), between the guide plate (17) for the flue gas and the air nozzle (15) or between air nozzle (15) and flue gas outlet pipe (6), and that in the gradation (18) a discharge opening (18) is provided for ash.
2. A device according to claim 1,
   characterised in that the stack wall (4) is formed by pipes welded together in a gas-tight manner.
3. A device according to claim 1,
   characterised in that the closing piece (10) is composed of pipes welded together in a gas-tight manner.
4. A device according to claim 1,
   characterised in that the auxiliary inlet opening (13) for combustion air is provided at a distance from the closing piece (10).
5. A device according to claim 1,
   characterised in that the stack (3) contains a convection heating surface (8) at the end of the stack with the outlet pipe (6) for flue gas and that the supply opening (11) for fine-grained coal and the inlet opening (12) for combustion air for the coal-dust burner are located in front of the convection heating surface (8), when seen in the direction of flow of the flue gas.
6. A device according to claim 1,
   characterised in that the gradation (18) formed by altering the cross-section of the stack (3) is located between air nozzle (15) and convection heating surface (8).
7. A device according to claim 1,
   characterised in that a liquid pump (24) is allocated to the coal-dust burner to supply a pumpable mixture of water and fine-grained coal.
8. A device according to claim 1,
   characterised in that the cross-section of the combustion chamber (5) has the form of a circle or a regular polygon.
9. A device according to claim 4,
   characterised in that the auxiliary inlet opening (13) for combustion air opens tangentially into the combustion chamber (5) in the stack (3) in the direction in which it produces a twist in the combustion air supplied, which has the same direction of rotation as that of the combustion air supplied through the inlet opening (12) for the combustion air.
10. A device according to claim 4,
    characterised in that the auxiliary inlet opening (13) for combustion air opens radially into the combustion chamber (5) in the stack (3).
11. A device according to claim 4,
    characterised in that the cross-section of the combustion chamber (5) is enlarged in front of the auxiliary inlet opening (13) for the combustion air, seen in the direction of flow of the flue gas, starting from the stack end with the closing piece (10).
12. A device according to claim 1,
    characterised in that the guide plate (17) for flue gas is formed from pipes welded together and is a convection heating surface.
13. A device according to claim 1,
    characterised in that the same air compressor (48) is connected to the intermediate space (7) between the hollow-cylindrical housing (2) and the stack wall (4) as well as to the air nozzle (15) and that the inlet opening (12) for combustion air and/or the auxiliary inlet opening (13) for combustion air are connected to the intermediate space (7) or to the air compressor (48), according to supply requirements
14. A device according to claim 5,
    characterised in that a heating surface (20) composed of pipes welded together in a gas-tight manner is arranged in the middle of the stack (3) between the auxiliary inlet opening (13) for combustion air and the convection heating surface (8).
15. A device according to claim 13,
    characterised in that a further air compressor (49) is connected before the air compressor (48) which has a drive unit (50), the speed of which can be regulated.

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