WO1998011337A1

WO1998011337A1 - A combustion plant and a separating device

Info

Publication number: WO1998011337A1
Application number: PCT/SE1997/001516
Authority: WO
Inventors: Roine Brännström; Anders Lövgren
Original assignee: Asea Brown Boveri Ab
Priority date: 1996-09-11
Filing date: 1997-09-09
Publication date: 1998-03-19
Also published as: SE509381C2; SE9603308D0; CN1176364A; SE9603308L

Abstract

A combustion plant comprises a combustion chamber (1) in which combustion of a fuel is intended to be performed while producing combustion gases, and a purifying equipment for purifying said combustion gases with respect to dust particles. Via a conduit member a flow of combustion gases is conducted from the combustion chamber via the purifying equipment to a gas turbine for extracting energy therefrom. A separating device (11) is provided between the conduit device and the gas turbine and arranged to permit separation of objects, including welding wires, screws, nuts, sheet pieces, from the flow of combustion gas and prevent these particles from getting into the gas turbine (18). The separating device (11) comprises an inlet channel (30) for the combustion gases, a capturing member (32) which is arranged to capture said object, and an outlet member (31) for the combustion gases. The inlet channel (30) comprises a main inlet direction (30') which extends towards said capturing member (32, 32a, 51).

Description

A combustion plant and a separating devxce

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to a combustion plant comprising a combustion chamber m which a combustion of a fuel is intended to be performed while producing combustion gases, a purifying equipment which is arranged to purify said combustion gases with respect to dust particles, and a conduit member which is arranged to conduct a flow of said combustion gases from the combustion chamber via the purifying equipment to a gas turbine for extracting energy therefrom. The invention also relates to a separating device arranged to permit separation of objects, including welding wires, screws, nuts, sheet pieces, from a flow of combustion gases and preventing these objects from reaching a gas turbine .

The invention will now be discussed and enlightened in different applications in connection to a pressurized, fluidized bed, a so called PFBC-power plant (pressurized flu dized bed combustion) . However, the invention is not restricted to such applications, but can be employed in all possible power plants, for example in connection to different types of gas turbine plants.

It is known to combust different fuels in a bed of particulate non-combustible material which is supplied with combustion air from below through nozzles in such a way that the bed becomes fluidized. The combustion gases formed at the combustion process pass a freeboard above the bed, whereafter they are purified and brought to a gas turbine. The combustion gases drive the gas turbine which in its turn drives an electric generator on one hand and a compressor that supplies the pressure vessel with the compressed air on the other hand. In the bed the fuel is combusted at a temperature in the order of 850 °C. The purification of combustion gases usually takes place by means of cyclone separators. Said separators have a relatively high efficiency and the combustion gases that leave the cyclone separator may, principally, be supplied to the gas turbine without causing damages thereon. However, to obtain a higher purity degree of the combustion gases leaving the plant, it is known to arrange a high temperature filter downstream of the cyclone separators. As such a filter has to stand high temperatures, it has to be made of a temperature resistant material. A suitable such material is ceramics. However, ceramics is a very hard and brittle material that does not stand particularly large mechanical tensions. This fact leads to that such filters often crack or fail, for example due to the tensions formed as a result of significant temperature variations. The ceramic, active filter parts are namely supported in metallic support structures, and as the metal expands substantially at high temperatures, more or less unavoidable tensions are formed in the ceramic filter material. This results in a significant risk of objects, that may be relatively large, getting broken away from the filter and following the combustion gases into the gas turbine. Thereby, very significant damages may be formed on vital parts in the gas turbine. The repairs of the gas turbine are very costly due to the expensive components on one hand, and due to the plant standing still during the repair period on the other hand.

Attempts have been made to arrange a separating device in the shape of a laying T of the conduit member upstream of the gas turbine to solve said problems. Thereby, the combustion gases are conducted through one of the parts of the top of the T and out through its leg. The separated material is collected in the second part of the top of the T. Although this device presents a low fall of temperature and pressure it has the disadvantage that collected objects may be sucked up and into the gas turbine when the plant is stopped and the pressure rapidly decreases . Accordingly, it does not operate satisfactorily.

SUMMARY OF THE INVENTION

The object of the present invention is to remedy the above problem. More precisely, there is a strive for a device by which objects possibly existing in a combustion gas flow can be separated in a reliable way before the flow is introduced into a gas turbine or some similar sensitive device. Furthermore, it is striven for that the separating device should give rise to a very small fall of pressure and temperature in order not to deteriorate the total efficiency of the plant.

This object is obtained by means of the combustion plant initially defined, which is characterized m that the separating device is provided between the purifying equipment and the gas turbine and arranged to permit separation of objects, including welding wires, screws, nuts, sheet pieces, from the flow of combustion gases and prevent these objects from reaching the gas turbine, that the separating device comprises an inlet channel for the combustion gases, a capturing member which is arranged to capture said objects transported by the combustion gases, and an outlet channel for the combustion gases, and that the inlet channel comprises an inlet direction which extends towards said capturing member. With such a separating device between the purifying equipment and the gas turbine the operational security of the combustion plant may be substantially improved. The separating device makes sure that possible objects that originate from the purifying equipment or that are constituted by other objects that normally should not be present in the conduit system of the plant, such as for example welding wires, screws, nuts or sheet pieces, and that by mistake have gone into the conduit members for the combustion gases, are effectively stopped before the inlet of the gas turbine. The objects that are required to be separated by means of the inventive separating device and that can cause damage in the gas turbine are relatively large and will get a significant kinetic energy through the flow of combustion gases . Therefore they will continue in rectilinear movement also if the combustion gas flow turns off or is redirected from such a rectilinear movement. Advantageously, the capturing member may comprise a funnel-like member that tapers in the inlet direction.

According to another embodiment of the invention the outlet channel is extending in an outlet direction that forms an angle with said inlet direction, such that the flow of combustion gases is redirected at least once. By such a relatively small redirection of the combustion gas flow a very small fall of pressure by the inventive separating device is obtained. Thereby, said angle may be between approximately 45° and 180°.

According to another embodiment of the invention, the capturing member comprises a tempering member which is arranged to give a suitable temperature to the captured objects that are to be discharged. Thereby, the captured objects can be kept at such a temperature that no moisture precipitation with subsequent corrosion problems takes place in the capturing member, on one hand, and that objects captured can be given such a temperature that, by means of conventional aids, they can be discharged from the separating device in a simple way. Thereby, the tempering member may comprise a tube loop which is arranged to conduct a medium with a temperature of approximately 110-250 °C, preferably 150-200^CC. Furthermore, the capturing member may be delimited by a wall, the tempering member possibly extending m at least a part of said wall.

According to another embodiment of the invention, the capturing member is connected to means which are arranged to discharge the objects captured during the operation of the plant. By such means that are arranged to discharge the objects captured during the operation of the plant, the risk for such captured objects being sucked into the gas turbine, for example at a rapid change of pressure that may occur when the plant is shut down in emergency, is diminished. Moreover, said discharging means may comprise a discharge passage arranged immediately downstream of the capturing member and comprising control means for controlling the discharge of said object. Said control means may comprise a valve member arranged downstream of the capturing member, a collecting tank arranged downstream of the valve member, and a valve member arranged downstream of the collecting tank. By means of these control means arranged m the discharge passage the object captured may be intermittently discharged from the separating device during the operation of the plant, even though there is a substantial overpressure in the conduit member and the separating device.

According to another embodiment of the invention the purifying device comprises a ceramic filter. Thereby, the separating device will prevent possible ceramic parts from reaching the gas turbine in an efficient manner.

According to another embodiment, the separating device is arranged in such a way that the inlet direction of the inlet channel extends generally vertically. In that way not only the kinetic energy of the object is taken advantage of, but also the gravitation, in order to guide the object towards the capturing member. The object defined above is also obtained by the separating device initially defined, and comprising an inlet channel for the combustion gases, a capturing member, which is arranged to capture said objects transported by the combustion gases, and an outlet channel for the combustion gases, the capturing member being connected to means which are arranged to discharge the object captured, the inlet channel comprising an inlet direction which extends towards said capturing member.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described more in detail by means of different embodiments indicated by way of example and with reference to the annexed drawing figures.

Fig 1 schematically shows a PFBC-power plant with a separating device according to the invention.

Fig 2 shows a sectional view of a separating device according to a first embodiment of the invention.

Fig 3 shows a cross-section along the line III-III in Fig 2.

Fig 4 shows a sectional view of a separating device according to a second embodiment of the invention.

Fig 5 shows a sectional view of a separating device according to a third embodiment of the invention.

Fig 6 shows a sectional view of a separating device according to a fourth embodiment of the invention.

Fig 7 shows a sectional view of a part of the embodiment shown in Fig 6 according to an alternative embodiment. Fig 8 shows a sectional view of a separating device according to a fifth embodiment of the invention.

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS

The invention will now be explained with reference to a so called PFBC-power plant. However, it should be noted that the invention is applicable also to other types of plants. Such a PFBC-plant, that is a plant for the combustion of a particulate fuel m a pressurized, fluidized bed, is schematically shown in Fig 1. The plant comprises a combustion chamber 1 which is housed in a pressure vessel 2, which may have a volume in the order of 10⁴ m³ and which may be pressurized up to between 7 and 30 bar (abs), for example. Compressed gas containing oxygen, air in the example shown, is supplied to the pressure vessel 2 at 3 for pressurizing the combustion chamber 1 and for fluidizmg a bed 4 m the combustion chamber 1. The compressed air is supplied to the combustion chamber via schematically indicated fluidizmg nozzles 5 that are arranged at the bottom of the combustion chamber 1 for fluidizmg the bed 4 enclosed in the combustion chamber 1. The air is supplied in such a way that a fluidizmg velocity of approximately 0,5- 2,0 m/s is obtained. The bed 4 is of a bubbling type and has a height of approximately 2-6 m. The bed 4 comprises a non- combustible particulate bed material, a particulate absorbent and a particulate fuel. The particle size of the bed material, the absorbent and the fuel is between approximately 0,5 and 7 mm. The bed material comprises for example ash and/or sand and the absorbent comprises a calcareous material, for example dolomite or limestone for the absorption of the sulphur and possibly other unwanted agents that are released during the combustion. The fuel is supplied m such an amount that it constitutes approximately 1% of the bed. Fuel is referred to as all fuels that can burn, such as for example of pit coal, brown coal, coke, peat, biofuel, oil shale, petroleum coke, waste, oils, hydrogen gas and other gases, etc. The bed material, the absorbent and the fuel are supplied to the bed 4 via a schematically shown conduit 6. The fuel is combusted m the fluidizmg air supplied to the bed 4, while forming combustion gases. These gases are collected in a space 7, a so called freeboard, above the bed 4 and are then conducted via conduit member 8 to a purifying equipment comprising different purification stages that, in the example shown, are constituted by, in that order, a schematically shown cyclone stage 9 with one or more cyclones, a high temperature filter 10, and a schematically shown separating device 11 which will be described more m detail later. The high temperature filter 10 is of a ceramic type and may comprise a large amount of porous ceramic tubes through the walls of which the combustion gases pass. Between the high temperature filter 10 and the separating device 11 there is also an intercept valve 12 in order to make a fast shut off of the plant possible. From the separating device 11 the combustion gases are conducted to a topping combustion chamber 13 which is also supplied with a combustible gas via a conduit 14 from a gasifying reactor 15 of a known type via another high temperature filter 16. In the topping combustion chamber 13 the combustible gases are combusted together with compressed air from the high pressure compressor 17 by means of a burner, not shown, and are mixed with the combustion gases from the combustion chamber 1 in order to increase the temperature thereof, so that the gases leaving the topping combustion chamber 13 have a temperature of approximately 1200-1500 °C which makes them well suited as a driving gas for driving a first gas turbine 18 the form of a high pressure turbine. The high pressure turbine 18 and the high pressure compressor 17 are arranged at the same shaft as a generator 19 from which useful electric energy may be extracted. The high pressure compressor 17 also delivers compressed air to the combustion chamber 1 via the conduit 20. Thereby, an intercept valve 21 is arranged between the high pressure compressor and the combustion chamber 1. The high pressure compressor 17 also delivers air via the conduit 22 for the gasification in the gasifying reactor 15. The rest fuel formed in the gasifying reactor 15 during the production of the combustible gas may be supplied to the bed 4 via a fuel conduit 23. The combustion gases expanded m the high pressure turbine 18 are conducted to the low pressure turbine 24. The combustion gases leaving the low pressure turbine 24 still contain energy that can be taken advantage of in an economizer 25. The low pressure turbine 24 is arranged on the same shaft as the low pressure compressor 26 which is supplied with air from the atmosphere via a filter 27. The low pressure compressor 26 is thus driven by the low pressure turbine 24 and from its outlet it supplies the high pressure compressor 17 with air that has been compressed in a first stage. Between the low pressure compressor 26 and the high pressure compressor 17 an mtercooler 28 is arranged to lower the temperature of the air which is supplied to the inlet of the high pressure compressor 17. Furthermore, the power plant presents a steam turbine side which is not shown here but indicated through an arrangement in the shape of a set of tubes 29 which is submerged into the fluidized bed 4 and in which water is circulated, evaporated and superheated through heat exchange between the tubes and the bed material m order to absorb the heat that is produced during the combustion taking place in the bed 4.

Due to the high temperature of the combustion gases, the high temperature filter m particular is subjected to significant stresses. The temperature variations lead to an expansion and contraction, respectively, of the metal support structure of the high temperature filter 10, resulting in significant mechanical tensions in the relatively fragile ceramic filter material, resulting in crack formation and tear-off of ceramic filter parts. This means that objects n the shape of ceramic parts that may be more or less significant will follow the flow of combustion gases through the conduit member 8. It shall be noted that the combustion gases may have a flow velocity in the order of approximately 40-50 m/s. In order to prevent these objects from being conducted into the high pressure turbine 18 and destroying the same, the combustion gases are conducted through the separating device 11. It shall be noted that also other objects will be stopped by the separating device 11. For instance, it may refer to objects that are forgotten in the interior of the plant during a repair, released sheet pieces, welding wires, screws, nuts, tools etc. The separating device 11 will now be described more in detail with reference to Fig 2-8.

Fig 2 shows a separating device 11 according to a first embodiment. The separating device 11 comprises an inlet channel 30 that constitutes a part of the conduit member 8 and an outlet channel 31 which also constitutes a part of the conduit member 8. Furthermore, the separating device 11 comprises a capturing member in the shape of container 32 which tapers downwards. The container 32 has a centre axis x that extends generally vertically. The inlet channel 30 comprises an inlet direction 30' which also extends vertically towards the container 32. The outlet channel 31 has an outlet direction 31' which also extends vertically out from the container 32. The incoming flow of combustion gases will thus be redirected only once generally by 180° in the container 32. Thereby, possible objects existing in the combustion gas flow will continue their course straight downwards due to their weight and get captured by the container 32. The container 32 comprises a lower part 33 which has a funnel-like shape that narrows in the direction of the centre axis x, at least as to the inner delimiting surface of the lower part 33. In the lower part 33 the object and the possible other material captured may be gathered. Thereby, the funnel-like lower part 33 is provided with a wall which a tempering member n the shape of a tube loop 34 extends. In the tube loop 34 a medium is flowing, for example a liquid, such as an oil or the like, which has a temperature of approximately 110-250 °C, preferably 150-200 °C, and which thus will cool the hot objects that are captured by the container 32 on one hand, and see to it that these objects, when they have been gathered, maintain said temperature on the other hand, and in that way it is made sure that no moisture is precipitated the container 32. The upper part 35 of the container has a wall with a heat insulation 36. Furthermore, the separating device 11 is provided with means arranged to discharge the objects captured during the operation of the plant. This discharging means comprise a schematically shown discharge conduit 37 which is provided with a first shut-off valve 38, a collecting tank 39 and a second shut-off valve 40. Moreover, the collecting tank 39 is, via a conduit 41, connected to the atmosphere for de-air g and pressure decrease of the tank 39. Thereby, the conduit 41 comprises a shut-off valve 42 and a throttling 43. During discharge of objects from the container 32 the valves 40 and 42 are closed, whereafter the valve 38 is opened. Thereby, the tank 39 will be pressurized, and objects and possible other material gathered in the container 32 will flow down m said container. When the container 32 is emptied the valve 38 is closed and the valve 42 is opened, the pressure in the tank 39 being lowered to atmospheric pressure. Thereafter, the valve 40 is opened and the objects are discharged from the collecting tank 39 and taken away.

In the first embodiment, shown m Fig 2, the inlet channel

30 and the outlet channel 31 are connected to each other via a tube bend 44. The tube bend is, as shown in the sectional view in Fig 3, open downwards in such a way that heavy objects will continue straight ahead in the mlet direction 30' without any difficulties, whereas the gas flow is redirected once, about 90°.

In Fig 4 a second embodiment of the invention is shown. It should be noted that elements with corresponding function have been given the same reference numerals m all embodiments of the invention described. The second embodiment differs from the first embodiment in Fig 2 mainly because the outlet channel 31 extends in an outlet direction 31' which is generally perpendicular to the let direction 30' and to the vertical centre axis x of the separating device 11. Accordingly, only a generally perpendicular redirection of the flow takes place, resulting in minimum pressure decrease losses and temperature losses. This also results the possibility of making the capturing member or container 32 somewhat narrower than accordance with the first embodiment. The lower part 33 of the container 32 comprises a funnel-like section 33a that narrows conically and a tempering member 34 that extends the wall of the container 32. The discharging means are constructed as in the first embodiment.

In Fig 5 a third embodiment of the invention is shown, reminding of the second embodiment but where the mlet channel 30 extends into the container 32 and thus results in the flow being redirected slightly more than 90° obliquely upwards and, thereafter, again slightly downwards out through the outlet channel 31 which forms an angle of 90° with the vertical centre axis x of the separating device 11. In th s case, the tempering member 34 is only arranged in a cylindrical part 33b that extends from the point of the funnel-like part 33a.

Fig 6 shows a fourth embodiment of the invention. According to this embodiment, the mlet channel 30 extends m an mlet direction 30' generally vertically along the centre axis x of the separating device 11 while the outlet channel 31' extends m an outlet direction 31' generally perpendicularly to said axis x. In this example, the container 32 is provided with an inner container 32a, which constitutes the very capturing member. The inner container 32 comprises an upper funnel-like part 45 which is slightly conical, a central part 46 which is generally cylindrical, and a lower funnel-like part 47 which is conical. Between the upper part 45 and the cylindrical part 46 there is a surrounding opening 48 with a conical funnel-like flange 49 in which the upper part 45 is partially introduced so that a surrounding opening 48 is formed between the flange 49 and the upper part 45. The combustion gas flow which is introduced to the mlet channel 30 m the vertical mlet direction 30' will thus turn around by almost 180° out through the opening 48 and will thereafter once again turn downwards by almost 180° and continue to flow down through the container 32 and be redirected by approximately 90° out through the outlet channel 31. Particles present in the combustion gas flow will continue straight ahead through the capturing member 32a and down into a lower cylindrical part 50 of the container 32. The wall of the cylindrical part 50 is provided with a tempering loop 34 in the same way as the tempering member 34 in the third embodiment shown m Fig 5. Also in this fourth embodiment the upper part of the container 32 is provided with an insulation 36. The discharge of the captured material takes place in the same way as in the other embodiments . Even though, according to this fourth embodiment, the flow is forced to a relatively complicated path, this embodiment has the advantage that the separating device 11 can be made very compact. As can be seen in the sectional view in Fig 7 several subsequent surrounding openings 48a, 48b may be arranged according to an alternative embodiment. Fig 8 shows a fifth embodiment of the invention, by which the inlet direction 30' of the inlet channel 30 is in alignment with the outlet direction 31' of the outlet channel 31. The capturing member comprises a slightly conical, funnel-like capturing member 51 which is introduced in the container 32 which is formed by an expansion of a channel portion that connects the inlet channel 30 to the outlet channel 31. The capturing member 51 comprises a lower part 52 which extends out of the wall of the container 32. The container 32 is provided with an insulation 36, and the lower part of the capturing member 51 comprises a tempering member 34 which extends into the wall of the lower part 52. Downstream of the lower part 52 there are discharging means that are constructed in the same way as m the other embodiments.

The invention is not delimited to the embodiments shown, but can be varied and modified within the frame of the following patent claims .

Claims

1. A combustion plant comprising

- a pressurized combustion chamber (1) m which a combustion of a fuel is intended to be performed while producing combustion gases,

- a purifying equipment (9, 10) which is arranged to purify said combustion gases with respect to dust particles, and

- a conduit member (8) which is arranged to conduct a flow of said combustion gases from the combustion chamber (1) via the purifying equipment to a gas turbine (18) for extracting energy therefrom, characterized in that a separating device (11) is provided between the purifying equipment (9, 10) and the gas turbine (18) and arranged to permit separation of objects, including welding wires, screws, nuts, sheet pieces, from the flow of combustion gases and thus prevent such objects from reaching the gas turbine, that the separating device comprises an mlet channel (30) for the combustion gases, a capturing member (32, 32a, 51) which is arranged to capture said objects transported by the combustion gases, and an outlet channel (31) for the combustion gases, and that the inlet channel (30) comprises a mam mlet direction (30' ) which extends towards said capturing member (32, 32a, 51) .

2. A combustion plant according to claim 1, characterized in that the capturing member (32, 32a, 51) comprises a funnel-like member (33, 33a, 45, 47, 51) that tapers in the mlet direction.

3. A combustion plant according to any one of the preceding claims, characterized n that the outlet channel (31) extends in an outlet direction (31') which forms an angle with said mlet direction (30' ) such that the flow of combustion gases is redirected at least once.

4. A combustion plant according to claim 3, characterized in that said angle is between approximately 45° and 180°.

5. A combustion plant according to any one of the preceding claims, characterized in that the capturing member (32, 32a,

51) comprises a tempering member (34) which is arranged to give a suitable temperature to the captured objects to be discharged.

6. A combustion plant according to claim 5, characterized m that the tempering member (34) comprises a tube loop which is arranged to conduct a medium with a temperature of approximately 110-250°C, preferably 150-200°C.

7. A combustion plant according to any one of claims 5 and

6. characterized m that the capturing member (32, 32a, 51) is delimited by a wall and that the tempering member (34) extends in at least a part of said wall.

8. A combustion plant according to any of the preceding claims, characterized n that the capturing member (32, 32a, 51) is connected to means (37, 39) which are arranged to discharge the captured objects during the operation of the plant.

9. A combustion plant according to claim 8, characterized in that said discharging means comprise an discharge passage (37) arranged immediately downstream of the capturing member and comprising control means (38, 40, 42) for controlling the discharge of said object.

10. A combustion plant according to claim 9, characterized in that said control means comprise a valve member (38) arranged downstream of the capturing member, a collecting tank (39) arranged downstream of the valve member (38), and a valve member (42) arranged downstream of the collecting tank (39) .

11. A combustion plant according to any one of the preceding claims, characterized m that the combustion chamber (1) is enclosed m a pressure vessel (2) and is constructed to enclose a pressurized, fluidized bed (4) and that the purifying equipment (9, 10) comprises at least one cyclone separator (9) arranged in the pressure vessel.

12. A combustion plant according to any one of the preceding claims, characterized in that the purifying equipment (9, 10) comprises a ceramic filter (10) .

13. A combustion plant according to any one of the preceding claims, characterized that the separating device (11) is arranged such that the mlet direction (30' ) of the mlet channel (30) extends generally vertically.

14. A separating device (11) arranged to permit separation objects, including welding wires, screws, nuts, sheet pieces, from a flow of combustion gases, and prevent these objects from reaching a gas turbine (18), comprising an inlet channel (30) for the combustion gases, a capturing member (32, 32a, 51) which is arranged to capture said objects transported by the combustion gases, and an outlet channel (31) for the combustion gases, the capturing member being connected to means (37, 39) which are arranged to discharge the captured objects, the mlet channel (30) comprising an mlet direction (30' ) which extends towards said capturing members (32, 32a, 51) .

15. A separating device according to claim 14, characterized n that the capturing member (32, 32a, 51) comprises a funnel-like member (33, 33a, 45, 47, 51) that tapers in the let direction (30' ) .

16. A separating device according to any one of claims 14 and 15, characterized in that the outlet channel (31) extends in an outlet direction (31' ) which forms an angle with said inlet direction (30' ) such that the flow of combustion gases is redirected at least once.

17. A separating device according to claim 16, characterized in that said angle is between approximately 45° and 180°.