FI114114B - Air supplying method for fluidized-bed boiler, involves supplying air flow from primary air jets and side air jets into furnace, where air flow supplied from primary air jets is stronger than that supplied from side air jets - Google Patents

Abstract

The method involves supplying air flow from primary air jets and from side air jets (17) into a furnace (2). The air flow supplied from the primary jets is stronger than the air flow supplied from the side air jets. The primary air jets are placed in a front wall (12) of the furnace. The side air jets are placed in side walls (14, 15) of the furnace. Independent claims are also included for the following: (a) an air arrangement for supplying upper air from an upper air supply level (b) a fluidized-bed boiler.

Description

114114 AIR FLIGHT SYSTEM FOR FLOOR FLOOR BOILER

The invention relates to a method according to the preamble of claim 1 for supplying upper air from upper air supply levels to a fluidized bed boiler. The invention further relates to an air system according to the preamble of the appended claim 4 and to a fluidized bed boiler according to the preamble of the accompanying claim 7.

Air is fed into the lower part of the furnace of the fluidized bed boiler through a grate into the fluidized bed formed by the fluidized bed material on top of the Ari-10 nan, thereby causing fluidization of the fluidized bed material. On the fluidized bed, fuel such as peat or bark is fed from the fuel channel. Approximately 40-70% of the air needed for fuel combustion is fed through a so-called grate. primary air. For maximum 15 combustion and low emissions, the boiler furnace is typically supplied with upper air from two upper air levels. A typical bed fluidized bed boiler has secondary air-level air nozzles above the fuel channel, above which are tertiary air-level air nozzles. In addition, the boiler typically has various burners 20 which serve as starter and support burners.

»« • · · · · · · · · · · · · · · · · · · · · · · · · · · · · Layer fluidized bed boilers typically supply to the top of the boiler furnace • upper air secondary and tertiary air planes so that 50-70% . By locating such secondary and tertiary air levels as far apart as possible, the NOx concentration of the flue gas from the boiler is preferably affected. For this reason, the tertiary air plane should be positioned as high as possible.

• # »30 In the known upper air systems of layered fluidized bed boilers, air is supplied *; · at the tertiary air level from the opposite sides or from one side of the boiler.

. ··. In practice, it has been found that the best way to bring the upper air is to place the air nozzles on both the front and rear walls. Hereby, the flow of flue gas * 'is easily obtained as desired, whereby the temperatures and flow rates in the furnace furnace 35 are optimal. Where the design of the boiler or power plant is such that it is not possible to provide air nozzles and ducts on the beaker side wall of the boiler, i.e. the 2 114114 rear wall, air is typically supplied from both side walls and in some cases only the front wall.

5 When supplying the upper air from the boiler side walls only, the flue gases hate upwards in either side of the furnace, so that the oxygen content of the flue gas varies, and the combustion process becomes poor.

10

When importing fuel from the front wall of the boiler, the combustion focuses on the front wall side. In this case, the proportion of carbon monoxide gases near the front wall of the boiler increases, while the oxygen content near the rear wall is higher. In order to provide sufficient air from the front wall to the rear of the furnace, very strong air jets must be used, resulting in unfavorable eddies in the furnace area. Such vortexes below the boiler nose reduce boiler efficiency.

The main object of the present invention is to provide an air-20 system which provides a uniform temperature distribution in a ·: fluidized bed boiler in which it is not possible to place air nozzles in the rear wall.

To accomplish this object, the method of the invention. '25 le is essentially characterized by what is set forth in the characterizing part of independent claim 1. The air arrangement according to the invention, in turn, is mainly characterized by what is disclosed in the characterizing part of independent claim 4. The layered fluidized bed boiler according to the invention, in turn, is mainly characterized by what is disclosed in the characterizing part of independent claim 7.

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Other dependent claims disclose some preferred embodiments of the invention.

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The basic idea of the invention is to supply air to the sandwich fluidized bed boiler from one or more upper air planes above the primary air plane in three directions. According to the invention, the main air flows are provided from the main air nozzles located on the opposite wall of the boiler nose, i.e. the front wall. The auxiliary air flows from the side walls are arranged so that the air flows supplied from the auxiliary air nozzles of the opposing walls are aligned. The main and auxiliary air flows are supplied at substantially the same level so that said main and auxiliary air flows are either at the same level or at slightly different levels.

10

The air system according to the invention enables the air to be supplied uniformly throughout the air supply plane, thereby enhancing the oxidation of the gases near the front wall. In addition, the airflow also moves the combustion process to the area near the rear wall below the beak, thereby improving the utilization of the boiler 15 volume.

Furthermore, in a boiler with an air system according to the invention, it is possible to use a lower upper air coefficient than conventional boilers in which the upper air is supplied solely from the side walls or front walls.

• ♦: · The air system according to the invention reduces the turbulence of the filamentous gases inside the boiler compared to a boiler in which the upper air is supplied only from the front wall, since smaller main air jets can be used in the system of the invention. In a preferred embodiment, the front wall is fed with main air jets 40-80% of the total plane air volume and the side walls with auxiliary jets a total of 20-60% of the total plane air volume.

30 By positioning the air nozzles on the front wall of the boiler in addition to the air nozzles on the side walls, the "flowing" of the rising flue gases to one side is prevented. Conventional solutions in which the air is introduced only from the air nozzles aligned or adjoining the boiler side walls typically have a "" spill "of the flue gases towards the other side wall whereby the oxygen content of the flue gases varies and the combustion process becomes poor.

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Furthermore, one advantage of a preferred embodiment of the invention is the reduction in corrosion and fouling of the superheaters, since the temperatures of the flue gases entering the superheater area are reduced.

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The invention will now be described in more detail with reference to the accompanying principal drawings, in which Figure 1 is a side elevation view of an air system 10 according to the invention, Figure 2 is a top view, Figure 3 is a top view of another air system according to the invention; the temperature distribution of the boiler, and 20 • | Fig. 5 shows the temperature distribution of the boiler with a conventional air supply system: *.

* »: ·. 25 For the sake of clarity, the drawings are merely such details as are necessary for an understanding of the invention. Unnecessary to the understanding of the invention, but obvious to one skilled in the art, single and single structures. details are omitted from the figures to emphasize features of the invention.

Fig. 1 schematically shows the fluidized bed boiler 1 and its furnace 2. From the air box 9 at the lower part of the fluidized bed boiler 1, primary air is supplied through the grate to the fluidized bed 4 formed by the fluidized bed material '' on top of the grate. On top of the fluidized bed 4, fuel is supplied from the fuel passage 5. Above the fuel passage 5 is a secondary air level 10, the individual air nozzles of which are not shown. Above the secundary air plane 10 is a tertiary air plane 11, whose individual air nozzles are also not shown in Figure 1. In addition, the fluidized bed boiler 1 typically has various burners which act as starter and 5 as burner burners. These burners are not illustrated.

The upper part of the furnace 2 of the fluidized bed boiler 1 has a beak 6 which is a structure projecting from the rear wall 13 of the furnace to the front wall 12. The cam 6 directs the flow of the flue gases to the superheaters 7 and further to the flue gas channel 10, but also 8. The cam 6 preferably acts as a shield for the superheaters 7, separating the superheaters from the direct contact with the flame.

Figure 1 shows that if, for example, the flue gas duct 8 is arranged to pass near the rear wall 13 of the fluidized bed boiler 1 and as low as possible, it is not possible to place the upper air plane 10,11 on the rear wall 13 of the boiler. Therefore, it is preferable to place the ventilation systems of the upper air planes 10,11 according to the invention, whereby the air nozzles 16,17 and the ducts are located on the three walls 12,14,15 of the furnace and the rear wall 13 20 remains intact.

* »·· Figure 2 is a top view of an air system according to the invention. This air system is suitable for use in the image *. 1 as a secondary and tertiary air plane 10,11,25, but the corresponding air supply solution can also be used at other levels, such as a quaternary air plane, while retaining the basic idea of the present invention.

Figure 2 shows that, from the main air nozzles located on the front wall 12, · * 30 16 the main air flows 18 are so strong that they ··. the flow preferably extends to the rear wall 13. In this case, the main air flows. 18 carry some of the flammable particles or combustible gases to the rear of the furnace 2, resulting in efficient utilization of the furnace volume. Preferably, the velocity of the main air stream 18 is 40-35 90 m / s and most preferably 50-60 m / s in a fluidized bed boiler 6 114114 1 having one side of the bottom of the furnace 2 of about 10 meters and 3-5 main nozzles.

From the auxiliary air nozzles 17, i.e. the side air nozzle 5, located in the side walls 14,15, the auxiliary air flows 19, i.e. the side air flows, which are significantly lower in intensity than the main air flows 18, are directed. From the opposite side walls 14,15, the auxiliary air flows 19 are directed so that the auxiliary air flows are facing each other. The intensity of the auxiliary air flow 19 supplied from the side wall 14,15 is equal to the intensity of the auxiliary air flow supplied from the opposite wall 10 in the opposite direction thereto. That is, according to the invention, the auxiliary air nozzles 17 of the opposite side walls 14,15 are mirror images of one another. In a preferred embodiment of the invention shown in Figure 3, the auxiliary air flows 19 are supplied such that their intensity varies from the front wall 12 of the sandwich boiler 1 to the rear wall 13.

In a preferred embodiment of the invention, during normal running of the fluidized bed boiler 1, 40-80% of the total amount of air brought in from the front wall 12 of the airplane 11 is provided, wherein 10-30% of the total amount of air brought from one level. It is advantageous from the point of view of use to arrange the main air flows 18 and; · the auxiliary air flows 19 separately adjustable. Thus, for example, the amount of auxiliary air flows 18 may be reduced first, and then the amount of main air flows 19 may be reduced.

'*. * 25% i. The main airflows 18 and the auxiliary airflows 19 are located at substantially the same level in the height direction of the boiler 1. In some cases, it may be advantageous to position the air nozzles 16,17 so that the main air flows; 18 and auxiliary air flows 19 are set at slightly different heights so that the air flows do not collide with each other. In another embodiment of the invention, main and / or auxiliary air flows 18,19 are provided. in the firebox 2 in a slightly oblique direction. Thus, in some embodiments, a better permeability to airflows 18.19 is obtained with flue gases than with perpendicularly supplied airflows.

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Figure 4 shows the temperature distribution of the bed fluidized bed boiler 1 shown in Figure 1 when the tertiary air supply level 11 of the boiler is implemented in accordance with the invention. Figure 5, in turn, shows a temperature cut-off for a conventional boiler in which the tertiary-5 air supply plane only supplies air from the air nozzles in the side walls. When comparing these results, it can be stated that the air supply system according to the invention makes better use of the furnace 2 of the entire boiler 1. Further, it is seen that the temperature of the furnace 2 below the superheater 7 is lower with the solution 10 according to the invention than with the conventional solution. For the sake of clarity, Figures 4 and 5 do not show the structures of the fluidized bed boiler 1, which are shown in Figure 1.

By combining the operating modes and structures presented in connection with the above various embodiments of the invention in different ways, various embodiments of the invention may be obtained which are in accordance with the spirit of the invention. Therefore, the foregoing examples are not to be construed as limiting the invention, but embodiments of the invention may freely vary within the scope of the inventive features set forth in the claims below.

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Claims (10)

114114 A method for supplying upper air from an upper air supply plane (10,11) to a sandwich fluidized bed boiler (1) comprising at least 5 - a furnace (2) bounded by a front wall (12), side walls (14,15) and a rear wall (13) ) a beak (6) provided on the rear wall (13), a fluidized bed (4) in the furnace (2), a lower air supply plane (9) arranged below the fluidized bed 10 (4), a fuel supply member (5) arranged above the fluidized bed (4) , one or more upper air supply planes (10,11) disposed above the fuel supply element (5) and below the cam 15 (6), and at least one air supply plane (10, 11) comprising at least one of the side walls (14,15) of the furnace (2) side air nozzles (17), characterized in that one or more air supply planes (10, 11), further comprising at least one or more main air nozzles (16) disposed in the front wall (12) of the furnace (2), institutional: ·; throw a stream of air (18) into the furnace which is stronger than the air stream (19) supplied from the side nozzle (17). Method according to claim 1, characterized in that 40-80% of the amount of air to be supplied from the upper air supply level (10, 11) is supplied from one or more main air nozzles (16) located in the front wall (12) of the furnace (2). A method according to claim 1 or 2, characterized in that the opposing side walls (14, 15) are supplied with mutually opposite air currents (19) and from the opposite side walls; . as much air is fed. 1 · 114114 An air arrangement for supplying upper air from the upper air supply plane (10, 11) to a fluidized bed boiler (1) comprising at least a furnace (2) bounded by a front wall (12), side walls (14,15) and rear wall (13) (13) an arranged nose (6), a fluidized bed (4) in the furnace (2), a lower air supply plane (9) arranged below the fluidized bed (4), a fuel supply member (5) arranged above the fluidized bed (4). , one or more upper air supply planes (10,11) disposed above the fuel supply element (5) and below the nose (6), and at least one air supply plane (10, 11) comprising at least fire side 15 (2) in the side walls (14,15). ) side air nozzles (17), characterized in that the air arrangement further comprises at least one or more main air nozzles (16) disposed on the front wall (12) of the furnace (2). An air arrangement according to claim 4, characterized in that the side air nozzle (17) disposed on the first side wall (14,15) is a side air nozzle located on the second side wall (14,15), and said side air nozzles are: at the same height and at the same distance from the front wall (12). • ·. 25 Air arrangement according to claim 4 or 5, characterized in that the main air nozzles (16) have their own air flow control system (18) and the side air nozzles (17) have their own air flow control system (19). * * A fluidized bed boiler (1),) comprising at least a ··· furnace (2) bounded by a front wall (12), side walls (14,15). and a rear wall (13), a fluidized bed (4) in the rear wall (13) of the furnace (2), a fluidized bed (4) in the '' furnace (2), a 35th air supply plane (9) arranged below the fluidized bed (4114). a fuel supply element (5) arranged above the fluidized bed (4), one or more upper air supply planes (10,11) disposed above the fuel supply element (5) and below the cam 5 (6), and at least one air supply plane (10); , 11) comprises at least side air nozzles (17) located in the sidewalls (14,15) of the furnace (2), characterized in that the air arrangement of the upper air supply plane (10, 11) further comprises at least one or more 10, the main air nozzle (16) having an air flow (18) formed by the main air nozzle which is stronger than the air flow (19) formed by the side nozzle (17). Layer fluidized bed boiler according to claim 7, characterized in that said air arrangement of the upper air supply plane (10, 11) is located on the secondary air supply plane or the tertiary air supply plane. A fluidized bed boiler according to claim 7 or 8, characterized in that the main air nozzles (16) are located on the same wall (12) as the fuel supply means (5). A fluidized bed boiler according to any one of the preceding claims 7 to 9, characterized in that, at said upper air supply plane (10, 11), there is a flue duct (8) behind the rear wall (13). * »* · Mil • * * • t • · •» • »114114