DESCRIPTION OF THE DRAWINGS
In the following, the invention will be described in more detail with reference to the appended principle drawings, in which
FIG. 1 shows a fluidized bed boiler
FIG. 2 shows an embodiment according to the invention
FIG. 3 shows a horizontal cross-section of the embodiment according to FIG. 2 on level A-A, i.e. seen from above
FIG. 4 shows a vertical cross-section of the embodiment according to FIG. 2 on level B-B
FIG. 5 shows a cross-section of a bed ash cooler in a side view
FIG. 6 shows a vertical cross-section of the embodiment according to FIG. 5 on level C-C
FIG. 7 shows another embodiment
FIG. 8 shows a third embodiment
FIG. 9 shows an embodiment below the grate
FIG. 10 shows an application
For the sake of clarity, the figures only show the details necessary for understanding the invention. The structures and details that are not necessary for understanding the invention but are obvious for anyone skilled in the art have been omitted from the figures in order to emphasize the characteristics of the invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a circulating fluidized bed boiler of fluidized bed boilers in a reduced manner. A circulating fluidized bed boiler comprises, inter alia, a furnace 1 and a cyclone 2, as well as different furnaces 3 at different phases. The invention relates primarily to the furnace 1 of the fluidized bed boiler and to its immediate vicinity.
FIG. 2 shows in principle a part of a boiler. The boiler comprises at least a furnace 1 defined by walls 11, 12, 13, 14, a grate 15 and a roof 16. The grate 15 is shown in the figures in a simplified manner. Inter alia, the fluidizing means typically connected to the grate 15 are not shown in the figures. The boiler also comprises means connected to feeding fuel and air, which can be on one or more levels on one or more walls 11, 12, 13, 14. These means are not shown in the figures either. In addition, the boiler comprises at least a mainly vertical partition wall 17 located between the grate 15 and the roof 16. Especially in large furnaces 1 pipe-panel-structured partition walls 15 extending from the grate 15 to the roof 16 are often used. The partition wall 17 is advantageously pipe-structured, in which case it is possible to connect medium circulation, such as, for example fluid and/or steam circulation, to it.
In addition, FIG. 2 shows a bed ash cooler 18 located in the lower part of the furnace 1. At lease one 181 of the walls of the bed ash cooler 18 is formed of a partition wall 17. It is also possible to implement the two walls 181, 182 of the bed ash cooler of the partition wall 17. This can be implemented, for example, by bending every other pipe of the partition wall panel into a second wall 182 of the cooling chamber 18 and by using the pipes that remain straight as the first wall 181. It is also possible that the first wall 181 comprises a different number of pipes than the second wall 182. Therefore, it can be considered that the partition wall 17 is formed of a first and a second part of the pipes, of which the first part forms the first wall of the bed ash cooler chamber 18 and the second part of the pipes forms the second wall of the bed ash cooler chamber 18. Advantageously the roof 185 of the bed ash cooler is also formed of the partition wall 17.
The bed ash cooler 18 can be formed of the pipes of the partition wall 17 by bending and/or by using different auxiliary structures, such as, for example supply and/or collection headers. In supply and collection headers two or more pipes are connected to each other. In addition, the number of pipes producing medium flow to the supply and collection headers may differ from the number of pipes taking medium away from the headers. For example, more pipes may leave the header than are coming in. Thus, it is, for example, possible to use more pipes in the walls of the bed ash cooler 18 than in the upper part of the partition wall 17. In an embodiment the pipes of the walls of the bed ash cooler 18 are connected to a collection header.
FIG. 3 shows a horizontal cross-section of a boiler according to FIG. 2 on level A-A, i.e. seen from above. The end walls 183, 184 of the bed ash cooler 18, i.e. the third and fourth walls can be implemented in various ways. They can be, for example, made as separate parts. If the cross-section of the partition wall 17 from above is, for example, L- or C-shaped, it is possible to utilize the partition wall also in implementing end walls 183, 184.
FIG. 4, in turn, shows a vertical cross-section of the boiler according to FIG. 2 on level B-B. As can be seen from FIGS. 3 and 4, the bed ash cooler 18 inside the furnace 1 does not in an advantageous embodiment reach the side walls 13, 14 of the furnace. Thus, the bed ash cooler 18 does not form inner corners in the furnace 1 that are problematic from the point of view of mixing, and the bed ash cooler does not significantly prevent the movement of particles. From the point of view of mixing it is also advantageous to use a partition wall 17 that does not extend from the side wall 13, 14 of the furnace to another. Advantageously both sides of the partition wall 17 are separate from the side walls 13, 14 of the furnace 1.
In some cases one side 183, 184 of the bed ash cooler 18 may extend to the side wall 13, 14 of the furnace. This type of a structure advantageously enables access to the bed ash cooler 18 from the outside of the furnace 1.
The input of the ash to be removed to the cooler chamber 18 can advantageously be arranged from either side. In an embodiment the ash is fed from the combustion chamber 1 to the ash cooler 18 via an inlet opening in the upper part of the cooler. The ash proceeds through the ash cooler 18 while cooling and is directed out of the outlet opening. In an embodiment of the bed ash cooler 18 the cooler comprises at least two cells, which are connected to each other via an opening. The number and dimensioning of the cells and openings can affect the capacity of the bed ash cooler 18 and the cooling effect.
FIGS. 5 and 6 show the structure of a four-cell bed ash cooler 18 in principle. The number of cells can affect the air consumption of the bed ash cooler 18. With more cells it is possible to decrease air consumption in comparison to a solution with fewer cells in order to reach the same cooling effect. In the solution according to the invention fluidizing air is directed to the bed ash cooler 18, which air moves thermal energy from the ash to the other process. Advantageously air is directed via the bottom part of the bed ash cooler 18. The structures connected to air supply are not shown in the figures. The speed of the air flow fed to the bed ash cooler depends on the application. In an embodiment the air flow rate is around 0.5 to 2 m/s.
In the example shown in FIGS. 5 and 6 the walls of the first cell of the bed ash cooler 18 comprise piping of the partition wall 17, where the medium circulates. The inside of said cell is non-insulated or it is protected with a heat conductive refractory. The insides of the next cells are insulated from the piping of the partition wall with a suitable heat-insulating structure 186. With the insulations 186 of the cells the ash is prevented from heating in the bed ash cooler 18, because typically a high-pressure medium circulates in the pipes of the partition wall 17, the temperature of which medium is higher than the temperature of the ash cooled with the bed ash cooler.
The ash to be cooled is directed in the solution according to the example to the first cell via an opening 187 in the lower part of the cell wall. The ash moves from one cell to another via an opening 188 in the partition wall of cells. The opening 188 is advantageously located in the lower part of the partition wall and the openings of consecutive partition walls are advantageously collated in such a manner that they are located on opposite edges of the bed ash cooler 18. From the last cell the ash is removed via an outlet opening 189, which may be located on the bottom or on the wall of the cell. The location of the openings 188, 189 has been attempted to be illustrated in FIG. 6, which shows the cross-section of the bed ash cooler according to FIG. 5 on level C-C as seen from above. The openings 188 between the cells may also be located in a way that differs from that described above. In a solution ash is fed to two cells, which are located at different ends of the bed ash cooler. From these cells the ash is conveyed to the cell in the middle of the bed ash cooler, from which the ash is removed.
The cells of the bed ash cooler 18 may be located either adjacently or on different levels depending on the application. In addition, the bed ash cooler 18 may comprise different cleaning opening and/or cleaning means, with which, inter alia, the openings of the cells can be kept open during operation.
If necessary, it is possible to form a heat exchange surface in the bed ash cooler 18 by bringing steam pipes from below through the grate 15 or by bending cooling lines from the selected wall pipes of the cell, which lines return to the wall line.
In circulating fluidized bed boilers a narrowing of the bottom part is used in the furnace 1 in order to decrease the surface area of the grate 15. This improves mixing in the fluidized bed area and the circulation of particulates. In an embodiment of the invention a slanted structure like the back and front walls 11, 12 of the furnace 1 is formed of the lower part of the partition wall 17. The structure can be implemented, for example, in such a manner that for the first wall 181 every other pipe of the partition wall panel 17 is bent to the same angle as the pipes of the front and back walls 11, 12 and by using the straight pipes as another wall 182, as shown in FIG. 7. It is also possible that the first wall 181 and the second wall 182 comprise a different number of pipes. In another solution shown in FIG. 8 the pipes of the partition wall 17 are divided by bending or by means of a supply/collection header both ways in such a manner that by means of them it is possible to narrow the two grate sections.
The narrowing part formed in the lower part of the partition wall 17 is used advantageously as a bed ash cooler 18. It is also possible to use the narrowing part for other purposes. For example, the narrowing part can be used to bring in air, additional material or circulating gas. In some cases it is possible to bring fuel via the narrowing part.
The above-described structure inside the furnace 1 can be used in connection with different boiler structures, such as, for example, in connection with circulating and bubbling fluidized bed boilers. With a corresponding structure it is possible to manufacture, for example, a cell in the middle of the furnace 1 of a fluidized bed boiler for a cooling heat delivery surface or ash removal.
In an alternative structure the ash cooler chamber 18 is made below the grate 15, as shown in FIG. 9. Thus it is possible form the bottom, roof 185 and side walls 181, 182 (the first and second wall) of the ash cooler chamber 18 from the partition wall 17. The end walls 183, 184 (the third and fourth wall) of the ash cooler chambers 18 are, in turn, possible to form advantageously by using the wall pipes of the furnace 1. It is advantageous to leave space for primary air feeding between the grate 15 of the furnace 1 and the roof 185 of the ash cooler chamber 18.
The furnace 1 and the rest of the boiler may comprise other known structures irrespective of using the structure according to the invention. For example, in some applications there may be a need to place “pocket model” bed ash coolers in the walls 11, 12, 13, 14 of the furnace 1. Especially in large furnaces 1 it may be advantageous to use several bed ash coolers 18, a part of which may be located on the edges of the furnace and a part in the middle. The principle of this kind of a structure is shown in FIG. 10. The system may also comprise one or more bed ash coolers 18 located below the furnace 1.
By combining, in various ways, the modes and structures disclosed in connection with the different embodiments of the invention presented above, it is possible to produce various embodiments of the invention in accordance with the spirit of the invention. Therefore, the above-presented examples must not be interpreted as restrictive to the invention, but the embodiments of the invention may be freely varied within the scope of the inventive features presented in the claims hereinbelow.
Patent Application
20070266915
