GB2064076A

GB2064076A - Water tube boilers

Info

Publication number: GB2064076A
Application number: GB7939935A
Authority: GB
Original assignee: Vosper Thornycroft UK Ltd
Current assignee: Vosper Thornycroft UK Ltd
Priority date: 1979-11-19
Filing date: 1979-11-19
Publication date: 1981-06-10
Also published as: GB2064076B

Abstract

The invention relates to water tube boilers of the three drum A-type or two drum D-type in which a fluidised bed grate is cooled by the tubes (14) of the boiler. In Figure 1, which is part or an A-type boiler, tubes extend from the drum on one side to the tangent wall (26) on the opposite side, cooling the grate in the process. The tubes may either be welded to a continuous plate (16) or individual membrane walls may be used to seal between each pair of adjacent tubes. <IMAGE>

Description

SPECIFICATION Water tube boilers This invention relates to water tube boilers, either three drum A type or two drum D type, designed specifically for burning solid fuel using the fluidized bed combustion process as described, for example, in co-pending patent application No. 7933621.

It will be seen in the latter specification that the three drum A type boiler has been designed with an open area between the bottom drums so as to allow a purpose-designed, but entirely separate, fluidized bed grate to be positioned at the appropriate height between the bottom drums so as to allow the fluidized combustion process when activated to immerse the boiler syphon tubes properly to obtain the desired heat transfer rates.

There are numerous advantages in having a separate fluidized bed grate, some of the most important being the ability to modify the grate details to suit varieties of solid fuels without disturbing the boiler pressure parts, and ease of inspection and maintenance of both the grate and boiler pressure parts when the separate grate is withdrawn from the boiler.

However, when burning certain solid fuels at high combustion intensities there exists the possibility that a separate bed, as described above, may be subject to temperature which would be harmful to the metal fabric of the grate or necessitate the use of expensive heat resisting steels despite the cooling effect of the combustion air passing through the grate. It may in addition be necessary to use combustion air containing a high degree of pre-heat for certain types of fuel.

For the above reason, the present invention provides a fluid bed grate which is water-cooled and provides in particular a fluidized bed grate which forms an integral part of a three drum A type water tube boiler, or a two drum D type water tube boiler, and as such has an inbuilt watercooled feature.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partial vertical section through a water tube boiler of the invention, Figure 2 is a schematic plan view looking down on the upper surface of the grate, Figure 3 is a schematic partial perspective view showing the grate welded to cooling tubes, Figure 4 is a view similar to Figure 3 of a variant of the construction of the grate, and Figure 5 is a schematic view showing a modification of the configuration shown in Figure 1.

Figures 1, 2 and 3 show a part of a three drum A type boiler 10 which contains a water-cooled fluidized bed grate 12 which is an integral part of the boiler pressure parts and is water-cooled by the natural circulation of the water through the boiler.

The fluid bed grate 12 is composed of a combination of boiler tubes 14 and steel plates 1 6 to seal fully the area between the bottom drums 18, 20. Air supply for combustion and for fluidization is provided by a plenum 22 below the sealed boiler bottom and is passed into the combustion zone above the sealed boiler bottom by a number of apertures of stand pipes 24 located in the sealing plate 1 6 and between the cooling tubes 14.The cooling tubes 14 to which the steel sealing plate 1 6 is attached are provided by bringing every other tube from the primary furnace zone tangent wall 26 across to the opposite bottom drum 1 8, 20. Thus, the first half of each tube crossing the boiler bottom provides direct cooling of the sealing plate 16 and the second half of each tube, being unattached to the plate 16, acts as a thermic syphon tube to accelerate the flow of cool water from the bottom drum 18,20.

An alternative construction to the sealing plate welded to the bottom of each first half of the floor tubes is shown in Figure 4. Here a membrane wall 30 is welded between the tubes 14' to provide the fluidized grate bottom. Although not shown, air distribution stand pipes are inserted through the membrane plates between the tubes to provide air for combustion and fluidization.

An alternative construction to that shown in Figure 1 is illustrated in Figure 5. Here large bore linking tubes 40 are connected directly between the two bottom drums 1 8', 20' and the layout of the thermic syphons 14" is such as to induce flow along the linking tubes. Once again in this embodiment, the linking bores 40 may either be attached to a steel plate in a manner analogous to Figure 3 or be interconnected by membrane walls in a manner analogous to Figure 4 to provide the fluid bed grate. Stand pipes are once again provided in this embodiment for the introduction of air for combustion and fluidization.

1. A water tube boiler for burning solid fuel using the fluidised bed combustion process wherein the fluidised bed is supported by a grate which is water cooled by the tubes of the boiler and forms an integral part of the boiler.

2. A water tube boiler as claimed in claim 1, wherein the boiler tubes are welded to a plate serving to support the fluidised bed, apertures being provided in the said plate for the introduction of air for fluidisation.

3. A water tube boiler as claimed in claim 1 or claim 2, having a three drum A-type configuration, wherein pipes extend between and connect the two lower drums so as to water cool and form part of the grate.

4. A water tube boiler as claimed in claim 1 or claim 2, comprising three drums in an A-type configuration, wherein water tubes connected to the drum on one side of the furnace extend across the grate to cool the grate and are subsequently

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Water tube boilers This invention relates to water tube boilers, either three drum A type or two drum D type, designed specifically for burning solid fuel using the fluidized bed combustion process as described, for example, in co-pending patent application No. 7933621. It will be seen in the latter specification that the three drum A type boiler has been designed with an open area between the bottom drums so as to allow a purpose-designed, but entirely separate, fluidized bed grate to be positioned at the appropriate height between the bottom drums so as to allow the fluidized combustion process when activated to immerse the boiler syphon tubes properly to obtain the desired heat transfer rates. There are numerous advantages in having a separate fluidized bed grate, some of the most important being the ability to modify the grate details to suit varieties of solid fuels without disturbing the boiler pressure parts, and ease of inspection and maintenance of both the grate and boiler pressure parts when the separate grate is withdrawn from the boiler. However, when burning certain solid fuels at high combustion intensities there exists the possibility that a separate bed, as described above, may be subject to temperature which would be harmful to the metal fabric of the grate or necessitate the use of expensive heat resisting steels despite the cooling effect of the combustion air passing through the grate. It may in addition be necessary to use combustion air containing a high degree of pre-heat for certain types of fuel. For the above reason, the present invention provides a fluid bed grate which is water-cooled and provides in particular a fluidized bed grate which forms an integral part of a three drum A type water tube boiler, or a two drum D type water tube boiler, and as such has an inbuilt watercooled feature. The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partial vertical section through a water tube boiler of the invention, Figure 2 is a schematic plan view looking down on the upper surface of the grate, Figure 3 is a schematic partial perspective view showing the grate welded to cooling tubes, Figure 4 is a view similar to Figure 3 of a variant of the construction of the grate, and Figure 5 is a schematic view showing a modification of the configuration shown in Figure 1. Figures 1, 2 and 3 show a part of a three drum A type boiler 10 which contains a water-cooled fluidized bed grate 12 which is an integral part of the boiler pressure parts and is water-cooled by the natural circulation of the water through the boiler. The fluid bed grate 12 is composed of a combination of boiler tubes 14 and steel plates 1 6 to seal fully the area between the bottom drums 18, 20. Air supply for combustion and for fluidization is provided by a plenum 22 below the sealed boiler bottom and is passed into the combustion zone above the sealed boiler bottom by a number of apertures of stand pipes 24 located in the sealing plate 1 6 and between the cooling tubes 14.The cooling tubes 14 to which the steel sealing plate 1 6 is attached are provided by bringing every other tube from the primary furnace zone tangent wall 26 across to the opposite bottom drum 1 8, 20. Thus, the first half of each tube crossing the boiler bottom provides direct cooling of the sealing plate 16 and the second half of each tube, being unattached to the plate 16, acts as a thermic syphon tube to accelerate the flow of cool water from the bottom drum 18,20. An alternative construction to the sealing plate welded to the bottom of each first half of the floor tubes is shown in Figure 4. Here a membrane wall 30 is welded between the tubes 14' to provide the fluidized grate bottom. Although not shown, air distribution stand pipes are inserted through the membrane plates between the tubes to provide air for combustion and fluidization. An alternative construction to that shown in Figure 1 is illustrated in Figure 5. Here large bore linking tubes 40 are connected directly between the two bottom drums 1 8', 20' and the layout of the thermic syphons 14" is such as to induce flow along the linking tubes. Once again in this embodiment, the linking bores 40 may either be attached to a steel plate in a manner analogous to Figure 3 or be interconnected by membrane walls in a manner analogous to Figure 4 to provide the fluid bed grate. Stand pipes are once again provided in this embodiment for the introduction of air for combustion and fluidization. CLAIMS

4. A water tube boiler as claimed in claim 1 or claim 2, comprising three drums in an A-type configuration, wherein water tubes connected to the drum on one side of the furnace extend across the grate to cool the grate and are subsequently welded to form part of the tangent wall on the opposite side of the furnace.

5. A water tube boiler constructed substantially as hereinbefore described with reference to and as illustrated in any of the embodiments in the accompanying drawings.