STEAM BOILER EQUIPPED WITH COOLING DEVICE
The steam boiler has a circulation system for boiler water that has water pipes arranged to circulate boiler water and steam through the water pipes with a cooled device arranged to cool a selected, exposed part of the steam boiler. The cooled device has an outer tube and an inner tube arranged in the outer tube. The outer tube, at an upper end thereof, has an open connection to one of the water pipes in which water pipe a flow is established.
The present invention concerns a steam boiler with a circulation system for boiler water that preferably has natural circulation.
BACKGROUND TO THE INVENTIONIn steam boilers in which combustible material is combusted in a furnace, hot flue gases are formed that are conducted out of the steam boiler while the hot flue gases emit thermal energy to the boiler water circulating in a circulation system for the boiler. A prior art method of transferring thermal energy from hot flue gases to boiler water in a small steam boiler of an older type involves using a Field's steam boiler system from the late 19th century in this steam boiler. To increase the heating area, vertical tubes (Field's tubes), closed at the lower ends, are used in this. They are suspended from the furnace roof. Inside these tubes are inner circulation tubes which are open at both ends. When the boiler is in operation, heat applied to the outer gap between the concentrically arranged tubes will achieve a steam/water mixture that has a lower density than the water in the inner tube. This creates natural circulation in these tubes which effectively increases the heat-absorbing area in the boiler. Heat is thus supplied to the stationary water volume above the sheet metal roof of the furnace from these Field's tubes. Despite early implementation, this application of Field's tubes has only been used to extend the heating area of a stationary, static volume of liquid to which heat is to be supplied. These Field's tubes are freely exposed in the furnace.
Regardless of how the heat is transferred to the boiler water, the flue gases, on their way out of the steam boiler, are conducted through ducts in which parts of the boiler are subject to extreme stress. If, for example, the steam boiler contains a cyclone for the separation of particles from the hot flue gases, the cyclone normally has an outlet tube which is extremely exposed to the hot flue gases. To allow it to last longer, it has been proposed, for example in U.S. Pat. No. 4,913,711, that the outlet tube can be cooled with cooling water fed using a pump to piping that leads to the outlet tube. A major disadvantage in this case is that a pump is required to cool this component. Another disadvantage is that the connection tube passes through the cyclone volume, thus disturbing the cyclone effect. This connection tube must be well protected against erosion.
There are also examples of cooled outlet tubes embodied by vertical water-bearing tubes next to each other. These tubes receive their water from below. One disadvantage of this is that these supply tubes are long and subject to severe erosion and may disturb the operation of the cyclone.
It is easy to see that, in a steam boiler, not only the outlet tube of a cyclone may be subject to stress on account of heat but that the high temperature may also constitute a problem for the material in the walls and other components in the entire steam boiler. The aim of the present invention is to offer an improved steam boiler in which various exposed parts of the steam boiler can become more durable by being cooled effectively.
DESCRIPTION OF THE INVENTIONThe present invention concerns a steam boiler with a circulation system for boiler water that preferably has natural circulation. The circulation system comprises water pipes arranged in such a way that, when the steam boiler is in operation, they can circulate boiler water through the pipes in a circuit in which water passes from the steam dome in the outer down tube to the furnace and convection parts and in which water and steam pass from the furnace and convection parts up to a steam dome in which steam is separated from the circuit.
The steam boiler comprises a device designed to cool a selected, exposed part of the steam boiler. The cooled device comprises an outer tube and an inner tube placed in the outer tube. The outer tube has an upper end with an open connection to one of the water pipes for boiler water and a sealed lower end. The inner tube has an upper open end connected to a water pipe for boiler water and a lower open end at the outer tube's sealed lower end. In some embodiments, the inner tube's upper open end is located at the outer tube's upper end and they are connected to the same water pipe or flow for boiler water. The cooled device extends at least partially in a vertical direction downwards from the point at which the outer tube is connected to a water pipe.
The steam boiler may comprise an element that is exposed to hot gases when the steam boiler is used. The element that is exposed to hot gases when the steam boiler is used may consist of a wall in the steam boiler or a holder for the heat exchanger in the path of the flue gas or the cooled device may be arranged in or in fact constitute this wall or holder.
The element that is exposed to hot gases when the steam boiler is used may also consist of, for example, a thermocouple or a through tube that extends through the pipe for boiler water and through the inner tube of the cooled device and, at its very end, connects to the outer tube of the cooled device.
The steam boiler may comprise a cyclone for separation of particles from hot flue gases, in which connection the cyclone has an outlet tube for the hot gases. In such case, the cooled device may be arranged to create a cooled outlet tube.
The cyclone's outlet tube may be constructed of or comprise a number of cooled devices, each of which cooled devices comprises an outer tube and an inner tube arranged in the outer tube, which outer tube, at an upper end, has an open connection to one of the pipes for boiler water and a sealed lower end and the inner tube has an upper end at the outer tube's upper end and a lower open end at the outer tube's sealed lower end and the cooled device may extend at least partially in a vertical direction downwards from the point at which the outer tube is connected to the water pipe.
In some embodiments, at least some of the pipes for boiler water may be inside the cyclone's walls and extend in a vertical direction from a lower part of the cyclone to a higher part of the cyclone. Some of the pipes for boiler water that extend inside the cyclone's walls may, in such case, be connected to cooled devices provided with an outer and an inner tube.
According to one embodiment, the steam boiler may have walls that form a flue gas duct in which one or more elements are suspended by means of a holder, which holder comprises a cooled device in accordance with the present invention, i.e. a cooled device with an outer tube and an inner tube arranged in the outer tube, which outer tube, at an upper end, has an open connection to one of the water pipes for boiler water and a sealed lower end, in which connection the inner tube has an upper open end at the outer tube's upper end and a lower open end at the outer tube's sealed lower end and the cooled device extends at least partially in a vertical direction downwards from the point at which the outer tube is connected to the water pipe.
According to another embodiment, a flue gas duct formed from the walls of the steam boiler may comprise a separating partition wall that separates two parts of the flue gas duct from each other. In such case, the partition wall may be at least partially constructed of cooled devices in accordance with the present invention, i.e. cooled devices comprising an outer tube and an inner tube arranged in the outer tube, which outer tube, at an upper end, has an open connection to one of the water pipes for boiler water and a sealed lower end, in which connection the inner tube has an upper open end at the outer tube's upper end and a lower open end at the outer tube's sealed lower end and the cooled device extends at least partially in a vertical direction downwards from the point at which the outer tube is connected to the water pipe.
According to another embodiment, the cooled device is used as a dust-separating beam in a flue gas duct formed from the walls of the steam boiler. In such case, a number of cooled devices may be placed next to each other in the flue gas duct. When the cooled device is used as a dust-separating beam, the cooled device may be provided with outer rails that extend along the cooled devices.
The inner tube's upper end may be funnel-shaped.
The inner tube may, at its upper end, have a mouth that is at a slant to the inner tube's longitudinal axis.
The connection to the water pipe for boiler water may be in an area in which the lower side of the pipe for boiler water has been expanded to meet the outer tube.
At the upper end of the outer tube a lid may be arranged to cover part of the gap area between the outer and the inner tubes.
At its upper end, the inner tube may be inclined towards the wall of the outer tube.
In
Other parts of the steam boiler 1 are also exposed to stress by the hot gases.
A cooled device 12 will now be explained with reference to
The normal water flow rate in the water pipe 3 is in the range 0.3 to 1.5 m/s. The water flow rate established in the downward tube 14 is 0.5 to 2.5 m/s and in the outer gap between tubes 13 and 14 it is 0.2 to 1.0 m/s.
In accordance with the present invention, a cooled device 12 is used that works according to the principle shown in
With reference to
In an embodiment best shown in
The water pipe 3 that is used is suitably one of the water pipes 3 that run inside the walls 8 of the cyclone 7. In practice, a number of such water pipes 3 pass through the cyclone 7 and meet higher up in the system.
The cooled device 12 may thus, in itself, form durable parts of the steam boiler 1 exposed to heat. Alternatively, the cooled device 12 may also be used to cool an element that, when the steam boiler 1 is used, is exposed to hot flue gases (directly or indirectly). Such an embodiment will now be explained with reference to
Another embodiment is shown in
Another embodiment will now be explained with reference to
Another embodiment will now be explained with reference to
Another embodiment is shown in
Another embodiment is shown in
A few more embodiments will now be explained with reference to
In conventional Field's boilers, the cooling tubes are designed to make it easier for the boiler water to be sucked down in the inner tube 14. Thus the inner tube 14 may, at its upper end 17, be shaped as a funnel 29 to reduce the pressure drop in this part and, to a certain extent, guide the rising steam/water mixture away from the inlet of the inner tube. This embodiment may also be applied when the cooled devices 12 are connected to a water pipe with boiler water in which a water flow is established.
In the embodiment in accordance with
In the embodiment in accordance with
Another aspect will now be explained with reference to
The embodiment in accordance with
The embodiment in accordance with
In accordance with the embodiment shown in
The embodiments shown in the figures may be used in steam boilers of different types and, in principle, everywhere there is a heated space or a part that is exposed to heating and where there is also a flow of water in a pipe that passes the area or the part that needs to be cooled.
The invention offers a simple method for cooling parts that are exposed to strong heat. When the invention is applied to the outlet tube in a cyclone, it offers the advantage that the existing flow of boiler water can be used and no separate pipe is required into the cyclone from outside with the additional complications this entails. In addition, no separate pump for the flow of cooling water is required.
Claims
1. A steam boiler, comprising:
- a furnace;
- a circulation system for boiler water, the circulation system having a water pipe connected thereto and adapted to circulate boiler water and steam through the water pipe in a circuit; the circulation system being in operative engagement with the furnace;
- a cooled device in operative engagement with the water pipe, the cooled device having an outer tube and an inner tube arranged in the outer tube, the outer tube, at an upper end thereof, having an open connection defined therein connected to the water pipe;
- the outer tube having a sealed lower end;
- the inner tube having an upper open end connected to the water pipe and a lower open end at the sealed lower end; and
- the cooled device extending at least partially in a vertical direction downwardly from the upper end of the outer tube.
2. The steam boiler according to claim 1 wherein the cooled device is in operative engagement with an element to cool the element.
3. The steam boiler according to claim 2 wherein the element consists of a wall in the steam boiler and the cooled device is arranged inside the wall.
4. The steam boiler according to claim 2 wherein the element consists of a thermocouple.
5. The steam boiler according to claim 2 wherein the element consists of a through tube that extends through the water pipe and through the inner tube and connects to the outer tube.
6. The steam boiler according to claim 1 wherein the steam boiler comprises a cyclone for separating ash from hot flue gases, the cyclone has an outlet tube for the hot flue gases and the cooled device is arranged to cool the outlet tube.
7. The steam boiler according to claim 6 wherein the outlet tube consists of a number of cooled devices each cooled device comprises an outer tube and an inner tube.
8. The steam boiler according to claim 6 wherein the steam boiler has a plurality of water pipes and at least some of the water pipes are inside walls of the cyclone and extend in a vertical direction from a lower part of the cyclone to a higher part of the cyclone and some of the water pipes which extend inside the walls of the cyclone are connected to the cooled devices by the outer tube and the inner tube.
9. The steam boiler according to claim 1 wherein the steam boiler has walls that form a flue gas duct and the cooled device constitutes a holder for an element that is suspended in the flue gas duct.
10. The steam boiler according to claim 1 wherein the steam boiler has walls that form a flue gas duct and the cooled device, together with a number of similar cooled devices, form a partition wall that separates two parts of a flue gas duct from each other.
11. The steam boiler according to claim 1 wherein the steam boiler has walls that form a flue gas duct and the cooled device is arranged in the flue gas duct as a separation beam and is provided with outer rails.
12. The steam boiler according to claim 1 wherein the upper open end of the inner tube is funnel-shaped.
13. The steam boiler according to claim 1 wherein the inner tube, at the upper end thereof, has a mouth that is at a slant to a longitudinal axis of the inner tube.
14. The steam boiler according to claim 1 wherein an area is disposed at a lower side of the water pipe that has been expanded to meet the outer tube.
15. The steam boiler according to claim 1 wherein a lid is arranged at the upper end of the outer tube to cover part of a gap area between the outer tube and the inner tube.
16. The steam boiler according to claim 1 wherein the inner tube, at an upper end thereof, is inclined towards a wall of the outer tube.
Type: Application
Filed: Apr 20, 2009
Publication Date: Mar 3, 2011
Inventors: Lennart Nordh (Goteborg), Karl-Erik Brink (Molndal)
Application Number: 12/988,682
International Classification: F22B 37/10 (20060101);