GB2049126A - Boiler - Google Patents

Abstract

A water-heating boiler comprises a plurality of heat-exchange units 1, 2, each mounted in a respective enclosure 9 which communicates directly with a flue 3a common to the heat-exchange units. The flue 3a is in a flue casing 3 provided with the enclosure 9. Each heat-exchange unit has a forced draft fan 4, a water inlet 5, a water outlet 6, a water manifold 7 and extended-surface tubes 8. The extended-surface tubes enclose a burner (not shown). The heat-exchange units 1, 2 are primary heat- exchangers, and are connect in parallel, and are further connected to a primary heat-exchange circuit. A secondary heat-exchange unit 19 is arranged perpendicularly to the flue 3a, and downstream of the two primary heat-exchange units 1, 2. The unit 19 is connected in a secondary heating circuit which is independent of the first and, in use, are connected to separate heat consumers external to the boiler. <IMAGE>

Description

SPECIFICATION Boiler This invention relates to hot water boilers.

Traditionally, groups of water-heating heatexchange units have been connected to a common flue by lengths of interconnecting ductwork. This was an unsatisfactory arrangement, since the potential surface area through which heat could be lost i.e. through the walls of the interconnecting ductwork was large.

The heat loss could be reduced if the ducts were adequately lagged, but lagging of pipes can be expensive. It is therefore desirable to reduce the length of interconnecting flue ducting to a minimum.

Recently, boilers have been advocated where a group of water-heating heat-exchange units are mounted in a common flue. In these boilers, there is no interconnecting flue ducting, and therefore there can be no heat loss through the walls of inter-connecting flue ducting. However, such boilers have disadvantages; firstly, any water condensing from the flue gases may fall on lower heat-exchange units; secondly flue gases entering the common flue may be unmixed; and thirdly any uneveness of gas temperature leaving the heat-exchange units may not be damped out, since there is no intermediate region between the heat-exchange units and the common flue.

According to one aspect of the present invention, a water-heating boiler comprises a plurality of heat-exchange units each mounted in a respective enclosure which communicates directly with a flue common to the heatexchange units, the flue being in a casing provided with the said enclosures.

The enclosures may project outwards from a wall of the casing, or may be defined by partitions within the casing with a region in the casing, outside the partitions, forming the common flue.

It is an advantage of the first aspect of the invention that the length of interconnecting flue ducting is eliminated. This means that there is a minimisation of heat transfer surface area. The design therefore improves the overall thermal efficiency of hot water boilers.

A further advantage of the invention is that any water condensed from the flue gas does not fall on lower heat-exchange units, since the heat-exchange units are mounted in enclosures. Also, flue gases entering the common flue are well mixed within the enclosures and any unevenness of gas temperature leaving the heat-exchange units is damped out, since there is a region (i.e. the enclosure) between each heat-exchange unit and the common flue.

The construction of a common casing having a plurality of heat-exchange units means the cost of building such boilers may be reduced.

Known hot water boilers have only a primary hot water circuit. The primary circuit in many cases is divided into parallel sub-circuits. In such boilers, low-grade heat is not recovered from the flue gases, and is lost.

According to a second aspect of the present invention, a water-heating boiler comprises primary heat-exchange means for heating a primary circuit, and secondary heat-exchange means for heating a secondary circuit independent of the primary circuit, the secondary heat-exchange means being disposed in a flue of the boiler downstream of the primary heatexchange means.

Preferably, the boiler is constructed according to the first aspect of the invention.

It is an advantage of the second aspect of the invention that the provision of a secondary circuit improves the overall thermal efficiency of hot water boilers. The secondary circuit is useful in that the heat of condensation of the flue or exhaust gases from the primary heatexchange units can be recovered. There is also a minimisation of heat transfer surface.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows an end elevation, partly in cross-section of a hot water boiler with two flue-mounted heat-exchange units; Figure 2 shows a side elevation, partly in cross-section of the boiler of Fig. 1; Figure 3 shows an end elevation of a further embodiment of a boiler with two fluemounted heat-exchange units; Figure 4 shows a side elevation, partly in cross-section, of the boiler of Fig. 3; Figure 5 shows an end elevation of a heatexchange unit as shown in Figs. 1 to 4; Figure 6 shows the heat-exchange unit in side view, partly in cross-section; Figure 7 shows an end elevation, partly in cross-section of a boiler with two primary heat-exchange units and a secondary heatexchange unit; Figure 8 shows a side elevation, partly in cross-section, of the boiler of Fig. 7;; Figure 9 shows schematically a side elevation of a boiler having a single bank of heatexchange units mounted in a common casing with internal partitions; and Figure 10 shows schematically a side elevation of a boiler having a double bank of heatexchange units mounted in a common casing with internal partitions and a secondary-heat exchange unit.

Figs. 1 and 2 show an end elevation and a side elevation respectively of a hot water boiler having two-heat-exchange units 1 and 2 mounted on the side of a common flue casing 3. The heat-exchange units are mounted within enclosures, which are directly open to the common flue casing, as shown by the heat-exchange unit 1, partly in cross-section, in Fig. 2. The heat-exchange units are con nected in parallel with each other.

Each heat-excharige unit has a forced draft fan 4, a water inlet 5, a water outlet 6, water manifolds 7 and extended-surface tubes 8.

The extended-surfacd tubes enclose a burner (not shown).

Two heat-exchanger units are shown mounted in enclosures. It is possible, however, to have more than two heat-exchange units mounted in enclosures; the enclosures being on the side of, and directly open toi a common flue casing.

Each heat-exchange unit is contained within a respective containment can 9. The cans may be integral with or attached to the wall or side of the flue casing. The interior of the can 9 is directly open to the flue casing to ensure that flue or exhaust gases from the heat-exchange unit can pass directly into the common flue 3a.

The containment cans may be cylindrical as shown in Fig. 1 or, they may be rectangular as shown in Fig. 3. Cylindrical cans are separate from each other, whereas adjacent rectangular cans 11 and 12 may be joined together by, for example, welding to form a common wall or surface 1 3. Instead of adjoining together adjacently rectangular cans, it is possible to construct a plurality of rectangular cans as a one-piece unit. The heat-exchange units in Figs. 3 and 4 are the same as those shown in Figs. 1 and 2.

Figs. 5 and 6 show a typical heat-exchange unit having a forced draft fan 4, a water inlet 5, a water outlet 6, water manifolds 7 and extended-surface tubes 8. The extended-surface tubes define a circle, concentric with a burner 14, which is shown partly in crosssection in Fig. 6. A typical burner may be a forced-draft register or diffusion burner with fuel gas emitted from holes drilled in the end of a supply pipe; other types of burners may be used.

Water enters the heat-exchange unit, when in use, through the water inlet 5. The water passes through the extended surface tubes 8 via the water manifold 7 and leaves the heatexchange unit through the water outlet 8. The extended water-surface tubes surround the burner 14. Flue or exhaust gases from each burner pass over and between the extendedsurface tubes surrounding the burner. The gases then enter the common flue. The water is therefore heated when passing through the extended-surface tubes.

The heat-transfer surface exposed to the burner is increased by extension of the tube surface. This can be done by addition of fins to the outside of the tubes. The fins are referred to as the extended-surface, and they increase the heat-transfer area substantially in a given amount of space.

A further embodiment of the invention, as a multiple-circuit hot water boiler, is shown in Figs. 7 and 8 which show an end elevation and a side elevation respectively of a boiler with two primary heat-exchange units 1 and 2 and a secondary heat-exchange unit 1 5.

The two primary heat-exchange units 1 and 2 are mounted on the side of a common flue casing 3, and project into the common flue 3a. The primary heat-exchange units are the same as those shown in Figs. 1, 2, 3 and 4.

The primary heat-exchange units are connected in parallel to a primary heating circuit.

A secondary heat-exchange unit 1 5 substantially encloses the two primary heat-exchange units. The secondary heat-exchange unit comprises a plurality of tubes 16, parallel to each other, which preferably have extended surfaces. The tube 1 6 surrounds the extendedsurface tubes 8 of the two primary heatexchange units 1 and 2. In end elevation, the tubes are arranged to have two sides 1 7 and 1 8 parallel to the wall of the flue casing 3 (i.e. parallel to the flow of flue gases through the flue). The two sides 1 7 and 1 8 are disposed between the two primary heat-exchange units and the wall of the casing.

Above and below the primary heat-exchange units, the tubes 16 are shaped so that they substantially enclose the primary heat-exchange units.

Since the primary heat-exchange units are substantially enclosed or surrounded by the secondary heat-exchange unit, and also, both the primary and secondary heat-exchange units are positioned in the common flue, flue or exhaust gases from the burners of the primary heat-exchange units will pass over and between the extended-surface tubes 8 of the primary heat-exchange units and then pass over between the tubes 1 6 on the secondary heat-exchange unit.

The secondary heat-exchange unit operates at a lower temperature than the primary heatexchange unit. In this way, a secondary heating circuit connected to the secondary heatexchange unit can recover heat of condensation of the flue or exhaust gases. This can lead to an increase in the overall thermal efficiency.

It is to be appreciated that the primary heating circuit and the secondary heating circuit are independent from one other and in use are connected to separate heat consumers external to the boiler. It should also be appreciated that the boiler may have more than two independent heating circuits.

The boilers shown in Figs. 1 to 4 may also be multiple-circuit hot water boilers; for example, Figs. 1 and 2 show a secondary heatexchange unit 1 9 positioned in the common flue 3a downstream of the two primary heatexchange units 1 and 2.

The primary-heat-exchange units are connected in parallel. The secondary heat-exchange unit 1 9 is arranged perpendicularly to the flue i.e. perpendicular to the flow of flue or exhaust gases through the flue, and can, for example, be secured to the flue casing by flanges 20 and 21. The secondary heat-exchange unit 1 9 has tubes 19a, which preferably have extended surfaces.

Flue or exhaust gases from the primary heat-exchange units enter the flue 3a. They pass over and between the tubes of the secondary heat-exchange unit 1 9. The secondary heat-exchange unit operates at a lower temperature than the primary heat-exchange units, and in this way, the secondary heatexchange unit can recover any heat of condensation of the flue or exhaust gases. This can lead to an increase in the overall thermal efficiency.

The secondary heat-exchange unit 1 9 has a water inlet and outlet, and an inlet or outlet port is shown by reference numeral 22 in Fig.

1. A header 22a, also shown in Fig. 1, connects the tubes to one another on the secondary heat-exchange unit 1 9.

As in the first embodiment of the multiplecircuit hot water boiler shown in Figs. 7 and 8, each circuit, i.e. the primary heating circuits and secondary heating circuits are independent of one another, and may be connected to separate heat consumers separate to the boiler. It should also be appreciated that the boiler may have more than two independent circuits.

Two further embodiments of the invention are shown schematically in Figs. 9 and 10, and each comprises a plurality of heat-exchange units 23 mounted in a common casing 24. The heat-exchange units may be similar to units 1 and 2 described above. The heat-exchange units are connected in parallel with each other.

Each heat-exchange unit is substantially closed or surrounded by a partition 25. A common flue 26 is defined by a region in the common casing, which is outside the partitions but within the- common casing.

The internal partitions are preferably shaped sheets of metal, such that a vertical portion 27 of each partition, immediately adjacent to the common flue, is substantially parallel to an adjacent wall of the common casing. Fig. 9 shows a single bank of heat-exchange units mounted in a common casing, where the common flue 26 is the region between the substantially parallel portions 27 of each partition 25 and the adjacent wall of the common casing. Fig. 10 shows a double bank of heatexchange units mounted in a common casing, where the common flue 26 is the central region between the substantially parallel portions of the partitions enclosing the heatexchange units in the two banks.

Flue or exhaust gases leave the heat-exchange units which are located in enclosures 28, and enter the common flue 26 via apertures 29. The apertures are preferably located at the top of each enclosure so that the flow or exhaust gases can leave each enclosure easily. The apertures are preferably circular.

The enclosures may be defined by shaped sheets of metal secured to the wall of the common casing, or as boxes mounted independently of each other on the wall of the common casing.

The partitions help to prevent water which condenses from the flue gases from falling back on to lower heat-exchange units mounted in the common casing. The enclosures may also have drain holes 31 located at the base of each vertical portion 27 of each internal partition, as shown in Fig. 10. The base 32 of each enclosure slopes downwardly from the common casing 24 towards the common flue 26.

The partitions are preferably made of a metal, such as stainless steel, which can withstand the harsh conditions found within the boiler and in the region surrounding each heat-exchange unit. The partitions may be secured to the common casing by, for example, welding.

The boiler may be a multiple-circuit hot water boiler (as shown in Fig. 10). A secondary heat-exchange unit 30 may be positioned in the common flue 26 downstream of the primary heat-exchange unit 23. The secondary heat-exchange unit comprises tubes positioned perpendicularly to the flow of the flue or exhaust gases through the flue. The primary heat-exchange units and the secondary heat-exchange unit are independent of each other and may be connected to separate heatconsumers external to the boiler.

Claims (28)

1. A water-heating boiler comprising a plurality of heat-exchange units, each mounted in a respective enclosure which communicates directly with a flue common to the heat-exchange units, the flue being in a casing provided with the said enclosures.

2. A water-heating boiler as claimed in claim 1, wherein the enclosures project outwards from a wall of the casing.

3. A water-heating boiler as claimed in claim 1 or 2, wherein the enclosures are integral with the wall of the casing.

4. A water-heating boiler as claimed in claim 1 or 2, wherein the enclosures are attached to the wall of the casing.

5. A water-heating boiler as claimed in claim 3 or 4, wherein the enclosures are cylindrical.

6. A water-heating boiler as claimed in claim 3 or 4, wherein the enclosures are rectangular.

7. A water-heating boiler as claimed in claim 6, wherein adjacent rectangular enclosures have a common wall or surface.

8. A water-heating boiler as claimed in claim 1, wherein the enclosures are defined by partitions within the casing, with a region in the casing, outside the partitions, forming the common flue.

9. A water-heating boiler as claimed in claim 8, wherein the partitions are shaped sheets of metal secured to wall of the common casing, and are substantially parallel to an adjacent wall of the common casing.

10. A water-heating boiler as claimed in claim 8, wherein the enclosures are boxes mounted independently of each other on a wall of the casing.

11. A water-heating boiler as claimed in claim 9, wherein the common flue is defined by a region between substantially parallel portions of the partitions and the adjacent wall of the common casing.

12. A water-heating boiler as claimed in claim 8, wherein the common flue is defined by a central region between substantially parallel portions of the partitions enclosing two parallel banks of heat-exchange units mounted in the common casing.

1 3. A water-heating boiler as claimed in claim 9, wherein the partitions are secured to the common casing by welding.

14. A water-heating boiler as claimed in any of claims 8 to 13, wherein the partitions are made of stainless steel.

1 5. A water-heating boiler comprising primary heat-exchange means for heating a primary circuit, and secondary heat-exchange means for heating a secondary circuit independent of the primary circuit, the primary and secondary heat-exchange means being positioned in a common flue within a casing, and the primary heat-exchange means being substantially enclosed by the secondary heatexchange means.

1 6. A water-heating boiler as claimed in claim 15, wherein the primary heat-exchange means are heat-exchange units, connected in parallel, mounted on the side of and projecting into the common flue casing.

1 7. A water-heating boiler as claimed in claim 15, wherein the secondary heat-exchange means is a secondary heat-exchange unit having sides parallel to the common flue casing, and disposed between the primary heat-exchange means and the common flue casing.

1 8. A water-heating boiler comprising primary heat-exchange means for heating a primary circuit, and secondary heat-exchange means for heating a secondary circuit indepentent of the primary circuit, the secondary heat-exchange means being disposed in a flue of the boiler downstream of the primary heatexchange means.

1 9. A water-heating boiler-as claimed in claim 18, wherein the primary heat-exchange means are primary heat-exchange units connected in parallel, each mounted in a respective enclosure which communicates directly with a flue common to the heat-exchange units, the flue being in a casing provided with a said enclosure.

20. A water-heating boiler as claimed in claim 18, wherein the secondary heat-exchange means is a secondary heat-exchange unit arranged perpendicularly to the flue.

21. A water-heating boiler as claimed in claim 20, wherein the secondary heat-exchange unit is secured to the flue casing by flanges.

22. A water-heating boiler as claimed in claim 19, wherein the enclosures project outwards from a wall of the casing.

23. A water-heating boiler as claimed in claim 1 8 or 19, wherein the enclosures are integral with the wall- of the casing.

24. A water-heating boiler as claimed in claim 1 8 or 19, wherein the enclosures are attached to the wall of the casing.

25. A water-heating boiler as claimed in claim 22 or 23, wherein the enclosures are cylindrical.

26. A water-heating boiler as claimed in claim 22 or 23, wherein the enclosures are rectangular.

27. A water-heating boiler as claimed in claim 26, wherein the adjacent rectangular enclosures have a common wall or surface.

28. A water-heating boiler substantially as herein described with reference to the accompanying- drawings.