GB2280494A - Boiler with baffled combustion chamber - Google Patents

Abstract

A boiler comprises a combustion chamber 10 surrounded by a water jacket 12. The combustion chamber includes internal baffle plates 30, for directing the flow of hot gases from a burner 14 through the chamber 10 to an outlet 16. Plates 30 are supported on supports 32 on wall 20 and on a plate (38, Figure 3) welded to a metal wall 36. A gas passage, which extends substantially parallel to the wall 36, is defined by the wall 36 and the plate (38, Figure 3 or 238, Figure 8) which is spaced from the wall by fingers (40, 240). The boiler may comprise an upstand (22, Figure 2 or 222, Figure 6) formed on a combustion chamber wall in a position at which the boiler burner flame impinges on the wall. The boiler may further comprise a water inlet pipe having an opening to allow water from the water jacket to combine with water flowing in through the inlet pipe (see Figure 9). <IMAGE>

Description

A BOILER This invention relates to a boiler and in particular to a water heating boiler for domestic use. These boilers are typically used for heating water for household use and/or for a domestic central heating system. Such boilers are likely to have a rating of 40,000-90,000 BTU, but the invention is not restricted to these values.

The invention is applicable to both gas and oil fired boilers.

Boilers require periodic servicing, in particular to clean the combustion chamber from accumulations of solid combustion products. It is conventional to provide access at one end of the boiler to allow the internal baffle components from the combustion chamber to be withdrawn and cleaned. An example of such a boiler is shown in British Patent Specification 2 195 009.

Many boiler installations at the current time call for a boiler to be built-in, beneath a worktop in a kitchen, and the presence of the fixed worktop makes servicing very difficult. Some boilers, such as that shown in British Patent Specification 2 248 918 require access from above which is difficult to provide in a built-in installation.

According to the present invention there is provided a boiler comprising a combustion chamber surrounded by a water jacket, wherein the combustion chamber includes internal baffles for directing the flow of hot gases from a burner through the chamber, and wherein at least some of the baffles are metal, are welded to a metal wall which separates the combustion chamber from the water jacket, and form a gas passage extending substantially parallel to the wall.

Preferably at least one baffle comprises a baffle plate, supported by baffle plate supports, and a flow retarder for retarding the flow of hot gases through the gas passage.

The flow retarder may be welded to a wall of the combustion chamber. The supports for the baffle plate may each be welded to an opposing wall of the combustion chamber.

Alternatively, one baffle plate support may be welded to a wall, and the flow retarder may be provided with a second support for the baffle plate. The support may be integrally formed as part of the flow retarder, or it may be mounted on the flow retarder by welding, bolts or other suitable means.

By welding the flow retarder and baffle plate support to one wall, and welding a baffle plate support to the opposing wall, the baffle plate may be readily mounted and demounted from the combustion chamber for cleaning or other purposes.

The use of baffles welded to the wall markedly increases the rate of heat exchange from the hot gases to the water in the water jacket, because the hot gases are forced to flow through the gas passage in close proximity to the wall.

Furthermore, the gases heat the material of the baffle, and particularly of the flow retarder, as well as the wall itself, and baffle is in direct thermally conducting relationship with the wall so that heat is readily transferred from the baffle to the wall.

In a preferred embodiment at least one of the baffles is generally disposed at an acute angle to the horizontal.

This exposes a greater area of a primary heating surface to the hot gases. The rate of heat exchange is therefore increased because the hottest gases, on the underside of the baffle, are forced to flow in a turbulent state in close proximity to the conductive wall.

Preferably the acute angle of the baffle is between 10 and 60 degrees to the horizontal.

According to a second aspect of the present invention, there is provided a boiler comprising a combustion chamber surrounded by a water jacket, wherein the combustion chamber includes a peripheral upstand formed on a combustion chamber wall around the position at which the boiler burner flame impinges on the wall.

The upstand is generally circular in the preferred embodiment, and causes the hot combusted gases to be reflected into the central region between the mouth of the burner and the opposing wall of the combustion chamber. The hot combusted gases that are reflected will therefore mingle with the gases from the burner directed at the opposing wall of the combustion chamber. The intense heat resulting from this mingling of hot combustion gases helps to promote more complete combustion of the fuel, and it may also improve the heat exchange between hot gases and the water in the water jacket.

Because of the efficiency of combustion, it is possible to operate the boiler with a relatively high back pressure.

This characteristic can be utilised by making the combusted gases flow through relatively narrow passageways prior to being expelled from the combustion chamber. The use of such narrow passages can help to silence boiler operation, particularly if the narrow passageways are lined with sound absorbing material.

According to a third aspect of the present invention, there is provided a boiler comprising a combustion chamber surrounded by a water jacket which has an inlet pipe and an outlet pipe, wherein the inlet pipe traverses the water jacket at a first location, passes through the combustion chamber and enters the water jacket at a second location, and wherein there is an opening at the first location to allow water from the water jacket to pass into the inlet pipe at the first location.

Preferably the opening is arranged so that a flow of water through the inlet pipe will cause water to be drawn from the water jacket to combine with water flowing in the inlet pipe.

The water in the water jacket, especially at the first location, will generally be hotter than the water flowing in the inlet pipe, and the admission of this hotter water will then raise the temperature of the water entering the water jacket at the second location. This will help to prevent condensation arising inside the combustion chamber which might result if very cold water could be in contact with the wall of the combustion chamber. Such condensation may have an adverse effect upon the combustion of the fuel within the combustion chamber and would cause corrosion of the combustion chamber walls.

In an alternative embodiment the burner may be directed into the combustion chamber at an acute angle to the horizontal.

Accordingly, the upstand formed on the opposing wall will be at a position diametrically opposite the mouth of the burner at a position where the hot combusted gases will impinge. In this way the effective length of the combustion chamber may be increased without increasing the internal or external dimensions of the boiler.

Access may be provided to the interior of the combustion chamber, for servicing, through an access door provided in a vertical wall of the boiler. This avoids the necessity to obtain access from the top of the boiler for servicing.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross section through a first boiler in accordance with the invention; Figure 2 is a detail view of part of the combustion chamber; Figure 3 shows a first form of baffle plate for incorporation into the boiler of Figure 1; Figures 4a and 4b are views from opposite sides of a second form of baffle plate for use in the invention; Figure 5 shows a baffle plate for use in the water jacket; Figure 6 is a perspective view of a second boiler according to the invention; Figure 7 is a cross section through the boiler of Figure 6; Figure 8 shows a baffle support detail; and Figure 9 shows, on an enlarged scale and viewed from the opposite side, the area enclosed within the circle A from Figure 7.

The boiler shown in Figure 1 has a combustion chamber 10 surrounded by a water jacket 12. A burner 14 (which may be gas or oil fired) is arranged to burn fuels so that the hot combustion products are directed into the combustion chamber 10. The path followed by the combustion products through the chamber 10 is indicated by arrows, and the combusted gases eventually leave the chamber through a vent 16 at the top of the chamber. As the gases travel through the combustion chamber, they give up their heat to water in the water jacket 12, and this water is then circulated in a known manner to hot water pipes.

The construction of the burner 14 is conventional and needs no further description here.

The hot gases and possibly flames resulting from burner operation will'bye directed from the burner mouth 18 against an opposing wall 20 of the combustion chamber. On this wall 20 a circular upstand 22 is secured by welding. This upstand causes some of the hot combusted gases to be reflected and to mingle with the gases directed at the wall 20. The intense heat created will help to ensure that complete combustion of the fuel takes place in the area generally indicated at 24. The hot combusted gases will also be caused to swirl in the lower half of the combustion chamber thus producing good heat exchange conditions between the hot gases and the water in the water jacket 12.

The gases leave the combustion chambers by passing through two baffle sections 26, 28. Although two baffle sections are shown in Figure 1, there could be only one such baffle section, or more than two baffle sections. Each baffle section comprises a removable plate 30 which is supported on supports 32 and which serves to block most of the cross section of the chamber to the gas flow. The gas flow is therefore constrained to pass between a baffle plate 34 and the wall of the combustion chamber at 36. The baffle plate 34 is shown in more detail in Figure 3 and comprises a back plate 38 from which a number of fingers 40 project. Figure 3 shows the baffle plate 34 before being placed in the combustion chamber. When the baffle plate 34 is in place, the free ends of the fingers 40 are welded to the wall 36.

The hot gases then flow between the fingers 40 and between the back plate 38 and the combustion chamber wall 36. The gases therefore give up their heat both to the combustion chamber wall 36 and to the fingers 40 and back plate 38.

Because the fingers 40 are welded to the wall 36, this heat is immediately conducted to the wall 36.

In Figure 1 the second baffle section 28 is arranged so that the flow passage for the hot gases is diametrically opposite that of the lower section 26, to further enhance the turbulent flow of the gases.

The gases then pass through an exit channel 42. This exit channel is relatively narrow and is lined above and below with sound absorbing material 44. The narrowness of the passage 42 and the presence of the sound absorbing material produce a good silencing effect which means that the boiler operation is relatively quiet.

An access door 46 is provided in the front of the boiler to allow access for servicing. The door 46 is also provided with sound absorbing material 44. When the access door 46 is opened, the baffle plates 30, 30a can be lifted out to allow access to the bottom of the boiler, but the plates 34, 34a cannot be removed. However the interior of the combustion chamber is then fully available for servicing and cleaning.

A second access opening to the combustion chamber is available by removing the burner 14 from the combustion chamber.

Figure 4 shows an alternative baffle plate construction.

The baffle plate 134 in Figures 4a and 4b has a back plate 138 to which bar section 140 are welded. The bar sections (which may be solid or hollow) are welded to the back plate through a slot 139 (Figures 4b). The back plate 138 also includes an inwardly directed flange 132 on which the removable plates 30, 30a can be supported.

The water jacket 12 of Figure 1 also includes a water baffle 48 the construction of which is shown in more detail in Figure 5. The baffle 48 is intended to prevent the incoming cold water from making direct contact with the combustion chamber wall, ' because this can result in condensation appearing inside the combustion chamber which is a bad thing. The incoming water will therefore impinge on the surface of the baffle 48 facing away from the combustion chamber 10, but the water will be able to circulate between the baffle 48 and the combustion chamber wall. The narrow gap 50 at the base allows a small volume of water to pass downwards to aid circulation through the bottom of the waterway. The wider gaps 52 at the upper edge allow water to flow upwards.The width of the gap 50 as indicated at 54 can for example be 3 mm and the depth of the baffle, ie the distance of the back plate from the combustion chamber wall could be between 5 mm and 15 mm.

By constructing the internal baffles in the boiler in this way, particularly good heat exchange is achieved between the combusted gases and the water, producing a boiler which can be made smaller for a given heat output or can have a larger heat output than a conventional boiler of similar size.

The boiler shown in Figures 6 and 7 has a combustion chamber 210 which is surrounded by a water jacket 212. A burner 214 (which may be gas or oil fired) is arranged to burn fuels so that the hot combusted products are directed into the combustion chamber 210.

The path followed by the hot combusted products through the combustion chamber 210 is indicated by arrows, and the combusted gases eventually leave the chamber through a vent 216 at or near the top of the chamber. As the gases pass through the combustion chamber 210, they give up their heat to water in the water jacket 212, and this water is then circulated to hot water pipes in a known manner.

The construction of the burner is conventional and requires no further description here.

The hot gases and possibly flames resulting from the burner operation are directed from the burner mouth 218 against an opposing wall 220 of the combustion chamber. On this wall 220 a circular upstand 222 is secured by welding. This upstand 222 causes some of the hot combusted gases to be reflected and to mingle with the gases directed at the wall 220. The intense heat created will help to ensure that complete combustion of the fuel will take place in the area indicated at 224. The hot combusted gases will be caused to swirl in the lower half of the combustion chamber, producing good heat exchange conditions between the hot gases and the water in the water jacket 212.

The gases leave the combustion chamber by passing around the baffles 226, 228 and 230. Although three baffles are shown in Figure 7, there could be just one, two or more than three baffles. Each baffle comprises a removable baffle plate 230 which blocks most of the cross section of the combustion chamber 210 to the flow of the hot gases and is supported on supports 232, and a flow retarder 234. The flow of hot gases is therefore constrained to pass beneath the baffle plates 230, 230a & 230b, then being directed upward between the flow retarder 234 and the wall of the combustion chamber 236.

A flow retarder 234 is shown in more detail in Figure 8, and comprises a back plate 238 from which a number of fingers 240 project. The fingers 240 projecting from the flow retarder 234 are welded to the wall of the combustion chamber 236. The hot gases therefore flow between the fingers 240, the back plate 238 and the combustion chamber wall 236. The gases give up their heat to both the combustion chamber wall 236 and the back plate 238 of the flow retarder 234. The back plate 238 is provided with an integral support 232 for the baffle plate 230.

The baffle plates 230 & 230b are set at an acute angle to the horizontal. This allows the surface areas of the combustion chamber wall 236 and of the baffle plates 230, 230b along which the hot gases flow to be increased.

Increasing the surface area of the combustion chamber 210 with which the hot gases are in contact will also help to improve the transfer of heat from the hot combusted gases to the water jacket 212.

It has been found in tests that inclining the baffles 226 and 230 at an angle to the horizontal makes it possible to reduce the gap between the back plate 238 and the wall 236 and thus to shorten the length of the fingers 240 with an increase in the rate of heat exchange to the wall 236.

Increasing the effective length of the combustion chamber results in a reduction in the level of oxides of nitrogen produced by high flame tip temperatures.

Figure 6 shows a perspective view of the boiler. An access door 246 is provided in the front of the boiler to allow access for servicing. The door is provided with sound and heat absorbing material 244. When the access door 246 is opened, the baffle plates 230, 230a and 230b can be lifted out to allow access to the bottom of the boiler, but the flow retarders 234 and 234a cannot be removed. However, the interior of the combustion chamber 210 is then fully available for servicing and cleaning.

A second access opening to the combustion chamber 210 is available by removing the burner 214 from the combustion chamber.

Figure 9 shows the cold water return pipe 260, where it passes through the water jacket 212. A quantity of the heated water is drawn into the cold water return. This warms the returning cold water and prevents cold water from making contact with the combustion chamber wall 236 which could otherwise result in condensation forming on the inside of the combustion chamber which is undesirable.

In an alternative embodiment the upstands 22 and 222 shown in Figures 2 and 6, which are used to reflect the hot combusted gases toward the areas indicated respectively by 24 and 224, may be non-circular.

Figures 6 & 7 show the mouth 218 of the burner 214 to be directed vertically downwards. In alternative embodiments the burner 214 may be inserted into the floor or a vertical wall of the combustion chamber 210, and the mouth of the burner may consequently be directed at the roof or a vertical wall of the chamber.

In another embodiment the burner may be inclined at an acute angle to the horizontal.

By constructing baffle sections in the boiler in this way, particularly good heat exchange is achieved between the combusted gases and the water, producing a boiler which can be made smaller for a given heat output, or can have a larger heat output than a conventional boiler of similar size.

Because of the efficiency of combustion, it is possible to operate the boiler with a relatively high back pressure. The efficiency of a boiler of the form described above has been calculated to give a net calorific efficiency of 90-92%, in tests at maximum fuel input rate.

Claims (14)

1. A boiler comprising a combustion chamber surrounded by a water jacket, wherein the combustion chamber includes internal baffles for directing the flow of hot gases from a burner through the chamber, and wherein at least some of the baffles are metal, are welded to a metal wall which separates the combustion chamber from the water jacket, and form a gas passage extending substantially parallel to the wall.

2. A boiler as claimed in claim 1, wherein at least one baffle comprises a baffle plate, supported by baffle plate supports, and a flow retarder for reducing the flow of hot gases through the gas passage.

3. A boiler as claimed in claim 2, wherein a first baffle support is welded to a first wall of the combustion chamber, and a second baffle support is mounted on the flow retarder which is welded to a second wall of the combustion chamber.

4. A boiler as claimed in any one of the preceding claims, wherein at least one of the baffles is generally disposed at an acute angle to the horizontal.

5. A boiler as claimed in any one of the preceding claims, wherein at least one of the baffles is generally disposed at an angle between 10 and 60 degrees to the horizontal.

6. A boiler as claimed in any one of the preceding claims, wherein the combustion chamber includes a peripheral upstand formed on a combustion chamber wall around the position at which the boiler burner flame impinges on the wall.

7. A boiler as claimed in claim 6, wherein the upstand is generally circular.

8. A boiler as claimed in any one of the preceding claims, wherein the burner is directed into the combustion chamber at an acute angle to the horizontal.

9. A boiler as claimed in any one of the preceding claims, wherein a door is provided in a vertical wall of the boiler for service access.

10. A boiler comprising a combustion chamber surrounded by a water jacket, wherein the combustion chamber includes a peripheral upstand formed on a combustion chamber wall around the position at which the boiler burner flame impinges on the wall.

11. A boiler as claimed in claim 10, wherein the upstand is generally circular.

12. A boiler comprising a combustion chamber surrounded by a water jacket which has an inlet pipe and an outlet pipe, wherein the inlet pipe traverses the water jacket at a first location, passes through the combustion chamber and enters the water jacket at a second location, and wherein there is an opening at the first location to allow water from the water jacket to pass into the inlet pipe at the first location.

13. A boiler as claimed in claim 12, wherein the opening is arranged so that a flow of water through the inlet pipe will cause water to be drawn from the water jacket to combine with water flowing in the inlet pipe.

14. A boiler substantially as hereinbefore described with reference to and as shown in any one of the drawings.