IE20040793A1 - Secondary heat exchanger - Google Patents

Abstract

A secondary heat exchanger (18) for a boiler assembly (10) comprises a housing (31) having a first part (31a) and a second part 31b independent of the first part (31a). The first part 31a defines a first flow path for a first fluid, and the second part (31b) defines a second flow path for a second fluid. The first part (31a) has at least two distinct first galleries (38) and the second part has a second gallery (40) which extends between the two first galleries (38) of the first part (31a). The second gallery (40) is oriented so that, in use, the second fluid flows generally vertically in the second gallery (40). <Figure 3>

Description

This invention relates to a secondary heat exchanger and more particularly, but not exclusively, to a boiler assembly having such a secondary heat exchanger.

It is generally accepted in the industry that, by 2005, all oil-fired boiler assemblies should meet the Sedbuk A or B rating standardfor efficiency. This is presently best achievable by the utilisation of a secondary heat exchanger to pre-heat domestic heating liquid prior to it entering the primary heat exchanger.

However, a problem with the inclusion of a secondary heat exchanger is that there is limited space within an existing boiler body to allow fitment. This is especially apparent with domestic boiler assemblies which have recognised standard dimensions to enable fitting under a kitchen work-surface or on a wall between cupboards.

Another problem with the inclusion of a secondary heat exchanger is being able to clean out deposits left in the secondary heat exchanger by incomplete combustion of the oil in the primary heat exchanger. If the secondary heat exchanger can be opened, then cleaning can be achieved by brushing or scraping. However, this then generates a further problem of being able to collect and remove from the boiler assembly the deposits brushed or scraped out of the secondary heat exchanger. If the deposits, during cleaning, collect in the condensate area of the secondary heat exchanger, then removal becomes particularly difficult and troublesome.

It is a further requirement to provide easy access to the secondary heat exchanger, to facilitate servicing and cleaning.

A further problem occurs due to inadequate condensate draining from the secondary heat exchanger. This promotes corrosion of the secondary heat exchanger, particularly at joints and in crevices.

The present invention seeks to provide a solution to these problems.

According to a first aspect of the present invention, there is provided a secondary heat exchanger for a boiler assembly, the secondary heat exchanger comprising a housing having a first part and a second part independent of the first part, the first part defining a first flow path for a first fluid, and the second part defining a second flow path for a second fluid, the first part having at least two distinct first galleries and the second part having a second gallery which extends between the two first galleries of the first part, the second gallery being oriented so that, in use, the second fluid flows generally vertically in the second gallery.

Preferably, the first part of the secondary heat exchanger housing has at least three first galleries and the second part has at least two second galleries which extend between the first galleries.

According to a second aspect of the invention, there is provided a secondary heat exchanger for a boiler assembly, the secondary heat exchanger comprising a E04079} housing having a first part and a second part independent of the first part, the first part defining a first flow path for a first fluid, and the second part defining a second flow path for a second fluid, the first part having three distinct first galleries and the second part having two distinct second galleries interposed between the first galleries.

Preferably, the second galleries are oriented so that, in use, the second fluid fiows generally vertically in the second galleries. This facilitates condensate run off, and thus reduces the tendency for corrosion.

Other preferable and/or optional features of the first and second aspects of the invention are set forth in claims 5 to 14, inclusive.

According to a third aspect of the invention, there is provided a secondary heat exchanger for a boiler assembly, the secondary heat exchanger comprising a housing having a first part and a second part independent of the first part, the first part defining a first flow path for a first fluid, and the second part defining a second flow path for a second fluid, the first part having at least two distinct first galleries and the second part having a second gallery which extends between the two first galleries of the first part, each first gallery being solely formed by two inter—connected heat transfer plates.

Preferable and/or optional features of the first, second and third aspects of the invention are set forth in claims 16 to 19, inclusive.

|E040793 According to a fourth aspect of the invention, there is provided a boiler assembly comprising a secondary heat exchanger in accordance with the first, second or third aspects of the invention.

Preferable and/or optional features of the third aspect of the invention are set forth in claims 22 to 26, inclusive.

The invention will now be more particularly described, ‘by way of example only, with reference to the accompanying drawings, in which : Figure l is a partial sectional schematic side view of part of a boiler assembly, in accordance with the present invention, showing a secondary heat exchanger; Figure 2 is a side elevational view of the secondary heat exchanger shown in Figure 1; Figure 3 is a part-sectional bottom plan view of the secondary heat exchanger; and Figure 4 is View along the line A-A in Figure 2.

Referring now to the drawings, there is shown part of a boiler assembly 10 which comprises a boiler body (not shown) in which is housed a down—firing burner having an electrically operated intake fan (not shown), a primary heat exchanger E040793 on the top of which the burner 14 is removably mounted, and a secondary heat exchanger 18 which is located behind the burner 14 and adjacent to the top of the primary heat exchanger 16. The secondary heat exchanger 18 is connected to the primary heat exchanger 16 via a first flue housing 22, and a second flue housing 24 leads from the secondary heat exchanger 18 to a conventional flue 25.

The boiler body is a container of standard or substantially standard boiler dimensions. The boiler body typically includes front and back panels, two side panels, a top panel and a bottom panel. At least one of the panels, or part of one of the panels, is an openable cover to enable access to the interior of the boiler body.

The basic arrangement of a suitable boiler assembly is essentially known from GB O203466.8. In this case, the front panel of the boiler body is the openable access cover. The primary heat exchanger 16 has inner and outer shells fixed together in spaced relationship so as to define a fluid-tightly enclosed or sealed main space therebetween. The main space, in use, acts as a water jacket in which water flows to be heated. Water inlets and outlets, in fluid communication with the main space between the inner and outer shells, are fonned in the sides or top of the primary heat exchanger 16.

The primary heat exchanger 16 has a full front access cover 26, which matches or substantially matches the height and width of the inner shell. The front cover 26 is openable, for example removable or hingable, to provide full access to the interior of ‘L/I |E040793 the inner shell. A flue gas outlet 30 is formed through the inner and outer shells at, or adjacent to, the rear of the primary heat exchanger 16.

As disclosed in GB 0203466.8, a pair of removable baffles may be located in the interior of the inner shell. The baffles are slidably received in the primary heat exchanger and can be fully accessed and removed through the opening exposed by removal of the front cover 26. The removable baffles are not essential, and in certain boiler assemblies, may be dispensed with. Alternatively, more than two baffles may be provided.

With the front cover 26 and baffles removed from the primary heat exchanger , unhindered or unobstructed full access to the interior 37 of the inner shell and to the flue gas outlet is achieved.

The burner 14 is any suitable known type of down-firing oil burner or gas burner. The burner 14 projects through the top of the primary heat exchanger 16 at or adjacent to the front edge 28.

Further details of the boiler assembly of GB 0203466.8 are not required, and will therefore be omitted. It will be understood that other arrangements of boiler assembly are equally applicable, and the arrangement disclosed in GB 02034668 is purely used by way of example.

HE040793 Instead of providing a flue discharge pipe from the flue gas outlet 30 of the primary heat exchanger directly to an external flue, as is common practice, the first flue housing 22 is connected to the flue gas outlet 30. The first flue housing 22 provides a flow path that angles through slightly more than 90 degrees. The rear of the secondary heat exchanger 18 is fluid—tightly connected to the first flue housing 22.

Due to the flow path defined by the first flue housing 22 and due to the secondary heat exchanger 18 being spaced from the top of the primary heat exchanger 16, the secondary heat exchanger slopes slightly downwards in a direction towards the front of the primary heat exchanger 16. The slope of the secondary heat exchanger 18 allows condensate, formed during use of the boiler assembly, to run off.

The second flue housing 24 is fluid-tightly and releasably connected to the front of the secondary heat exchanger 18. The second flue housing 24 connects the secondary heat exchanger 18 to the flue 25. The second flue housing 24 also includes a run—off channel 29 in the bottom thereof which is connected to a condensate collector (not shown). The condensate collector is a well—la1own collector which is conveniently located inside the boiler body. The condensate collector may, for example, comprise a simple U-bend trap. The outlet of the condensate collector is generally connected to a drain pipe which exits through a side of the boiler body to a drain.

The secondary heat exchanger 18 comprises a generally tubular housing 31 which has a liquid inlet port 32 for connection to a primary liquid system outlet 33, such as the outlet of a central heating system. The heating liquid enters the boiler body |E040793 from outside the boiler assembly 10. Having the inlet port 32 in the lower surface of the secondary heat exchanger housing 31 allows straightforward access by an installer when connecting the boiler assembly to the primary liquid system.

An outlet port 34 (not shown in Figure 1) is provided in the upper surface of the secondary heat exchanger housing 31. The outlet port 34 is in fluid communication with an inlet (not shown) to the main space defined between the inner and outer shells of the primary heat exchanger 16. The heating liquid can thus flow from the secondary heat exchanger 18 to the primary heat exchanger 16 within the boiler assembly 10. An outlet from the main space of the primary heat exchanger 16 is connected to a primary liquid system inlet (not shown), such as the inlet of the central heating system, via an electric pump (not shown).

The fan of the burner 14 thus, in use, draws ambient air into the burner 14, causing generated hot flue gas to be pushed into and through the primary heat exchanger 16. The hot flue gas exits the interior of the primary heat exchanger 16 through the flue gas outlet 30 in the top of the primary heat exchanger 16, passes into the first flue housing 22 and then into the secondary heat exchanger 18. The hot flue gas pre—heats the heating liquid as it flows therethrough, prior to the heating liquid entering the main space between the inner and outer shells of the primary heat exchanger 16. The hot flue gas then flows into the second flue housing 24 before entering the flue 25.

|E040793 To simplify cleaning of the secondary heat exchanger 18 during maintenance and servicing, the secondary heat exchanger 18 is a plate heat exchanger having a plurality of interconnected heat transfer plates 36 defining first and second independent parts 31a and 31b within the secondary heat exchanger housing 31. The first part 31a defines a first flow path for the hot flue gas flowing from the primary heat exchanger 16 to the secondary heat exchanger 18, and the second part defines a second flow path between the inlet and outlet ports 32, 34 for the heating liquid.

The first flue gas part 31a comprises a plurality of distinct first flue gas galleries 38, and the second heating liquid part 31b comprises a plurality of second distinct heating liquid galleries 40. The first galleries 38 are solely formed by first opposing surfaces 42 of the plates 36 and have rectangular or substantially rectangular transverse cross-sections. The first opposing surfaces 42 are spaced by approximately mm.

The first galleries also have fluted or belled end openings 43, which effect the gas side pressure drop. The fluted or belled end openings 43 are also formed by the heat transfer plates 36. The heat transfer plates 36 only Contact the secondary heat exchanger housing 31 at, or adjacent to, the fluted or belled end openings 43, as can be seen in Figire 3.

The first galleries 38 extend longitudinally in a front—to-back direction of the boiler assembly 10.

IN <3 IE0407 The second galleries 40 are solely formed by second opposing surfaces 44 of the plates 36, and thus extend between the first galleries 38. The second opposing surfaces 44 are spaced by approximately 3 mm. The second galleries 40 are oriented so that the second flow path follows a generally vertical direction, i.e. the heating liquid flows generally upwards through the second galleries 40. The second flow path defined by the second galleries 40 also extends transversely to the first flow path defined by the first galleries 38. In particular, the second flow path defined by the second galleries 40 extends at right angles to the first flow path defined by the first galleries 38.

The second part 31b also includes third galleries 41 defined between the interior surfaces of the secondary heat exchanger housing 31 and the outermost heat transfer plates 36. The third galleries 41 extend in parallel, or substantially parallel, with the first and second galleries 38 and 40. The heating liquid also flows in the third galleries 41, and the third galleries 41 thus provide a heating liquid jacket around the first galleries 38. The second galleries 40 are in fluid communication with the third galleries 41.

The use of heat transfer plates 36 to define the first, second and, in part, third galleries 38,40,4l allows for an extremely compact secondary heat exchanger 18, when compared to the traditional cylindrical channel secondary heat exchangers. The plate secondary heat exchanger 18 can thus be located more easily in available space within the boiler body, without the necessity of redesigning the boiler body layout or increasing the size of the boiler body.

|E0407Furthermore, by orienting the second heating liquid galleries 40 upwardly or vertically, condensate drainage is promoted in the first galleries 38. This results in reduced corrosion.

In addition, due to the relatively open rectangular cross—section of the first flue gas galleries 38 of the secondary heat exchanger 18, carbon deposits which build up in the first flue gas galleries 238 during use of the boiler assembly 10 can be more easily brushed and/or scraped loose. Once loose, the deposits can be brushed out of the front and/or back of the secondary heat exchanger 18. If the deposits are moved out of the back of the secondary heat exchanger 18, they simply enter the first flue housing 22 and fall directly into the back of the primary heat exchanger 16 through the flue gas outlet 30. It is then a simple matter of removing the front cover 26 and the baffles to gain full unhindered access to the back of the interior of the primary heat exchanger with a vacuum cleaner or other cleaning device to remove the deposits.

Cleaning and servicing of the secondary heat exchanger 18 is simplified due to the removable burner 14 and removable second flue housing 24, which acts as an openable access cover. The second flue housing 24 can be part of, or independent of, the secondary heat exchanger 18. The second flue housing/access cover 24 is independent of the front access cover 26 of the primary heat exchanger 16. The first flue gas galleries 38 of the secondary heat exchanger 18 can then be easily accessed through the front cover of the boiler assembly 10.

IE0407In the above-described arrangement, the heat transfer plates 36 of the secondary heat exchanger 18 are partly arcuate in a transverse direction. This enables the first hot flue gas galleries 38 to have partly concave walls, as can be seen in Figure 4. The concavity of the walls increases the gallery strength and rigidity when subjected to pressurised flow of the heating liquid.

An alternative to‘ concave gallery walls is the formation of transverse corrugations along the longitudinal extent of the plates. This also increasesgallery strength and rigidity, while also increasing the available heat transfer area between the heating liquid and the hot flue gas.

A further advantage of using rectangular galleries is that baffle elements, typically in the form of plates (not shown), can be easily inserted, allowing greater heat transfer and thus increased efficiency. The baffle elements may be solid, skeletal (i.e. defining a framework), or a combination thereof.

Additionally, the use of rectangular galleries reduces pressure differentials across the secondary heat exchanger, allowing increased flue gas velocity and desirable turbulence through the secondary heat exchanger. This results in improved heat transfer between the flue gas and the heating liquid.

Fifteen flrst flue gas galleries and fourteen second heating liquid galleries are provided. lEO40793 l3 The secondary heat exchanger can be positioned on its side. In this case, the heating liquid flow through the second galleries will be substantially horizontal.

The heating liquid inlet may be formed in a side of the secondary heat exchanger housing adjacent to the lower surface, instead of in the lower surface; and the outlet may be formed in a side adjacent to the upper surface, instead of in the upper surface.

The first galleries are separate from each other, and only communicate via the first and second flue housings. The second galleries are separate from each other and only communicate via the third galleries.

It is envisaged that the secondary heat exchanger could be formed as part of the primary heat exchanger, rather than being spaced apart. However, by arranging the secondary heat exchanger to be separate of the primary heat exchanger enables simple replacement if a fault occurs.

The first flue housing could be formed as an integral part of the secondary heat exchanger, as an integral part of the primary heat exchanger, or as a completely independent part which is connected between the primary and secondary heat exchangers.

Preferably, the secondary heat exchanger is formed from stainless steel. The stainless steel can be brazed or welded. However, any material which is able to |EO40793 withstand the operating pressure of the heating liquid and which does not tend to corrode could be used.

The secondary heat exchanger can be mounted in any suitable position or orientation within the boiler body, for example on, or adjacent to, one side of the primary heat exchanger, or with the first galleries oriented to extend upwardly or generally vertically. However, it is preferable that the flue gas channels extend in a direction towards the access cover of the boiler body.

It is thus possible to provide a secondary heat exchanger which is extremely compact, whilst promoting heat exchange, and which reduces the tendency for corrosion. It is also possible to provide an easy-access secondary heat exchanger which is simple to clean and maintain. It is further possible to not only obtain at least a Sedbuk B efficiency rating by the inclusion of a secondary heat exchanger in an existing boiler assembly, without requiring a re-design of the boiler assembly layout or components nor enlargement of the boiler body, but it is also possible to provide a boiler assembly which has a secondary heat exchanger that can be fully accessed through the front cover of the boiler assembly.

The embodiments described above are given by way of examples only, and other modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims. For example, access to the interior of the boiler body can be achieved through the top panel, or any of the other panels, instead of the front panel; the burner can be up or side firing, and, IE0/907 as such, can be mounted beneath the primary heat exchanger or on one side; and the flue gas and heating liquid can be any suitable fluids.

Claims (20)

1. A secondary heat exchanger for a boiler assembly, the secondary heat exchanger comprising a housing having a first part and a second part independent of the first part, the first part defining a first flow path for a first fluid, and the second part defining a second flow path for a second fluid, the first part having at least two distinct first galleries and the second part having a second gallery which extends between the two first galleries of the first part, the second gallery being oriented so that, in use, the second fluid flows generally vertically in the second gallery.

2. A secondary heat exchanger as claimed in claim 1, wherein the first part of the secondary heat exchanger housing has at least three first galleries and the second part has at least two second galleries which extend between the first galleries.

3. A secondary heat exchanger for a boiler assembly, the secondary heat exchanger comprising a housing having a first part and a second pait independent of the first part, the first part defining a first flow path for a first fluid, and the second part defining a second flow path for a second fluid, the first part having three distinct first galleries and the second part having two distinct second galleries interposed between the first galleries.

4. A secondary heat exchanger as claimed in claim 3, wherein the second galleries are oriented so that, in use, the second fluid flows generally vertically in the second galleries.

5. A secondary heat exchanger as claimed in any one of the preceding claims, wherein the first galleries are separate from each other. 20 lE040793 l7

6. A secondary heat exchanger as claimed in any one of the preceding claims, wherein the second galleries are separate from each other.

7. A secondary heat exchanger as claimed in any one of the preceding claims, wherein the first and second galleries are parallel or substantially parallel to each other.

8. A secondary heat exchanger as claimed in any one of the preceding claims, wherein the parts of the first and second flow paths defined by the first and second galleries are transverse to each other.

9. A secondary heat exchanger as claimed in any one of the preceding claims, wherein the first and second galleries are formed by heat transfer plates.

10. A secondary heat exchanger as claimed in any one of the preceding claims, wherein adjacent first and second galleries are defined, in part, by a common heat transfer plate.

11. A secondary heat exchanger as claimed in any one of the preceding claims, wherein the first galleries are oriented so that, in use, the first fluid flows generally horizontally in the first galleries.

12. A secondary heat exchanger as claimed in any one of the preceding claims, wherein the first galleries are readily accessible to facilitate cleaning.

13. A secondary heat exchanger as claimed in any one of the preceding claims, further comprising a first access cover which is openable to provide access to the first galleries.

14. A secondary heat exchanger as claimed in claim 13, wherein the first access cover provides full and unhindered access to the first galleries.

15. |E0"l07l5. A secondary heat exchanger for a boiler assembly, the secondary heat exchanger comprising a housing having a first part and a second part independent of the first part, the first part defining a first flow path for a first fluid, and the second part defining a second flow path for a second fluid, the first part having at 5 least two distinct first galleries and the second part having a second gallery which extends between the two first galleries of the first part, each first gallery being solely formed by two inter—connected heat transfer plates.

16. A secondary heat exchanger as claimed in any one of the preceding claims, wherein the first galleries have a rectangular or substantially rectangular transverse l0 cross~section to promote ease of cleaning.

17. A secondary heat exchanger as claimed in any one of the preceding claims, wherein sides of the first galleries are, at least in part, concave.

18. A secondary heat exchanger as claimed in any one of the preceding claims, wherein sides of the first galleries include corrugations to promote rigidity and heat 15 exchange.

19. A secondary heat exchanger as claimed in any one of the preceding claims, further comprising one or more baffle elements insertable into the first galleries.

20. A secondary heat exchanger substantially as hereinbefore described with reference to