GB2415032A

GB2415032A - High efficiency boiler with flue gas heat recovery

Info

Publication number: GB2415032A
Application number: GB0414786A
Authority: GB
Inventors: Grosso Lamberto Del
Original assignee: BAXI SpA
Current assignee: BAXI SpA
Priority date: 2004-06-11
Filing date: 2004-07-01
Publication date: 2005-12-14
Anticipated expiration: 2024-07-01
Also published as: RO123007B1; GB2415032B; GB0414786D0; ITMI20041181A1; IE20040439A1

Abstract

The boiler includes a deflector means 13 positioned above a primary heat exchanger 3 to direct and distribute combustion flue gases onto and over the primary heat exchanger before they are drawn off by a fan 7. The deflector has a body 15 with a first portion 16 positioned at an aperture 6 for the fan. A second portion 17 is disposed above a large surface part of the primary heat exchanger. The boiler includes a burner, casing, conduit 8, secondary heat exchanger 9, and flue gas discharge 10.

Description

24 1 5032

HIGH EFFICIENCY BOILER WITH FLUE GAS HEAT RECOVERY

The present invention relates to a boiler in accordance with the

introduction to the main claim.

High efficiency boilers of both conventional and condensation type are currently available. These latter, by suitable heat transfer between the combustion products or flue gases and the thermovector fluid or water "treated" in the boiler, recover the sensible heat of the flue gases and the latent heat of vaporization of the steam contained in said flue gases and reuse this energy (which would otherwise be lost by the forced expulsion of the flue gases) to heat the water or thermovector fluid. This enables seasonal efficiencies to be achieved which are very high, and higher than those obtainable in a high efficiency boiler of traditional type.

Condensation boilers are however very sophisticated and costly both to acquire and to maintain.

The present invention relates to a boiler of conventional type. With reference to this latter type of boiler, it is known to construct a boiler presenting a burner with an overlying heat exchanger through which the thermovector fluid or water circulates to reach at least one radiator element positioned in an environment to be heated. The burner and said heat exchanger are preferably contained In a casing (within the boiler shell) having its top connected to a fan to draw off the combustion flue gases to be fed to a stack.

To recover the energy contained In these flue gases (delving from the aforesaid flue gas sensible heat and latent heat of vaporization), it is known to construct boilers of the aforesaid type presenting a first heat exchanger positioned above the burner, and a second heat exchanger, external to the said casing downstream of the fan, through which the flue gases pass before their expulsion from the boiler. In this secondary heat exchanger heat transfer takes place between the flue gases and the water returning from the radiator element. The water from the secondary heat exchanger is fed to the primary heat exchanger.

By virtue of this arrangement, the heat obtained in the secondary heat exchanger downstream of the prfrnary results in cooling of the flue gases to a temperature determining condensation of the water vapour present therein; this process also enables the heat of condensation of the steam to be recovered and hence increases the boiler performance in terms of efficiency, with a resultant substantial energy saving.

However to obtain this energy recovery, the boiler/radiator "system" has to operate with a temperature lower than usual and possibly lower than the flue gas condensation temperature (which depends on the type of fuel and the excess air present). For this reason, and as boilers of the aforesaid type usually have their primary heat exchanger of copper, with a temperature close to or lower than the flue gas dew point this heat exchanger can undergo oxidation, which is accentuated by the combustion products passing therethrough. It therefore requires frequent maintenance, with possible replacement in the worst cases.

An object of at least the preferred embodiments of the present invention is to provide a boiler of traditional type with flue gas energy recovery at the primary heat exchanger, which represents an improvement over similar known boilers.

Another object of those embodiments of the invention is to provide a boiler of the aforesaid type in which the said heat exchanger oxidation present in known boilers is at least considerably limited.

Another object of those embodiments is to provide a boiler of the stated type achieving high efficiency though of limited cost, which is certainly less than that that of condensation boilers.

A further such object is to provide a boiler of the stated type which is of simple construction.

The invention provides a boiler of traditional type comprising a burner and an overlying primary heat exchanger, all enclosed in a casing from which a fan is arranged to draw off the combustion flue gases and direct them towards a secondary heat exchanger and from there to discharge, the heat exchangers being adapted to heat water or other thermovector fluid which in operation is circulated through the boiler, characterized in that within the casing enclosing the burner and the primary heat exchanger there is positioned, above this latter, deflector means to direct and distribute the combustion flue gases onto and over the primary heat exchanger before they are drawn off by the fan, whereby to assist transfer of sensible heat from the flue gases and of the latent heat of vaporization of the steam contained in said flue gases, to the water or other thermovector fluid.

Some preferred but optional features are set out in the subordinate claims.

The present invention will be more apparent from the accompanying drawing, which is provided by way of non-limiting example and in which: Figure 1 is a perspective view of a boiler according to the invention; Figure 2 is an enlarged view of a portion of the boiler of Figure 1; Figure 3 is a perspective view of a part of the boiler of Figure 1; Figure 4 is a perspective view from below of the boiler part of Figure 3; Figure 5 is a plan view from above of a variant of the boiler part of Figure 3.

With reference to said figures, these show a boiler 1 of traditional type comprising a burner 2 and a primary heat exchanger 3; this burner and said head exchanger are enclosed in a usual casing 4 presenting a top 5 provided with an aperture or through hole 6 at which a usual fan 7 is disposed to draw off the combustion flue gases generated within the casing 4. The fan 7 is preferably of the "modulating" type able to regulate its r.p.m. on the basis of the flow of fuel (for example gas) to the burner 2. This increases the boiler yield/efficiency.

The primary heat exchanger 3 is connected to a secondary heat exchanger 9 by a conduit 8. A thermovector fluid (eg. water) passes on its return from at least one usual radiator element located in an environment heated by the boiler 1, firstly through the secondary heat exchanger 9, then via conduit 8 to the primary heat exchanger 3 and thence back to the radiator elements. The combustion flue gases pass through the secondary heat exchanger 9 directed towards a discharge 10 connected in known matter to a stack for discharging said flue gases to the outside.

To recover the sensible heat of the flue gases and the latent heat of vaporization of the contained steam before they are drawn from the casing 4 by the fan 7, deflector means 13 are positioned between the top 5 of this casing and the primary heat exchanger 3 to direct and distribute the combustion flue gases onto and over said primary heat exchanger. Said means 13 are specifically arranged to distribute the flue gases in the opposite direction to that towards the fan 7, is. in a direction towards the inlet conduit 8 for the water to be heated in the heat exchanger.

In detail, the deflector means comprise a deflector body 15 rigid with the casing 4 and preferably with its top 5. In the embodiment of the figures, the body 15 comprises a first portion 16 positioned at the aperture or hole 6 for the fan 7, and a second portion 17 disposed above a large surface part of the primary heat exchanger 3. The first portion 16 comprises a large through hole 19 disposed at the hole 6 and provided at or close to a first end 20 of the first portion 16 of the deflector body 15. The second portion 17 of this latter comprises a second end 21 of the body 15, positioned in proximity to that end 24 of the primary heat exchanger to which the conduit 8 is connected, said second end 21 of the body 15 being distant and separated (ie. not fixed thereto) from the casing 4 or s from a wall 5A of the top 5 facing the burner 2. In this manner, between said end and said casing a second aperture 27 is formed for passage of the combustion flue gases, said aperture communicating with a space or recess 28 present between the deflector body 15 and the top 5 of the casing 4, said space 28 being in communication with the hole or aperture 6 for the fan 7.

To fix this latter to the top 5 of the casing 4, the deflector body 15 presents through holes 29 (in the figures these are provided in the first portion 16 and second portion 17 of said body) corresponding with holes provided in the top 5 about the hole 6, to receive usual members (for example screws) for fixing the fan 7 to the top 5.

The deflector body comprises lateral sidewalls 33 and 34 positioned at the larger opposing sides 3A, 3B of the primary heat exchanger.

Preferably these sidewalls present perimetral edges which are skew, i.e. not parallel, to each other (as in Figure 5). By this arrangement, the deflector body 15 frees a portion of the primary heat exchanger 3 present at its side 3A, to enable the combustion flue gases to transit between the casing 4 and that sidewall 34 towards the aperture or hole 6 by passing through said recess 28.

Because of the presence of the deflector body 15 above the primary heat exchanger 3, the combustion flue gases are not drawn directly towards discharge by the fan 7 but, by striking the body 15 in their path towards the hole 6, they are obliged to undergo distribution along said body and over a large surface of said heat exchanger before leaving the casing 4 through the hole 6. By virtue of this distribution said flue gases graze the heat exchanger 3 to transfer energy thereto, this energy being used to heat the entering water. The sensible heat of the flue gases is hence recovered, together with the latent heat of vaporization of the steam contained in said flue gases, so improving the performance of the boiler 1. In a variant of the invention (see Figure 5) the aperture 27 is divided into two portions 27a, 27b by a separator baffle 39 extending from the second end 21 of the deflector body 15, said baffle presenting a free end 42 bent over and fixed to the bent wall part 5A of the top 5 of the casing 4. In this manner, the chimney effect generated by the body 15 on the combustion flue gases directed to the recess 28 via the portions 27A and 27B of the aperture 27 is increased, hence drawing a larger quantity of flue gases towards the end 24 of the heat exchanger 3.

In another variant, the deflector body is completely flat.

Some variants of the invention have been described. Others are however possible (such as one in which the sidewalls 33 and 34 are parallel) while remaining within the scope of the present invention.

Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features.

Statements in this specification of the "objects of the invention" relate to preferred embodiments of the invention, but not necessarily to all embodiments of the invention falling within the claims.

The description of the invention with reference to the drawings is by way of example only. Reference numerals appearing in the claims are illustrative only and the claims shall be interpreted as if they are not present.

The text of the abstract filed herewith is repeated here as part of the specification.

A high efficiency boiler of traditional type comprises a burner and an overlying primary heat exchanger, all enclosed in a casing above which a fan draws off the combustion flue gases and directs them towards a secondary heat exchanger and from there to discharge, the heat exchangers receiving the thermovector fluid or water cooled by at least one radiator element located in an environment heated by said boiler, the heated fluid or water being fed from said heat exchangers to said radiator element in order to heat said environment. Within the casing enclosing the burner and the primary heat exchanger there are positioned, above this latter, deflector means to direct and distribute the combustion flue gases onto and over the primary heat exchanger before they are drawn off by the fan.

Claims

1. A boiler of traditional type comprising a burner (2) and an overlying primary heat exchanger (3), all enclosed in a casing (4) from which a fan (7) is arranged to draw off the combustion flue gases and direct them towards a secondary heat exchanger (9) and from there to discharge (10), the heat exchanger being adapted to heat water or other thermovector fluid which in operation is circulated through the boiler, characterized in that within the casing (4) enclosing the burner (2) and the primary heat exchanger (3) there are positioned, above this latter, deflector means (13) to direct and distribute the combustion flue gases onto and over the primary heat exchanger (3) before they are drawn off by the fan (7), whereby to assist transfer of sensible heat from the flue gases, to the water or other thermovector fluid.

2. A boiler as claimed in claim 1, characterized in that the deflector means (13) are an at least partially flat deflector body (15) positioned in proximity to and below the top (5) of the casing (4) enclosing the primary heat exchanger (3), said body being rigid with said casing (4) and presenting in a first end (20) at least one first aperture (19) to be positioned in proximity to an aperture (6) in said top (5), with which the flue gas draw-off fan (7) is associated.

3. A boiler as claimed in claim 1, characterized in that the deflector body (15) extends above at least part of the primary heat exchanger (3) in a direction facing a conduit (8) through which water enters said heat exchanger (3).

4. A boiler as claimed in claim 3, characterized in that the deflector body (15) presents at least one second aperture (27) in proximity to that end (21) thereof distant from the end (20) adjacent to the fan (7).

5. A boiler as claimed in claim 2, characterized in that said deflector body (15) comprises two portions (16, 17) at an angle to each other, a first portion (16) presenting said first end (20), the second portion (17) presenting said second end (21).

6. A boiler as claimed in claim 2, characterized in that the deflector body (15) is fixed to the top (5) of said casing (4).

7. A boiler as claimed in claim 2, characterized in that said deflector body (15) presents through holes (29) corresponding with holes (30) provided in said end (5) of the casing (4), to receive elements for fixing the fan (7) to this latter.

8. A boiler as claimed in claim 7, charactersed in that the through holes (29) are provided in the first (16) and in the second (17) portion of the deflector body (15).

9. A boiler as claimed in claim 2, characterized in that the deflector body (15) presents lateral sidewalls (33, 34) Joining together its first and second ends (20, 21), said lateral sidewalls (33, 34) having perimetral edges skew to each other.

10. A boiler as claimed in claim 9, characterized in that the skew edges bound the sidewalls of the second portion (17) of the deflector body (15).

11. A boiler as claimed in claim 1, characterized in that the fan (7) is of modulating type able to vary its r.p.m. on the basis of the fuel flow to the boiler (2).

12. A boiler substantially as herein described with reference to and as shown in the accompanying drawings.