GB2178513A

GB2178513A - Heat recovery units for boilers

Info

Publication number: GB2178513A
Application number: GB08514263A
Authority: GB
Inventors: William Robertson Cunn Erskine; David Missions
Original assignee: ORIGINAL FUEL CO Ltd
Current assignee: ORIGINAL FUEL CO Ltd
Priority date: 1985-06-06
Filing date: 1985-06-06
Publication date: 1987-02-11
Also published as: GB8514263D0

Abstract

A heat recovery unit for installation in the flue of a domestic boiler includes an outer jacket 10 having an upper inlet 13 and a lower outlet 14 for water returning to the boiler. The jacket bounds a plurality of discrete open-ended stainless steel tubes 11 through which the flue gases flow. Accordingly water is progressively heated as it passes from the inlet 13 to the outlet 14, the walls of the tubes 11 being continuously heated by the waste heat in the redundant flue gases flowing upwards from the boiler. The flow of water is controlled by the arrangement of the tubes 11 in rows and the baffles B1, B2, B3. <IMAGE>

Description

SPECIFICATION Heat recovery units This invention relates to a heat recovery unit for a domestic boiler.

It is known to fit a heat recovery unit in the flue of a boiler so that cold water diverted from the return pipe of the heating system is preheated by the waste heat contained in the redundant flue gases before returning to the boiler.

A problem associated with such units is that of removing the soot which inevitably accumulates over a period of time. The units are generally difficult to clean because they normally include water-carrying coils or transverse pipes located in the path of the hot gases flowing upwardly through the flue. These coils or pipes also undesirably restrict the flow of gas along the flue. Corrosion of the coils or pipes is also a problem, particularly in units fitted to oil-fired boilers if the amount of heat extracted from the flue gases is substantial and the temperature of the gases falls to the acid dew point. Accumulation of soot may intensify this corrosion problem.

In a heat recovery unit according to the present invention the flue gases from a domestic boiler are passed through a plurality of discrete open-ended passages located in the path of water returning to the boiler. The passages are preferably straight passages aligned with the direction in which the flue gases are flowing so that a substantially unrestricted flow of gas passes through the unit. The combined cross-sectional area of the passages is preferably substantially equal to the cross-sectional area of the boiler flue.

A unit embodying the invention is therefore simple to clean and maintain, while also providing an effective and reliable heat transfer mechanism which can be easily controlled to ensure that the correct amount of heat is extracted from the flue gases.

The passages are preferably arranged within a bounding wall of the unit so that the water is constrained to follow a predetermined path around the outside of the passages between an inlet to an outlet.

For example, at least some of the passages may be grouped into discrete rows or columns forming successive barriers to the flow of water from the inlet to the outlet, the water being permitted to flow around only one end of each barrier.

By way of example only, an embodiment of the invention is illustrated in the accompanying drawings in which: Figure 1 is a plan view of a heat recovery unit for fitting in the flue of a domestic boiler, and Figure 2 is a sectional elevation on line X-X in Fig. 1.

Referring to these drawings, the heat recovery unit consists of a cylindrical jacket 10 bounding five discrete rows R1 to R5 of thinwalled stainless steel tubes 11, the tubes in each row being bonded or welded to one another. The top and bottom end of the tubes 11 are welded to respective discs 12 having slots 16 aligned with the respective rows or tubes, the circumference of the discs in turn being welded to the tubular jacket 10 so that the tubes are fixed within the jacket.

The jacket 10 also includes an upper inlet 13 and a lower outlet 14 through which water returning to the boiler enters and leaves the jacket. The inlet and outlet comprise screwthreaded ports for receiving respective screwthreaded connectors which engage the water return pipe of the heating system at respective upstream and downstream locations.

The jacket 10 is fitted into the flue of a domestic boiler by respective top and bottom connectors, only the bottom connector 15 being illustrated in the drawings. To maintain a constant cross-sectional area for the flue gases, the combined cross-sectional area of the twenty seven tubes 11 substantially equals the cross-sectional area of the flue. Accordingly, the diameter of the tubular jacket 10 exceeds the diameter of the flue, and the connector 15 therefore includes an upper portion 15a having a diameter substantially equal to that of the jacket 10, and a lower portion 15b having a reduced diameter substantially equal to that of the flue.

The flow of water within the jacket 10 is illustrated by the arrows in Fig. 1, the flow being controlled by the rows of tubes 11 and by additional baffles Bl, B2 and B3. The water initially flows on both sides of the tubes in row R1, performs a first U-turn around the left hand end of row R2 and flows back between rows R2 and R3. It then performs a second U-turn around the right hand end of row R3 and flows back between rows R3 and R4 before performing a final U-turn around the left hand end of row R4 and passing out on both sides of row R5 through the outlet 14.

Accordingly water is progressively heated as it passes from the inlet 13 to the outlet 14, the walls of the tubes 11 being continuously heated by the waste heat in the redundant flue gases flowing upwards from the boiler.

1. A heat recovery system wherein waste heat in the flue gases from a boiler is recovered by passing the gases through a plurality of discrete open-ended passages disposed in the boiler flue, the external surfaces of the passages being disposed in the path of water returning to the boiler such that the water is preheated.

2. A system according to claim 1 wherein the passages are substantially straight passages aligned with the direction in which the flue gases are flowing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Heat recovery units This invention relates to a heat recovery unit for a domestic boiler. It is known to fit a heat recovery unit in the flue of a boiler so that cold water diverted from the return pipe of the heating system is preheated by the waste heat contained in the redundant flue gases before returning to the boiler. A problem associated with such units is that of removing the soot which inevitably accumulates over a period of time. The units are generally difficult to clean because they normally include water-carrying coils or transverse pipes located in the path of the hot gases flowing upwardly through the flue. These coils or pipes also undesirably restrict the flow of gas along the flue. Corrosion of the coils or pipes is also a problem, particularly in units fitted to oil-fired boilers if the amount of heat extracted from the flue gases is substantial and the temperature of the gases falls to the acid dew point. Accumulation of soot may intensify this corrosion problem. In a heat recovery unit according to the present invention the flue gases from a domestic boiler are passed through a plurality of discrete open-ended passages located in the path of water returning to the boiler. The passages are preferably straight passages aligned with the direction in which the flue gases are flowing so that a substantially unrestricted flow of gas passes through the unit. The combined cross-sectional area of the passages is preferably substantially equal to the cross-sectional area of the boiler flue. A unit embodying the invention is therefore simple to clean and maintain, while also providing an effective and reliable heat transfer mechanism which can be easily controlled to ensure that the correct amount of heat is extracted from the flue gases. The passages are preferably arranged within a bounding wall of the unit so that the water is constrained to follow a predetermined path around the outside of the passages between an inlet to an outlet. For example, at least some of the passages may be grouped into discrete rows or columns forming successive barriers to the flow of water from the inlet to the outlet, the water being permitted to flow around only one end of each barrier. By way of example only, an embodiment of the invention is illustrated in the accompanying drawings in which: Figure 1 is a plan view of a heat recovery unit for fitting in the flue of a domestic boiler, and Figure 2 is a sectional elevation on line X-X in Fig. 1. Referring to these drawings, the heat recovery unit consists of a cylindrical jacket 10 bounding five discrete rows R1 to R5 of thinwalled stainless steel tubes 11, the tubes in each row being bonded or welded to one another. The top and bottom end of the tubes 11 are welded to respective discs 12 having slots 16 aligned with the respective rows or tubes, the circumference of the discs in turn being welded to the tubular jacket 10 so that the tubes are fixed within the jacket. The jacket 10 also includes an upper inlet 13 and a lower outlet 14 through which water returning to the boiler enters and leaves the jacket. The inlet and outlet comprise screwthreaded ports for receiving respective screwthreaded connectors which engage the water return pipe of the heating system at respective upstream and downstream locations. The jacket 10 is fitted into the flue of a domestic boiler by respective top and bottom connectors, only the bottom connector 15 being illustrated in the drawings. To maintain a constant cross-sectional area for the flue gases, the combined cross-sectional area of the twenty seven tubes 11 substantially equals the cross-sectional area of the flue. Accordingly, the diameter of the tubular jacket 10 exceeds the diameter of the flue, and the connector 15 therefore includes an upper portion 15a having a diameter substantially equal to that of the jacket 10, and a lower portion 15b having a reduced diameter substantially equal to that of the flue. The flow of water within the jacket 10 is illustrated by the arrows in Fig. 1, the flow being controlled by the rows of tubes 11 and by additional baffles Bl, B2 and B3. The water initially flows on both sides of the tubes in row R1, performs a first U-turn around the left hand end of row R2 and flows back between rows R2 and R3. It then performs a second U-turn around the right hand end of row R3 and flows back between rows R3 and R4 before performing a final U-turn around the left hand end of row R4 and passing out on both sides of row R5 through the outlet 14. Accordingly water is progressively heated as it passes from the inlet 13 to the outlet 14, the walls of the tubes 11 being continuously heated by the waste heat in the redundant flue gases flowing upwards from the boiler. CLAIMS

3. A system according to claim 1 or claim 2 in which the combined cross-sectional area of the passages is substantially equal to the cross-sectional area of the boiler flue.

4. A heat recovery unit for installation in the flue of a boiler, the unit comprising an outer jacket having an inlet and an outlet for water being fed to the boiler, the jacket bounding a plurality of discrete open-ended passages through which, in use, the flue gases flow.

5. A unit according to claim 4 wherein at least some of the passages are grouped into discrete rows and/or columns providing successive barriers to the flow of water whereby the water is constrained to follow a predetermined path between the inlet and the outlet.

6. A unit according to claim 4 or claim 5 wherein the passages comprise substantially straight passages extending from top to bottom of the jacket, and wherein the top and bottom of the jacket, and wherein the top and bottom of the jacket are closed by respective members having openings communicating with the respective opposite ends of the passages.

7. A heat recovery unit substantially as herein described with reference to the accompanying drawings.