GB2156954A

GB2156954A - Heat exchanger

Info

Publication number: GB2156954A
Application number: GB08408255A
Authority: GB
Inventors: Sydney Cairns
Original assignee: MID ULSTER ENGINEERING
Current assignee: MID ULSTER ENGINEERING
Priority date: 1984-03-30
Filing date: 1984-03-30
Publication date: 1985-10-16
Also published as: GB8408255D0

Abstract

A heat exchanger (1) adapted to be installed between an existing domestic or commercial boiler, to remove heat from the boiler flue gases to the extent that their temperature drops below their dew point, has its outlet port (17) directly above its inlet port (16), a canopy (24) above the inlet port to deflect corrosive condensate into a receptacle (21) surrounding the inlet port and a plurality of heat exchange surfaces in the form of blanked-off pipes (20) cantilevered forwards from the rear face of the heat exchanger cavity. The zig-zag upward flow of the flue gases over the pipes tends to keep them clear of deposited soot and, in any case, the pipe surfaces are rendered accessible for cleaning by detaching the front wall (18) of the cavity. <IMAGE>

Description

SPECIFICATION Heat Exchanger This invention relates to a heat exchanger for location on top of an existing domestic or commercial boiler, for the gaseous products of combustion of a domestic or commercial combustion boiler, before the gases are discharged into the boiler flue. The heat exchanger comprising a plurality of waterways to carry heat-exchange liquid to be heated by the flue gases as they pass up flueways between the waterways, the heat exchange surfaces separating the waterways and flueways being adapted to withstand attack by the liquid products of condensation of the flue gases.

It has been proposed to locate a heat exchanger on top of a domestic or commercial wet central heating combustion boiler, which reduces the temperature of the flue gases to below their dew point, before entering the boiler flue, by heating the heat exchange liquid of the system in the waterways of the heat exchanger, as it flows to the central heating boiler. The products of condensation of the flue gases within the heat exchanger include sulphuric acid, so that special measures need to be taken to prevent corrosion. In the previous proposal of EP 57095A, dripping of corrosion products into the boiler below the flue is avoided by causing the flue gases to flow up, over, and then downwardly past what can be termed a "weir" to the bottom of a heat exchanger cavity.Then, as the flue gases rise through the waterways of the heat exchanger, and corrosive condensation products are collected in a stainless steel tray in the base of the heat exchange cavity, for disposal as convenient.

As fuel prices continue to increase, there is a need to provide an equivalent heat exchanger in the vertically extending flues of conventional boilers and in boilers already installed and in use. In these circumstances, it is not feasible to provide a heat exchanger of the above-described, up-and-over design, because the inlet portforflue gases is displaced laterally from the outlet port for the gases.

What is needed between an existing boiler and flue is a heat exchanger wherein the inlet port and outlet port are arranged one above the other and in line with each other.

Accordingly, the invention provides a heat exchanger of the above-identified form having an inlet port in its base surface, an outlet port in its top surface and heat exchange surfaces above the inlet port, the heat exchanger further including a canopy spaced above the inlet port and beneath the heat exchange surfaces, adapted to channel condensate from the heat exchange surfaces laterally beyond the periphery of the inlet port, to be collected in a receptacle surrounding the inlet port, both the upper surfaces of the canopy and receptacle being resistant to corrosion by the products of condensation of the flue gases.

The canopy can be planar, but it is preferred that it should be pitched or have the form of a wide angled cone, with a vertex aligned with the centre of the inlet port. It is convenient to fabricate the canopy and receptacle from stainless steel.

For a better understanding of the invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a transverse vertical section of a heat exchanger; Figure 2 is a transverse vertical section perpendicular to that of Figure 1 and along the line Il-Il in Figure 1; and Figure 3 is a plan view of the heat exchanger.

The heat exchanger cavity 10 is defined on three sides by the hollow walls of a tank 11 which are adapted to contain heat exchange liquid which flows through the walls from either a lefthand inlet port 12 or a righthand inlet port 13 to one of the outlet ports 14 and 15. Flue gases flow through the cavity 10 from an inlet port 16to an outlet port 17 directly above it. Usually, these flue gas ports will be of diameter 5 inches or 6 inches, depending upon what is required for the boiler being served. The front of the cavity is defined by a detachable plate 18 which does not include any waterways.

Bridging the cavity between the front and rear walls of the tank 11 are nine tubes 20 which are blanked off at their front ends and which, when the heat exchanger is in use, are filled with water. This is heated by the flue gases flowing around the exterior of the pipes 20. The pipes 20 are sized (here 3" diameter) and spaced such as to reduce the temperature of the flue gases from a temperature of around 300"C to a temperature of around 10000. The condensation on the pipes 20 which results from the fall in temperature is collected in a stainless steel tray 21 surrounding the upstanding rim 22 of the inlet port 16. Condensate is drained from the tray 21 by a drain 23, the corrosive condensate being channelled from the drain 23 to a safe receptacle or location external of the building in which the boiler is housed.

Above the inlet port 16 is a canopy 24 which takes the form of a stainless steel plate which is pitched along a fold axis 25 directly above a diameter of the circular inlet port 16. The canopy 24 is circular and of slightly larger diameter than the port 16 so that its rim 26 extends radially some way beyond the upstanding rim 22 of the port 16. Thus, any condensate falling on to the canopy 24 from the pipes 20 above it will be channelled by the canopy 24 clear of the inlet port 16 into the tray 21.

A particular advantage has been found with the arrangement of pipes 20, relative to arrangements with flat, planar, spaced waterways parallel with one of the vertical walls of the cavity which allow flue gases to flow in a straight line from the bottom to the top of the heat exchange cavity. This advantage is that the imposition of sideways velocity on the flue gases as they zig-zag past the pipes up the heat exchange cavity has been found to have a "scrubbing" effect on the external surfaces of the pipes 20 which tends to keep them clear of soot deposit.

In the particularly preferred arrangement illustrated, removal of the front plate 18 permits easy maintenance of the components within the heat exchanger cavity. It will be appreciated that all or substantialiy all of the surface area of all of the pipes 20 are accessible for attention, simply by removal of this one wall of the cavity.

Claims

1. A heat exchanger for location on top of an existing domestic or commercial boiler, for the gaseous products of combustion of a domestic or commercial boiler, before the gases are discharged into the boiler flue, the heat exchanger comprising a plurality of waterways to carry heat-exchange liquid to be heated by the flue gases as they pass up flueways between the waterways, the heat exchange surfaces separating the waterways and flueways being adapted to withstand attack by the liquid products of condensation of the flue gases, characterised by an inlet port in a base surface of the heat exchanger, an outlet port in a top surface thereof and heat exchange surfaces above the inlet port, and by a canopy spaced above the inlet port and beneath the heat exchange surfaces, adapted to channel condensate from the heat exchange surfaces laterally beyond the periphery of the inlet port, to be collected in a receptacle surrounding the inlet port, both the upper surfaces of the canopy and receptacle being resistant to corrosion by the products of condensation of the flue gases.

2. A heat exchanger as claimed in claim 1, wherein the canopy is planar.

3. A heat exchanger as claimed in claim 1, wherein the canopy is pitched.

4. A heat exchanger as claimed in claim 1, wherein the canopy has the form of a wide angled cone, with a vertex aligned with the centre of the inlet port.

5. A heat exchanger as claimed in any one of the preceding claims, wherein the canopy and receptacle are fabricated from stainless steel.

6. A heat exchanger as claimed in any one of the preceding claims, wherein the heat exchange surfaces between the waterways and flueways are cantilevered from one wall of a heat exchanger cavity as far as the opposite wall of the cavity, which is detachable for giving attention to the heat exchange surfaces.

7. A heat exchanger as claimed in any one of the preceding claims, wherein the heat exchange surfaces define flueways which exhibit a zig-zag path from the bottom to the top of the heat exchange cavity.

8. A heat exchanger as claimed in claim 7, wherein the heat exchange surfaces are constituted by a plurality of pipes cantilevered from a rear wall of the heat exchange cavity and blanked off at the front of the cavity.

9. A heat exchanger substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.