GB2114275A

GB2114275A - Boiler

Info

Publication number: GB2114275A
Application number: GB08302120A
Authority: GB
Inventors: Denis Henry Desty
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1982-01-30
Filing date: 1983-01-26
Publication date: 1983-08-17
Also published as: GB2114275B; GB8302120D0

Abstract

A boiler has a downwardly fired burner 1 the flue gases from which pass over a heat exchanger 2 capable of extracting heat from the flue gases and transferring it to a working fluid. A plenum chamber 8 beneath the heat exchanger collects flue gas condensate, the condensate then being removed along a run-off pipe 9. <IMAGE>

Description

SPECIFICATION Boiler The present invention relates to boilers and more particularly to boilers for domestic or industrial heating systems.

Conventional water heating boilers using gas or oil fired burners generally have efficiencies of up to 75%. A significant amount of heat loss occurs in the flue gases as the boilers are designed to operate at a sufficiently high temperature to prevent condensation of the flue gas water content in the heat exchanger which otherwise causes operating and corrosion problems.

Thus according to the present invention there is provided a boiler comprising a burner having an air supply and a fuel supply, the burner being fired downwardly, and a heat exchanger for extracting heat from the burner flue gas and transferring the heat to a working fluid, there also being a plenum chamber for collecting flue gas condensate and means for removal of the condensate.

The flat short uniform flames typical of the burners claimed in UK patent number 1 205432 (a) allow downward firing of the burner, (b) facilitate construction of a compact boiler and (c) give a more uniform temperature across the inlet face of the heat exchanger. The downward firing avoids flue gas condensation running back onto the burner as in the case of upward firing burners. This tends to reduce corrosion, malfunctioning of the burner and allows easier drain-off of condensation.

The fuel supply is usually a fuel gas, e.g.

natural gas; however, a liquid fuel, e.g. kerosene may possibly be used.

The heat exchanger is of a conventional suitable type and the working fluid is preferably water. The heat exchanger preferably has fins and most preferably the lower edges of the fins are serrated to assist condensate runoff into the plenum chamber and to reduce blockage by condensate trapped between the fins.

The plenum chamber preferably tapers in cross-sectional area towards an outlet at its base and is located beneath the heat exchanger. The plenum chamber is linked to a condensate disposal means such as a run-off pipe.

The invention will now be described by way of example only and with reference to Figs. 1 to 3 of the accompanying drawings.

Fig. 1 is a perspective view of a boiler according to the invention which is partially cut away to show the interior of the boiler.

Fig. 3 is a diagrammatic end view of the fins of the boiler heat exchanger. Fig. 2 is a perspective view of a burner element of the boiler.

A boiler for supplying hot water to a heating system has been developed to operate at up to 35,000 Btu/hour (10 kilowatts), with an efficiency of approximately 88% on a hot water return. The boiler is shown in Fig. 1 and includes a burner 1 and a finned heat exchanger 2.

The burner 1 of the matrix type comprises a fuel chamber through which a plurality of combustion air tubes or passageways pass.

The fuel is supplied to the chamber by an inlet line. The air tubes 3 are of rectangular or square cross-section. The burner 1 is of the diffusion flame type and the fuel emerges into the combustion zone 4 through fuel outlet holes 1 2. The outlet holes 1 2 are of circular crosssection and they are arranged so that there is one fuel outlet per side of each square cross section air passageway.

Downstream of the burner is a finned heat exchanger unit 2 carrying pipes 5 for hot water outlet. The heat exchanger 2 is heated by the hot flue gases passing downwards from the burner 1.

A plenum chamber 8 which tapers towards its outlet is bolted to the burner housing beneath the heat exchanger 2. The base of the plenum chamber 8 has a run-off pipe 9 connected to a drain (not shown). The materials of construction are chosen to be corrosion resistant.

The various sections are surrounded by a main housing 6 which may contain a viewing window (not shown) for observing the performance of the burner flame.

A fan in a housing 7 is bolted onto the side of the main housing 6 for supplying inlet air from a flue terminal to the burner 1.

Fig. 3 shows an end view of the fins 11 of heat exchanger 2 showing alternating serration of the lower edges of adjacent fins. The serration of the fins 11 assist condensate runoff in the plenum chamber 8 and reduces blockage of gas flow by condensate trapped between adjacent fins of the heat exchanger.

In use of the boiler, fuel gas is fed at a low rate to the burner 1 via the inlet and mixes with air from fan 7. The gas is ignited to form a pilot diffusion flame on the lower face of burner 1. This flame is then proved, i.e.

checked that ignition has occurred. Then normal operating fuel gas flow is supplied to the burner. The flue gases pass into heat exchanger 2 thereby heating an external water load system. The condensate from the flue gases runs off the heat exchanger 2 and into the plenum chamber 8. The condensate is then drained off via the run-off pipe 9. The flue gases then pass to the flue terminal at the rear of the boiler via an outlet pipe 10 which is coaxial with the air inlet.

The boiler start up sequence is designed to be operated automatically. Thus a timer may be used to activate the system and then thermostatic operation causes a sequence of on-off cycling to occur to maintain the desired boiler water temperature.

Claims

1. A boiler comprising a burner having an air supply and a fuel supply, the burner being downwardly fired and a heat exchanger for extracting heat from the burner flue gas and transferring the heat to a working fluid, there being a plenum chamber for collecting flue gas condensate and means for removal of the condensate.

2. A boiler according to claim 1 in which the heat exchanger has fins adapted to assist condensate run off into the plenum chamber.

3. A boiler according to claim 2 in which the lower edges of the fins are serrated.

4. A boiler according to any one of claims 1 to 3 in which the plenum chamber tapers in cross sectional area towards an outlet at its base.

5. A boiler according to any of the preceding claims in which the downwardly firing burner is a diffusion flame burner.

6. A boiler according to claim 5 in which the downward firing burner comprises a plurality of air passageways through a fuel chamber, the fuel chamber having fuel outlets adapted to convey fuel and air passing through the air passageways to a combustion zone adjacent to the lower surface of the burner.

7. A boiler according to claim 6 in which the bore of each combustion air passageway has a cross sectional area of 0.01 - 1.0 cm2 where the passageway opens into the combustion zone and the bores of the combustion air passageways account for at least 25% of the surface area of the burner adjacent to the combustion zone.

8. A boiler according to claims 6 or 7 in which the combustion air passageways have a square or circular cross section.

9. A boiler according to any one of claims 6 to 8 in which the combustion air passageways are arranged with their axes parallel to one another.

10. A boiler as hereinbefore described and with reference to the accompanying drawings.