WO1987000910A1

WO1987000910A1 - An arrangement in a heating boiler

Info

Publication number: WO1987000910A1
Application number: PCT/SE1986/000355
Authority: WO
Inventors: Rolf Dellrud
Original assignee: Komfortventilation Teknik Ab
Priority date: 1985-08-09
Filing date: 1986-08-06
Publication date: 1987-02-12
Also published as: SE8503766D0; SE449130B; SE8503766L

Abstract

A positive pressure boiler (2) for central heating purposes comprises a burner unit (3) provided with a fan (4). The burner unit is mounted on a furnace cover member (1) so as to extend into the furnace chamber of the boiler. The fan and adjacent parts of the burner unit are embraced by a casing (9) mounted externally on the cover member. The fan maintains a subpressure in the casing, and any combustion gases leaking from the boiler are collected in the casing and are recycled to the furnace chamber, via the burner unit.

Description

An arrangement in a heating boiler

Field of the Invention.

The present invention relates to an arrangement in central heating boilers of the kind which operate at positive pressures or overpressures, and which incorporate a furnace cover member having mounted thereon a fan-equippedburner assembly which extends through an aperture in the cover member and partially into the furnace chamber of the boiler, and of the kind which incorporates a plurality of convection tubes through which combustion gases pass for collection in a preferably annular space to which a stack pipe is connected and also of the kind which is provided with means for recycling any combustion gases which might leak from the furnace chamber back to the fan of the burner assembly.

Such positive pressure central-heating boilers, or overpressur boilers, have particular requirements placed thereon. For example, they must be fitted with reliable sealing devices and located at a given distance from an adjacent wall. Such boilers must also be inspected regularly, in order to establis the Quantities of any carbon monoxide produced, etc.

In these respects a positive pressure boiler of the kind de- scribed is at a serious disadvantage to boilers of the kind in which the pressure is maintained in the combustion chamber is lower than the boiler ambient pressure. The efficiency of a subpressure boiler, however, is normally lower than that of a positive pressure boiler. The main reason for this differen in boiler efficiency is because in the case of a positive pressure boiler, the fall in pressure in combustion and con¬ vection zones (e.g. in tube boilers, "sack boilers" etc.) is overcome with the aid of a fan located upstream or downstre of these zones. The aforesaid pressure drop is overcome by the fan provided in a boiler of the aforesaid kind, and the presence of a fan is therefore to be preferred, not least for economic reasons and in particular in respect of oil-fired and gas-fired systems, although encumbered with the aforementioned disadvantages and other drawbacks.

Background Prior Art.

SE-B-7310640-3 (Publication Number 376.962) (Ifδ AB) describes a positive pressure boiler of the aforedescribed kind which is designed to prevent combustion gases or smoke gases escaping from the boiler furnace into surrounding rooms or areas. According to this publication, however, it is also important, at the same time, to satisfy two further requirements, namely that the outer surface of the furnace cover member shall be kept at a low temperature, and that the burner assembly shall be capable of operating at the lowest possible sound levels. These two latter purposes are fulfilled primarily by the furnac cover member described in the publication and defined in the claims. The publication fails to suggest, however, an acceptab solution to the problem of preventing the leakage of gas in a reliable manner. The casing referenced 20 in the publication and carried by the cover member thus does not provide a seal against combustion gases escaping centrally in the region of the sleeve provided, referenced 10 in the publication. It is in this region, however, that the risk of leakage is greatest.

CH-A-442 593 (Berger) and DE-A1-32 36 822 (A. Brδtje GmbH) describes similar solutions encumbered with corresponding disadvantages.

The Object of the Invention.

One object of the present invention is to provide a boiler of the aforedescribed kind in which the drawbacks associated with known positive pressure boilers are eliminated, by enabling all combustion gases escaping from the cover member side and the burner side of the boiler to be recovered and recycled ba into the boiler, despite the fact that the pressure prevailin in the boiler itself is higher than the pressure of the sur¬ roundings.

Summary of the Invention.

The invention relates to an arrangement of the aforedescribed kind and is mainly characterized in that said recycling means includes a casing which is mounted on the cover member and embraces the fan and adjacent parts of the burner unit. The fan maintains in the casing a pressure which is lower than th pressure prevailing in the boiler and also lower than atmos- pheric pressure. Combustion gases escaping in the region are collected in the casing and recycled to the furnace chamber via the fan.

The invention ensures that all combustion gases escaping into the region of the cover member, including those gases which escape through the burner lead-through in the cover member - which is a critical location, since the positive pressure is highest at this point and consequently it is here that the greatest pressure difference with regard to atmospheric pres- sure lies - and the gases which escape peripherally around th cover member, are recovered and recycled to the furnace cham¬ ber.

A preferred embodiment of the arrangement is characterized in that the casing presents to the surroundings an opening which is intended for maintaining the desired subpressures within the casing.

The desired subpressure for a given operating condition of th burner (i.e. at a given burner fan air flow) can be achieved through suitable degrees of throttling in the opening. Accor ingly,the opening can be provided to this end with an adjustabl plate valve, a displaceable throttle plate or like valve means for facilitating the setting of the desired subpressure.

A further development of an arrangement according to the in¬ vention in which a further space, preferably annular space, is located externally of the aforesaid annular space and sealed with the aid of seal means is characterized in that the further space communicates with the interior of the casing through a channel extending through the cover member.

In order to eliminate the influence of thermal drive forces in this case, the subpressure in the annular chamber should reach at least 5Pa in relation to the surrounding atmosphere.

The throughflow area of the channel in relation to the leakage areas is preferably sufficiently large to create in the outer annular space a subpressure which is so adapted in relation to the ambient pressure that no leakage will occur past the afore- said seal.

In this respect, it has been found in practice that in order for the channel to have the correct area, the difference between the pressure prevailing in the annular chamber and the pressure externally of' the casing, i.e. the "drive pressure" should also be at least 5Pa.

Consequently, this means that subpressure in the suction box should be at least 10Pa.

Further characteristic features of the invention will be ap¬ parent from the following description of a number of embodiment of the invention. The description is made with reference to th accompanying drawings. Brief Description of the Drawings.

Figure 1 is a perspective, vertical view in section of a positive pressure boiler provided with an arrangement accord¬ ing to the invention.

Figure 2 is a vertical sectional view of the upper part of a boiler according to Figure 1.

Figure 3 is a vertical sectional view of a boiler which is a modified version of the boiler illustrated in Figures 1 and 2.

Description of Preferred Embodiments.

Figures 1 and 2 illustrate a boiler 2 provided with a boiler cover member 1. The cover member is attached to the boiler by means of hinges, for example. The cover member carries, in a conventional manner, an oil burner 3 provided, inter alia, with a combustion fan 4, which forces combustion air into the boiler through a burner neck 5. The fan is provided with a sound damping hood, which does not seal against the cover member 1 however. The oil delivered to the burner is atomized in the burner nozzle 6 and ignited. The smoke gases generated turn and pass through a plurality of convection tubes 7> and collect thereafter in an annular space 8, to which a stack pipe (not shown) is connected. Possible leakage paths followed by the combustion gases have been marked with the letters A, B and C in Figures 1 and 2.

In order to ensure that all leakages resulting from the positive pressure in the boiler are steered in a controllable manner,.. an do not escape into the surroundings, pre-determined pressure differences are created by encasing the burner in a casing 9, which is either a complete entity in itself or complementary to the conventional sound damping hood. The casing 9 communicates with the surroundings through an opening 10, which is intended for maintaining the desired subpressure within the casing 9. Thus, gases leaking through the pathA are never able to enter the surroundings. Gas leaking via the leakage path B do not pass directly into the surroundings but are instead conducted together with cooled flue gases out into the annular space 8. Gas leaking through the leakage path C is conducted via a further annular space 11 , which has been provided with the aid of a seal 12. The further space 11 communicates with the subpressure in the casing 9, through a channel 13 which has a through-passage area of sufficient size in relation to the areas of the leak¬ age paths to ensure that the requisite subpressure in rela¬ tion to the surroundings is created in the space 11 , thereby preventing passage of the gases past the seal 12.

The described and illustrated arrangement ensures that all leaking combustion gases are collected and recycled to the furnace chamber via the fan 4. This has particular signifi- ance in respect of the leakage passage A, where the burner 3 extends through the cover member 1 , which is a particularly critical location, since the positive pressure in*the boiler is greatest at the centre of the boiler. In other words, the difference between the boiler pressure and atmospheric or ambient pressure is greatest at this location.

The subpressure desired in the casing 9 can be obtained by ensuring a suitable degree of throttling in the inlet opening 10 for a given operating condition of the burner, i.e. for a given air flow of the fan 4. To this end, the opening may be provided, for example, with a displaceable throttle plate (not shown) capable of being adjusted to a position in which the desired subpressure is obtained. Alternatively the opening 10 may be given a circular shape and provided with an adjustable disk valve (not shown) which can be adjusted readilyto a desired throttle setting.

In order to eliminate the influence of thermal drive forces, the subpressure in the annular chamber 11 should reach at least 5Pa in relation to the surrounding ambient or atmos¬ pheric pressure.

In order for the channel 13 to be given a reasonable cross- sectional area, the pressure difference between the annular chambers 8 and 11 should be at least 5Pa. Consequently, the subpressure in the space defined by the casing 9 should be at least 10Pa.

Under these conditions, the cross-sectional area of the chan¬ nel 13 should be at least equal to the total cross-sectional areas of the leakage path C and the leakage path (not refer- enced) extending outwardly from the space 11, i.e. extending beyond the seal 12. The aforegiven function is achieved when this condition is satisfied.

In the case of other conditions, corrections are made in accordance with conventional aerodynamic laws. Thus, the cross-sectional area of' the channel 13, for example, can be reduced by a factor =v 2 when the difference betweeen the . pressure in the chamber 11 and the pressure prevailing ex¬ ternally of the casing 9 increases by the factor 2.

It will be understood that the chamber 11 may have a shape other than circular.

Figure 3 illustrates schematically the application of the invention in another type of boiler, namely a so-called sack boiler. The annular space 11 and the seal 12 have been identified in Figure 3.

Claims

CLAIMS .

1. An arrangement in central heating boilers operating at positive pressure and comprising a furnace cover member (1) on which there is mounted a burner unit (3) having a fan (4) , said burner unit extending partially into the boiler furnace chamber through an aperture in said cover member, and which boiler has a plurality of convection tubes (7) through which gases of combustion pass for collection in a space (8) , preferably of annular configuration, to which a stack pipe is connected, and which boiler is provided with means for re- cycling combustion gases leaking from the furnace chamber back to the burner fan (4) , characterized in that said re¬ cycling means includes a casing (9) which is mounted adjacent the cover member (1) and embraces the fan (4) and adjacent parts of the burning unit (3) , and in which the fan maintains subpressure relative to the boiler pressure and atmospheric pressure, and in which combustion gases leaking in the region of the cover member are collected for recycling to the fur¬ nace space via said fan.

2. An arrangement according to Claim 1, characterized in that the casing (9) has an opening (10) which communicates with the surroundings and is intended for maintaining a subpressure within said casing.

3. An arrangement according to Claim 2,characterized by means for throttling the flow passing to the interior of the casing via the opening (10) .

4. An arrangement according to Claim 3, characterized in that the opening is provided with a displaceable throttle plate, an adjustable disk valve or like valve means.

5. An arrangement according to any of claims 2-4 in which a further space (13) , preferably of annular shape, sealed by means of a seal (12) is located externally of the preferably annular space (8) , characterized in that the further space (13) communicates with the interior of the casing (9) through a channel (13) extending through the cover member (1).

6. An arrangement according to Claim 5, characterized in that the cross-sectional area of the channel (13) is suffi- ciently large in relation to the leakage areas to ensure that a subpressure is created in the outer space (11) in relation to the ambient pressure such as to prevent leakage past the seal (12) sealing said outer space.