GB2240842A

GB2240842A - Improvements in and relating to gas burners

Info

Publication number: GB2240842A
Application number: GB9102329A
Authority: GB
Inventors: Nicco Polidoro
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-02-09
Filing date: 1991-02-04
Publication date: 1991-08-14
Also published as: GB9102329D0; IT9085520A1; IT1240864B; FR2658268A1; DE4103846A1; IT9085520A0

Abstract

A gas burner includes a Venturi tube 2 which communicates with a duct 5 of diverging construction. A plate 6 is supported on the outlet of the divergent duct. The plate is produced from a material having a very low coefficient of heat transfer and is perforated 7 to allow the gaseous mixture to flow out. It may be ceramic felt with a heat transfer coefficient of between 0.15 and 0.25 Watts metre degree. The construction ensures that "hyperstoichiometric" combustion occurs ie there is excess air, both when the burner is started up and when it is running in its steady state, giving rise to a consistently low emission of nitrous products (NOx). <IMAGE>

Description

:Z C:) t3.9::.d Improvements in and Relating to Gas Burners This invention

relates to gas burners.

Gas burners including Venturi tubes for the through flow of comburent and combustible gases have been known for some time. in such a burner, the Venturi tube leads into a divergent duct which supports a plate formed with appropriately sized and arranged holes. The plate defines the head of the burner and the point at which combustion occurs. With such an arrangement, when the mixture of comburent and combustible gases passes through apertured plate and are combusted, the temperature increases.

As a result the specific volume of the gas mixture increases to produce, in turn, an increase in gas velocity A c 1 in the proximity of the aforementioned holes, the mass of the gas mixture remaining constant. It is well known that under these conditions resistance to the flow of the gas mixture will increase, this resistance being proportional to the square of the velocity of the gas mixture.

Such burners are especially designed to operate in a so-called "hyperstoichiometric" state, that is to say with an excess of combustion air. As is well known, this condition gives rise to products of combustion which have a low NOx content.

At the present time, such burners are fitted with plates formed with transverse holes for the outflow of the gaseous mixture and are manufactured from heat conducting materials. As a consequence, the temperature of the ducts through which the gaseous mixtures are conveyed to the burner increases with time. In order to prevent this occurring, it has previously been proposed to use ventilators. 'These are difficult to adjust in relation to the amount of gaseous mixture flowing through the ducts. Alternatively, it has been proposed significantly to reduce the power per unit of burner surface.

Inhibiting the flow of air from the Venturi tube means that the required surplus of air is no longer present. Thus, whereas initially the burner emits products of combustion having a low NOx content, this desired effect is not maintained during continued operation of the burner.

1 An object of this invention is to provide a burner of the kind described in which, in terms of nitrous products, emission both on start-up and during steady operation, is satisfactory.

According to the present invention a gas burner includes a Venturi tube in communication with a duct whose interior diverges outwardly from its point of communication with the Venturi tube, the outlet of the duct supporting an apertured plate produced from a material having a very low coefficient of heat transfer.

The apertured plate is typically produced from materials having a heat transfer or conductivity coefficient (X) of between 0.15 and 0.25 W I.S units) mK at 8000C, a typical operating temperature. A preferred material is ceramic felt.

The presence of the plate having a low coefficient of heat transfer means that the heat produced during combustion is not propogated inwards to any significant extent, and therefore the temperature of the passageways through which the gaseous mixture flows to the burner does not increase to any significant extent.

A surplus of air is therefore maintained at the point of combustion and the combustion remains substantially hyperstoichiometric to achieve the desired result.

The invention will now be described by way of example only with reference to the accompanying diagrammatic drawings, in which:- 9 Figure 1 is a side view of a series of burners in accordance with the invention; Figure 2 is a plan view from above of the burners illustrated in Figure 1; and Figure 3 is a cross-section to an enlarged scale of a feature of the burners illustrated in Figures 1 and 2.

Figures 1 and 2 show burners 1 including Venturi tubes 2 in which a combustible gas emitted from nozzles 3 is mixed with comburent air drawn in from the atmosphere. The structure illustrated in Figure 1, which is of a well known type, includes a plurality of burners suplied with combustible gas from a single gas manifold/header 4. Connected to the end of each Venturi tube 2 is a duct 5 which diverges outwardly from its connection to the respective Venturi tube 2. A plate 6 is supported by each duct 5 and is produced from a material which has a very low coefficient of heat transfer, such as ceramic felt, and is formed with a series of holes 7 of various shapes and positions for the throughflow 6f the mixture of combustible and comburent gases. The holes may be formed by drilling. The plates 6 reduce significantly the propogation of heat from the external surface of the plate, which means that the ducts 5 remain at a relatively low temperature sufficient to produce the previously described advantages.

1 1 4 The apertured plate is typically produced from materials having a heat transfer coefficient (X) of between 0.15 and 0.25 W International System of units where W = Watts, M = Metres and X = degrees Kelvin) at 8000C, a typical operating temperature. A preferred material is ceramic felt.

It is to be understood that the foregoing is merely exemplary of gas burners in accordance with the invention and that modifications can readily be made thereto without departing from the true scope of the invention.

Claims

1. A gas burner including a Venturi tube in communication with a duct whose interior diverges outwardly from its point of communication with the Venturi tube, the outlet of the duct supporting an apertured plate produced from a material having a very low coefficient of heat transfer.

2. A gas burner as claimed in claim 1 wherein the material has a coefficient of heat transfer of between 0.15 and 0.25 W at 8000C. mK

3. A gas burner as claimed in Claim 2 in which the plate is produced from a ceramic felt material.

4. A gas burner substantially as herein described and as described with reference to Figures 1 to 3 of the accompanying drawings.

PubUhed 1991 atThe Patent Office. State Houge.66171 High Holborn. LondonWC1R41P. Further copies nay be obtained frorn Sales B. Unit 6. Nine Mile Point Cwnifehr&ch. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques lid. St Mary Cray, Kent- j j -., j 1 h