Burner system having premixed burners and flame transfer means

0001The invention relates to a burner system as defined in the preamble of claim 1. Such a burner system is known from <patcit id="pcit0001" dnum="US2875820A"><text>US 2 875 820 A</text></patcit>.

0002A premixed burner, also referred to as a premix burner, is understood to mean a burner wherein the mixing of gas and a quantity of air necessary for the complete combustion thereof takes place prior to or in the burner head. This premixing can for instance be realized with a venturi system or with a mechanical system with fans. The thus formed combustible gas/air mixture, which often even comprises a slight excess (up to for instance 25%) of air, is then ignited as it leaves the outflow opening.

0003When several of such premixed burners are disposed adjacently of each other in order to thus form a burner system or burner bed, it is of great importance in the igniting of this burner bed that all burners are ignited simultaneously. If specific burners were to be ignited later, too much combustible gas/air mixture would otherwise have flown out already, which would then combust explosively when ignited.

0004A burner bed is in practice usually ignited at a central location, after which the flame is then supposed to spread to or overflow onto the adjacent burners from the ignited burner. In order to ignite all burners as far as possible simultaneously, it is therefore important that the overflowing of the flame takes place rapidly.

0005A problem here is that the outflowing gas/air mixture, when it is not ignited at the burner, mixes directly with the ambient air that is present and thereby becomes incombustible. The overflow of the flame is hereby made considerably more difficult.

0006The above-mentioned prior art document <patcit id="pcit0002" dnum="US2875820A"><text>US 2 875 820 A</text></patcit> discloses a burner structure 1 having a number of parallel burner tubes which are supplied with a combustible gas/air mixture through a central inspirator tube and a semicircular manifold. Gas is injected into the inspirator tube through a nozzle, entraining a part of the necessary air. The gas/air mixture that is formed is distributed over the burners and flows out of corrugations, entraining further air. The burner structure further includes a pilot member which serves to ignite the gas/air mixture flowing from two adjacent burners.

0007The invention now has for its object to provide a burner system with fully premixed burners, wherein this problem does not occur, or at least does so to lesser extent. According to the invention this is achieved in a burner system as defined in claim 1.

0008By making use of flame transfer means, the burner system of the invention can be ignited at one of the burners, wherein the flame then overflows sufficiently rapidly to the other burners in order to ignite them before a dangerously large quantity of the combustible gas/air mixture has flown out. A safe ignition of the burner system is thus guaranteed.

0009The flame transfer means define at least one flame path between the burners for the purpose of guiding the flame during overflow.

0010Because the at least one flame path is formed by an overflow pipe mutually connecting the burners, the flame is safeguarded during overflow against being extinguished as a result of an excess of air.

0011And since the burners are placed adjacently of each other with interspaces in the burner system, and the overflow pipe extends through the interspace, the flame can be transferred over relatively large distances.

0012Because the burner system according to the invention is provided with at least one injection member directed toward the flame path for the purpose of injecting the combustible gas/air mixture therein, overflow of the flame from one burner to another is enhanced. The flame is thus as it were "collected".

0013The burner system of the invention is provided with a mixing chamber for forming the combustible gas/air mixture, this mixing chamber comprising at least one feed opening for air, at least one feed opening for gas and at least two outflow openings for the combustible gas/air mixture, each connected to one of the burners, and the at least one injection member is connected via a branch conduit to the mixing chamber. The injection member is thus supplied directly from the mixing chamber and receives the gas/air mixture at a higher pressure than prevails behind the burner. A more rapid overflow of the flame is hereby achieved.

0014The at least one injection member is preferably adapted here to inject the combustible gas/air mixture into the flame path such that a reliable flame transfer is ensured without overheating of the flame path occurring. Overheating of the flame path could after all result in premature ignition of a gas/air mixture injected therein.

0015The interspace can herein form part of a duct for a medium to be heated by the burners, so that the burner system can be applied in a heat exchanger.

0016The invention is now elucidated on the basis of an example wherein reference is made to the accompanying drawing, in which: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a schematic representation of a burner system according to the invention,</li><li><figref idref="f0002">Fig. 2</figref> is a perspective front view of a practical application of the burner system in a heat exchanger,</li><li><figref idref="f0002">Fig. 3</figref> and <figref idref="f0003">4</figref> are partially cut-away perspective detail views of the burner system of <figref idref="f0002">Fig. 2</figref>, and</li><li><figref idref="f0003">Fig. 5</figref> is a perspective detail view of a single burner of the system of <figref idref="f0002 f0003">Fig. 2-4</figref>.</li></ul>

0017A burner system 1 is provided with at least two, and in the shown example even eight, premixed burners 2 placed upright adjacently of each other. Each burner 2, which tapers in longitudinal direction and thus has a decreasing height, is provided with a feed opening 8 and has on the top side a slot-like outflow opening 4 for a combustible gas/air mixture M. This gas/air mixture M is fed to each burner 2 by a distribution chamber 5 which is provided on its underside with one or more openings. Flue gas discharge pipes 9 are placed beneath burners 2.

0018The gas/air mixture M is formed in a fan (not shown) and then passes to a mixing chamber or distribution chamber 5 in which gas G is injected through a gas feed opening 6, while air A is drawn in through an air feed opening 7. This suctioning takes place by means of the fan. Distribution chamber 5 is connected to the different burners 2 and has for this purpose a number of outflow openings 8 corresponding to the number of burners 2. These outflow openings 8 are formed in distribution chamber 5 at the outflow end thereof.

0019Burner system 1 is ignited from a central location. In the shown example the first burner 2 (shown on the right in the drawing) is provided for this purpose with an ignition mechanism 10. In the shown example this is a per se known electric ignition pin arranged directly above outflow opening 4. In order to ignite all other burners 2 at substantially the same time, burner system 1 is provided according to the invention with means 11 for transferring from the one burner 2 to another of the flame formed after ignition of first burner 2. These flame transfer means 11 define in each case a flame path between two adjacent burners 2. In the shown example these flame paths are formed by a set of overflow pipes 12 mutually connecting the burners 2. These overflow pipes 12 are dimensioned such that they provide sufficient space to allow the flame to spread from one burner 2 to another.

0020Flame transfer means 11 further comprise a number of members 13 directed toward overflow pipes 12 for the purpose of injecting the combustible gas/air mixture M therein. These injection members 13 are each connected via a branch conduit 14 to distribution chamber 5 and have a nozzle 19 directed toward the relevant overflow pipe 12. In the shown example the injection members 13 are adapted in each case to inject the combustible gas/air mixture M into overflow pipe 12 such that a reliable flame transfer is ensured while overheating of overflow pipe 12 is avoided. For this purpose each member 13 injects a quantity of gas/air mixture M which is sufficient to obtain a good in-depth effect, whereby the flame is transferred in reliable manner to the following burner 2. The injected quantity is on the other hand so small that the flame is only transferred and complete combustion does not take place in overflow pipe 12. The appropriate quantity and injection pressure can be determined by the skilled person on the basis of tests and/or calculations.

0021Injection members 13 are otherwise arranged in each case on the burners 2 still to be ignited adjacently of the outflow opening 4 thereof and they inject the gas/air mixture M in the direction of the already ignited burner(s) 2 so that the flame is as it were "collected".

0022The burner 2 which is furthest removed from ignition mechanism 10, in this case the burner 2 on the left-hand side, is provided with a flame safety mechanism 16. This flame safety mechanism 16 is likewise formed in conventional manner by a pin which is placed directly above outflow opening 4 and in which an ionization current is generated by the flame when burner 2 is ignited. When there is no flame, there is no further ionization current, and the gas feed will be closed.

0023Further arranged over the burners 2 are covers 17, thereby forming heating elements closed off from the environment. Thus formed between these heating elements are ducts 18 through which can flow a medium for heating, for instance air. The sides of burner covers 17 herein determine the walls of ducts 18.

0024The invention thus makes it possible with relatively simple means to ignite a burner system consisting of a number of fully premixed burners in reliable manner from a central point.

0025The number of burners, the form of the burners and their disposition could thus be varied. In addition, the flame transfer means could be embodied otherwise than shown here, for instance with differently formed overflow pipes. The form and position of the injection members could also be modified, as could the manner in which these are provided with gas/air mixture. The location from which the burners are ignited and the manner in which this takes place could also be varied. Finally, the burner system according to the invention can be used not only in heat exchanges but also for different applications.