Patent Grant
9528699
Technical Field
The present invention relates to a premix gas burner for operation in blue flame mode that is having a burner deck comprising a fiber based substrate and a screen or perforated plate supporting the fiber based substrate. The premix gas burner is further comprising contact wires forming a thermocouple fixed to the burner deck.
Background Art
Premix gas burner with operation in blue flame mode are known. The gas premix is burnt on a burner substrate and blue coloured flames are visible. The flue gas is containing the caloric value and will transfer its energy onto another medium, e.g. through a heat exchanger to water in a water heater. A different type of burners are radiation burners that operate in red flame mode to transfer their energy via radiation. Both types of burners (for operation in blue flame mode or for operation in red flame mode) are different in construction in order to be optimized for their mode of operation.
One way to control the combustion of a premix gas burner for operation in blue flame mode makes use of a measurement of a temperature at or on the burner deck.
GB 2 270 748 discloses a gas burner that is provided with a thermocouple for sensing the temperature of the surface of the burner, the burner deck may have a metallic perforated plate or a ceramic burner. The thermocouple is fixed to the underside (=non-combustion side) of the burner deck.
EP 1 039 220 discloses a premix gas burner that is having a perforated plate diffuser to which one or more thermocouples are attached.
EP 2 180 253 is describing prior art in which thermocouples are welded to the inner (=gas supply) side or outer (=combustion) side of a burner. Furthermore, EP 2 180 253 is disclosing a temperature sensor for a gas premix burner. The temperature sensor comprises two metal wires implementing a thermocouple, a protection sheath receiving the two metal wires, and a head in metal material having a front side intended to be facing the environment, the temperature of which is intended to be measured, and a rear side opposite the front side, in which the two metal wires are connected in a thermal exchange relationship to the head rear side, and the head comprises a front portion connectable to a burner wall of the burner so that the thermocouple is connectable to the burner by means of said metal head. The temperature sensor is used for gas premix burners having a perforated plate as burner deck.
It is a problem of the temperature measurement systems as known in the art (as described in GB 2 270 748, EP 1 039 220, in the prior art part as well as in the disclosing part of EP 2 180 253) that these temperature measurement systems do not result in reliable temperature results when a fiber based substrate supported by a screen or by a perforated plate is used as burner deck in gas premix burners.
It is the object of the invention to overcome the drawbacks of the prior art. It is a specific object of the invention to provide a gas premix burner for operation in blue flame mode that is having a fiber based substrate supported by a screen or perforated plate as burner deck; with a temperature measurement system that is providing reliable and reproducible temperature values.
A first aspect of the invention is a premix gas burner for operation in blue flame mode. The burner deck of the premix gas burner comprises a fiber based substrate and a perforated plate or a screen supporting the fiber based burner substrate; and at least two contact wires forming a thermocouple. The contact wires are directly or indirectly fixed to the burner deck to measure the temperature of the burner deck when the premix gas burner is in operation. With measurement of the temperature of the burner deck is meant that a temperature is measured representative for the temperature of a location of the burner deck; and wherein the measured temperature is reproducible. The fiber based substrate is locally at least partly connected directly or indirectly to the perforated plate or the screen in the region where the contact wires of the thermocouple are directly or indirectly fixed to the burner deck. The local at least partly direct or indirect connection of the fiber based substrate to the perforated plate or screen in the region where the contact wires of the thermocouple are directly or indirectly fixed to the burner deck has shown to stabilize the combustion in that region, resulting in a reliable and reproducible temperature measurement with the thermocouple.
The contact wires can be directly or indirectly fixed to the burner deck. With “directly fixed to the burner deck” is meant that the contact wires are in direct contact with the burner deck (meaning with the fiber based substrate or with the perforated plate or the screen supporting the fiber based burner substrate) and fixed to the burner deck (meaning to the fiber based substrate or to the perforated plate or the screen supporting the fiber based burner substrate). With “indirectly fixed to the burner deck” is meant that the contact wires are fixed to an additional member which is itself fixed to the burner deck (meaning to the fiber based substrate or to the perforated plate or the screen supporting the fiber based burner substrate, or to both).
With “the fiber based substrate is directly connected to the perforated plate or the screen” is meant that there is a direct contact and a direct connection between the fiber based substrate and the perforated plate or screen in the region where the contact wires of the thermocouple are directly or indirectly fixed to the burner deck. To this end, several techniques are available, the fiber based substrate can be welded, glued (using a temperature resistant glue, e.g. a ceramic glue), stapled, riveted, stitched or clamped to the perforated plate or screen.
With “the fiber based substrate is indirectly connected to the perforated plate or the screen” is meant that the fiber based substrate is itself connected to another element (e.g. a plate structure) which is itself connected to the perforated plate or screen supporting the fiber based substrate. An example is where the fiber based substrate is connected to an additional plate element which is locally positioned between the fiber based substrate and the perforated plate or screen supporting the fiber based substrate; with the additional plate element itself connected to the perforated plate or screen.
In a preferred execution of the invention, the at least partly connection of the fiber based substrate in the region where the contact wires of the thermocouple are directly or indirectly fixed to the burner deck, is within an area defined by a circle with diameter of 50 mm around the projection of the centerpoint of the contact wire connections to the burner deck.
Preferably, the at least partly connections of the fiber based substrate in the region where the contact wires of the thermocouple(s) are directly or indirectly fixed to the burner deck, are within an area defined by a circle with diameter of 24 mm around the projection of the centerpoint of the thermocouple(s) onto the burner deck. More preferably, the at least partly connections of the fiber based substrate in the region where the contact wires of the thermocouple are directly or indirectly fixed to the burner deck, are within an area defined by a circle with diameter of 15 mm around the projection of the centerpoint of the thermocouple(s) onto the burner deck. Most preferably, the at least partly connections of the fiber based substrate in the region where the contact wires of the thermocouple(s) are directly or indirectly fixed to the burner deck, are within an area defined by a circle with diameter of 10 mm around the projection of the centerpoint of the thermocouple(s) onto the burner deck.
With the fiber based substrate is locally “at least partly” connected in the region where the contact wires of the thermocouple directly or indirectly fixed to the burner deck; is meant that the direct or indirect fixation or connection of the fiber based burner deck to the perforated plate or screen can e.g. be over a certain zone, or e.g. via spot connections, e.g. a number of spot weldings.
The fiber based substrate can e.g. be a knitted fabric, a woven fabric or a nonwoven fabric. The burner deck can also be made out of sintered fibrous material.
In an embodiment of the invention, the perforated plate supporting the burner deck is made out of stainless steel. In another embodiment of the invention, the screen supporting the burner deck is a woven metal wire screen. The perforated plate supporting the burner deck can also be an expanded metal plate (preferably made out of stainless steel).
Experiments have shown that a thermocouple of the premix gas burner according to the invention provided reliable and reproducible temperature measurements.
The premix gas burner can be of the flat type, or having a burner deck curved in one direction, or can be cylindrical, conical or frustoconical or be of any shape as is known in the art. Preferably, the contact wires are connected in a central zone of the burner deck.
In a specific embodiment of the invention, the contact wires of the thermocouple are in a housing. In a more specific embodiment, the housing is comprising ceramic material.
In order to obtain appropriate temperature measurements, it is possible to modify locally at or around the position of the thermocouples the porosity of the fiber based substrate and/or of the perforated plate or screen that is supporting the fiber based substrates. Examples are locally modified perforation patterns in the perforated plate, local holes in the fiber based substrate or locally different thickness of the fiber based substrate, locally a different structure of the fiber based substrate.
In a preferred embodiment of the invention, a hole is present in the fiber based substrate around where the contact wires of a thermocouple are fixed directly or indirectly to the burner deck. The at least partly (direct or indirect) connection of the fiber based substrate to the perforated plate or the screen is at least at the edges of the hole in the fiber based substrate. In a preferred execution of the invention, the hole in the fiber based burner substrate is within a diameter range of 5 to 55 mm, preferably within a diameter range of 5 to 24 mm, of the projection of the centerpoint of the thermocouple(s) onto the burner deck. The hole can be circular, oval, rectangular, square or have another shape. Preferably, if a perforated plate is used to support the fiber based substrate, there are no holes present in the perforated plate at the location of the hole in the fiber based substrate, with the possible exception of holes (e.g. through holes) in which the contact wires can be fixed onto the perforated plate.
The presence of the hole in the fiber based substrate has shown to increase the speed of reaction of the thermocouple to changing conditions. It results also in a higher measured temperature, which means that the resolution of the measurement system is improved. The at least partial fixation of the fiber based substrate at the edges of the hole has been proven to be a safety feature to prevent the flame from going back, under the fiber based substrate and into the premixing chamber. This is known as a flash back.
In another embodiment of the invention; a hole is present in the perforated plate or the screen that is supporting the fiber based substrate around where the contact wires are indirectly fixed to the burner deck. The contact wires of a thermocouple are fixed onto an additional member. The additional member is fixed to the burner deck, creating the indirect fixation of the contact wires of a thermocouple onto the burner deck. In a specific embodiment, the additional member can be a ceramic housing in which the contact wires of the thermocouple are fixed. In a preferred execution of the invention, the hole in the perforated plate or the screen that is supporting the fiber based substrate around where the contact wires are indirectly fixed to the burner deck, is within a diameter range of 5 to 55 mm, preferably within a diameter range of 5 to 24 mm, of the projection of the centerpoint of the thermocouple onto the burner deck. The hole can be circular, oval, rectangular, square or have another shape.
In a specific embodiment the additional member is a metal plate structure or an additional plate. The additional plate can be circular, square, rectangular, polygonal or oval. Preferably, the vertical projection of the additional member (e.g. a metal plate structure or additional plate) onto the surface of the burner deck falls within a diameter range of 5 to 60 mm, preferably within a diameter range of 10 to 30 mm, of the projection of the centerpoint of the thermocouple onto the burner deck. It can have a bent shape, so as to form the shape and curvature of the burner deck it is fixed onto. Preferably, the additional metal plate structure is heat resistant and has preferably a low thermal conductivity. In a specific execution of the invention, the additional metal plate structure is comprising stainless steel; in an even more specific execution, it is made out of stainless steel. Even more preferred, the metal plate is made out of the same material as the perforated plate or screen that is supporting the fiber based substrate. In one embodiment of the invention, the additional metal plate structure is having the same thickness as the perforated plate or the screen that is supporting the fiber based burner substrate. Preferably, the additional metal plate structure has a thickness between 0.1 and 1.5 mm. More preferably between 0.1 and 0.75 mm. Most preferably, the additional metal plate structure is as thin as possible. In a specific execution, the additional metal plate structure can be fixed at the side of the burner deck where the fiber based substrate is located. In an alternative execution of the invention, the additional metal plate structure can be fixed in between the fiber based substrate and the perforated plate or the screen supporting the fiber based substrate. In another alternative execution, the additional metal plate structure can be fixed at the side of the burner deck where said perforated plate or said screen is located; it is a specific benefit of this execution that a faster response of the temperature measurement to changes in the temperature of the burner deck is obtained. Preferably, the additional metal plate structure has neither perforations nor holes in it, with the possible exception of holes (that can be through holes) for the fixation of the thermocouples.
In yet an alternative embodiment, the additional member is a head, the head is having a front side where the temperature is measured, and a rear side opposite the front side. The contact wires can be connected via or to the rear side of the head. The head comprises a portion connectable to the perforated plate or to the screen supporting the fiber based substrate, so that the contact wires are connectable to the premix gas burner by means of the head. In a specific execution of this embodiment, the head is comprising metal material. In a more preferred execution, the head is comprising stainless steel. In a more preferred embodiment, the head is made out of material having the same thermal expansion coefficient of the perforated plate or of the screen that is supporting the fiber based substrate. More preferred, the head is made out of the same material as the perforated plate or the screen supporting the fiber based substrate.
In a specific execution of the invention, the head is clamped into a hole in the fiber based substrate and into a hole of the perforated plate or of the screen supporting the fiber based burner substrate. It is a specific benefit of this embodiment that a fast and easy installation can be made of the temperature measurement system onto the burner deck.
As an example, the contact wires that form the thermocouple are connected to a metal connecting piece. The metal connecting piece is clicked into a hole in the supporting perforated plate or screen. The fiber based substrate is connected to the supporting perforated plate or screen at the edges of the hole made into it where the thermocouple device is going through the supporting perforated plate or screen and the fiber based substrate. The connection of the fiber based substrate can be done via spot welding, via welding over the circumference of the hole, or via clamping by means of the metal connecting piece. The benefit of this embodiment is a rapid installation of the temperature measurement system onto the burner deck.
In yet another embodiment of the first aspect of the invention, the at least two contact wires of a thermocouple are connected into through holes that fit the size of the contact wires. The through holes can be provided in the perforated plate or in the screen that is supporting the fiber based substrate or in the additional member or in the additional metal plate structure. This embodiment of the invention provides a faster reaction of the thermocouple measurement to changes of the temperature at the burner deck. A higher temperature is measured when the burner is in operation, and hence the resolution of the measurement system is higher. The response to changes of the temperature of the burner deck is also faster.
In a specific embodiment, at least three contact wires are fixed to the burner deck and used to form thermocouple arrangements. The benefit of an arrangement of at least three contact wires is that a double check of the temperature can be performed. This use can also include a failure check of the thermocouple systems. Furthermore, the temperatures of the different thermocouples can be averaged, in order to reduce the measurement error. A more reliable and more accurate temperature measurement is obtained. In a more preferred embodiment, at least four contact wires are used, which result in a more secure measurement system.
A second aspect of the invention is the use of a gas premix burner according to the first aspect of the invention. Examples of such use include heating systems and water heaters, e.g. instantaneous water heating systems.
A third aspect of the invention is a burner control system comprising the premix gas burner and the thermocouple according to the first aspect of the invention. The benefit is that an efficient and effective temperature value is available and used in the control system, ensuring a reliable control of the premix gas burner.
A fourth aspect of the invention is the use of a burner control system according to the third aspect of the invention. Examples of such use is in heating systems or in water heaters, e.g. in instantaneous water heaters.
Example embodiments of the invention are described hereinafter with reference to the accompanying drawings.
A number of examples to carry out the invention will be described.
It is possible to modify the porosity of the perforated plate or the fiber based substrate 14 locally at or around where the contact wires of the thermocouple are fixed to the burner deck. For instance (but not shown in
In yet another embodiment as shown in
The cross section 1200 in
The cross section 1300 in
In one embodiment of the invention, the fiber based burner deck is a metal fiber knitted fabric. In another embodiment, the fiber based burner deck is a metal fiber woven fabric. In another embodiment, the fiber based burner deck is a metal fiber nonwoven fabric. In another embodiment, the burner deck is made out of sintered fibrous material.
In a first embodiment, the metal fibers used for the fiber based substrate, e.g. stainless steel fibers, with a diameter less than 40 micrometers, e.g. less than 25 micrometers, are obtained by a bundle drawing technique. This technique is disclosed e.g. in U.S. Pat. Nos. 2,050,298, 3,277,564 and in 3,394,213. Metal wires are forming the starting material and are covered with a coating such as iron or copper. A bundle of these covered wires is subsequently enveloped in a metal pipe. Thereafter the thus enveloped pipe is reduced in diameter via subsequent wire drawing steps to come to a composite bundle with a smaller diameter. The subsequent wire drawing steps may or may not be alternated with an appropriate heat treatment to allow further drawing. Inside the composite bundle the initial wires have been transformed into thin fibers which are embedded separately in the matrix of the covering material. Such a bundle preferably comprises no more than 2000 fibers, e.g. between 500 and 1500 fibers. Once the desired final diameter has been obtained the covering material can be removed e.g. by solution in an adequate pickling agent or solvent. The final result is the naked fiber bundle.
In a second embodiment, metal fibers for the burner deck, such as stainless steel fibers are manufactured in a cost effective way by machining a thin plate material. Such a process is disclosed e.g. in U.S. Pat. No. 4,930,199. A strip of a thin metal plate is the starting material. This strip is wound around the cylindrical outer surface of a rotatably supported main shaft a number of times and is fixed thereto. The main shaft is rotated at constant speed in a direction opposite to that in which the plate material is wound. A cutter having an edge line expending perpendicularly to the axis of the main shaft is fed at constant speed. The cutter has a specific face angle parallel to the axis of the main shaft. The end surface of the plate material is cut by means of the cutter.
Elements of different embodiments and/or elements of different examples of the invention can be combined within the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 11165054.5 | May 2011 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/057430 | 4/24/2012 | WO | 00 | 10/30/2013 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2012/152571 | 11/15/2012 | WO | A |
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| Number | Date | Country | |
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| 20140080074 A1 | Mar 2014 | US |
