BEKAERT COMBUSTION TECHNOLOGY B.V. (J.C. van Markenstraat 19, AR Assen, NL-9403, NL)
TEN HOEVE, Dirk (Haakswold 37, LD Ruinerwold, NL-7961, NL)
CLAIMS
1. A fuel-fired heating appliance comprising a combustion chamber thermally communicatable with a fluid to be heated, at least one fully premixed burner with a burner deck having flame openings in the form of elongate slots, whereof the ratio width/depth of each of said openings is a value selected to avoid flash back; said at least one premixed burner being located inside said combustion chamber and being airtight insulated therein; said at least one premixed burner including fuel supply means for receiving a flow of gaseous fuel from a source thereof and operating in response to the flow of fuel to aspirate and combine primary air from the environment to form a combustible air-fuel mixture; said primary air entering the burner via a cleanable or replaceable air filtration material; said at least one premixed burner receiving said combustible air-fuel mixture for burning in blue mode; said flame openings being arranged so close to one another as to assure cross ignition; ignition means being associated with the flame openings for igniting the air-fuel mixture to generate flames; said fuel-fired heating appliance further comprising an autonomous temperature detecting system attached to the deck and sensing the temperature of said burner deck said temperature detecting system being connected to a reversible gas-shutoff system.
2. A stand-alone, flammable vapour resistant method of fail-safe, low NOx and low CO heating, the method comprising: a) providing a burner with a body having a diffuser which carries a plurality of apertures through which a fully premixed mixture of combustion air and fuel flows; said apertures being in the form of elongate slots whereof the ratio width/depth of each of said apertures is a value selected to avoid flash back and thereby provides the flammable vapour resistance; b) providing a replaceable filtering structure, covering the combustion air inlet, to allow easy maintenance; c) filtering out lint, dirt and oil from combustion air via said replaceable filtering structure; d) causing the combustion of said fully premixed fuel-air mixture thereby providing low
NOx and low CO combustion; e) detecting a temperature, said detecting being obtained using a stand-alone temperature sensor arranged on the surface of said diffuser; f) generating a temperature signal; g) closing the flow of said fuel, in a purely mechanical way, when said temperature signal exceeds a preset temperature limit, as a function of the clogging of said filter.
3. The method according to claim 2 further comprising the step of replacing the clogged filter with a new filter, thereby providing an easy maintenance of the system.
4. The method according to claims 2 or 3 wherein the temperature sensor is integrated in the gas-shut-off -feed back system. |
Stand-alone, low NOx and low CO, FVIR, heating appliance with an easy maintenance
Field of the invention
The present invention relates to the field of domestic heating appliances. More specifically, the present invention relates to a low NOx and low CO burner system for domestic heating appliances. More in particular, the present invention relates to low NOx and low CO gas-fired heating appliances which can be placed in an environment which occasionally might contain volatile flammable substances.
Background of the invention
Lean combustion is desirable, and generally required for safety reasons as well as for regulatory purposes. Presently, regulations are getting more strict concerning CO and NOx emissions, forcing water heater manufacturers to develop fuel-fired water heaters which are capable of producing less than 15 ppm NOx and less than 400 ppm CO during operation. Fuel burners that are capable of achieving these emission limitations are susceptible to clogging by particulate matter entrained in the combustion air being supplied to the burners. US 20060070585 provides a solution for these high restrictions by using a radiant gas burner which is capable of achieving these emission limitations, while also capturing entrained particulate matter with a cyclonic separation. On the other hand, heating appliances are frequently installed in basements, garages and other areas which also serve to store fuel or any other flammable substances. Therefore, should any such flammable substances be spilt for any reason, its vapours would surround the heating appliance, creating a big fire risk. Further, there also is a need for detecting abnormal situations during the operation of the burner, such as, for example, overheating of the burner, or an operative condition in which the temperature of the burner is lower than a pre-established optimal temperature. But also detecting a possible clogging of the heating appliance should be possible. Another need exists with regard to an "electricity/electronica free" heating appliance, which enables the heating appliance to be installed in places where no electricity is available or/and which provides heating appliances which keep on functioning even when there is an interruption in the electricity supply.
And probably the most important need is to furnish a heating appliance whereof the maintenance is a very simple operation, without the need to open up the complete heating appliance.
Therefore the need exists for heating appliances which
comply with the strict regulations regarding NOx and CO; are safe to use in a flammable vapour environment; have a control system for detecting abnormal operating situations; have a control system for detecting clogging of the heating appliance; work in a fail-safe manner, the system should switch off in a safe way; have a capturing system for particulate matter entrained with the combustion air into the system, thereby filtering out lint, dirt and oil; be autonomous/ electricity independent/independent of electronic devices; with a simple maintenance.
Accordingly, the present invention seeks to provide a heating appliance which incorporates all of the above indicated aspects into one straight-forward system.
Summary An aspect of the claimed invention provides a heating appliance comprising a combustion chamber thermally communicatable with a fluid to be heated. Inside this combustion chamber there is at least one fully premixed atmospheric burner receiving combustible air-fuel mixture for burning in blue mode. The burner deck is having flame openings in the form of elongate slots. This thin sheet-metal diffuser generates bladed flames. The elongated slots have a ratio width/depth of each of said openings being a value selected to avoid flash back. To design openings so as to prevent flashback is well known to technical people skilled in the art. Examples of such openings are elongate slots with a maximum width of the slots between 0.4 and 0,5mm, with a depth of the opening between 0,4 and 0,6 mm; in the case of circular slots, with a depth of the openings between 0,4 and 0,6 mm and a diameter between 0,4 and 0,9 mm.
The premixed burners are located inside said combustion chamber and are airtight insulated therein, alternatively the burners are not airtight insulated but secured with flame arresters. The premixed burners include fuel supply means for receiving a flow of gaseous fuel from a source thereof and the burners operate in response to the flow of fuel to aspirate and combine primary air from the environment to form a combustible air-fuel mixture. This primary air enters the burner via a cleanable or replaceable air filtration material for filtering out lint, dirt and oil.
The flame openings in the burner deck are arranged so close to one another as to assure cross ignition. Ignition means are associated with the flame openings for igniting the air-fuel mixture to generate flames.
The fuel-fired heating appliance further comprises an autonomous temperature detecting system attached to the deck and sensing the temperature of the burner deck. The temperature detecting system is connected to a reversible gas-shutoff system.
Another aspect of the invention provides a stand-alone, flammable vapour resistant method of fail-safe, low NOx and low CO heating. This method comprises providing a burner with a body having a diffuser which carries a plurality of apertures through which a fully premixed mixture of combustion air and fuel flows. Those apertures are in the form of elongate slots whereof the ratio width/depth of each of those slots is a value selected to avoid flash back, thereby providing the flammable vapour resistance. The method further comprises providing a cleanable or replaceable filtering structure, covering the combustion air inlet. This cleanable or replaceable filtering structure filters out lint, dirt and oil from the combustion air and its easy replaceability allows easy maintenance of the heating appliance. The fully premixed fuel-air mixture is then combusted in blue flame mode generating very low NOx and CO emissions. The method further comprises detecting a temperature wherein this temperature detection is obtained using a stand-alone temperature sensor arranged on the surface of the diffuser, the generated temperature signal will cause the closing of the flow of the fuel, in a purely mechanical way, when temperature signal exceeds a preset temperature limit, as a function of the clogging of said filter.
Another aspect of the claimed invention provides an easy maintenance of a heating appliance. The above described method further comprising the step of cleaning the clogged filter or replacing the clogged filter with a new filter.
Another aspect of the claimed invention provides the above described method wherein the temperature sensor is integrated in the gas-shut-off -feed back system, e.g. the temperature sensor can be part of a pressure switch.
Brief description of the drawings
Example embodiments of the invention are described hereinafter with reference to the accompanying drawings in which
- Figure 1 shows a cross section of a heating appliance according to the present invention;
- Figure 2 is a section of the appliance of figure 1 , taken along line N-Il of figure 1 ; - Figure 3 is a section of the appliance of figure 1 , taken along line Ill-Ill of figure 1.
Reference numbers used in the drawings
10 water heater
1 1 floor/ horizontal support surface
12 tubular inner wall structure 14 tank
16 water to be heated 18 domed bottom end wall of tank 14 20 combustion chamber 22 wall of combustion chamber 24 flue pipe
30 metal outer structure of water heater 32 insulation material
39 flame openings
40 atmospheric gas burner 42 ignition means
44 temperature sensor 46 reversible gas shut off system 50 gas supply tube 52 fuel supply means 60 venturi tube
61 burner body
62 burner deck
63 aperture, combustion air inlet
64 cleanable or replaceable air filtration means
Description
Schematically depicted in Figures 1 and 2 is a fuel-fired heating appliance, in the form of a gas-fired low NOx water heater which embodies the principle of the present invention. While the principle of the present invention is illustrated herein as a water heater, the present invention is not limited to water heaters, and may also be advantageously incorporated in a variety of other types of fuel-fired heating appliances such as, for example but not by way of limitation, boilers and air heating furnaces.
Water heater 10 is of a free-standing type, it can rest on the floor or on another horizontal support surface 1 1. Water heater 10 works autonomously, it is electricity/electronica free.
This enables the water heater 10 to be installed in places where no electricity is available
or/and provides a water heater 10 which keeps on functioning even when there is an interruption in the electricity supply.
The water heater 10 has a vertically oriented tubular inner wall structure 12. Inner wall structure 12 defines, along an upper portion thereof, a tank 14 adapted to hold a quantity of water 16 to be heated and having a domed bottom end wall 18, a combustion chamber 20 extending downwardly from a peripheral portion of the end wall 18. Extending upwardly from the bottom tank end wall 18, through the stored water 16, is a flue pipe 24 that communicates at its lower end with the interior of the combustion chamber 20.
A vertically oriented tubular metal outer wall structure, representatively in the form of a metal jacket 30, outwardly circumscribes the inner wall structure 12 and forms therewith an annular space which is filled with a suitable insulation material 32.
Water heater 10 also includes an atmospheric gas burner 40 of a total premixed type, i.e. of a type where in the combustion chamber 20 only a gas-air mixture is burnt which is produced by a venturi tube 60 contained in a burner body 61 which forms a plenum chamber. A suitable fuel supply means 52 is connected to the inlet of the venturi tube 60 within the interior of the burner 40, adjacent its primary combustion air inlet opening 63 which is covered with filter 64. Due to the excess of combustion air entrained in the venturi tube 60, the combustion is in blue flame mode.
The combustion chamber 20 is sealed with respect to the environment outside the appliance.
Thus, the venturi tube 60 is the only means of fluid communication between the combustion chamber 20 and the outside environment through flame openings 39 on the body 61 at one side and the combustion air inlet 63 in the lower end portion of the wall 22 of the combustion chamber. The combustion air inlet 63 is covered by a replaceable air filtration means 64 for filtering out lint, dirt and oil as shown in figure 3.
The burner body 61 has a burner deck 62 which has a plurality of flame openings 39 in adjacent groups arranged so close to each other as to assure cross ignition. The dimensions of the openings are designed to prevent flashback into the burner body 62, and have a slitwidth of 0,5 mm and a depth of 0,5 mm. Such burners are known by the persons skilled in the art and are commercially available. This design of the slotted burner deck, together with the sealed combustion chamber provides the water heater 10 with flammable vapor ignition resistance (FVIR) to substantially prevent flames within the combustion chamber 20 to go out of the system. On the other hand is the water heater 10 also insulated
with the suitable insulation material 32, which prevents the water heater 10 to get so hot it can ignite flammable vapours which are available in the surroundings of the water heater 10. Any mixture, air-fuel, air-fuel-flammable vapours, air-flammable vapours entering the combustion chamber 20 will be ignited inside the combustion chamber 20 and will be burnt inside this combustion chamber 20.
During firing of the burner 40, fuel gas is discharged from the supply means 52 into the interior of the burner 40, and combustion air from outside the water heater 10 sequentially flows inwardly through the filter 64 on the combustion air inlet opening 63 into the interior of the burner 40 through its venturi 60. During firing of the burner 40 the burner generates hot combustion products which flow upwardly through the flue pipe 24 and heat the stored water 16 to maintain it at a predetermined heated temperature.
All of the primary combustion air supplied to the burner 40 comes from outside the water heater 10 and the flame front obtained with this type of burners is not touching the burner deck 62. Accordingly, the NOx and CO emissions generated by the burner 40 are quite low. Thus, the representatively illustrated water heater 10, in a simple, efficient and economical manner, integrates a low NOx fuel burner with a flammable vapor ignition resistance structure.
This type of slotted premix burners 40 give a very specific flame front. Each group generates a lamellar flame appearing as a pair of divergent wings, butterfly-like in form. This specific feature is used for controlling the correct operation of the combustion process. When the replaceable air filtration means 64 gets clogged by dirt, lint and/or oil, the combustion air pressure gets lower resulting in the butterfly-like flames getting nearer the burner deck 62. This heats up the burner deck 62. A temperature sensing structure 44, located at the surface of the burner deck 62, can accordingly measure this heating up of the burner deck 62, being a result of the clogging of the filter 64. The temperature sensing structure 44 is connected to a reversible gas shut off system 46. The reversible gas shutoff system 46 functions to terminate combustion in the combustion chamber 20 in case the flame front obtained by this type of burners heats up the burner deck 62 above a preset temperature. This preset temperature is chosen in the interests of the durability of the burner, in order to prevent a) the burners to become too hot, which through cycle loading would corrode and burst and b) too high CO emissions would be reached.
In a preferred embodiment, the temperature sensing and the shutoff system are integrated in one single solution. The reversible gas shut off system 46 is a spring-loaded gas shutoff
damper assembly which is normally held in its indicated open position in which it permits fuel gas to flow into the venturi 60 of the burner 40. Upon detecting a predetermined, undesirably high temperature of the burner deck 62, the temperature sensing structure 44 permits the damper structure 46 to be spring-driven upwardly in a manner causing the damper structure 46 to close off the gas supply 50. This will also shut off the gas supply of the ignition means, which will further preventing the gas supply in a traditional way.
After the shut off of the gas supply, maintenance of the water heater 10 is due. In this solution, this is a very simple operation as only the filter device 64 needs to be replaced or the filter device 64 needs to be cleaned. Thereafter, the whole system is again operational for a low NOx and CO combustion complying with the strict emission regulations of today.
While various principles of the present invention have been representatively illustrated and described herein as being incorporated in a fuel-fired water heater, it will be readily appreciated by those of skill in this particular art that the present invention is not limited to water heaters, but could also be advantageously incorporated in other types of fuel-fired heating appliances such as, for example, boilers and fuel-fired air heating furnaces. Additionally, while the various water heater embodiments representatively illustrated and described herein have been indicated as incorporating radiant fuel burners therein, it will also be readily appreciated by those of skill in this particular art that other types of fuel burners could alternatively be utilized if desired without departing from principles of the present invention.