US20090145419A1

US20090145419A1 - Furnace heat exchanger

Info

Publication number: US20090145419A1
Application number: US12/326,551
Authority: US
Inventors: Dirk Ten HOEVE
Original assignee: Bekaert Combustion Technology BV
Current assignee: Bekaert Combustion Technology BV
Priority date: 2007-12-05
Filing date: 2008-12-02
Publication date: 2009-06-11

Abstract

The present invention provides an alternative single burner heat exchanger combination for a gas-fired furnace for hot air generation to be used to heat spaces in residential and commercial settings. The fuel fired furnace is compiled of the known set-up of a plurality of spaced heat exchangers wherein each heat exchanger has an inlet port for receipt therein of combustion gases. The single burner is a premix burner providing an excellent combustion of the gas-air mixture. The burner is in fluid communication with each port of each heat exchanger through a dilution zone and a distributor. Preferably, these are all airtight connected to each other as can be seen in FIG. 2. The combustion gases produced by the premix burner are mixed with secondary air flows entering the system in this dilution zone, whereby diluted combustion gases are obtained. These diluted combustion gases will then enter the heat exchangers via the distributor. The combustion gases, having a temperature of about 1600° C. are diluted with the secondary air flows to a temperature of about 600° C. The premix burner is surrounded by a shield, which prevents a direct cooling of the flames on the burner membrane. When flames are cooled by an air flow, CO levels rise because complete combustion of the combustible air/gas mixture is prevented. In the system of the invention a complete combustion of the combustible air/gas mixture is achieved and the right temperature of gases is delivered to the heat exchangers, without creation of undesirable combustion products since cooling of the flames is avoided.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims benefit of priority to U.S. Provisional Application Ser. No. 60/992,545, filed Dec. 5, 2007, the entire contents of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to gas-fired furnaces for hot air generation to be used to heat spaces in residential and commercial settings. More in particular, the present invention relates to a single burner used in combination with multipass heat exchangers.

BACKGROUND ART

A typical residential furnace has a bank of heat exchange panels arranged in parallel relationship such that the circulating blowing air passes between the panels or heat exchanger elements to be heated before it passes to the distribution duct. The panels define an internal flow path for hot combustion gases supplied by burners. Each of the panels is typically formed of a clamshell structure which has an inlet end into which the flame of a burner extends to heat the flue gas, an outlet end which is fluidly connected to an inducer for drawing the heated flue gas there through, and a plurality of legs or passes through which the heated flue gas passes.
A common arrangement for gas fired furnaces is to provide an individual burner associated with each heat exchanger, as can be seen in EP1318362. A fuel gas mixture is delivered through a manifold. The manifold has a plurality of outlets corresponding with the number of heat exchangers employed in the furnace. Interposed between the heat exchangers and the manifold outlets are a horizontally spaced series of shot-type fuel-air burners provided in one-to-one correspondence to the number of heat exchangers. The gas/air mixture is injected by burner into the open end of a heat exchanger. As a part of the injection process, additional air is drawn into the heat exchanger so that the gas may be fully combusted within the heat exchanger. The hot combustion gases are caused to flow in a tortuous path within each heat exchanger, by an induction draft fan which creates a negative pressure through the heat exchangers.
A blower receives cold room air from the area which is to be heated, forces that air over the heat exchanger, where after the air is collected and returned to the rooms to be heated.
Further examples of such heat exchanger arrangements can be seen in U.S. Pat. No. 4,467,780; U.S. Pat. No. 5,271,376 and U.S. Pat. No. 7,096,933.
In similar arrangements as described above, each heat exchanger has its own burner. Use of multiple burners generally increases the cost of the furnace unit. Furthermore, as multiple burners must be individually ignited, a manifold must be used to bring the gas fuel to the burner. The manifold must employ specifically configured orifices at the openings to provide the proper amount of gas to each burner. The manufacture and maintenance of this manifold device also increases the cost of manufacture and maintenance of the furnace. Furthermore, the efficient operation of the furnace depends largely on the proper burning of each burner. In a multiple burner situation, it is often difficult to detect improper operation of an individual burner. Improper operation of any individual burner may result in the creation of undesirable combustion products and/or reduce the operating life of the heat exchanger.
Most of above addressed problems are solved by US 2005/0161036 providing a unitary burner for producing combustion gases, the burner having a burner face for passing there through a combustible gas. The inlet port of each heat exchanger is disposed adjacent to and in fluid communication with the burner face, whereby combustion gases may flow from the burner into each of the inlet ports of the heat exchangers. In above described system, a flame is formed in each heat exchanger or panel. This implicates that an extra cooling air needs to be drawn into the panel or heat exchanger as they can only withstand temperatures up-to 800° C. This extra cooling air also cools the flame, thereby increasing the levels of undesirable combustion products (e.g. CO) in the flue gases.
It would be desirable to have a system wherein an efficient combustion, without creation of undesirable combustion products, is guaranteed in a cost effective way.

DISCLOSURE OF INVENTION

An aspect of the claimed invention provides an alternative single burner heat exchanger combination for a gas-fired furnace. The fuel fired furnace is compiled of the known set-up of a plurality of spaced heat exchangers wherein each heat exchanger has an inlet port for receipt therein of combustion gases. The single burner is a premix burner providing an excellent combustion of the gas-air mixture. The burner is in fluid communication with each port of each heat exchanger through a dilution zone and a distributor. Preferably, these are all airtight connected to each other as can be seen in FIG. 2. The combustion gases produced by the premix burner are mixed with secondary air flows entering the system in this dilution zone, whereby diluted combustion gases are obtained. These diluted combustion gases will then enter the heat exchangers via the distributor 150. The combustion gases, having a temperature of about 1600° C. are diluted with the secondary air flows to a temperature of about 600° C. The premix burner is surrounded by a shield, which prevents a direct cooling of the flames on the burner membrane. When flames are cooled by an air flow, CO levels rise because complete combustion of the combustible air/gas mixture is prevented. In the system of the invention a complete combustion of the combustible air/gas mixture is achieved and the right temperature of gases is delivered to the heat exchangers, without creation of undesirable combustion products since cooling of the flames is avoided.
Another aspect of the claimed invention provides a single burner heat exchanger combination 1 as described above wherein the premix burner 130 comprises a self regulating system 210 for proper gas-air ratio supply to the mixing chamber 136 of the premix burner 130. The burner is self-regulating with regard to the gas-air ratio needed for a low CO and NOx producing burner. As the induction draft fan 170 creates a negative pressure, thereby moving a constant volume through the heat exchangers, the mass of flue gases going through the system lowers, thereby drawing less heat from the burner chamber which heats up the burner chamber. Due to this, the burner chamber is provided with less air, resulting in an improper combustion, raising CO and NOx levels. This problem is overcome by the self-regulating system incorporated in the burner. This self-regulating system causes an extra primary airflow 220 to enter the mixing chamber of the burner, thereby raising the oxygen content in the gas air mixture to a preset value of λ (gas-air ratio) of preferably 1,3. This allows the burner 130 to burn the gas-air mixture in a proper way, with production of minimal quantities of noxious gases, through the whole operating time of the furnace. This property makes the total burner heat exchanger combination 1 independent from the length of the induction blower duct or possible leaks in the system.
Preferably, this self regulating system comprises a bi-metal, but also alternative thermally responsive switches can be used.
Preferably this premix burner is a tubular burner with a burner membrane at the cylinder surface and an endcap at the end of the cylinder. The burner membrane comprises preferably a perforated sheet metal. More preferably the burner membrane comprises a metal fiber burner membrane as known from e.g. WO97/04152. The use of such a tubular burner with endcap combined with a bi-metal containing self regulating system is particularly advantageous, as, by the system described above, when the induction fan draft pulls a lower mass through the system, also less heat is drawn from the combustion chamber, which heats up the burner. As the burner is made out of metal, and the impermeable endcap, also made out of metal, the endcap will heat up more than the burner membrane, as the burner membrane is cooled by the fresh gas-air mixture flowing through for combustion. The metal endcap will start irradiating into the burner body and onto the bi-metal which will thereby open the extra primary air inlet 220, the inlet being more or less opened depending on the heat radiated onto the bi-metal. In a preferred embodiment, the bi-metal is configured in such a way that when the burner is cold, the bi-metal closes of the extra primary air inlet 220 completely, and when the burner gets warmer, the bi-metal opens the extra primary air inlet 220 gradually by bending of the bi-metal. Such a burner is known from utility model DE 29611179, which was used for a tumble dryer, and which is hereby incorporated by reference.

DEFINITION

Premix burner is to be understood as a burner which is provided with a fully premixed air-combustible gas mixture and therefore equipped with means for obtaining such a fully premixed air-fuel mixture. As an overstoichiometric mixture (preferably an gas-air ratio λ or 1,3) of combustible gas and air is present at the moment of combustion, a blue flame combustion of the combustible gas is obtained.

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

FIG. 1 is a schematic side view cross-section of an embodiment of the present invention.

FIG. 2 is a schematic top view cross-section of the embodiment of FIG. 1.

FIG. 3 is a schematic representation of a burner used in a preferred embodiment.

REFERENCE LIST

- 1 single burner heat exchanger combination
- 110 heat exchanger element
- 120 inlet port of heat exchanger element
- 130 premix burner
- 132 primary air
- 134 fuel gas
- 136 mixing chamber of burner
- 138 hot combustion gases
- 140 dilution zone
- 142 secondary air
- 144 diluted combustion gases
- 150 distributor
- 160 shield around burner
- 170 induction draft fan
- 210 self regulating system for proper gas-air ratio supply
- 220 extra primary air via self regulating system

MODE(S) FOR CARRYING OUT THE INVENTION

FIGS. 1 and 2 show schematically a cross-section of an embodiment of the present invention. FIG. 1 is a view from the side, FIG. 2 is a top view. In FIG. 1 the arrows show the flow path of the gases of the combustion system through the heat exchanger system. The flow of gases is driven by the induction draft fan 170. FIG. 2 shows the details of the present invention, the drawing being cut away where the known heat exchanger setup starts. This embodiment has four spaced apart heat exchangers 110. Each heat exchanger 110 has an inlet port 120 for receipt therein of combustion gases. The single burner is a premix burner providing an excellent combustion of the gas-air mixture. In this exemplary embodiment the premix burner is a tubular burner with a burner membrane at the cylinder surface and an endcap at the end of the cylinder. The burner membrane comprises a perforated metal sheet. But also a metal fiber membrane can be used. The burner 130 is in fluid communication with each port 120 of each heat exchanger 110 through a dilution zone 140 and a distributor 150. These are all airtight connected to each other. The combustion gases 138 produced by the premix burner 130 are mixed with secondary air flows 142 entering the system in this dilution zone 140, whereby diluted combustion gases 144 are obtained. These diluted combustion gases 144 will then enter the heat exchangers 110 via the distributor 150. The combustion gases 138, having a temperature of about 1600° C. are diluted with the secondary air flows 142 to a temperature of about 600° C. The premix burner 130 is surrounded by a shield 160, which prevents a direct cooling of the flames on the burner membrane.
FIG. 3 shows an alternative embodiment of the present invention. FIG. 3 only shows the details of this embodiment, the drawing being cut away where this embodiment overlaps the previous embodiment of FIGS. 1 and 2. The premix burner 130 comprises a self regulating system 210 for proper gas-air ratio supply to the mixing chamber 136 of the premix burner. In this exemplary embodiment, the self-regulating system 210 is a bi-metal which closes of the extra primary air intake 220 in cold conditions. When the burner heats up, the bi-metal bends gradually thereby opening the extra primary air intake 220.

Claims

1. A single burner heat exchanger combination for a gas-fired furnace, comprising:

at least one or a plurality of spaced apart heat exchanger elements, each heat exchanger element having an inlet port for receipt therein of combustion gases,

and a premix burner for producing combustion gases,

said burner being in fluid communication with each port through a dilution zone and a distributor,

said dilution zone being fed by said combustion gases and a secondary air flow and providing diluted combustion gases,

said distributor feeding said diluted combustion gases to said heat exchanger elements,

said burner being surrounded by a shield.

2. The single burner heat exchanger combination of claim 1, wherein said burner comprises a self regulating system for proper gas-air ratio supply to the mixing chamber of the premix burner.

3. The single burner heat exchanger combination of claim 2, wherein said self regulating system comprises a bi-metal.

4. The single burner heat exchanger combination of claim 1, wherein said burner is a tubular burner comprising a burner membrane and an endcap, wherein said burner membrane comprises a perforated sheet metal, preferably made of refractory steel.

5. The single burner heat exchanger combination of claim 1, wherein said burner is a tubular burner comprising a burner membrane and an endcap, wherein said burner membrane comprises a metal fibre burner membrane.

6. A gas fired furnace comprising a single burner heat exchanger as defined in claim 1.

7. Use of a single burner heat exchanger combination as defined in claim 1, in a gas-fired furnace for hot air generation.

8. The single burner heat exchanger combination of claim 2, wherein said burner is a tubular burner comprising a burner membrane and an endcap, wherein said burner membrane comprises a perforated sheet metal, preferably made of refractory steel.

9. The single burner heat exchanger combination of claim 3, wherein said burner is a tubular burner comprising a burner membrane and an endcap, wherein said burner membrane comprises a perforated sheet metal, preferably made of refractory steel.

10. The single burner heat exchanger combination of claim 2, wherein said burner is a tubular burner comprising a burner membrane and an endcap, wherein said burner membrane comprises a metal fibre burner membrane.

11. The single burner heat exchanger combination of claim 3, wherein said burner is a tubular burner comprising a burner membrane and an endcap, wherein said burner membrane comprises a metal fibre burner membrane.

12. A gas fired furnace comprising a single burner heat exchanger as defined in claim 2.

13. A gas fired furnace comprising a single burner heat exchanger as defined in claim 3.

14. A gas fired furnace comprising a single burner heat exchanger as defined in claim 4.

15. A gas fired furnace comprising a single burner heat exchanger as defined in claim 5.

16. Use of a single burner heat exchanger combination as defined in claim 2, in a gas-fired furnace for hot air generation.

17. Use of a single burner heat exchanger combination as defined in claim 3, in a gas-fired furnace for hot air generation.

18. Use of a single burner heat exchanger combination as defined in claim 4, in a gas-fired furnace for hot air generation.

19. Use of a single burner heat exchanger combination as defined in claim 5, in a gas-fired furnace for hot air generation.