DE2207410A1 - Method of generating heat using a gas burner - Google Patents

Description

220741Q

PATENT LAWYERS DR. HUGO WILCKEN DIPL.-ING. THOMAS WILCKEN D - 24 LÜBECK. WIDE STREET 52-54

16, raised. i: .i Th.W./Al.

Applicant: COLUMBIA GAS SYSTEM SERVICE CORPORATION, Wilmington, Montchanin Road. 20, Delaware, USA

Method of generating heat 'using

a gas burner

The invention relates to a method for generating heat using a gas burner, and in particular burners with a so-called burner plate or distributor plate with a number of openings, channels or mouths through which a mixture of air and combustible gas runs and is ignited around a flame front of high heat intensity the surface of the burner plate.

Burner plates provided with passages and orifices can consist of ceramic material, and it is because the air-gas mixture exits at the openings or passages and in combustion zones adjacent to these passages or openings burns, there adjoining or neighboring parts of the plate intensively heated until glowing, by infrared radiation or to generate an infrared radiant heat flux. To ensure the correct operation of the burner, it is It is of fundamental importance that the speed of the air-gas mixture flowing through each of the openings

■ S Lübeck (0451) 7 58 88, private: Dr. H. Wilcken, Curau (04505) 210 Dipl.-Ing. Th. Wilclcen, Lübeck (0451) 251 59 Bank, Commerzbank AG, FiI. LObeck, account no. 39 0187 Post check: Hamburg 1331 19

20 9 84 A / 067 2.:

or orifices moved in the burner plate, is greater than that Speed of propagation of the flame in such a mixture * thus a flashback or breakthrough of the flame into the gas space is prevented, through which the mixture is fed to the various mouths or passages.

As described in detail in the German patent application P 19 49 797 · 3, a breakthrough of the flame through the passages in the burner plate can be avoided, while enabling the burner to operate within a relatively large range for the amount of gas flow through each opening receives a venturi-like shape. If each opening or passage is venturi-like, then a neck part with a small cross-section leads to a widening or diverging outlet part, in such a way that at least the required flow rate is maintained within the neck part to allow the gas backlash over a relatively wide range of the extent of the To prevent gas flow, while the flow velocity in the widening outlet part changes depending on the actual flow rate in order to determine the point within the outlet part at which the combustion of the mixture of air and gas begins. With previously proposed burner plates with venturi-like passages, it has been observed that within the flow dimensions used in each case, the S + rom of the air-gas mixture in the neck part and also in the widening or diverging outlet part of each opening to achieve a

209844/0672

economical combustion of the mixture is or should be maintained, the heat flow radiated from the burner generally in relation to the selected gas flow rate. > changes. Such burners generate radiant heat from the ceramic material of which the burners are made and it results heat release of relatively high intensity. However, one often wishes to have even greater heat dissipation through such To obtain burner and such heat in flame front or blue flame operation instead of or in addition to radiant heat to create.

All that? It is an object of the invention to very substantially increase the _{H 1 -tse and heat output generated by gas burners of the aforementioned type.}

Another object is to increase the heat output of a previously described burner by creating a flame front on the downstream surface of the detector plate.

According to According to one aspect of the invention, a burner is used, the passages or openings of which have a neck part with a relatively small cross section, which extends from an inlet for the air-gas mixture to an expanding or diverging outlet part, into the, in particular at Supply of the heated mixture to the burner at a relatively high mass flow rate, a substantially laminar flow or a jet,

209844/067?

ORIGINAL INSPECTED

: which is generated or built up in the neck part, initiated centrally ; becomes, in such a way that the jet separates from the surface of the diverging outlet part, around a turbulent circulating flow to create the central and laminar flow or jet. The diverging outlet portions of the orifices form edges along the surface of the burner plate, and it will, as the

[Jet of gas from the openings adjacent to the surface icons emerges, a second turbulent and circulating flow is generated on the surface of the plate, as the jet mentioned it separates on the downstream side of the plate and the velocities of the turbulent flow are reduced, ^ if this current moves over the edge of the plate. the [The resulting turbulent and circulating flow on the surface of the plate has a self-igniting or conductive or leading effect for the ignition of the air-gas mixture that comes out of the diverging part of the mouth, so on This way it is ensured that the burn occurs along the surface of the plate and not at a point within the jiiverging part of the mouth takes place, especially when relatively high flow rates of gas are used come. In addition, according to the invention, the generation of a dull flame front can be generated on the plate surface by means of the heat is produced with great intensity. The flame front generated with a burner of the type described above will not detach from the burner surface, as occurred and was to be expected with all of the previously proposed burners,

which results in the present invention that the

l - 5 -

2098U / Q672

Flame front can be kept on the burner surface to cause an increasing heat intensity when the mass flow rate is increased.

The invention is based on one in the accompanying drawing illustrated embodiment for a burner unit explained in more detail. Show it:

1 shows a side view of a gas burner unit in partial section,

2 shows a section through an orifice or a passage in a burner according to FIGS. 1 and _;

3 shows a representation similar to FIG. 2! to illustrate the type of air-gas mixture flow through the passages in the burner plate. ;

First of all, reference should be made to FIG. 1, which shows a gas burner! shows unit 10 used to practice the invention ! can and from a burner 12 with a burner plate 14! ; consists, which is preferably made of a ceramic material

exists and a number of mouths or openings 16 on-

which extend through the plate, while ^l the burner further comprises a chamber 18 over the top thereof; Part of the burner plate 14 extends such that a combustible mixture of air and gas supplied to the chamber 18; flows from this chamber through the mouths or passages 16 of the plate 14. The air-gas mixture is supplied to the collecting chamber or the gas space 18 via a pipe 20 from a schematically illustrated source 22, _ g

209844/0672

As mentioned before, there is air and the combustible Gas mixture supplied to the chamber 18 in one Mixing ratio suitable for firing, preferably almost or approximately stoichiometric, and therefore a complete combustion of the gas is guaranteed without the supply of auxiliary air into the combustion zone.

As can be clearly seen in particular from FIG. 2, each of the Mouths 16 a venturi-like shape and consists of a neck portion 26, which extends from an inlet opening 28 at the lower

! Surface 30 of the plate 14 to a widening or diverging Outlet portion 32 extends to the downstream Surface 34 of the burner plate ends. The inlet portion 28 each;

The mouth can have a rounded surface, not shown, on its inlet edge 29, which converges in the direction of the neck part 26 in order to ensure a smooth, undisturbed inlet flow of the air-gas mixture from the chamber 18 into _; to reach the estuary. The neck portion 26 has a relatively small cross-sectional area, which is preferably along its length

! is uniform, while the expanding or diverging

I outlet portion 32 generally has the shape of an inverted, ab-;

, flattened cone, so that cross-sectional areas result ! that of the neck part 26 in the direction of the mouth opening at the outlet part 32 and in the direction of the downstream surface 34 and thus become progressively larger in the direction of flow of the mixture through the mouth 16. In addition, each mouth preferably has a circular cross-section over its entire length.

- 7 209844/0672

2207-1 Q

The diverging part 32 of the various mouths in the plate each form edges 36 on the upper surface of the Burner plate along which, as will be described in detail later, a separation and circulation of the through flowing gas occur in the mouth to create a flame front on the plate surface.

In operation of the burner unit 10 described above, an air-gas mixture is supplied to the plenum chamber 18 via the pipe 20 from the source 22, the mixture then flowing upwards through the mouths 16 of the plate 14 and the mixture initially adjacent to the upper surface 34 the burner plate ignited], for example with a conventional elek- _;

tric igniter or with a pilot light. Before that, the Adjusting the operation of the burner unit 10, the range of j length flow rates of the mixture selected so that the upper and lower limits of this range are set such that the velocity of the flow through the neck portion 26 of each opening; is greater than the flame propagation speed in the mixture, which causes the flame to flash back through the! Openings into the chamber 18 is prevented. The angle of the! Divergence of the outlet part 32 of the mouth 16 and the maximum Amount of gas flow rates to be used are selected in relation to one another in such a way that all occurring . and a substantially laminar flow of the mixture through the neck portion 26 with changing flow rates and is also present in the diverging outlet part 32. In other words, this means that the speed

20984W0672

Flow passing through the neck portion 26 progressively expands in the outlet portion 32 to be substantially uniform Maintain flow velocity over the entire area of each cross section in the outlet part 32, the velocity speed of the outer parts of the flow is slightly less than that of the middle flow part and with these velocities decrease progressively in the longitudinal direction of the neck part 26 towards the exit or opening of the outlet part 32.

If the range of the gas flow rates is selected so that a laminar flow of the mixture in the outlet portion 32 each! Fatigue is maintained, then the burning of the mixture in the diverging outlet part will begin at a point or at a J ¹ level at which the flow velocity is reduced to the

Flame propagation speed was significantly reduced. I.

In the range of relatively low mass flow rates, at which the;

Burner is initially operated, the burning of the laminar ι Air-gas mixture flow emerging from each orifice 16 at or near the opening of each orifice on the Surface 34 occur, so that the combustion an intense j heat development and glowing of the ceramic plate 14 in the outlet;

1 I.

part 32 caused. Although the previously proposed mode of operation [ allows the burner unit 10 to change the infrared radiation generated by the burner 12 i to a relatively large extent without running the risk of flashback when the radiant heat is reduced to its lowest level the maximum achievable heat radiation flux in general

20984 4/0672

limited by the small areas of the plate 14 which are made glowing at the maximum flow rate, the laminar flow in the outlet portion 32 being maintained. It has been found that if the rate of gas flow is further increased beyond the point at which laminar flow occurs, a central jet will be ejected into the divergent outlet portion 32 of the orifice and that the jet will move away from the surface of the orifice diverging outlet part 32 separates and lifts off, whereby a zone of turbulent, orbiting and circulating flow of relatively low velocity between the central jet and the surface of the outlet part 32 is created. In this circulation! zone, turbulence flows are formed with a relatively lower speed and pressure than in the central jet. When the air-gas mixture emerges from the mouth 16! and is ignited, gases located in this zone are with _; causes the ignition to occur at a lower speed. The burning gases in this area are extremely effective in transferring heat to the conical wall of each outlet member 32 to bring that ceramic wall to a temperature at which it glows. In this way, the area of the glowing ceramic material is considerably increased, which also significantly increases the infrared radiation emitted by the burner.

It was previously assumed that any increase in the mass flow rate of the air-gas mixture through the orifices over beyond the point at which maximum radiant heat can be reached

- 10 -

209844/0672

is bar, that is, beyond the rate of the mass flow at which the gases burn in the entire diverging part 32, a "lift-off" j of the flame fronts from the surface 34 of the plate 14, i.e. that the combustion of the mixture above of the surface 34 of the burner plate 14 in an ineffective and would occur in an undesirable manner, namely with an inevitable reduction of the glow and thus the radiation of infrared radiation through the plate.

However, it has surprisingly been found that the heat or amount of heat generated by the burner 10 increases drastically becomes, if at a certain divergence angle of the outlet part 32 of each mouth the amount of the flow of the air-gas mixture is increased sufficiently to prevent the burning of gases within the divergent outlet / part 32, even with a consequent loss of infrared radiation generated by the heated walls of the outlet part.

Thus, according to the present invention according to FIG. 3, the mass flow rate of the air-gas mixture is increased sufficiently so that that a central jet or laminar flow generated within the neck portion 26 of each orifice into and through the diverging outlet part 32 is pushed as a central jet 38, in conjunction with a turbulent, circulating Zone 39 of relatively high velocity adjacent the walls of the outlet part 32, said jet and the mentioned zone extend in the direction of edges 3b, where a

209844/0672

second turbulent circulating flow 40 on the surface 34 of the Plate is made adjacent to the edges. The speeds generated in this way in zone 39 are too high to to support a flame stabilization, so that there the air-gas mixture does not burn, while on the other hand at the Zone 40 is the flows from the air-gas mixture at relative low speed and low pressure and can therefore be ignited. With an increase in the mass flow rate accordingly, the flame front at outlet portion 32 moves toward surface 34, but the flame front rises from the burner plate because of the presence of the second turbulence zone 40.

When the air-gas mixture emerges from the orifices 16 and is ignited, those located in the zone 40 are likewise Causes gases to ignite at lower speeds. Burning gases in zone 40 are extremely effective at creating one intense heat that is significantly greater than the heat generated by operating conditions with a lower flow rate, .which produce radiant heat. The gases burning in zone 40 create a relatively flat flame front along the top surface 34 of the plate, i.e. a blue flame front covering essentially all of the burner generated heat.

Since the swirling streams and the circulating gas stream in the zone 40 cause a constriction of the orifices 16, the

- 12 -

2098U / Q672

2207A1 O

Pressure drop across plate 14 increases and high velocity jet 38 is maintained.

The burning gases in circulation zone 40 also serve as a pilot flame to ignite the air-gas mixture, if this occurs from the mouth 16 in the region of the edges 36. Thus, the mixture begins to burn in jet 38 when it enters the Zone 40 occurs, due to the self-regulating action described, whereby a lifting of the flame front from Burner is prevented. These previously explained circumstances enable the application of a mass flow to an air-gas-

Mixture through the plate 14, which is several times greater than in the case of the previously known, based on the burning surface unit ι burners was possible. Because a much larger volume If fuel is consumed in the process, a significantly larger amount of heat is also provided by the burner.

As noted earlier, the rate of mixture through the neck portion 26 is greater than the rate of spread the flame front, so that a flashback of the flame ι will not occur. The flow of non-burning gases in the neck portion 26 also ensures that the temperature of the ceramic material at the inlet of each orifice, i.e. at the upstream located side of the plate 14, is maintained at a value which is substantially below the temperature value at the surface 34 of the Brenners lies.

- 13 -

2098U / 0672

The mass flow rate at which the described flow separation or flow separation occurs is of course a function of the angle of divergence of the outlet portion 32 of each orifice Greater divergence a lower mass flow rate may be required to separate or detach the flow from the surface of the outlet part 32 to effect.

For example, suppose that a burner plate has orifices the neck portion of which is 8.26 mm long and diameter of 1.17 mm and the diverging outlet part thereof having a length of 7.62 mm and an included angle of divergence of about 13 °, then the volume flow rate required for the aforementioned separation or detachment is included nearly 1,100 standard cubic feet of a stoichiometric combustible Mixture (town gas and T, uft) under standard conditions pro Square feet of burner area and per hour. For a burner plate with similar mouths where only the diverging outlet part has an angle of 11 °, that is for the above-mentioned detachment required bulk flow rate at nearly 1200 standard cubic feet the stoichiometric combustible mixture at standard conditions per square foot of burner area per hour. Overall blue flame operation can be achieved by increasing the mass flow rate to close to 2200 standard cubic feet is increased per square foot of burner area and per hour, while the burner plate has a MünrlimgsdiTergenzwinkel -von

-H-209844/0672

2207 A 1 O

13 °, and on the other hand, this mentioned operating condition can be achieved if the mass flow rate is increased to almost 1650 standard cubic feet per square foot per hour when the openings have an angle of divergence of 11.

The circulation zone 40, which consists of fuel gases and is generated along the surface 34, is caused by the turbulence that occurs in the Gas flow or gas jet 38 is present, and caused by the gas discharge from the zone 39 when this the edges 36 on the Pass mouth surfaces. This so generated turbulence zone j enables a substantial increase in the amount of burning Gases, so that a greater heat output is generated, and it also prevents the flame front from lifting off the burner surface. It should be noted that the flame front generated in this way could also be generated with a muzzle, which has only one diverging part 32 without the neck part 26. However, the neck portion 26 allows a modulation of the Air-gas mixture through lower mass flow rates, so that the Heat dissipation or the heat output can be varied over a larger range, including the lower Heat output ranges that are given in infrared operation of the burner j.

It has been found that by substantially increasing the amount of flow of the air-gas mixture through the burner 10 the amount of heat generated when operating the burner flame can be significantly increased. With the one suggested earlier

- 15 -

2098U / 0672

Radiant heat burner operation "at lower mass flow rates a maximum of 1300 to 1400 BTU per hour and per square inch burner area could be achieved. By increasing the Hengea flow rate by the burner 10 according to the present invention, the BTU output can be increased considerably, up to at least 1200 BTU per hour and per square inch burner area.

As already mentioned, the radiation generated by the burner decreases amount of heat from increasing the mass flow rate, since or when the operation of the burner is the operation with a flat flame front approaching. When the mass flow rate reaches the level at which the burner is producing 1300 BTUs per hour, the '

to decrease the amount of radiant heat caused thereby, while ] the amount of radiant heat generated by the combustion of the gases within zone 40 increases. With continuous

An increase in the mass flow rate could possibly reduce the

The amount of radiant heat generated by the burner approaches the value 0; taking all of the heat by burning the gases in the zone

40 would be generated. ι

It should be noted that the source 22 for the air-gas;

Mixture preferably supplies pressurized gas and air,. to achieve a mass flow rate through the mouths 16! with which the described flow characteristics according to the invention, , are achievable. However, a conventional venturi supply system could also be used be used. In this case must

209844/0672

2207-1O

the gas can be supplied at a sufficiently high pressure so that the mixture of gas and aspirated air reaches a sufficiently high mass flow rate to separate the flow on the surface of the plate 14 as described above.

2096U / 0672

Claims (4)

PATENT LAWYERS ^^ DR. HUGO WILCKEN DIPL.-ING. THOMAS WILCKEN D - 24 LÜBECK. WIDE STREET 52-54 Feb 16, 1972 Th.W./Al. Applicant: COIUMBIA GAS SYSTEM SERVICE CORPORATION, Wilmington, Montchanin Road 20, Delaware, USA Patent claims (1. / Method for generating Hitae or heat using a gas burner unit with a plate which has a number of mouths or passages, each inlet and Having outlet openings on opposite surfaces of the plate, characterized in that a combustible air-gas mixture through the mouths at such a mass flow rate is directed that a central jet is formed from the mixture mentioned, which through each of the mouths flows from the inlet opening in the direction of the outlet opening, and that there is a relatively high velocity turbulence zone from the air-gas mixture between the jet and the walls of the mouths, and that a flow separation of the jet and the zone of turbulence is caused at the edge portion of the outlet opening of each orifice to form a zone of a turbulent, low speed and circulating flow along the outlet surface of the plate to bil- '»on, in there essentially unhindered flame propagation IT lOhnrlr (0451) 7 58 88, private ι Dr. H. Wilden, Curau (04505) 210 Dipl.-Ing. Th. Wilcken, Lübeck (0451) 2 51 59 B'jnki C'jmrntr / borik AG, FiI. Lübeck, toilet no. 39 0187 Post check: Hamburg 1381 19 209844/0672 2. A method for generating heat in a gas burner unit with an orifice plate, in which each Mühduhi ' ^{v has} a neck part which leads into a conical outer part which has a cross-section that increases in the direction of the gas flow the outlet surface "of the plate" opens and forms mouth edges, characterized in that a relatively high velocity flow is generated from a combustible air-gas mixture in each mouth, the flow having a substantially uniform cross-sectional area that a relatively lower velocity circulating flow is created from the air-gas mixture at the surface of the plate adjacent the edges and that the lower velocity flow is caused to burn to produce a relatively flat flame front along the surface. 3. The method according to claim 2, characterized in that such a degree of the existing from the air-gas Geaiis-h Flow created through the orifices is that speed the flow of the mixture through the neck portion of each mouth is greater than the speed of flame propagation of the mixture and a substantially laminar flow in the Neck part produced that one consisting of the mixture mentioned Beam is directed centrally into the outlet part, wet a lower one Velocity circulating flow from the mentioned mixture is generated on the surface of the burner adjacent to the shrouds and that initially from the mouths 209 * 44/0872 the mixture leaking adjacent to the edges is ignited, whereupon an intense combustion of the mixture occurs on the surface of the plate, around the one emerging from the mouths To produce mixture and thereby a relatively flat flame front cause high heat intensity on the plate surface, 4. The method according to claim 3, characterized in that the air and the gas oa; s are pressurized to achieve the required flow rate. 209844/0672 Blank page