US3902840A

US3902840A - Dilution burner

Info

Publication number: US3902840A
Application number: US338468A
Authority: US
Inventors: Paul Baguet
Original assignee: PARTICIPATIONS IND COMP D ET
Current assignee: D'ETUDES ET DE PARTICIPATIONS INDUSTRIELLES Cie; PARTICIPATIONS IND COMP D ET
Priority date: 1972-03-16
Filing date: 1973-03-06
Publication date: 1975-09-02
Anticipated expiration: 1992-09-02
Also published as: FR2175800A1; FR2175800B1; GB1408824A; IT981442B; LU64978A1; ES412485A1; JPS492128A

Abstract

A dilution burner comprising at least two separate injectors with different injection cross-sections, for a fuel gas and a comburent gas, opening into the entry of a combustion chamber, means being provided in order that, when the injection flow of gas in the combustion chamber drops below a value preset in terms of the minimum speed of the gases needed at the outlet of the injectors in order to prevent a flash back, the injector with the largest cross-section shall be cut out of service, the supply of the combustion chamber being then solely carried out by the remaining injector or injectors.

Description

United States Patent Baguet Sept. 2, 1975 54 1 DlLUT/ION BURNER FOREIGN PATENTS OR APPLICATIONS [75] Inventor: Paul Baguet, Brussels, Belgium 508,850 7/1971 Switzerland [73] Assignee: Compagnie dEtudes et de 1'465 5/1969 f f Participations Industrielles, M81445 4/1970 United Kingdom Grand Rue Luxembur 1,138,699 1/1969 United Kingdom g 1,810,976 6/1970 Germany 22 Filed; Man 6, 97 1,918,896 /1969 Germany [21] Appl' N07 338468 Primary Examiner-Carroll B. Dority, Jr. [30] Foreign Application Priority Data Attorney, Agent, or FirmSughrue, Rothwell, Mion,

Zinn & Macpeak Mar. 16, 1972 Luxemburg ..64978 [52] US. Cl. 431/61; 431/90; 431/115',

431/158; 431/284 [57] ABSTRACT [51 Int. C1. F23Q 9/08 A dilution burner p sing at ast two separate in- [58] Field of Search 431/30, 31, 61, 89, 90, jectors with different injection cross-sections, for a 431/115, 158 fuel gas and a comburent gas, opening into the entry of a combustion chamber, means being provided in [56] References Cited order that, when the injection flow of gas in the com- UNITED STATES PATENTS bustion chamber drops below a value preset in terms 2,046,767 7/1936 Campbell 431/174 of the l l spfaed of the gases needed at the 2335.471 l H1943 Ashcraft I I 131/31 let of the In ectors In order to prevent a flash back, the 3939522 6/1962 Soho 431/9O injector with the largest cross-section shall be cut out 3,146,821 9/1964 Wuetig 431/115 of Service, the p y of the Combustion Chamber 3,173,483 3/1965 Br d ct al 431/90 being then solely carried out by the remaining injector 3,322,178 5/1967 Nah-as 431/61 or injectors. 3,376,098 4/1968 Pryor 431/158 3.529.915 9 1970 Tsuji Ct a1. 431/284 Clams, 4 Drawlng Flgul'es 3.749.546 7/1973 Reed ct a1 431/89 3,779,689 12/1973 Reed ct a1 431/61 PATENTED SEP 2x175 sum 1 0r 2 FIG.1

DILUTION BURNER The present invention relates to a dilution burner comprising in succession at least one ejector fora fuel gas and a comburent gas, a combustion chamber wherein terminates suchinjector, a dilution chamber wherein diluting gases are added to the gases leaving the combustion chamber, and'a terminal element comprising an outlet opening through which the gases, both those originating from the combustion chamber and the dilution gases, enter the furnace whereon is mounted the burner.

By the term dilution burner is to be understood a burner wherein air or waste gases are added to the gas issuing from the burners.

The conventional dilution burners known up to the present, if they are based on premixing' the fuel and the comburent, only pennit varying the calorific flow and the volumetric flow within fairly narrow limits. This results essentially from the risks of flash back to the injector. Indeed, in order to prevent such flash back, it 'is mandatory for the rate of the discharge of the gases at the injector to be always higher than the rate of combustion of the combustion gas comburent gas mixture. One of the principal objects of this invention is to overcome this drawback and, moreover, to make avail able a dilution burner permitting the simultaneous variation of these two flows.

There are also known on the market dilution burners to the flames of which is added air or the gases picked up inside the furnace to be heated by such burners. The mixture of air-formed dilution gases is carried out in the combustion chamber. Q

This presents inter alia the drawback that the excess quantity of air and, consequentlyfthe dilution thereby is limited by the conditions of combustion.

Another reason because of which the known burners only permit achieving a very limited dilution and, consequently, a setting of the temperature inside the furnace for a specific calorific flow within very narrow limits is the fact that the mixture of fuel gas and of comburent gas is carried out within the actual combustion chamber. v

For that purpose, according to the invention, the burner comprises at least two separate injectors of different injection cross-sections, opening into the entry of the combustion chamber, means being provided in order that, when the injection flow of gas in the combustion chamber drops below a value preset in terms of the minimum speed of the gases needed at the outlet of the injectors in order to prevent a flash back, the injector with the largest cross-section shall be cut out of service, the supply of the combustion chamberbeing then solely carried out by the injector with. the smallest cross-section.

According to a particular advantageous embodiment of the invention, at least one delivery pipe for the dilution gases ends in the said dilution chamber, means being provided to adjust the flow of this dilution gas in such pipe independently of the kinetic energy of the combustion gases crossing the-dilution chamber.

A constructional embodiment of a burner according FIG. I shows a diagrammatic elevational sectional view along line Il in FIG. 2.

, FIG. shows a sectional view along line IIII in FIG.

FIG. 3 shows an elevational sectional view of a detail of the burner shown in FIGS. 1 and 2.

FIG. 4 shows a diagrammatic view of an assembly of burners of the type shown in FIGS. 1 and 2 and of pipes supplying these burners with a mixture of fuel gas comburent gas prepared beforehand.

According to the invention, the dilution burner shown in FIGS. 1' and 2 comprises in succession two concentric injectors l and 2, a combustion chamber 3 wherein end these injectors, a dilution chamber 4, wherein dilution gases are added to the gases leaving the combustion chamber 3, and a terminal element 5 provided with a central outlet opening 6 through which the gases originating from the combustion chamber 3 and mixed with the dilution gases enter the furnace, not shown in the Figures, whereon is mounted the burner. The burner comprises mainly an outer casing 7 of prismatic shape and a cylinder 8 inscribed within such prism and determining externally the combustion chamber 3. Both such the casing 7 and the cylinder 8 are produced from ceramic material.

In the embodiment shown in FIGS. 1 and 2, the casing 7 is of square internal cross-section, so that between such casing and the external periphery of the combustion chamber 3 are formed four longitudinal ducts 9 of whichone end terminates in the dilution chamber 4. The other end of the ducts 9 terminates in an admission chamber 10 for air or another dilution gas extending around the injectors l and 2.

The combustion chamber 3 communicates with the dilution chamber 4 by means of a throttle terminating in a port 1 1 having a diameter less than that of the outlet opening 6 provided in the terminal element 5 and coaxial with such opening. Accordingly, by selecting thewidth of the dilution chamber 4 and the thickness of the element 5, the unit comprising the port 11, the opening 6, and the space of the dilution chamber 4 extending between such port and such opening, provides an injector by means of which it is possible to establish in such space, thanks to the considerable kinetic energy of the gases escaping from the combustion chamber 3 through the port 11, a depression sufficient to ensure that the dilution gases are drawn by the gases of combustion through the outlet opening 6 into the furnace, not shown, whereon is mounted the burner.

If no substantial amount of air or other diluting gas is introduced in the chamber 4 by the ducts 9, the depression in the chamber 4 also draws, through channels 12 passing right through the terminal element ,5 and extending. ring-like around the central opening 6, waste gases positioned inside the furnace. These gases drawn from the furnace are admixed with the waste gases leaving the combustion chamber 3 and are drawn by the latter, thanks to their considerable kinetic energy, through the opening 6 back again into the furnace. The burner according to the invention is thus, because of this phenomenon, self'diluent under these conditions.

If air or other diluting gases, such as waste gases are introduced in the 'dilution' chamber 4 by the ducts 9, such air or other diluting gas is drawn in part by the stream'of waste gases leaving the combustion chamber 3 in order to be thus admitted through the opening 6 inside the furnace; the otherportion ,of the air or of such dilution gases leaves'through the channels 12 provided in the terminal element 5 in order to be drawn by the stream escaping from the opening 6 so as to provide an additional dilution of the waste gases leaving the combustion chamber 3. Under these conditions-the burner is likewise diluted, and there exists thus a double dilution.

The temperatureof such stream is determined, for a given flow of dilution gas, by the flow of the burner.

The dilution burner according to the invention thus ejects at its outlet opening 6 provided in the element a stream of gas which is stable, diluted, and towhich is imparted a high velocity, the latter resulting from the narrowness of the opening, from the considerable volume of waste gases, caused by the. high temperature ruling inside the combustion chamber, and from the addition of dilution gas.

A mixing-measuring valve, not shown in the FIGS. 1 and 2, to which lead a duct for comburent gas and a fuel gas delivery pipe is mounted upstream of each injector l and 2 in such a manner that the latter shall be supplied with a fuel mixed with a comburent beforehand.

The selection of the volume of comburent gas fuel gas mixture admitted by means of the said valve inside the injectors l and 2 controls the calorific flow of the burner, while the adjustment of the quantity of dilution gas, admitted by the channels 9 to the dilution chamber, controls the temperatureand the volume of the gases ejected by the burner through the opening 6. The quantity of dilution gas admitted by the channels 9 can be adjusted, for example, by a manually controlled valve 38 located in the pipe 39 leading to the admission chamber 10. It is also possible, in the case of specific uses, to adjust right away the temperature of the dilution gases admitted to the dilution chamber 4 through the ducts 9.

The limits of adjustment of the calorific output are dependent on the characteristics of the injectors, of the maximum feed pressure and of the minimum feed pressure of the latter. The upper control limits of the dilution gas flow are set by the feed pressure. As regards the lower limits, they are practically nil, as all the components making up the burner are of fire-proof material of suitable quality and able to resist the release of heat, by conductivity, of the combustion chamber.

In order that the calorific output may drop below the total flow of the fuel gas comburent gas mixture which risks causing the flash back, according to the invention, the burner comprises a double injector or two injectors as already mentioned above, in order that the reduced flow may only be admitted by,-a reduced sec- I tion of injection.

In the embodiment shown in FIG. 1 and illustrated in greater detail in FIG. 3, the two injectors or the double injector comprise two coaxial ducts.

The two injectors l and 2 have different injection cross-sections, the injector 1 having the larger section.

Means are provided in order that, when the injection flow of the gases into the combustion chamber drops below a value preset in terms of the minimum speed of the gases needed at the outlet of the injectors to prevent a flash back, the injector 1 with the larger crosssection, shall be cut out of service, the supply of the combustion chamber being then solely carried out by i the injector 2 having the smaller injection section.

The said means comprise

automatic valves

13 and 14 mounted on the feed. pipe 15 of the injector l and on the feed pipe 16 of the injector 2, respectively. The

' l3 and 14 are controlled in terms of the pressure present in the

pipes

15 and 16 downstream of these valves. This pressure is measured by the gauges l7 and 18 provided in the said

pipes

15 and 16 respectively, downstream of the

valves

13 and 14.

As soon as the pressure of the fuel gas comburent gas mixture flowing in the pipe 15 drops below the critical value of the flash back, the valve 13 closes and the burner is solely supplied through the injector 2. The purpose of the valve 14 will be obvious from the subsequent explanation of the purpose of the

valves

26 and 28.

In order to prevent the mixture fuel gas comburent gas, remaining in the pipe 15 between the valve 13 and the outlet of injector 1 from burning and giving rise to a detonation, according, to the invention the composition of such mixture flowing in the pipe 15 may be modified before closing the valve 13 in order that such composition shall fall outside the limits of combustion of the said mixture.

A particular embodiment of the invention making it possible to implement such modification of composition is shown in FIG. 4.

In that Figure only ,two burners mounted in parallel are shown, but it is evident that this quantity may vary in accordance with the dimensions of the furnace.

The injectors 1 and2 are separately fed by means of mixing-measuring

valves

23 and 24 of a type suitable to assure a constant fuel gas comburent gas ratio for all flows.

Theequipment illustrated in FIG. 4 comprises a common pipe 19 for the two injectors l and 2 supplying the comburent gas, particularly the combustion air, to these injectors. A main valve 20, motor driven or otherwise, is provided in this pipe 19, such valve permitting the adjustment of the flow of the burners, mounted in parallel, according to the calorific output required.

This common pipe 19 is forked downstream of the valve 20 in order to provide two

separate pipes

15 and 16 for the two injectors l and 2. A tubing 21 and a tubing 22 for supplying the fuel gas are led off each of these

separate pipes

15 and 16 respectively by means of mixing-measuring

valves

23 and 24 respectively for these two gases. Intermediate valves 25 and 26 are provided for each of these

separate pipes

15 and 16 respectively upstream of the mixing-measuring

valves

23 and 24.

As in the embodiment shown in FIG. 3, pressure gauges 17 and 18 are mounted in each of these

separate pipes

15 and 16 downstream of the

valves

23 and 24. The pressure gauge 17 actuates the valves 25 and 27, and the pressure gauge 18 actuates the

valves

26 and 28.

The separate pipes terminate at each one of the

injectors

1 and 2 of each burner and feed the latter with a mixture of fuel gas and comburent gas in preset quantities.

As soon as the pressure of the fuel gas comburent gas mixture, monitored by the gauge 17, drops below a pressure slightly above the critical pressure value causing a flash back, the valve 27 (which may, for example, be a magnetic valve) is closed by the motor 31, causing a depletion of fuel gas in the feed pipe 15. Subsequently valve 25 is closed by motor 33, stopping any flow in the pipe 15 supplying the injector l.

The time lag between the closure of valve 27 and that of valve may be controlled by a time relay according to the nature of the fuel gas in order that the gaseous mixture, remaining in the pipe 15, shall not be inflamed. The calorific fiow is then solely supplied by the injector 2.

When an increase of the calorific flow is required, valve 25 opens again. As soon as the pressure in the pipe 15, monitored by the gauge 17, exceeds the critical value, below which there is a risk of a flash back to injector l, valve 27 opens and injector 1 is cut in again for service. I

Should, however, the calorific flow required be less than that corresponding to the minimum velocity of the gases at the outlet of the injector 2 to prevent a flash back to this injector, a contactor 37 actuated by the gauge 18, causes the closure of valve 28 via a motor 32. The main valve 20 or the valve 26 may then be closed by a motor 34 without any flash back arising asthe gaseous mixture has been sufficiently depletedin the pipe 16.

From the description hereinbefore given of a particular embodiment of a burner according to the invention, it follows that the range of dilution by means of air or another gas, such as a waste gas, is practically unlimited. When no further injection of dilution gas originating from the ducts 9 takes place, the dilution by the fumes of the furnace drawn into the chamber continues.

An ejection of gas at reduced temperature and of large flow is thus always assured at the burner outlet. This establishes in the furnace chamber a very extensive isotherm because of the entraining action of the furnace atmosphere from the high speed of the gas stream on leaving the burner.

The entraining action of the furnace atmosphere may be advantageously enhanced by an appropriate lay-out of the burners within the enclosure to be heated, for example by providing a substantially tangential injection.

From the description hereinbefore given, it also follows that the thermal output of the burner according to the invention may be adjusted within very wide limits without risk of a flash back. It is, indeed, possible to select the outlet cross-sections of the

injectors

1 and 2 taking the rate of combustion of the fuel gas used into account.

Thanks to the use of mixing-measuring valves of a suitable type, the ratio of the comburent gas fuel gas mixture supplied to all the burners of the same run remains constant when the flow of the run considered varies.

It is well understood that the invention is not limited to the described embodiments, but that many modified versions may be contemplated without departing from the scope of the present patent application.

Thus, two, quite separate, non-concentric injectors might, if need be, be provided or even more than two of such injectors with different injection cross-sections.

What I claim is:

l. A dilution burner comprising:

a. a combustion chamber;

b. a first injector opening into the entry of said combustion chamber; I

c. a first feed pipe leading to said first injector;

d. a second injector, separate from: and independent of said first injector and having a larger crosssection than said first injector, likewise opening into the entry of said combustion chamber;

e. a second feed pipe leadjng to said second injector;

f. first means for cutting said second injector out of service when the injection flow of gas in said combustion chamber drops below a value. preset in terms of the minimum speed of the gases needed at the outlets ,of said injectors to prevent a flash back, said first means being located in said second feed pipe, said first means comprising an automatic valve mounted in said second feed pipe, the opening and closing of said automatic valve being controlled in terms of the pressure ruling in said feed pipe downstream of said automatic valve;

g. second means for modifying the composition of the fuel-comburent mixture i. in the portion of said second feed pipe located between said said second injector and said first means,

' -ii. to a composition which is' outside the limits of combustion of the mixture, and iii. prior to the operation of said first means;

h. a common pipe for supplying comburent gas to both said first injector and said second injector;

i. a main'valve mounted in said common pipe;

j. a first separate pipe leading from said common pipe downstream of said main valve to provide comburent gas to said first feed pipe;

k. a second separate pipe leading from said common v pipe downstream of said main valve to provide comburent gas to said second feed pipe, said first means being located in said second separate pipe;

1. a first mixing-measuring valve for the comburent and fuel gases entering said first feed pipe;

m. a second mixing-measuring valve for the comburent and fuel gases entering said second feed pipe;

n. a first intermediate valve located in said first separate pipe;

0. a first fuel supply pipe leading to said first mixingmeasuring valve; 1

p. a second fuel supply pipe leading to said second mixing-measuring valve, said second means being located in said second fuel pipe;

q. a second intermediate valve located in said first fuel supply pipe; and

r. means for controlling said valves with reference to the pressure ruling in said first and second separate pipes downstream of said first and second mixingmeasuring valves such that: I i. when the pressure in either of said first and second separate pipes drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said second means is first caused to close and, subsequently, said first means is caused to close, the time lag occurring between these two closures being calculated so that the composition of the fuel-comburent mixture remaining in said second feed pipe and the portion of said second separate pipe downstream of said second mixingmeasuring valve is sufficiently depleted of fuel, prior to cutting said second injector out of service, to prevent the burning of the mixture; ii. when subsequently an increase of the flow is again required, said first means is first opened and, subsequently, said second means is opened when the pressure ruling in said second separate pipe exceeds said preset value, and' iii. when said second injector has been cut out of service and the velocityof the gases at the outlet of said first injector is less than the velocity required to prevent a flashback, said second intermediate valve is first closed and, subsequently, said first intermediate valve is also closed,'thus cutting said first injector out of service.

2. A dilution burner comprising:

a. a combustion chamber;

b. a first injector opening into the entry of said combustion chamber; 1

c. a first feed pipe leading to said first injector;

d. a second injector having a larger cross-section than and being coaxial to said first injector, said second injector being separate from and independent of said first injector but likewise opening into the entry of said combustion chamber;

e. a second feed pipe leading to said second injector;

f. first means for cutting said second injector out of service when the injection flow of gas in said combustion chamber drops below .a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said first means being located in said secondifeed p p g. second means for modifying thecomposition of the fuel-comburent mixture i. inthe portion of said second feed pipe located between said second injector and said first means,

ii. to a composition which is outside the limits of combustion of the mixture, and

iii. prior to the operation of said first means;

i. a main valve mounted in said common pipe;

j. a first separate pipe leading from said commonpipe downstream of said main valve to providecomburent gas to said first feed pipe;

k. a second separate pipe leading from said common pipe downstream of said main valve to provide comburent gas to said second feed pipe, said first means being located in said second separate pipe;

l. a first mixing-measuring valve for the comburent and fuel gases entering said first feed pipe;

n. a first intermediate valve located in said first separate pipe;

o. a first fuel supply pipe leading to said first mixingmeasuring valve;

p. a second fuel supply pipe' leading to said second mixing-measuring valve, said second means being located in said second fuel supply pipe;

q. a second intermediate valve located in said first fuel supply pipe; and i i r. means for controlling said valves with reference to the pressure ruling in said first and second separate pipes downstream of said first and second mixingmeasuring valves such that:

i. when the pressure in either of said first and Second separate pipes drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said second means is first caused to close 8 land, subseque'ntly, said first means is caused to closejthe tirne lag occurring between these two closures being calculated so that the composition of the fuel-comburent mixture remaining in said second feed pipeand the portion of'said second separate pipe downstream of said second mixingmeasuring valve is sufficiently depleted of fuel, 'prior to cutting said second injector out of service, to prevent the burning of the mixture;

ii. when subsequently an increase of the flow is again required, said'first means is first opened and, subsequently, said second means is opened when the pressure ruling in said second separate pipe-exceeds said preset value, and

'iii. when said second injector has been cut out of service and the velocity of the gases at the outlet of said first injector is less than the velocity required to prevent afiashback, said second intermediate valve is first closed, and subsequently, .said first intermediate valve is also closed, thus cutting said first injector out of service.

3.- A dilution burner comprising:

a. a-* combustion chamber;

b. a first injector for a mixture of a fuel gas and a comburent gas, said first injector opening into the entry of said combustion chamber;

c. a second injector having a smaller cross-section than and being coaxial to said first injector, said second injector likewise opening into the entry of said combustion chamber but said second injector being separate from. and independent of said first injector,

d. means for cutting said first injector out of service when the injection flow of gas in said combustion chamber drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said first and second injectors inorder to prevent a flashback; v

e. a feed pipe leading to said first injector, said means being mounted in said feed pipe;

f. a pressure gauge mounted in said feed pipe between said means and said first injector; and

g. means for closing said means when said pressure gauge senses a value which indicates that the injection flow of gas in said combustion chamber has dropped below the preset value referred to in subparagraph (d).

4. A dilution burner comprising:

a. a combustion chamber;

c. a second injector for a mixture of a fuel gas and a comburent gas, said second injector likewise opening into the entry of said combustion chamber but said second injector beingseparat'e from and independent of said first injector;

d. first meansfor cutting said first injector out of service when the injection flow of gas in said combustion chamber drops below a value preset in terms of minimum speed of the gases needed at the outlets of said first and second injectors in order to prevent a flashback;

e. second means for modifying the composition of the fuel-comburent rr lixturein said first injector so that the composition isoutsijde the limits of combustion of the mixture;

f. third means for modifying the composition of the fuel-comburent mixture in said second injector so that the composition is outside the limits of combustion of the mixture;

g. a feed pipe leading to said first injector, said first means being mounted in said feed pipe;

h. a pressure gauge mounted in said feed pipe between said first means and said first injector; and

i. means for closing said first means when said pressure gauge senses a value which indicates that the injection flow of gas in said combustion chamber has dropped below the preset value referred to in subparagraph ((1).

5. A burner comprising at least two separate independent injectors of different injection cross-sections opening to one another mounted into the entry of a same combustion chamber and a mixing measuring valve to which lead a feed duct for cumburent gas and a fuel gas delivery pipe being mounted upstream of each injector in such a manner that each injector is supplied with a fuel mixed with a comburent beforehand, means being provided, so that, when regulating the gas output the injection speed decreases, just before the injection speed of gas into the combustion chamber drops below a value preset in terms of the minimum speed of the gas needed at the outlet in the injectors in order to prevent a flashback, the injector with the larger or largest cross-section is automatically cut out of service, the supply of the combustion chamber being then solely carried out by the remaining injector or injectors, said means comprising automatic valves mounted in feed pipes leading to each of the injectors, the opening and closure of which are controlled in terms of the pressure ruling in the pipe, downstream of such valves.

6. A burner comprising at least two separate independent injectors of different injection cross-sections opening to one another mounted into the entry of a same combustion chamber and a mixing measuring valve to which lead a feed duct for cumburent gas and a fuel gas delivery pipe being mounted upstream of each injector in such a manner that each injector is supplied with a fuel mixed with a comburentbeforehand, means being provided, so that, when regulating the gas output the injection speed decreases, just before the injection speed of gas into the combustion chamber drops below a value preset in terms of the minimum speed of the gas needed at the outlet in the injectors in.

order to prevent a flashback, the injector with the larger or largest cross-section is automatically cutout of service, the supply of the combustion chamber being then solely carried out by the remaining injector or injectors, and further comprising a dilution chamber wherein diluting gases are added to the gases leaving the combustion chamber and a terminal element comprising an outlet opening through which the gases, originating from the combustion chamber admixed with the dilution gases, are expelled, characterized in that at least one delivery pipe for the dilution gases ends in the said dilution chamber, means being provided to adjust the flow of this dilution gas in such pipe independently of the kinetic energy of the combustion gases crossing the dilution chamber.

7. A dilution burner comprising:

a. a combustion chamber;

b a first injector opening into the entry of said combustion chamber;

c. a first feed pipe leading to said first injector;

d. a'second injector, separate from and independent of said first injector and having a larger crosssection than said first injector, likewise opening into the entry of said combustion chamber;

e. a second feed pipe leading to said second injector;

f. first means for cutting said second injector out of service when the injection flow of gas in said combustion chamber drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said first means being located in said second feed p p g. second means for modifying the composition of the fuel-comburent mixture i. in the portion of said second feed pipe located between said said second injector and said first means,

iii. prior to the operation of said first means;

i. a main valve mounted in said common pipe;

in. a second mixing-measuring valve for the comburent and fuel gases entering said second feed pipe;

n. a first intermediate valve located in said first separate pipe;

0. a first fuel supply pipe leading to said first mixingmeasuring valve;

q. a second intermediate valve located in said first fuel supply pipe; and

r. means for controlling said valves with reference to the pressure ruling in said first and second separate pipes downstream of said first and second mixingmeasuring valves such that:

i. when'the pressure in either of said first and second separate pipes drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said second means is first caused to close and, subsequently, said first means is caused to close, the time lag occurring between these two closures being calculated so that the composition of the fuelcomburent mixture remaining in said second feed pipe and the portion of said second separatepipe downstream of said second mixing-, measuring valve is sufficiently depleted of fuel, prior to cutting said second injector out of service, to prevent the burning of the mixture;

ii. when subsequently an increase of the flow is iii. when said second injector has been cut out of service and the velocity of the gases at the outlet of said first injector is less than the velocity required to prevent a flashback, said second intermediate valve is firs't closed and, subsequently, said first intermediatevalve is also closed, thus cutting said first injector out'of service.

8. A dilution burner comprising:

a. a combustion chamber;

b. a first injector opening into the entry of said combustion chamber;

c. a first feed pipe leading to said first injector;

e. a second feed pipe leading to said second injector;

f. first means for cutting said second injector out of service when the injection flow of gas in said combustion chamber drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said first means being located in said second feed P p g. a common pipe for supplying comburent gas to both said first injector and said second injector;

h. a main valve mounted in said common pipe;

i. a first separate pipe leading from said common pipe downstream of said main valve to provide comburent gas to said first feed pipe;

j. a second separate pipe leading from said common pipe downstream of said main valve to provide comburent gas to said second feed pipe, said first means being located in said second separate pipe;

k. a first mixing-measuring valve for the comburent and fuel gases entering said first feed pipe;

I. a second mixing-measuring valve for the comburent and fuel gases entering said second feed pipe;

m. a first intermediate valve located in said first separate pipe;

n. a first fuel supply pipe leading to said first mixingmeasuring valve;

0. a second fuel supply pipe leading to said'second mixing-measuring valve;

p. a second intermediate valve located in said first fuel supply pipe;

q. a third intermediate valve iocated in said second fuel supply pipe; and

i. when the pressure in either of said first and second separate pipes drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said third intermediate valve is first caused to close and, subsequently, said first means is caused to close, the time lag occurring between these two closures being calculated so that the composition of the fuel-comburent mixture remaining in said second feed pipe and the portion of said second separate pipe downstream of said second mixing-measuring valve is sufficiently de pleted of fuel, prior to cutting said second injector out of service, to prevent the burning of the mixture;

ii. when subsequently an increase of the flow is again required, said first means is first opened and, subsequently, said third intermediate valve is opened when the pressure ruling in said second separate pipe exceeds said preset value, and

iii. when said second injector has been cut out of service and the velocity of the gases at the outlet of said first injector is less than the velocity required to prevent a flashback, said second intermediate valve is'first closed and, subsequently, said said first intermediate valve is also closed,

thus cutting said first injector out of service.

9. A dilution burner as claimed in claim 5, characterized in that means are provided in order to modify in the portion of the feed pipe to the injector having the largest cross-section located between the latter and the said automatic valve; the composition of the fuelcornburent mixture in order that it shall be outside the limits of combustion of such mixture prior to such injector being cut out of service.

jectors, a pipe for the fuel gas supply being led off each of these separate pipes by means of a mixing-measuring valve of the comburent and fuel gases, while an intermediate valve is provided for each of these separate pipes as well as in each of the pipes ledoff the latter upstream of the mixing-measuring valves, these separates pipes terminating each at one of the injectors, means for controlling said different valves with reference to the pressure ruling in the separate pipes downstream of such mixing-measuring valves in such a manner that, when the pressure drops, in one of these separate pipes, below a value preset in terms of the minimum speed of the gases needed at the outlet of the injectors in order to prevent the flash back, the intermediate valve mounted in the fuel gas supply pipe led off the separate pipe supplying the-injector of larger cross-section is caused to close, and subsequently also the intermediate valve, mounted in the separate pipe supplying the latter, the time lag occurring between these two closures being calculated in such a manner that the composition of the fuel-comburent mixture remaining in the portion of the separate injector of large cross-section downstream of the mixing-measuring valve mounted in the latter, shall be sufficiently depleted of fuel, prior to cutting the latter injector out of service, to prevent the burning of such mixture and so that, when subsequently an increase of the flow is again required, the intermediate valve mounted in the separate pipe supplying the large cross-section injector shall be opened and that subsequently takes place the opening of the corresponding intermediate valve mounted in the fuel gas feed pipe at the time when the pressure ruling in such separate pipe shall exceed the said minimum value, and lastly, in such a manner that, when the large section injector has been cut out of service and the velocity of the gases at the outlet of the injector of smaller crosssection shall be less than the velocity required to prevent the flash back, the intermediate valve mounted in the fuel gas supply pipe led off the supply pipe of the injector with the smaller cross-section shall be first closed and subsequently the said main valve and/or the remaining intermediary valve shall also be closed, thus cutting the injector of smaller cross-section also out of service.

11. A dilution burner according to claim 6, characterized in that the combustion chamber communicates with the dilution chamber by means of a throttle terminating in a port having a diameter less than that of the said outlet opening provided in the terminal element and coaxial with such opening, so that the unit comprising such throttle, such opening and the space of the dilution chamber extending between the port and the opening provides an injector permitting to establish in such space, thanks to the considerable kinetic energy of the combustion gases escaping from the combustion chamber through such port, a depression sufiicient -to ensure that the said dilution gases shall be drawn by the gases of combustion through the said outlet opening into the furnace whereon is mounted the burner.

12. A dilution burner according to claim 11, characterized in that it comprises several dilution gas supply ducts terminating in the dilution chamber in locations uniformly distributed around the said port through which the combustion gases are admitted in such chamber.

13. A dilution according to claim 11, characterized in that the centres of the said port and opening are located in the longitudinal axis of the burner.

14. A dilution burner according to claim 6, characterized in that the said terminal eler'nent comprises at least one channel passing right through such element, permitting the furnace to be heated to communicate with the dilution chamber, thus making it possible to draw through such channel gases from the furnace into the dilution chamber, such gases thus providing dilution gases for the gases originating from the combustion chamber,

15. A dilution burner according to claim 9, characterized in that the means provided to modify in the portion of the feed pipe to the injector having the largest cross-section the composition of the fuel-comburent mixture, prior to cutting such injector out of service, comprise a pipe common for both injectors supplying the comburent gas for the latter and wherein is mounted a main valve, such common pipe being forked downstream of such valve in order to provide separate pipes for the two injectors, a pipe for the fuel gas supply being led off each of these separate pipes by means of a mixing-measuring valve of the comburent and fuel gases, while an intermediate valve is provided for each of these separate pipes as well as in each of the pipes led off the latter upstream of the mixing-measuring valves, these separate pipes terminating each at one of the injectors, means for controlling said different valves with reference to the pressure ruling in the separate pipes downstream of such mixing-measuring valves in such a manner that, when the pressure drops, in one of these separate pipes, below a value preset in terms of the minimum speed of the gases needed at the outlet of the injectors in order to prevent a flash back, the intermediate valve mounted in the fuel gas supply pipe led off the separate pipe supplying the injector of larger cross-section is caused to close, and subsequently also the intermediate valve, mounted in the separate pipe supplying the latter, the time lag occurring between these two closures being calculated in such a manner that the composition of the fuel-comburent mixture remaining in the portion of the separate injector of large cross-section downstream of the mixing-measuring valve mounted in the latter, shall be sufficiently depleted of fuel, prior to cutting the latter injector out of service, to prevent the burning of such mixture and so that, when subsequently an increase of the flow is again required, the intermediate valve mounted in the separate pipe supplying the large cross-section injector shall be opened and that subsequently takes place the opening of the corresponding intermediate valve mounted in the fuel gas feed pipe at the time when the pressure ruling in such separate pipe shall exceed the said minimum value, and lastly, in such a manner that, when the large section injector has been cut out of service and the velocity of the gases at the outlet of the injector of smaller cross-section shall be less than the velocity required to prevent the flash back, the intermediate valve mounted in the fuel gas supply pipe led off the supply pipe of the injector with the smaller cross-section shall be first closed and subsequently the said main valve and/or the remaining intermediary valve shall also be closed, thus cutting the injector of smaller cross-section also out of service.

Claims

1. A dilution burner comprising: a. a combustion chamber; b. a first injector opening into the entry of said combustion chamber; c. a first feed pipe leading to said first injector; d. a second injector, separate from and independent of said first injector and having a larger cross-section than said first injector, likewise opening into the entry of said combustion chamber; e. a second feed pipe leadjng to said second injector; f. first means for cutting said second injector out of service when the injection flow of gas in said combustion chamber drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flash back, said first means being located in said second feed pipe, said first means comprising an automatic valve mounted in said second feed pipe, the opening and closing of said automatic valve being controlled in terms of the pressure ruling in said feed pipe downstream of said automatic valve; g. second means for modifying the composition of the fuel-comburent mixture i. in the portion of said second feed pipe located between said said second injector and said first means, ii. to a composition which is outside the limits of combustion of the mixture, and iii. prior to the operation of said first means; h. a common pipe for supplying comburent gas to both said first injector and said second injector; i. a main valve mounted in said common pipe; j. a first separate pipe leading from said common pipe downstream of said main valve to provide comburent gas to said first feed pipe; k. a second separate pipe leading from said common pipe downstream of said main valve to provide comburent gas to said second feed pipe, said first means being located in said second separate pipe; l. a first mixing-measuring valve for the comburent and fuel gases entering said first feed pipe; m. a second mixing-measuring valve for the comburent and fuel gases entering said second feed Pipe; n. a first intermediate valve located in said first separate pipe; o. a first fuel supply pipe leading to said first mixing-measuring valve; p. a second fuel supply pipe leading to said second mixing-measuring valve, said second means being located in said second fuel pipe; q. a second intermediate valve located in said first fuel supply pipe; and r. means for controlling said valves with reference to the pressure ruling in said first and second separate pipes downstream of said first and second mixing-measuring valves such that: i. when the pressure in either of said first and second separate pipes drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said second means is first caused to close and, subsequently, said first means is caused to close, the time lag occurring between these two closures being calculated so that the composition of the fuel-comburent mixture remaining in said second feed pipe and the portion of said second separate pipe downstream of said second mixing-measuring valve is sufficiently depleted of fuel, prior to cutting said second injector out of service, to prevent the burning of the mixture; ii. when subsequently an increase of the flow is again required, said first means is first opened and, subsequently, said second means is opened when the pressure ruling in said second separate pipe exceeds said preset value, and iii. when said second injector has been cut out of service and the velocity of the gases at the outlet of said first injector is less than the velocity required to prevent a flashback, said second intermediate valve is first closed and, subsequently, said first intermediate valve is also closed, thus cutting said first injector out of service.

2. A dilution burner comprising: a. a combustion chamber; b. a first injector opening into the entry of said combustion chamber; c. a first feed pipe leading to said first injector; d. a second injector having a larger cross-section than and being coaxial to said first injector, said second injector being separate from and independent of said first injector but likewise opening into the entry of said combustion chamber; e. a second feed pipe leading to said second injector; f. first means for cutting said second injector out of service when the injection flow of gas in said combustion chamber drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said first means being located in said second feed pipe; g. second means for modifying the composition of the fuel-comburent mixture i. in the portion of said second feed pipe located between said second injector and said first means, ii. to a composition which is outside the limits of combustion of the mixture, and iii. prior to the operation of said first means; h. a common pipe for supplying comburent gas to both said first injector and said second injector; i. a main valve mounted in said common pipe; j. a first separate pipe leading from said common pipe downstream of said main valve to provide comburent gas to said first feed pipe; k. a second separate pipe leading from said common pipe downstream of said main valve to provide comburent gas to said second feed pipe, said first means being located in said second separate pipe; l. a first mixing-measuring valve for the comburent and fuel gases entering said first feed pipe; m. a second mixing-measuring valve for the comburent and fuel gases entering said second feed pipe; n. a first intermediate valve located in said first separate pipe; o. a first fuel supply pipe leading to said first mixing-measuring valve; p. a second fuel supply pipe leading to said second mixing-measuring valve, said second means being located in said second fuel supply pipe; q. a second intermediate valve located in said fiRst fuel supply pipe; and r. means for controlling said valves with reference to the pressure ruling in said first and second separate pipes downstream of said first and second mixing-measuring valves such that: i. when the pressure in either of said first and second separate pipes drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said second means is first caused to close and, subsequently, said first means is caused to close, the time lag occurring between these two closures being calculated so that the composition of the fuel-comburent mixture remaining in said second feed pipe and the portion of said second separate pipe downstream of said second mixing-measuring valve is sufficiently depleted of fuel, prior to cutting said second injector out of service, to prevent the burning of the mixture; ii. when subsequently an increase of the flow is again required, said first means is first opened and, subsequently, said second means is opened when the pressure ruling in said second separate pipe exceeds said preset value, and iii. when said second injector has been cut out of service and the velocity of the gases at the outlet of said first injector is less than the velocity required to prevent a flashback, said second intermediate valve is first closed, and subsequently, said first intermediate valve is also closed, thus cutting said first injector out of service.

3. A dilution burner comprising: a. a combustion chamber; b. a first injector for a mixture of a fuel gas and a comburent gas, said first injector opening into the entry of said combustion chamber; c. a second injector having a smaller cross-section than and being coaxial to said first injector, said second injector likewise opening into the entry of said combustion chamber but said second injector being separate from and independent of said first injector, d. means for cutting said first injector out of service when the injection flow of gas in said combustion chamber drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said first and second injectors in order to prevent a flashback; e. a feed pipe leading to said first injector, said means being mounted in said feed pipe; f. a pressure gauge mounted in said feed pipe between said means and said first injector; and g. means for closing said means when said pressure gauge senses a value which indicates that the injection flow of gas in said combustion chamber has dropped below the preset value referred to in subparagraph (d).

4. A dilution burner comprising: a. a combustion chamber; b. a first injector for a mixture of a fuel gas and a comburent gas, said first injector opening into the entry of said combustion chamber; c. a second injector for a mixture of a fuel gas and a comburent gas, said second injector likewise opening into the entry of said combustion chamber but said second injector being separate from and independent of said first injector; d. first means for cutting said first injector out of service when the injection flow of gas in said combustion chamber drops below a value preset in terms of minimum speed of the gases needed at the outlets of said first and second injectors in order to prevent a flashback; e. second means for modifying the composition of the fuel-comburent mixture in said first injector so that the composition is outside the limits of combustion of the mixture; f. third means for modifying the composition of the fuel-comburent mixture in said second injector so that the composition is outside the limits of combustion of the mixture; g. a feed pipe leading to said first injector, said first means being mounted in said feed pipe; h. a pressure gauge mounted in said feed pipe between said first means and said first injector; and i. means for closing said first means when said pressure gauge senses a valuE which indicates that the injection flow of gas in said combustion chamber has dropped below the preset value referred to in subparagraph (d).

6. A burner comprising at least two separate independent injectors of different injection cross-sections opening to one another mounted into the entry of a same combustion chamber and a mixing measuring valve to which lead a feed duct for cumburent gas and a fuel gas delivery pipe being mounted upstream of each injector in such a manner that each injector is supplied with a fuel mixed with a comburent beforehand, means being provided, so that, when regulating the gas output the injection speed decreases, just before the injection speed of gas into the combustion chamber drops below a value preset in terms of the minimum speed of the gas needed at the outlet in the injectors in order to prevent a flashback, the injector with the larger or largest cross-section is automatically cut out of service, the supply of the combustion chamber being then solely carried out by the remaining injector or injectors, and further comprising a dilution chamber wherein diluting gases are added to the gases leaving the combustion chamber and a terminal element comprising an outlet opening through which the gases, originating from the combustion chamber admixed with the dilution gases, are expelled, characterized in that at least one delivery pipe for the dilution gases ends in the said dilution chamber, means being provided to adjust the flow of this dilution gas in such pipe independently of the kinetic energy of the combustion gases crossing the dilution chamber.

7. A dilution burner comprising: a. a combustion chamber; b. a first injector opening into the entry of said combustion chamber; c. a first feed pipe leading to said first injector; d. a second injector, separate from and independent of said first injector and having a larger cross-section than said first injector, likewise opening into the entry of said combustion chamber; e. a second feed pipe leading to said second injector; f. first means for cutting said second injector out of service when the injection flow of gas in said combustion chamber drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said first means being located in said second feed pipe; g. second means for modifying the composition of the fuel-comburent mixture i. in the portion of said second feed pipe located between said said second injector and said first means, ii. to a composition which is outside the limits of combustion of the mixture, and iii. prior to the operation of said first means; h. a common pipe for supplying comburent gas to both said first injector and said second injector; i. a main valve mounted in said common pipe; j. a first separate pipe leadiNg from said common pipe downstream of said main valve to provide comburent gas to said first feed pipe; k. a second separate pipe leading from said common pipe downstream of said main valve to provide comburent gas to said second feed pipe, said first means being located in said second separate pipe; l. a first mixing-measuring valve for the comburent and fuel gases entering said first feed pipe; m. a second mixing-measuring valve for the comburent and fuel gases entering said second feed pipe; n. a first intermediate valve located in said first separate pipe; o. a first fuel supply pipe leading to said first mixing-measuring valve; p. a second fuel supply pipe leading to said second mixing-measuring valve, said second means being located in said second fuel pipe; q. a second intermediate valve located in said first fuel supply pipe; and r. means for controlling said valves with reference to the pressure ruling in said first and second separate pipes downstream of said first and second mixing-measuring valves such that: i. when the pressure in either of said first and second separate pipes drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said second means is first caused to close and, subsequently, said first means is caused to close, the time lag occurring between these two closures being calculated so that the composition of the fuel-comburent mixture remaining in said second feed pipe and the portion of said second separate pipe downstream of said second mixing-measuring valve is sufficiently depleted of fuel, prior to cutting said second injector out of service, to prevent the burning of the mixture; ii. when subsequently an increase of the flow is again required, said first means is first opened, and, subsequently, said second means is opened when the pressure ruling in said second separate pipe exceeds said preset value, and iii. when said second injector has been cut out of service and the velocity of the gases at the outlet of said first injector is less than the velocity required to prevent a flashback, said second intermediate valve is first closed and, subsequently, said first intermediate valve is also closed, thus cutting said first injector out of service.

8. A dilution burner comprising: a. a combustion chamber; b. a first injector opening into the entry of said combustion chamber; c. a first feed pipe leading to said first injector; d. a second injector having a larger cross-section than and being coaxial to said first injector, said second injector being separate from and independent of said first injector but likewise opening into the entry of said combustion chamber; e. a second feed pipe leading to said second injector; f. first means for cutting said second injector out of service when the injection flow of gas in said combustion chamber drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said first means being located in said second feed pipe; g. a common pipe for supplying comburent gas to both said first injector and said second injector; h. a main valve mounted in said common pipe; i. a first separate pipe leading from said common pipe downstream of said main valve to provide comburent gas to said first feed pipe; j. a second separate pipe leading from said common pipe downstream of said main valve to provide comburent gas to said second feed pipe, said first means being located in said second separate pipe; k. a first mixing-measuring valve for the comburent and fuel gases entering said first feed pipe; l. a second mixing-measuring valve for the comburent and fuel gases entering said second feed pipe; m. a first intermediate valve located in said first separate pipe; n. a first fuel supply pipe leading to said first mixing-measuring valve; o. a second fuEl supply pipe leading to said second mixing-measuring valve; p. a second intermediate valve located in said first fuel supply pipe; q. a third intermediate valve located in said second fuel supply pipe; and r. means for controlling said valves with reference to the pressure ruling in said first and second separate pipes downstream of said first and second mixing-measuring valves such that: i. when the pressure in either of said first and second separate pipes drops below a value preset in terms of the minimum speed of the gases needed at the outlets of said injectors to prevent a flashback, said third intermediate valve is first caused to close and, subsequently, said first means is caused to close, the time lag occurring between these two closures being calculated so that the composition of the fuel-comburent mixture remaining in said second feed pipe and the portion of said second separate pipe downstream of said second mixing-measuring valve is sufficiently depleted of fuel, prior to cutting said second injector out of service, to prevent the burning of the mixture; ii. when subsequently an increase of the flow is again required, said first means is first opened and, subsequently, said third intermediate valve is opened when the pressure ruling in said second separate pipe exceeds said preset value, and iii. when said second injector has been cut out of service and the velocity of the gases at the outlet of said first injector is less than the velocity required to prevent a flashback, said second intermediate valve is first closed and, subsequently, said said first intermediate valve is also closed, thus cutting said first injector out of service.

9. A dilution burner as claimed in claim 5, characterized in that means are provided in order to modify in the portion of the feed pipe to the injector having the largest cross-section located between the latter and the said automatic valve, the composition of the fuel-comburent mixture in order that it shall be outside the limits of combustion of such mixture prior to such injector being cut out of service.

10. A dilution burner according to claim 9, characterized in that the means to modify in the portion of the injector feed pipe with the largest cross-section the composition of the fuel-comburent mixture, prior to cutting such injector out of service, comprise a pipe common for both injectors supplying the comburent gas for the latter and wherein is mounted a main valve, such common pipe being forked downstream of such valve in order to provide separate pipes for the two injectors, a pipe for the fuel gas supply being led off each of these separate pipes by means of a mixing-measuring valve of the comburent and fuel gases, while an intermediate valve is provided for each of these separate pipes as well as in each of the pipes led off the latter upstream of the mixing-measuring valves, these separates pipes terminating each at one of the injectors, means for controlling said different valves with reference to the pressure ruling in the separate pipes downstream of such mixing-measuring valves in such a manner that, when the pressure drops, in one of these separate pipes, below a value preset in terms of the minimum speed of the gases needed at the outlet of the injectors in order to prevent the flash back, the intermediate valve mounted in the fuel gas supply pipe led off the separate pipe supplying the injector of larger cross-section is caused to close, and subsequently also the intermediate valve, mounted in the separate pipe supplying the latter, the time lag occurring between these two closures being calculated in such a manner that the composition of the fuel-comburent mixture remaining in the portion of the separate injector of large cross-section downstream of the mixing-measuring valve mounted in the latter, shall be sufficiently depleted of fuel, prior to cutting the latter injector out of service, to prevent the burning of such mixture and so that, when subsequentlY an increase of the flow is again required, the intermediate valve mounted in the separate pipe supplying the large cross-section injector shall be opened and that subsequently takes place the opening of the corresponding intermediate valve mounted in the fuel gas feed pipe at the time when the pressure ruling in such separate pipe shall exceed the said minimum value, and lastly, in such a manner that, when the large section injector has been cut out of service and the velocity of the gases at the outlet of the injector of smaller cross-section shall be less than the velocity required to prevent the flash back, the intermediate valve mounted in the fuel gas supply pipe led off the supply pipe of the injector with the smaller cross-section shall be first closed and subsequently the said main valve and/or the remaining intermediary valve shall also be closed, thus cutting the injector of smaller cross-section also out of service.

11. A dilution burner according to claim 6, characterized in that the combustion chamber communicates with the dilution chamber by means of a throttle terminating in a port having a diameter less than that of the said outlet opening provided in the terminal element and coaxial with such opening, so that the unit comprising such throttle, such opening and the space of the dilution chamber extending between the port and the opening provides an injector permitting to establish in such space, thanks to the considerable kinetic energy of the combustion gases escaping from the combustion chamber through such port, a depression sufficient to ensure that the said dilution gases shall be drawn by the gases of combustion through the said outlet opening into the furnace whereon is mounted the burner.

14. A dilution burner according to claim 6, characterized in that the said terminal element comprises at least one channel passing right through such element, permitting the furnace to be heated to communicate with the dilution chamber, thus making it possible to draw through such channel gases from the furnace into the dilution chamber, such gases thus providing dilution gases for the gases originating from the combustion chamber.