US2973808A

US2973808A - Flame stabilizer-mixer

Info

Publication number: US2973808A
Application number: US749426A
Authority: US
Inventors: Jr William B Fox
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-07-18
Filing date: 1958-07-18
Publication date: 1961-03-07
Anticipated expiration: 1978-03-07

Description

w. B. FOX, JR 2,973,808

FLAME STABILIZER-MIXER Filed July 18, 1958 March 7, 1961 k k I INVEN TOR WILLIAM B. Fox, JR-

ATTORNEYS FIG.3

United States Patent FLAME STABILIZER-MIXER William B. Fox, Jr., Carnegie, Pa. (3692 Elmira Drive, Dayton 39, Ohio) Filed July 18, 1958, Ser. No. 749,426

4 Claims. (Cl. 158-1) The present invention is concerned broadly with combustion of fuels and high conversion and throughput in chemical reactors. Specifically, the invention is concerned with a novel form of mixer for fluids or solids before entering a combustion zone and imparting mixing action to such fluids or solids within a combustion zone of a fuel burner or a reaction zone of a chemical reactor.

It is well known that in the usual combustion processes the mixture of fuel and air entering the combustion zone are seldom at 'an optimum and the required further mixing therein within the combustion zone is even less efficient. In most any commercial or industrial process minimum size of apparatus is desirable both from the standpoint of space and economy. Exothermic reactions such as result in combustion of fuels suggests obtaining higher heat release by increased volumes of fuel combusted or increased heat release per unit of combustion volume. In the present invention a higher heat release per unit of volume of combustible fuel is obtained by improved mixing of the fuel-air components of combustion.

When the volume of the fuel-air mixture combusted in a given unit of time is increased the problem of flame blowout is troublesome. Such problems increase where a minimum size of equipment is desirable such as in aerodynamic applications, compact reaction designs and mixing in small volumes. In the present invention the mixer also acts as a flame stabilizer particularly when operated at atmospheric pressure, and gives improved results at less than atmopheric as Well as greater than atmospheric pressures.

Pre-heating of fuels is often resorted to in order to increase the combustion efiiciency of air-fuel mixtures. In the present invention the manner of mixing the fuelair components has eliminated the necessity for preheating to obtain high heat release from selected fuels. Tests have demonstrated that with the burner of the invention using non-preheated propane air stoichiometric mixtures, heat releases on the order of 60 million Btu. per hour per cubic foot of combustion zone volume were obtained without flame blowout, when operated at atmospheric pressure.

One object of the invention is to provide a combustion burner for improved mixing of fuels before and after entering the combustion zone.

Another object of the invention is to provide a new and improved mixer giving a high rate of conversion with high output in chemical reactors.

A further object of the invention is to provide a mixer burner of the character described which is operable at atmospheric pressures in obtaining high'heat release per unit of combustion zone volume when using gases, liquids, fine solids or any combinations thereof.

These and other objects of the invention will be made apparent from the following description and the drawings forming a part thereof, wherein:

Fig. 1 shows a longitudinal section through one form of a burner of the invention;

Fig. 2 shows a full section taken on lines l'I-II of Fig. 1;

Fig. 3 shows another form of burner of the invention in which a plurality of stabilizer-mixers are mounted upon a perforated plate within a tube;

Fig. 4 shows a full cross-section taken on line IV-IV of Fig. 3.

Referring now in detail to Fig. l of the drawing, the flame stabilizer-mixer comprises an annular member 1 having a hollow cylindrical portion 2 and a reduced diameter hollow cylindrical extended portion 3. which are connected by a converging portion 4. Within portion 2 is a second converging member 5 disposed in spaced relation to portion 4 of member 1. The diameter of the opening 6 therein is preferably not greater than the diameter of the opening 7 in member 1. Within converging portion 4 are a plurality of perforations 8 for a purpose to be hereinafter described. The small end portion 3 of member 1 terminates in a combustion zone 9. Members 1 and 4 may advantageously be of metal and the combustion zone should have an internal refractory lining 10. The

members

1 and 10 may be housed in any suitable form of housing such as the cylindrical member 11. Obviously, the member 11 may be of other forms to suit the particular installation where the flame stabilizermixer may be used. The liner 10 has an internal diameter larger than the internal diameter of portion 3 of member 1 for a purpose to be discussed. The fuel to be combusted is introduced into the member 5' by any suitable means such as the tube 12 and nozzle 13. The combustion air may be also introduced into member 5 by any suitable means, and where atmospheric pressure air is used it may be introduced into member 11, upstream of the tube 12 or in any other suitable manner.

During operation of the stabilizer-mixer of Fig. 1, the air and fuel entering member 5 is initially mixed and mixing continues during passage through portion 3 of member 1 and enters the combustion zone 9 where the mixture is'ignited by any suitable means (not shown). The primary air and fuel moving through member 1 creates a suction in the chamber 14 formed by the member 5 and member 1. The suction acting through perforations 8 withdraws products of combustion from within the the combustion chamber 9 into the member 1 where they mix with the primary fuel and again pass into the combustion chamber. Such action creates an additional turbulence in the combustion which in turn restricts flame blowout. the burner.

The advantage of such a burner lies in the high heat release obtained per volume unit of combustion zone volume at atmospheric pressures. Hence, by reason of the unique mixing obtained by such a burner, very large heat release can be obtained with a minimum size of combustion zone at atmospheric pressure. Likewise when used in chemical reactors a high rate of conversion with high throughput of reactants is obtainable for a given reactor volume. 1

The exact nature of the mixing operation is not completely understood, it appears, however, that the entering primary fluids, air and combustible fuel, entrain burner gasesfrom the reaction zone and mix them intimately with the entering primary fuel within a relatively low pressure zone before discharging into the combustion zone. Such reverse circulation from the combustion zone results in a high throughput and combustion in a relatively small combustion zone.

A modification of the invention as disclosed in Fig. 3, utilizes a large size tube or housing 20 within which is mounted a transversely disposed plate 21 having a plurality of suitably arranged rows of openings 22 therein. The connection between plate 21 and tube 20 being gas tight. Over each opening 22 is arranged a member 1 having the converging member 5 therein as disclosed in Fig.. l. A suitable combustible fuel inlet conduit 23 extends into housing 20 and is provided with branch inlet tubes 23a which are smaller in diameter than open This cycle is continued during operation of ings 22 in plate 21 and are entered into each member 1 as in Fig. 1. Upstream of plate 21 a suitable connection to housing 20 provides inlet air for combustion purposes. The air-fuel mixtures issuing from members- 1 are ignited and the operation is carried out as pre-- viously described in regard to Fig.1. A refractory lining 24 is provided in the combustion chamber portion of housing 20.

The relative sizes and shapes of the stabilizer-mixers disclosed and described may be varied to suit any par ticular installation. Optimum results have can obtained with atmospheric pressures when the following basic design relations are maintained. The member 1 should be connected with the housing or other support so that no by-pass of gases or fluids at the-point of connection occurs. The opening 6 in member should be no larger than opening -7 in member 1. The length of portion 3 of member 1 is preferably 3 to 8 times the internal diameter thereof. The openings 8 in member 1 should be adjacent or upstream of opening 5a in member 5, preferably never downstream relative to said opening. The primary fluid is adequately mixed by introducing one fluid or fluid mixture into the upstream opening of member 1 and preferably slightly downstream from said opening. The other primary fluid may be introduced at some point upstream for flow into the member 1. Where exothermic reactions are involved, as in a combustion burner, the combustion zone should be insulated with an internal refractory lining.

When using atmospheric pressures, adequate suction through apertures S of portion 4 of member 1 are obtained when the end of member 5 is spaced from the adjacent end of portion 3 of member 1, a distance about equal to the diameter of the opening 7 in said portion 3. The length of said portion 3 provides adequate mixing of the primary fuels during passage therethrough. The mixed fuels entering the combustion zone have little or no turbulence at atmospheric pressures, and the volume throughput of mixed fuels tends to cause flame blow out in the well known manner, Where, however, the internal diameter of the combustion zone exceeds the external diameter of the portion 3 of member 1 some of the products of combustion within the combustion zone, adjacent the end of member 1 are withdrawn upstream over said portion 3 and enter the stream of primary fuel through opening 8 of the member I. This recirculation, i.e.; reverse flow, at the ignition end of the combustion burner creates a turbulence within the combustion zone and restricts flame blow out. Where design requirements dictate a constriction of the outer end of the combustion zone increased pressures upstream of the combustion zone are necessary to obtain the desired turbulence.

I claim:

1. A burner comprising a tubular housing, a tubular member disposed within said housing having a cylindrical portion in gas tight contact with the inner walls of the housing and secured thereto; a downstream extending converging continuation of said cylindrical portion disposed in spaced relation to said housing and terminating in an elongated cylindrical extension in spaced relation to the adjacent'portion of the housing, said elongated cylindrical extension terminating in inward spaced relation to the downstream'end of the housing providing a combustion chamber within the housing, a second tubular member mounted upon the inner walls of the cylindrical portion of the first named member, a downstream extending converging continuation of said second tubular member extending into and spaced from the converging continuation of the first named member and terminating upstream from the said elongated-cylindrical extension of the first member, a plurality of radially disposed perforations in the converging portion of said first. named member disposed in upstream relation to the downstream end of the converging portionof the second named mem I ber, a fuel nozzle. extending inwardly'..of=.'said tubulari housing upstream of said first named member and delivering fuel within said second named member converging portion, and an air intake in said housing upstream of said members.

2. In a burner, in combination, an open housing providing at one end an inlet for air andcombustible fuel and at the other end an inwardly extending combustion zone, a flame stabilizer and fuel mixer extending inwardly of the housing from said combustion zone and comprising a hollow cylindrical member disposed in annular spaced relation to the adjacent housing portion and adjecent the combustion zone, a diverging fmstoconical member forming an upstream continuation of said cylindrical member and extending therefrom to engagement with the housing to form a gas tight seal therewith, a second hollow frusto-conical member within said housing in upstream spaced parallel relation to and extending into the first named frusto-conical member forming a suction chamber between them, the small end opening in said second frusto-conical member being in axial alignment with the opening through said hollow cylindrical member and of an inside diameter not greater than that of said cylindrical member, apertures arranged in radially spaced relation about the periphery of the first named frusto-conical member in upstream relation to the small end of the second said frusto-conical member, means for introducing combustible fuel through said burner housing into said second named frusto-conical member and an inlet on said housing upstream of said mixer for introduction of combustion air.

3. In a burner, in combination, a hollow tubular housing, a plate disposed transversely of said housing, inwardly from one end thereof blocking off flow of air through the housing, a plurality of spaced openings extending through said plate in a direction axially of the housing, a fuel mixer associated with each plate opening and comprising a hollow tubular member secured to the downstream side of said plate enclosing said opening, an axially extending forwardly converging hollow cxtension on said tubular member and terminating in an axially extending hollow tubular extension, a downstream extending hollow member disposed within said fuel mixer hollow tubular member and having a converging portion extending into and in parallel spaced relation with said mixer converging extension and terminating short of said mixer hollow tubular extension, a plurality of apertures in said mixer converging extension, a fuel supply tube extending through said housing upstream of said plate, a conduit extending from said fuel supply tube through each said plate opening in spaced relation to the periphery thereof, and an air inlet opening in said housing upstream of said plate.

4. In a flame stabilizer burner, in combination, a housing, a fuel receiving member mounted in gas-tight relation to the inner face ofthe housing and having a downstream converging portion terminating in a mixing chamber extending axially of the housing in inwardly spaced rela tion thereto forming a recirculation chamber, a combustion chamber in said housing extending downstream from said mixing chamber in radially spaced relation thereto, a second converging member disposed within said fuel receiving member and having a converging portion in spaced relation with and extending into the converging portion of said fuel receiving member forming a suction chamber, and apertures in said fuel receiving member converging portion connecting said burner suction chamber with the combustion chamber through said recirculation chamber.

References Cited in the fileof this patent UNITED STATES PATENTS 2,547,276 Marsh et a1 Apr. 3, i 2,701,608 Johnson Feb. 8, 1955 2,857,961 Brown et al. Oct1'28j 1958