Gas mixing device

April 5, 1966

3,244,221

D. LABINO

GAS MIXING DEVICE

Filed Dec. 23, 1963

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United States Patent Office

3,244,221

Patented Apr. 6, 1966

3,244,221

GAS MIXING DEVICE

Dominick Latino, Grand Rapids, Ohio, assignor to JohnsManville Corporation, New York, N.Y., a corporation of New York

Filed Dec. 23,1963, Ser. No. 332,406 5 Claims. (CI. 158—118)

This invention relates to improvements in mixing devices for mixing the components of a gaseous combustible mixture, which combustible mixture is subsequently delivered to a burner for burning. More particularly, the invention relates to improvements in a mixing device for delivering a premixed homogeneous admixture of fuel and air to a burner for combustion.

It is generally recognized that high combustion efficiency of a gaseous admixture can be obtained only if the components of gases are thoroughly and intimately mixed to form a substantially homogeneous admixture. To achieve a homogeneous admixture of air and fuel, various devices have been relied upon.

One of the devices that has been employed is the central mixing station. At the station the fuel and air are mixed and the admixture is delivered throughout the plant by pipe lines. The presence of the explosive mixture in the delivery system creates a very definite hazard. Additionally, a large number of fire and exposion checks are necessary and these are quite costly. Further, with such central mixing stations, all burners being fed from a single station must operate with the same admixture and thus it is difficult to accurately control the operating pressures of the burners.

Among other devices is the inspirator-type mixer in which one of the component gases under pressure inspirates another component gas. Generally, this type of mixer comprises a Venturi throat and defines an apparatus which may be termed a jet pump. One of the most important factors in a: successful Venturi mixer is the quality of manufacture. Because of the high velocities in the entry and throat sections, any irregularities will have a large effect on performance. It is manifest that the smaller the Venturi, the more significant the quality of manufacture. Disturbances to the flow in the entry and mixing sections can produce an uneven velocity profile at the entrance to the diffuser section and thus decrease the efficiency of the diffuser. Furthermore, because of the critical relationship between the Venturi throat and the ports through which the inspirated gas component as emitted, such mixers are limited as to their “turndown” or ability to project different ratios of gas to air.

It is an important and specific object of this invention to provide a mixer which preserves the basic advantages of Venturi-type mixer and through the provisions of the novel arrangement of the components obviate the disadvantages thereof and the disadvantages of the central mixing station.

It is a further object of this invention to provide a novel mixer assembly for controlling the flow of gas and air and to provide optimum combustion efficiency over a wide range of operating and varying pressures and ratios between the gas and air.

To accomplish the objects of this invention, a preferred embodiment of the novel apparatus of this invention comprises an air conduit having a terminal portion defining a discharge orifice for emitting air under pressure, an annular member embracing the terminal portion of the air conduit and in spaced relation therewith to provide an annular space between the terminal portion of the discharge nozzle and the member, said member defining a plurality of ports through which gas is radially emitted to the annular space, and said annular member preferably comprising a downstream portion of substantially constant cross section where the gas and air are intimately mixed by diffusion.

Other objects and advantages of this invention will 5 become apparent during the course of the following description when taken in connection with the accompanying drawings.

FIG. 1 is an elevational view of a combustion burner system which utilizes the mixer assembly of this inven10 tion;

FIG. 2 is a cross-sectional elevational view of the mixer assembly;

FIG. 3 is a view similar to FIG. 2 illustrating the normal diffusion pattern of the air stream; and

FIG. 4 is a view illustrating the normal diffusion pattern of the fuel gas.

The present invention may be used to supply a premixed gaseous mixture to various types burners. In the present case, however, the invention will be described in 20 connection with a refractor tunnel-type burner having a plenum feeding chamber since the invention finds particular utility in the supply of a premixed fuel to a burner. The mixer assembly of this invention is adapted to premix the combustion gases prior to delivery to the burner 25 and thus is distinguished from those burner and mixer assemblies wherein the combustion components are mixed at or in the burner per se.

The burner 10, as shown in FIG. 1, generally comprises a tunnel 12 defined by refractory walls 14 and 16 and 30 encased by a metal housing 18. A plenum chamber 20 is provided adjacent the inlet opening 22 of tunnel 12 for directing an admixture of gases in a preferred pattern into the tunnel 12 as supplied from the mixer 30. A wall 26 separates the tunnel 12 and the plenum cham35 ber 20 and defines an elongated orifice 28 for emitting the combustible admixture to the tunnel 12. In order to facilitate ignition of the combustible admixture, ignition means shown to be in the form of a sparkplug 32, may be optionally provided.

⁴⁰ In a preferred form of the present invention, air under pressure is provided through air conduit 40 to air nozzle 42 for discharge under pressure through the terminal portion or discharge orifice 44 into the mixing chamber 46 defined by annular member 48. The chamber 46 is -³ preferably of essentially constant cross section. The annular member 48 embraces the downstream terminal end of nozzle 42 and is in spaced relation with nozzle 42 to define therebetween an annular space 50. A manifold 52 surrounds a portion of annular member 48 to ⁵⁰ direct the gaseous fuel under pressure to the plurality of ports 54, defined by annular member 48 and arranged in circular array. The gas is emitted inward through the ports 54, preferably radially, into the space 50 from __r whence the fuel gas passes into the mixing chamber 46 ⁰⁰ for intermixing and dispersion with the air passing through nozzle 42. Nozzle 42 is preferably provided with a tapered terminal portion in order to facilitate the diffusion of the fuel gas With the air. The pressures at which the fuel gas and air are introduced may be suitably ⁶⁰ regulated by commercially available pressure regulators (not shown) suitably interposed into the fuel gas and air feed lines.

The manner in which the gaseous components, the fuel gas and the air, are dispersed in chamber 46 is illustrated ° in FIGS. 3 and 4. In FIG. 3 the normal diffusion pattern of the air as it is emitted from nozzle 42 is illustrated, while in FIG. 4 the normal diffusion pattern of the fuel gas passing from the space 50 is illustrated. It will be „ apparent that the diffusion pattern of the commingling fuel gas and air will be a composite of the diffusion patterns illustrated in FIGS. 3 and 4.

3,244,221

One of the advantages of the instant invention is that the various components of the mixer assembly are manufactured from standard elements that are readily available. For example, the fuel gas manifold 52 is constructed from a cast iron T member, which T member is undercut at 5 the central portion 56 to define the annular passage 58 between the manifold member 54 and the annular member 48. The annular member 48 is constructed from a standard pipe nipple which is also undercut at the central portion 60 corresponding to the central portion 56 of the ₁₀manifold member and ports 54 are drilled around the circumference of the pipe nipple. The air nozzle 42 may be constructed from stainless steel tubing. The various components are then assembled and suitably secured as by welding. 45

It has been found that the introduction of both the air and the fuel gas components under pressure that better diffusion can be attained and also a greater turndown ratio between the fuel gas and air may be obtained because the introduction of the fuel gas does not rely upon the 20 inspirating effect of the central air stream.

As illustrated in FIGS. 3 and 4, the fuel gas diffusion pattern is inwardly from the outer wall of the mixing chamber whereas the diffusion pattern of the air is outwardly from the central axis of the mixing chamber. 25 Since the two diffusion patterns at this point are flowing across each other at different velocity pressures, considerable turbulence in the resultant mixture results. This action continues as the mixture passes through the chamber 46. However, the turbulent flow of the admixture 30 stream may be converted to essentially laminar flow by providing a sufficient chamber length (at least equal to four diameters) from the mixer to the burner.

A further advantage of the instant invention resides in the fact that the combustible mixture is formed im- 35 mediately preceding the burner, as opposed to a central mixing station, and hence the explosive hazard of a central mixing station is obviated.

The invention may be embodied in other specific forms without departing from the spirit or essential character- 40 istics thereof. The disclosed embodiment is to be considered as illustrative and not restrictive, the scope of the invention is indicated by the appended claims.