US2321483A - Proportional mixer - Google Patents

Description

June 8, 1943.

l, E. J. HAEDIKE l BROPORTION'AL MIXER 2 Sheets-Sheet 1 Filed Jan. 6, 1941 .'Fune E8, 1943.

` E. J. HAEDIKE PROPORTIONAL MIIXER Filed J'an'. ,6, 1941 2 sneevtsl-sneet 2 Il l i Patented June 8, 1943 PROPORTIONAL MIXER Edward J. Haedike, Chicago, Ill., assigner to National Machine Works, Chicago, Ill., a corporation o! Illinois Application. January 6, 1941, Serial No. 373,217

1I)y Claims.

The invention relates to mixer apparatus of the general type commonly used in effecting a proportioned mixture of combustible gas and air in the supply system of a blast burner. The function of the mixer apparatus is to retain automatically a predetermined ratio of gas to air so that by simply controlling thev` quantity of air supplied, the quantity of combustible mixture passing to the burner will be similarly controlled and the gas-air ratio for most efficient operation retained. customarily, the air is supplied under substantial pressure and this pressure is varied to eiect the desired control of the quantity of air, and hence mixture, which is fed to the burner. In order to obtain precision of results the arrangement must be such that the proportion of gas to air is maintained substantially constant throughout a wide turndown range for the air pressure, i. e., variation in air pressure.

Moreover, ythe retention of such xed ratio must obtain whether the changes in air pressure result from a deliberate control operation or from some inadvertent change in supply pressure.

One object of the invention is to provide a mixer apparatus of the type set forth embodyingl a novel arrangement for maintaining a substantially uniform ratio of gas to air throughout an extremely wide turndown ratio for the air pressure.

Another object is to provide a mixer of the type set forth in which a novel and simpliied arrangement is provided for adjusting the airgas ratio at will and without the use of auxiliary or supplementary adjusting apparatus or connections.

Still another object is to provide a novel proportional mixer -for multiple gases, such as combustible gasand air, which is characterized particularly by its ruggedness and simplicity of construction as well as by the precision of gas-air ratio adjustment which may be effected.

Another object is to provide a proportional mixer apparatus of the type in whichA one gas is fed at high velocity through the throat of a Venturi type flow-way and entrains a second gas supplied at constant low pressure to an opening in the throat from a suitable regulator, and which apparatus is particularly characterized by the fact that the flow-way has a substantially unity coeilicient of discharge and the opening in the throat also constitutes an adjustable orifice having a substantially unity coefiicient of discharge, the line from the regulator to the orifice being free of any other orifices` so that a virtually constant proportionality of the second gas entrained by the rst at the throat will be obtained throughout a. wide range of pressures for the iirst gas.

The invention also resides in the novel arrangement Ior sealing the mixer to prevent tampering with its adjustment.

Further objects and advantages of the invention will become apparent as the following description proceeds, taken in connection with the accompanying drawings in which:

Figure 1^is a plan view, partially broken away, of a proportional mixer of novel form and which is a key element of the mixer apparatus herein disclosed, embodying the invention.

Fig. 2 is a longitudinal sectional View of the mixer.

Fig. 3 is an end elevation of the mixer.

Fig. 4 is a generally diagrammatic plan view of a fuel supplyV system for av` blast burner incorporating as one of its elements the propor' tional mixer herein disclosed.

Fig. 5 is a sectional view of the zero governor, taken substantially along the line 5-5 in Fig. 4.

While the invention is susceptible of various modifications and alternative constructions, I have shown in the drawings and will herein describe in detail the preferred embodiment, but it is to be understood that I do not thereby intend to limit the invention to the specic form disclosed, but intend to cover all modiilcations and alternative constructions falling within the spirit and scope. of the invention as expressed in the appended claims.

In'the instant embodiment, the mixer system 'shown (Fig. 1) is of a form particularly adapted for mixing combustible gas and air, preparatory ,to feeding the mixture through suitable manifolding to the burner of a furnace or they like. The illustrated system includes a mixer proper which comprises (see Fig. 2) three major structural elements, namely, a Venturi mixer mem'- ber I0, a nozzle or jet member II and a body I2, the latter being fixed to the end of the member I0 and telescoped over the member II.v All three of these parts are,'for the sake of durability and opposed ends of the members I and II. The width of this gap I5 determines the gas-air ratio, and a suitable adjustment mechanism, designated generally as I6 is provided for adjusting the member II endwise in the body I2, to thereby.

octagonal head I9 shaped to be readily engaged by a wrench. Intermediate its ends, but adjacent the inner one, the member III is formed withan encircling, integral enlargement 20 upon which is threaded the body I2, to iix the parts I0 and I 2 rigidly together. The member I0 tapers, as a whole, toward its inner end and an axially extending passage or flow-way 2I in itsinterior is shaped to form a smoothly tapering, accurately dimensioned now-way for the gas-air mixture, whichilows through it in the direction of the arrow 22. Y

The body I2 is generally tubular in form and is tapped at its outer end, as indicated at 23, to

, receive an air supply pipe 24. This outer end of the body is shaped in the formof an enlarged,

. wrench-engageable, octagonal head 25. The interior of the body I2 is shaped to form anv annular seat 26 of substantial length in a direction longitudinally of the body, and in which the inner nozzle member II is slidablymountedif In 4 somewhat exaggerated in the drawings. In acassembling the device,n the member II is rst slipped into the body I2, then the latter` is screwed onto the member I0.

As to the adjustable nozzle member II, it will be observed (see Fig. 2) that it comprises a as well as an end portion which tapers-longitudinally ytoward the inner nose ofthe Venturi mixer member I 0. The nozzle member II has a sliding fit within the body I2 with a clearance of preferably only about 0.003 inch in the seat 26. Annular grooves 2'1 at spaced points in the seat 26 form a labyrinthine passage to bafiie and restrict any possible air leakage along the 'exterior of the nozzle II. In this way any objectionable air leakage along the exterior of the nozzle is obviated. An axially extending passage 26 within the nozzle member II is shaped to form a smoothly tapering flow-way. for the entering air and which converges towardthe alined small end of the flow-way 2|. in the member I0. l

Combustible gas is supplied to the chamber I4 Furthermore, the terminal portion 2li is slightly less in width than the cylindrical entry portion 22a of the now-way 2|. The opposed end faces of the members I 0 and II are machined fiat and precisely parallel, and their peripheries are chamfered as indicated at 29.

Also notable are the now characteristics of the n detail, there are no other oriiices or the like in through a conduit connected to a tapped hole 29 (Fig. 2) in the side ofthe body I2. As indicated generally above, the gas from this chamber I4 ls entrained by the stream of air passing through the flow-ways 28, 2|. During this inspirating operation, the gas passes through the adjustable gap I5 between the ends oi: the members I0. and II. With such an arrangement the shapes of the adjacent portions ofthe members I0 and II are important in obtaining precision results, it being especially necessary to guard against the creation of eddy currents or turbulence at this point in the system. In this connection, it has been found desirable to form the flow-ways 26 and 2I with adjacent end portions of round or cylindrical cross section as indicated at 28n and 22. Also the cylindrical terminal portion 28* of the nozzle ilow-way26 is made slightly smaller in diameter desired gas-air ratio.

comprises a sheet metal cover member 31, di`

the gas line from the gas supply regulator to the orice I5 so that the characteristics of the gas and air paths remain perfectly matched, as noted.

For accurate adjustment of the gap I5 it will be seen that the motion of the member II must be rigidly ,guided so as to maintain parallelism, throughout the range of adjustment, between the opposed faces `of the members I0 and II. The long bearing seat 26 within the body I2, in which the member I I is telescoped, aords precisely this typeof guide. This accurate guiding of the adjusting motion of the member II also assures maintenance of alinement between the now-ways 28 and 2|.

The adjustment mechanism ls for shifting the tual practice it is ordinarily of the order of magnitude of 0.015 to' 0.025 inch in width. 'I'he particular adjustment mechanism shown comprises `a'stud 30 projecting into a hole in the member I.I and rigidly secured thereto by a tapered thread. f 'Ihe stud 30 projects outward through a slot 3| -in the body I2, this slot being bordered by a rectangular housing 32 integral with the body I2. A lead screw 33 .projects through opposite side walls of this housing 32 and is xed against rotation by a set screw 34. The lead screw also projects through a transverse hole 35 in the stud 30. A pair of adjusting nuts 36 are threaded on the lead screw and by rotating these nuts the stud 30, and hence the nozzle member II fixed to it, can be shifted endwise of the body I2.' 'I'he threads onvthe lead screw 33 have quite a short lead so as to afford a very ne adjustment for the nozzle member II.

The adjusting mechanism I6 described above is of a form which. can be readily sealed to prevent tampering by unauthorized persons after the nozzle member II has been adjusted to effect a The sealing arrangement mensioned to overlie the top of the rectangular housing32, and having a depending end ilange 38 with a hole in it to receive the projecting end of the lead screw 33. A screw 39 holds the cover removably in place and a sealing wire 40 led through a hole in the projecting end of the lead screw 33 prevents removal of the cover.

In use, the mixer described above may, for example, be incorporated in a system of the general form indicated in Fig. 4. In this system air under pressure is supplied from a suitable source (not shown) throughthe pipe 24 under the control of a single valve or blast gate4I. 0n the other hand, the combustible gas is supplied from a pipe 42 under the control of a manual shutof! valve 43 and a zero pressure gas governor 44.

The latter device is, aside from an adjustment arrangement hereinafter described, oi' well known construction and serves, in general, to maintain 'the gas enteringthe mixer at substantially constant and low pressure such, for example, as at so-called zero or atmospheric pressure. The gasair mixture leaving the mixer through the pipe Relative to the constancy ofthe gas-air ratio l it should bemobscrved that there is no control I8 enters a system of manifold piping 45 through which it is supplied to a plurality of burners of any suitable form such, for example, as the blast line burners 68 illustrated.

In the operation of the systemv as so far described, the valve 43 is normally left full on' and only closed when it is desired 'to shut down the furnace completely. 'I'he gas-air ratio desired is initially set up by adjusting the width of the clearance gap or orlce I5 in the mixer through the medium of the adjustment mechanism I6.

for example, with a maximum available pressure head of seventy inches W. C., this pressure being varied as desired by the valve #il and ordinarily maintained within a range of from three to thirty inches W. C.A For operation outside this latter range, adjustment of the zero governor t, in the manner later described, is desirable andfor the` present it will be assumed that Ithe system is operating with an air pressure Within the range noted. The incoming high pressure air streams through the entrance flow-way 28 of the mixer (see Fig. 2), its pressure head being converted to velocity he'ad as the flow-way converges. Finally, the stream of air attains amaximum ve locity substantially at the point at which it passes across the gap or orifice I5. The gas, at approximately atmospheric pressure in the chamber IS, is thus entrained by the high velocity stream of air, and enters it, being thoroughly mixed with the latter as the gas and air move through-the mixers exit iioW-way 2|. During the/passage of the mixture through the expanding exit iloW-way 2l, the velocity head of the mixture is reconverted to pressure head. The high pressure mixture, on leaving the mixer, passes through the manifolding (seeFig. 4) and is burned in the usual manner.

As the heat requirements of the installation change from time to time the setting of the blast gate or valve 4I is varied accordingly. As a resultthe pressure of the air entering the mixer is correspondingly changed, and a commensurate change effected in its velocity as it crosses the orifice I5. The amount of gas entrained is, however, dependent, in the present arrangement, on this velocity and so the ratio of gas to air remains substantially constant. In fact, in actual test it has been found that with the illustrated apparatus the gas-air ratio is maintained within a 'tolerance of plus or minus ve percent throughout a turn-down ratio of seven-to-one for the air. This represents a change in the analysis of the products of combustionv of less than one percent of carbon dioxide. Such accurate control of gas-air ratio throughout such a wide range of air pressures is so notable as' to I be unique in the field of commercial proportional mixers.

valve4 or other oriiicing or restricting device between the pressure regulator or governor I4 and the orice I5.

` Such freedomfrom oriiices or valves is made possible by the adjustment of the orifice I5 itself to get desired changes in `ratio. But since there are no other orices or the like to` introduce another and .disturbing coeillcient of discharge inthe gas line, the coeiilcient of discharge for the orifice I5 can be, and is, made to match that-,ofthe air supply flow-way. Accordingly,

a change in air pressure, and hence velocity, is

reflected in an almost precisely proportionate change in gas flow and, thereby, a high degree of uniformity preserved in the gas-air ratio.

Not only does the disclosed arrangement accomplish extreme accuracy of maintenance of gasfair ratio, but italso affords maximum eiliciency with respect to the ratio of'intake air pressure to discharge mixture pressureg As a generalization, it may be noted that there is an energy exchange between the air and the gas which it entrains, this being necessary to raise the static potential energy of the gas to manifold 1.

pressure. The mixer exit or manifold pressure will always be less than the intake air pressure by an amount necessary to compensate for the v kinetic and potential energy imparted to the gas plus friction and heat losses. In the present mixer a very high percentage of the initial potential energy of the air is recoverable as useful pressure inthe manifold. In fact it is possible to attain a-manifold pressure of twenty-five inches W. C., with` an input pressure of seventy y inches W. C. This represents a gain of at least seventy percent over `proportional mixers of older and less eilicient design.

When operating outside the usual range of air pressures' indicated above, that is, below three inches W. C.,`or above thirty inches W. C.,

it is sometimes desirable to make some further adjustment of the system to retain the gas-air :proportionality with the requisite exactitude.

Thus at very low pressures the air velocity is so far diminished as to entrain insufficient gas, Y*

which at very high air pressures the gas delivery tends to be excessive. I have found that the rangeof usable air pressures can be very substantially increased byrincorporating in thesystem described a simple adjusting' arrangement for the zero governor M.

InV the illustrated governor (see Fig-5) the usual, generally disk shaped casing 67 is provided and across the interior of which extends a flexible diaphragm 48. Fixed to opposite sides of the diaphragm are reenforcing disks 49. Bolted on the .lower side ofthe casing 48 is a valve body'50 having Aan inlet 5I and an outlet 52 and cored out of to form a passage therebetween with a valve disk 53 interposed in ther passage. This valve disk 53 is normally urged to closed position by a helical compression spring 54 seated in the bottom of the valve body. ,A` thrust pin` 55, exea to the valve diskss, contacts the center of the diaphragm and operatively con-A 60. The opposed springs are so balanced, relative to the pressures involved, that the diaphragm will open the valve disk 53 when the outlet gas pressure from the regulator drops to a predetermined point relative to atmospheric pressure.

In the event that very high air pressures are applied to the mixer, the'latter will, as heretofore noted, tend to draw too much gas. To obviate this diiculty provision is made for yieldably, and adjustably, limiting the opening of the regulator valve 53 so as to throttle the gas in it under the condition noted. For this purpose an adjusting screw 6l is threaded in the lower end of the valve body 50 and connected to the valve disk by a compression spring 62, disposed within the spring 54. The spring 62 thus forms a yieldable stop for the valve disk and the latters travel can be adjusted by the screw 6I. By thus limiting the opening of the valve disk 53 a substantialorificing effect can be introduced for large gas flows, accompanying high air pressures, so that the rationing of gas and air is retained quite uniform even at high air pressures.

At'the other extreme of air pressures, that is, with very low pressures, it is desirable to vadjust the spring 56 in the governor (by the plug 51) so that the regulator valve will open to maintain a pressure in the mixer's chamber slightly above atmospheric pressure. For example, if the gas pressure in the chamber I4 is run up to 0.5 to 0.75 inchW. C. the gas-air ratio will be retained substantially uniform when the air pressure is brought down to only one inch W. C. or, in some instances, as little as 0.5 inch W. C. Extreme range of air pressures is thus made possible..

From the foregoing it will be seen that a very eilicient and high precision instrumentality has been provided. Nevertheless it is extremely simple and rugged in construction so that low cost ansrir long life are assured.

I claim as my invention:

1. In a proportional mixer of the type set forth, the combination of ilrst and second members having respectively entrance and exit flow-ways formed therein, said flow-ways being axially alined and tapered toward each other, a generally tubular body fixed to one of said members and telescoped over the other for guided endwise rectilinear sliding movement of the latter, means operable from the exterior of said body for adjusting the position of said member within it, whereby to position the latter with a clearance gap of preselected width between it and the other member/fand said body being shaped interiorly to provide a chamber for a gaseous medium substantlally encircling said gap, whereby when gas is supplied to said chamber and a second gas passed through said flow-ways the rst mentioned gas will be inspirated through said gap into the gas passing through said flow-ways and with a ratio to the second gas fixed by the width of said clearance gap.

2. In a proportional mixer of the type set forth, the combination with two members arranged endto-endwith a small clearance gap between their adjacent ends and having axially alined owways therethrough tapered toward each other to points of minimum diameter for each on opposite sides of said gap, of a generally tubular body rigid with one of said members and telescoped over the other, said other member having limited rectilinear endwise adjusting movement within the body,.and said vbody beingsiiapedinteriorlyto by one gaseous-medium may be inspirated from said chamber through said gap and into a stream Y of a second gaseous medium passing through said i flow-ways, such stream reaching its maximum velocity adjacent the juncture of said now-ways at said gap.

3. In a proportional mixer of the type set forth, the combination of two members arranged endto-end and having axially alined flow-ways therein fashioned to form a Venturi type Passage comprising entrance and exit passages tapered axially toward a throat which joins them and which constitutes the minimum diameter portion of the Venturi passage; the plane of juncture of said members being adjacent said throat, a generally tubular body rigid with the one of said members in which the said exit passage is formed and telescoped over the other of said members, means within said body guiding said other member for rectilinear endwise adjusting movement therein while maintaining the same rigidly against side play, and said body being shaped interiorly to form a gas supply passage embracing a clearance gap between the opposed ends of said members.

4. In a proportional mixer of the type set forth,l the combination of two members arranged endto-end with a small clearance gap between their ends and having axially alined now-ways therethrough tapered toward each other, said flowways terminating at their adjacent minimumdiameter ends in short portions of cylindrical contour, a generally tubular body rigid with one of said members and telescoped over the other, said other member being guided and supported lby said `body for axial sliding movement toward and away from said one member to adjust the width of the clearance gap betweenV them, adjusting means for shifting said other member endwise, and said body being shaped interiorly lto form a gas supply passage embracing the clear- :nce gap between the opposed ends of said memers.

5. In a proportional mixer of the type set forth, the combination of two members arranged endto-end with a small clearance gap between their adjacent ends and having, respectively, entrance and exit flow-ways therethrough disposed in axial alinement and tapered toward each other, said flow-ways terminating at their adjacent minimum-diameter ends in short portions of cylindrical rather than tapered contour, the cylindrical portion of said entrance now-way being of slightly smaller diameter, and also of slightly less axial length, than the cylindrical portion of said exit flow-way which lies on the opposite side-of said clearance gap therefrom, a generally tubular bodyy rigid with one of said members and telei scoped over the other to guide and support the latter for endwise movement, said body being shaped interiorly to form a gas supply chamber embracing the periphery of said gap, and adjusting means for shifting said other member endwise to adjust the `width of saidv clearance gap.

body having a mixer member rigid with one end thereof, said body and mixer member having inlet and outlet openings in their respective outer ends, said mixer member having an axially extending mixer passage therein tapered away from said outlet opening into which it leads, a nozzle member telescopedwithin said tubular body and guided therein for endwise ysliding adjusting movement, said nozzle member having a passage therein tapered toward that in said mixer member and extending between said inlet and the adjacent end of said mixer passage, manually operable means for adjusting said nozzle member endwise within said body to vary. the clearance between the opposed ends of said nozzle and mixer members, and said body having a gas inlet in the side thereof for supplying gas to ow through such clearance into the mixer passage at its point of juncture with the passage of said nozzle member. 1 .7. A proportional mixer comprising, in combination, a pair of elongated generally frusto conical members disposed in axial alinementwith their small ends toward each other, said members having alined now-ways therethrough tapering toward each other, a generally tubular body telescoped over one of said members and xed to a portion of the other intermediate the latters ends, the exterior of said one member and the interior of said body presenting mating surfaces supporting and guiding said one member for rectilinear endwise movement in said body` and forming a seal peripherally about said one member, means for adjusting said one member endwise to vary the widthof a gap between its inner end and the opposed end of the other member,

and said body having a gas inlet communicating with a chamber encircling the periphery of said gap and formed within said body, between said seal and the line of juncture of said body with said other member, by the clearance between the tapered noses of said member and the interior wall ci said tubular body into which they project.

8. In a proportional mixer `of the type set forth, the combination of two members arranged endto-end with a small clearance gap between their adjacent ends and having laxially alined owways therethrough tapered toward each other to points of minimum diameter for each on opposite sides of said gap, a generally tubular body rigid with one of said members and telescoped over the other, said other member having limited endwise movement within the body, said body being shaped interiorly to form' a gas supply passage embracing the gap between the adjacent ends of said-members, whereby one gaseous medium may be inspirated from said chamber,

through said gap and into a stream of a second gaseous medium passing through said ow-ways,

such stream reaching its maximum velocity adjacent the juncture of said now-ways at said gap, a stud fixed to said other member and projecting through a slot in the side of said body, and means body and cooperating with said stud for shifting said other member endwise within said body to vary the width of said clearance gap.

9. In a proportional mixer of the type set forth,

the combination of two members arranged endto-end with a small clearance gap between their opposed ends and having axially alined flow-ways therethrough tapered toward each other to points of minimumA diameter for each on opposite sides of said gap, a generally tubular body rigid with one of said members and telescoped over the other, said other member being guided and supported by said body for rectilinear axial sliding movement toward and away from said one member, adjusting means including a threaded member operable from the exterior of said body for shifting said other member endwise to adjust the widthv of said clearance gap, said body being shaped interiorly to form a gas supply passage embracing the gap between the adjacent ends of ,said members, and means for sealing said adjusting means against movement, to prevent tampering therewith.

10. An apparatus for mixing gases in prede- I termined proportion comprising, in combination, two members arranged end-to-end and having axially alined :dow-ways therein fashioned to form a Venturi type passage comprising entrance and exit portions tapered axially toward a throat which joins them and which constitutes the minimum diameter portion of the Venturi passage, the plane of juncture of said members being adjacent said throat, means supporting said members for relative movement toward and away from each other in order adjustably to vary the clearance between their adjacent ends, means for supplying one gas to said Venturi passage, whereby a high velocity ow of the same through said throat results, means including a conduit for supplying a second gas to the clearance gap between said members for entry into the stream of said one gas in said throat, the width of said adjustable clearance serving to control the ratio of said Bases one to the other, said clearance gap forming an orice having a coemcient of discharge substantially equal to that of said Venturi passage, land pressure control means interposed in said conduit for maintaining the pressure of said second gas at a low and relatively constant value, the portion of said conduit between said" control means and said clearance gap being free of any orice or similar restriction.

EDWARD J. HAEDIKE-` including a lead screw on the`exterior of said

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