US2160408A

US2160408A - Air control for furnaces

Info

Publication number: US2160408A
Application number: US74581A
Authority: US
Inventors: Earle W Ballentine
Original assignee: FROD E HUMMEL
Current assignee: FROD E HUMMEL
Priority date: 1936-04-15
Filing date: 1936-04-15
Publication date: 1939-05-30
Anticipated expiration: 1956-05-30

Description

ay 1939- E. w. BALLENTINE 2,160,408

LAIR CONTROL FOR FURNACES Filed April 15, 1936 4 Sheets-Sheet l y 19139- E. W.YBALLENTINE AIR CONTROL FOR FURNACES Filed April 15, 19:56

4 Sheets-Sheet 2 y 1939- E. w. BALLENTINE 2,160,408

AIR CONTROL FOR FURNACES Fild April 15, 1936 4 Sheets-Sheet 3 my Z67 Z? M y 1939- E. BALLENQVTINE $160,408

AIR CONTROL FOR FURNACES Filed April 15, 1936 4 Sheets-Sheet 4 Z9 Z6- Z6 jaw Patented May it .l'!" .manent-trmtcc of i l -co i- 9- Chicago, Ill, asaigno'a by Russell Electric Company,

i Chicago, Ill... corporationof' llllnois Application and .15. ms, Serial No. 14.581

9 Claims. v (01. 110-45) This invention relatesto air control for furnaces, and .more particularly to means for controlling the volume of air positively fed to the combustion chamber of a furnace.

5 One feature of this invention is that it main tains the volume of air positively fed to the combustion chamber of a' furnace substantially constant despite variations in the resistance of the furnace system to the flow of air therethrough; 10 another featureof this invention is that it maintains the velocity of the air entering the fuel in the retort substantially constant; another feature of this invention is that it varies the volume of air fed to the combustion chamber in accordance 15 with the rate of fuel feed thereto, whereby proper stoichiometric proportions of fuel and air are maintained; still anotherjeature of this invention is that it regulates the volume of air delivered by a substantially constant speed centrifugal 20 blower by means responsive to pressure changes between theblower and a valve or blast gate in the duct leading from the blower to the furnace; yet another feature of this invention is that it regulates the pressure at which the control means 25 is operative, and consequently the volume of air delivered to the furnace, in accordance with the rate of fuel feed to the furnace; a further feature of this invention is that all motor means for the system are electrically'operated; other features and advantages of this invention will be apparent from the following specification and the drawings,

in which- I Fig. 1 is a side elevation, partly in section and partly diagrammatic, of a furnace equipped with 35 this invention; Fig. 2 is a plan view, partly broken away, of the installation of Fig. 1; Fig. 3

is a sectional view of the retort along the line 3-3 of Fig. 1; Fig. 4 is a view along the line 4-4 of Fig. 3; Fig. 5 is a sectional view of the control 40 means for the valve or blast gate motor; Fig. 6

is a view along the line 66 on Fig. 5; Fig. '7 is a vertical view, partly in section, of the motor means regulating the valve; Fig. 8 is a top plan view of this motor; Fig. 9 is a view along the line 5 9-9 of Fig. 7; Fig. 10 is an elevation, partly broken away, of the rheostat housing; and Fig. 11

is an end elevation, partly broken away, of the rheostat housing.

It is well known that variations in the relative 50 quantities of fuel and air fed to the combustion chamber of a furnace system result in variations in combustion efficiency. A deficiency of air for a given quantity of fuel results in a failure to consume all of the fuel, with part thereof pass- 55 ing out of the flue with the gases of combustion as soot and the like. Too great an excess of air for a given quantity of fuel results in a waste of heat in raising the temperature of the unused air and then allowing it to pass out of the stack, with the consequent loss of useful heat. Stoichio- 5 I metric proportions have been worked out for practically all types of fuel, and it is recognized that these proportions must be closely followed for maximum elliciency. Regulation of the volume of air delivered to the combustion cham- 10 her of a furnace by a centrifugal blower operating at a substantially constant speed, for example, has many difficulties, principally because of the changes in the resistance of the furnace system to the flow of air therethrough. Changes in the 15 direction of the wind, variations in the resistance of the flue and walls of the combustion chamber, variations in the compactness of the fuel bed where coal is used, and the like, all impose a varying resistance load on the blower. This varylog resistance, of course, results in undesired variations in the volume of air passing through the combustion chamber.

This invention contemplates the introduction of another variable resistance in the system in the form of a valve on blast gate'in the delivery duct and preferably a second variable at the point of entrance of the air into the body of fuel in the retort leading from the .blower to the furnace. The blast gate, being adjustable, introduces a variable resistance in the system which is capable of adjustment, and by means of which variations in the otherresistances may be compensated for to maintain a substantially constant over-all resistance to air flow through the furnace system. The blast gate is operated by a reversible shapedpole electric motor which is automatically controlled by a switch responsive to pressure existing in the duct between the valve and the blower. Because of the rather definite pressure-volume relationship of the output of a substantially constant speed centrifugal blower, maintaining the pressure substantially constant behind the valve maintains the volume of air delivered to the combustion chamber of the furnace at the desired tive'sise of the openings in the retort through which air enters the retort to support cumbustion of the fuel. The volume of air entering the retort varies with the rate of fuel feed, and it has been found advantageous to reduce the size of the openings as the'volume of air is reduced, so that the stream of air entering the fuel always has sufllcient turbulence and velocity to penetrate substantially to the center of the retort. This means is also interlocked with the speed regulating means for the fuel feed.

Referring more particularly to Fig. 1, l3 indicates a furnace having a retort -l I, fuel-feed conveyor means i2, air feed means i3, and boiler tubes l4. The other portions of thefurnace system are not here illustrated, since they form no.

part of this invention. The fuel it is here shown as coal of the proper size, which coal is placed in the hopper I3 and carried into the combustion retort ii by the conveyor I2 which is driven by a motor here indicated as 13, of a variable speed type. The speed at which the motor drivesthe conveyor i2 is controlled through a standard rheostat means in the housing 1|, comprising a resistance element 12 and a movable contact arm 13 manually set by the handle i9. A centrifugal blower 23, driven at a substantially constant speed by an electric motor, is connected'by a delivery duct 2i to the air inlet I 3 of the furnace. Control of initiation and termination of feed to the furnace is by means of a standard limit switch 92 and room thermostat 93, connected to the system here illustrated through the pipe i1 and conduit It.

An air control valve or blast gate 22 is mounted in the delivery duct 2| on a shaft 23, which shaft is connected through a gear reduction box 24 to a reversible electric motor 25. The motor has one side thereof connected to the line 29, and two wires 21 and 28-connecting it to contacts in the control means 29, which control means is responsive to the pressure in the duct 2i between the valve 22 and the blower 20, to which duct it is connected by the pipe 30. The pressure at which the contact 34 makes and breaks contact with the

contacts

32 and 33 connected to the lines 21 and 23 is regulated by the setting of the plunger 3|, which is controlled by the setting of the handle i9 which also controls the rate of fuel feed.

Referring more particularly to Figs. 5 and 6, the control means 29 will be described in more detail. The control means has therein a pair of

contact points

32 and 33 connected to the lines 21 and 23, and adapted to be contacted by the point 34 carried by the resilient member 35, which member is preferably of spring metal. The member 35 is mounted upon, although electrically insulated from, the movable member 36 rockably mounted on the pivot 31. The movable member 36 is contacted by the saddle 38 mounted on the rod 39, which rod is connected to the diaphragm 43 in the diaphragm chamber 4|. It will be noted that the pipe 33 opens into the chamber on one side of the diaphragm 43, and the position of the diaphragm is thus a result of two opposed forces, one exerted by the air pressure in the duct between the valve and the blower, and the other exerted by the spring 42. The compression or pressure of the spring 42 is regulated by the plunger 3|, and is a function of the position of the arm 43 carried by the shaft carrying the manual handle i9 which regulates the rate of fuel feed to the furnace. The system is so arranged that the movement of the manual con- ,trol handle '13 to afsetting rate of fuel feed to the i'urn'acere'aults', through the arm 43 and the plunger 3|, in'incress'ing the pressure in the spring 42. point 34then closes with contact 33, completing a circuit which rotates the motor 23in a direction closing the valve vor blast gate 23. The valve is -closed until the pressure between it and the decrease in air maintains the proper stoichiometric proportions with the decreased rate of fuel feed. Current is supplied to the strip 34 from the line or source of electric current by'the wire 44,

throughthe flexible pigtail 34. The strip 33 is free to assume a position dependent upon the pressure upon the diaphragm 43, and when the pressure is at the desired point-the contact 34 floats between the two

contacts

32 and 33; it is only when the pressure is above -or below the desired value for any given fuel feed rate that the contacts close to change the positionv of the valve and bring" the pressure to the desired value. A small permanent magnet 43 is mounted iust behind the contact 32, and the relation between the flexible member 33 and the pull of the permanent. magnet 43 on the contact point 34 results in a snap action of the switch.

Referring more particularly to Figs. 7, 8 and 9,

the electric motor and reducing gear system controlling the position of the valve 22 will now be described in more detail.

The motor 25 has a frame 43, which frame, in addition to supporting the various parts of the motor, serves as a path or core for the flux produced by the

coils

41 and 43. These coils have pole pieces 49 and 53 mounted therein, which pole pieces are of the shaded type adjacent the disk 5i carried by the shaft 32, having portions thereof surrounded by the shading coils 14 and 15. The position of the shaded portions of the

po1e pieces

49 and 93 with respect to the disk Si is such that when coil 41 is operative and coil 43 inoperative the disk revolves in one direction, and when coil 43 is rendered operative and coil 41 inoperative through the action of the control switch 29 the disk 5i revolves in the opposite direction. The shaft 52 is connected through a train of reducing gears to the shaft 23, which carries the valve or blast gate 22. The position of the valve is thus controlled by the reversible electric motor, controlled in turn by the switch 29. Since the position of the contacts in the switch 29 is a result of two factors, the speed setting of the fuel feed and the air pressure in the duct 2|, the setting of the valve 22, and consequently the volume of air passing through the combustion chamber of the furnace system, is thus a function of these two factors.

The capacity of the blower 23 is chosen to be suflicient for the highest rate of fuel feed of the system and the highest resistances to air flow expected to be encountered in the furnace system. Changes in the setting of the fuel feed means effects a change in the pressure to which the control switch 29 is responsive, and consequently introduces another resistance in the system, through change in' the position of the valve 22, such that the new volume of air delivered maintains the proper stoichiometric proportion with the new rate of fuel feed. Constant changes in the variations of pressure in the furnace system resulting from changes in the fire bed, changes in wind direction, and the like, are compensated for by changes in the position of the valve 22 so that the over-all'resistance of the system is constant, at such a value as maintains the proper volume of air flow.

Referring more particularly to Figs. 1-4, it will be seen that the combustion chamber of the furnace III is provided with a retort ll adapted to support combustion by underfed stoking of its fuel content 6!. The retort II has openings 82 through the sides thereof, through which openings the air delivered by the centrifugal blower 20 through the duct 2| passes on its way to the combustion chamber of the furnace Ill. The retort has around it a sleeve 63, here shown as a light gauge sheet of metal, which sleeve is so mounted as to be able to rotate through a limited arc about its axis, which is also the axis of the retort. The sleeve is provided with openings 64 which are adapted to register with the openings 62 in the retort, either wholly or in part, in accordance with the position of the sleeve. The sleeve has attached thereto on one side thereof a lug 65 to which is connected a rod 66 projecting outside of the combustion chamber of the furnace and connected at its other end to a bell crank 61 mounted on the outside of the furnace. The rod 66, where it passes through the wall of the combustion chamber, is provided with a substantially air-tight packing of any well-known type, in order to prevent leakage of the air being delivered to the retort by the blower 20. The other end of the bell crank 81 is connected by the rod 68 to the control lever "which regulates the rate of fuel feed to the retort, and also, through the plunger 3|, the volume of air delivered to the combustion chamber of the furnace.

It is, of course, necessary to make the openings 62 in the retort and the corresponding openings 64 in the sleeve large enough to pass, without substantial resistance, the volume of air necessary for proper stoichiometric proportions at the highest rate of fuel feed of which the stoker system is capable. being delivered to these openings, the velocity of the air therethrough and its turbulence after it has passed therethrough is suiflcient to insure penetration practically to the center of the fuel conduit of the retort. Heretofore, no provisions have been made in the art for decreasing the effective size of these openings when the fuel and air feed rate was decreased, and poor combustion in the center of the fuel bed resulted. It has been found that if the openings remain of the same size while the volume of 'air delivered is cut to one-fourth, for instance, the air has not sufficient velocity to penetrate more than a few inches into the fuel content of the retort, and

then passes upwardly into'the combustion chamber, thus leaving a central mass of fuel to which sufiicient air is not being delivered to properly support combustion.

Applicant has discovered that if the effective size or area of the openings is reduced, as by his supplemental sleeve, the velocity of the air enteringthe retort may be maintained high enough to insure proper penetration and distribution through the fuel content even when a smaller volume of air is being delivered to the combustion chamber to maintain proper stoichiometric proportions with a smaller quantity of fuel being fed thereto. It will be thus seen that in the sys- When a large volume of air is tem disclosed herein the control lever I8 not only controls the rate of fuel feed to the furnace, but also controls the volume of air delivered to the combustion chamber and the penetration of that air into the fuel content of the retort. The controls are, of course, so set that the volume of air delivered to the combustion chamber at any given stoker rate setting is substantially that proportion found to provide most eflicient combustion.

While I have shown and demribed certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangementmay be made without departing from the spirit and scope of the invention as disclosed in the appended claims, in which it'is my intention to claim all novelty inherent in my invention as broadly as possible in view of the prior art.

What I regard as new and desire to secure by Letters Patent, is:

1. Apparatus of the character described, including: a furnace; a substantially constant speed centrifugal blower;'a duct for delivering the air from said blower to said furnace; a valve in said duct; means for varying the position of said valve by and in accordance with the pressure in said duct between said valve and said blower'; and means for varying the position of said valve by and in accordance with the rate of fuel feed to said furnace.

2. Apparatus of the character described including: a furnace; a substantially constant speed centrifugal blower; a duct for delivering the air from said blower to said furnace; a valve in said duct; motor means for varying the position of said valve; control means for said motor, said control means being responsive to variations in air pressure in the duct between said valve and said blower; and means for varying the pressure level to which said control means is responsive by and in accordance with the rate of fuel feed to said furnace.

3. Apparatus of the character described, including: a furnace; variable fuel feed means; a substantially constant speed centrifugal blower; a duct for delivering the air from said blower to said furnace; a valve in said delivery duct; motor means for varying the position of said valve; a pressure responsive switch for controlling said motor, said switch being responsive to the pressure existing in the delivery duct between the valve and the blower; and interconnecting means between said switch means and said variable fuel feed means whereby the volume of air delivered to said furnace is proportional to the amount of fuel fed thereto. j

- 4..Apparatus of the character described, in-

cluding: a furnace; fuel feeding means therepression means is regulated by and in accordance with the rate of fuel feed; and means so constructed and arranged that the pressure in said duct between said valve and said blower is maintained substantially proportional to the compression in said compression means, whereby the volume of air delivered to the combustion chamber of said furnace is maintained substantially constant at any set rate of fuel feed despite variations in the resistance to the flow of air through said furnace.

5. Apparatus of the character described, including: a furnace having a combustion chamber; a retort in said chamber, said retort having openings therethrough for the admission of air thereto; means for delivering a volume of air togaid retort, said volume being variable; and means for varying the eiifective size of said openings substantially in accordance with the volume of air delivered to said retort.

6. Apparatus of the character described, including: a furnace having a combustion chamher; a retort in said chamber, said retort having openings therethrough' for the admission of air thereto; means for feeding fuel to said retort; means for varying the rate of said fuelfeed; means for delivering anto said retort; means for varying the volume of air delivered thereto by and in accordance with the rate of fuel feed; and means for varying the effective size of said openings substantially in accordance with the volume of air delivered to said combustion chamber, whereby proper distribution of said air through the fuel content of said retort is maintained.

'7. Apparatus of the character described, including: a furnace having a combustion chamber; a circular retort in' said chamber, said retort having openings through the walls thereof communicating with an air chamber for the admission of air to said retort; a sleeve surrounding said retort and rotatable axially with respect thereto, said sleeve having openings theret'hrough adapted to register'thbseitlirough the wall of the retort; for fieedin'g" fuel to said 'of air delivered to said chamber in accordance with the rate of fuel feed; and means for rotating said sleeve about its axis to vary the effective size of the openings through which said air passes.

8. Apparatus of the character claimed in claim 7, wherein the means for rotating said sleeve is operated by and in accordance with the rate of fuel feed to said retort.

9. Apparatus of the character described, including: a furnace having a combustion chamber; a circular retort in said chamber having openings through the wall thereof; a sleeve around said retort having openings therethrough adapted to register with said first-mentioned openings to afford communication thereof with an air chamber therearound; means for feeding fuel to said retort; a substantially constant speed centrifugal blower; a duct for delivering the air from said blower to said air chamber; said air may pass through the openings in said sleeve and said retort wall to said combustion chamber; a valve in said duct; motor means for varying the position of said'valve; control means for said motor, said control means being responsive to air pressure in the duct between said valve and said blower; means for varying the pressure to which said control means is responsive by and in accordance with the rate of fuel feed to said furnace; and .means for varying the registry of said openings by and in accordance with the rate of fuel feed to said furnace.

e EARLE W. BALLEN'I'INE.