US2088023A - Air regulating apparatus - Google Patents

Description

July 27, 1937. E.A G. BAER Er AL VAIR,REGULATING APPARATUS A VFiled May 24, 1933 l. l/ENT nsw I Patented July 27, y1937 f UNITED STATESVPATENT ori-*Ica AIR REGULATmG V.irrAltA'rUs Edward G. Baer, omine, ohio, ananobert n. Donaldson, Jr., Pittsburgh, Pa., assignors to Will-Burt Company, a corporation of Ohio `Applnation May 24, 1933, serial No. 672,584 -1 claim. (c1. 23o-.114)

This inventionrelates' to automatic air regulating apparatus to be used for example with stokers, of the type to which fuel isfed intermittently, to control the rate of delivery of air to the fuel or fire bed of such stokers, as disclosed 'in our application Serial No. 552,645, filed July 2, 1931 of which this application is a continuation in part.

Domestic stokers, that is, stokers used with small home or apartment house furnaces, are necessarily of the intermittent feed type. While fuel is being fed to the furnace, air is supplied to the fuel bed under considerable pressure by a forced draft fan or blower; and during the intervals between the feeding periods, combustion maintained by natural or chimney draft.

The length of time that the Stoker is operated under forced feed and draft and the llength of time that the fuel is burned under natural draft,

are taken to insure the proper relation between the rate at which air is supplied to the fuel bed and the rate at which fuel is fed thereto.

Variations in the quality of the. fuel `being burned also affect the resistance of the re bed to air flow.'

In order to burn fuel efdcientlyin a stoker and 'thereby realize the economies to be had over hand fired methods, it is necessary that the forced air supply be closely regulated so that the .40 air is delivered at substantially a constant rate regardless of the degree of thickness or thinness of the fuel bed. It is alsoessential that suflicient natural draft be supplied to maintain the' fire alive during the inactive periods' `of' the 45 stoker.

An object of thel inventionis to provide apparatus that shall automatically respond to con.. ditions affected by a change in the resistance'to j the flow of air, for examplel the resistance of a 50 fuel bed and make automatic adjustments Vin'thea air supply to compensatefor variations in the resistance to the Il ow of air through the re bed.

, Since thevelocity of the air delivered 'by' a fan or blower to the fuel bed of a stokeris, for all 5 5 practical purposes, a function of the air flowv resistanceof the fuel bed, it is proposed to so utilize the velocity of the air as a regulating medium, that a damper may be operated in such manner as to maintain a substantially constant supply of air to the re bed. To accomplish 5 such regulation, it is proposed to utilize a swinging target or vane, placed inthe conduit, through which air is delivered by a fan or blower to thev stoker, at a point between the damper and the air box or chamber of the Stoker. It is proposed 10 also to so proportion the target or vane that it shall offer substantially no resistance to the total flow of air to the fuel bed, so that the draft regulation may be accomplished solely by the damper.

Other objects of the invention will, in part, be 15 apparent and wil1,in part, be obvious from the following description taken in conjunction with the accompanying drawing, in which:

' Fig. l is a fragmentaryv view in perspective of a furnace provided with a stoker embodying one 2'0 form of the invention; Fig. 2 is a fragmentary view showing the nre pot and an air chamber of the Stoker and a portion of the feed screw in operative relation to the.

furnace; and 25 Fig. 3 is an enlargedjskeleton view in per- I spective showing the mechanism employed for controlling the supply of air to the fuel bed of. the Stoker.l

Throughout the drawing and the specifcation, 30 like references indicate like parts.A 'Ihe air regu-. lating apparatus ,embodying thel invention will be described in connection with its application to a stoker fired furnace. y

With reference to Figs. 1 and 2 of the draw- .35 ing, a furnace l is shown thatl is providedwith a stoker, 2 adapted to feed fuel tothe furnace intermittently in accordance with the demand for heat. While fuel is being fed to the combustion chamber of the furnace, air for combustion 40 is supplied by forced draft, natural draftmaintaining the fire alive between heating periods.

.Successful `and economical operationrof intermittently operated stokers depends largely upon the proper relation being maintained between Al the rate of fuel feed and the rate at which airis supplied tothe fuel or re Since stokers of this type are designed to deliver fuel at a con-l stant or rate, itis essential to 'efficient operation that the-air forcombusrtion be supplied at a substantially constant rate. Best Aresults are also obtained if the thickness of the fuel The thickness of the fuel bed is. nearly alwaysA .subject to change,.unless the proper relation isl 55 vduced to CO2. y

coming 'in contact with incandescent carbon will 2. maintained between the rate'of air supply and fuel feed. If the bed becomes too thick, there is a' tendency to reduce the air flow therethrough;.

therefore the air, being insuilicient, in passing through a thick fuel bed willv come in contact with such' a quantity of. fuel in a state of combustion that the oxygen of the air will all be re- But CO2 in a highly heated state be converted to CO. This results-in the carrying away of a large amount of heat-that would have been available for useful work had lthe reaction been stopped when all of the oxygen, or the larger part of it had been converted to CO2.

f the fuel bed is too thin, the air ow through Athe re bed tends to increase and become excessive. As a consequence, there is not sufficient contact between the air and the incandescent fuel to convert the larger part ofthe oxygento CO2, and this excess oxygen passing through the fuel bed results in a loss of heat energy. Whenever an excess of air is used, a considerableA the air supply, because the air ow resistance of the fuel bed remains fairly constant. This is apparentif it is taken into account that as the fuelbed becomes thinner, the resistance to air ow decreases; therefore the air supply increases which results in a further burning down and a further reduction in the thickness of the fuel bed.

Thus, a thin fuelbed when once developed, tends to become thinner and thinner, until a point is reached ywhere efcient combustioncannot be maintained.

On the other hand, if the fuel bed becomes too heavy, the increased air flow resistance thereof reduces the air flow 4through it and this in turn reduces the rate at which fuel will be burned.

Since, however, fuel is preferably delivered at a constant rate, the fire tends to build up, further increasing the vfuel bed resistance, and again reducing the air ow until a very unsatisfactory operating condition is attained. Therefore, in View of the foregoing, it is quite essential to-efcient operation, that the proper relation be maintained *between the rate of supplyA of air and the rate of fuel feed; in order that the thickness of the fire bed will be maintained 'at a substantially constant value, neither too thick nor too thin. The air regulating apparatus operates to vso regulate the air supply that the proper amount of air is delivered as the fuel bed'thjckness and its resistance varies.

The Stoker includesl a' pot 3 having a. burner' ring 4 mounted thereon, and an air box 4or'chamber 5. `The top of the burner ring is formed with a vented flange 6 that bridges the space `between the top of the air box and the burner ring.; The bottom of the pot is 'formed with an inlet 9 to which a fuel feedpipe I .is connected.

-Fuel is fed through pipe I0. by a motor driven feed screw Il to pot 3. Air for combustion is supplied to the fuel bed by a 'conduit I6 connec d to a. forced draft fan or blower I5. 'I'he air elivered toA chamber 5 is delivered to the fuel /via burner ring ports I1, and ports yI8.

Convenient, eicient and accurate regulation of the air supply may be obtained by means of a damper 2| and a device 22 that responds automatically to changes in velocity of the air delivered through conduit I6 to the re bed and automatically adjusts the damper to maintain vthe air flow vconstant. v

In practice,` it s preferred to utilize a fan or blower that has a capacity to deliver air in excess of the amount that would be required with the stker operating at maximum capacity so that damper 2| will at all times be effective to regulate the air flow and maintain it at the rate required for eflcient combustion. Thus, when the velocity responsive device 22 is once adjusted to give the requiredv air ow to a' fuel bed ofthe desired thickness andfair flow resistance, th'e damper will always occupy the proper position.l

With such an arrangement, it follows that upon an increase in thickness of the fuel bed,

resulting in an increase in the air flow resistance thereof, damper 2| will automatically be shifted to a position that reduces the air flow resistance through the damper by an amount equal to the" increase in resistance of the fuel bed. Likewise, if the fuel bed tends to become thin, the air flow resistance decreases and the velocity of the ai1 tends to increase, whereupon the .damper is automatically shifted towards closed position, until the decrease in fuel bed resistance is made up by the damper4 and the velocity of the air restored to normal. In this manner, the damper is so adjusted that the total resistance to the flow of air through the damper andthe fuel bed is maintained substantially constant. Under these conditions, eicient combustion can be obtained, because the proper relation between the supply of fair and the rate of fuel feed is maintained.- k y The velocity responsive device 22 comprises a vane or target 23 that is suspended by narrow straps 24 at its opposite ends from a shaft 25 extending through conduit I6 at the top thereof. The target is disposed near the bottom of the conduit and at such a distance from damper 2,| that theturbulence of the air on the down stream side of the damper willV not affect the true or actual velocity of the air impinging on the target. The target is relatively small in area, so that it offers substantially no resistance to the total flow of air through the conduit, but the area thereof is sulcient to offer the resistance required to swing it in response to and in accordance with variations in athe velocityof the air. y

One end of shaft 25 on which the target or vane ,issecuredis provided with a crank arm 26disposed on the outside of the Kconduit and this crank arm'is connected by a link 21 to a crank arm A28 attached to 'the shaft on which damper 2l is' mounted. The tar-get shaft 25 is also provided with an arm 29, that extends at substantially right angles to crank arm 26, on which a counterweight 30 is adjustably mounted. v'I'hiscounterweight may be moved towards or away from the target .shaft so that the target and damper may be counterpoised and urgedtowarcls sucha posi- 'tion that the damper willbeopened when the forced-draft fan and the feed screw are not operating.-

counterweight may-also be utilized to adjust .the damper to the proper position for a'given or desired rate of I, air flow to the fuel betl of the furnace.

In operation, assuming that the stoker is feed- .ing fuel-to the furnace at -a predetermined rate, `the counterweight 29 is adjusted to such a'posi- 75 when once attained by manual adjustments, will Y tion that the target will hold the damper in the proper position for efficient combustion. For this rate -of fuel feed and air supply, the damper will occupy a certain definite position. But, if for some reason or other the air supply increases, the

4 target will swing in the direction of the air ovv and move the damper towards its closed position until the velocity of the air is restored to the proper value.

On the other hand, if the velocity ofthe air decreases, as the result of an increased thickness of the fuel bed or a change in the condition of the fuel bed which increases the resistance of the air flow through the same, the target will swing toa position such that thedamper will loe adjusted towards/ open position until the velocity of the air is restored to the proper value.

When the feed screw and the forced draft fan or blower stopped, counterweight 29 will swing the target to a position such as shown in Fig. 3,

in which position the damper will be in substantially Wide openV position.

` Since the regulation of the air supply by the damper is accomplished entirely in response to the velocity of the air supplied to the fuel bed,

it follows that the total resistance to air flow oiferedby the damper and the fuel bed will be maintained at a substantially constant value.

Therefore, for a givenrate of'fuel feed, the proper relation between the air'supply and the fuel feed,

be maintained automatically.

.Having thus described our invention, what we` claim as newand desire to secure by Letters Patent is:

Automatic air regulating apparatus comprising a conduit and a forced draft fan' for delivering vair under pressure through the conduit, a damper in the conduit, a freely movable target in and adjacent one wall of the conduit and disposed on the downstreamside of the damper and having` an air impinging surface of such small area compared to the transverseK area or the conduit that it oiers substantially no obstruction to air ow through the conduit, a roel; shaft adjacent the opposite Wall of the conduit, means for rigidly suspending said target from said rock shaft, a counterweight con'- nected to said rock shaft and urging` said target in a direction opposite to that inwhich it is urged by the velocity of the air iiow, a crank arm on said rock shaft, and a link connecting said crank arm and damper whereby as the target moves to diHerent positions in response to changes in velocity of the air, the damper is shiitedto positions tending to maintain the rate

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