US2612319A - Draft control - Google Patents

Description

Sept. 30, 1952 O. E. WADENSTEIN DRAFT CONTROL Filed June 3, 1949 ama- QM m- W Patented Sept. 30, 1952 DRAFT CONTROL 7 Oscar E.'Wadenstein, St. Paul, Minn., assig nor,

" by-mesne-assignments, toFueLReduction Engineers; Inc., St. Paul, Minn., a corporation, of

Minnesota.

PATENT OFFICE App1ication June-3, 1949, Serial No. 97,018:

be" maintained by more or less closing the by-pass damperin the br'eeching tdinci'ease over-fire draft or by opening" th'edamper' to a' greater or lesser extent to decrease over-fire'diaft by by-' passing stack suction". However; the common types off motor'ized by-pass 'dam'pers described above ar'e limited toa single rate'of overfire draft dependent upon the' setting 'of the staticpressure regulatorin iisei f I t I have fiound that boilers or furnaces'will-operate niore' economically if over-fire draft is variedto su'ppl'y more or less draft'as the'volume of; fuel'and air is increased or decreased. Thus in my variable'air new control I p'rovide lip to three static pressureregulators with each regulator adifisted to pro'vide a difl'erent fixed rate of over-fire draft "depending "upon the requirementsof the are; I

rates' or draft; for'example .i2-;draft by {Water for a peak boiler load, .08"' for a half load and .04 for a quarter mad.) Two static 'pressure regulat'o'rs' will provide two" 'rates of over-fire draft. contr 'i's switched from one static pressure regulator toth'e otherby electricity, the over-fire draft will modulate oF'varybetween the fixed settingsof' the regulators consequentl modulatin'g'dr'aft is also a parrot the rese t inventioil." V L An added featureof'the present invention lies the provision of a'mansfor controlling overfiie'draft atiowestd'esirame rates or draft. I

have-demonstratedthat the combustion 'efiiciency or a'ilie, whether-coated, or gas, can be maid tamed at a high point of fiicie'ncy when over-fire draftis decreased as fuel and blower air'ratios aredecreasem 1 I These and? other objects and novel features of my. inv'eritioniwill be rirore clearly and fullyset forth in the 'followingspecificatioh and claims.

. 8 Claims, (Cl.'236- 15 I reestau pressure regulators, each acti Viifid separately byelectricity; WiH'pIDVide three Inthe drawingsforming apart of my specification: Figure-1 is a diagrammatic perspective view showing afurnace to which, my control has been applied.-

hem f I v s. The control system is used in coniunction with a furnaceor boiler 10 which may-burn any desired type of fuel. In the furnace illustrated: an oil burner l l is employed. -The oilburner is provided with a blower ['2 to supply primary forced air, and a dampered opening-into the furnace below the oil burner to supply secondary air by stack suction. The furnace I0 is connected to f the breeching l3which connects the furnace with the chimney stack 14. I

'The oil burner II is supplied with oil from-an oil supply line indicated at 51; which passes through a control valve 2. A lever 3 controls the valve 2 and also an electric control such as. a-

multi-position switch or a rheostat 4. Pivotal movement of the lever 3 simultaneously increases or reduces the oil supply and the air supply provided by the blower I2. The rheostat' l is connected to the blower I2 by an electric conduiti.

The lever 4. is connected by a'chain or other.

linking meanst to the switch which'will-be" later described in detail. A means is provided foractuating the lever 4, such as "the pressure actuated apparatus. 1 'connectedtothe leverg4 by a 1mm; When the pressure actuated device I indicates a needfor-increased fueland. air feed the lever 4' is oscillated upwardly: When the necessary pressure is built up in the device [the lever I is swung downwardly to decrease the fuel and air supply. The'switch 35 is "connected tothe re-' mainder 'of the system by azconduit'9. This'sys-t,

tem is onJy'illuStr'ative of manywhich could "be used. f

obv'iously the oilburner is optional, and gas 'or' coalcan also be used. The gas maybe suppliedin the usual manner and ablowersuch as I 2 mayv be used in conjunction therewith to'supply' a forced draft of air. Similarly :the *furnace or- .boiler l0 may comprise a 'coalburning apparatus supplied with coal by a suitable .stoker or "similar device. A blower such as ['2' is alsousedin con:

junction with this type of furnaceor boiler. The

breeching I3 is provided with aby-pass-passage l5 provided with adamperiG-at its'outer extremity. The position of the damper I6 is controlled bymeans of a jdampercontrol motor 11.- The motor I! may operate ineitherdirection to open or close the damper I 6, v;

Figure 2 is a diagram of the wiring ofmy sysone terminal of a triple throw switch 35.

fi V '1- ff; 2,612,319

A static pipe I 9 extends into the furnace above tial to provide a low draft rate, while the regulator 20 is set to maintain a relatively high static pressure differential, to provide a high rate of draft. With the use of a third static pressure regulator 2| a medium rate of over-fire'draft can be provided. Over-fire draft will modulate up or down as electric current activates the various. static pressure regulators, one at a time.

With reference to Figure 2 of the drawings, it will be noted that two terminals 22 and 23 and the first static regulatorl 8 are connected by conductors 24 and 25 to terminals 26 and 21 of the damper motor 'I.' Terminals 29 and 30 of the second static pressure regulator 20 are provided with conductors 3| and 32 which are electrically cdnne'ctedto the conductor 24'and 25 respectively. A thirdterminal 33 of the first pressure regulator |8"is connected by a conductor34 to The third terminal 36 of the pressure regulator 20 is connected'by a conductor 31 to the opposite pole of thetriple-throw switch 35. A third terminal 39"o'n the damper'motor I is connected by a conductor to a line wire 4| or a suitable source of current of the desired voltage. The terminals 42 and 43 of the triple throw switch 35 may be alternatel'y'connected to the other line wire 44, providing asuitable source of supply of electrical current.

Where a third static pressure regulator 2| is empleyei the terminals 45 and 46- thereof are connected by conductors 41 and 49 to the conductors' 3| and 32, and consequently the conduc-' tors 24 and 25, respectively. In other words, the

three-static pressure regulators I8, 20, and 2| are wire" 4| is a commonwire to the motor and forms one side of the circuit tothe motor regardless of the direction ofrotati'on thereof. The conductors 24 'and' 25 and" the extended conductors 3| and 321; and 4T, 49' connectedv thereto, respectively, form the remaining two sides of the circuits'to the m'o'tor 1'. When the conductor 24 and its 'extensions 3| and 41 are in circuit, the motor I! will operate in'one direction to open the damper.

When the conductor 25 and its extensions 32 and 49;are in circuit-the motor I! will operate 'inthe opposite directinn to close the connected damper. The switch 35 is controlled. by some portion of the operating mechanism which is actuated si-f multaneously 'with any change of the fuel and air feed; "The switch 35 acts to'connect the line wirej 44.to the conductor 34 through the switch terminal"42 when the boileris being supplied with fuel andairat azmin'imum rate, Thus during the periods' of relatively slow fuel feeding operation (as for-"example, one-quarter load), the static pressure regulatorl8is electrically connected in the circuit? andvariations in "pressure above the fire bed will act'to connect either the conductor 24 or the conductor 25into the circuit and thus to move the damper motor I! in one direction or the other. When the terminal 33 of the pressure regulator I8 i connected to the terminal 22, a circuit is closed through the conductor '24 so as to operate the damper motor I! to open the connected damper Hi. When the'terminal33 is connected to the third terminal 23, the circuit is closed from the conductor 34 to conductor 25. thus closing the circuit to the damper motor IT to operate this motor in a direction to close the connected damper l8.

The pressure regulator is not specifically illustrated in detail in the drawings, a this device is known in the art. The regulator acts to maintain a fixed static pressure above the fire bed by opening or closing the by-pass damper to a greater or lesser extent. For example if the differential static pressure desired to be maintained by the regulator I8 is .04 inch of water, a switch contact will connect terminals-33 and 23, when thepressure decreases below this amount. As a result the damper 6 will beclosed until the pressure above the'fire bed again becomes .04 inch of water. When the static differential pressure above theflre bed increases above .04 inch, a contact will be formed between terminals 33 and 22, thus rotating the damper motor to partially open the damper l6 until the pressure above the fire bed again becomes .04 inch. 7

.The static pressure regulator 20 acts in a similar manner when thefumaceis feeding fuel at a maximum rate; When the fuel feeding apparatus is actuated to feed the furnace or boiler'at full speed, the regulator 20 comes into action, and the damper setting of thedamper I6 is controlled by this regulator 20, As a result, thedraftv will be maintained at ahigher level during these feeding operations. i p

When the switch 35 shifts control ofithe damper motor from one pressure --control--to. another,.a gradual change in differential pres-. sure is experienced within the furnace-or boiler. For example, as the control shifts from the regulator l8 to the regulator 20, the static pressure differential must be increased due to the higher. setting of the regulator 20. The by-pass' damper "5 will therefore close to a greater extent until the static pressure called for by the-regulator-20 is reached. Any increase of staticpressure over the desired amountresults in a closing of thecircuit to open the damper l6 somewhat. Contact between the terminals 36 and 29 actuates the motor H to open the damper I5, while contactbetween terminals 36 and 30 actuates the motor to close the damper 6. Wherea third pressure regulator 2| is employed to maintain; an intermediate static pres.- sure differential, as for example .08 inch of water, this regulator is cut into the circuit by the switch 35 when the fuel feed mechanism is feedingfuel at an intermediate rate; as for example, half speed. 1 Whenthe regulator 2| is incircuih' -it acts in the manner described to maintain the desired static pressure differential.

If the pressure differential i excessive when the regulator 2| is placed in the circuit (as would bethe case when the fuel .and air feed to the furnace is reduced), the terminals 50 and 45 will be connected and a" circuit will be formed through conductors 41, 3| "and 24, opening the. damper until the draft is reduced to the desiredzextent;

' Any reduction of draft below .this will act to con- Similarly,- if the pressure: differentialfs too little when the regulator 21 i's' placed 'inithe circuit fas would b'ethe case "when the fuel and'air feed to the fuma'ce is increased from' 'a. lower speed) the regulator-will tend to close-the damper until the properly increased static pressure differential'is reached.

The triple throw control 1 the fuel -1'eedinechanism in any desired'manner; If'the furnace orboileris provided' with-controls to o'perate the-fuel and air feedatthree set speeds, the switch 35 maybe controlled thereby-to cut a corresponding regulator into controlling position. If the fuel feed fluctuates 'or modulates gradually from one feed range to anothem the feed 'range'm'a y be divided into suita ble smaller rangesxeach' of Y which. may haveits'respectiveregulatory; 1 l 'I' have found that myfsystem operates with particular effectiveness-in,- conjunction with a system including an air by-passand lay-pass damper in-the breechingor stackr With this type ct -system"thepressure ab'ove the fuel bed is: controlledbyallowing more or less air to enter the'stack or breeching. As the by-pass damper opens, a greater'amount of air enters the stack or breeching and the draft acting upon thefire bed is-decreased. In other words, the suction effect upon the fire bed decreases and' accordingly the'pressureat this po'intincreases, decreasing the static pressure differential. Conversely as the by-pass damper moves toward closed position less air isallowedto enter the by-passso that a greater draft or suction effect is created to work upon the fire bed.-- As a result the pressure above the fuel bed decreases as the by-pass damper closes, and the static pressure differential increases. V I

This type of control functionsmore effectively than a control in which an internal damper is located in the breeching, stack, or boiler up-take. As-such an internal damper moves toward closed position the air passing the damper merely tends to move at a higher velocity-5 Thus the damper does not greatly change the static pressure-above the fuel bed until the damper nears closed position in many installations. Thus the maximum control is provided at a time when the internal damper is almost closed. Where the stack is high and there is substantial draft acting against a practically closed internal damper, boiler vibration or pulsation is severe. This fact combined with the fact that such a damper is subjected to high temperatures and may be injured thereby tends to cause my system to operate more effectively in conjunction with a Iby-pass system employin a bypass damper.

It will be noted that during the peak operation of my furnace or boiler I maintain a fixed rate of draft over the grate level which has been found proper to produce good combustion. If the same rate of draft were maintained above the grate level during the low operation period of the'boiler, poor combustion efficiency would result because of air due to excess draft. However, by decreasing the over-fire draft on low operation as fuel feed is decreased, greater combustion efficiency will result, because desirable fuel and air ratios are maintained and temperature loss is minimized.

In accordance with the patent statutes, I have 7 described the principles of construction and operation of my draft control and while I have endeavored to set forth the best embodiment thereof, I desire to have it understood that ohswitch may :be connected for v made. within-the: scope- 9! the vicuse'change'szmay e the following claims without departln zzfrom spirit of my invention. i v 'I'claimi:

1.;A. damper-co trol for use in eonjunctionwith a furnace having a gasandsmoke outlet,- a hypass into said outlet, a by-passdamperin said bi -pass, and, a fuel feeding mechanism which may-operate at full or .low speed intermittently; a first static pressure regulator for maintaining an above fire rate of draft of one relatively high value, a second static pressure regulator for maintaining: an above fire-rate of 'draft-ofiasec-. ond relatively low value, .a damper opera-ting means, and means connecting each of saidpres sure regulators selectively to said damperoperats. ing" means, and means controlled" by th inter mittent operation ofzsaid fuel feedin meang forconnected to said damper operatingmeansi 3. The structure described in claim =1 in-' which the pressure regulator operates upon' an increase of draft to open saidby-pass damper' 'and op erates upon a decrease in pressure above the fire to close the by-pass damper. f v

' 4. A variable air flow control foruse inconjunction with'a furnace provide diwitha stack through which gas and smoke may flow, a by pass for' by passing air intothe gasan'd-smoke, a damper for regulating" the by-pass of air through said by-pass, and a fuel feeding mechanism operable at various fuel feedin rates, the control including a static pressure regulating means, said regulating means including aplurality of elements each operable to' ma'intain a predetermined static pressure differential'above the grate level of the furnace, a damper motor connected to said damper for actuating the same, means connecting said elements with said damper motor for actuating said motor to maintain any of the predetermined static pressure, differentials, and selectin means sensitive to variations in fuel feeding rates for selecting an element of said plurality of elements so as to maintain the desired pressure differential, said selecting means acting to select a greater pressure differential upon an increase in fuel feeding rate.

5. A variable air flow control for use in conjunction with a furnace provided with a stack, a connection between the stack and the furnace, a damper controlling the flow through said connection, and fuel feeding mechanism operable at a plurality of fuel feeding rates, the control including a first static pressure regulating means capable of maintaining a relatively high overfire rate of draft, a second static pressure regulator capable of maintaining a relatively low above-fire rate of draft, each of said static pressure regulators being connected to the furnace and sensitive to changing conditions within the furnace, a member associated with said fuel feeding mechanism and sensitive to variations in fuel feeding I rates, means for actuating the damper to open or close the same, means connecting each of said static pressure regulators to said damper actuating means to control the bperation thereof, a" selector in said connecting me'ansfor'selectively connecting either ofsaid static pressure regulators to said damper actuating means, and means connecting said member sensitive to variations in fuel feeding rate to said selector and operable to select said first pressure regulator when said fuel feeding mechanism operates at a relatively high speed, and selecting said second pressure regulator when said fuel feeding mechanism is operated at a relatively lower rate.

' 6. A damper controlfor use in conjunction with a furnace having a gas and smoke outlet, a bypass into said outlet, a by-pass damper -.in said by-pass; and a'fuel feeding mechanism which may operateat a relatively high speed or a relatively lowerspeed, said control including a first static pressure regulator capable of maintaining an above-fire rate of draft of a relatively high value, a second static pressure regulator capable of, maintaining anabove-fire rate of draft of a second relatively lowvalue, a damper motor, a circuit tothedamper, motor including a switch actuated by variations in static pressure in said first static pressure regulator, a second circuit to saiddamper motor'including switch means controlled by variations in static pressure inv said second static pressure regulator, and means selectively connecting. either of said circuits to said damper motor,-and means actuated by variations in fuel feeding rate of said fuel feeding mechanism connected to said selector for actuatin the same, said last named means actuating said selector for selecting the first pressure regulator when said fuel feeding mechanism operate at a relatively-high speed and selecting said second pressure regulator when said fuel feeding mechanism operates at a relatively lower speed.

7'. The structure described in claim 6 and including a third static pressure regulator capable of maintaining an above-fire rate of draft of an intermediate value, and a third circuit to said dampermotor including switch means actuated by variations in static pressure in said third regulator, said selector being capable of selecting said 8 third circuit whensaid fuel feeding mechanism actuates at an intermediate rate." r v '8. A' damper control for use in conjunction with a. furnacewhavinga gas and smoke outlet, a by-'-pass-into said'outlet, a by-pass damper in said by-pass, and a fuel feeding mechanism which may operate at two different rates of rfuel feed, the control including a first static pressure regulator formaintaining a relatively high above-fire rate of draft, a second static pressure regulator capable of maintaining a relatively low over-fire rate of draft, a damper operating motor, a first circuit: to'said damper motor including a switch actuated by variations in static pressure in said first regulator; and said circuit also including a selector switch, a second circuit to said damper motor including a switch sensitive-to variations in static pressure in said second regulator, and also including said selector switch, said selector switch being capable of connecting either of said-circuits to a source of current, and means sensitive to variations in fuel feeding rate connected to said selector switch for actuatingthe same to select the circuit including said first pressureregulator when said fuelfeeding mechanism operates at a relatively high 'rate and selecting said second pressure regulator when said fuel feedin mechanism operates at a rela'-' tively low rate.

OSCAR E. WADENSTEIN."

REFERENCES CITED The following references are of record in the file of this patent:

Adams Mar. 10, 1942

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