US2334679A

US2334679A - Flow control of fuel

Info

Publication number: US2334679A
Application number: US294931A
Authority: US
Inventors: Clesson E Mason; Ralph A Rockwell
Original assignee: Foxboro Co
Current assignee: Schneider Electric Systems USA Inc
Priority date: 1939-09-14
Filing date: 1939-09-14
Publication date: 1943-11-16
Anticipated expiration: 1960-11-16

Description

Nov. 16, 1943. c. E. MASON ET AL FLOW CONTROL F FUEL 2 SheetQ-Sheet 1 Filed Sept. 14, 1939 INVENTOR CLlssso/v E. MASON. BY RALPH ,4. ROCKWELL.

1943- c. E. MASON ET AL FLOW CONTROL OF FUEL F iled Sept. 14, 1959 2 Sheets-Sheet 2 I INVENTOR CLfJSO/V E. M450. 6 BY R01 4.1QOCAWELL.

fin. Guills *u i d ATToRNEks Patented Nov. 16, 1943 2,334,679 now CONTROL OF FUEL Clesson E. Mason; Fo xboro, Mass and Ralph A.

Rockwell, Cranford, N. 1., assignors to The Foxboro Company, Foxboro, Mass, a corporation of Massachusetts I Application September 14, 1939, Serial 294,991

(o1. Isa-36,3)

11 Claims.

This invention relates to oil burning systems utilizing mechanical atomizers for atomizing fuel oil burned and more particularly to a method and apparatus for varying the rate of fuel consumption while maintaining efllcient atomization. The various types of burners used in the oil firing art may be roughly classifiedin two groups. In one type of burner the heavy fuel oil used for firing industrial equipment such as furnaces, boilers, and the like, is dispersed or atomized by mixing a pressure fluid such as steam with the mass of cit and forcing the mixture of steam and oil through a nozzle to form a finespray. In

. which causes the oil when forcedfrom the chamber through the discharge nozzle to form a fine conical spray. The combustion efiiciency of the turner depends in largemeasure on the degree of atomization produced and hence it is desirable ing the oil to the burner tip chamber against the maximum static pressure in the burner tip chamber. A valve is provided in the return line and as the valve is opened it permits part of the oil supplied to the burner to leave the burner through the return line and thus reduces the static pressure in the burner tip chamber. This system has the disadvantage that as the valve in the return line is opened and the pressure in the chamber is reduced the flow through the tangential passages of the burner increases, although the outputofthe burner has been decreased by opening the valve. This increased flow changes the characteristic of the spray.

Aside from this disadvantage such a system of varying the oil burner output has other inherent limitations and disadvantages in operation which militate against its use with automatic control apparatus to satisfactorily correlate rate of oil burning with the behavior of the temperature being controlled.

Another attempt to satisfy the problem of maintaining the desired whirling motion of the oil in the burner tip chamber for varying rates of fuel consumption is disclosed in U. S. Patent No. 1,824,952 to Graham. In this disclosure, as

in Peabody, Graham varies the quantity of fuel that oil be supplied to the tip chamber at such a rate as to maintain an adequate whirling or centrifugal action in the chamber.

The present invention is directed to an improved method and apparatus for manually or automatically controlling the quantity of oil burned by a mechanical burner of this general character and at the same time maintaining the desired burner efficiency.

As the oil firing art has developedone of the problems encountered has been the difllculty of obtaining a mechanical burner having a sufficient degree of rangeability, that is, a burner which atomizes oil at rates of flow varying from a relatively low rate to a relatively high rate, and which at the same time produces substantially the same kind of spray for the different rates of flow. Several ways have been proposed for solving this problem. According to one system, as described in' U. S. Patent No. 1,628,424 to-Peabody, oil is supplied to the burner. under pressure but not at a constant rate of flow and a retum line is provided from the burner either to the pump intake or to the oil source. When the return line is closed off all the oil supplied to the burner tip chamber flows out through the d scharge nozzle of the burner and under. this condition the tangential passages are, supplysprayed by changing the opening of a valve in a return line and in addition provides diiferential pressure control which is intendedto maintain a constant pressure difference between the burner input line and the return line. Thus, as the static pressure in the burner tip chamber is reduced by opening the valve in the return line the supply pressure is reduced an equal amount which tends to maintain constant the amount of fuel supplied the burner tip chamber.

Inasmuch as this system employs a variable restriction in the return line to effect variations in the rate of fuel consumption it has the same disadvantages when used in connection with automatic control as those described above inconnection with the Peabody system.

In any type of mechanical atomizingburner using a return flow the quantity being sprayed is the difference between the rate of oil .flow to 1 the burner and the rate of oil flow returned from Therefore, any quantity change in return flow-will appear as a magnified percentage change in the fuel discharge rate. Thus, it is cause it provides for the desired correlation of the fuelconsumption with the demands of a control instrument which in turn is responsive to the behavior of the controlled temperature. Further, the present invention provides for the removal of one or more burners, for cleaning or repair, from a plurality of burners connected in parallel without disturbing the total fuel consumption at the time the burners are removed.

In the accompanying drawings,

Figure 1 shows a diagrammatic layout of a system embodying the invention; and

Figure 2 shows diagrammatically the crosssection of a mechanical burner of the type described; and v Figure 3 is a section taken along. the line 3-3 of Figure 2. I g V Referring to Figure l, the numeral I. indicates the combustion space of a furnace 2, which may be equipped with a plurality of mechanical atomizing burners 3 connected in parallel and which may be of the type shown diagrammatically in Figure 2.

Referring to Figure 2, the burner 3 includes an inner cylindrical conduit and an outer concentric conduit 16. Oil flowing to the burner passes through an inlet connection I1 and the annular space between the conduits I5 and 16 to the burner tip I8. At the burner tip the oil flows through a plurality of small passages or jets I9 to a cylindrical burner tip chamber 80. The axes of the passages 19 are approximate y tangent to the cylindrical inner surface of the chamber 80 so that the oil is given a rapid whirling motion as it enters this chamber. A portion of the whirling mass of oil in the chamber 80 flows out of the discharge orifice BI and is atomized to form a fine conical spray whereas the remainder of the oil passes through a passage 82 to the inner conduit I5 and thence through the burner outlet or return connection 83. The rate at which oil is discharged through'the orifice 8| may for practical purposes be considered as depending upon the static pressure in the cham ber 80.

Referring again to Figure 1, suitable ducts 4 may be provided to admit air to the combustion space I. A constant volume pump 5, such as a motor driven gear pump, is connected by a line 6 to the burners and serves to supply oil to the burners. Since for the reasons pointed out above it is desirable to supply oil through the tangential jets of the burners at a constant rate regardless of the burner output, a constant volume pump is preferably used to pump the oil to the burners. However, since it may often be impractical to select a constantvolume pump of the exact capacity or one with an adjustable speed to supply the oil to the burner at the rate desired, provision is made by the present invention for use of a constant volume pump of larger capacity than that required and a by-pass 5a having a manually operable Valve 5b is connected across the output line 6 and the suction side of the pump. As will be described, the net output of the pump to the burners may be adjusted jets IQ of the burner.

by adjusting the valve 5b and for each adjustment the rate of gil flow through the tangential jets remains substantially constant regardless of the output of the burners.

That portion of the oil supplied to the burners which is not discharged into the combustion space I passes without restriction through the return line I. to the suction of the pump 5. Thus, the

lines 6 and 1, the pump 5, and the burners 3 form a. closed circulating system.

Each of the burners 3 is provided with a bypass line 3a containing a restriction 3b. The

restriction 3b is constructed in such a manner as to have the same flow capacity and preferably the same flow characteristic as the tangential necessary to take one of the burners out of service to clean it or for other purposes and in such a case valve 3d in branch line 3e and valve 3 in branch line 3g are closed and valve 30 in by-pass line 3a is opened. Due to the presence of the restriction 3b in the by-pass line 3a the same quantity of oil will flow throughthe branch lines 3g when the burner is not in service as when the burner is in service. A further advantage resulting from the use of the bypass 3a is that since a flow of oil through the branch lines is maintained when the burner is out of service, the viscous oil frequently used as a fuel will not cool and congeal in the branch lines. For the same reason the by-pass 3a=should be short and located in the block'of the burner so that it will stay hot. Although the output of the burners remaining in service increases, the quantity of oil flowing to the burner tip chambers of the burner or burners which remain in operation will be maintained constant and hence the spray characteristic of the remaining burners and their efficiencies will be the same as before. As the description proceeds it will become apparent that the burner or burners left in service will automatically assume the load normally carried by the burner taken out of service, and the quantity of oil discharged into the combustion space I will also remain constant.

Referring to the lower left-hand corner of Figure 1, there is shown anoil storage tank 8 from which oil to make up the oil discharged from the burner nozzle flows to the circulating system through a pipe 9 under the pressure supplied by a suitable positive displacement pump I 0 in the line 9 between the tank 8 and the pump 5. When the fuel being burned is a heavy residual fuel oil suitable heating means may be provided at various points in the system to maintain the fuel in a desirably fluid condition.

Since oil is a non-compressible fluid and the circulating system is completely filled with oil,

the rate at which oil is discharged into the combustion space I by the burners 3 is precisely equal to the rate of flow of oil in line 9, and in accordance with the'present invention the flow of oil in the line 9 is metered and controlled to control the discharge of the oil from the burners. This metering and control of the oil flow in the line 9 is accomplished by a flow controller, generally indicated at I3, which includes an orifice I4 in the 'line 9. The operating means of the flow controller is a pneumatic pressure which operates a valve I2 in a liquid return line II.

The valve I2 serves as a variable restriction in the line II to vary the flow in the line 9. The flow controller thus acts in response to the pressure difference across the orifice l4 to maintain the flow through the line 9 at a desired value Occasionally it becomes heaters; as it moves to the right the pressure in lines 49 which may be considered as the control point of the flow controller.

This desired value or control point may itself be varied or set up or down by a temperature controller, generally indicated at 29. The temperature controller is responsive to a temperature sensitive element 90 in thefurnace 2 and the operating means of the temperature controller is a pneumatic pressure the value of which determines the setting of the control point or the flow controller I3. Thus, with this system an accurate correlation between the behavior of the temperature of the furnace 2 and the oil burner is obtained.

The orifice meter shown is essentially a U- .tube comprising a high pressure leg I5, a low.

and 50 decreases.. The operation of the valve 48 is such that as the flapper 49 'and nozzle 4| approach one another, pressure tends to build whereas as the flapper 49 and nozzle 4| recede from one another pressure in line 45 tends to decrease, contracting bellows 5| to move plunger 41 to the left, as shown, thus increasing pressure in lines 49 and 59.

Nozzle 4| is positioned by link 59 which is in 7 turn positioned by a compound lever 56 and in pressure leg I6. and a pipe l1 connecting the two. The meter is partially filled with mercury,

the level of the mercury in the high pressure downstream of the orifice l4 through'aline 22.

Suitable se'als (not shown) may be used when necessary to prevent the fuel flowing in the line 9 from entering the. meter piping or chambers.

Floating on the surface |5a of the mercury in high pressure leg I5, there is a float 28 provided the arrangement shown link 59 is positioned through compound lever 59 by either or both of the bellows 59 and 91 acting through

links

55 and 99, respectively. The bellows 53 and 61 are rigidly secured at one end and at their other end move against-the action of springs 54 and 98 to move

links

55 and 99 which are pivotally connected to the compound lever 55 at the lower end 58 and upper end 51 of the lever 55.

The line 59 communicates with the interior of the bellows 53, and if-tl1e pressure in bellows 61 is maintained at a constant value changes in pressure in line 50 will produce corresponding with a vertical mast 29 connected by a chain 39 to an arcuate member 3|. The arcuate member 3| is mounted on a lever arm 32 which is secured to and supported by a rotatable shaft 33 mounted in a suitable bearing 34 located in thewall of the high pressure leg 15. The shaft 33 carries a, lever arm 35 located outside of the high pressure leg IS. The construction is such that if, for example, the difierential across the orifice plate l4 increases, mercury flows from the high pressure leg into the low pressure leg to balance vary the pressure on the valve 2 and so position it in the following manner. At its lower end 'the lever 35 is connected by a link 36 to flapper 40, and thus the flapper is positioned in accordance withthe difierentialpressure across the orifice plate Hi. The position of the flapper is translated into a proportional pneumatic pressure for operating valve l2 by follow-up mechanism that will now be described.

Cooperating with the flapper is a movable nozzle 4|. A portion of the air from a supply line 42 passes through abranch line 43, a restriction 44, and branch line 45 to the nozzle 4| and to a bellows 5| operating a valve plunger 41 of a double-seated valve 49. The'double-seated valve regulates the pressure in a line 49 connected to the control valve l2 and in a line 50 connected with a bellows 53 which forms a part of the follow-up mechanism. The operation of the double-seated valve is such that as the plunger 41 moves to the left, as shown in the drawings, the pressurein lines 49 and 59 increases and changes in the position of the nozzle 4|. Since a static balanced pressure condition would require the plunger 41 to be in some mid-position between its two seats, the follow-up mechanical arrangement will require the nozzle to be sub:- stantially tangent to the flapper, and since the pressure in' lines 49 and 5|) also governs the opensure in the bellows 51 or the position of the pivot 51. If the pressure in bellows 61 is increased the initial operation is to move nozzle 4| clockwise a proportionate amount, thus separating nozzle 4| from flapper 40. This initial operation causes the pressure in lines 49 and 59 and in bellows 53 to increase which will retard or reverse the clockwise movement of nozzle 4| and at the same time increase the flow through the orifice plate M. The increased diiferential pressure across orifice M will rotate flapper 40 in a clockwise direction and a new static pressure and static flow condition will be established such that the increase in flow is proportional to the increase in pressure in bellows 61. If the pressure in bellows 61 is decreased the operation of the parts is reversed and flow in the line 9 is decreased in proportion to the decrease in pressure in bellows B1.

In the present embodiment a pneumatically operated temperature controller is used to reset the control point of the flow controller I3 in the manner described above and hence control the amount of oil sprayed by the burners 3 in response to variations in the temperature of the .furnace 2.

The temperature controller 20 will now be described more in detail.

The temperature sensitive element 60 in the with the value of the measured temperature. The position of the flapper 84 is translated into a pneumatic pressure in the line 6 6 in a manner similar to that described in connection with the flow controller l3.

Cooperating with the flapper 64 there is a variable nozzle 65, A portion of the supply air passes through a .restriction I4 to the nozzle 65 and to a bellows 13 operating the plunger of a double-seated valve 12. The double-seated valve 12 regulates the pressure in line-58 and a bellows 10 which, like bellows 53, operates to maintain the nozzle substantially tangent to the flapper flapper 64 rotates in a clockwise direction, thus increasing the pressure in bellows 13, reducing the pressure in line and in bellows 10 to cause the nozzle to follow the flapper. This reduction in pressure is transmitted through line H to bellows 61 and the resulting initial counterclockwise movement of nozzle 4 increases the pressure in bellows to cause the double-seated valve 46 to decrease the pressure in bellows 53 to hold the nozzle 4| tangent to the flapper 40. The resulting decreasing pressure in line 49 opens valve l2 and decreases the flow through orifice l4 until the change in flow in line 9, and thus in the amount sprayed'by the burners, is proportional to the change in pressure in bellows Bl. The resulting proportionate fuel reduction tends to prevent further increase of the measuredtemperature, and the action continues until a new static temperature, new operating air pressures. and a new flow balance are reached. If the load on the furnace 2 increases so that the present amount of fuel being burned by the burners causes the temperature of the furnace todrop, by similar and opposite reactions the flow of fuel is increased until a new static temperature, new operating air pressures, and a new flow balance are reached.

v Thus, the flow of fuel is positively correlated with the operating means of the temperature controller. It should be understood that the control characteristics of the temperature controller 20 as well as of the flow controller I3 may be changed from that shown in the drawings by adding other instrumentalities to overcome lag complications in the process being controlled.

It is apparent that in order to maintain a uniform spray characteristic with varying quantities of fuel sprayed it is necessary to maintain a uniform flow through the tangential jets of each burner. Since in the system embodying the present invention there are no appreciable restrictions in the return line under any condition of flow in the return line the pressure on the suction of the pump 5 is substantially equal to the static pressure in the burner tip chamber. Therefore, the pressure drop acrossthe by-pass valve 512 is substantially equal to the pressure drop across the tangential jets of the burner. Furthermore, the pressure drop across the tan gential jets and across the by-pass valve 512 is constant for all rates of flow of make-up oil and hence for all burner discharge rates. The reason for this is that the pump 5 is a constant volume pump which is operating on a non-compressible fluid and so the sum of the flows through the by-pass line and the tangential jets is equal to the pump output and is constant. Further, since the pressure drops across the by-pass valve and the tangential jets are always equal, the ratio of the flow through the by-pass line to the how through the tangential jets is constant. Therefore, the rate of flow through the tangential jets is constant and is unaflfected by variations in the rate of flow of make-up oil.

4 Since many embodiments might be made in the above invention, and since many changes might be made in the embodiment above described, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative only and not in a limiting sense.

We claim:

1. The method of regulating the temperature of a furnace fired by an oil burner of the oil recirculating type utilizing mechanical means to atomize the oil burned, which comprises establishing a constant volume flow from a pump to said burner at a rate in excess of the rate at which oil is atomized for burning by said burner, recirculating excess oil not atomized back to said pump in a closed circulating system, supplying make-up oil from a source of oil to said circulating system and controlling the rate of flow of make-up oil to said system at a point intermediate said source and said circulating system and in response to a variable condition influenced by the temperature in said furnace.

2. Method of regulating the temperature of a furnace fired by an oil burner of the oil recirculating type utilizing mechanical means to atomize the oil burned, which comprises pumping oil into said burner at a constant volume rate in excess of the rate at which oil is atomized for burning bysaid burner, recirculating excess oil not atomized back to said pump in a closed circulating system, supplying make-up oil to the low pressure side of said circulating system, metering the flow of said make-up oil and using a variable condition influenced by temperature variations of saidfurnace to vary the metered flow to maintain said temperature at a substantially constant value.

3. Method 'of controlling the oil sprayed by a mechanical atomizing burner of. the oil recirculating type, which comprises establishing a constant volume flow from a pump to the burner, returning an unrestricted flow of excess oil not sprayed back to the pump, supplying make-up oil to said pump, measuring the quantity of the make-up oil thus supplied, and controlling the amount of oil sprayed by-regulating the amount of make-up oil in response to variations in the measured quantity of make-up oil.

4. Method of controlling the burning characteristics of the oil flame of a mechanical atomizing burner of the oil recirculating type, which comprises establishing a constant volume flow of oil to the burner in excess of the quantity of oil burned, recirculating excess oil not burned to establish a closed system, supplying make-up oil to the said system, measuring the rate at which make-up oil is supplied to said system, and controlling the amount of oil burned by controlling the make-up oil supplied in response to variations in the measured rate of flow of make-up oil.

5. Apparatus for controlling at a control point a condition of a furnace fired by an oil burner of the oil recirculating type utilizing mechanical means for atomizing the oil burned, comprising, in combination with said burner, an oil circulating system including a constant volume pump for supplying oil to said burner at a constant volume rate in excess of the rate at which oilis atomized by said burner, and means for recirculating excess oil to said pump, means including a conduit for supplying make-up oil to said system, a flow controller associated with said conduit for controlling the rate of flow of makeup oil supplied through said conduit to said cirof a furnace fired by oil burners utilizing mechanical means to atomize th oil burned and uring the quantity of make up oil supplied, and

culating system, and means for regulating said i flow controller in response to the said condition of said furnace.

6. The method of regulating the temperature of a furnace fired by an oil burner of the oil said burner at a rate in excess of the rate at' which oil is atomized for burning by said burner, recirculating excess oil not atomized back to said pump through an unrestricted passage to form a closed circulating system, supplying make-up oil from a sourceof oil to said circulating system, and controlling the rate at which make-up oil is supplied to said system at a point intermediate said source and said circulating system and in response to a variable condition influenced by the temperature in said furnace.

7. A method for controlling the burner output of a plurality of mechanically atomizing oil burners of the oil recirculating type connected in parallel to the discharge of a pump, each burner being also connected through an unrestricted return line with the intake of the said pump to return excess oil not burned and each burner having a predetermined resistance coeificient to the flow of oil therethrough, comprismg pumping a constant volume of oil. to said burners regardless of the burner output, retur n ing all not burned through said unnrestricted return line, supplying oil to the intake side 01 said pump to make up the oil burned, and insertmgin the return line of a burner taken out of service a restriction having substantially the same flow coeflicient as the burner removed whereby the volume of oil pumped to each burner remaining in service remains the same, and the flame characteristic of the burners remaining in service remains substantially the same.

8. Apparatus for regulating the temperature of a furnace fired by an oil burner otthe oil recirculating type using mechanical means to atomize the oil burned, comprising, in combination, a closed oil circulating system including one or more burners, a constant volume pump provided with a by-pass containing a variable restriction, an oil supply line for supplying oil to said burners from said pump, and an oil recirculating line providing an unrestricted passage for now of oil from said burners to said pump, a source of oil,

means for supplying make-up oil from said source to said system, and means responsive to the temperature or said furnace for controlling at a point intermediate said source of oil and said circulating system the rate at which makeup oil is supplied to control the rate at which oil is atomized by said burner.

9. Apparatus for regulating the temperature means responsive to the temperature of said furnace' and to the measured quantity of make-up oil for controlling the rate at which make up oil is supplied to control the rate at which oil is atomized by said burners.

10. In apparatus for controlling the quantity of oil burned by oil burners utilizing mechanical means to atomize the oil burned and wherein for efllcient atomization oil is supplied to said burnrs at a constant volume rate in excess of the rate at which oil is atomized by said burners, in combination, a, supply line and means for supplying oil to said line at a constant volume rate, a plurality or burners connected in parallel to said line and each provided with a plurality of tangential jets providing restriction to flow of oil therethrough, and means for cutting out one of said burners from service without changing the total restriction to oil flow through the system,

' said means including an oil by-pass -line around each of said burners containing a predetermined fixed restriction having the same flow capacity as the tangential Jets of said burner to permit continual flow past said out out burner through a fluid path having the same flow resistance as the jets of said burner, whereby the volume rate of oil now to each of the remaining burners remains unchanged.

11. In apparatus. for controlling the quantity.

of oil burned by oil burners utilizing mechanical means to atomize the oil burned and wherein for efllcient atomization oil is supplied to said burners at a constant volume rate in excess of the rate at which oil is atomized by said burners, in combination, a closed oil circulating system in-.-

cluding a constant volume pump for circulating oil in said system, an oil supply line for supplying oil to said burners, a plurality of burners cutting out one of said burners from service including an oil by-pass line around each of said burners containing a predetermined fixed restriction having the same flow capacity as the tangential jets oi said burner to permit continual flow past said out out burner throughv a fluid path having the same flow resistance characteristics as the jets of said burner, whereby the volume rate of oil flow to each or the remaining burners remains unchanged.

CLESSON E. MASON.

, RALPH A. ROCKWELL.