US3248854A - Apparatus and method for prevention of secondary combustion - Google Patents

Description

May 3, 1966 3,248,854

R. J. PLASS APPARATUS AND METHOD FOR PREVENTION OF SECONDARY COMBUSTION Filed NOV. 14, 1962 FIG. I.

}TO PRECIPITATOR 1 I 3Q] f-32 INVENTOR. Y fir- ROBERT J. PLASS T0 T0 ELECTRICAL MM SUPPLY SUPPLY ATTORNEY United States Patent 3,248,854 APPARATUS AND METHOD FOR PREVENTION OF SECONDARY COMBUSTION Robert J. Plass, Studio City, Calif., assignor to Joy Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 14, 1962, Ser. No. 237,581

9 Claims. (Cl. 554) This invention relates to the prevention of secondary combustion and more particularly to the prevention of secondary combustion in an electrical precipitator attached to a material processor such as a direct heated cemented kiln, to remove finely divided solids from a stream of gases exiting from the kiln.

Operation of a direct heated material processor such as a cement kiln is characterized by combustion of a mixture of fuel and air introduced into one end of the processor and conducted therethrough so that products of combustion issuing from the other end of the processor can be conducted into an electrical precipitator Where particulate matter entrained in the stream of gases issuing from the material processor is removed by the action of the electrical precipitator as is known. It sometimes happens that combustion within the material processor is interrupted by circumstances which produce an excess of fuel over that required for complete combustion within the processor. When combustion has thus been interrupted, unburned fuel can pass through the processor and connecting equipment, where additional air through inleakage is introduced, and into the electrical precipitator possibly forming therein a combustible mixture which can be ignited by electrical discharges common to such electrical precipitators with a resulting dangerous and sometimes damaging explosion which is the secondary combustion which the apparatus and method of this invention is designed to prevent. Those concerned with the application of electrical precipitators to direct fired material processors have long recognized the need for a method of preventing the secondary combustion hereinabove described. The present invention fulfills this need.

Earlier attempts at prevention of such secondary combustion employed devices sensitive to the presence of products of combustion such as carbon monoxide or of uncombined oxygen in the gases exiting from the processor to control the action of the electrical precipitator and thus prevent the secondary combustion. These attempts were uniformly unsuccessful because the reaction time of the detection devices was much greater than the time necessary for the gases to pass from the exit portion of the processor to the precipitator. The present invention contemplates the use of pressure sensitive devices at the end of the processor Where the fuel and air are admitted to form the combustible mixture.

Variation of the fuel or air pressures outside of certain preselected limits would indicate that a combustible mixture could be forming in the processor prior to passing to the precipitator. Such indication is used to turn otf the precipitator before the unburned mixture passing through the processor can reach the precipitator.

It is therefore an object of this invention to provide a new and novel method for prevention of secondary combustion in an electrical precipitator.

It is another object of this invention to provide a new and improved apparatus for the prevention of secondary combustion in an electrical precipitator.

A further object of this invention is the provision of a new and improved method and apparatus for the prevention of secondary combustion in an electrical precipitator cleaning the gases exiting from a direct fired ma- 3,24sas4 Patented May 3, 1966 "Ice terial processor, which apparatus and method comprise the application of pressure sensitive devices to pipes supplying fuel and air,.respectively, at a point where the fuel and air enter the material processor to form a combustible mixture therein; such sensing devices being responsive to variations in the supply pressure of the air and fuel to shut off the electrical precipitator when such pressures vary beyond preselected limits.

It is a specific object of this invention to provide a new and novel method for'the prevention of secondary combustion in an electrical precipitator cleaning gases exiting from one end of a material processor in which combustion is being maintained by continuously supplying fuel and air to the other end of such processor consistting of the steps; supplying fuel and air to said other end of such material processor under relative pressures necessary to provide a combustible mixture; sensing a variation in either of such pressures likely to interrupt the combustion and allow unburned fuel to exit from the first end of such processor and entering the electrical precipitator making possible a secondary combustion therein; applying the sensed variation in pressure to an electrical control of the electrical precipitator to turn off the precipitator and prevent secondary combustion in the precipitator being initiated by electrical discharges.

These and other objects and advantages of the present invention will become more apparent upon consideration of the following description and drawings in which:

FIG. 1 is a side elevational view of a direct fired material processor and an electrical precipitator constructed according to the principles of this invention;

FIG. 2 is an enlarged sectional view taken substantially on the line 22 of FIG. 1 looking in the direction indicated by the arrows;

FIG. 3 is a schematic representation of the electrical connections necessary to apply the principles of this invention. I

In FIG. 1 there is shown a direct fired material processor such as a cement kiln generally indicated at 6 comprising a feed end housing rotatably supporting a rotating cylindrical portion 8 sloping slightly downwardly from the feed end housing 7 to a discharge end housing 9 so that material to be processed such as crushed rock fed in at the housing 7 progresses downwardly through the rotating cylinder portion 8 and is discharged at the discharge end of housing 9 after having been suitably heated during its passage through the cylinder portion 8 in a manner well known in the art.

For direct heating of the material being processed, the discharge end housing 9 is provided with a burner mechanism generally indicated at 11 and hereinafter more fully described which provides fuel and air for a combustion desirably taking place within the cylinder 8 to heat the crushed rock therein. The flame and products of combustion from the burner 11 progress upwardlythrough the cylinder portion 8 and the feed end housing 7 exiting therefrom through a conduit 12 and auxiliary devices generally indicated at 13, such as waste heat boilers, proceed through a communicating conduit 14 into an electrical precipitator 15 in which rock dust or other solid particulate matter is removed from the stream of gases in a manner well known in the art. The stream of gases having been cleansed of entrained solid particles exits through an exhaust system (not shown) as is known.

The bumer mechanism 11 (see FIG. 2) comprises a fuel supply pipe 17 provided with a restricted end portion or nozzle 18, coaxial with and surrounded by an air supply pipe 19 with a nozzle portion 20, both nozzles being directed inwardly with respect to the discharge end housing 9 and the cylinder portion 8 and are so arranged and located that fuel entering through the pipe 17 and the nozzle 18 will be mixed with the air entering through the pipe 19 and the nozzle 20 to form a combustible mixture in which combustion is initiated by suitable means (not shown) to furnish a flame for the direct heating of the cylinder 8 and the material to be processed. As is known such flame will be continuously furnished during normal operation of the cement kiln 6.

In the present embodiment the burner mechanism 11 is provided with an annular secondary air supply duct 22 coaxial with and surrounding'the air supply pipe 19 hereinafter designated the primary air supply. The secondary air supply duct 22 communicates with a conduit 23 connected with a source of heated air such as the clinker cooler of a cement processing plant for the purpose of salvaging some of the heat which was supplied to a material being processed. Such secondary air supply is not essential to the operation either of the cement kiln 6 or of this invention but is included as a point of future reference.

Communicating with the primary air supply pipe 19 is a pressure pipe 25 which internally communicates with a pressure sensitive device 26 hereinafter more fully described. In like manner a pressure pipe 28 communicates 1 with the fuel pipe 17 and extending outwardly, transversely through the air supply pipe 19 communicates internally with a second pressure sensitive device 29.

In FIG. 3 a pressure sensitive device 26 is shown schematically as an electric switch which is closed as long as a preselected pressure difierence exists between 'a fluid pressure in the pipe 25 and the ambient air but will open and interrupt the flow of electric current therethrough whenever the pressure difference departs from that preselected one by a predetermined amount. Desired primary air pressure varies rather widely from one application to another especially in relation to the size of the apparatus and the design of the nozzle but typical values would be of the order of 3 of mercury for the desired air pressure with an allowable variation in this burner of 1" of mercury either plus or minus so that the sensitive device 26 would be set to maintain its closed position for any pressure between two and four inches of mercury and to open whenever the pressure Was greater than four inches or less than two inches. The pressure sensitive device 29 is entirely similar to the device 26 except that it is adjustable for a different range of pressures desirable for fuel delivery. In the case of a gaseous fuel being used the pressures would be of the order of 8 p.s.i. with an allowable variation of perhaps 2 p.s.i. plus or minus so that the device 29 would be closed during the application of a pressure difference in the range from 6 to p.s.i. relative to the ambient pressure and would open whenever the pressure fell below 6 p.s.i. or exceeded 10 p.s.i.

It is to be appreciated that the above pressures are used only for purposes of illustration and are not limitative upon the invention since, for instance, oil firing pressures would be much greater, anywhere from 150 to 400 p.s.i while coal firing pressures would be somewhat less probably blow 3 p.s.i.

Referring again to FIG. 3 there is shown a pair of electrical conductors 31 and 32, respectively, communicating with a device (not shown) furnishing primary alternating current electric power for the operation of the electric precipitator and communicating therewith through a precipitator power pack (not shown) of a type well known in the art. This power pack comprises a step-up transformer and a high voltage rectifier providing a high voltage unidirectional operating potential for the charging and collecting electrodes of the electrical percipitator 15. The operating potential must be high enough to provide a corona current at the charging electrodes and as a result some sparking normally occurs within the precipitator. The conductor 32 is connected directly to the power pack while the conductor 31 leads to a normally open relay 33 I having contacts 34 and 35, biased toward an open posi- 2. tion by an extension spring 36, which relay 33 when closed provides communication between the conductor 31 and a further electrical conductor 38 communicating with the other side of the precipitator power pack so that when the contacts 34 and 35 are closed there is a continuous path for the alternating current from the conductor 31'through the relay 33 and the conductor 33, through the power pack and the conductor 32, back to the device furnishing alternating current power.

It is to be realized that reduction of the electrical potential applied to the precipitator 15 to a value less than the potential at which sparking occurs will accomplish the purposes of this invention. If such reduction in potential is desired conductors 31 and 32 can be used to furnish only part of the electric power for the precipitator 15 and other conductors (not shown) used to provide the remainder of the power.

In FIG. 3 there is also shown an auxiliary circuit comprising a pair of electrical conductors 40 and 41 respectively provided with electric current by another electrical device (not shown) which furnishes electric power. The conductor 40 communicates with the device 29 and therethrough when closed with another conductor 42, the conductor 42 communicates between the devices 2% and 26 and through the device 26 with a conductor 43, electrically connected to a solenoid coil 44 within the relay 33. The coil 44 is connected to the conductor 41 so that when the pressure sensitive devices 26 and 29 are in their closed positions the flow of electrical current follows the path from the conductor 41 through the device 29, through the conductor 42 and the device 26, through the conductor 43 and the solenoid coil 44 back to the conductor 41 c011- nected with the second side of the power supply.

From the diagram of FIG. 3 it is obvious that when the devices 26 and 29 are in their closed position the solenoid 44 of the relay 33 will apply magnetic fonce to overcome the biasing of the spring 36 so that the contacts 34 and 35 are closed and power is furnished to the electrical precipitator. It is further obvious that any deviations of the pressures within the pipes 25 and 28, respectively, will cause either the device 26 or the device 29 to open with the result that the current flow through the solenoid 44 will be interrupted allowing the spring 36 to open the contacts 34 and 35 and interrupt or reduce the flow of power to the precipitator 15.

It is to be noted that the devices 26 and 29 are of a latch open type which, once the contacts have been opened by lack of the preselected pressure diiference, will remain in the open position even though a pressure difference of the desired amount is re-established, until the device, 26 or 29, is reset in the closed position.

Operation of the apparatus of this invention is begun by starting rotation of the cylinder portion 8 of the cement kiln 6, providing air at a pressure within the above indicated desired range through the pipe 19 and the nozzle 20, providing fuel, for example natural gas, through the fuel pipe 17 and the nozzle 18 so that a combustible mixture is formed within the rotating cylinder 8. This combustible mixture is lighted in the usual manner and aflame forms extending within the cylinder 8 and turning into a stream of hot gaseous combustion products traveling through the cylinder portion 8 to the feed end housing 7. As this stream of gases passes through the cylinder portion 8 it picks up finely divided solid partioulate matter from the material being processed and,

carrying this particulate matter through the end housing '7, the conduit 12, the waste heat boilers 13, the conduit 14 and the electrical precipitator 15, exhausts to the atmosphere as hereinbefore mentioned. As soon as the flame has been well established manual closing of the devices 26 and 29 establishes the electrical circuittherethrough which closes the relay 33 as hereinbefore described so that the electrical precipitator is energized to remove the particulate matter from the stream of gases in a manner well known in the art. As long as normal operation, as above described, continues the secondary combustion preventive apparatus of this invention remains inoperative.

With the material processor 6 operating as described a small change in the pressure within the fuel pipe 17 or the air supply pipe 19 is Without significance. However, should the air pressure, for instance, drop to an undesirably low value unburned fuel would be carried through the cylinder 8 and the communicating parts into the electrical precipitator 15 where such unburned fuel mixed with an adequate volume of infiltrated air admitted in connecting equipment 12, 13 and 14 prior to the precipitator could form an explosive mixture which would be ignited by electrical discharges common to such precipitators. Such damaging explosions are relatively common in apparatus of the prior art but in the case of the apparatus of this invention the lowering of pressure in the air supply pipe 19 results in a lowered pressure in the pressure pipe 25 with a resultant opening of the electrical contacts in the device 26 which as hereinbefore described results in shutting off or reducing the power in the electrical precipitator. A latching mechanism (not shown) in the device 26 holds the contacts in the open position after the undesirable pressure drop in the fuel supply pipe 19 has been corrected. After such correction has been accomplished and the pressure difference within the device 26 has been re-established the contacts of the device 26 having been manually unlatched return to the closed position which acting through the solenoid 44 closes the relay 33 and re-establishes the alternating current circuit through the precipitator power pack putting the precipitator into operation again. In like manner a pressure in the air supply pipe 19 too high for proper operation will turn off the precipitator and keep it turned ofl until the correct pressure is re-established within the pipe 19 and the device 26 has been reset.

In an entirely similar manner excessive pressure in the,

fuel pipe 17 can result in incomplete combustion within the cylinder member 18 with the attendant danger of damaging secondary combustion in the electrical precipitator 15. The danger of such secondary combustion is removed by operation of the pressure sensitive device 29, under the excessive pressure difference, into its open position. In like manner the device 29 will remain in open position after the desired pressure difference has been re-established until it is manually operated into the closed position causing the relay 33 to close and returning the precipitator to operation. An undesirable drop in pressure in the fuel pipe 17 acts in the same manner to interrupt precipitator operation until optimum conditions have been re-established.

Under certain conditions of operation and with certain types of apparatus the pressure of the secondary air in the air supply duct 22 becomes a determining factor with regard to proper combustion, under such conditions it is desirable to install a pressure sensing device such as the device 26 in communication with the duct 22 to operate in a manner entirely analogous to that described for the operation of the sensing device 26 hereinabove.

Two advantages of this invention reside in the positioning of the sensing devices at the material delivery end of the cement kiln 6 namely; after the sensing devices 26 or 29 sense an undesirable change in pressure there is a relatively long period of time, of the order of several seconds, during which the precipitator can be de-energized by action of the devices 26 or 29 before the possibly combustible mixture caused by the pressure change can reach the electrical precipitator 15 so that, even though a residual charge could remain upon the elements of the electrical precipitator for a fraction ofa second after shut-off, the combustible mixture susceptible of secondary combustion would not reach the precipitator 15 during this period of time. The second such advantage resides in the fact that the sensing devices 26 and 29 and their communicating tubes are situated in a cool portion of the apparatus and not subject to the action of flame or hot gases as they would be were they situated in a downstream portion of the apparatus, relative to the stream of hot gases, such as the feed end housing 7.

A third advantage over the prior art is the very short reaction time of pressure sensing devices as compared with gas composition detection devices. This coupled with relatively long delay before action is required makes the system operable and novel.

A preferred. embodiment of this invention having herein been described and illustrated it is to be realized that modifications therein may be made without departing from the broad spirit and scope of this invention. It is therefore respectfully requested that this invention be interpreted as broadly as possible and be limited only by the prior art.

What I claim is:

1. In an electrical precipitator receiving a stream of gases from a material processor, which processor is supplied with fluid streams of fuel and air for combustion therein, such stream of gases including the products of combustion from said processor which occasionally include various amounts of unburned fuel, which unburned fuel is capable of forming a combustible mixture with air within said precipitator, the method of preventing combustion in said electrical precipitator comprising the steps of: sensing a deviation in at least one of the respective fluid pressures in said streams of fuel and air entering said material processor from a predetermined range of pressures; reducing the electrical potential of said precipitator from an operating potential at which sparking occurs to prevent sparking within said precipitator during the time of said deviation from said range of pressures and; increasing said electrical potential to said operating potential after said entering pressures have returned to said predetermined range of pressures.

2. The method of preventing combustion in an electrical precipitator receiving a stream of gases from a material processor, said processor being supplied with fluid streams of fuel and air for combustion therein, said stream of gases including the products of combustion from said processor which occasionally include various amounts of unburned fuel, said unburned fuel being capable of forming a combustible mixture with air within said precipitator, comprising the steps of: sensing a deviation in at least one of the respective fluid pressures in said streams of fuel and air, entering said material processor, from a predetermined range of pressures; reducing the electrical potential of said precipitator, from an operating potential at which sparking occurs, to prevent sparking within said precipitator during the time of said deviation from said range of pressures and; increasing the electrical potential to said operating potential after said entering pressures have returned to said predetermined range of pressures.

3. The method of preventing combustion in an electrical precipitator receiving a stream of gases from a material processor, said processor being supplied with fluid streams of fuel and air for combustion therein, said stream of gases including the products of combustion from said processor which occasionally include various amounts of unburned fuel, said unburned fuel being capable of forming a combustible mixture with air within said precipitator, comprising the steps of: sensing a deviation in both of the respective fluid pressures in said said entering pressures have returned to said predetermined range of pressures.

4. The method of preventing combustion in an electrical precipitator receiving a stream of gases from a material processor, said processor being supplied with fluid streams of fuel and air for combustion therein, said stream of gases including the products of combustion from said processor which occasionally include various amounts of unburned fuel, said unburned fuel being capable of forming a combustible mixture with air within said precipitator, comprising the steps of: sensing a deviation in at least one of the respective fluid pressures in said streams of fuel and air, entering said material processor, from a predetermined range of pressures: de-energizing said electrical precipitator during the time of said deviation; and re-energizing said electrical precipitator after said entering pressures have returned to said predetermined range of pressures.

5. The method of preventing combustion in an electrical precipitator receiving a stream of gases from a material processor, said processor being supplied with fluid streams of fuel and air for combustion therein, said stream of gases including the products of combustion from said processor which occasionally include various amounts of unburned fuel, said unburned fuel being capable of forming a combustible mixture with air within said precipitator, comprising the steps of: sensing a deviation in .at least one of the respective fluid pressures in said streams of fuel and air, entering said material processor, from a predetermined range of pressures; reducing the electrical potential of said precipitator, from an operating potential at which sparking occurs to a potential below the minimum potential at which sparking'can occur, to prevent sparking within said precipitator during the time of said deviation from said range of pressures and; increasing the electrical potential to said operating potential after said entering pressures have returned to said predetermined range of pressures.

6. The method of preventing secondary combustion in an electrical precipitator collecting finely divided solid particles entrained in a stream of gases received from a material processor, said processor being supplied withfluid streams of fuel and air for primary combustion therein, which stream of gases includes the products of combustion from said processor and occasionally includes various amounts of unburned fuel, said unburned fuel being capable of forming a combustible mixture with air within said precipitator, said electrical precipitator being energized to an electrical operating potential sufficiently high to collect said finely divided solid particles, and at which potential sparking occurs between the electrodes of said electrical precipitator, which sparking is suflicient to initiate a secondary combustion within said electrical precipitator, comprising the steps of: sensing a deviation in at least one of the respective fluid pressures in said streams of fuel and air, entering said material processor, from a predetermined range of pressures; reducing the electrical potential of said precipitator to prevent sparking Within said precipitator during the time of said deviation from said range of pressures and; increasing said electrical potential to said operating potential after said entering pressures have returned to said predetermined range of pressures.

7. The method of preventing secondary combustion in an electrical precipitator collecting finely divided solid particles entrained in a stream of gases received from a material processor, said processor being supplied with fluid streams of fuel and air for primary combustion therein, which stream of gases includes the products of combustion from said processor and occasionally includes various amounts of unburned fuel, said unburned fuel being capable of forming a combustible mixture with air Within said precipitator, said electrical precipitator being energized to an electrical operating potential sufiiciently high to collect said finely divided solid particles, and at which potential sparking occurs between the electrodes of said electrical precipitator, which sparking is suflicient to initiate a secondary combustion within said electrical precipitator, comprising the steps of: sensing fluid pressures in said streams of fuel and air, entering said material processor; sensing a departure of at least one of said fluid pressures from a predetermined range of pressures; reducing the electrical potential of said precipitator below said operating potential to prevent sparking within said precipitator during the time of said deviation from said range of pressures and; increasing said electrical potential to said operating potential after said entering pressures have returned to said predetermined range of pressures.

8. In an electrical precipitator receiving a stream of gases from a material processor, which processor is supplied with fluid streams of fuel and air for combustion therein, which stream of gases includes the products of combustion from such processor and occasionally includes various amounts of unburned fuel, which unburned fuel is capable of forming a combustible mixture with air within said precipitator, apparatus for preventing combustion in said electrical precipitator comprising: an electrically energized electrical controlcircuit electrically connected to said electrical precipitator to vary the electrical potential of said electrical precipitator; fluid pressure responsive sensing means communicating with such fluid streams of fuel and air to sense deviations in the fluid pressures of at least one of such fluid streams, respectively; said sensing means electrically connected in said electrical circuit; and said sensing means acting through said electrical circuit to reduce said electrical potential of said electrical precipitator to prevent sparking within said electrical precipitator during the time of such deviation from said predetermined range of pressures.

9. In the combination of a material processor and an electrical precipitator wherein fluid fuel and air under inlet pressures are fed to said material processor for com-- bustion therein and wherein said precipitator receives the products of combustion from said processor the improve ment comprising: an electrical circuit for providing electric current to said precipitator at an operating potential; normally non-operative potential reducing means in said circuit; pressure sensing means responsive to the deviation of at least one of said inlet pressures from a predetermined range of pressures to actuate said potential reducing means to reduce said electrical potential below said operating potential.

References Cited by the Examiner UNITED STATES PATENTS 1,947,447 2/1934 Brassert et al. 55106 X 2,050,367 8/1936 Mydre 55-l05 2,704,134 3/1955 White 554 2,783,420 2/1957 Thompson et al. 317-246 2,867,285 1/1959 Wintermute 55--l06 2,896,138 7/1959 Grinstead 317-246 2,911,061 11/1959 Peterson et al 55-106 X 3,039,252 6/1962 Guldemond et al. 55105 FOREIGN PATENTS I 377,343 6/ 1923 Germany.

HARRY B. THORNTON, Primary Examiner.

ROBERT F. BURNETT, Examiner.

D. E. TALBERT, JR., Assistant Examiner.

Claims (1)

1. IN AN ELECTRICAL PRECIPITATOR RECEIVING A STREAM OF GASES FROM A MATERIAL PROCESSOR, WHICH PROCESSOR IS SUPPLIED WITH FLUID STREAMS OF FUEL AND AIR FOR COMBUSTION THEREIN, SUCH STREAM OF GASES INCLUDING THE PRODUCTS OF COMBUSTION FROM SAID PROCESSOR WHICH OCCASIONALLY INCLUDE VARIOUS AMOUNTS OF UNBURNED FUEL, WHICH UNBURNED FUEL IS CAPABLE OF FORMING A COMBUSTIBLE MIXTURE WITH AIR WITHIN SAID PRECIPITATOR, THE METHOD OF PREVENTING COMBUSTION IN SAID ELECTRICAL PRECIPITATOR COMPRISING THE STEPS OF: SENSING A DEVIATION IN AT LEAST ONE OF THE RESPECTIVE FLUID PRESSURES IN SAID STREAMS OF FUEL AND AIR ENTERING AND MATERIAL PROCESSOR FROM A PREDETERMINED RANGE OF PRESSURES; REDUCING THE ELECTRICAL POTENTIAL SAID PRECIPITATOR FROM AN OPERATING POTENTIAL AT WHICH SPARKING OCCURS TO PREVENT SPARKLING WITHIN SAID PRECIPITATOR DURING THE TIME OF SAID DEVIATION FROM SAID RANGE OF PRESSURES AND; INCREASING SAID ELECTRICAL POTENTIAL TO SAID OPERATING POTENTIAL AFTER SAID ENTERING PRESSURES HAVE RETURNED TO SAID PREDETERMINED RANGE OF PRESSURES.

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