US3049168A

US3049168A - Method and means for controlling a combustion apparatus operated by at least two different fuels

Info

Publication number: US3049168A
Application number: US767437A
Authority: US
Inventors: Litwinoff Richard
Original assignee: Sulzer AG
Current assignee: Sulzer AG
Priority date: 1957-10-25
Filing date: 1958-10-15
Publication date: 1962-08-14
Anticipated expiration: 1979-08-14

Description

Aug. 14, 1962 R. LlTWlNOFF 3,049,168

METHOD AND MEANS ,FOR CONTROLLING A COMBUSTION APPARATUS OPERATED BY AT LEAST TWO DIFFERENT FUELS Filed Oct. 15, 1958 3 Sheets-Sheet 1 II "B kg 7 v INVENTOR.

El C'HA ED L 1 T'W/NOFI'T ATTOR/VEK Aug. 14, 1962 R. LITWINOFF' METHOD AND MEANS FOR CONTROLLING A COMBUSTION APPARATUS OPERATED BY AT LEAST TWO DIFFERENT FUELS Filed Oct. 15, 1958 OPE N 3 Sheets-Sheet 2 GAS OPEN

CLOSED OPEN OPEN o s/v OPEN CLOSED I CLOSED cLassa I CLOSED GROUP I GROUP.

INVENTOR.

ATTORNEYS.

Aug. 14, 1962 R. LITWINOFF METHOD AND MEANS FOR CONTROLLING A COMBUSTION Filed Oct. 15, 1958 APPARATUS OPERATED BY AT LEAST TWO DIFFERENT FUELS 3 Sheets-Sheet 3 1P1 chm/P0 LITW/NOFE' ATTORNEY 3,049,168 METHOD AND MEANS FOR CONTROLLING A COMBUSTION APPARATUS OPERATED BY AT LEAST TWO DIFFERENT FUELS Richard Litwinoff, Winterthur, Switzerland, assignor to Snlzer Freres, S.A., Winterthur, Switzerland, a corporation of Switzerland Filed Oct. 15, 1958, Ser. No. 767,437 Claims priority, application Switzerland Oct. 25, 1957 8 Claims. (Cl. 158-11) The present invention relates to a method for controlling a combustion apparatus which is fired by at least two different fuels at a plurality of localities, an individual burner for each fuel being provided at each locality whereby the total output of the apparatus can be produced either by one fuel alone or by at least two different fuels.

The invention also relates to a combustion apparatus capable of being heated by at least two different kinds of fuel, the apparatus comprising a plurality of combustion devices of which each is provided with a plurality of burners whose number corresponds to the number of difierent fuels used for operating the combustion apparatus.

in the present specification different fuels are such fuels Whose chemical and physical qualities are so different that a different type of burner and, in most cases, a different fuel conveying system is required for each fuel.

In the present specification gases, liquid, and solid fuels are considered different fuels; also a gas having a relatively high heating value, for example, methane gas is considered a fuel which is different from a gas having a relatively low heating value, for example, blast-furnace gas. Similarly, pulverized anthracite coal is a fuel different from pulverized lignite. However, crude oil and fractions of tar distillation, if they can be burned with a substantially equal volume of air and if they produce approximately the same amounts of heat, are not considered different fuels in the present specification.

In combustion apparatuses which must produce a desired output either with one kind of fuel alone or simultaneously with several different fuels and having a plurality of localities where fuel burners are located, each locality is usually provided with a different burner for each of the fuels to be fired. In the conventional operating method all burners are simultaneously supplied with the respective different-fuels through common distributing conduits or conveyors for each fuel whereby the desired amounts of fuels are adjusted for the individual distributing conduits and/ or conveyors. If, for example, 80 parts of a fuel A and 20 parts of a fuel B are supplied, all burners for the fuel A are adjusted to operate at 80% of their maximum output and all burners for the fuel B are adjusted for 20% of the maximum output. With this conventional method difiiculties with respect to combustion and control accuracy are experienced with the burners for the fuel B because the load thereon is relatively small. These difliculties are considerably increased, if the total output of the combustion apparatus is reduced, for example, to 50% of the maximum output. In this case an individual burner for the fuel B would operate only at 10% of its maximum output. In addition to the above-mentioned difiiculties it is difiicult to obtain equal fuel distribution to the burners which are arranged in parallel with respect to the fuel supply. Although the resistance of the individual burners to fuel flow is substantially the same a much greater portion of the fuel goes to those burners whose resistance is somewhat smaller so that relatively more heat is produced by some of the burners than by other burners Whose resistance to fuel flow is somewhat greater. This entails ununi-form heating, for example, of the interior walls of a combustion chamber served by the combustion apparatus.

In order to avoid the aforedescribed difficulties the invention proposes that in each locality Where burners for different fuels are grouped only some of the burners are operated whereby the burners are so designed and so supplied with fuel and combustion air that the heat output of the burners multiplied by the number of localities is equal to the desired output of the combustion apparatus and that the number of burners operated for each kind of fuel is adjusted according to the desired ratio between the different fuels whereby the total output of the plant is adjusted by simultaneously proportionally changing the heat output of all burners which are in operation.

The method is simplified, if in each locality only the burner for one kind of fuel is operated.

It is of advantage to connect all burners for the same kind of fuel to a common fuel supply system for this kind of fuel whereby the fuel supply in the system is so regulated that the heat production of each operating burner is proportional to the desired total heat output of the plant and independent of the number of burners which are operated with the same kind of fuel.

The control mentioned in the paragraph next above can be improved by controlling the supply of fuel to the respective fuel supply system according to a value or characteristic which determines the heat output of an individual burner.

An operating characteristic of a burner is, for example, its fuel consumption or, in the case of liquid or gaseous fuels, the difference between the fuel pressure at the burner inlet and the pressure in the combustion chamber. The fuel supply may be so controlled that this pressure difference is adjusted, independently of the number of burners for the same fuel kind which are in operation, according to the total heat output of the combustion apparatus and is maintained constant when the total heat output of the apparatus is constant.

The fuel supply to a burner may be controlled so that the fuel consumption of the burner is proportional to the desired total output of the apparatus or plant. This fuel consumption is maintained constant at constant total output of the apparatus, notwithstanding the number of burners which are in operation for the same kind of fuel.

In plants in which individual burners are provided with return or recirculating conduits for the fuel whereby the recirculating conduits of all burners firing the same kind of fuel terminate in the same recirculating system, the individual heat production of a burner may be regulated by controlling the difference between the pressure in the fuel supply system for the burners firing the same kind of fuel and the pressure in the fuel return or fuel recirculating system of these burners, the regulation being performed proportional to the total heat output of the plant whereby the pressure difference is maintained constant when the total output of the plant is constant, independently of the number of burners which are in operation for each kind of fuel.

A combustion apparatus in which the method according to the invention may be performed when simultaneously burning, at a plurality of localities, different kinds of fuel which require substantially the same amount of combustion air for producing substantially the same amount of heat is characterized by'the provision, at each combustion locality, of a burner for one kind of fuel and at least one different burner for a different kind of fuel and of an air supply system which is common to the burners at the same locality.

A plant according to the invention is particularly suitable and easy to supervise, if the individual burners at the same locality are so designed in relation to their common combustion air supply means that, at constant total output of the plant, the burner for one kind of fuel produces the same heat as the burner for a different kind of fuel.

In combustion plants having one burner for each kind of fuel in each locality whereby all burners for the same kind of fuel are supplied by the same fuel supply system, control means for the fuel supply systems may be provided for controlling the heat output of the burners connected to the same system and in operation proportionally to the total heat output demanded from the plant, independently of the number of burners which are in operation for the same fuel, the control means for the supply systems for different kinds of fuel being operatively interrelated for efiecting the same heat output of the burners firing different kinds of fuel and simultaneously operated and maintaining this heat output constant at constant total heat output of the plant.

Since in the method and apparatus according to the invention the number of burners which are in operation and firing the same kind of fuel defines the ratio. of the amounts of different fuels fired, only even numbered ratios can be produced. For example, in a plant having 16 burners for each kind of fuel a maximum of 15 parts of a fuel A can be fired simultaneously with 1 part of a fuel B. Other possible ratios are: 14:2, 13:3, 12:4, etc.

Should the aforementioned ratios not suflice, at least two groups of localities where fuel is fired may be provided whereby the size of the burners and the air supply means for each kind of fuel are alike in each locality and the burners and air supply means of the localities of the same group are so arranged that at each locality of one group a greater amount of heat is produced than at each locality of another group, at constant output of the plant.

The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, and additional objects and advantages thereof will best be understood from the following description of embodiments thereof when read in connection with the accompanying drawing in which:

FIG. 1 is a diagrammatic illustration of a combustion apparatus for firing two different kinds of fuel.

FIG. 2 is a part sectional diagrammatic illustration of valves forming part of the apparatus shown in FIG. 1 and of an operating mechanism therefor.

FIG. 3 is a diagrammatic illustration of a remote control for valves forming part of the apparatus shown in FIG. 1.

FIG. 4 is a diagrammatic illustration of a combustion apparatus according to the invention and having recirculatingburners.

FIG. 5 is a diagrammatic illustration of a combustion apparatus having three groups of combustion devices and in which the heat outputs of the combustion devices of each group are the same and the heat outputs of the devices of different groups are different.

The apparatus diagrammatically illustrated in FIG. 1 is operated by two different kinds of fuel, one fuel being an oil and the other being natural gas, for example, methane gas. Nine uniformly constructed combustion devices 2 are provided in a combustion chamber 1, each device 2 comprising a gas burner 3 and an oil burner 4. Each device 2 is provided with a common air supply means 5 for supplying the combustion air required by the two burners 3' and 4.

The oil burners 4 of all nine combustion devices 2 are connected to a common fuel supply system which includes a fuel oil stop valve 6 for each oil burner, three oil pipes 7 whereby each oil pipe is connected for oil flow to the valves 6 of three combustion devices, a manifold 8 to which the three oil pipes 7 are connected, an oil pump 9 pumping fuel oil from a reservoir 10 into the manifold 8, a recirculating pipe 8 connecting the manifold 8 with the reservoir 10, a valve 36 interposed in the pipe 8 for controlling the pressure of the fuel oil in the manifold 8, an actuating means 11 connected to the pressure control valve 36 for operating the latter and a fuel oil quantity measuring means 12 connected with the actuating means 11 and including, for example, an orifice plate 13 which is interposed in one of the pipes 7 for controlling the fuel oil pressure control valve 36 according to the flow of the fuel oil through one of the pipes 7.

The methane gas burners 3 of all fuel burning devices 2 are connected to a common gas supply system which comprises a gas stop valve 14 for each gas burner, three gas pipes 15, a manifold 16 to which the three gas pipes 15 are connected, a gas compressor 17 pumping gas into the manifold 16, a throttle valve 18 interposed in the gas fiow between the compressor 17 and the manifold 16, an actuating means '37 connected with the valve 18 for actuating the latter, and means 19 connected with the means 37 for controlling the latter according to the difference between the pressure 20 of the gas entering the gas burners and the pressure 20 in the combustion chamber.

A common air supply system is provided for all combustion devices 2, the system comprising a stop valve 21 for each combustion device, three air supply ducts 22, each supplying three combustion devices 2, one of the ducts 22 including a manifold portion 23 to which the other two ducts 22 are connected, a blower 24 supplying combustion air to the air supply system, a throttle valve 25 placed in the inlet of the blower 24, actuating means 26 connected to for operating the throttle valve 25, and measuring means 27 measuring the difference between the pressure 28 in the air supply system and the pressure 28' in the combustion chamber and being connected with the actuating means 26 for controlling the latter.

It is assumed that the combustion chamber 1 served by the combustion apparatus according to the invention is part of a steam generator, not shown, having a superheater 29supplying steam to a stream main 30 and through a valve 32 to a turbine 31.

With the control system according to the invention the heat outputs of the individual burners 3 and 4 are adjusted proportionally to a value corresponding to the desired total output of the plant. Such a value, for example, is the pressure of the live steam which pressure is measured at 33. Other suitable values are the speed of the turbine 31, the temperature of a cooker which may receive steam from the turbine 31, manually or automatically operated means for controlling the steam flow from the steam main 36 to consumers, and the like. The value which'is proportional to the load condition of the turbine 31, in the illustrated case, the pressure of the live steam measured by the device 33 is transmitted as a modulated reference value through a reference value setting device 34 by means of

pulse transmitting conduits

35, 38, 40 to the servomotors or actuating means 11, 37 and 26, respectively, which operate the control means 36, 18 and 25, respectively.

The actuating means 11 for the fuel oil pressure controlling means 36 is a conventional device which is adapted to produce a signal which corresponds to the difference between the signal received from the device 34 and a signal corresponding to a characteristic of the oil supply to the oil burners 4 which characteristic is, in the example shown in FIG. 1, the oil consumption of the burner 4' measured at 13 and transformed at 12 into a signal which can be subtracted in 11 from the signal produced in 34. The burner 4' is the last one connected to an oil distributing pipe 7. Also suitable for use as the actuating means 11 is a conventional device adapted to produce a signal corresponding to the quotient of the signals produced in the

devices

34 and 12. Since a difference producing as Well as a quotient producing device is suitable, the device 11 has been termed comparing device for describing the invention. The fuel 'oil pressure control valve 36 is actuated by the device 11 according to the difference signal or the quotient signal produced therein depending on what kind of device is used. The valve 36 is opened for decreasing the fuel supply to the pipes 7 when the difference between or the quotient of the output signal of the device 34 which corresponds to the steam pressure and the output signal of the device 12 which corresponds to the fuel consumption, increases beyond a predetermined value, i.e., when the pressure at 33 rises because of decreased steam consumption. If the difference or the quotient, i.e. the ratio, between the output signals of the

devices

34 and 12 decreases below a predetermined value because of increased steam consumption, the valve 36 is closed to increase the fuel supply.

The pressure controlling means 37, 18 of the fuel supply system for the methane gas burners is actuated similarly to the aforedescribed control of the fuel oil system. The device 37 is connected with the reference value setting device 34 by means of a pulse transmitting conduit 38 and compares the reference value with the amount of fuel gas which is supplied to the burners and defined by the difference of the pressure 20 of the gas supplied to a burner and of the pressure 20' in the combustion chamber. This difference is measured by the device 19 and a corresponding pulse is transmitted through conduit 39 to the actuating means 37. The latter adjusts the position of the gas pressure control valve 18 until the measurement of the device 19 corresponds to the reference value pulse transmitted from the device 34 to the device 37.

The pressure, i.e., the supply of the combustion air is controlled similarly. The combustion air control means 26, is connected through a conduit 49 to the reference value setting device 34. The control means 26 is also connected with a device 27 which measures the difference between the pressure of the air flowing to the combustion devices and measured at 28 and the pressure 28' in the combustion chamber. The device 26 compares the reference value pulse received from the device 34 with the pulse received from the pressure difference measuring device 27 which corresponds to the actual air consumption of the combustion devices. The controlling device 26 actuates the throttle 25 until the combustion air supply corresponds to the reference value measured by the device 34.

As shown in FIG. 2, the fuel oil stop valve 6, the methane gas stop valve 14 and the combustion air stop valve 21 of each combustion device 2 are actuated by a common mechanism including a shaft 41 which can be revolved by manipulating a crank 42 and a cam on said shaft for each of the

valves

6, 14 and 21. The cams are so shaped that when the shaft 41 is in the angular position A gas can flow from the pipe 15 through the valve 14 to the burner 3. The oil valve 6 is closed and the air valve 21 is open. When the shaft 41 is in the angular position B the fuel oil valve 6 is open, the gas valve 14 is closed and the air valve 21 is open. In the diagram on top of FIG. 2 the closed position of a valve is inidcated by an X and the open position is indicated by an arrow. It is advisable that the cams are so shaped that if the shaft 41 is in the angular position C, all three valves are closed. In this position repairs or replacements can 6 be made in the respective combustion device 2. The

valves

6, 14, and 21 and the actuating mechanism shown in FIG. 2, of course, are outside of the combustion chamber 1 in contradistinction to the diagrammatic illustration, FIG. 1.

Instead of the hand operation of the shaft 41 shown in FIG. 2, the shafts may be provided With worm gears 42' whose worms are actuated by electric motors 42" which are remotely controlled from a switch box 48. Two shafts are shown only for actuating the stop valves of two devices 2. The upper shaft is in the position B in which the fuel oil valve of the respective device 2 is open and the gas valve is closed. The lower shaft is shown in the position A in which the fuel gas valve is open and the oil valve is closed. Instead of the electric remote control shown in FIG. 3 a conventional mechanical or hydraulic remote control may be provided.

FIG. 4 is a diagrammatic illustration of a combustion apparatus according to the invention in which the oil burners are of the oil recirculating type. The oil burners 4" are arranged in three groups of four burners which are individually connected by means of valves 6 to oil supply pipes 7 of which there is one for each group. The pipes 7 are connected to a manifold 8 receiving fuel oil from a reservoir 10 through a pump 9. Each burner includes an oil recirculating pipe 43 in which a valve 6 is interposed. All recirculating pipes 43 terminate in a common oil return system comprising oil return pipes 44 which individually serve the oil burners of four combustion devices and which terminate in an oil return manifold 45 which returns fuel oil through a throttle valve 36' to the oil reservoir 10.

The throttle valve 36' forms part of an oil pressure controlling means including an actuating means 11' which is connected with the reference value settin'g device 34 through a pulse transmitting conduit 35'. The actuating means 11 are not only responsive to the pulses received from the device 34 but also to pulses received from a device 46 which is responsive to the pressure in the fuel oil return system. The pressure in the fuel oil supply system is measured by a device 47 which transmits control pulses to actuating means 11" for a throttle valve 36 which is arranged in series relation with the fuel oil pump 9 in the oil supply system. The actuating means 11" is connected through a pulse transmitting conduit 35 with the reference value setting device 34 and actuates the valve 36" until the oil pressure in the fuel oil supply system corresponds to the pressure of the live steam measured at 33.

FIG. 5 shows an arrangement in which three groups of fuel burning devices 2 are provided, each device being adapted to burn different fuels at the same time whereby the same amount of heat is produced by the individual devices of the same group and the devices of different groups produce different amounts of heat. The handles or cranks 42 for manipulating the cam shafts 41 for opening and closing the burners for different fuels of the individual devices are diagrammatically indicated and the air supply means are omitted in FIG. 5. If the heat output of a device 2 of group I is taken as fundamental unit and if group I has n devices 2, the heat output In of each device of group II preferably is n+1. If group II has I devices the heat output s of each fuel burning device of group III preferably is t.m+n+l. The desired different capacities of the burners of different groups can be obtained, for example, by making the nozzles of the burners of one group larger than the nozzles of the burners of another group.

If group III has r fuel burning devices, the accuracy of the distribution of the total desired heat production on the different fuels is n+t-m+r-s If there are four fuel burning devices in each of three groups I, II and III and the heat output of each device Group I II III Oil Gas Device 1234 1234 1234 Example A 0 0 0 0 0 0 0 0 0 o 0 1/124 123/124 ExampleB 0 o 0 0 o 0 0 0 0 35 124 89/124 Example 0.. 0 0 0 0 92 124 52 124 Example D- 0 0 0 0 112/124 12/124 Example D corresponds to the setting of the individual burners shown in FIG. 5. With the system according to the invention for burning different fuels a great flexibility of the division of the load on the individual fuels is possible although the division is produced by operating the burners at full on and full off condition only so that inefiicient operation of burners operating at low load is avoided.

Aside from the described and illustrated examples many other variations of the number of groups of fuel burning devices and of the number and size of the devices in each group are possible.

The control method and the combustion apparatus according to the invention are not limited to the described and illustrated embodiments in which only two different kinds of fuel are used. The method and apparatus are also applicable to plants in which more than two different kinds of fuel are fired. In this case each combustion device includes as many burners as there are kinds of fuel to be fired and there are, of course, a corresponding number of fuel and air supply systems. The individual combustion devices may be so arranged that burners for two different fuels may be operated simultaneously in one locality and the burner or burners for the other fuel or fuels are not operated. If the air consumption of two different kinds of fuel is substantially different for producing the same amount of heat by each kind of fuel, the combustion device according to the invention may include separate air supply means for each burner. These combustion air supply means may be connected to the same air supply system whereby stop valves are provided for stopping air supply to burners which are not in operation.

In the example shown in FIG. 1 and described separate air supply means for the different burners of the individual fuel burning devices are unnecessary because the methane gas produces 8770 kg.-cal. with 11.2 normal cubic meter combustion air and fuel oil produces with the same amount of air 8815 kg.-cal. In this case the two burners can be provided with a common air supply means.

What is claimed is:

1. The method of firing at least two different kinds of fuel at variable ratios in a combustion apparatus and altering the heat output of the entire combustion apparatus to satisfy varying heat demands, including the steps of separately distributing each kind of fuel to a plurality of burners, of operating a number of the burners receiving one kind of fuel and a number of burners receiving the other kind of fuel at a ratio between said numbers corresponding to the desired ratio between the quantities of the different kinds of fuel fired, and of uniformly increasing the heat output of all burners which are in operation upon an increase of the total heat demand and decreasing the heat output of all burners which are in operation upon a decrease of the total heat demand.

2. The method defined in claim 1 wherein the difierent kinds of fuel are supplied to a plurality of groups of bumers, each group including a burner for one kind of fuel and a burner for the other kind of fuel, only the burner for one kind of fuel being operated at a time in each group.

3. The method defined in claim 1 wherein the fuel supply to all burners supplied by one kind of fuel and in operation is increased as the difference between the total heat demand and a value corresponding to the heat output of one of the burners supplied by said one kind of fuel and in operation increases and the fuel supply to all burners supplied by one kind of fuel and in operation is decreased as the difference between the total heat demand and a value corresponding to the heat output of one of the burners supplied by said one kind of fuel and in operation decreases.

4. The method according to claim 3 wherein said one kind of fuel is of the fiuid type and wherein said value is the difference between the pressure of said one kind of fuel entering said one of said burners and the pressure in the combustion space of the apparatus.

5 In a combustion apparatus for simultaneously burning different kinds of fuel which fuels require substantially the same amount of combustion air for producing substantially the same heat of combustion: a plurality of fuel burning devices individually including at least one fuel burner for each kind of fuel, separate fuel supply means for the different kinds of fuel, said supply means being individually connected to all burners burning the same kind of fuel, means for supplying combustion air to all of said burners, means individually connected to said burners for stopping the supply of fuel and combustion air to the individual burners, whereby the number of burners in operation for one kind of fuel relative to the number of burners in operation for a different kind of fuel can be adjusted corresponding to the desired ratio between the different kinds of fuel to be fired, and means responsive to a value corresponding to the total heat output demanded from the apparatus and connected to said fuel and combustion air supply means for individually controlling the amounts of different fuels and of air supplied to the burners which are in operation.

6. In a combustion apparatus as definedin claim 5 and wherein said fuel burning devices are alike and adapted to produce the same amounts of heat.

7. In a combustion apparatus as defined in claim 5 and wherein at least two groups of fuel burning devices are provided, the fuel burning devices of each group being alike and adapted to produce the same amounts of heat, and the fuel burning devices of different groups being different for producing different amounts of heat by the fuel burning devices of different groups.

8. In a combustion apparatus as defined in claim 5 and wherein said means for stopping the supply of fuel to the individual burners include means operatively connected to the individual fuel burning devices and including means for stopping the fuel supply to the burner for one kind of fuel in the individual devices and simultaneously starting the fuel supply to the burner for another kind of fuel in the respective fuel burning device and vice versa.

References Cited in the file of this patent UNITED STATES PATENTS 1,512,132 Pfahl Oct. 21, 1924 2,390,806 Nagel Dec. 11, 1945 2,470,996 McGrath May 24, 1949 2,657,347 Bristol Oct, 27, 1953