US3243116A

US3243116A - Combustion control by means of smoke density

Info

Publication number: US3243116A
Application number: US288001A
Authority: US
Inventors: Jacob S Dijt; Hoeksema Haje
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1962-06-21
Filing date: 1963-06-14
Publication date: 1966-03-29
Anticipated expiration: 1983-03-29
Also published as: NL280005A

Description

March 29, 1966 J. s. DlJT ETAL- 3,243,115

COMBUSTION CONTROL BY MEANS OF SMOKE DENSITY Filed June 14, 1965 2 Sheets-Sheet 1 CONTROLLER FLOW METE;

l5 l7 COMBINING SMOKE 18 CIRCUIT CONTROLLER FIG. I

CONTROLLER i 1 6 F J l6 ,1? L RATIO SMOKE l8 CONTROLLER CONTROLLER FIG. 2

INVENTORSI JACOB S. DIJT HAJE HOEKSEMA THEIR ATTORNEY March 29, 1966 J. 5. DIJT ETAL 3,243,116

COMBUSTION CONTROL BY MEANS OF SMOKE DENSITY Filed June 14, 1965 2 Sheets-Sheet 2 M CONTROLLER CONTROLLER 6 J) 9 [:1 I L |6 CONTROLLER I8 SMOKE MULTIPLIER OLLER FIG. 3

INVENTORSI JACOB s. DiJT HAJE HOEKSEMA THE IR ATTORNEY United States Patent ()flice Patented Mar. 29, '1966 COMBUSTION CONTROL BY MEANS OF SMOKE DENSITY Jacob S. Dijt and Haje Hoeksema, Amsterdam, Netherlands, assignors to Shell Oil Company, New York, N .Y., a corporation of Delaware 7 Filed June 14, 1963, Ser. No. 288,001

Claims priority, application Netherlands, June 21, 1962, 280,005 3 Claims. (Cl. 236-14) The invention relates to a method and apparatus for automatic control of the combination process in a heating or an' evaporation apparatus. More particularly, this invention relates to a method and apparatus wherein signals arising from the measured values of the fuel flow or of the air flow or of both of them, of one or more variables of the heated or evaporated medium, and of the smoke in the combustion gases are utilized to adjust the fuel-air ratio to a value which results in the most economical operation of the system to produce a desired result.

In order to reach and maintain a desired result in a heating or evaporating operation, such as the temperature of a stream of liquid that is heated in an industrial furnace, or the quantity and pressure of the steam supplied by a boiler, it is essential that the operating conditions of the combustion process are controlled for the purpose of producing the required quantity of calories. For this purpose the fuel flow is generally controlled in a direct and automatic manner by the temperature signal or pressure signal from the heated liquid or steam. In order to reach maximum economy of operation, however, it is necessary to attempt to supply only that quantity of air which is required for complete combustion of the fuel. In mo st cases, and particularly in those where solid or liquid fuel is burnt, the limit in these attempts is set by the quantity of smoke formed in the combustion gases. The prevention of smoke "formation is of importance not only for an economical operation but also for the prevention of air pollution.

Various attempts have been made in the prior art to devise systems for optimizing a combustion process using a signal derived from the smoke in the combustion gases. One such system is described in the United States Patent No. 2,285,564. According to the system described in this patent, the signal for the control of the fuel flow and of the air flow is supplied solely by the measured temperature or pressure of the heated or evaporated medium, while the smoke signal from the combustion gases intervenes in the airflow control if the smoke density differs from a certain predetermined value.

A-second system utilizing a signal derived from the smoke in the combustion gases is shown in commonly assigned United States patent application Serial No. 134,396, filed 'August 28, 1961, now Patent No. 3,184,686. According to an example given in this patent application of a system for the control of a process under optimum operating conditions, the signal for the control of the fuel flow is derived from the measured temperature or pressure of the heated or evaporated medium while the air flow is controlled by an optimizing controller, likewise under the influence of the signal derived from the measured temperature or pressure of the heated or evaporated medium. Whenever the smoke density in the combustion gases rises above a certain predetermined value a signal indicating this fact is supplied to the optimizing controller which then varies the air flow. The optimizing controller causes the air flow to increase and decrease continually, so that the system is constantly oscillating relative to the desired value.

In order to obtain maximum efiiciency of the combustion and to attain near-smokeless combustion, it is essential that the air flow matching the fuel flow is supplied continuously and instantly. Although both of the abovementioned systems give satisfactory results when slow variations in the fuel supply occur, for instance owing to pressure disturbances in the fuel supply line, they will not respond instantly to large and rapid variations in the fuel flow since the system only responds to changes in the temperature or pressure of the heated medium and the smoke'in the combustion gases. This is caused by atime lag which occurs before the temperature or pressure gauge located in the heated or evaporated medium or the smoke density meter located in the stream of combustion gases indicates variations occasioned by a variation in the fuel flow. In this connection the size of the furnace or of the boiler plays an important part. If the control of the air flow takes place under the influence of these signals which are delayed by a time lag, there will continually be periods when combustion takes place with an excess of air or when smoke formation occurs. Particularly with rapid and large variations in the fuel flow, large deviations from the fuel/air ratio desired for an economical and near-smokeless combustion will occur. If the regulation takes place under the influence of signals derived from, for instance, the fuel flow without a smoke density meter, then a rapid'change of the air flow is obtained upon a variation in the fuel flow. It is not, however, automatically verified whether the ratio of the fuel flow to the air flow is the proper ratio to ensure combustion which is as economical as possible and. near-smokeless. I

It is, therefore, a primary object of this invention to provide a system for optimizing the fuel-air ratio in 'a combustion process used in a heating or evaporating apparatus.

It is a further object of this'invention to provide a system for optimizing the fuel-air ratio in a combustion process which system is instantly responsive to large and rapid fluctuations in the fuel supply.

- It is still a further object of this invention to provide a system for controlling the fuel-air ratio in a combustion process, which system is instantly responsive to large and rapid variations in the fuel supply and which results in near-smokeless operation of the combustion process.

It is another object of this invention'to provide 'an improved control system for a combustion process used in a heating or evaporating apparatus which control system rapidly adjusts the fuel-air ratio for the desired heating requirements and near-smokelesscombustion.

Briefly the above objects of this invention are achieved by controlling the ratio of the fuel flow to the air flow by signals derived from the measured values of at leastone of these flows and of the smoke in the combustion gases. The control of, for instance, the air flow under the infiuenceof a signal derived from the fuel fiow willeven if the latter varies rapidly-provide for an immediate rough adaptation of the air't-o the fuelflow, while after that the signal from the smoke density meter regulates the fuel/air ratio in such a way that'a high combustion efliciency is reached with little smoke formation. The fuel flow in turn is controlled by a variable of the medium which has been heated in the system. This variable may for example be the temperature of a heated liquid, the steam pressure of an evaporated substance or any-other variable property of a heated medium which can be directly related to the amount of heat applied to the medium.

The above objects and advantages of this invention will be more easily understood from the following detailed description of the invention when taken in conjunction with the attached drawings wherein:

FIGURE 1 is a schematic diagram of a heating system controlled according to the invention wherein the air flow is controlled by signals proportional to the fuel flow and the smoke in the combustion gases;

FIGURE 2 is a schematic diagram of a heating system controlled by a modification of the invention in which the air flow is controlled by signals proportional to the fuel flow, the air flow and the smoke in the combustion gases; and

FIGURE 3 is a schematic diagram of a heating system controlled by a further modification of the invention wherein the air flow is controlled by signals proportional to a variable of the heated medium, the air fiow and the smoke in the combustion gases.

Referring now to FIGURE 1, there is shown a furnace 1 containing a pipe system 2 through which a liquid to be heated is continuously flowing. The liquid in pipe system 2 is continuously heated by means of a burner 3 which is supplied by fuel through a pipe or conduit 4. Air for combustion is supplied to the burner 3 via a pipe or conduit 5. The combustion gases escape from the furnace through a flue or stack 6.

The quantity of fuel supplied to the burner 3 via pipe 4 is controlled by a control valve 7 having a valve operator 8 which positions the control valve 7 in accordance with a signal proportional to a desired parameter or variable of the output from the furnace 1. In the instant application the derived variable is the temperature of heated liquid flowing in the pipe system 2. It is understood, however, that in other applications, other variables may be measured, e.g., in a steam boiler, the desired output variable would be the steam pressure.

In order to measure the temperature of the liquid flowing in the pipe system 2, a transducer 9 is suitably connected in the output side of the pipe system 2. The transducer 9 produces a signal proportional to the temperature of the liquid in the pipe system 2 and supplies the signal to one input of a conventional controller 10. To the second input of the controller 10 is applied a variable external signal 11 which is preset, e.g., manually, to a value proportional to the desired temperature for the liquid in the pipe system 2. The controller 10 compares the two input signals and produces an output signal proportional to the difference between the two input signals. The output signal from the controller 10 is then applied to the valve operator 8 which then further opens or further closes the valve 7 according to whether the signal proportional to the temperature of the heated liquid is less than or greater than the preset external signal. Should the two input signals to the controller 10 be equal, then the output signal from the controller 10 will leave the valve 7 in its present position.

In order to adjust the flo-w of air to the burner 3 to optimum conditions, i.e., the proper fuel-air ratio, a control valve 12 having a valve operator 13 is inserted in the air supply pipe 5. The valve operator 13 adjusts the valve 12 in response to both the flow of fuel in pipe 4 and the density of smoke in the combustion gases.

In order to measure the flow of the fuel in pipe 4, a flow meter 14, or other suit-able device which produces a signal proportional to flow, e.g., a pressure gage, is iiiserted in the fuel supply pipe 4. The output signal from the flow meter 14 is supplied to one input of a combining circuit 15 which may, for example, be an adding or a multiplying circuit. To the second input of the combining circuit 15 is supplied a signal related to the quantity of smoke in the combustion gases.

The signal related to the quantity of smoke in the combustion gases is measured by means of a smoke density meter 16 which is suitably connected to the furnace stack 6. The signal from the smoke density meter 16, which is proportional to the density or quantity of smoke in the combustion gases, is supplied as one input to a controller 17 which preferably is of the type which will integrate the signals from the smoke density meter over a short period of time. The controller 17 compares the smoke density signal to a preset external signal 18 and produces an output signal proportional to the ditference. The output signal from ti t: Controller 17 is then 4 f applied as the second input to the combining circuit 15 where it is combined with the fuel flow signal and then applied to the control valve operator 13 which then adjusts the control valve 12 to the optimum fuel-air ratio.

Although for absolute optimum combustion conditions, the external signal 18 should be set at such a value that the air flow will be adjusted to produce no smoke in the combustion gases, there is a risk when trying to adjust the system to this condition of the air flow control becoming adjusted to an excess of air. In order to avoid this situation, the signal 18 is preferably set at a value such that the controller 17 adjusts the air flow so that the desired amount of smoke formation is a small value other than zero.

Referring now to FIGURE 2, there is shown a second modification of a control system according to the invention. In this figure reference numbers which are the same as those in FIGURE 1 denote like parts. As in the embodiment of FIGURE 1, the liquid in the pipe system 2 is heated in the furnace 1 and the fuel flow is adjusted in response to a signal proportional to the temperature of the heated liquid from the transducer 9 via the controller 10, control valve operator 8 and control valve 7. In order to adjust the air flow, however, a signal proportional to the air flow is used in addition to the signals proportional to the fuel flow and the quantity of smoke in the combustion gases. In order to produce a signal proportional to the flow of the air, a flow meter 21, or other suitable flow measuring device, is inserted in the fuel supply pipe 5. The signals from the fuel flow meter 14 and the air flow meter 21 are then supplied to a ratio controller 22 which determines the fuel-air ratio, compares the ratio to a set point value corresponding to the desired fuel-air ratio, and supplies an out-put signal proportional to the difference between the actual fuel-air ratio and the set point value. The output signal from the ratio controller 22 is then applied to valve operator 13 which then further opens or further closes control valve 12 depending on whether the actual fuel-air ratio is greater than or less than the set point value. In order to further adjust the fuel-air ratio so that only the desired amount of smoke formation results, a signal related to the amount of smoke in the combustion gases is supplied to the ratio controller 22 via the smoke density meter 16 and the controller 17. The signal from the controller 17 varies the set point value of the ratio controller 22 and thereby further adjusts the air flow to a value which will result in the smoke formation being reduced to the desired quantity.

Referring now to FIGURE 3, there is shown still a further embodiment of a control system of the invention wherein reference numbers which are the same as those of FIGURES l and 2 denote like parts. Unlike the previous two embodiments, the fuel flow in the fuel supply pipe 4 is controlled not only by the variation of the temperature of the liquid in the pipe system 2 but is also responsive to a signal proportional to the fuel flow. In order to control the fuel flow in this manner, the signal from the fuel flow meter 14 is supplied to one input of a conventional controller 25 which compares the signal from the fuel flow meter 14 with a signal related to the temperature of the liquid in the pipe system 2. As in the previous embodiments the signal related to the tempera ture of the heated liquid in pipe system 2 is supplied via transducer 9 and controller 10. In the event that a change in fuel flow is required due to either a change in the fuel flow rate or to a change in the temperature of the heated liquid the controller 25 will immediately produce an output signal which causes the control valve operator 8 to either further close or further open the control valve 7 an amount proportional to the output signal. By controlling the fuel flow in this manner, the fuel flow is instantly corrected for pressure variations in the fuel supply pipe 4 and thus eliminates any time lag in the re sponse of the system due to the time it takes for changes in the fuel flow rate to show up as temperature variations of the heated liquid. In this Way it is possible to maintain the value of the fuel flow at the desired value with respect to the temperature of the heated liquid, regardless of any pressure variations in the fuel supply pipe 4.

In order to adjust the air flow to the desired fuel-air ratio, the output signal from the air flow meter 21 is supplied to one input of a conventional controller 26, the output of whch controls the air flow in the air supply pipe 5 via control valve operator 13 and control valve 12. The second input signal to the controller 26 is supplied from the multiplier 27 wherein the signal related to the temperature of the heated liquid, which is supplied via the transducer 9 and controller 10, and the signal related to the smoke in the combustion gases, which is supplied via smoke density meter 16 and controller 17 as previously explained, are multiplied together. By controlling the flow in each of the supply pipes 4 and 5 by a signal proportional to the flow in the respective pipes and a second signal responsive to the one or more output parameters of the heating system, it can easily be appreciated that the system will immediately compensate for both pressure variations in the supply lines and changes in the output parameters resulting in a more rapid and thus more economical combustion control system.

Although no details of the specific components utilized in the various embodiments of the invention have been disclosed, it is understood that the various measuring and control instruments are all conventional devices and per se form no part of applicants invention. Furthermore it is understood that the various measuring and control instruments may operate in response to electrical, penumatic, hydraulic or mechanical power signals of any combinations of these various types of signals.

Obviously, various modifications of the present invention are possible in view of the above teachings, for example, the ratio controller of FIGURE 2 could be replaced with a multiplying circuit and a conventional controller. It is therefore further understood that the invention is not limited to the particular forms illustrated, but is capable of embodiment in other forms without departing from the spirit and scope of the appended claims.

We claim as our invention:

1. Apparatus for controlling the combustion process in a heating system comprising: a burner; a fuel supply line and an air supply line connected to said burner; means connected in said fuel supply line for producing a signal proportional to the flow of said fuel; means for measuring the smoke in the combustion gases from said burner and producing a signal related thereto; first controller means for comparing said smoke signal with a first external signal having a preset value and producing an error signal proportional to the diiference; means for combining said signal proportional to the fuel flow and the error signal from said first controller means; means responsive to the output signal from said combining means for varying the flow in said air supply line; means for measuring a variable of the medium heated in the system and producing an output signal proportional thereto; second controller means for comparing the signal proportional to a variable of the medium heated in the system to a second external signal having a preset value and producing an error signal proportional to the difference; and, means responsive to the output signal from said second controller means for varying the flow in said fuel supply line.

2. The method of optimizing the fuel-air ratio in a heating system wherein the fuel flow rate and the air flow rate may be varied consisting of: measuring a variable of the medium heated in the system; comparing said measured value of the variable with a first preset external signal to produce a first difference signal; utilizing said first difference signal to control the fuel flow rate; measuring the density of the smoke in the combustion gases; comparing the measured value of the smoke density to a second preset external signal to produce a second difference signal; measuring the fuel flow rate and producing an output signal proportional thereto; combining said second difference signal and said signal proportional to the fuel flow rate to produce a combined output signal; and controlling the air flow rate in accordance with said combined output signal.

3. The method of claim 2 wherein said second preset external signal is adjusted to a value such that the fuel-air ratio will result in a small amount of smoke being formed.

References Cited by the Examiner UNITED STATES PATENTS 2,196,700 4/1940 Holby 236-14 2,412,739 12/1946 McCracken 23614 3,049,300 8/1962 Lewis et a1. 236l5 FOREIGN PATENTS 627,448 3 193 6 Germany. 3 07,53 6 3/ 1929 Great Britain.

OTHER REFERENCES Lancaster, A. L., A Modern Automatic Fuel Shut-01f System for Soaking Pits, in Iron and Steel Engineer, 30 (12), pp. 69-76 (seven pages), December 1963.

Truxal, J. G., Control Engineers Handbook, 1st Ed., New York, McGraw-Hill, 158, pp. 16-12 and 16-13 (2 PP-)- Grabbe, E. M., et al., Handbook of Automation, Computation and Control, vol. 1, Control Fundamentals, New York, John Wiley, 1958, pp. 20-60 and 20-61 (two pages).

Amber, G. H., et al., Special Purpose Computers in the Control of Continuous Processes, in Automatic Control, May 1958, pages 43 and 45-48.

ALDEN D. STEWART, Primary Examiner.

Claims

1. APPARATUS FOR CONTROLLING THE COMBUSTION PROCESS IN A HEATING SYSTEM COMPRISING: A BURNER; A FUEL SUPPLY LINE AND AN AIR SUPPLY LINE CONNECTED TO SAID BURNER; MEANS CONNECTED IN SAID FUEL SUPPLY LINE FOR PRODUCING A SIGNAL PROPORTIONAL TO THE FLOW OF SAID FUEL; MEANS FOR MEASURING THE SMOKE IN THE COMBUSTION GASES FROM SAID BURNER AND PRODUCING A SIGNAL RELATED THEREON; FIRST CONTROLLER MEANS FOR COMPRISING SAID SMOKE SIGNAL WITH A FIRST EXTERNAL SIGNAL HAVING A PRESET VALVE AND PRODUCING AN ERROR SIGNAL PROPORTIONAL TO THE DIFFERENT; MEANS FOR COMBINING SAID SIGNAL PROPORTIONAL TO THE FUEL FLOW AND THE ERROR SIGNAL FROM SAID FIRST CONTROLLER MEANS; MEANS RESPONSIVE TO THE OUTPUT SIGNAL FROM SAID COMBINING MEANS FOR VARYING THE FLOW IN SAID AIR SUPPLY LINE; MEANS FOR MEASURING A VARIABLE OF THE MEDIUM HEATED IN THE SYSTEM AND PRODUCING AN OUTPUT SIGNAL PROPORTIONAL THERETO; SECOND CONTROLLER MEANS FOR COMPARING THE SIGNAL PROPORTIONAL TO A VARIABLE OF THE MEDIUM HEATED IN THE SYSTEM TO A SECOND EXTERNAL SIGNAL HAVING A PRESET VALUE AND PRODUCING AN ERROR SIGNAL PROPORTIONAL TO THE DIFFERENCE; AND, MEANS RESPONSIVE TO THE OUTPUT SIGNAL FROM SAID SECOND CONTROLLER MEANS FOR VARYING THE FLOW IN SAID FUEL SUPPLY LINE.