US2889114A

US2889114A - Control by indirect measurement

Info

Publication number: US2889114A
Application number: US523177A
Authority: US
Inventors: Jack F Shannon
Original assignee: Bailey Meter Co
Current assignee: Elsag Bailey Inc
Priority date: 1955-07-20
Filing date: 1955-07-20
Publication date: 1959-06-02
Anticipated expiration: 1976-06-02

Description

June 2, 1959 J. F. SHANNON CONTROL BY INDIRECT MEASUREMENT Filed July 20, 1955 m2 5528 96 55mm @565 mm z mmm 95 R N 0 O T. 5/ m M J W M I S W F w 2 A J Hf Q k m m al N vm m wwwmm 7 od 5 5: Bod m2 fiww zmwm it? 255 965 255 N in? V United States Patent CONTROL BY INDIRECT MEASUREMENT Jack F. Shannon, Euclid, Ohio, assignor to Bailey Meter Company, a corporation of Delaware Application July 20, 1955, Serial No. 523,177

8 Claims. (Cl. 236-14) The present invention relates to control systems for variables which can not be measured directly. More specifically, the invention utilizes variables which can be measured directly and demonstrates their subtraction to obtain control impulses for those variables which can not be measured directly.

The present invention was conceived while evolving a control system for the combustion of two dissimilar fuels in a common combustion zone. The total air used for the combustion process was subject to direct measurement, as well as the total steam produced by the cornbustion in the common zone, but due to limitations of furnace construction, only the air used to burn one of the fuels could be measured directly and individually.

The specific control system evolved was applied to the combustion process utilizing a sugar cane waste product, commonly called bagasse, and natural gas, as the two fuels. In developing the control system, it became apparent that although the air flowing to the grate on which the bagasse burned could be directly measured, there was no provision made to measure the air going to the burner boxes of the natural gas. There was a location in the duct work, for the combustion air, for the direct measurement of all of the air of combution. Therefore, utilizing these direct measurements, the control system was evolved which ascertained a control index which was proportional to the air-equivalent of the demand for gas and the quantity of steam produced by that part of the combustion for which the burning of the natural gas was accountable. Further, the problem of controlling the burning of the bagasse alone, and under manual direction, with the alternate possibility of burning the bagasse alone, or in combination with the natural gas, automatically, was solved. Although specifically developed in connection with the combustion of natural gas and bagasse, it is obvious that the teachings of this disclosure are applicable to the combustion of other fuel combinations.

It can now be appreciated that, with the indices of steam pressure as representative of demand, air flow to the bagasse-burning stoker, total steam flow produced by combustion, total air flow utilized in combustion, and the natural gas burned in combustion, a system was required for separately controlling the air supplied to each fuel burned as well as the individual supplies of fuel to the combustion process. With the need of at least an index of air how to the natural gas combustion, a primary object of the invention is seen as the application of indirect measurements to the control of variables.

Another object of the invention is to ascertain control indices included in direct measurements which may be used to directly control variables establishing the indices.

Another object of the invention is to subtract a directly measured portion of a variable from a measurement of the variable in order to ascertain the value of the remaining portion of the variable and to separately apply the portions in control of the variables.

Another object of the invention is the control of combustion of two fuels where the total steam produced by the burning of the fuels is measured and the total utilized by the combustion of both fuels is measured but the air to one of the fuels cannot be measured directly.

Another object of the invention is the provisions for burning one fuel alone, and under manual direction, with the alternate possibility of burning that fuel alone, or in combination with a second fuel, automatically.

In the drawings:

The drawing diagrammatically represents a combustion control system in which the invention is embodied.

In understanding the drawing, it should be noted that the directly measured variables are indicated by numerous transmitters along the top of the drawing while reg ulators and their positioning means, shown in block form, for the variables controlled by the direct and indirect measurements are represented along the bottom of the drawing. The basic purpose of burning the fuels is the production of steam, and the primary impulse is the pressure of this steam, designated as an index of demand on the combustion control system. Generally, under automatic operation, and when burning both fuels, the demand index is applied, in parallel, to the control of sep-- arate air supplies regulated for the combustion of both fuels in a common zone of combustion. The two fuels are bagasse and natural gas, referred to supra.

The regulation of the supply of the bagasse can be brought under the direct parallel control of the demand index applied to the regulation of air going to the bagasse stoker. However, the air to the combustion of natural gas can not be regulated directly in parallel with its air supply because direct measurement of this air supply is not available.

An index of the air supply neededfor natural gas combustion must be derived. The total air flow to the combustion can be measured directly by a transmitter and a relay is employed to receive an impulse representative of this total air supply as well as an impulse representative of the air to the stoker burning bagasse. The relay receiving these impulses subtracts one from the other to produce a resulting output impulse as an index of the air.- equivalent of the demand for natural gas combustion and which is applied directly to the control of the regulator of the natural gas supply.

Certain secondary indices, for control, are desired. These indices readjust the response of the regulatorsto the basic demand impulse in accordance with a measurement of the variable element of combustion actually supplied by the regulator. As an example, it has already been appreciated that the steam pressure demand index calls for air fiow regulation to the bagasse stoker as a basic control. However, the actual flow of combustion air to this stoker is measured and an impulse representative of this how continually compared with the demand index in a relay to balance the demand index when the actual flow equals the demand for it. Considering the regulation of the natural gas from the indirectly obtained impulse representative of the air-equivalent of the demand for natural gas combustion, it can be appreciated that the natural gas is also measured directly and an impulse formed which is balanced against the indirect impulse when the indirect impulse is satisfied.

Turning now to the problem of. establishing a readjusting index for regulation of the bagasse fuel supply, it is pointed out that an indirect impulse is derived from the steam flow produced by the bagasse combustion. This index is obtained by subtracting from the actual steam flow produced by both fuels, the index representative of air flow to the natural gas combustion, now to be considered as representative of steam flow produced by natural gas combustion. This derivation. is practical be cause the regulation of the natural gas is maintained proportional to the air required for efficient combustion.

Returning to the measurement of steam pressure, as ademand .index, .transmitter 1 ,is to be appreciated as directly, responsive to the pressure in order to establish ajfluidpressure impulserepresentative of the pressure. The internal structure of transmitter 1 is depicted in sufiicie'nt detailto appreciate that a Bourdon tube directly respondsto the steam pressure imposed through pipe 2 in order to position a fluid pressure couple consisting of nozzle 32 and vane 33 whose output controls a so-called booster 34 whose output is the fluid pressure impulse representative of the steam pressure as the demand index.

The' cooperation of the

halves

32 and 33 of the fluid pressure couple and the booster 34 are disclosed in Gorrie t al.72,737,963. The fluid pressure couple maybe actuated bya Bourdon tube as shown at 1, a flow-responsive bell, a'dilferentially responsive bellows, or other actuating mechanisms. The

other transmitters

16, 17, 18 and 19 responsive to the various variables measured directly are depicted in somewhat less detail but all may utilize the structure disclosed in Patent 2,737,963.

The fluid pressure output of transmitter 1 is established in pipe 3 in order thatit may be imposed upon a relay structured. This relay may take the form of that disclosedinthe application to Gorrie, S. N. 311,098 filed September'23, 1952, now Patent No. 2,776,669. The particular form of the structure disclosed here is shown indetail suflicientto illustrate it as a standardizing type. The relays subsequently depicted in this disclosure may not have this standardizing feature, however, their structure aregenerally similar, in other respects, to that of relay 4. V

For purposes of making the subsequent disclosure easily understood, it is to be noted that these relays have four pressure responsive chambers, consistently designated A, B, C and D. Chambers A and B are opposed across the fulcrum of a beam and chambers C and D are opposed across the fulcrum of a second beam. Each beam operates half of a fluid pressure couple whose output is amplified by a booster similar to booster 34 utilized in transmitter 1. The relative movements of the A-B and -D beams are depicted as regulated by a manually adjustable linkage. Adjustment of this linkage determines the proportional response of the output from the booster to the input to the A-B beam. The relay output signal can be considered to be a control signal which can be sent directly to the regulator operating means or to other relays for computing purposes.

The output of relay 4 is imposed upon pipe 5 which routes this pressure to a manually operable selector station 6. Although station 6 is depicted diagrammatically, it is to be understood that the details of its structure may be fully understood from the disclosure of Dickey 2,747,- 595. The subsequently disclosed selector stations are similar to station 6 and may be generally appreciated as devices for selecting one of several methods of utilizing the control fluid pressure routed to them. Said pressure may be routed through the device to obtain a form of automatic control. The device may also be used for terminating control fluid pressures routed through them and substituting therefor manually determined fluid pressures. Further, certain forms of these stations enable a manually determined bias pressure to be imposed upon the control pressure routed through them.

From selector station 6, the control fluid pressure is taken by pipe 7 and applied to branches 8 and 9 for simultaneous, parallel regulation of the air flows to the combustion of the two fuels. V

There is diagrammatically depicted, in branch pipe 8, another manually controlled selector station 10. Selector station 10 includes the terminating features of selector station 6 as well as provision for biasing the fluid pressure it tr'ansmitsfNot only can the demand index be isolated from regulation of fuel and air to the stoker, and manual control be applied, but indicators on the gages of the station are available for guidance in the operation. A visual guide to the amount of stored bagasse is not shown but presumed available for the manual control. The amount of fuel (bagasse) burned is governed by the speed of the stoker. Following selector station 10, pipe 12 branches to simultaneously, or in parallel, apply its pressure relays 14 and 15.

Relays 13, 14 and 15 receive the pressures of pipes Q and 12 to establish the controlled pressures applied directly to the regulation of two air flows and bagasse feed.

It is in order to next consider the four transmitters responsive to those variables of the combustion process which can be directly measured. All of these transmittors are basically similar in structure to transmitter 1. Transmitter 16 responds to the measured air flow going to'the stoker, transmitter 17 responds to the measured total steam flow produced by the combustion ofbothfuels, transmitter 18 responds to the measured total air flow utilized in burning both fuels, and transmitter 19. responds to the measured flow of natural gas going to the burners of the furnace. These transmitters establish fluid :pressure outputs in pipes 20-23, representative of the variables to which they respond;

Considering the fluid pressure in pipe 20, it is first observed as readjusting the basic index applied to relay 14, for the regulation of air flow to the stoker. Pipe branch 24, to relay 13, indicative of the air flow to the stoker, is subtracted from the basic demand index, applied to the air regulators in parallel, to allow a proper proportion of the demand index to be eitective in control of the regulator of the air to the natural gas combustion.

Pipe branch 25 transmits the output of transmitter 16 to the B chamber of relay 26. Pipe 22 imposes the output of transmitter 18 upon the C chamber of relay 26. Relay 26 performs the vitalfunction in this control system, of subtracting the values of one of these two fluid pressures from the other to obtain a control index representative of air flow. required for efficient combustion of natural gas when the fuels are burned together in the common combustion zone. The output of relay 26 then becomes of major importance in the present disclosure. This fluid pressure, established in

branch pipes

27 and 28, is an indirect measurement of a variable in the controlled process which was applied in regulation of the variables so indirectly measured. In branch pipe 27 the fluid pressure output of relay 26 is considered as representative of the air flow required for efiicient combustion of natural gas. So characterized, this fluid pressure of branch pipe 27 is applied as a basic control index to relay 29 for the regulation of the flow of natural gas to the burners of the furnace. Transmitter 19, establishing its fluid pressure in pipe 23 balances the fluid pressure in branch pipe 27 when the actual flow of natural gas equals the demand made for it by the impulse in pipe 27. Thus, by the output of relay 29, the natural gas is demanded by the fluid pressure in branch pipe 27, an indirect measurement of the air flow required for the eflicient combustion of the natural gas.

Discussion may now return .to the output of relay 26 as established in branch pipe- 28. The fluid pressure in branch pipe 28, as an output of relay 26, may be considered'as representative ofthe steam produced by the combustion of the natural gas. This assumption is prac'- tical since the natural gas flow is controlled to be proportional to the air required for its eflicient combustion.

Relay 30 is now considered in the same view tak'enrof relay 26. The fluid pressure in branch pipe 28 is received by the B chamber of relay 30 and the fluid pressure of pipe 21 is received by the C chamber of relay 30. In this arrangement, relay 30 subtracts the value of one of the'two fluid pressures from the other to establish an output in pipe 31 as representative of the steam produced by the combustion'of bagasse 'on the stoker.

Thus, the fluid pressure in pipe 31 is an indirect measurement of this variable which is utilized as a readjustment index in control of the regulation of the supply of bagasse as a fuel to the combustion process. The basic control index is the fluid pressure of pipe 12 which calls for bagasse as a fuel and air flow to the stoker on which the bagasse is burned, in parallel. The fluid pressure in pipe 31 readjusts that control on the regulator for the bagasse fuel until the basic demand is satisfied.

The control system for the regulation of the individual supplies of air and the individual supplies of fuel may now be considered complete from, and by, the control indices represented by the fluid pressures established in

pipes

3, 20, 21, 22 and 23. The fluid pressures established by the transmitters responsive to total steam flow and total air flow are broken down by the control system, including

relays

26 and 30, into fluid pressures indirectly representative of variables controlled by the regulators of the individual supplies of fuel and air to the combustion process.

While I have chosen to illustrate and describe one preferred embodiment of my invention, it will be appreciated that the invention is not thus limited.

What I claim as new, and desire to secure by Letters Patent of the United States, is:

1. A system for controlling combustion in a steam generator including, fluid pressure actuated regulators for adjusting the magnitude of air and two different fuels of the combustion respectively, a first transmitter establish ing a fluid pressure in accordance with the pressure of the steam generated, a second transmitter directly responsive to total air flow and establishing an output fluid pressure representative of it, a third transmitter directly responsive to the portion of the total air flow combining with a first of the fuels and establishing an output fluid pressure representative of it, a first subtracting relay responsive to the fluid pressures of the second and third transmitters to establish a fluid pressure output proportional to air available for combustion of a second of the fuels, and means for applying the fluid pressures of the first transmitter and the second transmitter and the first subtracting relay to the regulators to effect positioning of said regulators in accordance with the magnitude of said fluid pressures.

2. The system of claim 1 including, a fourth transmitter directly responsive to the fuel flow of the second fuel and establishing an output fluid pressure representative of it, and a first balancing relay responsive to the outputs of the fourth transmitter and the first subtracting relay to establish a fluid pressure output for that regula tor controlling the flow of the second fuel.

3. The system of claim 2 including, a fifth transmitter directly responsive to total steam flow and establishing an output fluid pressure representative of it, a second subtracting relay responsive to the outputs of the fifth transmitter and the first subtracting relay to establish a fluid pressure output representative of that portion of the steam resulting from combustion of the first fuel, and a second balancing relay responsive to the outputs of the first transmitter and the second subtracting relay to establish an output fluid pressure for regulation of the flow of the first fuel.

4. The system of claim 3 including, a third subtracting relay responsive to the outputs of the first and third transmitters to establish a fluid pressure output for regulation of the combustion air for the second fuel.

5. The system of claim 4 including, a third balancing relay responsive to the outputs of the first and third transmitters to establish a fluid pressure output for regulation of the combustion air for the first fuel.

6. A system for controlling combustion in a steam generator burning bagasse on a stoker and natural gas in a burner including, transmitters directly responsive to steam pressure, air flow to the stoker, total air flow, total steam flow and flow of gas and establishing fluid pressure outputs representative of these measured items, regulators for controlling the amounts of each fuel supplied for combusion and the amounts of air supplied for their combustion, a first and second relay conjointly receptive to the outputs of the transmitters responsive to steam pressure and air flow to the stoker and establishing output pressures for the positioning of separate regulators for air flow for combustion of each of the fuels, a third relay responsive to the outputs of the transmitters responsive to stoker air flow and total air flow to establish an output pressure representative of air for combustion for the gas and steam resulting from its combustion, a fourth relay responsive to the outputs of the transmitter responsive to gas flow and the third relay to establish an output fluid pressure for the positioning of the gas regulator, a fifth relay responsive to the outputs of the transmitter responsive to steam flow and the third relay to establish an output fluid pressure representative of steam resulting from combustion of bagasse, and a sixth relay respon sive to the outputs of the fifth relay and the transmitter responsive to stoker air flow to establish an output fluid pressure for the regulation of the amount of bagasse.

7. In a combustion control system for multiple fuels, the combination comprising a first transmitter responsive to total air flow and establishing an output fluid pressure representative of it, a second transmitter responsive to the portion of the total air flow combining with a first of the fuels and establishing an output fluid pressure representative of it, a subtracting relay responsive to the fluid pressures established by said first and second transmitters to establish a fluid pressure output proportional to air available for combustion of a second of the fuels, and a fluid pressure actuated regulator responsive to the output pressure of said subtracting relay for adjusting the flow of said second fuel.

8. A combustion control system for multiple fuels including, a transmitter establishing a fluid pressure in accordance with demand on the combustion system, a transmitter for establishing a fluid pressure in accordance with total air for combustion, a transmitter for establishing a fluid pressure in accordance with air for a first fuel of the combustion, a relay receiving the fluid pressure of the transmitter responsive to total air and the fluid pressure of the transmitter responsive to the air for the first fuel to produce a fluid pressure output proportional to e air available for combustion of a second of the fuels, means responsive to the fluid pressure established by the demand transmitter for regulating the air supply to the first and second fuels, and means responsive to the fluid pressure established by the relay for regulating the supply of the second fuel.

References Cited in the file of this patent UNITED STATES PATENTS 2,143,820 Payn Jan. 10, 1939 2,459,689 Dickey et a1. Jan. 18, 1949 FOREIGN PATENTS 581,374 Germany July 26, 1933