US1897845A - Control system - Google Patents

Description

Feb. 14, 1933. HILGERS 1,897,845

CONTROL SYSTEM Filed Sept. 16, 1930 Inventor: nine Hilgers,

His Attorney.

Patented Feb. 14, 1933 UNITED STATES PATENT, OFFICE ELECTRIC COMPANY, A CORPORATION OF NEW YORK CONTROL SYSTEM Application filed September 16, 1930, Serial No. 482,245, and in Germany November 9, 1929.

In the regulation or control of factors of a flowing fluid which vary as the result of variations in the rate of flow or independently through some external cause, it is often true that a factor other than the one which it is desirable to control is the first to vary, and variations in the factor to be controlled may be anticipated or checked sooner if the actual regulation of the factor which is to be controlled is accomplished by means sensitive to variations in another factor.

My invention relates toan improved control system wherein this fact is made use of to accomplish regulation of a factor varying with operation of an apparatus.

As an example, but in no wise a limitation, I have chosen to illustrate and describe the control of the temperature of steam to a turbine. I

In modern steam power stations it is ad'- visable to use as high steam temperatures as possible for the thermal advantage to be gained and to keep down the moisture content of the steam in the low pressure stages of the turbine without the necessity of expensive and complicated intermediate re heating. The allowable temperature may be limited, however, by the strength and temperature-resisting properties of the mate- 80 rials of construction. Thus it is desirable to have the steam temperature lie between certain limits and serious damage might result if the temperature of the steam were allowed to exceed the predetermined maximum or minimum limits. These limits may be different for different installations.

If the load on the turbine were to decrease, the flow of steam would decrease, the pressure would rise and the temperature would rise due to the decreased velocity through the boiler superheater, and assuming a certain time lag before any change could be made in the rate of fuel supplied to the furnace. The temperature rise, however, will not occur or be felt at the turbine until a relative time interval has elapsed between the decrease in steam demand, the decrease in velocity through the superheater and the effect of this decrease in velocity revary fIOIlI other causes,

sulting in an increased temperature having been transmitted to the turbine.

Temperature of steam to a turbine may however, than change in demand; for instance, changes in the rate'of supply of fuel or air to the furnace. Also certain designs of superheaters have other than a straight line characteristic with rating; i. e., the total temperature of the steam in what is commonly called the convection type superheater, increases as the rate of steam generationincreases and in what is commonly called the radiant type of superheater the total temperature of the steam decreases as the rate of steam generation increases.

One object of my invention is to provide a control of temperature of the steam to a turbine, wherein the controller is positioned or actuated by variations in a factor or factors whose variations precede or tend to cause variations in the temperature.

A further object is to have the control action checked or modified by variations in the temperature. Still another object is to provide a control which may be actuated by either pressure variations or steam temperature variations, or both simultaneously, to the end that steam temperature is maintained at the desired value.

Other objects of the invention are in part obvious and in part will appear more in detail from the description hereinafter.

In the drawing, wherein like numerals of reference represent like objects, Fig. 1 is a. diagrammatic view of a system. embodying my invention, and,

Fig. is a similar view of a modification.

1 represents conventionally any suitable boiler having a drum 2-from the steam space of which a conduit 3 leads to superheater 4. 5 is a conduit through which the superheated steam passes from superheater 4 to turbine 11 of conventional design and shown only in part.

A heat exchanger 7 is connected by means of conduits 12 and 13 with the water system of boiler 1 in a manner such that due to temperature differences relatively hotter water will rise in heat exchanger-7 and pass through conduit 12 to drum 2 of boiler 1, being replaced in heat exchanger 7 by relatively cooler water/passing from the boiler through conduit 13.

A by-pass to conduit 5 comprises conduit 6, any suitable coils or passages in heat exchanger 7 and in suitable heat-,conducting relation with the water contained in heat exchanger 7, conduit 8, stop valve 9 and conduit 10.

In conduit 5, intermediate the points of connection of conduits 6 and lOis a regulating valve 14 positioned relative to its seat 14a by movement of the stem 15. The position of valve 14 relative to its seat 14m determines the percentage of the steam leaving superheater 4 through conduit '5, which will be by-passed through heat exchanger 7 Beyond the bypass there is connected to conduit 5, a pipe 29 leading to an expansible metal bellows 28 having a movable abutment 27 to which is rigidly connected rod 26 articulated to a floating lever 17 at pivot point 25.

Beyond the by-pass in conduit 5 is a thermometer well 24 containing a bulb 23, part of the'thermostatic system comprising the' bulb 23, the connecting capillary 22 and the expansible metal bellows 21, of a common type wherein changes in temperature at bulb 23 result in changes in pressure in the expansible metal bellows 2 1 through the medium of an expansible gas or by vapor tension principles, A movable abutment 20 of bellows 21 carries rigidly a rod 19 articulated to floating lever 17 at pivot point 18.

Intermediate pivot points 18 and 25 the lever 17 isconnected at pivot point 16 with the movable stem 15 of valve 14.

In Fig. 2, a nozzle 30 is inserted in conduit 5, creating from flow a pressure differential in conduits 29a and 29?), applied internally and externally to expansible metal bellows 28 to cause motion of'the rod 26. 1

The rod 19 of the temperature responsive device is articulated to lever 17 intermediate the pivot points 16 and 25.

Springs 19a and 260 form the calibrating media of the expansible metal bellows 21 and 28, bearing against the movable abutments 20 and 27.

In operation, assume that the load on turbine 11 has decreased, then the flow of steam through conduit 5 decreases, and assuming a time lag before any change in the rate of heat supply to the boiler occurs, the pressure in conduit 5 increases. This pressure increase transmitted through pipe 29 to expansible bellows 28 moves the abutment 27 downwardly against spring 260, carrying rigidly connected rod 26 downwardly. Lever 17 pivots about point 18 causing a downward movement of rod 15 tending to bring valve 14 closer to its seat 14a, resulting in a throttling of the flow through conduit 5 past valve 14 and a by-passing of some of the steam of conduit 5 through bypass 6, heat exchanger 7, and backto conduit 5 through conduit 10. The steam so The slowing down of the velocity of the steam through the .superheater will tend toward a higher steam temperature in conduit 5 approaching the by-pass, but with a certain portion of this higher temperature steam by-passed through the heat exchanger where its temperature will be lowered, the resultant temperature at the admission to the turbine will tend to remain constant. Actual temperature variations, however, to which bulb 23 is sensitive, will result in a change in pressure within the bellows 21, acting on the movable abutment-20 to move rod 19 upwardly or downwardly and causing lever 17 to pivot around point 25 and reposition stem 15 and valve 14 relative to the valve seat 14a to modify or check the action of control from pressure.

Thus a change in temperature caused by a change in rate of flow will be anticipated,

and the micrometer adjustment or checking action will be accomplished from any changes in temperature which may occur.

In Fig. 2 I have shown the arrangement of linkage and control means whereby the initial regulation or by-passing eifect is accomplished from a change in the rate of flow rather than from a change in the steam pressure. Here again, the modifying or checking action is accomplished from atemperature-responsive control.

Assuming the same condition, namely that the load on the turbine decreases, then the rate of flow of steam to the turbine decreases, causing a decrease in the differential pressure existing between connections 29a: and 29b to the end that movable abutment 27 will move upwardly, carrying with it rigidly connected rod 26 and lever 17 pivoted at 18 causing valve stem 15 to move downwardly so that valve 14 approaches its seat 14a and causes a by-pass of part of the steam If conversely the correction has been of too great an amount, then the opposite temperature effect is felt upon expansible bel lows 21, to the end that movable abutment moves upwardly, carrying with it rod 19 to the end that lever 17 pivoted at causes valve stem 15 to move upwardly and valve 14to move away from its seat 14a, thus decreasing the percentage of the total flow of steam which passes through the by-pass.

It is of course understood that the resistance to flow through the by-pass is greater bulb 23, capillary 22 and bellows than it would be through conduit 5 valve 14, so that normally with valve 14 wide open practically all of the flow of steam would be through valve 14. The flow through the by-pass is accomplished only by throttling down valve 14 and thus introducing a restriction to flow.

Assuming no change in steam demand of turbine 11, and correspondingly no change in flow through nozzle or past pressure connection 29, but a change in B. t. u. input at the boiler or some other reason for change in temperature of the steam flowing through conduit 5. Temperature-responsive system 21 of each of Figures 1 and 2 immediately act to position lever 17 around pivot 25 to the end that n so valve stem 15 is moved to so position valve 14 relative to valve seat 14a that a change will be made in the amount of steam bypassed through the heat exchanger-7.

It will be apparent that I have a control of the temperature of steam to a turbine, wherein a corrective measurevis introduced from a factor, for example steam pressure or steam flow, which would tend to cause a variation in the temperature after a certain time interval. I have a control sensitive to a variation in either" of two factors or to variations in both of them simultaneously in the same or opposite directions, to the end that one of the factors may be maintained at a desired value.

Obviously in illustrating and describing this one preferred embodiment of my invention, wherein the temperature of steam to a turbine is controlled, I am not limiting myself other than is disclosed in the claims 1n view of prior art.

It is apparent that in the operation of any apparatus having factors which vary in value with the operation, there will be possibly certain factors by whose variations other factors will be affected, and that by a control from variations in the first factor a change or variation in the second or depending factors can be anticipated or obviated.

What I claim as new and desire to secure by Letters Patent of the United States, 1s:

. 1. In combination, a vapor generator having a superheater, a conduit for the passage of superheated vapor therefrom, a bypast duit connecting the two pass to a portion of the conduit, fluid surrounding the by-pass in heat conducting relation with the vapor flowing therethrough, the fluid in thermal circulation with the vapor generator, a valve in the conduit between the exit and re-entrant points of the by-pass thereto, a pressure responsive device sensitive to vapor pressure beyond the by-pass and adapted to position the valve in a closing direction when the vapor pressure increases and in an opening direction when the vapor pressure decreases, and a temperature responsive device sensitive to vapor temperature beyond the bypass and adapted to position the valve independently of the pressure responsive device.

2. In combination, a vapor generator, vapor utilizing apparatus, a conduit connecting the two for vapor flow therethrough, a heat exchanger connected in the liquid circuit of said generator, a bypass connection to the conduit in heat conducting relation to the heat exchanger, a control valve in the conduit intermediate the exit and re-entrant points of connection of said by-pass, and a regulator for the Valve sensitive to variations in a factor of the vapor which is a function of the rate of operation of the vapor utilizing apparatus adapted on an increase in the rate of operation of said apparatus to operate said valve to decrease the amount of vapor and upon a decrease in the rate of operation of the apparatus to operate the valve to increase the amount of vapor by-passed through the heat exchanger and further responsive to variations in a factor of the va or which is a function of the operation o the vapor generator.

3. In combination, a vapor generator, vapor utilizing apparatus, a conduit connecting the two for vapor flow therethrough, a heat exchanger connected in the liquid circuit of said generator, a by-pass connection to the conduit in heat conducting relation to the heat exchanger, a control valve in the conduit intermediate the exit and re-entrant points of connection of said by-pass, and a regulator for the valve sensitive to variations in temperature of the vapor entering the apparatus and further sensitive to variations in a factor of the operation of the apparatus which factor upon change in the rate of operation of the apparatus will vary earlier than the vapor temperature and adapted upon an increase in the rate of o eration of said apparatus to operate said valve to decrease the amount of vapor and upon a decrease in the rate of operation of the apparatus to operate said valve to increase the amount of vapor by-passed through the heat exchanger.

4. In combination, vapor generating apparatus, vapor utilizing apparatus, a confor vapor flow therethrough, a heat exchanger connected in the liquid circuit of said generating apparatus, a by-pass connection to the conduit in heat conducting relation to the heat exchanger, a controlvalve in the conduit intermediate the exit and re-entrant points of connection of said by-pass, and a regulator for the valve sensitive to two factors conjointl eflective for positioning the valve, each 0 said factors varying with the operation of both the vapor generating apparatus and the vapor utilizing apparatus, said regulator adapted upon an increase in the rate of operation of said utilizing apparatus to decrease the amount of vapor by-passed and upon a de crease in the rate of operation of the utilizing apparatus to increase the amount of vapor by-passed through said heat exchanger. I

In witness whereof, I have hereunto set my hand this 29th day of August, 1930.

NINO HILGERS.

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