US3250259A

US3250259A - Method and apparatus for controlling rate of temperature changes of heat generators during startup and shutdown

Info

Publication number: US3250259A
Application number: US289612A
Authority: US
Inventors: Profos Paul
Original assignee: Sulzer AG
Current assignee: Sulzer AG
Priority date: 1959-08-19
Filing date: 1963-06-21
Publication date: 1966-05-10
Anticipated expiration: 1983-05-10

Description

P. PRO FOS 3,250,259 METHOD AND APPARATUS FOR CONTROLLING RATE OF TEMPERATURE May 10, 1966 ND SHUTDOWN 4 SheetsSheet l CHANGES OF HEAT GENERATORS DURING STARTUP A Original Filed Aug. 1

INVENTOR Poul Profos t'r' zkH'ORNEYS May 10,

Original 1966 P. PROFOS 3,250,259

METHOD AND APPARATUS FOR CONTROLLING RATE OF TEMPERATURE CHANGES OF HEAT GENERATORS DURING STARTUP AND SHUTDOWN Filed Aug. 19, 1959 4 Sheets-Sheet 2 FIG. 2

\ T max.

[Kl/[.1 11/11/1211 ZZ/[Z 4444/41/11! [/1 1 (dT/dHmax.

- (dT/dflmin.

INVENTOR BY Paul Profos GWIWFM ATTOR N EYS May 10, 1966 P. PROFOS 3,250,259

METHOD AND APPARATUS FOR CONTROLLING RATE OF TEMPERATURE CHANGES OF HEAT GENERATORS DURING STARTUP AND SHUTDOWN Original Filed Aug. 19, 1959 4 Sheets-Sheet 3 FIG.3.

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INVENTOR Paul P rofos BY tzfdzw ATTORNEYS May 10, 1966 P. PROFOS 3,250,259

METHOD AND APPARATUS FOR CONTROLLING RATE OF TEMPERATURE CHANGES OF HEAT GENERATORS DURING STARTUP AND SHUTDOWN Original Filed Aug. 19, 1959 4 Sheets-Sheet 4 Mil-um mul 0 I06 ltllln V g! n r 11' I05 INVENTOR BY Poul Profos W W akaa j M1 41. I ATTORNEYS Patented May It), 1966 METHOD AND APPARATUS FOR CONTROLLING RATE ()F TEMPERATURE CHANGES OF HEAT GENERATORS DURING STARTUP AND SHUT. DOWN Paul Profos, Winterthur, Switzerland, assignor to Sulz er Brothers Limited, Wintcrthur, Switzerland, a Swiss company Original application Aug. 19, 1959, Ser. No. 834,683, now Patent No. 3,102,513, dated Sept. 3, 1963. Divided and this application June 21, 1963, Ser. No. 289,612 Claims priority, appiication Switzerland Sept. 4, 1958 17 Claims. (Cl. 122-406) This application is a division of my application entitled Method and Apparatus for Controlling Rate of Temperature Changes of Heat Generators During Startup and Shutdown, Serial No. 834,683, filed August 19, 1959, now Patent No. 3,102,513, which is assigned to the same assignee as the present invention.

This invention relates to apparatus for controlling the rate of temperature change in different sections of heat transfer or exchange systems during startup and shutdown, particularly heat transfer or exchange systems having wall parts bathed by a flowing medium the temperature of which varies and which serves for heating and for cooling different parts of the heat transfer system.

When starting up steam generators and, especially, when shutting them down, it is known to allow a cooling medium to flow through the tube system or at least through a part thereof, in order to control the cooling of the parts heated during operation, more especially those parts in the radiation zone, for the purpose of protecting the material composing those parts and to carry off the heat radiated from the heated chamber walls in the radiation zone, which radiation continues to act on those parts after the extinction of the tire. In the startup of an ordinary steam generator the amount of water being circulated is customarily adjusted as a function of a temperature, usually a temperature measured at the output end of the evaporating section of the boiler. Consequently the amount of working substance flowing through those portions of the boiler downstream of the evaporator is not adjusted to the variation in time rate of temperature change occurring in those downstream heating surfaces. In accordance with the invention such surfaces are protected by the provision of suitable coolant flow irrespective of the main control of circulating water. Moreover the invention permits accelleration of the startup process by control of the rate of flow of working substance over such downstream surfaces at values corresponding or nearly corresponding to the maximum time rate of change of temperature which can be tolerated by those surfaces.

Apparatus according to the invention effects controlled discharge of a fluid medium from the tube system to be protected both upstream and downstream of a particular part thereof, which part may constitute a wall lining of the boiler, whereby the rate of temperature change of that particular part of the tube system is controlled by varying the rate of discharge of the medium both upstream and downstream of the part according to the temperature T and/or the time rate of change of temperature of dl /dt, which quantity is measured at a predetermined location in that part of the tube system. The discharge is so effected that the quantity remains within predetermined positive or negative limits.

Heat exchange apparatus constructed in accordance with this invention comprises a main channel forming a part of the tube system in a heat transmission installation. This main channel is bounded at least in part by a heat exchange surface which is exposed to a variable source of heat, such as a furnace, exterior to this main channel. The apparatus further comprises means to drive a heat exchange medium through the main channel. A by-pass channel is coupled across a section of the main channel including the heat exchange surface. The apparatus further comprises measuring means to measure the time rate of change of temperature at a point on the heat exchange surface and means responsive to the measured time rate of change of temperature for regulating the flow of the heat absorbing medium through the main and bypass channels so as to maintain the time rate of change of temperature of the heat exchange surface within predetermined positive and negative limits.

Exemplary embodiments of the invention are illustrated diagrammatically in the drawing in which:

FIG. 1 shows an installation for the exchange of heat with a by-pass;

FIG. 2 is a graph showing the curves of the temperature during startup and shutdown of a typical heat generator, and showing the desired limiting values of the rate of change of temperatures; and

FIGS. 3 and 4 show the regulating device usable in the apparatus of FIG. 1.

In the graph shown in FIG. 2 the temperature T of the surface .12 heat exchange surface comprising series-connected tube sections 36-, 37 and 38 of FIG. 1 is plotted against the time t. Starting from the operating temperature T the temperature curve 28 drops as cooling progresses. The slope of the curve 28 at each point thereof is an indication of the instantaneous rate of change of temperature (dT/dt). Owing to the nature of the material of which

heat exchange surface

36, 37, 38 is made, and other factors, a certain value of (dT/dt) must not be exceeded. In FIG. 2 the

boundary lines

29 and 30 are for (dT/dt) maximum and minimum; in consequence the inclination of the curve tangents must lie between these limits. A greater rise will give too abnupt heating and a steeper drop a too abrupt cooling of the material. Both are injurious, especially when the

heat exchange surface

36, 37,38 consists of temperature sensitive steel. The

boundary lines

29 and 30 may have the same or ditferent angles of inclination to the horizontal.

The temperature curve 28, FIG. 2, which constitutes only an example, first drops steeply thereafter even rising somewhat. This may occur when the hot walls of the furnace chamber effect a more intensive radiation of heat in the

heat exchange surface

36, 37, 38 upon the reduction in the rate of How of working substance through that heat exchange surface.

The curve 31 shows the variation of temperature with time when the installation of FIG. 1 is started up. The slope of the curve 31 should not exceed the limits indicated by the

lines

29, 30.

Referring now to FIG. 1, heat exchange apparatus constructed in accordance with the present invention comprises a tube system, consisting of the

sections

36, 37, 38, provided in the housing 35 of a heat exchanger. The tube system 36 to 38 is subjected to the flow of a gaseous medium, for example, which enters and leaves through the

connections

39, 42. A liquid medium for example flows through the tube system 36 to 38 and is supplied by means of the pump 43. When the valves 46,

47, 48, are opened, the medium flows through the

parts

37 and 38 and through the outlet line 49 to the consumer network.

The outlet 51 is provided between the

sections

36 and 37 while between the

sections

37 and 38 there is provided an outlet 52 with a constriction 50 limiting the maximum flow therethrough.

' In the section 36 there are provided a throttle valve 46, a measuring device 53 for the temperature T and separately, a chronometer 53a. The bypass 54 connects the

lines

44 and 51, and can be regulated by means of temperature measuring device 53 is read periodically at the end of a certain interval of time read off from the chronometer 53a.

The tubing section 37 is likewise provided with a throttle valve 47 and bypass 56 with a valve 57. The valves 47 and 57 are adjusted by a program regulating device 58. The drum 58 is driven by the electric motor 59 and has on its wall two contact cams 60 and 60a, which cooperate with the

contact bars

61 and 61a. The valves 47 and 57 are connected to the

contact bars

61, 61a. On rotation of the drum 58 the points of contact between the contact cam 60 and the contact bar 61 and between cam 60a and bar 61 shift. According to the magnitude of the change of effective resistance of the

contact bars

61, 61a in circuit, when the contact point moves upward, the valves 47, 57 are operated. By changing the contact cams 60, 60a on the drum 58 the valves 47, 57 may be adjusted in accordance with a different program. Moreover the motor 59 may be controlled, for example, by the temperature of the gas flowing through the housing 35.

The section 38 can be short circuited by means of the bypass 62 with the valve 63. The measuring device 64 measures the rate of change of temperature (dT/dt) and passes a signal to the regulator 65. By way of the

signal lines

66 and 67 the regulator 65 controls the

valves

48 and 63. The consumer network is disconnected from the tube system 36 to 38 by means of the Valve 68 during the starting and stopping period. The circulation of cooling medium is, however, continued during startup and shutdown notwithstanding closure of the valve 68, as by v the opening of a valve 49' in a bypass line 49".

FIG. 3 illustrates one

form which'the apparatus

64 and 65 of FIG. 1 may take for control of the

valves

48 and 63 in FIG. 1. In FIG. 3 a measuring tube 72 is fastened at 71 and bathes in the medium whose rate of change of temperature is to be measured. The tube 72 has an eccentric bore 73 which may be equally well disposed eccentrically on the inside instead of on the outside of the bent tube. The tube loop 74 is embraced by the clamp 75, which is connected to the measuring spring 76. The movement of the loop 74 is transmitted by the spring 76 to the bell 77 and by the admission and discharge of pressure oil by means of the lines 70 is converted into a pressure signal which acts on the slide 78.

The required value for the rate of change of temperature is given by the initial tension of the spring 79. The tension of the spring 79 can be altered by means of the hand Wheel 81. If the temperature gradient does not correspond to the required value, the servo-motor piston 82 moves, and in the first instance operates the valve 63, FIG. 1, by way of the angle lever 83. If the valve 63 is nearly open, the horizontal arm or" the angle lever 83 begins to press the push rod 84 down against the action of the compression spring 85 and thus close the valve 48, FIG. 1. The elements 7277 of FIG. 3 measure dT/dt in view of the eccentric location of the bore 73 in tube 72. The Walls of the tube 72 are therefore of non-uniform thickness and respond with unequal speed to temperature changes. In consequence the bending of the tube varies and this constitutes a measure of the rate of change of temperature in the medium to which the tube 72 is exposed.

The pressure fluid for the servo-motor 82 is supplied at the supply line 86 under pressure, while the discharge is effected from the container 87, the overflow of which determines the regulating pressure. The apparatus of FIG. 3 thus constitutes a servo-mechanism, employing the energy from the source (not shown) which supplies hydraulic fluid under pressure to the line 86, to adjust the

valves

48 and 63 of FIG. 1 in accordance with the time rate of change of temperature (measured by the 4 tube 63) and in accordance with the setting of hand wheel 81.

If the valve 63 is used for other purposes the piston 82 can move freely by the opening of the valve 88, irrespectively of the position of the measuring tube 72.

FIG. 4 shows a measuring device 91 for measuring the rate of change of temperature using electricatl means in conjunction with a length of tube 92 through which the medium flows. The said length of tube 92 has a thickened part 93 and a thinner part 94, each provided with a

thermocouple

95, 96. The

thermocouples

95, 96 are connected in series. The difference voltage corresponding to the rate of change of temperature is amplified in the amplifier 97 and passed to a fixed coil 98. In the coil 98 a permanent magnet 99 is disposed to be slidable against a compression spring connected to .the slide 101. The latter controls the servo-motor piston 102, from which by way of the two-armed lever 103 the valve 104 is operated and from which further by way of the cam 105 the valve 106 is operated. The difference in temperatures to which the

thermocouples

95 and 96 are exposed is a measure of the rate of change of temperature because of the unlike heat capacity of the tube sections 93 and 94 of unlike thickness. Upon a change of temperature in the medium flowing through pipe 92, this change affects thermocouple 96 sooner than it does thermocouple 95. The greater the difference in temperatures between 95 and 96 the greater the rate of change of temperature.

Valves

104 and 106 do not completely open or close because variation in the opening of these valves affects the flow through line 92. This variation in flow is perceived by the

thermocouples

95 and 96 which provide a feedback signal at slide 101 and control piston 102.

The valve 104 may in addition also be used for other purposes in the operating phase of startup and shutdown. If the lever 107 is lifted, the slide 108 opens the pressure oil admission for the servo-

motor pistons

109, 110, 111, 112 which move against the action of the compression springs. In consequence, the following occurs. The admission of pressure oil to the servo-motor 102 is stopped by closing of the valve 113. In addition, the piston 102 becomes freely movable by the opening of the valve 114 At the same time, the two-armed lever 115 receives a fixed pivot point 116, in view of the fact that the hollow piston 110 is pressed against the stop 117, and the piston 118 against the piston 110. The valve 104 can now be operated by the supplementary control 119 instead of by the piston 102.

By the operation of the servo-motor 112 the valve 120 preceding the throttle element 106 is closed. Conversely, the valve 120 could be installed in a bypass to the valve 106 and be opened by the movement of the servo-motor piston 112.

While the invention has been described in terms of a number of preferred embodiments, it will be understood that the invention is not limited thereto and that various variations are possible Within the spirit and scope of the invention as defined in the following claims.

I claim:

1. A process for starting up or shutting down a heat exchanger including a main fluid medium flow channel 2. A process for starting up or shutting down a heat exchanger including a main fluid medium flow channel having a rate of temperature change-sensitive boundary surface and a bypass channel connected into said main channel upstream and downstream of said surface to provide a channel in parallel therewith, said process comprising the steps of measuring the time rate of change of temperature of said surface, and varying in opposite senses the relative rates of flow in said main and parallel channels upon transgression by said rate of a limiting value to increase the flow of fluid medium through said main channel when said rate of change of temperature exceeds an upper limit.

3. A process for starting up or shutting down a heat exchanger including a main fluid medium flow channel having a rate of temperature change-sensitive boundary surface and a bypass channel connected into said main channel upstream and downstream of said surface to provide a channel in parallel therewith, said process comprising the steps of measuring the time rate of change of temperature of said surface, and varying in opposite senses the relative rates of flow in said main and parallel channels upon transgression by said rate of a limiting value to reduce the flow of fluid medium through said main channel when said rate of change of temperature falls below a lower limit.

4. Heat exchange apparatus comprising a main channel bounded at least in part by a heat exchange surface, means to drive a heat exchange medium through said channel, a bypass channel coupled to said main channel in parallel with at least a portion of said heat exchange surface, means to measure the time rate of change of temperature at a point on said heat exchange surface, and means responsive to said measured time rate of change of temperature for regulating the flow of said heat absorbing medium through said main and bypass channels so as to maintain said time rate of change of temperature within predetermined positive and negative limits.

5. Heat exchange apparatus comprising a main channel bounded at least in part by a rate of temperature change-sensitive heat exchange surface, means to drive a fluid through said channel, a bypass channel connecting into said main channel upstream and downstream of said surface whereby two channels are provided in parallel, flow control means in one of said parallel channels, means to measure the time rate of change of temperature of said surface, and means responsive to transgression of a limiting value by said rate to adjust said flow control means.

6. Heat exchange apparatus comprising a main channel bounded at least in part by a rate of temperature changesensitive heat exchange surface, means to drive a fluid through said channel, a bypass channel connecting into said main channel upstream and downstream of said surface whereby two channels are provided in parallel, flow control means in one of said parallel channels, means to measure the time rate of change of temperature of said surface, and means responsive to transgression of a limiting value by said rate to adjust said flow control means to increase the flow of fluid through said main channel when said rate exceeds an upper limit.

7. Heat exchange apparatus comprising a main channel bounded at least in part by a rate of temperature changesensitive heat exchange surface, means to drive a fluid through said channel, a bypass channel connecting into said main channel upstream and downstream of said surface whereby two channels are provided in parallel, flow control means in one of said parallel channels, means to measure the time rate of change of temperature of said surface, and means responsive to transgression of a limiting value by said rate to adjust said flow control means to reduce the flow of fluid through said main channel when said rate declines below a lower limit.

8. Heat exchange apparatus comprising a main channel bounded at least in part by a rate of temperature changesensitive heat exchange surface, means to drive a heatabsorptive fluid through said channel, a bypass channel connected into said main channel upstream and downstream of said surface, flow control means in said bypass channel, means to measure the time rate of change of temperature of said surface, and means responsive to transgression of a limiting value by said rate to adjust said flow control means.

9. Heat exchange apparatus comprising a main channel bounded at least in part by a rate of temperature change-sensitive heat exchange surface, means to drive a heat-absorptive fluid through said channel, a bypass channel connected into said main channel upstream and downstream of said surface, flow control means in said bypass channel, means to measure the time rate of change of temperature of said surface, and means responsive to transgression of a limiting value by said rate to adjust said flow control means to reduce the flow of fluid through said bypass channel when said rate exceeds an upper limit.

10. Heat exchange apparatus comprising a main channel bounded at least in part by a rate of temperature change-sensitive heat exchange surface, means to drive a heat-absorptive fluid through said channel, a bypass channel connected into said main channel upstream and downstream of said surface, flow control means in said bypass channel, means to measure the time rate of change of temperature of said surface, and means responsive to transgression of a limiting value by said rate to adjust said flow control means to increase the flow of fluid through said bypass channel when said rate declines below a lower limit.

11. Heat exchange apparatus comprising a main channel bounded at least in part by a rate of temperature change-sensitive heat exchange surface, means to drive a fluid through said channel, a bypass channel connecting into said main channel upstream and downstream of said surface whereby two channels are provided in parallel, separate flow control means in each of said channels, means to measure the time rate of change of temperature of said surface, and means responsive to transgression of a limiting value by said rate to adjust said separate flow control means in opposite senses.

12. Heat exchange apparatus comprising a main channel bounded at least in part by a rate of temperature change-sensitive heat exchange surface, means to drive a fluid through said channel, a bypass channel connecting into said main channel upstream and downstream of said surface whereby two channels are provided in parallel, separate flow control means in each of said channels, means to measure the time rate of change of temperature of said surface, and means responsive to transgression of a limiting value by said rate to adjust said separate flow control means in opposite senses to increase the flow of fluid through said main channel when said rate exceeds an upper limit.

13. Heat exchange apparatus comprising a main channel bounded at least in part by a rate of temperature change-sensitive heat exchange surface, means to drive a fluid through said channel, a bypass channel connecting into said main channel upstream and downstream of said surface whereby two channels are provided in parallel, separate flow control means in each of said channels, means to measure the time rate of change of temperature of said surface, and means responsive to transgression of a limiting value by said rate to adjust said separate flow control means in opposite senses to reduce the flow of fluid through said main channel when said rate declines below a lower limit.

14. Heat exchange apparatus comprising a main channel bounded at least in part by a rate oftem-perature change-sensitive heat exchange surface, means to drive a fluid through said channel, a bypass channel connecting into said main channel upstream and downstream of said surface whereby two channels are provided in parallel, flow control means in said main channel intermediate the intersections therewith of said bypass channel, means to measure the time rate of change of temperature of said surface, and means responsive to said measuring means to adjust said flow regulating means to maintain said rate between predetermined positive and negative limits.

15. Heat exchange apparatus comprising a main channel bounded at least in part by a multi-sectioned heat exchange surface, means to drive a heat exchange medium through said channel, a bypass channel coupled to said main channel in parallel with at least two sections of said heat exchange surface, a discharge conduit connecting at one of its ends into said main channel at the junction of two sections of said heat exchange surface which are in parallel with said bypass channel and connecting at its other end in to said bypass channel at a point intermediate the extremities of said bypass channel, means to measure the time rate 'of change of temperature at a point on one section of said heat exchange surface which is coupled in parallel with said bypass channel, and means responsive to said measured time rate of change of temperature for regulating the flow of said heat absorbing medium through said one section of said main channel and through the bypass channel in parallel with said one section so as to maintain said time rate of change of temperature within predetermined positive and negative limits.

16. Heat exchange'apparatus according to claim- 15, further comprising means for regulating the flow of said heat absorbing medium through a section of said main channel other than said one section and through the bypass channel in parallel with said other section so as to regulate the heating and cooling of said other section in a predetermined manner, the flow of said heat absorbing 'medium through any one section of said main channel being substantially independent of flow through other sections thereof.

17. Heat exchange apparatus comprising a main channel bounded at least in part by a 'multi-sectioned heat exchange surface, means to drive a heat exchange medium through said channel, a multi-sectioned bypass channel, remote from said source of heat, coupled to said main channel in parallel with a like number of sections of said tion of two sections of said main channel and the junction of two sections of said bypass channel, a valve in each section of said main channel and in each section of said bypass channel upstream and downstream, in the sense of flow of said medium through said channels, of each of said discharge conduits, program controlled means operatively associated with. the valve in a first section of said main channel and the valve in the parallel section of said bypass channel for controlling the flow of medium through. said first section of said main channel and said parallel section of said bypass channel, means to measure the time rate of change of temperature at a point on a second section of said heat exchange surface which is coupled in parallel with'a second section of said bypass channel, and control means operatively associated with the valve in said second section of said main channel'and the valve in the parallel section of said bypass channel, said control meansbeing responsive to said measured time rate of change of temperature so as to regulate flow of heat absorbing mediumthrough said second section of said main and bypass channels, independently of flow through said first sections thereof, so as to maintain said time rate of change of temperature Within predetermined positiveand negative limits.

References Cited by the Examiner UNITED STATES PATENTS 3,102,513 9/1963 Profos 122-406 JAMES W. WESTHAVER, Primary Examiner.

KENNETH W. SPRAGUE, Examiner.

FREDERICK L. MATTESON, JR., Assistant Examiner.

Claims

1. A PROCESS FOR STARTING UP OR SHUTTING DOWN A HEAT EXCHANGER INCLUDING A MAIN FLUID MEDIUM FLOW CHANNEL HAVING A RATE OF TEMPERATURE CHANGE-SENSITIVE BOUNDARY SURFACE AND A BYPASS CHANNEL CONNECTION INTO SAID MAIN CHANNEL UPSTREAM AND DOWNSTREAM OF SAID SURFACE TO PROVIDE A CHANNEL IN PARALLEL THEREWITH, SAID PROCESS COMPRISING THE STEPS OF MEASURING THE TIME RATE OF CHANGE OF TEMPERATURE OF SAID SURFACE, AND VARYING IN OPPOSITE SENSED THE RELATIVE RATES OF FLOW IN SAID MAIN AND PARALLEL CHANNELS UPON TRANSGRESSION BY SAID RATE OF A LIMITING VALUE.