US3172266A

US3172266A - Automatic start-up devices for a steamelectric generating plant

Info

Publication number: US3172266A
Application number: US261177A
Authority: US
Inventors: Jr Charles Strohmeyer
Original assignee: Gilbert Associates Inc
Current assignee: Gilbert Associates Inc
Priority date: 1963-02-26
Filing date: 1963-02-26
Publication date: 1965-03-09
Anticipated expiration: 1982-03-09

Description

March 9, 1965 c. STROHMEYER, JR 3,172,266

AUTOMATIC START-UP DEVICES FOR A STEAM-ELECTRIC GENERATING PLANT Filed Feb. 26, 1963 2 Sheets-Sheet 1 STEAM GENERATOR 5 coususnou 9 i CONTROL WATER m STEAM our SYSTEM WATER LEVEL l3 I4 1. .2 l 3 REGENERATIVE FIXED OR RATE OFMETAL FEEDWATER 5E5??? EEQIG RQELER cm: CONTROLLER F lg. 3.

Fig.l.

I04u 78 o A 73 INVENTOR. CHARLES STROHMEYER ,JR.

IS ATTORNE March 9, 1965 c, STROHMEYER, JR 3,172,266

AUTOMATIC START-UP DEVICES FOR A STEAM-ELECTRIC GENERATING PLANT Filed Feb. 26, 1963 2 h hee 2 Fig. 2. INVENTOR CHARLES STROHMEYER,JR.

EXAM 66M his ATTORNEY United States Patent 3,172,266 AUTOIVIATIC START-UP DEVICES FOR A STEAM- ELECTRIC GENERATING PLANT Charles Strohrneyer, In, Wyomissing, ia, assignor to Gilbert Associates, Inc, Reading, Ya. Filed Feb. 26, 1963, Ser. No. 261,177 4 Claims. (Cl. 50-105) This invention is a continuation-in-part of patent application Serial No. 42,194, filed lune 7, 1960; Serial No. 81,187, filed January 6, 1961; and Serial No. 154,087, filed September 5, 1961, now abandoned.

This invention relates to devices and systems for improving the operating flexibility of steam-electric generating units including steam generator, turbine generator and auxiliary equipment.

An object of the invention is to provide a novel apparatus and a system which will reduce unit start-up time and costs, as well as provide the steam generator with capability to vary primary outlet steam temperature to control the rate of metal temperature rise within the turbine during startup.

A more specific object of the invention is to provide a simplified automatic control system for the steam generator during startup whereby the conventional automatic combustion control system is fed a fixed or programmed loading signal from the startup control system which is limited by a rate of metal temperature rise with respect to the strength or gain of the signal.

A further specific object of this invention is to provide a means for using the above mentioned control system with a steam generator having a throttling valve means located intermediately in the steam generator fluid circuits between the water inlet and superheated steam outlet, a flash tank, a flow controlled bypass conduit from an intermediate part of the steam generator through fluid circuit upstream of said throttling valve means which discharges to said flash tank after pressure reduction through said flow control means, conduit and flow control means connecting the separated steam spare of said flash tank with the steam generator intermediate fluid circuits downstream of said throttling valve means, a regenerative feedwater makeup cycle and a heat sump, means to selectively flow flash tank separated steam to said steam generator downstream circuits, regenerative feedwater makeup cycle and to said heat sump, and means to selectively flow flash tank separated liquid to said regenerative feedwater cycle and to said heat sump.

Other objects and advantages of the invention will become more apparent from a study of the following description taken with the accompanying drawings wherein:

FIG. 1 is a diagrammatic or schematic showing of a startup combustion control loading system wherein a fixed or programmed loading signal to the steam generator automatic combustion control system is over-ridden by measurement of rate of metal temperature rise in the steam generator or connected turbine driver;

FIG. 2 is a detailed application of the FIG. 1 control system;

FIG. 3 is a schematic showing of a steam generator startup fluid flow control system as described above in the further specific object of this invention; and

FIG. 4 is a schematic showing of the integrated steamelectric generating plant arrangement, including the startup combustion control loading system and the steam generator fluid control system.

General description of present invention In the specification below, the following control action descriptions apply:

Proportional control action.Position of final control element is linearly proportional to value of controlled variable;

Reset (integral) control action-Rate of motion of final control element is-linearly proportional to deviation of controlled variable from normal;

Rate (derivative) control action.Position of final control element is linearly proportional to rate of change of controlled variable.

FIG. 1 shows a startup combustion control loading system for a steam generator wherein a fixed or programmed loading signal to the steam generator automatic combustion control system for controlling firing rate, including fuel and air flow, is over-ridden by measurement of rate of metal temperature rise. The startup control system for the steam generator may consist of manually adjustable controller 1 which sends a fixed or programmed variable loading signal to the steam generator automatic combustion control system 4. Measurement of rate of metal temperature rise in controller 3 varies the signal from controller 3 to summing relay 2 which may decrease or increase, or alternately increase or decrease the loading signal from controller 1 on its way to combustion control system 4 to increase or decrease the steam generator firing rate so as to control steam generator outlet steam temperature in a way which will hold the rate of metal temperature rise within limit values established by settings in the rate of temperature rise controller 3. Rate of metal temperature rise may be measured at any critical steam generator part, as the superheater steam outlet header or any critical part of a turbine receiving steam from the steam generator, as the steam admission parts or turbine inner cylinder.

The above described system can be constructed from standard pneumatic or electric control components available from manufacturers of steam generator automatic combustion control systems.

FIG. 2 is a practical detailed application of the FIG. 1 startup combustion control loading system. The

box control systems

1, 2, 3 and 4 are shown by dot-dash lines. During startup when warming up the steam generator from a cold state, the superheater outlet steam header metal temperature causes thermocouple 46 embedded in the metal to generate an electrical voltage potential in thermocouple leads 47 and 47a which terminate in

cold reference junctions

48 and 48a. The cold reference junc tions are connected through

circuits

49 and 49a to a direct current receiver 50 as manufactured by the Bailey Meter Co., Class E3 shown in page 7 of their product specification E12-5, copyright by Bailey Meter Co., 1958, Form No. CEl2-5E printed June 1961. A 0 to 50 volt direct current output signal from the receiver 50 retransmitting slidewire is sent through circuit 51 to direct current operational amplifier rate action unit 52, as manufactured by the Bailey Meter Co., Part No. 66l13001 as shown on page 3 of their product specification E933, copyright by Bailey Meter Co. 1960, Form No. CE93-3 printed January 1960. The 0 to 5 volt direct current output from rate action unit 52 is transmitted through circuit 53 to direct current operational amplifier proportional action unit 54 as manufactured by the Bailey Meter Co., Part No. 6611297-1 as shown on page 3 of their product specification E933 referenced above. The O to 20 volt direct current output signal from action unit 54 is transmitted through circuit 55 to direct current receiver 56 as manufactured by the Bailey Meter Co., Class E7 as shown on page 7 of their product specification E12-5 referenced above.

Receiver 56 output is in the form of mechanical positioning through rotating lever arm 56a which is connected to a similar lever arm 58a through linkage 57. Lever arm 56a drives lever arm 58a a relative amount. Lever arm Patented Mar. 9, 1965 a 58a acts on the pneumatic transmitter 58 so as to regulate the control air pressure in conduit 59. Transmitter 58 is as manufactured by the Bailey Meter Co., Class P as shown on page of their product specification E12-5 referenced above.

Thus, the control air pressure in conduit 59 is a function of metal temperature change in superheater outlet steam header 45. As the rate of metal temperature rise increases, the pressure in conduit 59 will decrease to a minimum of 3 p.s.i.g. As the temperature in header 45 stabilizes so that there is no change, pressure in conduit 59 increases to a maximum of 27 p.s.i.g. The conduit 59 feeds through check valve 60 to conduit 59a. Conduit 61 bypasses check valve 60 and contains a needle valve 62 for throttling purposes. Flow through valve 62 is small compared with How through valve 69. Flow in conduit 61 is two directional.

Conduit 59a feeds to volume chamber 63 which is provided with a vent conduit 64 exhausting to atmosphere. Conduit 64 contains a needle valve 65 to permit only very small leakoif flows through the vent line 64. The

needle valves

62 and 65 in conjunction with check valve 60 pre vent rapid pressure decay in volume chamber 63 as a result of sudden pressure drops in conduit 59. The volume chamber also slows up pressure increase as a result of momentary pressure rise surges in conduit 59. In effect this arrangement stabilizes and averages air pressure for short periods of time in the volume chamber 63. The downstream conduit 66 connects to proportional plus reset computing relay 67 as manufactured by the Bailey Meter Company and as shown in FIG. 10 on page 4 of their product specification P99-3, copyright by Bailey Meter Co., 1956, Form No. CP99-3D, printed Mach 1960. Conduit 66 connects to the B chamber of relay 67. The A chamber is vented and the C and C1 connections are plugged. The A-B beam (not shown) is spring loaded to increase the control air output pressure from chamber D to conduit 63 as the pressure in chamber B through conduit 66 decreases below the balance loading of the spring, the output pressure from chamber D will integrate down to 3 p.s.i.g. minimum.

The A-B beam spring loading corresponds to the limit allowed for rate of metal temperature rise in superheater outlet steam header 45 before control action to steam generator firing rate is initiated from system controller 3. From operatin experience and observation of actual measured rate of temperature rise, the spring can be calibrated to control the process so that firing rate adjustment at system controller 1 will not cause the rate of metal temperature rise to exceed say 500 degrees F. per hour.

The block control system 4 is a segment of the overall combustion control system for the steam generator. Only those features used for control of fuel and air flow for startup are shown in elemental form as the specific form of the fuel and air feed mechanisms are not a part of this invention. Fuel oil firing is shown for illustrative purposes.

Control box 1 sends a signal to control box 4 through

conduits

73 and 78 which automatically controls the rate of fuel and air feed to steam generator furnace 95. As long as rate of metal temperature rise in header 45 does not exceed the limit of relay 67, there will be no adjustment to the control signal between 1 and 4 from temperature measurement. As rate of metal temperature rise in header 45 exceeds the limit in relay 67, control box 2, or relay 69 will reduce the strength of the control signal from control box 1 and reduce firing rate in control box 4 until the limit of relay 67 is restored.

Metal temperatures in thick walled structures for high pressure steam generators do not change rapidly in the superheat zones. Therefore, by applying corrective control action'before the physical maximum limit is reached, allows time for correction before damage occurs. The control limit in relay 67 should be set below the actual maximum physical allowable limit in header 45.

Control box 1 contains a manual loader 70 which has a control knob 70a which regulates the output air pressure in conduit 71 from 3 to 27 p.s.i.g. Air pressure is registered on scale 7%. Manual loader 70 is manufactured by the Bailey Meter Co., Type AS2300 and as shown in FIG. 6 on page 3 of product specification P992, copyright by Bailey Meter Company 1957, Form No. CP99-2B printed July 1960. Increases in air pressure from loader 70 increase firing rate in control box 4. Conduit 71 connects to remote adjustable computing relay 72 as manufactured by the Bailey Meter Co., Type No. AR8031A and as shown in FIGURE 4 on page 2 of product specification P99-9, copyright by Bailey Meter Company 1957, Form No. CP999A, printed August 1960. The control signal in the form of air pressure may pass through relay 72 proportionally without alteration of the proportional setting or the proportional setting may be programmed to change with time.

Program controller 75 as manufactured by the Bailey Meter Co., Class T and as shown on page 9 of their product specification E12-5 referenced above, is provided with a cam which can be shaped to rotate lever arm 75a with time. The speed of rotation of the cam can be lengthened by interrupting the power supply to the controller 75 drive unit at preset intervals using known power supply interrupting devices thereby adjusting the time constant suitable for various conditions of the steam generator from cold to hot startup.

Controller 75 through lever arm 75a and connecting link 76 to lever arm 77a controls the output air pressure from pneumatic transmitter 77 which is identical to item 58 above. The output air passes through conduit 74 to chamber L in relay 72 adjusting the proportion band setting and changing the output air pressure in conduit 73 with respect to the input air pressure in conduit 71. Thus, for any given loading signal in conduit 71 from loader 70, the output signal from relay 72 can be programmed to increase with time. As a substitute for

items

77 and 75, air pressure variations in conduit 74 can be controlled proportionate to steam flow variations to a steam consumer connected to the superheater outlet of the steam generator.

The output from relay 72 feeds through conduit 73 to proportional computing relay 69 as manufactured by the Bailey Meter Co. and as shown in FIG. 8 on page 4 of their product specification P99-3 referenced above. Conduit 73 feeds to item 69 chamber A and conduit 68 feeds to item 69 chamber B and thus item 69 performs the function of subtracting the conduit 68 significant air loading pressure from the conduit 73 significant air loading pressure. Item 69 can be considered as a summing relay where the increasing pressure in conduit 68 is functionally reverse to the increasing pressure in conduit 73.

The 3 to 27 p.s.i.g. air output signal from item 69 chamber D to conduit '78 feeds to combustion control system 4 and to three-way valve 79 which transfers master control of fuel and air flow to

controllers

1, 2 and 3 during startup. During normal operation, the control of fuel oil flow would be initiated through control air conduit 81 with the valve 79 rotated 90 degrees counter clockwise as shown. Valve 79 discharges to conduit which connects to positioning relay 82 as manufactured by the BaileyMeter Company and as shown in their product specification P99-5, copyright by Bailey Meter Co. 1957, Form No. CP995A, printed April 1960. Relay 82 feeds power air through conduit 33 to diaphragm air power operator 84 which opens or closes the fuel oil supply valve 85. Relay S2 is provided with a cam and mechanical position indicating linkage 105 to the valve 85 operator so that valve opening can be compensated in a way which will linearize flow quantity through the valve with respect to changes in conduit 80 control air pressure to the relay 82. Fuel oil flow will be approximately proportional to control air pressure in conduit 80. Thus,

control boxes

1, 2 and 3 regulate fuel feed to the steam generator.

The same control signal to valve positioner 82 may also be supplied in a similar fashion to the furnace combustion air flow controls, not shown, or air flow maybe controlled as shown in box 4. Fuel flow through valve 85 and conduit 86 passes through flow measuring orifice 87.

Conduits

88 and 89 on both sides of the orifice conduct fuel oil pressure to flow meter and transmitter 90. Flow measurement in the form of air pressure is transmitted from 90 through conduit 91 to proportioning and reset computing relay 92 as manufactured by the Bailey Meter Company and as shown in FIG. 10 on page 4 of their product specification P99-3 referenced above. Combustion air is fed through conduit 97 to burner windbox 96 which distributes air to fuel oil burner 100 through damper registers 102. Pressure drop from the windbox to the furnace is a function of flow. Pressure differential measurement is made by sensing and computing means 94 from the windbox 96 to the furnace 95 through

pressure conduits

98 and 99 respectively. Fuel flow measurement signal vs. air flow measurement signal through

conduits

91 and 93 are adjusted so that air flow is truly compared with fuel flow in relay 92 and the control air output signal through conduit 103 impulses the combustion air supply controller 104 to maintain the preset fuel-air ratio established in relay 92 by adjustment of damper 104a in air supply conduit 97. Such type of air flow control has been in standard use for many years.

In FIG. 2 electric power and air supplies to the various controllers have not been shown and are covered in the referenced product specifications. FIG. 2 shows the electric and pneumatic control circuits and their interrelation one with the others.

16. 3 shows a steam generator startup fluid flow control system which may be used in conjunction with the combustion control loading system shown in FIG. 1. In the flow control system of FIG. 3, the steam generator 5 has a throttling valve means 9 located intermediately in the main fluid flow circuit between the water inlet and main steam outlet. A bypass conduit from an intermediate location in the main flow circuit upstream of valve means 9 discharges to flash tank 6 after pressure reduction throughthrottling valve means 7. Steam from flash tank 6 may be returned through conduit and valve flow control means 8 to the'steam generator main flow circuit at some intermediate point downstream of valve means 9.

The flash tank is normally operated during startup at an intermediate pressure whose saturation temperature is substantially above the designed operating limit of any associated heat sump as heat sump and which intermediate pressure is substantially below that in the steam generator fluid circuits upstream of valve means 9, especially when first opening valve means 9.

When the valve means 8 is open, valve means or is throttling to a pressure not in excess of the flash tank 6 design pressure. For higher downstream pressures in the main flow circuit, valve means 8 is closed or flow from the main circuit downstream of system 9 to the flash tank is prevented by means of a check valve or other reverse flow preventer in conjunction with or as a substitute for valve means 8.

When the startup combustion control loading system of FIG. 1 is used for a steam generator having a fluid flow control system shown in FIG. 3, increasing firing rate will increase the enthalpy of the steam generator outlet steam as will as the amount of heat in the fluid discharging to the flash tank. Surplus flash tank heat may be discharged to a heat sump 10 as a condenser in the form of steam through flow control valve 12, or as liquid drains through flow control valve 14. Flash tank heat may be used in the regenerative feedwater cycle as steam through flow control valve 15, or as liquid drains through flow control valve 13. When the firing rate is in balance with the steam generator outlet steam flow 9 is shut and. the regenerative feedwater cycle flow requirements from the flash tank, there will be no flow through

control valves

12 and 14. Increasing the firing rate above the balanced condition is the means used for raising outlet steam temperature and superheater metal temperatures. Heat may be extracted from the drain flow from flash tank 6 before it is discharged to heat sump 10 through control valve 14 by means of a heat exchanger in the feedwater cycle (not shown) so that for any given heat input to the flash tank through flow control valve 7, the amount of drains to the heat sump 10 may be increased. Flow of fluid from the flash tank to the heat sump 1i) permits cooling of the fluid so that it may be passed through low temperature water purification equipment as a liquid before return to the steam generator circuits.

Pressure in the steam generator main flow circuit downstream of valve means 9 may be controlled to suit desired outlet steam conditions as described in patent applications Serial Nos. 42,194 and 81,187, filed June 7, 1960 and January 6, 1961, respectively. 7 FIG. 4 shows the integrated arrangement of a steamelectric generating plant including the startup combustion control loading system and the steam generator fluid control system. Outlet steam from steam generator 5 passes through outlet steam header 45, through conduit 17 and turbine steam admission valve 18 to turbine 19 where the energy of the fluid is converted to work to drive shaft 20 and connecting electric generator 21. Steam exhausts from turbine 19 through conduit 21 to heat sump condenser 10. Cooling water passing through conduit 32 condenses the steam. The condensed liquid collects in hotwell 22 and passes through conduit 23 to condensate pump 24 where the liquid is raised in pressure to the first working level. Pump 24 discharges through conduit 25, through heat exchanger 26, conduit 27 to the feedwater pump 28 which raises fluid pressure to the working level of steam generator 5. Pump 28 discharges through conduit 29, feedwater regulator valve 30, through heat exchanger 31 to conduit 16 which supplies feedwater to steam generator 5.

Other figure numbers are the same as shown in FIG. 3. Valve 7 controls fluid pressure in the upstream conduit to a value as preselected in pressure controller 33. Valve 8 is provided with motor operator 34. Valve 9 is provided with power operator 35 which is of the hydraulic type. Valve 12 is provided with pressure controller 36 which regulates upstream pressure to a preselected value which is the working pressure of the flash tank 6. As

firingrate in burner 160 is increased and surplus heat accumulates in flash tank 6 as a result of flow through valve 7, pressure rises in flash tank 6. The pressure increase opens valve 12 and dumps surplus steam to condenser 10. Valve 15 is provided with pressure controller 37 which regulates pressure in the downstream conduit and heat exchanger 31 shell. The preselected pressure in 37 regulates the feedwater temperature passing through conduit 16 to the steam generator inlet.

The flash tank 6 is provided with water level controller 38, which transmits a control signal to manual selective switch 39 which permits the signal to pass to either valve 13 or valve 14 operators or proportionally to both in a preselected ratio.

In this application the thermocouple 46 shown in FIG. 2 is located in a critical steam admission part of turbine 19, instead of the steam outlet header 45. Either location may be used for the thermocouple. Known selective means (not shown) may be provided to utilize the highest temperature of the two locations.

In starting up the steam generator, flow enters the steam generator through conduit 16 and passes through valve 7 to flash tank 6. Valve 9 is closed. Heat input from burner raises the temperature and enthalpy of the fluid in the steam generator. As steam is liberated at reduced pressure in flash tank 6, it passes through valve 8 to the superheating section of the steam generator 5 downstream of valve 9. Flash tank steam is initially used to bring turbine 19 up to speed and may apply some small amount of load on the turbine 19. Firing rate has been preselected in control element 1. The signal from 1 passes through conduit 73 to control element 2, through conduit 78 to the automatic combustion control component 4. The rate of firing preselected in element 1 is excessive to some moderate degree. The temperature of the steam will begin to rise. The temperature rise will be detected by thermocouple 46 in the turbine metal and control element 3. When the rate of metal temperature rise exceeds limits established in control element 3, control element 3 through conduit 68 adjusts the signal from element 1 as previously described to reduce the signal to element 4, thus reducing firing rate in burner 100. Air flow in conduit 97 is adjusted parallelly.

Thus firing rate in burner 109 is adjusted to control rate of metal temperature rise in turbine 19. The same may be made to apply with respect to rate of metal temperature rise of steam outlet header 45.

As the fiow of steam to the turbine is increased to the limit of flash tank capability, flow is transferred from valve 8 to valve 9. Pressure downstream of valve 9 is gradually increased to designed working level and the. startup combustion control loading system is disconnected from the automatic combustion control system in element 4 as shown in FIG. 2.

Thus it will be seen that I have provided efficient systems for improving the operating flexibility of steamelectric generating units having steam generator, turbine generator and auxiliary equipment, including a novel apparatus and system for reducing unit startup time and costs as Well as to provide the steam generator with capability to vary primary outlet steam temperature to control the rate of metal temperature rise or fall within the turbine during startup and shutdown, respectively; furthermore, I have provided a novel automatic control system especially for regulating the steam generator automatic combustion control system during unit startup; also, I have illustrated how this last mentioned control system may be used in conjunction with a steam generator having a startup fluid bypass control system.

While I have illustrated and described several embodiments of my invention, it will be understood that these are by way of illustration only, and that various changes and modifications may be made within the scope of the following claims.

I claim:

1. In a steam-electric generating plant comprising a steam generator having fluid conducting conduits including a feedwater inlet, a superheater steam outlet and heat absorption conduits disposed therebetween, an electric generator, a turbine drive connected to said electric generator, said turbine drive having fluid conducting conduits, a heat sump receiving exhaust steam from said turbine drive, fluid conducting conduits serially connecting said superheater steam outlet and said turbine drive, a combustion furnace as a source of heat input to said heat absorption conduits, a supply of fuel and air to said combustion furnace, a normal load carrying automatic combustion control system for regulation of said fuel and air supply including fuel and air supply flow control devices, said fluid conducting conduits being of metal and having a critical portion with respect to high temperature, said critical portion being external to the flow path of the products of combustion; the invention comprising a startup control system having means for integration with said normal automatic combustion control system and which is responsive to rate of metal temperature change of said critical portion of said fluid conducting conduits, said startup control system comprising means adapted to sense and measure metal temperature of said critical portion, means adapted to convert said measurement or" temperature to measurement of rate of temperature change, means for generating a constant control loading signal for regulating the said fuel and air supply flow control devices, limiting means in conjunction with said measurement of rate of temperature change which generates a variable output signal as said rate or" temperature change increases above a preset value, means for combining said limiting means output signal with said constant control signal to reduce fuel flow through said fuel flow control device as said rate of temperature change increases above said preset value to maintain said rate of metal temperature change of said critical portion below a critical value.

2. A startup control system as recited in claim 1 wherein means for generating a programmed control loading 7 signal substitutes for said means for generating a constant control loading signal.

3. A startup control system as recited in claim 2 Wherein said programmed control loading signal is programmed with time.

4. A startup control system as recited in claim 3 wherein said programmed control loading signal is programmed with turbine-generator load.

References Qited by the Examiner UNITED STATES PATENTS 2,962,860 12/60 vVintrode et a1. 236-l5 X 3,102,513 9/63 Profos l2240,6

FOREIGN PATENTS 2/59 Great Britain.

Claims

1. IN A STEAM-ELECTRIC GENERATING PLANT COMPRISING A STEAM GENERATOR HAVING FLUID CONDUCTING CONDUITS IN INCLUDING A FEEDWATER INLET, A SUPERHEAT STEAM OUTLET AND HEAT ABSORPTION CONDUITS DISPOSED THEREBETWEEN, AN ELECTRIC GENERATOR, A TURBINE DRIVE CONNECTED TO SAID ELECTRIC GENERATOR, SAID TURBINE DRIVE HAVING FLUID CONDUCTING CONDUITS, A HEAT SUMP RECEIVING EXHAUST STEAM FROM SAID TURBINE DRIVE, FLUID CONDUCTING CONDUITS SERIALLY CONNECTING SAID SUPERHEATER STREAM OUTLET AND SAID TURBINE DRIVE, A COMBUSTION FURNACE AS A SOURCE OF HEAT INPUT TO SAID HEAT ABSORPTION CONDUITS, A SUPPLY OF FUEL AND AIR TO SAID COMBUSTION FURNACE, A NORMAL LOAD CARRYING AUTOMATIC COMBUSTION CONTROL SYSTEM FOR REGULATION OF SAID FUEL AND AIR SUPPLY INCLUDING FUEL AND AIR SUPPLY FLOW CONTROL DEVICES, SAID FLUID CONDUCTING CONDUITS BEING OF METAL AND HAVING A CRITICAL PORTION WITH RESPECT TO HIGH TEMPERATURE, SAID CRITICAL PORTION BEING EXTERNAL TO THE FLOW PATH OF THE PRODUCTS OF COMBUSTION; THE INVENTION COMPRISING A STARTUP CONTROL SYSTEM HAVING MEANS FOR INTEGRATION WITH SAID NORMAL AUTOMATIC COMBUSTION CONTROL SYSTEM AND WHICH IS RESPONSIVE TO RATE OF METAL TEMPERATURE CHANGE OF SAID CRITICAL PORTION OF SAID FLUID CONDUCTING CONDUITS, SAID STARTUP CONTROL SYSTEM COMPRISING MEANS ADAPTED TO SENSE AND MEASURE METAL TEMPERATURE OF SAID CRITICAL PORTION, MEANS ADAPTED TO CONVERT SAID MEASUREMENT OF TEMPERATURE TO MEASUREMENT OF RATE OF TEMPERATURE CHANGE, MEANS FOR GENERATING CONSTANT CONTROL LOADING SIGNAL FOR REGULATING THE SAID FUEL AND AIR SUPPLY FLOW CONTROL DEVICES, LIMITING MEANS IN CONJUSTION WITH SAID MEASUREMENT OF RATE OF TEMPERATURE CHANGE WHICH GENERATES A VARIABLE OUTPUT SIGNAL AS SAID RATE OF TEMPERATURE CHANGE INCREASES ABOE A PRESET VALUE, MEANS FOR COMBINING SAID LIMIT MEANS OUTPUT SIGNAL WITH SAID CONSTANT CONTROL SIGNAL TO REDUCE FUEL FLOW THROUGH SAID FUEL FLOW CONTROL DEVICE AS SAID RATE OF TEMPERATURE CHANGE INCREASES ABOVE SAID PRESET VALUE TO MAINTAIN SAID RATE OF METAL TEMPERATURE CHANGE OF SAID CRITICAL PORTION BELOW A CRITICAL VALUE.