US3388553A - Control system for a turbogenerator and once-through steam generator plant - Google Patents

Description

2 Sheets-Sheet 1 June 18 1968 G. R. ANDERSON CONTROL SYSTEM FOR A TURBOGENERATOR AND ONCETHROUGH STEAM GENERATOR PLANT med oct. 2o, 196s George R. Anderson We? F Pmm ATTORNEY June 18, 1968 G. R. ANDERSON CONTROL SYSTEM FOR A TURBOGENERATOR AND ONCE-THROUGH STEAM GENERATOR PLANT 2 Sheets-Sheet 2 Filed Oct. 20, 1965 United States Patent CONTROL SYSTEM FOR A TURBOGENERATOR AND ONCE-THROUGH STEAM GENERATOR PLANT George R. Anderson, Mount Lebanon, Pittsburgh, Pa.,

assiguor, by mesne assignments, to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 20, 1965, Ser. No. 498,920 5 Claims. (Cl. 60-165) ABSTRACT OF THE DISCLOSURE A once-through steam generator is controlled within input iiow constraints to produce outlet working iluid at flow, temperature and pressure conditions required for meeting electrical load demand. The control system includes a constraint control feedback loop which responds to actual input water, fuel and air flows, compares the measured input flow values with known current minimum and maximum flow values, and automatically overrides electrical load demand requirements by advancing or cutting back (l) the input flows to hold them within constraints and (2) the outlet steam ow to hold it in step with the input ows.

Background of the invention The present invention relates to control systems for turbogenerator plants and more particularly to control systems for turbogenerator plants in which a once-through steam generator produces steamfor supercritical uid for driving the steam turbine.

In a once-through steam generator or boiler, feedwater is received at one end of one or more continuous tubes and discharged through a common output as steam or supercritical iiuid. The tubing is suitably disposed in the boiler walls and in the boiler chamber, and fuel (such as natural gas or pulverized coal) is burned in a combustion zone to provide for fluid heating and superheating. The boiler system is characterized as a once-through design since there is no steam drum nor other means provided for steam and water separation.

Since the boiler fluid iiow is continuous in the oncethrough design, variation in feedwater flow in relation to the input fuel flow produces a direct and substantial effect on boiler outlet uid temperature. Outlet steam pressure also varies as a function of the feedwater and the input fuel flows, and fuel combustion efliciency for any given fuel iiow is dependent on the input air flow.

With the use of a once-through steam generator to provide the working fluid for a turbogenerator, the generated electrical power must be made variable to meet overall system load dispatching requirements as determined by a computer or the station operator. In turn, the boiler input fuel, Water and air ows must be varied to produce outlet working flow which meets the electrical load demand. Simultaneously, the boiler input flows preferably are individually varied in a manner which results in the outlet working fluid having pressure and temperature parameters which are conducive to efficient turbine operation and which are held substantially constant so as to promote overall system eiciency. Further, variance in all of the input flows must be contained within safety constraint limits as determined by the respective iiow capabilities of the input ilow systems. If any of the input ows reach a maximum or minimum constraint limit, it is desirable that the boiler be automatically controlled to produce working fluid at the predetermined outlet temperature and pressure and at an electrical output consistent with the boiler input iiow constraints.

Patented June 18, 1968 VICC? Summary of the invention In accordance with the principles of the present invention, a control system for a turbogenerator and a oncethrough steam generator or boiler automatically regulates input and outlet boiler flows and the electric output with efficiency and within predetermined input flow constraint limits. The control system can be arranged in digital form, or partly in digital form, but preferably it is arranged in analog form to produce boiler flow and generator output contr-ol in response to Various feedback variables used as inputs to the control system. If a flow constraint limit is reached, feedback operation results in appropriate advancement or cutback of electrical load demand and the unconstrained input ows.

It is therefore an object of the invention to provide a novel control system for a turbogenerator and oncethrough steam generator plant which efficiently generates electric energy within boiler input ow constraints.

An additional object of the invention is to provide a novel control system for a turbogenerator and oncethrough steam generator plant which generates electric energy within boiler input flow constraints while producing working liuid at regulated temperature and pressure conditions conducive to turbine etliciency and overall system efficiency.

A further object of the invention is to provide a novel control system for a turbogenerator and once-through steam generator plant which operates with improved safety substantially without hazard of explosion due to excess fuel accumulation in the boiler.

Another object of the invention is tol provide a novel control system for a turbogenerator and once-through steam generator plant which efficiently regulates the electrical output and which safely maintains boiler water, air and fuel input flows within constraint limits and in step with the electrical output.

It is an additional object of the invention to provide a novel control system for a turbogenerator and oncethrough steam generator plant which controls the ratio of feedwater and input fuel flows and the ratio of input fuel and input air flows for efficient plant operation while regulating electrical output within boiler input ow constraint limits.

These and other more detailed objects of the invention will become more apparent upon consideration of the following detailed description along with the attached drawings.

Brief description of the drawings FIGURE l is a schematic diagram of a generator control system arranged in accordance with the principles of the invention;

FIG. 2 is a more specific schematic diagram of a oncethrough steam generator and turbogenerator plant which is controlled in accordance with the principles of the invention; and

FIG. 3 is a more specific circuit diagram of the control system shown generally in FIG. l.

Description of the preferred embodiment More specifically, there is shown in FIG. 1 in block diagram form an electric power generating plant 10 in which an electric synchronous generator 12 is driven by a steam turbine 14 to produce electrical power for transmission in a local utility system in which the generator 12 is parallel connected. The local power system may be networked through tie lines to other such systems, and the overall power or load demand on the turbogenerator plant 10 is determined by local and tie line needs. The load demand can be made by a load dispatch computing system or it can be made by an operator from a control panel. Although it is uncommon to do so, the generator 12 can be supplanted by an asynchronous device such as an induction generator.

Normally, the utility system or network is large enough t maintain the generator 12 at synchronous speed with power produced at the standard United States frequency of 60 cycles per second. However, the generator 12 may be isolated from the network or a large part of the utility system and it is then desirable that the generator be individually controlled to meet load demand with power at the standard frequency. It is also desirable that the generator 12 share in load demands on the entire utility system or network which tend to cause a system frequency disturbance.

Working fluid flows through a turbine admission valve 16 in a path 18 at a rate which drives the turbine 14 to meet electrical load demand. The working lluid is produced by means of a once-through steam generator or boiler 20 to which input water, fuel and air flows are provided through paths 22, 24 and 26. The boiler 20 is preferably operated to produce supercritical working tiuid (i.e. H2O at a pressure above 3206.2 pounds per square inch), but lower Working fluid pressures can be used if desired. The working fluid is preferably provided at a temperature and pressure which optimizes or nearly optimizes turbine operating efficiency, and the Working fluid temperature and pressure parameters are preferably maintained substantially constant so as to stabilize the fiow process and thereby promote overall plant eiciency. The boiler input flow variables are controlled to provide the demanded working fluid flow at the predetermined pressure and temperature parameter points or ranges and within safety constraint limits.

Plant control is provided by a multiple loop control system 28 which is preferably in electrical analog form but it can be in digital form (not shown) with suitable analog input and output converters (not shown) if desired. Electrical load demand is made at an input terminal 30 and it is compared to existing generator electrical output sensed through a feedback path 32 at a control systern input terminal 34. The resultant error signal is instrumental in controlling the boiler input flows through a path indicated generally at 36 in an output-input feedback loop. It is also instrumental in controlling the turbine admission valve setting through a path 37 in an output-interstage feedback loop so as to produce the working fluid flow needed to meet the electrical load demand. The generator electrical output is directly determind by the power supplied to the turbine 14.

Input iiow and flow constraint signals are transmitted to the control system 28 in an interstage feedback path 38, and parameter signals related to the outlet working tiuid are transmitted to the control system 28 in another interstage path 40. The system coordinates the input signal information from the paths 3S and 40 to regulate the electrical output safely and efficiently while retaining boiler input fiows within flow constraint limits.

In FIG. 2, the steam and electrical power generating portion of the plant 10 is shown in greater schematic detail. Block diagrams are again used to simplify the invention description since commonly available components or any suitable special components can be employed for the indicated system components.

The synchronous generator 12 is provided with a rotor 42 and generated electrical power is obtained from a stationary armature winding 44. A wattmeter 46 is connected to the generator armature winding 44 to provide a feedback power level signal through a terminal W. Similarly, a frequency meter 4S is connected to the generator winding 44 to provide a feedback frequency signal through a terminal FQ.

Working liuid passes through a conduit 49 from the once-through steam generator 20 to the turbine admission valve 16. A pressure detector S0 is connected to the conduit 49 and provided with a terminal P1 at which a signal `is produced as an analog of the working uid pressure at the outlet end of the boiler 20. A ow detector 52 is connected to a conduit 51 between the turbine admission valve 16 and the turbine 14, and it responds to pressure differential to produce a feedback signal at a terminal P2 as an analog of the working fluid flow rate.

Within the boiler 20, inlet fluid or feedwater ows through a continuous tube 54 (or a plurality of parallel continuous tubes having a common inlet) to a boiler outlet 56. Heat generated in the boiler 20 raises the temperature and pressure of the working fluid as it passes through the tubing. A temperature detector 5S is connected to the Working fluid How path near the boiler outlet S6, and it is provided with a terminal t1 at which a feedback signal is generated as an analog of the outlet working fluid temperature.

An intermediately located mixer 60 is connected in the boiler tube 54 to inject controlled amounts of inlet water through a spray valve 62 for purposes subsequently to be indicated. Temperature differential of the working fluid across the mixer 60 is indicated by a pair of temperature detectors 64 and 66 having respective terminals t2 and t3. The mixer 60 is preferably placed closer to the boiler outlet 56 than to the boiler inlet, and a suitable location is at a point about eight tenths of the distance along the length of the tubing 54.

Combustion occurs in a zone 63 of the boiler 20. Products of combustion are suitably discharged from the boiler 20 and monitored by an oxygen analyzer 70 having a terminal O at which an oxygen content signal is produced for use in controlling the fuel-air ratio.

A temperature detector 59 is also connected to the tubing 54 and it is provided with a terminal WW at which a Water wall temperature signal is produced for use in anticipating outlet working fluid temperature. Preferably, the temperature detector 59 is connected to the tubing 54 at a point Within the rst 10% to 50% of the length of the tubing S4.

Feedwater flow to the boiler 20 is produced by a pair of feedwater pumps 72 which drive water from a suitable source through the Water feedline 22 to the boiler Z0. Fewer or more feedwater pumps '72 can be employed if desired. A flow control valve 74 and a flow meter 76 are connected in series with each feedwater pump 72, and a water flow feedback signal is produced at a meter terminal WF. A valve terminal WV is provided for electrically controlling the setting of the valve 74.

Similarly, a plurality of fuel pumps 7 8 are provided for delivering fuel to the boiler 20 through the fuel flow path 24. As noted previously, the fuel can be pulverized coal or natural gas or it can be other suitable combustible material. A fuel flow valve and a fuel iiow meter 82 are connected in series with each fuel pump 78. A terminal FV on each fuel valve 80 is provided for receiving signals which electrically control the setting of the valves 8G. A terminal FF is provided on each fuel ow meter 82 at which an analog feedback signal is produced for the fuel oW from each fuel pump 78.

Inlet air flow is produced by a plurality of fans 84, and the air flow in the path 26 is controlled by dampers 86 respectively in series with the air fans S4. A terminal AD is provided on each damper 86 for adjusting the damper and controlling the air flow from each fan S4. An air flow meter 88 is connected in series with each damper S6 to provide a feedback signal representative of air flow at a terminal AF.

The preferred analog form of the control system 28 is shown in FIG. 3. It is also shown in block diagram form for the same reasons indicated for FIG. 2.

The electrical load demand signal is applied to the load demand terminal 30 which is connected to a ramp generator 90. Generally, except as subsequently otherwise indicated, a positive input increase demand signal produces positive subdemand signals in the control system 28 and a negative input decrease demand signal produces negative subdemand signals.

A set point terminal LDMX limits the maximum load demand that can be made on the system. It is normally set at rated full load but it can be reduced if some failure or other factor places a lower limit on the generator output. The object of the ramp generator 90 is to produce a delayed rise output signal d, which permits smooth system response without exceeding the dynamic capabilities of the boiler and the turbine. A set point terminal RC fixes the rise rate of the signal d1. (for example, at about a 5% /minute load change rate).

As is customary in boiler control systems generally, the signal dr is transmitted to an off-frequency adder 92 to which the frequency meter terminal FQ is connected. The load demand signal a'r thus is increased or decreased by the frequency control signal to form a basic demand signal drf depending on whether the generator output frequency is low or high respectively. The generator 12 is thus controlled to share in meeting load variations which cause system frequency disturbances.

Use is made of the demand signal dri in one feedback branch 94 which ultimately operates the turbine admission valve 16 through the terminal T to control the outlet working fluid ow from the once-through steam generator 20 to the turbine 14. The signal du is also used in another feedback branch 96 which has parallel sub-brances 98, 100 and 102 ultimately to control water, fuel and air input flows to the once-through steam generator 20 through the terminals WV, FV and AD. The input ow control ultimately regulates the input flows in step with the electrical load demand insofar as input flow changes are safely compatible with input flow capabilities. Simultaneously, boiler outlet working fluid is maintained at`substantially constant pressure and temperature parameters which are conducive to turbine operating efficiency. If input oW constraint limits are reached, the electrical load demand is appropriately advanced or cut back as subsequently described more fully.

To maintain substantially constant outlet working uid pressure, a working tiuid pressure error signal is generated by a constant pressure integrator 104 to which the pressure detector terminal P1 is connected. A constant pressure set point terminal KP provides an input reference level, and the input error signal is time integrated and transmitted to a load demand and pressure adder 106. Thus, if the boiler outlet pressure is high, the demand signal drf is cut back by the pressure error signal in the adder 106. Conversely, if the boiler outlet pressure is low, the demand signal d1., is increased by the pressure error signal.

For reasons considered subsequently, feedback signals in constraint feedback loops 108 and 110 are combined with the demand and pressure signal in a Water, fuel and air adder 107. A Water, fuel and air demand signal d from the adder 107 provides in-step control of all the input flows since percentage changes in electrical load demand normally can be met by substantially identical percentage changes in all of the boiler input Hows.

In the fuel control feedback branch 98, the demand signal d is fed to a multiplier 112 and the multiplier output signal is transmitted to a fuel demand integrator 114. The fuel flow terminals FF are also connected to the integrator 114 and any resultant input error signal represents a fuel flow error and it is time integrated to produce a fuel demand signal df at the terminals FV thereby to control the fuel valve settings in meeting the fuel demand ultimately required for meeting the electrical load demand.

Similarly, the demand signal d is conducted to a water demand divider 116 in the Water control feedback branch 100, and the divider output is transmitted to a Water demand integrator 118 to which the water ow terminals WF are connected. An input error signal indicates an inlet water ow error and it is time integrated to produce a feedwater demand signal dw thereby to control the water valve settings through terminals WV in meeting the feed- Water demand required for the electrical load demand.

Since the boiler 20 has a once-through design, the Water-fuel ratio is a substantial determinant of boiler outlet Working fluid temperature. The water-fuel ratio is accordingly controlled to regulate the fluid temperature. The fuel demand multiplier 112 and the water demand divider 116 are functioning units in the temperature regulating scheme as will subsequently be more fully described.

The demand signal d is also fed to an air demand multiplier 120 in the air feedback branch 102 and the resultant output is transmitted to another air demand multiplier 122. An output signal from the multiplier 122 is transmitted to an air demand integrator 124 to which the air flow meter terminals AF are connected. An input error signal in the air demand integrator 124 represents an input air flow error and it is time integrated to produce an air demand signal da which is applied to the damper terminals AD thereby to meet the air demand required for the electrical load demand.

The fuel-air ratio is adjusted so as to prevent excessive and` hazardous fuel accumulation in the boiler 20, and it is preferably also adjusted to provide for efficient combustion Without excessive oxygen. The air demand multiplier 120 functions to produce the preferred fuelair ratio control by multiplying the demand signal d and a ratio signal rfa which is produced by a fuel-air ratio integrator 126. The signal generated at the oxygen analyzer terminal O is referenced against a fuel-air ratio set point signal applied at a set point terminal 129. Any error signal represents an excess or a deficiency of input air flow and it is time integrated by the integrator 126 to generate the ratio signal rfa. The air demand multiplier 122 provides additional fuel-air ratio control as will subsequently be more fully described.

In order to provide substantially constant working uid temperature at the boiler outlet, a water-fuel ratio signal rwf is generated by a constant temperature integrator 128 and applied to the fuel demand multiplier 112, the water demand divider 116, and the air demand multi-plier 122. When the outlet fluid temperature is low, the signal rw: advances fuel demand and air demand and simultaneously reduces Water demand thereby limiting the extent to which temperature correcting input oW changes interact to alter the working fluid outlet pressure. When the fluid temperature is high, the fuel and air demands are cut back and the water demand is advanced. Hence, the single ratio signal rwf is used to vary the water-fuel ratio in achieving Working fluid temperature regulation and to vary the air ow and thereby directly aid in meeting new air flow requirements as the fuel flow is varied.

While the water-fuel ratio is varied to achieve temperature regulation with minimal interaction with working fluid pressure, it is noted that the boiler outlet working fluid pressure is regulated by proportional variation in the input water and fuel flows at any predetermined Water-fuel ratio thereby limiting interaction with the temperature regulation when the flows are varied to correct pressure. For example, assume that the ratio signal rw: is zero (Working fluid temperature is at regulated value) and that the working fluid pressure is at variance with the set value. The constant pressure integrator 104 then produces a demand signal d which proportionally raises water and fuel (and air) ows at the constant waterfuel ratio until the Working fluid pressure reaches the set value. The Working uid temperature tends to remain constant because the water-fuel ratio is maintained constant While the Water and fuel flows are increased or decreased.

In order to achieve rapid, stable and eicient response in the temperature regulating scheme (the total length of the boiler tubing may be up to 5,000 feet or more With a relatively long time delay between inlet Water iovv variations and outlet working Huid temperature regulation), a cascaded intermediate temperature control is preferably employed as indicated by the dotted box 130, particularly in relatively large generating plants. The temperature set point is made variable according to working lluid llow, and for set point control a temperature set point terminal KT and the ow terminal P2 are connected to a temperature set point amplifier 132. The amplifier 132 generates an output temperature set point signal having a magnitude determined by the extent to which the llow varies from the reference level set at the set point terminal KT.

The temperature set point amplifier output and the working fluid temperature detector terminal t1 are connected to an intermediate temperature demand integrator 134 which time integrates any input error to produce an output error signal thereby indicating that the intermediate fluid temperature must be varied in order to ultimately maintain the boiler outlet temperature constant under a new llow condition. To set the new intermediate tluid temperature, the relatively cool fluid flow through the intermediate spray control valve 62 is regulated by an intermediate temperature regulating integrator 136 through a terminal S. Preferably, the liow through the spray control valve 62 is normally less than about of the total flow to promote boiler thermal operating efliciency.

Any error between the newly demanded intermediate lluid temperature and the existing intermediate fluid temperature indicated at the temperature detector terminal t2 is time integrated and applied to the terminal S to Vary the spray control valve setting. For example, an increase in Working Huid flow would indicate that Working fluid outlet temperature will tend to decrease and injection ow through the spray control valve 62 thus must be cut back to raise the intermediate fluid temperature tz (assuming it is not at the raised temperature level because of other operating conditions). A fluid temperature change is thus immediately produced at the intermediate tube location to provide rapid regulation of the outlet fluid temperature (as opposed to the time delay involved with temperature regulation of the outlet Working fluid through boiler inlet ow variation alone).

The intermediate fluid temperature change is used to produce a demand for a water-fuel ratio change through the constant temperature integrator 128 so as to achieve the required change in input ow conditions required for steady state regulation of the outlet fluid temperature at the new outlet fluid flow condition. Thus, an intermediate temperature comparator 138 has an input connected to terminals t3 and t2 and produces an output signal proportional to the intermediate temperature differential (t3-t2) which is determined by the relative extent to which spray injection is being mixed with the main llow as a result of the operation of the intermediate cascaded control 130. The temperature differential (t3-t2) also clearly depends on the temperature t3 as determined by boiler input ilow conditions.

The differential intermediate fluid temperature signal and the outlet fluid temperature signal at the terminal t1 are fed to the constant temperature integrator 128. To anicipate outlet working fluid temperature changes due to changes in the Water wall temperature, the water wall temperature indicating terminal WW is connected to an anticipatory rate ampler 140 and its output is also fed to the -constant temperature integrator 18. If -desired, the output of the intermediate temperature regulating inegrator 136 can be cascaded into the constant temperature integrator 12S.

All of the input signals to the constant temperature integrator 128 are coordinated to produce an input error signal when outlet Working lluid temperature has changed from its regulated value (or when it is anticipated through the intermediate fluid temperature differential that it will ultimately do so without corrective input llow control action) and when it is anticipated through the water wall CFI temperature change rate that water wall lluid temperature will not of itself lead to outlet temperature regulation or correction. Thus, the magnitude and polarity of the water-fuel ratio signal rwf is determined by the degree and direction of present and anticipatory outlet fluid temperature correction needed, and the ratio signal rwf when applied to the fuel demand multiplier 112, the water demand divider 116 and the air demand multiplier 122, determines the water-fuel ratio and the input air ow as previously descri-bed. The water-fuel ratio and the fuelair ratio are thus controlled to regulate outlet uid temperature at the same time that all of the boiler input flows are controlled in unison by the liow demand signal d to keep in step with the electrical load demand. Smooth and stable system performance is thus provided in meeting electrical demand.

At the same time that the demand signal drf effects input flow control, it is applied in the path 94 directly to control working uid flow from the boiler 20 to the turbine 14. Thus, the demand signal drf is applied to a steam admission adder 142, and the adder output is applied to a load demand Vernier integrator 144 in a slow path of a steam admission cascaded control indicated by the dotted box 146. In the cascaded control 146, the adder output is also applied directly in a fast path to the input of a load demand multiplier 148.

The load demand vemier integrator 144 is provided with a reference point terminal formed by the wattmeter terminal W, and an error signal is produced by the difference between the actual generated power output and the power output demanded by the signal from the steam admission adder 142. The error signal is time integrated and applied to the load demand multiplier 148 where it is multiplied with the output from the adder 142.

The output product from the load demand multiplier 148 is transmitted to a flow and load demand integrator 151) where it is compared with the Working lluid ow signal from the llow detector terminal P2. If the Working lluid llow is different from that llow required for the electrical load demand, an input error signal is generated and it is time integrated to produce an output signal which controls the steam admission valve setting through the terminal T. Working fluid llow is then brought into step with electrical load demand, and the required flow is readily met by the once-through boiler 2t) substantially without perturbing the temperature and pressure parameters of the working uid at the boiler outlet because of the control provided by the input flow demand integrators 114, 118 and 124 on the input water, fuel and air llows.

For safety and operating eliciency, the electrical output is limited by maximum and minimum limits on each of the boiler input flows and each boiler input flow in turn is limited by limits on the other boiler inlet flows. As one example of an input flow constraint, if the load demand signal exceeds a predetermined value corresponding to maximum fuel flow, working fluid pressure decreases to produce lower operating eiciency and it is therefore desirable that generated output and the corresponding load demand signal be kept in step with the maximum fuel and other input flows.

As another example, if maximum input air flow is reached, it is preferable that further increase in the fuel How be quickly prohibited before an explosion hazard develops. Similarly, if maximum feedwater ow is reached, it is preferable that further increase in the fuel llow be quickly prohibited before boiler outlet temperature rises excessively. The converse situation is realized if maximum fuel ow is reached, that is, boiler outlet temperature can drop excessively.

As a further example of the need for restricting input llows within constraint boundaries, failure of a fuel pump, a water pump, an air fan, a fuel burner nozzle or any other input flow control component `can make it necessary that the load demand and the unaffected input flows be brought into step with the input flow which is suffering from the failure. It is also desirable that input ilows be maintained in step with electrical load demand above floor or minimum input values of water, fuel and air iiows.

The constraint feedback paths 108 and 110 provide for system operation within predetermined maximum and minimum input flow constraint limits. Thus, respective maximum integrators 152, 154 and 156 are provided with signals from the outputs of the input demand integrators 1111, 118 and 124 respectively. Each maximum integrator 152 or 154 or 156 is provided with a set point from a suitable maximum set point device 158 or 160 or 162.

As one example, each of the three maximum set points can be set in correspondence to the maximum flow setting of the associated valves or dampers as the case may be. If the total iiow capability is reduced because of a pump or fan or other failure, a correspondingly lowered set point is produced by the set point device 158, 160 or 162. The set point devices thus sense any reduction in the three input flow capabilities, that is they are suitably connected to respond to no ow or low ow conditions to reduce the set point for the associated maximum integrator 152 or 154 or 156. The maximum integrator 158, 160 or 162 produces a load demand cutback signal only when the corresponding input ow demand signal from the integrator 114 or 118 or 12d has reached the existing set point maximum value.

Any load demand cutback signals from the maximum integrators 152, 154 and 156 are added in a cutback adder 164 and transmitted in the feedback path 110 to the steam admission adder 142 to cut back on the working uid iiow demand, and to the water, fuel, and air demand adder 107 to cut back on all of the input ow demands in unison so as to keep the input flows and the electrical load demand in step within the maximum input liow constraint limits.

Minimum load demand and input llow constraints are similarly established. Thus, minimum set points are established by suitable devices 166, 168 and 170 for minimum integrators 172, 174 and 176 respectively. The minimum integrators 172, 174 and 176 produce load demand advance signals when minimum flow capabilities are reached for in-service input flow components. Any load demand advance signals are added in an advance adder 178 and applied additively to the steam admission adder 142 and the input flow demand adder 107 through the feedback path 108 to increase the outlet 110W and the input flows and the load demand above minimum input flow constraint limits.

In summary, the system 28 operates stably, safely and rapidly to control the operation of the once-through steam generator 20, the turbine 14 and the electric generator 12 to meet electrical load demand. The input fuel, water and air flows are kept in step with electrical load demand within input flow constraint limits while boiler outlet working uid is maintained at substantially constant pressure and temperature parameters which are conducive to turbine and generator operating eiliciency. Temperature regulation is facilitated by interstage injection and feedback control.

The foregoing description has been presented only to illustrate the principles of the invention. Accordingly, it is desired that the invention be not limited by the embodiment described, but, rather, that it be accorded an interpretation consistent with the scope and spirit of its broad principles.

What is claimed is:

1. A control system for a turbogenerator and oncethrough boiler plant, said system comprising means for controlling outlet working uid ow from the boiler to the turbine, means for controlling water and fuel and air input flows to the boiler, means for generating a representation of electrical load demand error, means responsive to the electrical load demand error representation for regulating said outlet ow controlling means normally to produce working fluid flow which meets the electrical load demand, means including respective fuel and airwater demand determining means responsive to the load demand error representation for regulating said input ow controlling means in step with the electrical load demand while regulating the temperature and pressure of the outlet working fluid within respective predetermined ranges, means for controlling said input and outlet liow regulating means to hold the regulated values of the input liows and the working liuid liow in step at an electrical load demand value within predetermined input flow constraint limits, said constraint controlling means including feedback means having its input coupled to the outputs of said demand determining means and its output coupled to said outlet flow regulating means and the inputs of said demand determining means.

2. A control system as set forth in claim 1 wherein said input ow regulating means further includes means coupled to the input of said fuel and water demand determining means for controlling the water-fuel ratio and regulating outlet iiuid temperature, means operated by said water-fuel ratio controlling means for injecting relatively cool fluid at an intermediate boiler tube location in response to predetermined changes in outlet flow conditions, and said water-fuel ratio controlling means including means responsive to predetermined effects produced on the boiler iiuid by fluid injection changes for varying the water and fuel input flows.

3. A control system as set forth in claim 2 wherein said water-fuel ratio controlling means further includes means responsive to changes in outlet liuid iiow, and said injecting means is responsive to the last mentioned means.

4. A control system as set forth in claim 1 wherein said demand determining means respectively include fuel and air demand multipliers and a water divider, and said electrical load demand error representation generating means includes a load demand error adder having its output coupled to said divider and said multipliers and having the output of said feedback means coupled to its input to control the water-fuel ratio and the fuel-air ratio notwithstanding constraint operation produced by said constraint controlling means.

5. A control system as set forth in claim 1 wherein said feedback means includes a plurality of integrators having respective predetermined liow capability set points, at least one of said integrators associated with each of said demand determining means, the ow capability set point for each integrator being selected from predetermined maximum and minimum values, said integrators having their inputs connected to the outputs of the respectively associated demand determining means and having their outputs coupled to said outlet ow regulating means and the inputs of said demand determining means.

References Cited UNITED STATES PATENTS 2,861,194 11/ 1958 Bristol 290-2 2,895,056 7/ 1959 Bristol 290-2 2,962,865 12/1960 Buri 60--105 2,986,645 5/ 1961 Smith et al 290-2 3,089,308 5/1963 Halle 60-106 3,109,102 10/1963 Jenkins 290-2 3,244,898 4/ 1966 Hickox 60-105 X 3,247,671 4/ 1966 Daniels 60-107 X 3,310,683 3/ 1967 Hottenstine 60--106 X MARTlN P. SCHWADRON, Primary Examiner.

ROBERT R. BUNEVICH, Examiner.

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