US3096744A

US3096744A - Method of and apparatus for regulating the steam temperature in a steam generator

Info

Publication number: US3096744A
Application number: US858657A
Authority: US
Inventors: Profos Paul
Original assignee: Sulzer AG
Current assignee: Sulzer AG
Priority date: 1958-12-23
Filing date: 1959-12-10
Publication date: 1963-07-09
Anticipated expiration: 1980-07-09
Also published as: NL111390C; CH364514A; NL235580A; FR1244634A; DE1205979B; GB937168A

Description

P. PROFOS 3,096,744 METHOD OF AND APPARATUS FOR REGULATING THE STEAM TEMPERATURE IN A STEAM GENERATOR July 9, 1963 5 Sheets-Sheet 1 Filed Dec. 10, 1959 July 9, 1963 P. PROFOS 3,096,744

METHOD OF AND APPARATUS FOR REGULATING THE STEAM TEMPERATURE IN A STEAM GENERATOR 5 Sheets-Sheet 2 Filed Dec. 10, 1959 fm emorz' Rial Profis 5 Sheets-Sheet 3 NG THE STEAM P. PROFOS F AND APPARATUS FOR REGULATI 149 Fly. 2 b

TEMPERATURE IN A STEAM GENERATOR July 9, 1963 METHOD 0 Filed Dec. 10, 1959 K s Z W 2 5 m PMM A 4 July 9, 1963 P PROFOS 3,096,744

METHOD OF AND APPARATUS FOR'REGULATING THE STEAM TEMPERATURE IN A STEAM GENERATOR Filed- Dec. 10, 1959 v 5 Sheets-Sheet 4 .3 77 Fly A florneys July 9, 1963 P. PROFOS 3,096,744

METHOD OF AND APPARATUS FOR REGULATING THE STEAM TEMPERATURE IN A STEAM GENERATOR Filed Dec. 10. 1959 5 Sheets-Sheet 5 .[rrrerrzon' Pa u/ Pro f 08 United States Patent 3,096,744 METHOD OF AND APPARATUS FOR REGULAT- ING THE STEAM TEMPERATURE IN A STEAM GENERATOR Paul Protos, Winterthur, Switzerland, assignor to Sulzer Freres, Societe Anonyme, Winterthur, Switzerland Filed Dec. 10, 1959, Ser. No. 858,657 Claims priority, application Switzerland Dec. 23, 1958 7 Claims. (Cl. 122-479) This invention relates to a method of and apparatus for regulating the steam temperature in a steam generator having at least two series connected heating surfaces or heaters through which the working medium flows one after the other, while at least the temperature of the working mediuum flowing to the heater later traversed by the said medium (i.e. the downstream heating surface) is regulated by quantitative variation of water fed into the Working medium upstream of the said downstream heater.

The invention is based on the concept of regulating the steam temperature in a steam generator by the supply of water, in such a manner that in the parts of the steam generator in which the working medium already has a high heat content, the amount of water to be introduced is varied as little as possible and any larger quantities of water necessary for regulation are introduced at those points of the steam generator at which the working medium still has low temperatures or still has a low heat content.

The invention solves the problem of regulating the steam temperature by a method which is characterizedin that the desired optimum temperature in a regulating circuit which belongs to the heater or heating surface first traversed by the working medium (i.e. the upstream heater or heating surface) is influenced by a signal or impulse derived from the adjusted value or magnitude of a regulating circuit which belongs to the heater or heating surface traversed later by the working medium (i.e. the downstream heating surface), in such a manner that the temperature is reduced when the amount of water in .troduced is increased by the regulating circuit which belongs to the downstream heating surface. Through this new method the thermodynamic losses are kept low, because through the displacement of the desired value the amount of water suupplied to the working medium in vapor form is varied only slightly, while the greater part of the amount of water required for the regulation of temperature is supplied to the working mediuum before it is in the vapor state. If, for example, viewed in the direction of flow of the working medium, the first of two serially disposed heaters is an evaporator and the second a superheater, the impulse derived from the adjusted magnitude of the superheater regulating circuit acts in the evaporator regulating circuit on the feed water supply to vary the feed valve or to vary the speed of rotation of the feed pump or of that of its drive.

The invention further relates to an apparatus arrangement for carrying out the new method in a steam generator having at least two heaters through which the working medium flows one after the other, in which at least the two heaters, each together with a temperature measuring or responsive device, a water supply device, and a regulator therebetween, form two regulating circuits, the invention being characterized in that a measuring device, responding to the adjusted magnitude of the regulating circuit which belongs to the heater traversed later by the working medium, and having an integrally acting regulating device, hereinafter sometimes called an I-regulator, is disposed, the output impulse line of which is connected together with one of the inputs of the regulator in the regulating circuit which belongs to the heater traversed earlier by the working medium.

ice

In one embodiment of the invention, the measuring device responding to the adjusted magnitude is a quantity measuring or rate of flow responsive device disposed in the appertaining water supply pipe. In this arrangement therefore the impulse for the displacement of the desired value is derived direct from the adjusted magnitude.

Further features of the invention will be clear from the following description of four embodiments given by way of example and illustrated in FIGURES 1 to 4 of the drawings.

-In the drawings:

FIG. 1 is a diagrammatic view or flow diagram illustrating one embodiment in accordance with the invention;

FIGS. 20 and 2b, when combined end to end with FIG. 2a at the top, comprise a diagrammatic view, partly in section, of another embodiment of the invention in which the structures of the elements of the regulating circuits are shown more in detail with some of them being shown in section; and

FIGS. 3 and 4 are views similar to that of FIG. 1 illustrating further embodiments according to the invention.

In the embodiment illustrated in FIG. 1, a starting vessci or water supply tank 1 is provided from which a feed pump 2 sucks feed water and forces it through a highpressure pre-heater 3 and a feed control valve 4 by way of a pipe 25 into an economizer 6. From the economizer, the water flows through a pipe 84 and an evaporator 7 in which it is at least partially evaporated, whereupon the steam-water mixture passes into a separator 9 in which the water is separated from the steam. The steam thereupon fiows through a pipe 85 and three serially connected superheaters 11, 14 and 17', connected by

pipes

86 and 87, and thereupon passes through a pipe 65 to a turbine 19 driving an electric generator 24-, and thence into a condenser 20. The condensate is pumped back to the tank 1 by means of a pump 21, by way of two

preheaters

22, 23.

At the outlet of the last of the three serially connected superheaters, 17, a thermostat 18 is provided before (i.e. upstream of) the superheater 17 is a water injection device 32 in a Water injection pipe 66 connecting into pipe 87, and between the latter and the thermostat 18 a proportionally and integrally-acting regulator 30 is provided which receives its optimum or setting value through an impulse line 3 1, which for example comes from a load control device (not shown) or from a manually adjustable control in the control room. A regulating circuit corresponding to the regulating circuit thus formed is also formed for the superheater 14, which is the last but one viewed in the direction of fiow of the working medium, and comprises a thermostat 15 provided for the pipe 87 at the outlet of the superheater 14, a water injection device 40 in a water injection pipe 68 connected into pipe 86 upstream of the superheater 14, and a regulator 39 which once again has a proportional and integral action (i.e. hereinafter sometimes termed a PI-regu-lator). The therrnostat 15 does not act only on the regulator 39 in this arrangement, but is inserted or connected simultaneously through a proportionallyaacting regulator 33 into the last regulating circuit, so that the inlet temperature at the inlet of the super-heater 17, measured by the thermostat 15, is imposed on the last regulating circuit as a modifying magnitude. In a similar manner a thermostat 12, provided for the pipe 86 upstream of the second superheater, 14, is inserted or connected into the last but one regulating circuit through a proportionally-acting regulator 60.

A quantity measuring or rate of flow responsive device 35 is built into the water injection pipe 66 leading into the pipe 87 upstream of the last superheater, 17 this measuring device cooperating with an integrally-acting regulator 67 which receives its desired or optimum setting value through an impulse line 36, the said desired value being for example adjusted by hand or by a control situated in the control room. From the integral regulator 67, an impulse line leads through a limiting device 37 to the PI-regulator 39 in the last but one regulating circuit. The Water injection pipe '68 of the last but one regulating circuit also contains a quantity measuring or rate of How responsive device 50 which in turn acts on an integral regulator 51 which receives its desired or setting value, which for example is adjustable by hand, through an im'- pulse line 69. An impulse line 70 leads from the I-regulator 51 to a prop'ortionallyand integrally-acting regul-ator 52 which, with a quantity measuring or rate of flow responsive device 5 in the pipe 25 leading to the economizer 6 and with the feed control valve 4, forms another regulating circuit. 7 7

An impulse line 72 is connected with the impulse line 70 and to a multi-thermostat 8 incorporated in the evaporator 7, so that an impulse originating from the thermostat '8 is superimposed on the integral impulse transmitted from the I-regulator 51, and the resulting impulse is fed through the line 70 to the PI-regulator 52 as the desired or optimum control value. The amount or rate of flow of working medium leaving the separator 9' is finally imposed on this regulating circuit as a modifying magnitude, owing to the fact that a quantity measuring or rate of flow responsive device 10 is provided in the pipe 85 leading from the separator to the first superheater 11. The impulses transmitted from the measuring device '10 are transmitted by the impulse line shown through a proportionally-acting regulator 73 into an impulse line 71 leading from the PI-regulator 52 to the feed control valve 4. Water under pressure for injection by

pipes

66 and 68 is conducted from the pipe 25 through a pipe 88.

The regulating operation in the installation described above proceeds in the following manner. If the temperature of the working medium at the outlet of the last superheater, 17, is too high, as measured by thermostat 18, an impulse is transmitted through the PI-regulator 30 to the adjusting member of the water injection device 32, and more Water is injected into pipe 87. Through the increased rate of injection of water, an impulse is transmitted from the quantity measuring or rate of flow responsive device 35 to the I-regulator 67. The impulse is compared with the optimum value received from the impulse line 36 and converted into an integral impulse. The resulting integral impulse is compared in the limiting device 37 with two limiting impulses a and b, the magnitude of which is adjusted, for example, by hand or by the load control apparatus of the installation. If the magnitude of the integral impulse lies between those of the two limiting impulses, the integral impulse is transmitted to the PI- regul-ator 39. If the integral impulse is smaller than the lower limiting impulse a, the latter is forwarded to the PI-regulator 39, whereas if the integral impulse is greater than the upper limiting impulse b, the latter is transmitted to the PI-regulator 39. Through this arrangement therefore the desired temperature value of the regulator in the last but one regulating circuit is influenced by the adjusted magnitude, namely the amount of water injected by the last regulating circuit, in such a manner that with a constantly increasing rate of Water injection by the last regulating circuit the desired temperature in the preceding regulating circuit is slowly reduced. The displacement of the temperature value is thus effected gradually, i.e. when the injection rate of the last regulating circuit varies for a long time from the desired or normal value. In a similar way, the temperature value in the preceding regulating circuit, which in this example varies the amount or rate of flow of feed water by adjustment of the feed valve 4, is also gradually influenced in dependence on the adjusted magnitude, namely the amount or rate of flow of water injected by the last but one regulating circuit. With this arrangement the efiect is therefore achieved that any action required in the working medium cycle because of the variation of temperature of the working medium is as far as possible transferred to the region in which the working medium still has a relatively low temperature, so that in the region of the high working medium temperatures it is possible to work with very small amounts or rates of water injection, whereby the thermodynamic losses are kept as low as possible.

The above-described mode of operation applies to the case in which the steam generator is operated under normal operating conditions, while the steam is in a critical or else a supercritical condition. During the starting up and shutting down of the steam generator, which takes place in the sub-critical range, the integral regulator 51 is switched off by means not shown or replaced by a fixed impulse.

In FIGS. 2a and 2b only the parts of a steam generating plant which are necessary for the understanding of the regulating process and apparatus according to the invention are illustrated. Here again as in FIG. 1 the feed water is forced by the feed pump 2 through the [feed control valve 4 and by way of the pipe 25 into the economizer 6 and the evaporator part 7 (for the sake of simplification the economizer and evaporator are represented by a single heating surface or heater). The steam separator of FIG. 1 is omitted in this example. After leaving the evaporator 7, the working medium flows through the pipe and the three serially connected superheaters 11, 14, and '17, inter-connected by the

pipes

86 and 87, into the pipe 65 leading to the turbine.

At the discharge end of the last superheater, 17, the temperature-responsive device or thermostat 18 is disposed, which here consists of a bar 18' having a small temperature expansion coefficient, such as for example Invar. The bar 18 is connected fast to the pipe 65 at one end and at the other end to a two-armed lever which is articulated at one end to the pipe 65 and at the other end to a rod 106 belonging to a control piston 1'01 operable in a cylinder 102. The cylinder 10-2 is closed at its bottom end. On the face end of the piston, which is at the top in FIG. 2a, a compression spring 104 is supported, the other end of which bears against a spring plate 105 which is fastened to the rod 106. In the cylinder wall, two

bores

107 and 108 are provided. Through these bores, oil is introduced and discharged through pipes (not shown). In the control piston 101 there is a bore 109 which in the normal position of the piston lies between the bores '107 and 108 in the cylinder wall. At the bottom end of the cylinder I102 a control pipe 110 is connected which leads into a cylinder 111, in which a piston 112 is slidably mounted. On the side of the piston 112 remote from the pipe 110, a compression spring 113 is provided which is supported between the piston and the cylinder end wall. On the same side of the piston 112, a pipe 114 is connected to the cylinder 1'11, and through this pipe a pressure medium, for example oil, is supplied, this pipe constituting the desired or optimum value impulse pipe. The piston 112 has on the spring side a piston rod 115, which is articulated to one end of a two-armed lever 116. The other end of the lever 116 is connected to the end of a tension spring 117. A rod 118 of a control slide 119 is attached to the middle of the lever 116, the said control slide having three control surfaces and being slidable in a control cylinder 120. The control cylinder 120 is provided on the right-hand side in the drawing with three pipes indicated by arrows, of which the two outer pipes supply pressure medium, for example oil, while the rniddle pipe discharges pressure medium. The control cylinder 12%) is'in communication on the other side through two pipes 121 and 122 with the cylinder 123 of a servop-iston 124'. On its bottom face the piston 124 carries a piston rod 125 which is articulated to one end of a twoarrn'ed lever 126. In the middle of the lever is attached a valve rod '127, which operates the valve in the water injection device 32 of the water supply pipe 66. At the upper "face of the piston 124 there is likewise provided apiston rod which is connected to a slidable cylinder 128.

In this cylinder is provided a piston 129 which is connected through a piston rod 130 to the tension spring 117 and the lever 116. The cylinder spaces on both sides of the piston .1-29 are filled with a pressure medium and connected through a bypass pipe with built-in throttle mem her 131 to one another, so that the

parts

128 and 129 constitute a resilient member.

In the water supply pipe 66 there is built in a rate of flow measuring or responsive device 35 which measures the amount of water flowing in pipe 66 through difierence in pressure and which is connected by two

pipes

135 and 136 to a diaphragm box 137. A rod 139' is connected to the diaphragm 138 in the box and is also connected to a pivoted cam disc 140 rockable about the pivot point 141. A control piston 142 is supported through a spring 143 against the cam disc 140' and is of similar construction to the control piston 101. It differs from the latter merely in that additionally to a pipe 144 corresponding to the pipe 110, a pipe 145 is connected to the cylinder for the piston and conducts pressure medium. The pipe 145 is in communication with a cylinder 146 in which a control slide 147 having three control surfaces is adapted to slide, the said control slide being supported through a spring 148 resting on a fixed point. On the right-hand side of the cylinder 146 in the drawing, two pipes are connected which supply and discharge pressure medium respectively as indicated by arrows. On the opposite side of the cylinder 146 there is connected a pipe 149 in which a throttle device 150 is incorporated and which, with the interposition of a vessel V filled with pressure medium, for example oil, leads into a cylinder 151 provided with piston 152. This piston system is constructed on the same principle as the piston system 111, 112 in the first regulating circuit described above. The piston 152 is in turn connected through a two-armed lever 116 to a control slide 11 9' in a control cylinder 120, which in turn has a servo-piston 124 with a resiliently connected, yielding

member

128, 129. The servo-piston 124 is connected to the water injection device 40 in the pipe 68 similarly to the arrangement in the first regulating circuit described above.

The cylinder 151 is connected on the side remote from the control slide 119 to a pressure pipe 153 which leads on the one hand to a control piston 101' like the control piston 101 and cooperating with the temperature-responsive device or thermostat 15, and on the other hand to a cylinder 154 provided with a piston 155. The side of the piston 155 remote firom the supply pipe 153 is provided with a piston rod 156, which is connected to the twoarmed lever 126 operating and controlling the valve in the injection control device 32. .In the space of the cylinder 154 on the piston rod side, a compression spring 157 is provided.

Similarly to the device 35, a rate of flow measuring device 50 is disposed in the water supply pipe 68 of the regulating circuit belonging to the superheater 14, this measuring device being connected to a cylinder 151 (FIG. 2b) through a diaphragm box 137, a rod 139", a cam disc 140', a control piston 142', a control slide 147, and a pipe 149, with a built-in throttle member 150' and vessel V'. The piston 152' in the cylinder 151 acts in turn in accordance with the regulating circuits described above, on the one hand with a control piston 101 or" the temperature-responsive device or thermostat 8, and on the other hand through a control slide 119" with a servopiston 1 24".

Upstream of the economizer 6, the 'feed water pipe 25 contains the quantity or rate of flow-responsive or measuring device '5 which is connected through pipes 160 and 161 to a diaphragm box 162. A control piston 164 constructed in a similar way to the control piston 1 is connected to the diaphragm 163 of the said diaphragm box and is connected through a pipe 165 to a cylinder having a piston 166 constructed and arranged in a similar .way to the piston 112. A pipe 167, here corresponding to the pipe 114 of the cylinder 111, leads to a cylinder provided with a control piston 168, which is connected through a spring 169 to the piston rod of the servopiston 124 which is constructed and arranged in a way similar to the control piston 101. The piston 166 is in turn in operative connection, in the same way as the piston 152', through a control slide 119" and a servo-piston 124" with a two-armed lever 175, on the middle of which a valve rod 176 of the feed water control valve 4 acts. To the right-hand end of the lever in FIG. 2b of the drawings the piston rod 177 of a piston 178 is articulated, this piston being constructed in the same way as the piston 112 and being connected through a control pipe 179 to a cylinder having a control piston 180. This unit, including piston 180, corresponds in principle to the

control piston

101, or 142, and cooperates with a cam disc 182 adapted to rock about its pivot point 181, while a rod 184 operated by a diaphragm 183 is connected to the said cam disc. The housing or box 187 enclosing the diaphragm 1 83 is in operative connection through pipes 185, 186 with the quantity measuring device 10 responsive to changes in the rate of flow in-the pipe 85 leading to the first superheater 11.

The temperature-responsive device or thermostat 12 disposed on the pipe 86 at the outlet to the superheater 11 is in communication with a control piston 190 corresponding to and arranged like the control piston 101 and is connected through a control pipe 191 toa cylinder having a piston 192 which is constructed and arranged "similarly to the piston 112. A piston rod 193 connected to the piston 192 is articulated to the two-armed lever 126 of the water injection device 40 in the pipe 68 and thus corresponds in construction and arrangement to the arrangement of the piston 155 on the lever 126.

The mode of operation of the apparatus arrangement illustrated in FIGS. 2a and 2b is as follows: It will be assumed that the steam temperature at the outlet of the last superheater, 17, rises above the desired normal. As a result, in consequence of the unalterable length of the rod 18' and the expansion of the opposite section of pipe 65, the lever 100 moves so that the spring 104 is compressed. The control piston 101 moves downwards proportionally to the variation in temperature, whereby the pressure beneath it rises, which is also the case of the pressure above the piston 112, so that the latter also moves downwards and moves the control slide 119 in the same direction. This has the result of causing pressure oil to pass through the pipe 122 into the cylinder space below the servo-piston 124 and pressure oil situated above this piston to escape through the pipe 121 and the control cylinder 121). The piston 124 thus moves upwards and through the two-armed lever 126 opens or increases the opening in the valve in the injection control device 32, so that a larger quantity or proportion of water is introduced into the working medium flowing in pipe 87 leading to the superheater 17. Through the arrangement of the piston 129 and its connection to the lever 116 and the spring 117, the control slide 119 is moved back resiliently so that this regulating circuit has a proportional and integral character.

The larger amount or higher rate of water now flowing through the water supply pipe 66 as a result of the control changes described above efiects a changed pressure difference in the measuring device 35, whereby the diaphragm 138, and thus also the rod 139, moves downwards. The said rod rocks the cam disc 140 about the point 141 in a counterclockwise directionso that the spring 143 is compressed and the pressure beneath the piston 142 rises. This rise in pressure is transmitted to the control piston 147 which moves downwards against the compressive force of the spring 148 and thus connects the pipe 149 to the outlet pipe of the cylinder 146, so that the pressure in the pipe 149 drops, which occurs gradually because of the throttle member 150. The pressure beneath the piston 152 accordingly also drops, which causes a reduction in the temperature of the Working medium in the superheater 14 through the regulating circuit associated with the superheater 14.

This is accomplished in the following manner since the downward movement of the piston 152, as a result of the pressure drop, effects a downward movement of the control slide 119 and thus an upward movement of the servo-piston 124'. The valve in the water injection device 40 is thus opened or its opening increased. The larger amount of water flowing through the water supply pipe 68 as a result causes a turning of the cam disc 140 in a counterclockwise direction, whereby the pressure beneath the piston 142' is increased and the control slide 147' is pushed downwards. The pressure in the pipe 149 drops and thus also the pressure beneath the piston 152' (FIG. 2b), which in turn has the ultimate effect of restoring the temperature in the pipe 65 to the desired value. Downward movement of the piston 152' causes a downward movement of the control slide 119", whereby the pressure beneath the servo-pistons 124" is increased and this piston moved upwards. As a result the piston 168 moves upwards, the pressure in the pipe 167 drops, and thus also the pressure beneath the piston 166. This effects an upward movement of the servo-piston 124" and hence an increase in the amount of water flowing through the feed water control valve 4. The adjustment of the feed water valve 4 is influenced not only by the foregoing operations but also by the temperature variations transmitted from the thermostat 8 and the flow variations transmitted from the flow responsive means and 10 in front of the economizer 6 and in front or" the first super-heater 11 respectively.

It will be understood that any temperature variation from the normal for the working medium flowing through the pipe 85 and transmitted by the thermostat 8 will, in turn, be transmitted to the cylinder 151 and the piston 152, to either augment or reduce the change caused by the pressure drop or rise in the hydraulic line 149, also that changes in the flow rate through the device 5 in the pipe 25, from the normal flow, will be transmitted through the line 165 and influence the movement of the piston 166. It will also be understood that the movement of the valve 4 will be influenced by the direction of the impulse transmitted through the line 179 to or from the space below the piston 178 in accordance with changes from normal in the flow rate through the device it} in the pipe 85.

Similar types of servo mechanisms are used in the different regulating circuits for controlling the flow of hydraulic fluid or transmission of impulses, and it will be understood from a consideration of the detailed description of the mechanisms shown in FIGS. 2a and 2b exactly how changes in the various variables influence the impulses transmitted through the regulating circuits. For example, it will be understood that the thermostat 15 may transmit an impulse to the line connecting the

cylinders

151 and 154, or change the pressures therein, and influence the operation of the water injection control valves in the

devices

32 and 40. The thermostat 12 is connected into the circuit control so that it influences only the control of the valve in the injection device 40.

It will be furthermore understood that the various control mechanisms shown in FIGS. 2a and 2b may be provided with adjusting devices of a conventional type for making the desired settings for the usual or normal operation of the steam generator. For example, the thermostat 18 will 'be set to maintain the desired normal outlet temperature for the superheated steam in the pipe 65 and any increase or decrease in the temperature from the normal will cause the thermostat to operate the control valve in the injection device 32 in a direction to counteract the temperature change in the line 65. The injection device 32 is not the only one influenced by the operation of the thermostat 18, but as described above, the change initiated by this thermostat is transmitted clear through the regulating circuits to the control valve 4, in the manner described above so that the increased water supply is provided at a point or points in the steam generator where the temperature of the working medium is low.

In the embodiment illustrated in FIG. 3, the following modifications have been made as compared with the embodiment illustrated in FIG. 1. Instead of measuring the variation in the amount of water in the water supply pipe 66, and thus indirectly deriving the desired value displacement at the PI-regulator 39 from the adjusted magnitude at the last regulating circuit, in accordance with FIG. 3, the displacement of the desired value is derived directly from the adjusted magnitude, as the magnitude of the adjustment part of the valve spindle in the injection device 32 is measured by a device 26 and passed as an impulse to the integral regulator 67. In addition, in the embodiment illustrated in FIG. 3, the temperatureresponsive means 12 is moved to a position (viewed in the direct-ion of flow of the working medium) downstream of the injection point in the last but one regulating circuit, ie to the opposite side of the pipe 68, so that the thermostat 12 is responsive to the amount of water introduced through the pipe 68 as a modifying influence and correspondingly influences the output impulse of the PI- regulator 39. Finally, instead of a trap type steam separator 9, a through-flow separator 9' is provided.

The embodiment illustrated in FIG. 4 is modified in relation to the embodiment illustrated in FIG. 1 in the sense that the impulses caused by the measured water quantity variation in the last but one regulating circuit by the control 50 are not passed to the regulating circuit controlling the feed water control valve 4, but these impulses, which are converted into integral impulses in a regulator 51', are inserted into a regulating circuit connected into the system in advance of the last but one regulating circuit, and comprised of the thermostat 12, a PI- regulator 80, and a water supply device 8 1. This supply device 81 consists of an injector, which is incorporated in the working medium pipe between the steam separator 9 and the first superheater, 11, and which sucks off working medium from the pipe 84 in advance of the evaporator 7 and draws it through a supply pipe 82 into the working medium pipe 85. In the pipe 82, a valve 83 is provided the through-flow cross-section of which is varied in dependence on the magnitude of the impulse transmitted thereto by the PI-regulator '80. In FIG. 4 the impulses from the thermostat 12 are transmitted to the regulator 60, as in FIG. 1, and also to the regulator 80.

The various control devices and regulators shown diagrammatically in FIGS. 1, 3 and 4 may be of known type or construction for performing the functions and operations described in connection with the regulating circuits of the modifications shown in these figures. They may also correspond to the devices and regulators shown in detail in the hydraulic control system shown in FIGS. 2a and 2b.

Instead of imposing the impulses from the thermostats '12 and 15 as a modifying magnitude on the output impulses of the regulators in the regulating circuit following in each case, viewed in the direction of flow of the working medium, according to another embodiment of the invention a device responsive to changes in the rate of steam flow is additionally provided at the respective points, the impulses of which device are inserted as a modifying magnitude into the respective following regulating circuit. Instead of using the rate of steam flow, an impulse dependent on the operation of the furnace of the steam generator could be inserted in the regulating circuit as the modifying magnitude. The water for injection through

pipes

66 and 68 may be supplied from another source instead of from pipe 25.

In the operation of the system in which the series of heaters, 6, 7, #11, 14 and 17 of the various embodiments are at successively higher temperatures, changes in the temperature of the superheated steam in the pipe 65 from 9 the desired temperature are reflected back through the regulating circuits, in some instances to and affecting the rate of water supply through the valve 4, so that water introduction into the pipe 87, for example, is kept as low as possible. This keeps thermodynamic losses low and improves the operation.

What I claim is:

1. A steam generator comprising series-connected upstream and downstream heat exchange surfaces over which a working substance flow-s successively, a temperature control circuit for each of said surfaces, each said control circuit comprising means to develop a signal representative of theoutput steam temperature of its heat exchange surface, means to develop a signal representative of a reference temperature, means to compare said firstnamed signal with said signal representative of a reference temperature, and means to adjust the steam temperature at the output of its heat exchange surface in accordance with the result of said comparison, said adjusting means in the control circuit of said downstream surface comprising water injection means upstream of said downstream surface and means to vary the quantity of water injected through said injection means directly with the steam temperature at the outlet of said downstream surface, said generator further comprising means to measure the rate of water injection upstream of said downstream surface, and means to adjust the reference temperature in the control circuit of said upstream surface as an inverse function of said Water injection rate.

2. A steam generator comprising series-connected upstream and downstream heat exchange surfaces over which :a working substance flows successively, a temperature control circuit for each of said surfaces, each said control circuit comprising means to develop a signal representative of the output steam temperature of its heat exchange surface, means to develop a signal representative of a reference temperature, means to compare said first-named signal with said signal representative of a reference temperature, and water injection means upstream .of its heat exchange surface controlled in accordance with the result of said comparison to increase the quantity of water injected with excess of output steam temperature over reference temperature on said comparison, said generator further comprising means to measure the rate of water injection upstream of said downstream surface, and means to adjust the reference temperature in the control circuit of said upstream surface as an inverse function of said water injection rate.

3. A steam generator comprising series-connected upstream and downstream heat exchange surfaces over which a working substance flows successively, a temperature control circuit for each of said surfaces, each said control circuit comprising means to develop a signal representative of the output steam temperature of its heat exchange surface, means to develop a signal representative of a reference temperature, means to compare said first-named signal with said signal representative of a reference temperature, and water injection means upstream of its heat exchange surface controlled in accordance with the result of said comparison to increase the quantity of water injected with excess of output steam temperature over reference temperature on said comparison, said generator further comprising means to measure the rate of water injection upstream of said downstream surface, means to adjust the reference temperature in the control circuit of said upstream surface as an inverse function of said water injection rate, and means to insert into the control circuit of said downstream surface a signal representative of the output steam temperature of said upstream surface.

4. A steam generator comprising an evaporator, upstream and downstream superheaters connected in series with each other and with said evaporator, upstream and downstream superheater temperature control circuits, each said control circuit including means to develop a signal 10 I representative of the output steam temperature of its superheater, means to develop a signal representative of a reference temperature, means to compare said firstnamed signal with said signal representative of a reference temperature, and 'water injection means upstream of its superheater controlled in accordance with the result of said comparison to increase the quantity of water injected with excess of output steam temperature over reference temperature on said comparison, said generator further comprising means to measure the rate of water injection upstream of said downstream superheater, means to adjust the reference temperature in the upstream control circuit as an inverse function of said water injection rate, means to measure the steam temperature upstream of said upstream superheater, and means to insert into each of said control circuits a signal representative of the steam temperature upstream of its respective superheater.

5. A steam generator comprising an evaporator, upstream and downstream superheaters connected in series with each other and with said evaporator, upstream and downstream superheater temperature control circuits, each said control circuit including means to develop a signal representative of the output steam temperature of its superheater, means to develop a signal representative of a reference temperature, means to compare said firstnamed signal with said signal representative of a reference temperature, and water injection means upstream of its superheater controlled in accordance with the result of said comparison to increase the quantity of water injected with excess of output steam temperature over reference temperature on said comparison, said generator further comprising means to measure the rate of water injection upstream of each of said superheaters, means to adjust the reference temperature in the upstream control circuit as an inverse function of the water injection rate between said superheaters, and means to modify the rate of sup ply of feed water to said evaporator in accordance with the water inject-ion rate upstream of said upstream superheater.

6. A steam generator comprising series-connected upstream and downstream heat exchange surfaces over which a working substance flows successively, a temperature control circuit for each of said surfaces, each said control circuit comprising means to develop a signal representative of the output steam temperature of its heat exchange surface and means to develop a signal representative of a reference temperature and means to compare said first-named signal with said signal representative of a reference temperature and means to adjust the steam temperature at the output of its heat exchange surface in accordance with the result of said comparison, said adjusting means in the control circuit of said downstream surface comprising water injection means upstream of said downstream surface, said generator further comprising means to measure the rate of water injection at said Water injection means and to develop a signal representative of said rate, signal limiting means, and means to apply said last-named signal via said limiting means as a reference temperature signal in the control circuit of said upstream surface.

7. In the operation of a steam generator including series-connected upstream and downstream heat-exchange surfaces over which the working substance passes successively and including separate water injection means upstream of each of said surfaces respectively for control of the temperature of the working substance downstream of said downstream surface, the method of regulating said temperature which comprises measuring said temperature, efiecting a first introduction of water upstream of said downstream surface for control of said temperature, measuring the temperature of the working substance at a point upstream of said first introduction and downstream of said upstream surface, effecting a sec- :ond introduction of water upstream of said upstream sur- 1-1 12 face for control of said last-named temperature, and FOREIGN PATENTS modifyin the control of said last-named temperature by said 'seoo nd introduction in acoordance with the rate of j 1923 said first introduction to reduce the level to which said 482,901 Great m f P 1938 last named temperature is held by said second introduc- 5 793,341 Great Bnt'am P 16; 1958 tion upon increase 111 saidfirst introduction and vice versa. OTHER REFERENCES References Cited in the file o this Patent Combustion, August 1956, pages 47 to 5 6. Published UNITED STATES PATENTS by Combustion Publishing Company.

2,848,983 Lieberherr Aug. 26, 1958 10 German pp i i 1,050,009, Feb. 5, 1959.

Claims

1. A STEAM GENERATOR COMPRISING SERIES-CONNECTED UPSTREAM AND DOWNSTREAM HEAT EXCHANGE SURFACES OVER WHICH A WORKING SUBSTANCE FLOWS SUCCESSIVELY, A TEMPERATURE CONTROL CIRCUIT FOR EACH OF SAID SURFACES, EACH SAID CONTROL CIRCUIT COMPRISING MEANS TO DEVELOPA SIGNAL REPRESENTATIVE OF THE OUTPUT STEAM TEMPERATURE OF ITS HEAT EXCHANGE SURFACE, MEANS TO DEVELOP A SIGNAL REPRESENTATIVE OF A REFERENCE TEMPERATURE, MEANS TO COMPARE SAID FIRSTNAMED SIGNAL WITH SAID SIGNAL REPRESENTATIVE OF A REFERENCE TEMPERATURE, AND MEANS TO ADJUST THE STEAM TEMPERATURE AT THE OUTPUT OF ITS HEAT EXCHANGE SURFACE IN ACCORDANCE WITH THE RESULT OF SAID COMPARISON, SAID ADJUSTING MEANS IN THE CONTROL CIRCUIT OF SAID DOWNSTREAM SURFACE COMPRISING WATER INJECTION MEANS UPSTREAM OF SAID DOWNSTREAM SURFACE AND MEANS TO VARY THE QUANTITY OF WATER INJECTED THROUGH SAID INJECTION MEANS DIRECTLY WITH THE STEAM TEMPERATURE AT THE OUTLET OF SAID DOWNSTREAM SURFACE, SAID GENERATOR FURTHER COMPRISING MEANS TO MEASURE THE RATE OF WATER INJECTION UPSTREAM OF SAID DOWNSTREAM SURFACE, AND MEANS TO ADJUST THE REFERENCE TEMPERATURE IN THE CONTROL CIRCUIT OF SAID UPSTREAM SURFACE AS AN INVERSE FUNCTION OF SAID WATER INJECTION RATE.