US3016711A - Steam turbine power plant - Google Patents

Description

Jan. 16, 1962 F. SHAKESHAFT 3,016,711

STEAM TURBINE POWER PLANT Filed Feb. 16, 1960 5 Sheets-Sheet 1 Inventor A ttorneyg Jan. 16, 1962 Filed Feb. 16, 1960 F. SHAKESHAFT STEAM TURBINE POWER PLANT 3 Sheets-Sheet 2 "Inventor jam y 2 E I Atto neyg Jan. 16, 1962 F. SHAKESHAFT 3,016,711

STEAM TURBINE POWER PLANT Filed Feb. 16, 1960 5 Sheets-Sheet 3 L50 F (f; I III F 1 v 97 v J i:

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TE Ii l J Z5 In venlo fmm ire rates ice 3,tlll6,711 STEAM TURBINE PUWER PLANT Frederick Shaheshaft, London, England, assignor to Babcoclr & Wilcox Limited, London, England, a British company Filed Feb. 16, 196i Scr. No. apes @Zlaims priority, application Great Britain Feb. 17, 1959 It (Ilaims. (6i. 6067) This invention relates to steam turbine power plant. In steam turbine power plant having a turbine arranged to receive superheated steam, it is known to provide for the bleeding of steam at one or more stages in the turbine and for the passage of the bled steam to feed heating means in which the bled steam is condensed, in order thereby to secure, primarily by virtue of the fact that the latent heat of the steam being bled is transferred to feed water instead of being rejected with the cooling water of the turbine condenser, an improvement in the thermodynamic efficiency of the Rankine cycle applicable to the system.

It has been observed that since the feed water to be heated in this expedient by a flow of bled steam must be at a temperature suificiently low to condense the steam at the saturation temperature corresponding to the bled steam pressure while the bled steam leaving the turbine has on the other hand a degree of super-heat, i.e., an excess, which may be substantial, of temperature above the saturation temperature, there is necessarily involved element of irreversibility in the thermodynamic cycle, i.e., an element of degradation of heat which, prima facie, represents an impairment of the efiiciency of the conversion of heat to work. The object of the present invention is to provide means adapted for an improved exploitation of the heat in bled steam.

The invention includes a steam turbine power plant having a turbine arranged to receive superheated steam and to operate with bleeding of steam at different pressures from the turbine to diiferent heat exchangers of a feed train adapted progressively to heat water passing in succession through the heat exchangers of the feed train, wherein connected in bleed lines between the turbine and the feed train are desuperheaters forming a heat exchan er system arranged to receive water diverted from the feed train, to cool bled steam in its passage to the feed train and in so doing to heat the diverted water and vaporise and superheat a proportion of the diverted water, to discharge a heated unevaporated part of the diverted water to augment the feed water discharged from the feed train and to discharge at an intermediate pressure point of the turbine steam generated in the desuperheating means and after superheating by bled steam.

The invention will now be described by way of example with reference to the accompanying schematic and partly diagrammatic drawings, in which:

FIGURES 1A, 1B and 1C, when placed side-by-side in sequence, show most of the working fluid interconnections of a steam boiler and turbine and associated constituents of an electric power generating installation,

FIGURE 2 is a plan of a downfiow gas pass in section on the line Il-II of FIGURE 1C. Referring to the drawings, an electric power generating installation comprises a steam generating, superheating and reheating unit It, a steam turbine power plant 2 arranged to receive steam from the unit 1 and an electric generator 3 driven by the power plant 2.

The unit 1 is a natural circulation boiler of a type having a vertically elongated water cooled furnace 4 and a gas passage 5 containing steam heating surfaces and leading rearwardly from the upper part of the furnace to a gas turning space 6 above a downfiow gas pass 7 containing further steam heating surfaces and economiser 8.

The gases flowing rearwardly in the gas passage 5 flow first through a convection tertiary superheater 9 and then through most of a convection secondary reheater 10 the remainder of which is traversed by the gases as the latter pass through the gas turning space 6. The downfiow gas pass 7 is divided to form two parallel gas paths side by side, in one of which, denoted by the reference numeral 11, is disposed at primary superheater 12 while in the other of which, denoted by the reference numeral 13, is disposed a primary reheater 14. The economizer 8 extends across both the gas paths 11 and 13 at a location below the primary superheater i2 and primary reheater 14 and also extends across a by-pass passage 21 extending vertically at the rear of the gas paths 11 and 13 and communicating with the gas turning space 6. From the bottom of the downfiow gas pass 7 a conduit 22 is provided for leading the gases to a regenerative air heater 23. Dampers (not shown) are provided near the bottom of the downfiow gas pass 7 for controlling the gases in the gas paths 1i and 13 and in the by-pass 21.

in the upper part of the furnace 4 a radiant secondary superheater 2M is formed by tube platens arranged in the path of gases flowing towards the gas passage 5. In its lower half the furnace is arranged to be fired by the combustion of natural gas discharged by burner apparatus 25; the natural gas is delivered to the burner apparatus 25 through a fuel gas heater 2 6 and combustion air is delivered to the burner apparatus 25 through the air heater 23 by a fan 27. In its lowermost part the furnace 4 terminates in a hopper bottom 28 at which there may be introduced into the furnace 4 a stream controllable in amount of cooled furnace gases withdrawn from the bottom of the downfiow pass 7 by a recirculating fan 29.

The reference numeral 30 denotes the steam and water drum of the boiler unit 1, which is connected by ordinary means (not shown) to receive steam and water mixtures from Wall tubes of the furnace and from the floor and roof of the gas passage 5. At each end the drum is provided with a downcomer 31 which is connected by ordinary means (not shown) to supply water to said wall tubes.

The steam turbine power plant 2 comprises a group of turbine stages in a high pressure cylinder 32, a group of turbine stages in an intermediate cylinder 33 and a group of turbine stages in a low pressure cylinder 34. The high pressure cylinder 32 is connected to receive steam from the tertiary superheater 9 and to pass partly expanded steam to the primary reheater 14, the intermediate pressure cylinder 33 is connected to receive steam from the secondary reheater 1t) and to pass further expanded steam to the low pressure cylinder 34 which discharges fully expanded steam to the usual condenser 35. The condensate is withdrawn from the condenser 35 by an extraction pump 41 and delivered thereby to a feed train 42, of heat exchangers at the outlet end of which feed train is the boiler feed pump 43 which returns water to the economizer 8 of the boiler unit 1. The main flow circuit of the working fluid, for which the necessary connections are provided in the boiler unit, is from the steam space of the boiler drum 3t) through side walls of the gas passage 5 and side, front and rear walls of the downfiow gas pass 7, through the primary superheater 12, the secondary superheater 24, the tertiary superheater 9, the high pressure turbine stages in the cylinder 32, the primary reheater 14, the secondary reheater 10, the intermediate pressure turbine stages in the cylinder 33, the low pressure turbine stages in the cylinder 34, the condenser 35, the extraction pump 41, the feed. train 42, the feed pump 43, the cconomizer 8, and to the water space of the boiler drum 30 and includes flow under the in licence of natural circulation through the tubes'of the furnace walls and of the floor and roof of the gas passage 5 which are associated with the drum.

The feed train 42 consists of first to eighth heat exchangers 51 to 58 through which the feed water passes in succession, which heat exchangers receive heat from steam passing thereto in respective first to eighth bleed lines 61 to 68 from respective first to eighth bleed points 71 to 78 provided on the turbine cylinders. The low pressure cylinder 34 is provided with the three bleed points 71, 72 and 73 for steam between the inlet and outlet pressures thereof, the first bleed point 71 being that nearest to the outlet of the low pressure cylinder and the third bleed point 73 being that nearest to the inlet thereof. The intermediate pressure cylinder is provided with the three bleed points 74, 75 and 76, the fourth bleed point 74 being at the outlet of the intermediate pressure cylinder and the sixth bleed point 76 being that nearest to the inlet thereof. The high pressure cylinder is provided with the two bleed points 77 and 78, the seventh bleed point 77 being at the outlet of the high pressure cylinder. The steam flows entering the first to eighth bleed lines 61 to 68 are at successively higher pressures. The steam flows entering the first to sixth bleed lines 61 to 66 are also at successively higher temperatures. The temperature of the steam entering the eighth bleed line 68 is higher than the temperature of the steam entering the seventh bleed line 67. The temperature of the reheated steam supplied to the intermediate pressure turbine cylinder 33 from the boiler unit 1 is the same as the temperature of the superheated steam supplied to the high pressure turbine cylinder 32 from the boiler unit 1. The temperature of the steam entering the sixth bleed line 66 from the intermediate pressure cylinder is higher than the temperature of the steam entering the eighth bleed line 68 from the high pressure cylinder.

The steam flows which enter the first to eighth heat exchangers 51 to 58 from the bleed lines 61 to 68 are condensed therein. The first, second and third heat exchangers 51, 52 and 53 are indirect contact heat exchangers. A connection 53A is provided between the drain cooler of the third heat exchanger 53 and the interior of the second heat exchanger 52, through which condensatefiows from the interior of the third heat exchanger 53 to the interior of the second heat exchanger 52 under the influence of the pressure difference therebetween. A similar connection 52A permits the condensate formed within the second heat exchanger 52, together with that supplied to the second heat exchanger 52 through the connection 53A from the third heat exchanger 53, to enter the interior of the first heat exchanger 51, similarly under the influence of pressure difference. A connection 51A from the drain cooler of the first heat exchanger 51 permits the total condensate formed within the three heat exchangers 51, 52 and 53 to join the condensate in the condenser 35, similarly under the influence of pressure difference.

The fourth heat exchanger 54 is a de-aerator, both the feed water heated in the three heat exchangers 51, 52 and 53 and the bled steam from the fourth bleed line 64 enter the interior of the de-aerator. The fifth, sixth, seventh and eighth heat exchangers 55, 56, 57 and 58 are in direct contact heat exchangers. A connection 58A is provided between the drain cooler of the eighth heat exchanger 58 and the interior of the seventh heat exchanger 57, through which condensate flows from the interior of the eighth heat exchanger 58 to the interior of the seventh heat exchanger 57 under the influence of the pressure difference therebetween. A similar connection 57A permits the condensate formed within the seventh heat exchanger 57, together with that supplied to the seventh heat exchanger 57 through the connection 53A from the eighth heat exchanger 58, to enter the interior of the sixth heat exchanger 56, similarly under the influence of pressure difference. A connection 56A from the drain cooler of the sixth heat exchanger 56 similarly leads to the interior of the fifth heat exchanger 55. Finally a connection 55A from the drain cooler of the fifth heat exchanger 55 carries into the de-aerator 54 the total condensate formed within the four heat exchangers 55 to 53. In the said connection 55A a booster pump 59 is provided the suction side of which draws from a drain tank 60. A booster pump 44 is arranged to draw feed water from the de-aerator and to deliver it for flow in series through the heat exchangers 55 to 58.

In the second to eighth bleed lines 62 to 68 respective desuperheaters S2 to 88 are interposed between the second to eighth blced points 72 to 78 and the second to eighth heat exchanges 52 to 58.

The desuperheater $2 in the second bleed line 62 contains heat exchange surfaces 92. adapted to serve as a water heater and the desuperheater 83 in the third bleed line 63 contains heat exchange surfaces 93 adapted to serve as a water heater and connected in series with the surfaces 92; a small auxiliary high pressure booster pump 101 is arranged to withdraw a stream of water from the feed water line between the first and second heat exchangers 51 and 52 and to deliver it to the heat exchange surfaces 92 through which it passes generally in counterflow to the bled steam in the desuperheater 82, whence it passes to the heat exchange surfaces 93 through which it flows generally in counterfiow to the bled steam in the desuperheater 83; the water heated in the desuperheaters 82 and 83 is led by line 102 to join the feed water flow from the seventh heat exchanger 57 to the eighth heat exchanger 58.

The desuperheater $4 in the fourth bleed line 64 and the desuperheater 85 in the fifth bleed line 65 contain heat exchange surfaces which are connected for the flow therethrough in parallel, and generally in counterfiow to the bled steam in the said desuperheaters, of high pressure water Withdrawn through "a line 103 from the feed water flow between the booster pump 44 and the fifth heat exchanger 55. The heat exchange surfaces in the desuperheaters 34 and 85 comprise sections 04A and A respectively adapted to serve as water heaters and surfaces 94B and 95B respectively adapted to serve as vapourizers. The steam and water mixtures from the vapourizers 94B and 95B are led, for the separation of the mixtures into water and steam, to a boiler pressure drum 104 provided internally with cyclone separators and scrubbers 106 of known kinds.

The desuperheater 86 in the sixth bleed line 66 comprises a casing 136 and a casing 286 connected in series in the said bleed line. The casing 286, receiving bled steam cooled in the casing 186, contains heat exchange surfaces comprising a section 96A adapted to serve as water heated and a section 96B adapted to serve as a vapourizer for water heated in the section 96A. The water for said sections 96A and 96B is withdrawn through a line 107 from the feed water flow from the sixth heat exchanger 56 to the seventh heat exchanger 57, and flows through the sections 96A and 96B generally in counter flow to the bleed steam.

The desuperheater 87 in the seventh bleed line 67 contains heat exchange surfaces comprising a section 97A adapted to serve as Water heater and a section 97B adapted to serve as vaporizer of the water heated in the section 97A. The water for said sections also comes from the line 107 and flows through the desuperheater 87 generally in counterfiow to the bleed steam. Similarly the desuperheater 88 in the eighth bleed line 68 contains a water heating heat exchanger section 98A also supplied from the line 107 and passing its water to a vaporizing heat exchange section 98B. The steam and water mixtures from all the heat exchange sections 96B, 97B and 98B of the respective desuperheaters 86, 87 and 88 are led, for the separation of the mixtures into Water and steam, into the drum 104.

A second or lower drum 99 is positioned below the drum 104 and is associated therewith by a plurality of vertical connectors 1% distributed along the lengths of the two drums and connecting with the water space of the first or upper drum 104. A discharge line 108 leads from the lower drum $9 to the feed water flow from the eighth heat exchanger 53 to the feed pump 43, through which line 108 the water component of the steam and water mixtures formed in the desuperheaters 84, 85, 37 and 88 and in the casing 28d of the desuperheater 86 may, under control of a reciprocating pump 119 in the said line, be delivered to augment the feed Water heated in the feed train 42.

The casing 186 of the desuperheater 86 in the sixth bleed line 66 contains heat exchange surfaces 96C adapted to serve as superheater and arranged on the one hand partially to desuperheat bled steam in the said line and on the other hand to superheat steam separated from the steam and water mixtures entering the drum, to which end steam is led in line 109 from the drum to the heat exchange surfaces 96C for flow therethrough generally in counterflow to the bleed steam. The steam heated in the superheater 96C passes to a line 110 which has two branches 111 and 112; the branch 111 leads to the high pressure turbine cylinder 32 at a stage thereof having a pressure slightly lower than the pressure at the eighth bleed point 73 and the branch 112 conducts superheated steam to the fuel gas heater 26 for the heating of the gas passing therethrough.

The fuel gas heater 26 is adapted for desuperheating and condensing the steam passing thereto and the water condensed and cooled therein is delivered by a pump 113 in a line 114 to the feed Water line between the third heat exchanger 53 and the de-aerator d. The aqueous fluid flows in the gas heater generally in counterfiow to the gas and is arranged to pass in succession through heat exchange surfaces 1155C adapted to serve as a desuperheating section, heat exchange surfaces 115B adapted to serve as a condensing section, and heat exchange surfaces lliliiA adapted to serve as a water cooling section.

The pressure in the superheated steam branch 113 leading to the gas heater 26 is substantially higher than the pressure in the feed water line between the third heat exchanger 53 and the de-aerator 54. For maximum fuel gas heating the de-superheating and condensing sections 1150 and 115B should operate at the full steam pressure but the Water cooling section 115A need not operate at high pressure and the throttle 116 required to reduce the aqueous fluid pressure is placed in the aqueous fluid path between the sections 11513 and 115A, thereby enabling the water cooling section 115A to be constructed for low pressure operation.

For the regulation of the water level in the steam and water drum 1M- automatic water-level control means (not shown) of known kind are provided which are arranged to operate upon feed regulating valves 121 and 122 provided in the lines 1113 and 107 through which water is withdrawn from the feed water flow through the feed train 42 to be passed into the drum after being partly vaporized in the desuperheaters 34 to 88. Such automatic control means may provide feed water controls of a kind known in connection with boiler installations as a three-element control; thus the feed regulating valves 121 and 122 may be adjusted by a difference between control signals suitably representative respectively of saturated steam flow rate in the line 109 and total water flow rates in the lines 103 and 107 and by an overriding control signal derived from a water level recorder associated with the drum 104. The water level in the drum 104 is also affected by the rate of operation of the pump 119 in the line 108, which is arranged to be controlled by a further three element automatic control; thus the operating rate of the pump 119 may be adjusted by a difference between control signals suitably representative respectively of the steam pressure in drum 104- and the total water flow rates in the lines 103 and 197 and by an over riding control signal de-- 6 rived from a water level recorder associated with the drum 104.

Isolating valves 131, 132 and 133 are provided respec'- tively in the saturated steam line 169, the branch 111. from the superheated steam line 132 and the water line 108; these valves will be arranged for automatic closure if, for example, there should be a complete loss of load on the electric generator.

A steam line 134, in which is provided a normally closed reducing valve 1135, leads from the steam outlet from the drum 311) of the boiler unit 1 to the branch 112 from the steam line 110, in order that, should the isolating valve 132 in said branch be closed, steam may nevertheless be made available for fuel gas heating.

The second heat exchanger 52 contains not only heat exchange surfaces 14-1 arranged in the feed water line for the heating of the feed water by the condensation of steam of the second bleed line 62 but also additional heat exchange surfaces 142 arranged in a closed circuit 143 containing a circulating water pump 144 and which includes an auxiliary air heater 145' arranged in the air duct between the fan 27 and the regenerative air heater 23. When the pump 144 is operated, heat absorbed by the surfaces 14 2 acting to condense bled steam is transferred through the air heater 14$ to combustion air on its Way to the air heater 23.

in the operation of the installation, steam is generated and superheated in the boiler unit 1, expanded in the high pressure turbine cylinder 32, reheated in the boiler unit, expanded in the intermediate and low pressure turbine cylinders 33 and 34 and condensed in the condenser as; the condensate from the condenser is heated in the feed train 42 and in the economizer 8 of the boiler unit. Frac tional amounts of the steam generated in the boiler unit flow only parts of the way through the turbine stages to the condenser 35 and leave the turbine cylinders at the various bleed points 71 to 78 to flow through the respective bleed lines 61 to 68. At the ends of the bleed lines bled steam is condensed by feed water passing through the heat exchangers of the feed train and rising in temperature as it encounters and condenses in heat exchanger after heat exchanger bled steam of progressively higher saturation temperatures.

The pump 101 delivering to the desuperheater 82 is driven so that the steam in the bleed line 62 is cooled by the water flow in the heat exchange surfaces 92 in the desuperheater 82 to or only a little above its saturation temperature. The desuperheaters 82 and 833 are designed with reference to the steam temperatures and pressures at the bleed points '72, and 73 so that with this water flow the steam in the bleed line 63 is cooled in the heat exchange surfaces 93 in the desuperheater 83 to or only a little above its saturation temperature. The heater water leaving the desuperheater 83 is at or close to the temperature of the feed water leaving the seventh heat exchanger 57 to which water it is added.

Desuperheaters 84 and receive water through the common line 103 but, in order that they may abstract all or substantially all the superheats of steam flows of respectively diiferent inlet pressures and temperatures, are designed for different water supply rates. Restrictive nipples 161 selected or set to give appropriate water flow restriction effects are inserted on the water inlet sides of the desuperheaters 84 and 85. For similar reasons the desuperheaters 86, 87 and 38 are also provided with restrictive nipples 161.

The arrangement provides that the feed water for the the desuperheaters 86, 87 and 88 is at a higher temperature than the feed water for the desuperheaters 84 and 85 since the saturation temperatures of the steam in the bleed lines through the former desuperheaters are higher than the saturation temperatures of the steam in the bleed lines through the latter desuperheaters. The bled steam flows leave the respective desuperheaters 84- to 88 at or near and above the respective saturation temperatures.

The steam flows in the bleed lines leading through the desuperheaters 82 to 88 to the heat exchangers 52 to 58 are greater than if the bled steam were not desuperheated on its way to the heat exchangers 52 to 58, thus the conservation of latent heat in the system instead of its rejection to the condenser cooling water is greater.

Since the desuperheaters 82 to 88 absorb the or most of the superheats in the steam flowing in the respective bleed lines 62 to 68, the heat exchangers 51 to 53 and 55 to 58 may, in view of the relatively low steam temperatures thereat, be of relatively inexpensive construction.

The steam separated from the steam and water mixtures formed in the desuperheaters 84. to 88 is superheated in the heat exchange section 96C of the desuperheater 86 in the bleed line 66 supplied by steam at highest temperature. The said steam, except that required for the purpose of gas heating in the gas heater 26, passes to the high pressure turbine cylinder 32 through the line 110 and joins the main steam flow therein.

The heats represented by degrees of superheat in the bled steam passing to the desuperheaters 84- to 88 and withdrawn from the steam therein are, instead of being wholly degraded to the temperature of the water in the feed train, utilized to generate steam at substantial pressure and in superheating the generated steam to a temperature at which the steam may usefully be employed by admission to a relatively early, high pressure and temperature stage of the turbine power plant. The said generated steam is at a higher pressure than the pressures in all the corresponding bleed lines except the bleed line 68 and the heat exchange system of the desuperheaters 84 to 87 may be regarded as a steam transformer system which utilizes the superheat of steam at relatively low pressure to generate high temperature steam at higher pressure.

Since steam is generated at high pressure in the desuperheaters 84 to 88, heat is withdrawn at relatively high temperature from the bled steam entering the desuperheaters 84, 85, 87 and 88 and suifers thereby less degradation than if the steam were generated at low pressure.

Moreover, the bled steam from the bleed point 76 of highest steam temperature entering the desuperheater 86 contacts first heat exchange surfaces 96C traversed by steam that, having been separated from steam and water mixtures, is considerably less in amount than the aqueous fluid required, for desuperheating purposes, to traverse the heat exchange surfaces in the desuperheater 84, desuperheater 85, casing 286, desuperheater 87 and desuperheater 88 and this latter steam is therefore superheated to a relatively high degree. The degradation of heat in the withdrawal of the upper range of superheat in the steam in the high temperature bleed line 66 is therefore particularly small.

It will be seen that superheats in the steam in the bleed lines 62 to 68 are very advantageously utilized.

Preheating of the combustion air by the heater 145 may be effected continuously or when circumstances warrant to prevent corrosion in the main air heater 23.

Should a lower degree of heating of the fuel gas in the gas heater 26 be contemplated, all the steam for the said heater may be taken from a source of steam of lower temperature than that in the line 110, for example, from the fifth bleed steam line 65 at a position therein between the bleed point 75 and the desuperheater 85.

The heat exchangers in the feed train 42 may be of constructions known in connection with feed trains and the extraction pump 41, booster pump 44 and feed pump 43 have flow-head characteristics also known in such connection. The arrangement permits the high-level disposition of the de-aerator 54, a measure for avoiding vapour binding or cavitation that might otherwise arise in certain circumstances in the booster pump 44 or feed pump 43.

Generally speaking, any of numerous constructions of indirect heat exchangers will be suitable for the desuperheaters 82 to 88. It is specifically envisaged, however,

that they may comprise more or less elongated pressure vessels as indicated in the drawings of US. patent application Serial No. 806,846, containing helical coils where water is to be heated, as in the lower part of FIGURE 1A and the outer part of FIGURE 5 of those drawings and containing an assembly of vapour generating units where steam is to be formed, as in the upper part of FIG- URE 1 and the inner part of FIGURE 5 of those drawings.

I claim:

1. Steam turbine power plant comprising steam generating means, a steam turbine, steam condensing means, means for circulating aqueous fluid in a circuit through the steam generating means, steam turbine, steam condensing means and back to the steam generating means, bled steam heating feed heating means including a plurality of steam condensing heat exchangers connected in succession in the aqueous fluid circuit between the steam condensing means and the steam generating means and a plurality of steam bleed lines from respective steam bleed points of the turbine of successively increasing pressure to the respective heat exchangers, the said heat exchangers being adapted to condense bled steam in heating feed water, a plurality of steam desuperheating heat exchangers connected in the respective steam bleed lines between the turbine and the steam condensing heat exchangers, means for delivering water to a steam desuperheating heat exchanger to be heated therein, steam and water separating means arranged to receive steam and water mixture generated in the last mentioned steam desuperheating heat exchanger, means for withdrawing steam from the steam and water separating means and passing it through at least one steam desuperheating heat exchanger to be superheated therein and delivering the resulting superheated steam to the turbine to assist the driving thereof, and means for withdrawing water from the steam and water separating means and introducing it into water in the aqueous fluid circuit.

2. Steam turbine power plant comprising steam generating means, a steam turbine, steam condensing means, circulating means for circulating aqueous fluid in a circuit through the steam generating means, steam turbine, steam condensing means, and back to the steam generating means, said circulating means including an extraction pump arranged for the withdrawal of condensate from the steam condensing means and a feed pump arranged for the delivery of water to the steam generating means, bled steam heated feed heating means including a plurality of steam condensing heat exchangers connected in succession in the aqueous fluid circuit between the extraction pump and the feed pump and a plurality of steam bleed lines from respective steam bleed points of the turbine of successively increasing pressure to the respective heat exchangers, the said heat exchangers being adapted to condense bled steam in heating feed water, a plurality of steam desuperheating heat exchangers connected in the respective steam bleed lines between the turbine and the steam condensing heat exchangers, means for withdrawing water from the aqueous fluid circuit at a location between the extraction pump and the feed pump and delivering said water to a steam desuperheating heat exchanger to be heated therein, steam and water separating means arranged to receive steam and water mixture generated in the last mentioned steam desuperheating heat exchanger, means for withdrawing steam from the steam and water separating means and passing it through at least one steam desuperheating heat exchanger to be superheated therein and delivering the resulting superheated steam to the turbine to assist the driving thereof, and means for withdrawing water from the steam and water separating means and introducing it into the aqueous fluid circuit between the location of water withdrawal and the feed pump.

3. Steam turbine power plant as claimed in claim 2, wherein one of the bled steam heated feed heating means is a de-aerator, a booster pump is provided in the said aqueous fluid circuit between the de-aerator and the next subsequent bled steam heated feed heating means and the said location of withdrawal of water from the aqueous fluid circuit lies in the aqueous fluid circuit subsequent to the booster pump.

4. Steam turbine power plant comprising steam gen erating means, a steam turbine, steam condensing means, circulating means arranged for circulating aqueous fluid in a circuit through the steam generating means, steam turbine, steam condensing means, and back to the steam generating means, said circulating means including an extraction pump arranged for the withdrawal of condensate from the steam condensing means and a feed pump arranged for the delivery of water to the steam generating means, bled steam heated feed heating means including a plurality of steam condensing heat exchangers connected in succession in the aqueous fluid circuit between the extraction pump and the feed pump and a plurality of steam bleed lines from respective steam bleed points of the turbine of successively increasing pressure to the respective heat exchangers, the said heat exchangers being adapted to condense bled steam in heating feed water, a plurality of steam desuperheating heat exchangers connected in the respective steam bleed lines between the turbine and the steam condensing heat exchangers, means for withdrawing water from the aqueous fluid circuit at a location therein between the extraction pump and the feed pump and delivering water in parallel streams to a plurality of steam desuperheating heat exchangers to be heated therein, steam and water separating means arranged to receive steam and water mixture generated in the last mentioned steam desuperheating heat exchangers, means for withdrawing steam from the steam and water separating means and passing it through at least one steam desuperheating heat exchanger to be superheated therein and delivering the resulting superheated steam to the turbine to assist the driving thereof and means for withdrawing water from the steam and water separating means and introducing it into the aqueous fluid circuit between the location of water withdrawal and the feed pump.

5. Steam turbine power plant comprising steam generating means, a steam turbine, steam condensing means, circulating means for circulating aqueous fluid in a circuit through the steam generating means, steam turbine, steam condensing means, and back to the steam generating means, said circulating means including an extraction pump arranged for the withdrawal of condensate from the steam condensing means and a feed pump arranged for the delivery of water to the steam generating means, bled steam heated feed heating means including a plurality of steam condensing heat exchangers connected in succession in the aqueous fluid circuit between the extraction pump and the feed pump and a plurality of steam bleed lines from respective steam bleed points of the turbine of successively increasing pressure to the respective heat exchangers, the said heat exchangers being adapted to condense bled steam in heating feed water, a plurality of steam desuperheating heat exchangers connected in the respective steam bleed lines between the turbine and the steam condensing heat exchangers, means for withdrawing water from the aqueous fluid circuit at a plurality of locations therein between the extraction pump and the feed pump and delivering water in parallel streams to a plurality of steam desuperheating heat exchangers to be heated therein, steam and water separating means arranged to receive steam and water mixture generated in the last mentioned steam desuperheating heat exchangers, means for withdrawing steam from the steam and water separating means and passing it through at least one steam desuperheating heat exchanger to be superheated therein and delivering the resulting superheated steam to the turbine to assist the driving thereof, and means for withdrawing water from the steam and water separating means and introducing it into the aqueous fluid circuit between the 10- cations of water withdrawal and the feed pump.

6. Steam turbine power plant comprising steam generating means, a steam turbine, steam condensing means, means for circulating aqueous fluid in a circuit through the steam generating means, steam turbine, steam condensing means, and back to the steam generating means, bled steam heated feed heating means including a plurality of steam condensing heat exchangers connected in succession in the aqueous fluid circuit between the steam condensing means and the steam generating means and a plurality of steam bleed lines from respective steam bleed points of the turbine of successively in creasing pressure to the respective heat exchangers, the said heat exchangers being adapted to condense bled steam in heating feed water, a plurality of steam desuperheating heat exchangers connected in the respective steam bleed lines between the turbine and the steam condensing heat exchangers, means for delivering water in parallel streams to a plurality of steam desuperheating heat exchangers to be heated therein, steam and water separating means arranged to receive the steam and water mixture generated in the last mentioned steam desuperheating heat exchangers, means for withdrawing steam from the steam and water separating means and passing it through at least one steam desuperheating heat exchanger to be superheated therein and delivering the resulting superheated steam to the turbine to assist the driving thereof, and means for withdrawing water from the steam and water separating means and introducing it into water in the aqueous fluid circuit.

7. Steam turbine power plant as claimed in claim 6, wherein the bleed steam line leading from the hottest steam bleed point of the' turbine leads successively through a superheater of steam from the steam and water separating means, and one of the plurality of steam desuperheating heat exchangers adapted for the generation of steam and Water mixture.

8. Steam turbine power plane comprising steam generating means including a furnace provided with fluent fuel burner means, a heater for fluent fuel, a steam turbine, steam condensing means, means for circulating aqueous fluid in a circuit through the steam generating means, steam turbine, steam condensing means, and back to the steam generating means, bled steam heated feed heating means including a plurality of steam con densing heat exchangers connected in succession in the aqueous fluid circuit between the steam condensing means and the steam generating means and a plurality of steam bleed lines from respective steam bleed points of the turbine of successively increasing pressure to the respective heat exchangers, the said heat exchangers being adapted to condense bled steam in heating feed water, a plurality of steam desuperheating heat exchangers connected in the respective steam bleed lines between the turbine and the steam condensing heat exchangers, means for delivering water to a steam desuperheating heat exchanger to be heated therein, steam and water separating means arranged to receive steam and water mixture generated in the last mentioned steam desuperheating heat exchanger, means for withdrawing steam from the steam and water separating means and passing it through at least one steam desuperheating heat exchanger to be superheated therein and passing the resulting superheated steam to the fluent fuel heater, and means :for withdrawing water from the steam and water separating means and introducing it into Water in the aqueous fluid circuit.

9. Steam turbine power plant as claimed in claim 8, wherein the fluent fuel heater is formed with a steam cooling section of heat exchange surfaces adapted to cool the superheated steam entering it, a steam condensing section of heat exchange surfaces adapted to condense the steam and a water cooling section of heat exchange surfaces adapted to cool the resulting water and means are provided for introducing the cooled resulting water into the aqueous fluid circuit at 'a location therein between two of the bled steam heated feed heating means.

10. Steam turbine power plant as claimed in claim 9, wherein a throttle is provided between the steam condensing section of the fluent fuel heater and the Water cooling section thereof and a pump is provided for withdrawing the cooled resultant water from the fluent fuel heater.

References Cited in the file of this patent UNITED STATES PATENTS

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