Power plant

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Drawing sheet — no readable text.

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upstream from the two parallel branches. The total

POWER PLANT feedwater flow is rejoined at a second junction down BACKGROUND OF THE INVENTION stream from the two parallel branches. The output tem perature at each branch is measured. Whenever the

This invention relates, in general, to steam turbine output temperature of the solar branch exceeds the generator power plants; and, in particular this invention output temperature of the extraction branch an auxil relates to feedwater preheating by means of solar en iary feedwater pump in the solar branch is energized so ergy. as to decrease the flow in the extraction branch. This In a steam turbine-generator power plant, a steam decrease in extraction branch flow causes a decrease in generator, or boiler, is used to provide steam for driving 10 extraction steam requirements and hence the turbine the steam turbine which in turn, drives the rotor of an power output is proportionately increased. The in electrical generator to produce electricity. Steam which creased turbine power output may be used to satisfy is exhausted from the turbine is thereafter condensed additional load requirements or alternatively, the steam and returned to feedwater. The feedwater is then recir generator firing rate may be cut back while maintaining culated to the steam generator where it is reheated to 15 a constant turbine power output.

provide more steam. It has been found economical to The novel features believed characteristic of the pre preheat the feedwater prior to its return to the steam sent invention are set forth in the appended claims. The generator using extraction steam from various points on invention itself, however, together with further objects the steam turbine as a heat exchange fluid. Preheating and advantages thereof, may be understood with refer feedwater raises the temperature of the feedwater and 20 ence to the following description taken in connection thereby decreases the heating requirements in the steam with the appended drawing.

generator resulting in a decrease in fuel requirements in the steam generator. Of course, extraction of steam BRIEF DESCRIPTION OF THE DRAWING from the steam turbine decreases the power output of The drawing shows a schematic diagram of a typical the turbine, but such a power loss is acceptable in terms 25 steam of satisfying the load demand and preferable in terms of whereinturbine generator power plant of the type extraction steam is used to preheat feedwater overall plant efficiency.

According to one aspect of the present invention, it to a boiler and wherein according to the present inven has been found that feedwater may be preheated by tion, the feedwater preheating is further augmented by applying solar heat to the feedwater. Dependent upon 30 solar heating.

ambient conditions, solar energy may be used to preheat DETAILED DESCRIPTION OF THE feedwater and thereby decrease the extraction steam INVENTION requirements in a manner to be disclosed as part of the The drawing shows one example of a typical power present invention. Since solar energy is available only on an intermittent basis, it is required that a system be 35 plant 10 which may include a high pressure turbine 15 devised which will take advantage of available solar and a low pressure turbine 17 arranged in tandem energy while maintaining a capability to meet load de through a mechanical coupling 19. Alternatively, any mand requirements when solar energy is not available. known arrangement of turbines may be used in combi Hence, it is one object of the present invention to nation with the present invention including a single provide a power plant wherein feedwater preheating is turbine used to drive a load. The two turbines shown augmented or replaced by solar energy. are used to drive a load 21 which may be the rotor of an It is another object of the present invention to pro electrical generator, the latter being joined to the output vide a power plant wherein solar energy is delivered shaft of the low pressure turbine through a mechanical into the power plant as it becomes available. coupling 23.

It is another object of the present invention to pro 45 The motive fluid to drive the high pressure turbine vide a power plant wherein the turbine power output and the low pressure turbine is supplied from a steam may be increased without an increase in boiler fuel generator 25 which delivers steam to the high pressure requirements. turbine inlet through a steam line 27. The steam line 27 It is still another object of the present invention to further includes suitable stop valves and control valves provide a power plant wherein the turbine power out 50 represented schematically by valve 29. Steam exhausted put may remain constant and the boiler fuel require from the high pressure turbine may be reheated in a ments decreased. reheater 31 incorporated into a steam inlet line 33 con

SUMMARY OF THE INVENTION

nected to the inlet end of the low pressure turbine.

Steam inlet line 33 also contains suitable stop valves and

According to the foregoing objects of the invention, 55 control valves schematically illustrated by valve 35. a steam turbine-generator power plant includes a means At the output end of the low pressure turbine the for preheating feedwater to the steam generator. Such exhaust steam is condensed whereupon the condensate feedwater preheating means include two parallel pre is returned to the feedwater input through condensate heater branches. A first preheater branch includes a line 41. Additional feedwater may be input into the plurality of feedwater preheaters connected in series feedwater supply through supply line 43 having a shut flow relationship, wherein each preheater is supplied off valve 45 whereas the condensate and make-up feed with feedwater and extraction steam in heat exchange water are joined at a pipe junction 47. Condensate pump relationship. A second solar branch includes at least one 49 delivers the total feedwater flow to a second pipe solar collector having feedwater passing therethrough junction 51. At junction 51, the feedwater flow is di so that there exists a heat exchange relationship be 65 vided, in a manner to be described, between two paral tween the available solar heat and the input feedwater. lel flow paths, namely an extraction branch and a solar The total feedwater flow from the turbine condenser branch. The two parallel branches are rejoined down and the makeup supply is divided at a first junction stream at a third pipe junction 55.

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A first branch or extraction branch may be comprised tor 25 to stabilize the temperature of the incoming feed of any suitable number (four shown) of feedwater pre water to the steam generator thus obviating small tem heaters 61, 63, 65 and 67 connected with one another in perature fluctuations which may occur in the feedwater a series flow relation. Each preheater receives an ex due to momentary differences in available solar heat traction steam flow from the low pressure turbine due to atmospheric conditions such as passing clouds. through extraction steam lines 71, 73, 75 and 77 respec Moreover, the additional feedwater heater will provide tively. Each extraction steam line contains a non-return a higher feedwater temperature and increase efficiency. valve 81, 83, 85 and 87 respectively. Each extraction Finally, non-return valves 125 and 127 protect their preheater is a heat exchanger which passes extraction respective heater branches against backflow while also steam in a heat exchange relation to the feedwater flow, 10 permitting the proper operation of pump 91. Moreover, the preheaters being non-contact or direct contact heat valve 127 protects heater 101 from being subjected to exchangers or any combination thereof. The amount of full boiler feedwater pressure and temperature should extraction steam withdrawn from the turbine is a func the driver (not shown) of pump 109 shut down. tion of the total feedwater flow volume and the feedwa The operation of the present invention will be de ter temperature. Nonreturn valves 81, 83, 85 and 87 15 scribed under two conditions; namely, when the turbine prevent the "flash back' of steam into the turbine from output is increased while the steam generator firing rate their respective preheaters in the event of a sudden loss remains constant; and, the turbine output remains con of turbine load. A decrease in feedwater flow causes a stant while the steam generator firing rate is decreased. decrease in extraction flow. The feedwater flow is Under the first condition, increased output at a constant maintained by means of a main boiler feed pump 91 20 firing rate, as the solar branch temperature T increases which may be driven through a separate drive (not above the feedwater branch temperature auxiliary shown) for variable speed control. The speed of the pump 109 will be activated. The controller 111 can be main broiler feed pump is in turn controlled by a con preset in a conventional manner so that auxiliary pump ventional and well known system which responds to 109 will not be actuated until Texceeds T. by a prese boiler demand for feedwater. If the boiler demand is 25 lected buffer temperature, e.g. 20 F. This will ensure augmented from the solar branch, then the main feed that the input from the solar branch will provide a sig water pump speed will decrease. nificant heat input and prevent undue cycling of the A second parallel branch or solar branch is comprised pump 109. The solar branch output at a higher tempera of at least one solar heater; or, as shown in the preferred ture and pressure than the extraction branch output will embodiment, may be alternatively comprised of a plu 30 cause the flow through the extraction branch to de rality of solar heaters 101 and 103 respectively. The crease proportionately and hence decrease the extrac solar heaters may be comprised of collector plates (not tion requirements into the extraction branch thus add shown) through which the feedwater is passed. The ing to the power output of the turbine by the amounts of solar heat energy may be directly or reflectedly ab extraction steam which now may be retained in the sorbed on the collector plates so that a heat transfer 35 turbine. As T increases above T2 the pumping rate of takes place between the absorbed solar heat and the auxiliary pump 109 proportionately increases until all feedwater passing through the collector plates. A pump extraction requirements from turbine 17 are ceased. The 105 is provided between the downstream (higher tem steam generator firing rate remains the same. In an perature) collector and the upstream (low temperature) electrical power plant it must be recognized that the collectors to increase the pressure in the downstream increased power output of the turbine must be matched collector so that increased temperatures may be to an increased load demand and hence the aforesaid achieved without steaming in the solar collector. mode of operation is particularly useful in day time The feedwater flow through the solar branch is con peaking applications wherein neither the electrical gen trolled by an auxiliary feedwater pump 109 at the down erator nor the turbine is design limited so that it cannot stream side of the solar heaters. Pump 109 is a variable 45 utilize the additional power output. speed pump which is responsive to the feedwater tem The second mode of operation wherein the turbine perature difference between the feedwater temperature output remains constant and the steam generator firing measurement at the outlet end of the solar heaters T. rate is decreased to conserve fuel is particularly useful and the temperature measurement taken at the outlet in retrofit applications wherein design limitations or end of the extraction preheater branch T. The output 50 demand requirements cannot be matched to an increase temperatures are compared in a controller 111 and a in turbine output. In this case, as the extraction require resultant speed signal is input into the drive means (not ments of turbine 17 are decreased, the steam input to shown) of pump 109 through line 113. The controller turbine 17 is also throttled back thereby allowing a 111 can be an electronic, hydraulic, or mechanical de decrease in the steam generator output such that the vice which compares input temperature signals T and 55 firing rate of the steam generator may be cut back and T2 and produces an output speed signal in line 113 pro fuel is thereby conserved.

portional to the difference. The temperature measure In summation, a solar heat branch is added to a con ments T1 and T are taken upstream from pipe junction ventional turbine-generator power installation in order 55 and jump 109 is also upstream from junction 55. As to utilize available solar heat to displace extraction the temperature Texceeds the temperature T, feedwa steam requirements. The applied solar branch inputs ter is taken from the solar branch to augment or replace solar heated feedwater to displace extraction branch the feedwater output of the extraction branch. The feedwater at a rate proportional to the temperature combination of the pump 109, temperature sensors T. difference between the extraction branch output and the and T; and, the controller 111 comprises a means for solar branch output. This input solar feedwater is deliv proportioning the feedwater flow between the extrac 65 ered by an auxiliary pump which responds to a control tion branch and the solar branch. ler which receives the temperature inputs. Under the A buffer extraction steam feedwater heater 121 is aforedescribed methods of operation, in both modes, included between the junction 55 and the steam genera the extraction requirements are decreased to increase

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the turbine power output. However, in the peaking and upstream from said steam generator whereby ex application, the increased output of the turbine is uti traction steam from said turbine may be applied to said lized to increase the electrical output of the plant with feedwater flow after it has been rejoined downstream out decreasing the steam generator firing rate whereas from said branches.

in the fuel conservation mode, as the extraction demand 4. The power plant recited in claim 1 wherein the decreases, the input steam is throttled back so that the solar branch includes a plurality of solar heat exchang turbine power output remains the same but the firing ers connected in series through a pressure feed pump rate of the steam generator is decreased. whereby the downstream solar heat exchanger is at a While there has been shown what is considered, at higher temperature than the next upstream solar heat present, to be a preferred embodiment of the invention, 10 exchanger.

other modifications may occur to those skilled in the 5. The power plant recited in claim 2 wherein the art. Such modifications may include using the present control means is programmed to actuate the pump invention on only one turbine or in a different arrange means whenever the solar branch temperature exceeds ment of turbines. It is intended to cover in the appended the extraction branch temperature by a predetermined claims all such modifications as fall within the true spirit 15 temperature difference.

and scope of the invention. 6. The power plant recited in claim 5 wherein the What is claimed is:

1. A power plant comprising a steam turbine which pump means is oriented at a variable speed increasing proportionately with the increasing temperature differ drives a load, a steam generator providing steam to said ence between the extraction branch temperature and steam turbine and a feedwater preheating system for 20 the solar branch temperature.

supplying preheated feedwater to said steam generator, 7. In a power plant of the type wherein a steam tur said feedwater preheating system comprising:

an extraction branch including at least one preheater, being bine is connected to drive a load, said steam turbine said preheater being fluidly connected to said tur supplied with steam from a steam generator bine through a steam extraction line whereby feed 25 ply; which, in turn, is fluidly connected to a feedwater sup water may be preheated by extraction steam; means are provided for preheating feedwater up a solar branch at least one solar heat exchanger, said 1ng: stream from said steam generator said means compris solar heat exchanger providing a heat exchange relationship between available solar heat and the an extraction branch including a plurality of preheat feedwater whereby feedwater may be preheated by 30 ers, each preheater being fluidly connected in a solar heat; heat exchange relation with said steam turbine a first flow divider junction upstream from said ex whereby extraction steam may be used to preheat traction branch inlet and said solar branch inlet feedwater to the steam generator; whereby feedwater is divided between at least two a solar branch including a plurality of solar heat ex branches; 35 changers, each solar heat exchanger providing a a second flow junction downstream from said extrac heat exchange relation between available solar heat tion branch outlet and said solar branch outlet and the feedwater flow;

whereby the feedwater flow is rejoined upstream a first junction upstream from said extraction branch from said steam generator; and, inlet and said solar branch inlet whereby the feed means for proportioning the feedwater flow between water may be divided between at least two said extraction branch and said solar branch branches;

whereby the solar branch flow is increased and the a second junction downstream from said extraction extraction branch flow is decreased during periods branch outlet and said solar branch outlet whereby when solar heat is available. the feedwater flow is rejoined upstream from said 2. The power plant recited in claim 1 wherein the 45 steam generator;

flow proportioning means comprises: a first thermal sensor means at the outlet end of said a first thermal sensor means at the outlet end of said solar branch;

solar branch; a second thermal sensor means at the outlet end of a second thermal sensor means at the outlet end of said extraction branch; and, said extraction branch; 50 pump means downstream from said first thermal sen pump means downstream from said first thermal sen sor means and upstream from said secondjunction; sor means and upstream from said second junction; and, and, control means for actuating said pump means when means for controlling the operation of the pump ever the solar branch temperature exceeds the ex means in accordance with the feedwater tempera 55 traction branch temperature whereby the extrac ture difference at the outlet ends of the extraction tion branch flow is decreased and the solar branch branch and the solar branch. flow is increased by an amount proportional to the 3. The power plant recited in claim 1 further compris temperature difference. ing a preheater downstream from said second junction k . . . .