CA1045922A - Energy storage by means of fluid heat retention materials kept at atmospheric pressure - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

More efficient use of the heat output of a constant output nuclear reactor, or constant output fossil fuel furnace, and boiler in an electricity generating plant that uses a multi-stage steam turbine and employs turbine extraction steam to preheat boiler feed water, is obtained by storing, during a period of low power demand, excess thermal energy in a liquid low vapor pressure thermal energy retention material maintained at high temperature at atmospheric pressure, and then, during a period of peak power demand, reducing or terminating the extraction of turbine steam and using the stored hot energy retention material, through heat exchange flow, to perform power plant support heating functions, including boiler feed water preheat and/or turbine interstage steam. The liquid heat retention materials include low vapor pressure organic materials such as hydrocarbon oils and aromatic ethers as well as molten metals, molten metal salts and molten metal hydroxides such as sodium hydroxide or potassium hydroxide.

Description

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This inventlon concerns a proeess for providlng

2 efficient u~ilization of the heat output of a nuclear reac-

3 tor or fossil fuel furnace that i9 used to produoe steam

4 for driving turblnes and generators in an electricity gen-erating plant. This invention provides a procedure wherein, 6 during periods of low power demand, the excess heat output 7 of a steady sta~e nuclear reactor, or of a furnace burning 8 a fossil fuel, can be stored in fluid thermal energy reten-9 tion materials at atmospheric pressure for use during peak demand perlods as means for reheating boiler ~eed water and 11 interstage steam The invention allows operating the reac~ .:
12 tor or furnace, and boiler, at maximum steady conditions 13 while the turbines, generstor3 and electrieal facilities 14 can fluctuate between about 75% and 120% of a base load o 100%.
6 Briefly stated, the invention operates in the fol-17 lowing manner. During periods of low power demand, portions I18 of extraction steam from various levels of expansion from :¦~ 19 the turbinesand a portion of the primary h~gh pressure steam :20 from the boiler are shunted to heat exchangers where they 21 heat a low vapor pressure liquid thermal energy retention 22 material which is thereafter stored at high temperature in ;:
23 a hot storage location. During periods o~ h~gh power demand, 24 the extraction rate from the steam turbines is decreased, or even discontinued, and the high temperature thermal ener- ` :
26 gy retention materials are taken from the hot storage loca~
27 tion and utillzed by means of heat exchange to preheat boil- :`
28 er feed water andlor to reheat interstage steam. In nuclear `
29 power plants and in fossil-fuel~fired power plants that use higher temperature boiler feed water that has been preheated ~ -~i31 with primary high pressure steam, use of stored hot thermal :1 32 energy retention material in place of primary high pressure - 2 - ~

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1()45922 1 steam during perlods of peak demand will facili~ate the re-2 lesse o~ high pressure ~team to the turbine8 where such 3 steam will be expended in the production of electrical pow- . :
4 er, thus enabling the plant tG achieve flexibility in the face of increased energy demandsO
6 In a typical nuclear powered electric generation 7 plant, the heart of the plant is the nuclear reac~or, the ~ ~
8 source of the heat used to generate the steam in the boiler ;:~ -9 utilized by the turbines and generator~. The nuclear reac~ ~ :
0 tor and steam boiler represent about 75% of the total invest-11 ment in nuclear powered eleetric generating stations and are 12 limited in the degree of flexibility ~hey ean e~hibitO The 13 steam turbines, condenser~, generators, fittings and general .
14 electrical acilities represent the remaining 25% of the 15 total investment, are strictly oonventional in de~ign and ::
16 operation and, further, are capable of operation over a 17 relatively wide variation of parameters~
18 There are many practical objections to throttling 19 the output of a nuclear reactcrO A reactor is most effici-ent when operating at maximum potentlal~ Periodically re-21 ducing the output of the reactor red~aes the efficiency, 22 increases operating difficulties and hazards and increases 23 the costs of running the plant. This inherent inflexibility 24 of nuclear plants means that they can only be utilized as ~ :
"base load" plants and that the intermediate load and peak-26 shaving service have to be met by conventional fossil~fuel-27 fired generators ~coal or oil-burning boilers ~ gas tur-28 bines, etc.). The expensive nuclear heart of the nuclear ~ powered generation plan~ is incapable of foll~wing'load de mands and, there~ore, a large part of the total daily power 31 requirements are no~ met by the nuclear pLant~
32 The present invention is also applicable to modern ~045~2;~
1 pow~r plants employ~ng fossil fuels, particularly those 2 lncorporating pollution abatement provisions e~ther ~n the 3 form of fuel gas preparation or flue gas scrubbing facili~
4 ties. Since such facilities are very expenslve, they~
similar to nuclear reactors, force the utility to operate 6 such plants all-out as base load stationsO Any provision ~.
7 to permit the plants to follow the losd wo~ld extend the 8 use of such plants into the intermediate and even peak sha~
9 ing load ranges.
o This invention offers the further advantage of 11 rapid response to demand. The unit can follow the load by 12 adjusting the steam rate to and rom the turbine, by regu-13 lating the amount of preheat and reheat done by extraction 14 steam and the amount of preheat and reheat done by hot ther- ~ .
mal energy retention material. There~ore, the present in~
16 vention must be considered as making to~ally available the 7 spinning reserve up to the maximum capacity of the turbine~
18 genera~or combinationO
19 The prior art demonstrates numerous ~nstances in -~
which more effieient utilization of energy by various means 21 and by variou~ types of machinery was sought~ For example, 22 British Patent 3811924 (October 10, 1932) di~clo~e~ a method 23 for varying the performance of a steam engine (turbine) by 24 increasing or decreasing the prelimi~ary heating of the feed water by tapping the steam stream utllized by the tur-26 bine. The preliminary heating of the feed water is eontrol-27 led in relation to the condition of the load on the subor~
28 dinate engine giving off the preheating ~teamO British 29 Patent 381,924 does not teach a me~hod of storing large quantities of thermal energy for use dur~ng peak power de-31 mand periodsO The hot feed water, according to the patent, ;~
32 is stored in the same container as the cold condensate~ the ~ 4 -~ S~2Z

1 cold water merely being in the bottom portion of the tank 2 while the hot is at the top.
3 Other repres~ntative prior art includ~ U.S. Patent -`-4 3,681,920 which discloses a power plant operating with a

5 varying production of electric power and coupled into an ~-

6 evaporation apparatus. The heat storage system utilized is

7 high temperature water, which of necessity would require

8 high pressure storage apparatus for efficient energy con-

9 ~ainmentO If no such pressure equipment is used, the water lo can only be stored to a maximum of 99C at atmospher~c pres-11 sures which means that only a small portion of the poten-1~ kially available heat energy can be storedO
13 The same disadvantage ~s inherant in the system 14 of U.S. Patent 3,166,910 wherein steam is tapped from the turbine for preheating the ~eed water and two vessels are 16 provlded, one for cold water stcrage and one or hct water ~ ;
17 storage. At periods of low energy demand, c~ld water is 18 drawn from the cdld water tank and preheated by steam bled 9 from the turbineO During this period, hot water is stored in the hot water tankO
21 In systems that employ hot water storage~ ef~ici~
22 ent energy storage can be achieved cnly at high pressure.
23 Storage costs skyrocket when pressure ~s required~ 500F
24 water means 700 PSI pressure, an uneconomical situation if ~ ;
storage of large quantities of potential power is desired.
26 Where a multi-stage steam turbine receives a given 27 amount of high pressure steam, maximum power is obtained 28 from this steam when all the steam is allowed to expand 29 through all the ~urbine stages and is ccndensed at the "thermal sink" temperature in the condenser. However, the 31 boiler then has to reheat the co~d boiler feed water and 32 evaporate the hot water at boiler pressure and temperature, - 5 ~

~L~45922 1 and this is a waste of high level hea~. It i8 m~ch more 2 economical to extract varying amounts of interstage inter-3 mediate pressure steam streams from the turbine8 in amounts 4 and at pressure levels commensurate with the boiler feed water preheat requirements. In ~his way, various ~reams 6 which have already done some work in the high pressure sta-7 ges of the turbine are used to preheat the boiler feed water 8 gradually, and ~or each Btu of intermediate pressure steam 9 used for this preheat service (ater some work was obtained o from it) a Btu of high level heat is freed from preheat ser-11 vice and made available to generate high pre~sure steam for 12 the turbi~e. Consequently, maxlmum power from a given capa-13 city boiler plus turbine can be obtained if judicious amounts 14 of intermediate pressure steam streams are extracted from between the various stages of the turbine and used for boil-16 er feed water preheatO The exact levels of pressure and 17 temperature, and the amounts of such streams, may vary rom 18 about 2~10% of the total steam at each extraction point and ~;
19 are at the discretion of the deslgnersO
&enerally, the high temperature, high pressure 21 steam coming directly from the boiler is not used for boiler 22 feed water preheat since there i5 no advantage in such a 23 "boot-strap" operationO High level heat wou1d be used, be-24 fore any work was extracted from it9 to save high level heat.
However, some of this high pressure steam is used for the 26 purpose oE reheating intermediate pressure turbine inter~
27 stage steam. This, in effect, superheats this intermediate 28 pressure steam so as to minimize the degree of condensation 29 occurring in the turbine during the subsequent adiabatic expansion.
31 The instant invention makes use of the above prin-32 ciples, regarding extraction, boiler feed water preheat and

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1 interstage steam reheat to allow storage of heat at differ-2 ent levels to the max~mum extent and ~se o~ thi~ stQred heat 3 at the appropriate time to maximize the power output from a 4 given plant.
s Steam turbines are v~ry fLexlble and can be oper-6 ated at partial load. A turbine driving a generator can 7 follow the electrical load by varying not only the amount 8 of high pressure steam being ed to it, but al80 the frac-9 tion of steam extracted interstage from ito Using this principle, it is now possible to use, during periods of

11 low load, extraction steam at different pressure levels,

12 as well as high pre~sure steam to heat a low vapor pressure

13 fluid heat storage medium, such as water at low temperature, or a hydrocarbon oil at high temperature, to a temperature level close to that of the boiler~ For example, if the 6 boiler operates at 550F and produces ~team at about 1050 17 psi, the oil can be heated to about 520~535Fo It should 18 be noted that since this oil heating is achieved by means of 19 extraction, as well as by high pressure steam, it is ther~
modynamically as efficient as the boiler feed water preheat-21 ing scheme outlined above~ In addition, this permits a 22 given power plant to operate steadily at maximum uel burn-23 ing capacity-efficiency (nuclear or fossil) but with a drop 24 in power output dependent on the amounts of high pressure and extraction steam diverted to water and/or oil heating 26 serviceO The loss in power output, however, represents no 27 loss in thermal efficiency, since any heat that ~s not used 28 to generate electrical power is stored in a fonm which can 29 be easily and efficien~ly recalled from storage~ During periods of low load9 steam extraction is maximized, oil heat-31 ing ~s maximized and power output is m~nimized, withou~ af-32 fecting the operation rate of the reactor, the feed water . 7 ':

1 temperature or steam rate of the boilerO Durlng periods of 2 high-load, withdrawal of high pressure steam and extraction 3 of intermediate pressure steam can be curtailed or dlseon-4 tinued with a consequential increase in turbine performance, but wlth no loss in thermodynamic efficiency ln the reactor 6 or boiler, as would happen lf the feed water temperature 7 were lowered. During this period, power plant support 8 hea~ing operations occurring in heat exchangers are assumed 9 by the fluid hot therm~l energy retentlon materials~ Feed water preheating and intersta~e steam reheatlng are simply 11 done by means of the heat stored in the fluid heat reten-12 tion materialsO Power plant support heatlng ~unctions occur-13 ring in heat exchangers, as used in the present disclosure,

14 mean those heating operations other than raising primary

15 live steam in the boiler~ .

16 By using this concept, it has been ealcul~ted that,

17 by storing about 25~35% of the heat output of a nuclear ~ .

18 plant, or modern fossil fuel furnace, about 15~20% of the l9 power output o such a plant can be shifted from low-load to high-load periodsO Thus, a nuclear p~ant cperating at 21 1015 psi and 545F, and generating a designed rate of 1000 22 MWe (megawatts electrical) can be made to drop its power 23 output to about 750~800 MWe during low Load periods and 24 increase its output to 1150~1200 MWe during high load peri-ods, without any variation in nuclear reactor or boiler op~
~ 26 eration. The plant was designed to generate 1000 MWe util .
i 27 izing some high pressure steam for interstage steam reheat 28 and extraction steam for boiler feed water preheatO By ~-;
29 using the hot fluid heat retention material to perform power 30 plant support heating functisns occurring ~n heat exchangers !
31 ~uch as the reheat of steam and preheat of feed water9 all 32 steam generated in the boiler can be sent to and fully util;
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1 lzed in the turbine with an accompanying lncrease in perfor-2 mance at that point. Overall thermcdynamic efficiency is 3 retained slnce the boiler feed wa~er is still being heated 4 to an efflcient temperature before introduction lnto the boiler, said temperature being the sam~ as during the low-6 load period of plant operation.
7 A particularly advantageous embodiment of this 8 invention is the use of higher boiler feed water preheat 9 temperatures than in conven~ional plants. Boiler feed water 0 can be heated almost to boiler temperatures by using the 11 heat in the fluid thermal energy retent~on materialO This 12 frees tremendous quantities of Btu's in the boiier from the 13 task of preheating water and releases them for the task of 14 generating high temperature high pressure steamO As pointed out previously, h~gh pressure steam is not normally used 16 directly as the last stage heating medium in conven~lonal 17 boiler feed water preheating. Consequently, the temperature 18 at which boiler feed water is currently introduced into high

19 pressure boiler is usually about 320~400, or about 100-200 or more Fahrenheit degrees below the boiler operating tem-21 perature- It has been found that by u9ing high pressure 22 steam directly from the boiler, a~ well as possibly scme 23 more o~ the 5team from the irst and sécond ~nterstage lev- `~
24 els, the boiler feed water (BFW) can be preheated to temper-2s ature levels much closer (such as to within 25-l00F) to the 26 boiler operating temperat~lre of about 550Fo The amount of 27 high pressure steam required for this additional preheat 28 duty may amount to 10-25% of the total h7gh pressure steam 29 producedO New boilers can be designed ~hat operate at thls new boiler feed water temperature and which use primary 31 high pressure steam as BFW preheat materialO Fox example, 32 a boiler can be designed which produces 1025 million units g ~0~59~ ~
l of steam per unit time. A high pressure steam by-pass line 2 takes 0.25 milllon units and uses it as BFW preheat material.
3 The turbine receives one million un~ts oE steam from the 4 boiler. Under normal conditions, this "boot-strap" opera-S tion serves little or no purpose. However, with this new 6 invention of BFW preheat by use of thermal energy stored in 7 a fluid medium, the preheat during peak demand periods can .
8 be done by hot fluid thermal energy retention material while 9 that 0.25 mlllion units of steam are now freed to go to the turbine for purposes of power generationO During periods ll of low load, additional steam, particularly in the high 12 pressure range can now be withdrawn to reheat e~en more oil 13 to an even higher temperature than in the previously des-14 cribed embodiments. This allows an even further drop in plant output to between 0.5 to 0.66 of rated capacity but 16 .it is important to note that the boiler and reactor are l7 o.p.erating at maximum efficiency, i.eO they remain steady 18 state. During periods of high demand, little or no high 19 .pre.ssure steam is diverted to BFW preheat nor to fluid energy retention material reheat. The primary high pressure 21 steam used for BFW preheat is directed to the tur~i~e while 22 the hot flu~d energy retention mater~l takes over the pre-23 heat duties 24 In summary, by the use of the exhaustive boiler feed water preheat scheme ~ust described, the output of a 26 nominal 1000 MWe nuclear plant can be varied from ~-6~ MWe :~

27 to 1350-1500 MWe without changing reactor or boiler opera-28 tions.
29 Although a simple heat storage fluid of good flui-dity, stability and low vapor pressure over the temperature 31 ra~e involved can be used, it will frequently be advantage-32 QUS to use sever~l ~luids in separate systems, each fluid ~0459ZZ
1 covering a preferred temperature range. While the amounts 2 of fluid l.nvolved and consequently inventory and tankage 3 requirements go up considerably, such a multiple fluid ar-4 rangement permits selection of optimum temperature ranges ~ ~
5 to fit the properties of par~icular fluids, such as bolling ~-6 ranges (~o allow a~mospheric pressure storage of all materi-7 als), freezing points, ~hermal stability and fluid viscosity, 8 ~.e. heat ~ransfer propertles. Thus~ although water is a 9 good heat storage medium with low viscosity and hlgh speci-fic heat, it cannot be used above about 210F because of the 11 excessive vapor pressure. Hydrocarbon oils or stable organ-12 ic compounds, with good heat transfer properties, such as 13 aromatic ethers or oxides, are excellent fcr te~peratures 14 below about 650F if kept isolated from the atmosphere to prevent oxidation. Such materials as hydrocarbon oils have 16 a satisfactory low vapor pressure at the maximum temperature 7 thus allowing convenient storage in atmospher~c pressure 18 tankage. Consequently, thermal energy up to about 600-650F
19 bulk temperatures can be stored at atmospherle pressure in a hydrocarbon oil or similar organic mater~al such as aro-21 matic ethers or oxides. On the other hand, hydrocarbon oils 2i ~end to become viscous and poor for heat transfer at the 80-23 100F range of the heat sink. Above 650F, long-term ther-24 mal stability problems beset most oils, and materials such as molten inorganic compounds with good heat transfer prop-26 erties, eOg. fused caustic or salts, become the materials 27 Of choice. However, since most of these materials are solids 28 at room temperature and even up to about 500F, an operat~on- -~
29 al temperature range for thase materials can be envisioned as between 600-1200F. From this, it can be seen that a 31 broad spectrum of stored ~emperatures can be achieved by 32 careful selection of storage medium and maximum efficiency - 11 - ; ':'' ~04S~2Z ~ `.
l thereby attained.
2 In the accompnying drawings, Figure 1 descrlbes a : ~ -3 conventional plant with boller operations designed to run 4 on boiler feed water preheated to about 320F and Figuré 2 s discloses the new boilers operating on 500F boiler feed i.
6 w~ter. Both systems can utilize the present invention to 7 achieve great flexibillty in operations. Figure 3 illus~
8 trates application of this invention to a hl~h temperature 9 fossil-fuel-fired power plant or nuclear power plant. :
Referring now to Figure 1~ high pressure steam ll comes from the nuclear reactor and steam boiler 1 and pa~ses .
12 through conduit 2, At fitt~ng 3, some h~gh pressure steam is shunted through conduit 4 to be used as the heat~ng medi- ..
14 um in an inters~age steam reheat unit 5~ The major portlon of the steam is fed to the turbines 6 through conduit 7, 16 and proceeds for reheating through oonduit 8 ~o the steam 17 reheat unit 5O Thi5 motive ste~m i3 then led ~n serles by 18 conduit 9 to medium pressure turb~ne 6aO Spent steam from 19 6a goes thrQugh conduit 10 to condenser llo In a plant

20 operating withou~ bene~it of ~he in3tan~ invention, the ~!
2l condensate from 11 moves through conduit 12 to pump 13 22 where i~ i9 in~roduoed to conduit 140 Condu~t 14 leads 23 through valve 15 to conduit 16 whi~h leads to a series o 24 heat exchangersO The cold condensate in conduit 16 is in ::
2s troduced to heat exchangers 17a and b, Heat exchangers 17a 26 and b are heated by extraction steam from l~w pressure tur~
27 bine 6a led through condui~s 18a and b, Extrac~ion steam 28 condensate from 17a passes through condult 19 to 17b where 29 additional hea~ is exehanged and thence through conduit 20 to condenser llo The now slightly warmed boiler feed water 31 in conduit 16 continues its journey ~nd passes ~hrough heat 32 exchangers 21a and 21b wherein extraction steam from turbine ~0 ~ 5 9 Zz l 6 i obtained ~hrou~h condui~s 22a and 22b~ Steam conden-2 sate from exchanger 21a pa~ses throu~h condult 23 to exchan-3 ger 21b, then through conduit 24 to the previousLy described 4 exchanger 17a, ~hen through conduit 19 to 17b and finally through conduit 20 to condenser 11. The now preheated 6 boiler feed water ln conduit 16 ~8 fed into the boiler 1.
7 The novel aspect of the instant ~nvention i8 as 8 follows~ In addition ~o the above standard boller feed 9 water system an energy storage process is utili~ed which ~
o can work in conjunction with the standard method or, and ~ ::
11 this is a ma~or advantage o~ the system, it can entirely 12 replace conventional boiler feed water heating processes 3 during periods of peak demand.
14 Referring again to Figure 1, during periods of low demand, boiler feed water is preheated as described above, 16 but, in addition, extraction steam ~rom the ~urblne~, some 17 high pressure s~eam ~rom the boller and the eondensates ~rom 18 the various extract~on steam condensers are also being used 19 to heat thermal energy retention materialO Ex~raction ~team ~r~m turbine 6 passes through condu~ts ~2a and 22bt Valves

21 25 and 26 are open, al.lowing ~eam both to preheat boiler

22 feed water as described above and ~o allow steam ~o pass

23 t~rough valves 26 through conduit3 27a and 27b ~o heat ex~ `~

24 changers 28a and 28b where cold oil from vessel 29 pass~ng through conduit 30 gains thenmal energyO In heat e~changer 26 31 primary high pressure steam from the reactor and boiler 27 1 passing through conduit 2, down conduit 32 and through 28 valve 33 is used to impart a final measure of ~hermal energy 29 ~efore the hct oil is stored in vessel 34t The expended high pressure steam condensate from 31 passes through con~
31 duit 35 to heat exchanger ~a where ~t imparts energy to 32 the oil and ~hen this steam condensate plus additional con-.
~ 13 ~

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~ densate from 28a pa~ses through condult 36 to exchan~er 28b 2 where cooler oil gains more energy Erom the ~team and con~
3 densate. This steam condensate i~ then utilized in the hot 4 water heating system now to be discussed.
Some low pre~sure steam from turbine 6a is ex-6 tracted through conduits 18a and 18b. Such steam pa~slng 7 through valves 37 is used for boiler feed water preheatO
8 That steam moving through valves 38 and along conduits 39a 9 and 39b to heat exchangers 40a and 40b is used to heat water o from vessel 41 moving along conduit 42 to hot water storage ~ `
ll vessel 43. Because the spent steam condensate in conduit 12 44 from exchanger 28b is still hot encugh to heat water, 13 it is channeled to exchanger 40a and thence through conduit 14 45 ~o exchanger 40b. The now fully expended steam conden-sate moves along conduit 46 to condenser 11. The amount of 16 boiler feed water moving through conduit 14 is constantO
17 However, the split of this stream between conduits 16 and ;~
18 52 is determined by regulation of val~es 15 and 500 During 19 periods of peak demand, valve 15 is closed, shutting ~low through condui~ 160 Valves 25 and 37 are also shut to heat 21 exchangers 21a and 21b and 17a and 17b3 Further, valves 22 26 and 38 are alsc ~hut, terminating steam 10w to oil and 23 water heat exchangers 28a and 28b and 40a and 40b. Valve 24 33 on conduit 32 to exchanger 31 is also closedO Boiler feed water from the condenser 11 now passes through conduit 26 12 to pump 13, through conduit 14 to conduit 51, and through 27 valve 50 to conduit 520 Conduit 52 passes through a ~eries 28 of heat exchangers Cold boiler feed water (B~) passes 29 through exchanger 53 where hot water from vessel 41 passing through conduit 54 transfers heat to ito Conduit 54 empties 31 into a cold water storage tank 410 The warmed BFW in con 32 duit 52 next contacts exchanger 55 where it gains more heat IL~4S922 1 from oil passlng through conduit 56. The oil in condult 2 56 comes from storage ve~sel 34~ The hot oil from 34 passes 3 through conduit 57 initially to the inter~tage steam reheat q unit 5 where it8 initial high temperature is mo3t effective-ly ut~lized. As the oil cools down, it mo~es throu~h con-6 duit 56 and is contacted with progre~sively cooler BFW in 7 numerou~ hea~ exchangers 550 Some hot oil c~ming initially 8 out of the storsge tank may be u~ed directly to heat boiler g feed water without first partially expending itself as inter-stage steam reheat materi~l by passing through conduit 58 to 11 heat exchanger 59 where the BFW is given lts 1nal thermal 12 boost before introduction into the boilerO This hot oil 13 then moves through conduit 60 to ccnduit 56. The above 14 arrangement can be used as described~ or can be used with lS both conventional and novel systems operating simultaneously, 16 that is, with boiler feed water being heated along both 17 conduit 16 and conduit 52O However, by shutting down con 18 duit 16 and all valves designated 25, 26, 3?~ 38, 33 and 66, ~:
l9 all boiler feed water preheat and interstage steam reheat operatlons are carried out using stored energy and 811 steam 21 produced is channeled to ~he turbines, enabling the plant to 22 achieve a high level of power output without afecting BFW
23 temperature, BFW rate and boiler performance~
24 Figure 2 represents a plant wherein high pressure primary steam is used directly for BFW preheat and wherein .
26 the boiler operates at much higher BFW temperature approach :~ ~ :
27 to boiler temperature than currently exists. In such a ~ :
28 plant, some high pressure steam from boiler 1 is shunted .
29 through line B to heat exchanger B2 on line 16 during low demand periods. Condensate from B2 passes through conduit 31 B4 to heat exchangers 21a and 21b. Steam passe~ through :~
32 conduit 32 to heat exchanger 31 where it is used to heat oil : - 15 .

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l for storage. Durlng periods of high demand) such s~eam 2 flows are curt~iled by closing valves Bl and 33. Conden~
3 sate from exchanger 31 passe~ through conduit 35 to exchan- -4 ~er 28a. These portions of high pressure steam, which could amount from 10 to 40% of the boiler output, now proeeed 6 through normal channels to ~he turbines while all sF~ pre-7 heat is done by hot thermal materi~l as previously described 8 in Figure 1 to exactly the same high temperature level as 9 during the low demand period. This embodiment offers the -advAntage of tremendous flexibility in a nuelear plant or 11 steady state fossil fuel plant to a degree heretofore unat-12 tainableO
13 In reactors or fossll fuel furnace3 and boilerq 14 where the high pressure steam temperature is hlgher and where hlgher pressure high temperature ~uperheated steam i9 16 used in the turbines, a third independent serie~ of heat 17 trahsfer vesse~ and heat excha~gers may be used wherein 18 the fluid thermal energy retention material is a molten 19 salt, molten hydrox~de such as sod~um hydroxide, potassium hydroxide or mixtures of hydroxides, or fluld metal storing 21 heat between 500O1000F and higher.
22 Figure 3 represents such ~n advanced high tempera~
23 ture high pressure power plant whieh operates at 1000-1200F
24 and 2500 psig wherein molten inorganic material is used as 2s the thermal energy re~ention materiàlO Turbines 6 and 6a 26 and the features and fitting associated with them are as 27 described in Figure lo Because cf the higher temperature of 28 the primary high pressure superheated steam coming ~rom the 29 boiler 1, a high capacity turblne 6x is n~w also in the plant, steam from 1 passing along conduit 2 ~o ~ltting 3 31 where some high pressure steam may be shunted through con-32 duit 4 to unit S where lt is usad for reheating interstage .
- ~ 16 ~

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sg22 1 5 team. The main portion of the primary superheated ~team 2 passes through conduit 7 to turblne 6x. Extractlon steam 3 from 6x is used for both conventional boiler feed water 4 preheat and/or ~or heating molten inorganic heat storage S compound. Extraction steam from 6x pa~ses through conduits 6 lOOa and lOOb and through valves lOl to heat exchangers 7 102a and 102b where boiler feed water in conduit 16 i~ heat~
8 ed. Again condensate from 102a passes through conduit 103 9 to heat exchanger 102b and thence through conduit 104 to o heat exchangers 21aO In this novel arrangement, extraction steam in conduits 100 passes through valves 105 and then 12 through conduits 106a and 106b to molten inorganic heat re-13 tention material heat exchangers 107a and 107b. Cold molten 14 inorganic material from storage vessel 108 mo~es through conduit 109 to exchangers 107a and 107b where it is heatedO
16 At heat exchanger 110, which is serviced by condu~t 111 and 17 valve 112 with primary high pre~sure steam9 the molten inor~
18 ganic material is heated even furtherO The spent heating ..
19 ma~erial from exchanger 110 passes through conduit 113 to heat exchanger 107a and then from 107a through conduit 114 21 to heat exchanger 107b and then from heat exchanger 107b 22 through conduit 115 to oil heat exchangers 28a and 28b in 23 seriesO The hot molten inorganic material ~s stored in ves-24 sel 1160 As previously discussed9 at periods of low power demand, interstage steam reheat and boller eed water pre 26 heat can be performed with primary high pressure steam and 27 turbine inters~age extraetion steam. During periods of high 28 power demand, all valves lOl, 105, 112 and 66, along wlth 29 all ex~raction ~team valves on turbines 6 and 6a can be closed, and all power plant support heating functions can 31 be carried out with hot thermal energy retention material~.
32 In the plant outlined in Figure 3, boller feed water in ~ 17 ~

~ 45~22 1 condul~ 52 upon lea~lng oil heat exchanger 55 i~ heated 2 in heat exchangers 117 by ho~ molten inorganic material 3 from 3torage ve~el 116 mo~ng through conduit 1180 The 4 hot material in conduit 118 can either be u~ed as interstage steam reheat in unit 5 or else xhunted ~long conduit 120 6 ~ heat exchanger 119 for use as BFW preheat material and 7 then through conduit 121 to conduit 118 for use in heat 8 exchangers 1170 9 While interseage steam reheat and highest tempera-lo ture level reheat of the molten inorganie heat retention ll material are shown here using prlmary high pressure super-12 heated steam, such reheating operations may be carried sut 13 directly in the furnace or nuclear reactor, i~eO in a high 14 temperature gas cooled reactor.
lS It is obviou~ that the improvement illu~trated in 16 Figure 2 of preheating boiler feed water with high pres~ure 7 live steam from the boiler during periods of low losd can 18 be easily incorporated into the system illustrated ~n Figure 19 3, where three heat retention mater~aLs are usedO
It should be noted that the feed water preheat 21 and intermediate s~eam reheat wlth oil and ho~ water, as 22 shown in exchangers 5, 539 55 and 59 (Figure 1~, 5,. 53, 55, 23 117 and 119 (Figure 3) may be in plaee of, as well as in 24 addition to exchanger units which perform a simllar duty with high pressure steam, extraction steam and condensate 26 streams~ It is therefore completely within the s¢cpe of 27 this invention to carry out ~he reheating and preheating 28 duties with circulating molten inorganie eompound, hot o~l ;
29 and hot water at all ti~s and only vary the amount of melt reheat, o~l reheat and heat storage water reheat being 31 done at any given time as a function of the power 1oadO
32 Maximum reheat would occur at low demand9 and minimum or no.

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1 reheat during high demand periods.
2 In ~ome cases it will be advantageous to omit 3 the hot water ~y~tem and carry out all the heat storage with 4 oil between the ~Ithermal sink" temperature, usually 60 100F
and the nuclear boiler temperature o~ 500~650F Wi~h high-6 er temperature reac~ors, it may be possible ~o use two fluid :~
7 thermal energy retention materials, cil from 100 to 500 or :~
8 600F, and molten inorganic compounds between 500~6Q0F and 9 1000F or soO
lo While separate exchangers are shown to heat the 11 heat retainlng materials with steam and ~o heat the BFW with 12 hot heat ret~ining materials, it may be advantageou~ to use 13 the same exchsngers for both serviees, whieh are normally l4 nu~ carried out at the same timeO
lS It must be emphasized that the precise heat ex~
16 change sequence~ numbers of exchangers and e~tent of steam 17 extraction, preheat and reheat are variables which are at l8 the discretion of the designerO The a~ve flow pla~ is 19 only one typical sequence which can easily be modified by those skilled in the art without depar~in~ rom the concept 21 of the present inv0ntionO
22 It is also within the scope o this invention to 23 heat the fluid heat retention materials by means other than ;~
24 extraction or high pressure steam, eOgO by solar heat or

25 sources Of waste heat such as turbine and staok exhaustsO ;~

26 This heating can be carried out in addf~ion to or separate

27 from the steam heating described here~naboveO However, the :.

28 use of the hot heat retention material to preheat boiler

29 feed water as well as for reheating interstage steam during high load periods ls s¢hieved in the m~nner described without 31 regard to the orig~n of the heat tha~ was s~ored in the ho~
32 heat retention fluido ' 19

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for making efficient use of the heat output of a constant output nuclear reactor, or fossil fuel furnace, and boiler in an electricity generating plant that uses a multi-stage steam turbine and employs turbine extrac-tion steam to preheat boiler feed water, said process also providing maximum flexibility in meeting load demands, which comprises the steps of storing, at a high temperature, ex-cess thermal energy in a liquid low vapor pressure thermal energy retention material at atmospheric pressure during a period of low power demand, and then, during a period of peak power demand, reducing the extraction of turbine steam while simultaneously using the stored hot liquid low vapor pressure thermal energy retention material to perform power plant support heating functions through heat exchange flow, thereby allowing the steam to fully expend itself in the turbine for the production of power.

2. The process of claim 1 which includes the fol-lowing steps:
(a) during a period of low power demand, shunting a portion of extraction steam from at least one level of turbine expansion to one or more heat exchangers;
(b) during a period of low power demand, shunting a portion of primary high pressure steam from the boiler to one or more heat exchangers;
(c) moving low vapor pressure liquid thermal energy retention material from a cold storage location to a hot storage location through the heat exchangers of steps (a) and (b);
(d) heating the low vapor pressure thermal energy retention material in the heat excehangers of (a) and (b) by means of said shunted extraction steam and primary high pressure steam;
(e) storing the heated low vapor pressure thermal energy retention material at high temperature at atmospheric pressure in isolation from the atmosphere, in a hot storage location;
(f) during a period of peak power demand, decrea-sing or terminating boiler feed water preheating by extrac-tion steam;
(g) moving the stored hot low vapor pressure thermal energy retention material from hot storage to cold storage locations through heat exchangers;
(h) heating boiler feed water in the heat exchan-gers of (g) by means of the moving hot low vapor pressure thermal energy retention material;
(i) passing the heated boiler feed water to the boiler.

3. The process of claim 2 further characterized in that the hot low vapor pressure thermal energy retention material is used to reheat turbine interstage steam before being used to preheat the boiler feed water.

4. The process of claim 2 or claim 3 which includes the step of shunting a large quantity of primary high pressure steam, during non-peak demand periods, to heat exchangers for use as a boiler feed water preheat material.

5. The process of claim 1 wherein the low vapor pressure thermal energy retention material is an organic material.

6. The process of claim 5 wherein the organic material is a hydrocarbon oil.

7. The process of claim 1 wherein the low vapor pressure thermal energy retention material is a molten inorganic material.

8. The process of claim 7 wherein the molten inorganic material is a molten metal.

9. The process of claim 7 wherein the molten inorganic material is a metal hydroxide.

10. The process of claim 1, 2 or 3 wherein a series of thermal energy retention materials are used to perform power plant support heating functions, each material kept separate from the other and each storing energy at atmospheric pressure in isolation from the atmos-phere to an extent and at a temperature of its own maximum efficiency.