US2593963A - Binary cycle power plant having a high melting point tertiary fluid for indirect heating - Google Patents

Description

L. R. BIGGS ER' PL Aprd 22, 1952 BINARY CYCLE Pow ANT HAVING A HIGH MELTING POINT TERTIARY FLUID FCR INDIRECT HEATING Filed Jan. 11, 195o 8., E C oB..m A o d ,t er .t Va A .mm e N L VJ Patented Apr. 22, 1952 UNITED STATES OFFICE Leonard R. Biggs, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application January il, 1950, Serial No. 137,993

(Cl. Sii- 38) Claims. 1

This invention relates to thermal powerplants, particularly to a powerplant of the type having three separate uid circuits, one of which is charged with a liquid which never reaches its boiling point, while the other two contain suitable liquids of a type which pass through liquid Y `and vapor phases as in more conventional elastic fluid turbine powerplants.

An object of the invention is to provide a thermal .powerplant especially adapted to extract thermal energy from a heat releasing reaction of extremely high intensity and occupying a comparatively small volume, and converting this thermal energy to mechanical energy with the maximum possible efliciency. Another object is to provide a thermal powerplant of the type described in which the primary liquid circuit includes only a single supply conduit and a single return conduit connecting a primary heating dcvice with heat exchangers which transfer energy to the secondary and tertiary fluid circuits, so that the secondary and tertiary circuits with their respective heaters may be located at a considerable distance from the heat generating reaction, without complex piping therebetween. A still further object is to provide a three iiuid powerplant in which the components operating at the highest temperature levels in the cycle also operate at a low pressure, so that the mechanical strength and life of the components may be adequate. Another object is to provide an improved powerplant arrangement having even greater thermal eliiciency than previously known binary Huid powerplants, yet requiring a smaller charge of operating liquid.

Other objects and advantages will be apparent from the following description taken in connection with the accompanying drawing in which the single ligure represents schematically the a1'- rangement oi a three uid powerplant in accordance with the invention.

Referring now more particularly to the draw ing, the heat generating reaction is represented to be the combustion of a suitable fuel in a boiler indicated generally at I as including a combustion chamber 2 lined with boiler tubes 3 and hav ing a suitable fuel burning device fl. Combustion air is supplied by a forced draft ian 5 through an air pre-heater 6 in accordance with conventional practice. The ue gases are drawn from the combustion space through a liquid pre-heater or economizer l and the air pre-heater 6 by an induced draft fan 8. While this rather conventional type of boiler arrangement has been disn closed for purposesof illustration, itis to be noted teiial.

t 2 i v that the present powerplant is particularly adapted for extracting and converting thermal energy from heat generation devices oi much more compact design which liberate energy at rates far exceeding those found in the ordinary steam boiler. For instance, a gas turbine combustor of the general type disclosed in the copending application of A. J. Nerad, Serial No. 750,015, led May V23, i9fl7,`and assigned to the same assignee `as the present application, might well be used as the heat generating device. In such a combustor, heat release space rates well above 5,000,000 B. t. u. per hour per cubic foot of combustion space volume may be obtained. Other heating means of very high intensity types will occur to those skilled in the art.

The primary fluid circuit is indicated by the solid arrows in the drawing. t is to be particularly noted that this primary circuit is charged with a material which remains liquid in all parts of the circuit, the temperatures in the heat generator being below those required to boil the ma- 'ihis charge may consist of liquid sodium metal, which melts at 208 F., or any one of several known mixtures of sodium salts, such as those previously used in the so-called saltcooled exhaust valves oi internal combustion enlt is also to be particularly noted that the pressure in this primary circuit is comparatively low, the static pressure being only that resulting from the hydraulic head `due to diilerences in level of the various parts of the circuit. To keep the primary circuit charged and to insure that the pressure does not rise above the static head of the liquid in the circuit, a surge tank shown at 9 is provided. rlhis is maintained at atmospheric pressure by means of the bellows 9d which freely provides expansion room to accommodate changes in volume of the liquid charge as the operating temperature varies, without creating pressures above atmospheric pressure. If the primary liquid is or a type which does not decompose in Contact with oxygen, the surge tank 9 may simply be vented to the atmosphere.

The heat released in the combustion space 2 is transferred to the primary liquid in the heat generator tubes 3 and extracted in a primary heat exchanger consisting of a series of four heat exchange devices in series iiow relation. It will be apparent that the hot primary liquid enters the top of the heat exchange device Il. then iiows progressively downward through the second heat exchange device l2, the third heat exchange device i3, and the fourth heat exchange device it, from which it is caused to circulate by the primary liquid circulating pump I5 through the return conduit I6. Conduit I6' conducts the cool liquid through the economizer l, from which it enters the upper header 3a communicating with the respective heater tubes 3. It will be observed that the cool liquid ows downwardly through the tubes 3 in counter-now relation with the hot gases in the combustion space 2. The hot liquid is collected by the lower header 3b which con municates with the supply conduit Ill.

It will be observed that the` piping connecting the heat generator with the primary heat exchanger is extremely simple, consisting of only one supply pipe and one return pipe. Thus the primary heat exchanger can be located immediately adjacent the turbines and their auxiliary equipment, while the heat generator may be conveniently located at a considerable distance from the rest of the powerplant. This means that a minimum amount of very simple piping is required between the heat generator and the heat converting equipment.

A number of important advantages may be noted in connection with the primary liquid circuit of this pOWerplant. In the first place, the heat transfer from the combustion gases to the primary fiuid is of optimum efficiency since the liquid never boils in the primary circuit. This means that the highest efficiency is obtained from the counterow heat exchange process in the heater I, since the temperature of the liquid increases progressively as it flows downwardly, while the hot gas temperature decreases progressively as it flows upwardly past the heater tubes 3. This is in sharp contrast with the usual steam or mercury boiler, in which there is a certain location in the tubes where the liquid phase changes kto the vapor phase, at which point considerable heat energy is absorbed without any change in temperature. This introduces an inherent loss of efficiency, which is avoided with the present arrangement. Thus the present arrangement eliminates a serious irreversibility which introduces substantial inherent losses in the thermal cycles of previously known mercury and steam turbine powerplants. Furthermore, the heat transfer process from the hot gases kthrough the metal walls of the tubes 3 to the liquid within the tubes is much more eilicient than the more usual transfer of heat from combustion gases through boiler tubes to a fluid which may be partly liquid, partly vapor, and sometimes a mixture of the two.

It may also be noted that the sodium or sodium salt mixture used as the primary liquid is much lower in cost than the mercury charge used in previously known binary fluid powerplants. Likewise, because of the more efficient heat transfer, the heat generating equipment may be smaller in size and therefore cheaper.

A most important advantage lies in the fact that the primary uid circuit, which operates at the highest temperatures occurring in the cycle, at the same time operates at a comparatively low pressure. Whereas in a mercury boiler of conventional arrangement, the boiler tubes may be required to operate at pressures in the neighborhood of 500 pounds per square inch, the static pressures existing in the present system may be only on the order of 50 pounds per square inch gage, and even this high a pressure will exist only in a portion of the tubes at the lower levels in the primary circuit. Therefore, because the mechanical stresses due to pressure Within the tubes are comparatively low in those portions of the circuit where the thermal stresses are highest, the heat transfer tubes and hot liquid conduits may be more conveniently designed to have adequate strength and life, with reasonable safety factors.

The secondary fluid circuit is represented by the dashed arrows in the drawing and comprises a mercury vapor turbine indicated at IS Vas being of the well-known double-flow type. After giving up some of its energy in the turbine rotor Ilia, the mercury vapor serves to heat a fifth heat exchanger I'I, a sixth heat exchanger I8, and a seventh heat exchanger I8. It will be appreciated by those skilled in the art that these heat exchangers I?, I8, I9 may be conveniently 1ocated within an exhaust casing common to the turbine I. Liquid mercury is withdrawn from the bottom of the turbine casing by a circulating pump 2Q, whence it flows through conduit 2| to heat exchanger I8, which serves as a mercury liquid pre-heater. From the pre-heater I8, the liquid mercury flows through conduit 22 to the second heat exchanger I2 which further pre-heats the liquid, the mercury flowing through heater I2 in counter-flow relation with the primary iiuid. From pre-heater I2, the liquid mercury flows through conduit 23 through the rst heater II, again in counter-now relation with Vthe primary fluid. The heater il is, of course, the boiler for the mercury cycle, from which mercury vapor passes through conduit 24 to the inlet of the mercury turbine IS. In accordance with conventional practice, a separator drum 25 may be arranged so that any liquid particles in the conduit 24 will return to the inlet side of the heater I I.

it will be observed that this arrangement of the mercury cycle facilitates placing the heaters I i, I2 immediately adjacent the mercury turbine i5, and as noted before the heaters I'I, I8, I9 are integral parts of the mercury turbine unit. Thus the mercury portion of the cycle can contain a liquid charge of comparatively small weight, which means that much less of the comparatively expensive mercury is required than is the case in conventional mercury powerplants. Likewise, the piping conveying hot mercury from heaters to turbine is comparatively short, thus reducing the complexity and cost of the high temperature piping, also reducing the probability of accidentally releasing mercury into the atmosphere which would constitute a serious health hazard.

The tertiary fluid circuit is indicated by the dotted arrows in the drawing. This comprises a high pressure steam turbine 26 in series with a low pressure turbine 21. The turbine 26 is of the extraction type, the steam extracted through conduit 2B serving as the heating medium in an extraction heater Z9, as described more particularly hereinafter. After passing through the rotor 21a, of the low pressure turbine, the exhaust steam passes throughsa feed-water heater 30 and then into the steam condenser SI. Condenser 3l is of conventional construction, having a suitable coolant pump 32 for circulating watel` at a low temperature through the intake conduit 32a and out the discharge conduit 32h. It will be noted that the heat transferred to the cooling water in the condenser 3l is the only thermal energy Arejected in this system, aside from the usual radiation losses, and, of course, the sensible heat in the flue gas from the furnace I. Also associated with condenser 3! is a hot-well or circulating pump 33 which supplies condensate to a boiler feed pump 34. In accordance with conventional practice, a suitable type of air ejector35 may be provided to remove any entrained air from the condensate. Also, there may be provided in cooperation with the boiler feed pump 34, as indicated diagrammatically at 36, a de-aerating heater, the heating medium for which is steam extracted through conduit 3I from the exhaust casing of the high pressure turbine 26. Condensed heating fluid from the extraction heater 29 drains to the deaerating heater 38 through conduit 38. A suitable surge tank 39, vented to the atmosphere, insures an adequate supply of liquid to the boiler feed pump, and provides expansion room for changes in volume of the hot water in the system.

It will now be apparent from the drawing that the hot-well pump 33 supplies water through the air ejector 35 to the feed-water heater 30, thence to the de-aerating heater 36 and the boiler feed pump 34. Pump 34 circulates liquid through the extraction pre-heater 29, thence to the mercury condenser-boiler I9, vwhich may be provided with a separator drum I9a. From this separator, steam passes by way of conduit 42 tothe fifth heat exchanger which serves as an extraction super-heater, whence the super-heated steam passes through conduit 43 to the third heat exchanger I3 where it absorbs further heat in counter-flow relation with the primary fluid. From heat exchanger I3, the highly super-heated steam passes by way of conduit 44 to the inlet of the high pressure turbine 2B. The principal portion of steam exhausted from turbine 26 passes by way of conduit 45 to the fourth heat exchanger I4, which serves as a reheater supplying motive uid through conduit 46 to the inlet of the low pressure turbine 2'I.

It will be apparent from the above description that this novel powerplant arrangement provides the most efficient form of counter-flow heat exchange in the heat generator I because the primary fluid remains liquid throughout the heater, while at the same time thermal energy is transferred from the primary liquid to the secondary and tertiary fluids in a series of heat exchangers which are also arranged for most effective utilization of the counter-flow principle. observed that the primary liquid works at extremely high temperatures but low pressures, the tertiary uid operates at high pressures, while the secondary fluid operates at intermediate pressures and temperatures. Thus, in general, it can be said that no component in the system is exposed to both extremely high temperature and extremely high pressure conditions.

In the arrangement shown in the drawing, the mercury turbine I 6 and the high and low pressure steam turbines 26, 21 are all geared to a common load device, shown as an electrical generator 41. The reduction ratios between the respective pinions 2lb, 25a, and Ib are so selected that the high pressure steam turbine rotor operates at a speed in the neighborhood of 5,000 R. P. M., the low pressure turbine operates at an intermediate speed in the neighborhood of 1,800 R. P. M., while the mercury turbine runs at a speed in the neighborhood of 900 R. P. M. Thus the three different types of turbines are permitted to operate at their most eilicient speeds although geared at fixed ratios to a common load device.

It will also be observed that the optimum use has been made of the pre-heating principle in connection with the tertiary fluid. That is, the feed-water pumped into the mercury condenserboiler rst `picks up heat, at a comparatively low` It will also be r I 1y lower temperature levels. Also, except for the usual radiation and stack losses, the only rejection of heat from the cycle is to the condenser cooling water, at a comparatively low temperature level. Throughout the system, optimum use is made of the counter-flow heat transfer principle, both in transferring heat from the hot reaction products to the primary heat transfer fluid, from the primary fluid to the secondary and tertiary working fluids, and from various portions of the working fluid to the liquids at the cold sides of the working circuits. The resulting powerplant promises to effect an overall thermal einciency substantially greater than that of previously known binary cycles using mercury and steam while at the same time necessitating a much smaller charge of the comparatively expensive mercury.

While the invention has been described as having uid circuits charged with sodium salts or liquid sodium metal, mercury, and water, it will be appreciated that other suitable operating, liquids might be used, for instance, the highboiling point diphenyl compositions known to the trade as Dow-Therm, the low-boiling chlorinated-fluorinated aliphatics known commercially as Freon, etc.

It will be obvious to those skilled in the art that many other minor alterations and substitutions of equivalent fluids and components might be made in the specific embodiment of the invention disclosed herein, and it is desired to cover by the appended claims all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. In a three fluid thermal powerplant, the combination of conduits defining a primary liquid circuit charged with a material which remains liquid at all normal operating temperatures and has a boiling joint substantially above the maximum temperature in the cycle and including a primary heater connected by one supply conduit and one return conduit to a primary heat exchanger, the latter comprising rst heat exchange means for a secondary fluid circuit and second heat exchange means for a tertiary duid circuit; conduits defining a secondary fluid circuit charged with a high-boiling liquid and including an elastic uid turbine having in the exhaust conduit therefrom a secondary liquid pre-heater receiving heat from the spent secondary fluid and a condenser-boiler for condensing the secondary vapor, and conduit means with a circulating pump for passing secondary liquid from the condenser-boiler through the liquid pre-heater and then through the first `heat exchange means in counter-flow relation with the primary liquid, the secondary fluid vapor atertiary fluid circuit charged vvitha` compara-V tively; low-boiling liquid and including a' high pressure' and a low pressure elastic fluid turbine in series flow relation with-a second liquid preheater disposed in a second condenser receiving fluid exhausted from the low pressure-turbine, and conduit means With a circulatingpump for passing condensate from the-tertiaryv uid condenser through the second liquid pre-heater; thence through the-secondary liquid condenserboiler and through the third heat exchangemeans in counter-flow relation" with theprimaryfluid and to the inlet of the high pressure turbine.

2. In a three fluid thermal powerplant; the combination of a primary fluid circuit including aprimary heater and primary heati exchanger means with onlyone high temperature conduit connecting the heater with the exchanger and only one lower temperature return conduitr to the heater, the primary circuit being charged with a primary* liquid having a boiling point substantially abovezthe maximum normal operating temperatures, aisurge tankconnected to the primary circuit and maintained substantially at-ambient atmospheric pressure whereby-the maximuml pressure in the primary circuit. is only that of the hydraulic head of the liquid-in saidcircuit, the primaryheat-exchanger includingrst, second, third, and fourth heat exchange devices in series flow relation, with thefirst devicereceiving the hot primary liquid', through the supply conduit directly from-the heater and the-fourth device discharging to the return line; a secondary fluid circuit includingafirst elastic fluid-pressure turbine, said secondary circuit being charged with a high-boiling fluid'and closed to the atmosphere, fifth, sixth, and seventh-heat exchange devices associated with-the first turbine and adapted to extract heat from motive fluid exhausted therefrom, a secondary fluid circulating pump, and conduits defining av circuit for the secondary fluid from the circulating pump through the lsixth heat exchange' device then through the second and first heat exchange devices serially and in counter-flow relation with the primaryl liquid, the secondary fluid vapor from the hot discharge end of the first heat exchange device returning to the inlet of the first turbine; and a tertiary fluid circuitcharged with a comparatively low-boiling fluid-and including a second high pressure elastic fluid tur,- bine of the extraction type, and a third low pressure turbine having heated by the exhaust therefrom an eighth heat exchange device-and a condenser for rejecting heat at the lowest temperature in the cycle to a coolant-fluid, said third fluid circuit including also condensate circulating and boiler feed pump means and a' ninth heat exchange device heated by high temperature fluid extracted from the second turbine, and conduit means arranged to pass condensate from the condenser through the eighth heat exchange device in counter-flow relation with fluid exhausted from the third turbine, thence through the boiler feed pump and the ninth heat exchange device, then through the seventh heat exchange device in counter-flow relation with the secondary fluid vapor exhausted from the first turbine, thence through the fifth heat'exchange device, and through the third heat exchange device in counter-flow relation with the primary liquid,A thence to the inlet of the second turbine, the exhaust from the second turbine vgoing through the fourth heat exchange deviceincounter-flow relation,- with` the primary liquid and thenceto the inlet of the-third turbine.

3. A- thermal powerplant, in accordance with claim .2 infw-hich the ysecondary fluid turbine-and thehigh andlovv-` pressure tertiary fluid turbines are allgeared-to-drive a-common-load output device, the--gear-,ratios being'such that the secondary fluid turbine operates at a--comparatively lowV speed; the .low pressure tertiary-z fluid turbine operates Aatan intermediate speed, and-the high pressure turbine operates at a high speed.

4. In a threefluid thermal powerplant, the combination ofa-primary liquid circuit charged Witha-material which is liquid at Vnormal operating temperatures and Ahas-a boiling-point substantially= above `the maximum temperature inthe cycle and-including4 a primaryheater connected by: one supply conduit and one return conduit to aprimary heat exchanger comprisingfirst heat exchange means for the secondary fluid` circuit and. secondi-heat exchange means for the tertiary fluid circuit, the secondary-circuitbeing charged withahigh-.boiling liquid and vincluding an elasticfluidrturbine, a liquid pre-heater associated with the secondary fluid turbine and adapted to be heated by the exhaust vapor therefrom, anda condenser-boiler for condensing secondary fluid in'thezsecondarycircuit andtransferring heat to the tertiary circuitl andconduit means with a circulating pumpv for passing Secondary liquid from the condenser-boiler through said preheater and then through `the first heat exchanger in counterflow. relation -With the primary liquid, vapor'from the'firstheatzexchange means returning to the inlet of the secondary fluid turbine, the tertiary circuit beingcharged with a-loWer-boiling liquid and-including a highfpressure anda low-pressure elastic fluid turbine in series-flow relation with a tertiary fluid vcondenser receiving fluid from the lowA pressure turbine,4 circulating pump f means with conduitmeans for passing condensatefrom the'tertiary fluid condenser to the secondary fluid condenser-boiler; then through the third heat exchange means in counter-flow relation with thc primary fluid and to the inlet ofthe high pressure turbine.

5. Afthree fluid thermal powerplant comprising conduitsdefining a primaryliquid circuit charged with a material which is liquid at all normal operating temperatures and has a boiling point substantially above the maximum temperature in the cycle, conduits defining a secondary fluid circuit charged with ahigh-boiling liquid, and conduits defining a tertiary-4 circuit charged With a lowerboilingv liquid, the primary circuit including a primary heater connected by one supply conduit and'one return conduit to rst heat exchange means adapted to vaporize the liquid in the secondary circuit, means kin the primary-circuit for preventing the staticpressure therein from rising substantially abovev ambient atmospheric pressure whereby the high temperature primary circuit. is maintainedlat a comparatively low pressure, the-secondary circuit including an elastic fluid-turbine havingassociated with the exhaust therefrom a condenser-boiler adapted to condense the secondary fluid in the secondary circuit and'vaporize liquid in the tertiary circuit, the secondary circuit also including pump means for passing liquid from the secondary fluid condenser throughthe first heat exchanger in counter-now relation with the primary liquid, conduits` for passing` secondary fluid Vapor from the firstheat exchangergto theinletof the secondary fluid turbine,- the=tertiary circuit being charged with a comparatively low-boiling liquid and including at least one elastic fluid turbine having a condenser for receiving the exhaust therefrom, circulating pump means in the tertiary circuit with conduit means for passing condensate from the tertiary uid condenser to the secondary uid condenserboiler, and conduit means for passing tertiary fluid generated in the condenser-boiler to the inlet of the tertiary fluid turbine.

LEONARD R. BIGGS.

REFERENCES CITED The following references are of record in the le of this patent:

l UNITED STATES PATENTS Number Name Date Chesebrough June 29, 1886 Grebe Nov. 15, 1932 Grebe Jan. 24, 1933 Thurm Aug. 15, 1933 Baumann Mar. 5, 1935 Rosencrants July 13, 1937 Amiek Aug. 31, 1937 Larrecq Dec. 14, 1937 Randel June 20, 1939 Lysholm Apr. 22, 1941 Mercier Apr. 12, 1949

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