Reheat cycle for a sub-ambient turbine system

An improved combined cycle low temperature engine system is provided in which a circulating expanding turbine medium is used to recover heat as it transverses it turbine path. The recovery of heat is accomplished by providing a series of heat exchangers and presenting the expanding turbine medium so that it is in heat exchange communication with the circulating refrigerant in the absorption refrigeration cycle. Previously recovery of heat from an absorption refrigeration subsystem was limited to cold condensate returning from the condenser of an ORC turbine on route to its boiler. By utilizing the turbine medium a more efficient system is provided. Specifically, a minimum of a double digit efficiency improvement when compared to the net power output of a conventional low-pressure steam turbine, is obtainable.

The present invention is directed to a reheat cycle for a sub-ambient 
turbine system. In particular, the present invention is related to a 
reheat cycle in a combined cycle consisting of an absorption-refrigeration 
(AR) system and an organic Rankine turbine system. 
BACKGROUND OF THE INVENTION 
U.S. Pat. No. 4,090,361 (Terry et al.) discloses the use of a heat cycle in 
a hydride-dehydride-hydrogen cycle (HDH). The HDH cycle is used as a 
absorption cycle to provide a very low temperature heat sink for a primary 
power cycle. The heat cycle involves the heating of the hydrogen leaving 
the hydride reactor bank upon dehydrating so as to impart a higher energy 
level prior to charging hydrogen to an expansion device for producing 
work, e.g., turbine. 
U.S. Pat. No. 4,503,682, the content of which is expressly incorporated 
herein by reference as if specifically recited, discloses a combined cycle 
low temperature engine system. The combined cycle consists of an 
absorption refrigeration sub-system in combined cycle relationship with 
organic Rankine turbine systems. The refrigeration sub-system provides a 
sub-ambient condenser temperature for a turbine cycle, greatly extending 
the temperature gradient across which the turbine cycle expands, while 
much of the heat energy rejected from the absorption refrigeration 
sub-system is internally recovered within the combined cycle system 
boundaries by regenerative heat transfer to the circulating turbine 
medium. The internal regenerative heat transfer reduces the net energy 
consumed to operate the refrigeration sub-system to the point of being 
less than the power output increase effected for the turbine sub-system. 
Extensive computer simulation studies have indicated that the low 
temperature engine system concept offers a potential double digit increase 
in power plant turbine cycle efficiencies, as compared with conventional 
low pressure steam turbine cycles, when the low temperature engine system 
is employed in an application where it becomes a bottoming cycle 
replacement for the low-pressure steam turbine in a conventional "all 
steam" turbine cycle turbine system. It has also been shown to be capable 
of increasing the power output yield from geothermal resources whose 
surface plant operating parameters are in a similar thermal regimen to 
that of a low pressure steam turbine cycle. 
U.S. Pat. No. 5,555,731, which is an improvement of U.S. Pat. No. 
4,503,682, also expressly incorporated herein by way of reference as if 
specifically disclosed, provides a power turbine system which employs 
turbine injectors to supply additional liquid phase turbine medium to the 
turbine at the elevated temperatures acquired after that liquid medium has 
performed its function in the low-temperature engine system of absorbing 
waste heat from the absorption refrigeration subsystem of the 
low-temperature engine system. 
The present invention is the result of a previously unrecognized capability 
of being able to improve the power output of the low-temperature turbine 
sub-system that becomes uniquely available to the turbine cycle when 
expansion of the thermodynamic medium circulating through the turbine 
enters the sub-ambient temperature range across which its expansion 
occurs. A well-known characteristics of all heat engine cycles is the fact 
that the potential output power they can deliver is related to the amount 
of heat energy that can be input to the expansion process. The higher the 
temperature at which it is supplied the greater the power output will 
become. Uniquely, when the turbine cycle of the sub-ambient turbine in 
this combined cycle enters the sub-ambient portion of its expansion, there 
are a variety of external heat energy sources, available at temperatures 
higher than those occurring in the turbine cycle, from which additional 
heat energy can be supplied to the expanding medium transiting its thermal 
range,--even including the cooling water temperature in use elsewhere in 
the turbine plant. 
Use of a "reheat cycle" in steam turbine has been practiced for some time. 
As steam expands to very low pressures, its isentropic path through the 
turbine converges toward the saturation curve for steam. In order to take 
maximum advantage of the thermal gradient available at the site of an 
installation between the best available external site cooling to condense 
the expanded vapor at the turbine exit, the exit pressure of the steam 
must enter a high vacuum condition, commonly in the vicinity of 1.5" 
Hg.abs (3.81 cm.Hg abs.). Generally, as steam approaches the vacuum level, 
it has already crossed the saturation curve and is in the process of 
becoming wet,--i.e.--it is in a mixed phase condition with a moisture 
content approaching a lower limit of 85% quality. Beyond that limit, the 
moisture content has an adverse impact effect on the turbine blading and 
increasingly causes a reduction in output power. To overcome the problem, 
it has been common practice to remove the expanding vapor from the turbine 
part way through its expansion cycle to send it back to the boiler for a 
reheat process. When it is returned from the boiler the second time, again 
at an elevated temperature, it can continue its expansion isentropically 
from a higher level of superheat, to arrive at its exit pressure at a 
higher quality level, with a smaller moisture content to adversely affect 
blading and efficiency. 
In the sub-ambient temperature regimen of the turbine in U.S. Pat. No. 
4,503,682, at any point below ambient in its cycle, expanding vapor taken 
from the turbine can be reheated from a variety of heat emitting sources 
to furnish additional input energy available in its combined cycle 
environment without resort to the external heat source supplying the 
system. The original concept of the low-temperature engine system combined 
cycle is dependent on its capacity to recover heat energy emitted from the 
associated absorption refrigeration sub-system by internal regenerative 
heat transfer. Heretofore, that recovery had been limited to recovery of 
heat emissions from the absorption refrigeration sub-system by use of very 
cold condensate returning from the condenser of an ORC turbine en route to 
its boiler as the cooling stream. In effect, it recovered some of the heat 
ordinarily rejected to ambient cooling water or air temperature as "waste 
heat" in a conventional "stand alone" absorption refrigeration system. 
The present invention recognizes that heat may be recovered by the 
expanding turbine medium vapor itself, as it traverses its turbine path, 
before it is ultimately condensed to its liquid phase beyond the discharge 
point at the bottom of its path through the turbine, when it became useful 
as a liquid cooling stream en route to its boiler to repeat its cycle. 
Furthermore, by the present invention it has been surprisingly found that 
use of the expanding turbine media itself in a working system designed to 
operate in accordance with the parameters indicated and employing the 
sequence of unit operations as diagramed in FIG. 1. will show a minimum of 
a double digit efficiency improvement when compared with the net power 
output of a conventional low-pressure steam turbine supplied with the same 
input steam source as that assumed as the external heat energy source for 
the alternative combined cycle low temperature engine system referenced. 
The reheat cycle of the present invention surprisingly offers both an 
additional mechanism for internal regenerative recovery of heat energy 
emissions from the absorption refrigeration sub-system otherwise being 
wasted externally to ambient cooling water, and also a mechanism for 
increasing the total heat energy input supplied to the expanding vapor 
circulating through the organic Rankine turbine cycle path in the turbine 
sub-system. 
It is therefore an object of the invention to provide a method of 
re-heating the turbine medium in a sub-ambient turbine system in combined 
cycle relationship with an absorption refrigeration system. 
It is a further object of the invention to provide a re-heat cycle, in a 
low temperature engine system combined cycle which is not dependent on the 
systems' capacity to recover heat energy emitted from the associated 
absorption refrigeration sub-system by internal regenerative heat 
transfer. 
It is another object of the present invention to provide a heat and energy 
efficient method for reheating turbine medium in a sub-ambient turbine 
system by recovering heat from the expanding turbine medium vapor itself. 
Further objects of the present invention will become apparent from the 
following description of the invention and drawings. 
SUMMARY OF THE INVENTION 
In accordance with a first embodiment of the present invention, an improved 
combined cycle low temperature engine system is provided, specifically an 
improvement over U.S. Pat. No. 4,503,682, in which a circulating expanding 
turbine medium is used to recover heat as it transverses it turbine path. 
The recovery of heat is accomplished by providing a series of heat 
exchangers and presenting the expanding turbine medium so that it is in 
heat exchange communication with the circulating refrigerant in the 
absorption refrigeration cycle. 
In accordance with a second embodiment of the present invention, an 
improvement in and relating to a combined cycle low temperature engine 
system is provided having an absorption refrigeration subsystem with a 
circulating refrigerant medium for providing to the engine system a 
continuous-flow low temperature heat sink, the circulating refrigeration 
medium having a refrigerant vapor condensation path and a turbine cycle 
having a turbine with an upper and lower turbine section each provided 
with a turbine inlet and turbine outlet and providing a circulating 
turbine media having a vapor expansion path through a sub-ambient 
temperature portion of the turbine cycle, the improvement comprising: 
a reheat energy source located along the absorption refrigeration subsystem 
for admitting sub-ambient vapor extracted from the sub-ambient temperature 
portion of the vapor expansion path in heat exchange communication with 
condensing refrigerant medium being of a temperature higher than that of 
the extracted vapor, thereby permitting heat energy from the condensing 
refrigerant medium to be transmitted to the extracted turbine vapor, said 
heated vapor being returned by conduit means to the inlet of the turbine 
at a temperature higher than it possessed at its extraction point to 
continue its expansion through the remaining portion of the turbine cycle. 
In accordance with a third embodiment of the present invention, a method 
for increasing the efficiency of a combined cycle low temperature engine 
system having a turbine cycle and circulating turbine media is provided 
which comprises recovering heat with the expanding turbine media as it 
traverses a turbine path within the turbine cycle.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention represents an application for the combined cycle 
system intended to become a bottoming cycle replacing the low pressure 
steam turbine in a conventional steam turbine system of a power plant 
installation. The external heat energy input source to the combined cycle 
system is therefore steam at the pressure and temperature at which it 
would have been directly supplied to the low-pressure steam turbine, 
generally about 75 psia (5.27 kg/sq.cm.) pressure and at a temperature of 
about 420 degrees F. (215.5 degrees C.), to be isentropic with its 
commonplace ultimate exhaust pressure at 1.5 ins (3.81 cm) Hg.abs., and 
85% quality. 
The absorption refrigeration sub-system exemplified employs the most common 
industrial scale absorption refrigeration system in current service with 
ammonia as the refrigerant and water as the absorbate; however, the use of 
any other pairing of refrigerant and absorbate might be employed in an 
embodiment that is suitable for the thermal regimen of the application 
without altering the purpose and intent of the invention. Similarly, 
propane has been assumed to be the thermodynamic medium circulating in the 
sub-ambient organic Rankin turbine cycle although other turbine media may 
be employed in other embodiments without affecting the principles on which 
the invention is based. Examples of other media for the refrigerant cycle 
include, but are not limited to hydrogen, ammonia/sodium thiocyanate and 
the like. Examples of other turbine cycle media include, but are not 
limited to, hydrocarbon media such as iso-butane, butane, iso-pentane and 
the like. 
In ammonia/water absorption refrigeration systems it is common to refer to 
the strong solution concentration formed in the absorber as "strong aqua" 
and the weakened solution concentration left in the generator, after some 
refrigerant is separated from the "strong aqua", as "weak aqua". 
FIG. 1 is a system diagram of the two sub-systems comprising the low 
temperature engine system in their combined cycle relationship. In the 
absorption refrigeration (AR) sub-system, strong aqua is formed in 
absorber 10 from the mixture of ammonia vapor returned from the evaporator 
at low pressure via conduit means 11 and weak aqua supplied via conduit 
means 9 after having passed through expansion valve 8 to reduce it to the 
same pressure as that of the vapor from the evaporator to permit mixing 
both in absorber 10. The absorption process is an exothermal one, and the 
heat evolved must be removed from the mixture by cooling to permit the 
strong aqua solution to form. Cooling of absorber 10 is illustrated as 
being made available by two external coolant streams in heat exchange 
communication with the mixture in the absorber by an upper and lower 
cooling section within absorber 10. The upper section is supplied with 
cooling water via conduit means 14 in heat exchange communication with the 
mixture in absorber 10 (with the cooling water return provided by means of 
conduit 15), while the lower section is supplied with the much colder 
coolant stream of turbine condensate in heat exchange communication with 
the mixture via conduit means 16, after its having partially been cooled 
by cooling water. The turbine medium condensate then leaves via conduit 
means 17. Use of that very cold coolant in the lower portion of the 
absorber permits a more highly concentrated strong aqua solution to be 
formed at a sub-ambient temperature at the low pressure operating 
condition in absorber 10. 
The strong aqua solution formed in absorber 10 leaves via conduit means 18 
at the low pressure existing in the absorber, and enters pump 20 where it 
is pumped to the higher pressure at which the generator operates. Pump 20 
delivers the high pressure strong aqua solution to aqua heat exchanger 6 
via conduit means 19. Aqua heat exchanger 6 receives the cold strong aqua 
solution from pump 20 via conduit means 19 and the hot weak aqua solution 
from the generator via conduit means 5. The two streams pass each other in 
heat exchange communication which allows the transfer of heat energy from 
the hot weak aqua solution to the cold strong aqua solution. The cooled 
weak aqua solution leaves via conduit means 7 to be delivered to expansion 
valve 8, and the warmed strong aqua solution leaves via conduit means 21 
to be delivered thereby to generator 1. 
Generator 1 receives strong aqua solution from conduit means 21. Generator 
1 is also equipped to receive external heat energy input from the external 
steam supply source via conduit 2 in heat exchange communication with the 
solution in generator 1. Steam condensate exits generator 1 via conduit 3. 
The input heat energy received from the external heat energy source 
releases some of the ammonia refrigerant from the strong aqua solution 
producing a vapor product containing the ammonia refrigerant separated 
from the strong aqua solution. That vapor leaves generator 1 via conduit 
4. The weak aqua remainder after the ammonia vapor has been separated (a 
distillation process) is returned to the absorber via conduit 5 to repeat 
its cycle. 
The vapor leaving via conduit 4 also contains a partial pressure of water 
vapor mixed with the ammonia vapor. The vapor mixture enters rectifier 63 
in heat exchange relationship with the still cold turbine medium 
condensate which enters rectifier 63 via conduit means 62 and leaves via 
conduit means 64. As the mixed vapor cools, the partial pressure of water 
vapor that accompanied the refrigerant vapor leaving generator 1 is 
condensed before the ammonia. As it condenses, a portion of the ammonia 
vapor is also absorbed by it, and the resultant ammonia/water solution is 
returned to the generator via conduit 35, the reflux fraction of the 
distillation process. Upon further cooling, the superheat content of the 
remaining ammonia vapor is removed by the coolant stream and saturation 
temperature for the pressure of the ammonia vapor is reached. 
At this point, a succession of heat exchangers are presented in the system 
diagram of FIG. 1, each representing a further cooling stage of the 
process of getting the high pressure high temperature refrigerant vapor 
received from generator 1 to be progressively desuperheated, condensed to 
its liquid phase, and sub-cooled as much as possible before being supplied 
to the pressure reducing valve for admission to the evaporator. The set of 
heat exchangers are illustrated in FIG. 1 as a set of unit processes 
arranged one below the other in a sequence of descending heat energy 
content as the refrigerant is cooled. Desuperheating is accomplished in 
rectifier 21 as described. The vapor, now at or near saturation 
temperature for its pressure, enters reheater 23 to accomplish the subject 
matter of the present invention. Turbine medium vapor, extracted from the 
upper portion 51 of the turbine at a temperature below ambient, is 
delivered to reheater 23 via conduit 55 to pass in heat exchange 
communication with the condensing refrigerant vapor entering reheater 23 
via conduit 22 and leaving via conduit 24. In the process, the turbine 
vapor medium acquires heat energy input from the cooling refrigerant vapor 
and is returned to lower portion 52 of the turbine at an elevated 
temperature now isentropic for its pressure with respect to exhaust 
conditions at the exit of turbine section 52. 
The refrigerant vapor leaving reheater 23 via conduit 24 is then further 
cooled in ammonia condenser 25 by being placed in heat exchange 
communication with cooling water supplied to ammonia condenser 25 via 
conduit means 38 and leaving via conduit means 39. In the process, the 
remainder of the latent heat of condensation may be removed from the 
refrigerant stream and the refrigerant leaves condenser 25 approximately 
in its completely liquid phase. What remains may then be removed in 
sub-cooler 27 along with an amount of sub-cooling heat energy contained in 
the liquid phase below saturation temperature for its pressure,--up to the 
limit of the cooling capacity of the turbine condensate supplied to 
sub-cooler 27 via conduit means 17 in heat exchange communication with the 
refrigerant fluid passing therethrough. The now warmer turbine condensate 
leaves sub-cooler 27 via conduit 26 and the sub-cooled refrigerant liquid 
leaves via conduit means 28 to enter ammonia pre-cooler 29. 
Cooling water from a cooling tower (not shown) is supplied to the turbine 
plant via conduit 36 and distributed to wherever it is needed by cooling 
water manifold 37. That manifold supplies conduit means 14 for the 
absorber requirement and conduit means 38 for the ammonia condenser 
requirement. Spent cooling water is returned from the absorber 10 via 
conduit means 15 and from the ammonia condenser 25 via conduit means 39 to 
a cooling water return manifold 40. From there it is returned to the 
cooling tower (not shown) via conduit means 41. 
Use of an ammonia pre-cooler as shown in FIG. 1 is a commonly used 
auxiliary device in ammonia/water absorption refrigeration systems. Cold 
returning refrigerant vapor from the evaporator is passed in heat exchange 
communication with the liquid phase ammonia refrigerant en route to the 
expansion valve for release into the evaporator. The cold vapor further 
sub-cools the liquid refrigerant prior to its use to develop refrigeration 
capacity in the evaporator. The colder the level of sub-cooling that can 
be developed, the greater the refrigeration capacity will become when it 
is ultimately released into the evaporator. The slightly warmed low 
pressure vapor leaves ammonia pre-cooler 29 via conduit 11 for return to 
absorber 10. The sub-cooled ammonia liquid leaves ammonia pre-cooler 29 
via conduit means 30 to enter expansion valve 31 and to the evaporator 33 
via conduit means 32. The pressure of the liquid ammonia stream is sharply 
reduced to evaporator pressure by passage through expansion valve 31 which 
causes flash evaporation of the liquid phase ammonia to a vapor in 
evaporator 33. Evaporator 33 is also the condenser for the associated 
turbine sub-system of the combined cycle. The refrigeration capacity 
developed in the evaporator absorbs the heat of condensation of the 
turbine medium entering evaporator/condenser 33 via conduit means 57 in 
heat exchange communication with the flashed refrigerant vapor. The 
refrigerant vapor leaves via conduit means 34 for return to ammonia 
pre-cooler 29 described above. 
In the above description of processes occurring in the absorption 
refrigeration sub-system, it should be noted that several opportunities to 
maximize internal heat recovery between the two sub-systems of the 
combined cycle exist. In the absorber 10, the amount of exothermal heat 
recovered by cold turbine medium in the lower end may be maximized by 
controlling the amount of cooling water supplied to the upper end up to 
the limit of assuring a minimum approach difference between the cooling 
turbine medium stream and the strong aqua solution formation taking place. 
An additional tube bundle might also have been introduced in the absorber 
to provide heat exchange communication means to permit a portion of the 
evolving exothermal heat to be recovered by extracted turbine medium vapor 
as another potential source of reheat energy. Similarly, by controlling 
the supply of cooling water to ammonia condenser 25, portions of the 
latent heat being removed at constant temperature may be removed 
successively by reheater turbine vapor flow, and sub-cooler turbine 
condensate flow, up to the limit of their cooling capacity, leaving only a 
minimum amount of the remainder to be removed by cooling water flow 
between those abutting two unit processes. The actual functions of the 
series of heat exchange processes will be seen to overlap at their 
boundaries limited only by the need to maintain minimum approach 
differences to assure heat transfer taking place. 
Finally, tracing the associated organic Rankine turbine sub-system, the 
propane turbine medium having acquired the maximum available feed stream 
heating after leaving rectifier 63 via conduit means 64 enters boiler feed 
pump 60. Pump 60 supplies the propane liquid to boiler 61 via conduit 
means 65 at the intended turbine medium supply pressure. An external heat 
source steam (not shown) enters the system via conduit 42 through manifold 
43 and is supplied to boiler 61 via conduit 44 in heat exchange 
communication with the propane turbine medium passing there through. Steam 
condensate exits boiler 61 via conduit means 45 to manifold 46. The cooled 
condensate exits manifold 46 via conduit means 47 to pump 48 where it is 
pumped via conduit 49 to a water heater or boiler (not shown). The heated 
pressurized turbine medium in its vapor phase exits boiler 61 via conduit 
means 50 to be supplied to the entry of turbine or upper portion of the 
turbine 51. The vapor expands isentropically through turbine 51 to arrive 
at an intermediate pressure and below ambient temperature at the reheat 
extraction point location of conduit 55. The cool vapor enters conduit 
means 55 where it is carried to reheater 23. It acquires reheat energy by 
heat exchange communication with hotter ammonia vapor flowing there 
through, and the now heated turbine medium vapor is returned at an 
elevated temperature at approximately the same pressure via conduit means 
56 to re-enter the turbine at the entry to the lower portion of the 
turbine 52. 
During the expansion process of the turbine medium through the turbine, the 
turbine delivers its output work by rotating shaft 53 to drive alternator 
54 which delivers output electrical energy to the transmission system for 
distribution. The turbine medium expands through the remainder of the 
turbine 52 at a pressure still slightly above ambient (to assure no vacuum 
conditions in the turbine system) but at a temperature on the order of 100 
degrees F. (59 degrees C.) below ambient. That expanded vapor leaves 
turbine 52 via conduit means 57 to enter turbine sub-system condenser 33 
(which is also the evaporator of the absorption refrigeration sub-system 
of the combined cycle). Propane condensate exits condenser 33 via conduit 
means 58 to enter condensate return pump 59. Pump 59 pumps the condensate 
at a pressure high enough to assure its ability to travel through all the 
piping between there and its return to the boiler feed pump, and to assure 
that it remain in its liquid phase after acquiring the feed stream heating 
it will receive along the route described above. 
To supply a set of operating parameters for the combined cycle described, 
with the external heat energy supplied in the form of steam at a pressure 
of 75 psia (5.27 kg,/sq.cm) and a temperature of 460 degrees F. (237.8 
degrees C.), generator operating conditions in the absorption 
refrigeration sub-system may be established at a pressure of 275 psia 
(19.3 kg./sq.cm) and a temperature of 320 degrees F. (160 degrees C.). For 
this condition, the saturation temperature at which ammonia refrigerant 
will condense will occur at 117.2 degrees F. (47.33 degrees C.). With the 
absorber and evaporator operating at 10 psia (0.703 kg/sq,cm), the 
evaporator will deliver refrigeration at a temperature of -41 degrees F. 
(-40.5 degrees C.), quite adequate to condense the propane turbine medium 
at -30 degrees F. (-34.4 degrees C.) at its exhaust pressure of 20 psia 
(1.41 kg/sq.cm). Similarly, the external heat source will enable the 
propane medium to be delivered from its boiler at a temperature of 320 
degrees F. (160 degrees C.) at a pressure isentropic with its reheat 
temperature at the reheat extraction pressure for its exhaust at 20 psia 
(1.41 kg/sq.cm). As illustrated, the reheat temperature acquired is an 
adequate approach difference below saturation temperature for ammonia at 
275 psia (19.3 kg./sq.cm.) About 110 degrees F. (43.3 degrees C.) leaving 
a 140 degree F. (60 degree C.) range across which further expansion in the 
turbine can take place. 
For these parameters, the strong aqua solution concentration leaving the 
absorber after being cooled to an exit temperature of 50 degrees F. (10 
degrees C.) becomes about 35.3% ammonia, and the weak aqua solution 
remaining in the generator after the ammonia refrigerant vapor fraction 
has been separated at the operating pressure and temperature of the 
generator would have an ammonia concentration of 17.6%. Cooling water 
available at an installation site has been assumed to be at a temperature 
of 75 degrees F. (30.7 degrees C.), the standard cooling water temperature 
used as a reference temperature by the Heat Exchanger Institute in 
establishing performance standards for materials used in fabricating a 
variety of heat exchanger equipment. 
FIG. 2 illustrates the vapor expansion path through the turbine including 
the reheat process described. The path has been plotted on a 
pressure-enthalpy diagram for propane as published by Gulf Publishing 
Company, Houston, Tex. Point "A" indicates the turbine entry conditions of 
the propane vapor as it left the propane boiler at a pressure of 1,500 
psia and a temperature of 320 degrees F. (160 degrees C.). The vapor 
expands isentropically to a pressure of 125 psia (8.78 kg/sq.cm.) where 
its temperature has become approximately 65 degrees F. (18.33 degrees C.). 
It is well below the saturation temperature of condensing ammonia leaving 
rectifier 21 in FIG. 1. It is extracted at point "B" and supplied to 
reheater 23 in FIG. 1 where it is heated to a temperature of 80 degrees F. 
(26.67 degrees C.), and returned to the turbine to re-enter the expansion 
path at point "C" now isentropic with respect to its exhaust pressure at 
20 psia (1.41 kg/sq.cm) at point "D". In the process, it removed its input 
heat energy from the amount that might otherwise have been wasted to 
cooling water in ammonia condenser 25 in FIG. 1, and the increase in heat 
content of the vapor became additional energy available to the turbine for 
conversion to output power in the remainder of its expansion path below 
the reheat extraction point. 
Although various changes and modifications can be effected in the preferred 
embodiments of the invention which have been described, it is to be 
understood that such changes and modifications can be effected without 
departing from the basic principles which underlie the invention in is 
most fundamental form. Changes and innovations of this type are therefore 
deemed to be circumscribed by the spirit and scope of the invention, 
except as the same may be necessarily limited by the appended claims or 
reasonable equivalents thereof.