Power Modulation Of A Thermal Generator

Abstract

A process for modulating the power of a gas turbine by variation of the inlet temperature of the working fluid in a compressor located upstream of a turbine. The compressor and turbine are each staged and the working fluid is cooled at least before the last compressor stage by gasification of a liquefied gas. A portion of the cooling energy produced by expansion of the liquefied gas can be returned to the liquefied gas in storage to cool the latter.

Description

BRIEF SUMMARY OF THE INVENTION

This invention relates to a process for increasing the efficiency of thermal generators, particularly for modulating their power by use of refrigeration, and to the application of this process, for example, for indirect electrical power storage.

The advantage of increasing the power of a thermal generator of a given size and of increasing its efficiency are obvious in themselves and need not be explained. As for electrical power storage, it is known that electrical power consumption varies on the one hand according to the season of the year, and on the other hand according to the time of day, but power production must closely follow consumption due to the inability to store electricity. This requirement causes substantial economic loss as it entails long periods of reduced output since the size of the generating installations must correspond to the highest power demand while such a demand need be actually satisfied only during a fraction of the operating time.

Indirect electrical power storage installations have already been realized in the use of artificial lakes in which pumps raise water during non-peak hours, but these gravitational storage installations are far from satisfactory, and are only possible in selected geographical sites.

The invention is based upon the known fact that lowering the temperature of the cold source of a thermal machine increases its thermodynamic efficiency and increases the power obtained per unit, weight or volume of the working fluid. For instance, when the working fluid is a non condensible gas, by lowering the temperature of the cold source, the density of the gas going through the cycle increases and consequently increases the power produced per unit volume of the working fluid.

An object of the invention is to provide a process in which the above is utilized in order to increase power production from a given thermal machine and/or to allow utilization of a smaller thermal machine to obtain a given power. In other words, the invention seeks to increase the gross power of thermal machines of a given size, as well as to improve their utilization and particularly to increase their efficiency.

The invention contemplates a process in which the output power of thermal machines can be modulated by refrigeration. The application of this process permits a more complete and more continuous use of the power of a thermal power generator, as well as a modulation of the power output of a thermal machine without changing, at least within wide limits, the speed of the machine, nor the maximum temperature in the operating cycle.

According to the invention, it is not necessary to produce the refrigeration effect near the thermal machine. The refrigeration machines may therefore be located in any place, particularly in a place where, due to production, utilization or storage of a product, the cooling effect is transferred to this product. This product may undergo, total or partial, transformation, and be stored near the thermal machine.

Liquefied gases are specific substances for storage of refrigeration effect and more particularly liquefied natural gases, liquefied petroleum gases and liquefied gases from the air. Liquefaction of these gases is effected to facilitate their storage and transportation, they must be re-gasified before use. This re-gasification produces a large quantity of cooling energy hereafter called "frigories" which may be used in numerous applications, and particularly in power production. Methane is an example of a gas which is liquefied, transported by ship, stored in depots, then re-gasified under pressure and distributed through pipe lines over great distances.

An object of the present invention is the specific implementation, giving a maximum efficiency to the utilization of the frigories contained in liquefied gas and permitting continuously or discontinuously to obtain high power and high efficiency in power generation by means of a gas turbine.

The thermal machine described above effects compression, then expansion of the working fluid.

The Applicant has established that it is advantageous to perform the fluid compression in several stages and to cool the working fluid between stages. Additionally, it is also advantageous to perform the expansion of the working fluid in several stages.

A further object of the invention is to provide a process for the modulation of gas turbine power production by variation of the inlet temperature of the working fluid in a compression device located ahead of the gas turbine inlet, said process being characterized in that the working fluid compression and subsequent expansion are performed in several stages, each compression stage following a cooling of the working fluid by means of the cold effect produced during the gasifying of a liquefied gas in a container connected on the one hand to the liquefied gas storage tank and on the other hand to a compressor.

The invention will be described hereafter in relation to an apparatus and method comprising two compression stages and two expansion stages.

It is necessary to dry to a maximum the inlet air in order to avoid a quick frosting of the low temperature coolers. This the reason why, before each stage of air cooling by means of the cooling fluid (a liquefied gas), the air is first cooled by a coolant consisting of water and anti-freeze. The air later goes through a separator of water droplets; the remaining water in the air will be frozen in the main cooler as very small particles which will be carried along by the air and will not lie in the main cooler as a film.

The first compressor preferably operates at a rather low compression ratio to serve the part of a supercharging device fulfilling two functions:

by variation of its speed, it permits adaptation of the entire circuit to the conditions of optimum efficiency when the air temperature varies;

by multiplying the air pressure by the compression ratio, it permits reduction of the surface area of the cooler located downstream.

BRIEF DESCRIPTION OF THE DRAWING

The following description will be made with reference to the appended drawings in which:

FIG. 1 diagrammatically illustrates a circuit for effecting the process according to the invention by means of a utilization device for the cold effect which is producted;

FIG. 2 shows another similar circuit according to the invention;

FIG. 3 shows a device for utilization of the cooling effect by cooling the liquefied gas and this device can be added to the utilization devices shown in FIGS. 1 and 2;

FIG. 4 diagrammatically shows another arrangement according to the invention for utilization of the cooling effect by cooling the liquefied gas stock; and

FIG. 5 shows a supplementary refrigeration generation devicr whose cooling effect is used to cool at least a portion of the liquefied gas stock and this device may be added to the utilization devices represented in FIGS. 1 and 2.

DETAILED DESCRIPTION

The various figures are simplified in that they do not include auxiliary equipment such as pumps, etc., the necessity and the use of which are obvious to those skilled in the art.

With reference to the apparatus of FIG. 1, therein is not contemplated any cooling of the liquefied storage gas.

Air is introduced through line 1 into a scrubber 2 into which a coolant consisting of water with added anti-freeze is sprayed by nozzle device 3. The air is thus cooled to a temperature between -2.degree.C. and +2.degree.C., at which temperature the greatest part of the water present in the air is condensed.

The coolant is introduced into the scrubber 2 through a line 4 at a temperature between -5.degree.C. and -10.degree.C., this temperature being obtained by passing the coolant, collected by line 5, through an exchanger 6 supplied with a refrigerating fluid through circuit or loop 7 connected to the outlet and of a gasification device of a liquefied gas.

In the upper part of scrubber 2, a cyclone 8 separates any remaining traces of water droplets from the air.

The air from scrubber 2 is introduced, at a temperature between -2.degree.C. and +2.degree.C., through line 9 into a compressor C1. The compressed air is introduced through a line 10 into a cold water cooler 11 in which water circulates through a line 12. Then, the air is introduced through line 13 into a scrubber 2' which operates similar to the scrubber 2 except that it is fed with air under pressure at a temperature in the neighborhood of 30.degree.C. Reference characters 3', 5' and 8' in the scrubber 2' designate structure corresponding to 3, 5 and 8 in the scrubber 2. In the scrubber 2' the air is substantially dried.

The dried air is discharged from scrubber 2' at a temperature between -2.degree.C and +2.degree.C and is introduced through lines 14 into a main cooler 15. Liquefied gas enters the main cooler through a line 16 and exits via a line 17 and serves as the refrigeration fluid in cooler 15. The cold energy in the liquefied gas is thus utilized to cool the air fed to compressor C.sub.2 and this increases the efficiency of the compressor and lowers the load on the turbines hence increasing the available output. The air is fed from cooler 15 at very low temperature to compressor C.sub.2 where it is compressed and then is passed to a heat recovery device 18 by opening valve 19 and closing valve 20. The air is heated in recovery device 18 and then passes to a combustion chamber 21 through valve 22 which is opened. A fuel is introduced into the chamber 21 through line 23. The resulting combustion gas from chamber 21 is passed to a turbine T.sub.1 through line 24. After a first stage, a part of the heat content in the gas is recovered by passing the exhaust gas from T.sub.1 into the heat recovery device 18 (valve 25 being opened and valve 26 being closed). The gas, after having given up heat in device 18 is admitted into turbine T.sub.2 through line 27 (valve 28 being opened) and exhaust is effected through line 30 at atmospheric pressure.

The liquefied gas 31, stored in tank 32, is pumped to the main cooler 15 through line 16. The gas discharged from line 17 is supplied either to other gasifiers or to utilization devices or the gas pipelines.

With reference to FIG. 2 which represents another embodiment of the process according to the invention employing a device for the utilization of the refrigeration effect, this embodiment as in FIG. 1 does not include a cooling of the liquefied gas stock.

In the embodiment of FIG. 2, air is introduced through line 1 into scrubber 2 similar to the scrubber described in FIG. 1, and reference characters 2-8 in FIG. 2 designate the same parts as in FIG. 1.

The air in line 50 at a temperature which is between -2.degree.C and +2.degree.C, is introduced into first main cooler 51. The liquefied gas refrigeration fluid is fed from tank 32 through line 16 to cooler 51. The cooled air from cooler 51 is introduced into compressor C1. The compressed air in line 54 passes into second main cooler 55, the refrigerating fluid of which is liquefied gas coming from tank 32 through line 16. The air in discharge line 58 from cooler 55 is fed to compressor C2 where it is further compressed to a maximum value. Turbines T.sub.1 and T.sub.2 are fed, as in FIG. 1, from the air compressed to a maximum coming from compressor C2.

The gas coming from the main coolers 51 and 55 is fed through line 17 to other gasifiers or to consumption devices.

The implementation of the process of the invention is accompanied by an important cooling of the air admitted into compressor C2 or into compressors C1 and C2, and this enables a high expansion ratio with a high efficiency and consequently allows installation of the heat recovery device 18 between turbines T.sub.1 and T.sub.2. Nevertheless, the two embodiments which have just been described, need not include heat recovery device 18 in which case the compressed air from compressor C2 is then directly introduced into the combustion chamber 21 (valve 20 being opened, and valves 19 and 22 being closed). Furthermore, the exhaust gas from turbine T.sub.1 is directly admitted into turbine T.sub.2 (valves 26 being opened). It is also possible to place the recuperating device not between T.sub.1 and T.sub.2 but after T.sub.2, nevertheless, the increase in compression ratio and efficiency which the invention allows to obtain, affords the possibility of placing the heat recovery device after T.sub.1, in which case it is less heavy and less bulky than if it were placed after T.sub.2 without loss and even with a slight gain in efficiency.

The magnitude of flow of the liquefied gas into the main coolers of FIGS. 1 and 2 depends upon the gas demand, and therefore it is not linked to the operating parameters of the process of the invention. Nevertheless, this may be the case when the liquefied gas is methane and generally, a natural gas whose peaks of consumption correspond to the consumption peaks of the power produced by the thermal machine. Besides, it is usual in gasifying centers to maintain the flow of liquefied gas more or less constant independently of the gas consumption by using gas storage means such as natural underground reservoirs, gasholders, very long pipelines under high pressure, etc. The power produced is then that of a basic power plant.

It is possible to accept variations in the supply of liquefied gas in the main coolers as long as these variations are not too sudden, as they could then entail damage to the compressors.

Another embodiment of the process according to the present invention, contemplates cooling the liquefied gas stock or a part thereof. Three configurations thereof have been represented in FIGS. 3, 4 and 5.

FIG. 3 shows a configuration which can be used instead of tank 32 of FIGS. 1 and 2 and is additive to the utilization arrangements represented in FIGS. 1 and 2. The cooled liquid can be mixed in variable proportions with non-cooled liquid before being introduced into the air coolers. The supplementary refrigeration effect produced by the cooling of the liquefied gas stock is stored in the container used for liquefied gas storage.

Next shall be described the configuration and its operation. To simplify, there will be distinguished two extreme cases of operation, one during off peak hours (during which supplementary refrigeration effect is stored), the other during peak hours (during which the stored supplementary refrigeration effect is consumed).

During off peak hours:

A flow of liquefied gas coming from the outlet 60 of tank 61 (valve 62 being opened) is expanded in the evaporator 63. The very cold liquefied gas collected in line 64 is introduced into the lower part of tank 61 through line 65 (valve 66 being opened and valve 67 being closed). The cooled liquefied gas introduced through a lower opening 68 is prevented from mixing with non-cooled liquefied gas by the presence of partition means, e.g., cylindrical vertical partition 69 in tank 61.

The flow of liquefied gas to be gasified is withdrawn from tank 61 through the outlet 70. Valve 71 is opened and liquefied gas flows through line 72 to a condenser 73 (valve 77 being opened) which condenses the gas compressed in C3 (valves 74 and 75 being opened). After condensing, this gas is introduced into the flow of liquefied gas in line 72 (valve 76 being opened). From the outlet of condenser 73 the liquefied gas is passed through line 16 to the main cooler 15 (FIG. 1) or to the main coolers 51 and 55 (FIG. 2).

During peak hours:

Compressor C3 does not operate, valves 62, 74, 75, 66, 71, 76 and 77 are closed, valve 67 is opened, so that the flow of liquefied gas to be gasified totally comes from the opening 68 of tank 61 and is therefore very cold. Condenser 73 is by-passed during peak hours by line 78.

The two types of operation which have just been described are extreme cases, but they are not the only ones: thus, during non-peak hours, valve 67 may be partially opened, conversely, during peak hours, valve 71 is generally opened, and additionally, compressor C3 may be operated.

With reference to FIG. 4 which represents a configuration for utilizing refrigeration effect including means for generating supplementary refrigeration effect from the cooling of at least a part of the liquefied gas stock, the cooled liquid first of all, passing through a special cooler before being mixed with the remainder of the liquid introduced into the air coolers. The cooling effect produced by the cooling of the liquefied gas stock is stored in the liquefied gas storage container. This configuration may be used instead of the system constituted by the tank 32 and the main coolers 51 and 55 represented in FIG. 2.

This configuration and its operation will next be described for the cases of operation during off peak hours and during peak hours.

During off peak hours:

Operation is very similar to that described with reference to FIG. 3. Valves 62, 74, 75, 76, 77 and 67 are opened, compressor C3 is in operation, the cooled liquefied gas coming from evaporator 63 is re-introduced into the tank 61 through the lower opening 68. Valves 79 and 80 are closed. The main coolers 55 and 51 are supplied with liquefied gas through line 16. The gas coming out of the main coolers 51 and 55 is supplied through line 17 to other gasifiers or to consumption means.

During peak hours:

Compressor C3 is not in operation, valves 62, 74, 75, 76, 77 and 67 are closed. Valves 79 and 80 are opened. The cooled liquefied gas is introduced into a special cooler 82 through line 83, and it is discharged through line 84 after heat exchange with the air coming from the main cooler 51. The main coolers 55 and 51 are supplied with liquefied gas through line 16, the condenser 73 is by-passed by line 78.

The modes of operation which have just been described are extreme cases and others are possible, e.g., during off peak hours valves 79 and 80 may be partially opened.

With reference to FIG. 5 which represents a configuration for the generation of supplementary cooling effect from the cooling of at least a portion of the liquefied gas stock, this configuration may be added to the configuration of the utilization of refrigeration effect represented in FIGS. 1 and 2. The supplementary refrigerating effect produced by cooling of the liquefied gas stock is stored separately from that used for liquefied gas storage. The cooled liquid may be either mixed in variable proportions with the non-cooled liquid before being introduced into the air coolers, or first introducted into the air cooler.

Next shall be described the configuration and its operation in two extreme cases:

During off peak hours:

Valves 85, 86, 87, 88 and 89 are opened, compressor C3 is operated. The liquefied gas coming from tank 32 and passing through valve 85 is expanded in the evaporator 90, a large refrigeration effect is generated during this expansion which is stored in the evaporator 90 and is not used. The compressed gas coming from C3 is condensed in the condenser 73, through which passes the flow of liquefied gas coming from tank 32 through lines 91 and 92. The liquefied gas is then fed through line 16 to the main cooler (reference character 15 in FIG. 1) or to the main coolers (reference characters 51 and 55 in FIG. 2).

During peak hours:

Valves 85, 86, 87, 88 and 89 are closed, compressor C3 is stopped.

Distinction must be made as to whether the configuration includes special cooler 82 or not.

When the configuration includes special cooler 82, it can replace the system in FIG. 4 including the special cooler 82, the tank 61 and the evaporator 63. The line with valve 93 is omitted, valves 94 and 95 are opened. The special cooler 82 is supplied with cooled liquefied gas through line 96 to cool the air coming from the main cooler 51. The resulting very low temperature air is then introduced into compressor C1.

The liquefied gas is then introduced into the main cooler 55 through line 16 via lines 97, 92 and 78 (condenser 73 is by-passed by line 78).

When the configuration is not provided with a special cooler 82, it can replace the system including the tank 61 and the evaporator 63 represented in FIG. 3. The line including valve 93 exists. Lines 96 and 97 as well as valves 94 and 95 are omitted. Valve 93 is opened, the cooled liquefied gas directly joins the liquefied gas coming from tank 32 through line 91.

The following examples which are given are not limitative, they relate to the use of methane as the liquefied gas. Examples I and II relate to the implementations of the process respectively represented in FIGS. 1 and 2. Example III relates to the configuration represented in FIG. 3 for the implementation of the process in FIG. 1.

The numerical data used in the example are as follows:

the compression of air:

C = 0.246 ; C - c/C = 0.28

Average compressor adiabatic efficiency (adopted for the simplification) : 0.83

Ambient air temperature : 290.degree. K

For air temperature rise : C = 0.26

Gas turbine inlet temperature: 1,173.degree.K

Gas expansion :

C = 0.26 ; C - c/C = 0.265

Average gas turbine adiabatic efficiency (adopted for the two bodies) : 0.85

Ratio of gas weight to air weight : 1.015

Recuperation : C = 0.26

Heat recovery efficiency :

Gas inlet temperature - gas exit temperature/Gas inlet temperature - air inlet temperature = 0.5

All calories are kilog calories.

EXAMPLE I

This example relates to FIG. 1.

A. In the absence of exchanger (18)

Compression: air admitted at + 2.degree.C (i.e., 275.degree.K) - total compression ratio : 34

First compression body (C1) : compression ratio : 2.5

Compression work

T'.sub.c = 0.246 275/0.83 [(2.5).sup.0.28 -1]

T'.sub.c = 0.246 .times. 94.5 calories

Air temperature after compression:

275 + 94.5 = 369.5.degree.K

Second compression body (C2) : compression ratio :

34.3/2.5 = 13.7

Air temperature at the inlet after cooling : 173.degree.K Compression work:

T".sub.c = 0.246 173/0.83 [(13.7).sup.0.28 -1]

T".sub.c = 0.246 .times. 223.5 calories

Air Temperature after compression:

173 + 223.5 = 396.5.degree.K

Total compression work:

T.sub.c = T'.sub.c + T".sub.c = 0.426 .times. 318 calories, = 78.5 calories

Air temperature rise

q = 0.26 (1173 - 396.5) = 0.26 .times. 776.5 calories = 202 calories

Expansion: total expansion ratio:

34.3/1.08 = 31.7

First expansion body (T.sub.1): Expansion ratio : 12.68

Expansion work :

T'.sub.t = 1.015 .times. 0.26 .times. 0.85 .times. 1173 [ 1 - 1/(12.68).sup.0.265 ]= 1.015 .times. 0.26 .times. 490 calories

Gas temperature after expansion : 1173 - 490 = 683.degree.K

Second expansion body (T.sub.2) - Expansion ratio 31.7/12.68 = 2.5

Expansion work :

T".sub.t = 1.015 .times. 0.26 .times. 0.85 .times. 683 [1 - 1/(2.5).sup.0.265 ]= 1.015 .times. 0.26 .times. 124.5 calories

Gas temperature after expansion :

683 - 124.5 = 558.5.degree.K

Total expansion work :

T.sub.t = T'.sub.t + T".sub.t = 1.015 .times. 0.246 .times. (490 + 124.5) = 1.015 .times. 0.246 .times. 614.5 calories = 162.5 calories

Useful work:

t.sub.u = T.sub.t - T.sub.c = 162.5 - 78.5 = 84 calories per kilog of air

Efficiency : .rho. = t.sub.u /Q = 82.4/202 = 0.408

B. In the presence of the exchanger (18)

Recuperator: gas temperature before recuperator 18 and before second expansion in T.sub.2 : 683.degree.K

Air temperature after compression: 396.5.degree.K

Gas temperature drop in the exchanger:

0.5 (683 - 396.5) = 143.5.degree.K

Heat recovery calories:

143.5 .times. 0.26 = 37.5 calories

Necessary heat for air temperature rise :

202 - 37.5 = 164.5 calories

Second expansion : temperature after exchanger :

683 - 143.5 = 549.5.degree.K

Expansion work :

T".sub.t = 1.015 .times. 0.26 .times. 0.85 .times. 549.5 [1 - 1/(2.5).sup.0.26 ]

T".sub.t = 1.015 .times. 0.26 .times. 100

Total expansion work :

T.sub.t = 1.015 .times. 0.26 (490 + 100) = 155.9 calories

Useful work : t.sub.u = (155.9 - 78.5) 0.98

T.sub.u = 77.4 .times. 0.98 = 75.8 calories per kilog of air

Efficiency : .rho. = 75.8/161.5 = 0.46

example ii

this example relates to FIG. 2.

A. In the absence of the recuperator 18

Compression : air admitted at - 100.degree.C (i.e., 173.degree.K) - Total compression ratio : 35

First body (C1) compression ratio : 2.5

Compression work

T'.sub.c = 0.246 .times. 173/0.83 [ (2.5).sup.0.28 -1 ] = 0.246 .times. 60.5

Air temperature after compression:

173 + 60.5 = 233.5.degree.K

Second body (C2) compression ratio: 35/2.5 = 14

Air temperature on inlet after cooling: 173.degree.K

Compression work:

T".sub.c = 0.246 .times. 173/0.83 .times. [ (14).sup.0.28 -1 ] = 0.246 .times. 225

Air temperature after compression: 173 + 225 = 398.degree.K

Total compression work:

T.sub.c = 0.246 (60.5 + 225) = 70.1 calories

Air temperature rise:

q = 0.26 (1173 - 398) = 0.26 .times. 775 = 202 calories

Expansion:

total expansion ratio: 35/1.08 = 32.3

First body T.sub.1): expansion ratio: 32.3/2.5 = 12.9

Expansion work:

T'.sub.t = 1.015 .times. 0.26 .times. 0.85 .times. 1173 [ 1- 1/(12.9).sup.0.265 ] = 1.015 .times. 0.26 .times. 492

Gas temperature after expansion : 1175 - 492 = 681.degree.K

Second body (T.sub.2): expansion ratio: 2.5

Expansion work:

T".sub.t = 1.015 .times. 0.26 .times. 681 [ 1- 1/(2.5).sup.0.265 ] = 1.015 .times. 0.26 .times. 124 calories

Gas temperature after expansion: 681 - 124 = 557.degree.K

Total expansion work:

T.sub.t = 1.015 .times. 0.26 (492 + 124) = 1.015 .times. 0.26 .times. 616

T.sub.t = 163 calories

Useful work:

t.sub.u = (T.sub.t - T.sub.c) 0.96 = (163 - 70.1) 0.98 = 91 calories per kilog of air

Efficiency: 91/202 = 0.45

b. in the presence of the recuperator 18

Recuperator: gas temperature before recuperation and before second expansion in T.sub.2 : 681.degree.K

Air temperature after compression: 398.degree.K

Gas temperature drop in the exchanger:

0.5 (681 - 398) = 141.5.degree.K

Recovery of heat in calories:

141.5 .times. 0.26 = 37 calories

Necessary heat for air temperature rise:

202 - 37 = 165 calories

Second expansion: gas temperature after recuperation:

681 - 141.5 = 539.5.degree.K

Expansion work:

T".sub.t = 1.015 .times. 0.26 .times. 0.85 .times. 539.5 1- [1/(2.5).sup.0.265 ] = 1.015 .times. 0.26 .times. 98.2 calories

Gas temperature after expansion: 539.5 - 98.2 = 441.3.degree.K

Total expansion work: T.sub.t = 1.015 .times. 0.26 (492 + 98.2) = 156 calories

Useful work: t.sub.u = (156 - 70.1) 0.98 = 84.2 calories per kilog of air

Efficieny: .rho. = 84.2/165 = 0.51

example iii

the air temperature at the inlet of the first compressor body, which in the case of Example I in the absence of the recuperator 18, was equal to 275.degree.K, is lowered by 40.degree.C and is equal to 233.degree.K during operation in peak hours. Let us assume for the time being that the opening of the gas turbine circuit is not modified, nor is the revolution speed of the two compression devices.

On the one hand, the density of the inlet air is increased according to the ratio of the absolute temperatures = 275/233.

On the other hand, the compression ratio of the first body rises from 2.5 to P.sub.1 /P.sub.o so that:

(P.sub.1 /P.sub.o).sup.0.28 -1 =[(2.5).sup.0.28 -1] .times. 275/233 = 0.29 .times. 275/233 = 0.342

without change in the compression work per kilog of air as opening and speed remain constant. We deduce therefrom:

P.sub.1 /P.sub.o = 2.87 and the pressure at the gas turbine inlet goes from 31.7 .times. P.sub.o to 31.7 P.sub.o .times. 2.87/2.5 = 36.4

To enable this new flow of gas to pass into the turbine, it would be necessary to increase the pressure at the inlet by the ratio 275/233 = 1.18 and not by the ratio 2.87/2.5 = 1.147. This adaptation requires that the speed of the first compression body be increased by the ratio .sqroot.1.18/1.147, that is to say about 1.5 percent. The expansion ratio is then increased by the ratio 1.18 as air densities.

For the remainder of the calculations, we shall neglect this slight adaptation which would only improve the useful work ratio per kilog of air.

If, therefore, we do not change the speed nor the opening, the total compression work is not modified and remains equal to 78.5 calories. The expansion work is slightly increased and the useful work per kilog of air goes from 84 to 85.9 calories.

The total useful work is thus increased in the ratio 85.9/84 multiplied by the ratio in weight of air flows, that is to say, finally, in the ratio:

85.9/84 .times. 275/233 = 1.21

The peak power is thus increased by 21 percent.

Efficiency is itself improved in the ratio 85.9/84 and goes from 0.408 to 0.408 .times. 85.9/84 = 0.416.

It would of course be possible to lower the air temperature below -40.degree.C at the inlet of the first compression body by increasing the refrigerating machine power. The available power during peak hours would thus be increased.

Claims

What is claimed is:

1. A process for modulating the power of a gas turbine by variation of the inlet temperature of the working fluid in a compressor located upstream of the gas turbine, said process comprising forming the compression and turbine steps each in a plurality of stages, cooling the working fluid before at least the last compression stage by heat exchange with liquified gas stored in a tank, producing a further refrigeration of the liquified gas stored in said tank by supplying at least a part of the liquefied gas during off-peak hours from said tank to an evaporator wherefrom are obtained a gas fraction at the top and a cooled liquefied gas fraction at the bottom, compressing the gas fraction produced in said evaporator, then condensing the thus compressed gas fraction by effecting heat exchange thereof with a flow of liquefied gas coming from said tank and going to cool the working fluid and introducing the now condensed gas fraction into said flow of liquefied gas coming from said tank and going to cool the working fluid, storing the cooled liquefied gas fraction collected in said evaporator during off-peak hours and utilizing the same during peak hours together with the liquefied gas from said tank to cool the working fluid.

2. A process as claimed in claim 1, in which the cooled liquefied gas fraction collected in said evaporator is stored during off-peak hours in the same tank used for storing the liquefied gas by partitioning the tank to prevent mixing of the cooled liquefied gas fraction with the non-cooled liquefied gas.

3. A process as claimed in claim 1, in which the cooled liquefied gas fraction collected in asid evaporator is stored during off-peak hours separately from the tank used for the non-cooled liquefied gas.

4. A process as claimed in claim 1 wherein the compression of the working fluid is effected in two stages, the process further comprising removing water from the working fluid before introduction into the first compressor stage by cooling said fluid by spraying at a temperature lower than 0.degree.C with a mixture of water and anti-freeze and then subsequently separating the condensed water from the working fluid.

5. A process as claimed in claim 4 wherein the working fluid coming out of the first compressor stage is passed through a first cooler, then through a container where it is freed from traces of water vapor by spraying, at a temperature lower than 0.degree.C, with a mixture of water and anti-freeze and subsequently separating the condensed water from the working fluid and finally passing the working fluid through a second, main cooler from which it is discharged at a temperature of about -100.degree.C before being admitted into the second compressor stage.

6. A process as claimed in claim 1 wherein the compression of the working fluid is effected in two stages, the working fluid being passed before being introduced into the first compressor stage through a container where it is freed from water vapor by cooling said fluid by spraying the same at a temperature lower than 0.degree.C, with a mixture of water and anti-freeze and subsequently separating the condensed water from the working fluid, then passing the working fluid through a main cooler from which it is discharged at a temperature of about -100.degree.C to be admitted into the first compressor stage.

7. A process as claimed in claim 6 wherein the working fluid coming from the first compressor stage is passed through a second main cooler from which it is discharged at a temperature of about -100.degree.C before being admitted to the second compressor stage.

8. A process as claimed in claim 1 wherein the working fluid compressed in two stages, wherein the first compressor stage operates at a relatively low compression ratio of about 2.5 and the second compressor stage compresses the fluid to a higher value therethan.

9. A process as claimed in claim 1 wherein the liquefied gas is methane.