Cogeneration process and installation.

Abstract

Cogeneration process and installation.The invention mainly relates to a method of cogeneration by a cogeneration installation, comprising the selective steps of: Heating by a condenser (5) of the heat transfer fluid of the stratified accumulator (6) when the temperature of said heat transfer fluid in the hot zone (9) is lower than a first determined threshold, by increasing the pressure and the temperature of the steam at the outlet (2s) of the turbine (2) up to two first determined values of pressure and temperature respectively; Reducing the pressure and the temperature of the steam at the outlet (2s) of the turbine (2) up to two second determined values of pressure and temperature respectively, and cooling the heat transfer circuit (5a) of the condenser (5) by the heat transfer fluid coming from the cold zone (8) of the stratified accumulator (6) when the temperature of said heat transfer fluid in the hot zone (9) is higher than a second determined threshold.Figure to be published with the abstract: Fig. 1.

Description

Title of the invention: Cogeneration method and installation. Technical field

[0001] The invention falls within the field of energy production, and more precisely in the field of cogeneration, that is to say in the simultaneous production of thermal energy and electrical energy. Prior art and disadvantages of prior art

[0002] In a known manner, a cogeneration installation comprises a heat source, originating for example from the combustion of a fuel in a thermal power station or from the fission of fissile material in a nuclear power station, a circuit, which makes it possible to generate steam under high pressure and high temperature which is conveyed via a dedicated circuit to the inlet of one or more turbines. The steam under high pressure and high temperature drives the shaft of a turbine, which shaft is connected to an alternator-type device to transform the mechanical work into electrical energy.

[0003] The cogeneration installation also includes a condenser which is connected to the so-called low-pressure steam outlet of the turbine. The condenser is used to transform this low-pressure steam from the gas phase to a liquid phase - also called condensate. The latent heat released by the low-pressure steam during this change of state is collected by a heat transfer fluid in the condenser and used later, for example in an urban hot water network. The condenser, which forms the cold source of the installation and which dissipates the heat of condensation, generates condensates which are then returned by the circuit to the hot source and the water / steam cycle begins again.

[0004] A disadvantage of these installations, which is also common to all thermodynamic installations, is that the energy efficiency of the installation depends directly on the temperature difference between the hot source and the cold source. Also, the greater the temperature difference between these two sources, the higher the thermodynamic efficiency of the installation. However, the temperature of the low-pressure steam leaving the turbine depends on the temperature of the cold source which also depends on the outside temperature. This parameter is therefore most of the time subject. To overcome this disadvantage, publication FR2935737 describes in particular an air condenser connected to the condenser forming the cold source of the installation, and whose role is to further reduce the temperature of the low-pressure steam leaving the turbine, in order to improve the thermodynamic efficiency of the installation.

[0005] Another disadvantage is that this steam at the turbine exhaust is at a pressure between 80 and 500 millibars and a temperature between 40 and 80 °C, and most of the time between 45 and 60 °C. Given these temperature and pressure levels, this thermal energy from the low-pressure steam at the turbine exhaust is difficult to export to a district heating network or to an industrial plant. Also, all or part of the heat collected by the condenser and / or the air condenser is lost to the environment.

[0006] To at least partially overcome this drawback, publication FR2984400 describes a thermo-compressor connected to a turbine draw-off pipe and which makes it possible to increase the temperature and pressure of the low-pressure steam leaving the turbine.

[0007] However, all these solutions do not allow the overall efficiency of the cogeneration installation to be optimized, in particular during variations in the pressure and temperature of the low-pressure steam at the turbine outlet, which have a direct impact on the quantity of electricity produced. Objectives of the invention

[0008] The invention therefore aims to propose an installation and a method making it possible to optimize the production of electrical energy and thermal energy as best as possible. Description of the invention

[0009] For this purpose, the invention relates to a cogeneration method by a cogeneration installation comprising a hot source producing expanded steam in a turbine, a so-called low-pressure steam outlet of which is connected to the inlet of a first condenser forming a cold source, the hot source being connected to the outlet of the condenser, the installation further comprising a stratified thermal accumulator connected to a heat transfer circuit of the condenser, which accumulator comprises a heat transfer fluid having a temperature gradient between a minimum temperature zone called the cold zone of the accumulator and a maximum temperature zone called the hot zone of the accumulator, which method comprises a step of periodically measuring the temperature of the hot zone of the stratified accumulator, followed by the selective steps of: • Heating by the condenser of the heat transfer fluid of the stratified accumulator when the temperature of said heat transfer fluid in the hot zone is lower than a first determined threshold, by increasing the pressure and the temperature of the steam at the outlet of the turbine up to two first determined values respectively of pressure and temperature; • Reduction of the pressure and temperature of the steam leaving the turbine up to two seconds determined values of pressure and temperature respectively, and cooling of the heat transfer circuit of the condenser by the heat transfer fluid from the cold zone of the stratified accumulator when the temperature of said heat transfer fluid in the hot zone is higher than a second determined threshold.

[0010] The method may also comprise the following optional characteristics considered in isolation or according to all possible technical combinations: • The stratified accumulator is a hydro-accumulator which comprises an intermediate zone between the hot zone and the cold zone, in that the heat transfer fluid of the stratified accumulator circulates in the heat transfer circuit of the first condenser between the cold zone and the intermediate zone or the hot zone of the accumulator during the step of heating said heat transfer fluid, and in that the heat transfer fluid of the stratified accumulator circulates in the heat transfer circuit of the first condenser at the cold zone of the accumulator during the step of cooling said heat transfer fluid. • The temperature value corresponding to the second threshold is higher than the temperature value corresponding to the first threshold. • The installation comprises a third second condenser connected to the stratified accumulator at its cold zone and configured to cool the heat transfer fluid in said cold zone, which method comprises a step of cooling the heat transfer fluid in the cold zone if the temperature of said heat transfer fluid in the hot zone is higher than the second determined threshold. • The first temperature threshold is between 50 and 80°C, and the second temperature threshold is between 35 and 45°C. • The first two values respectively of pressure and temperature of the steam at the turbine outlet are respectively between 300 and 500 millibars and between 70 and 80°C, and in that the second two values respectively of pressure and temperature of the steam at the turbine outlet are respectively less than or equal to 80 millibars and greater than or equal to 45°C.

[0011] The invention also relates to a cogeneration installation capable of implementing the cogeneration method as described previously, comprising: • a hot source capable of producing expanded steam in a turbine whose so-called low-pressure steam outlet is connected to the inlet of a condenser forming a cold source, the hot source being further connected to the outlet of the condenser, • a stratified thermal accumulator connected to a heat transfer circuit of the condenser and comprising a heat transfer fluid having a temperature gradient temperature between a minimum temperature zone called the cold zone of the accumulator, and a maximum temperature zone called the hot zone of the accumulator, which stratified accumulator is configured to distribute thermal energy in the form of heat to a heat utilization system, • low-pressure steam circulation means provided at the condenser inlet and controlled by installation control means, • means for measuring the temperature of the low-pressure steam entering the condenser which are connected to the control means, and • means for measuring the temperature of the heat transfer fluid in the hot zone of the stratified accumulator which are connected to the control means.

[0012] The installation may also include the following optional characteristics considered in isolation or in all possible technical combinations: • The installation comprises a second condenser connected to the stratified accumulator at its cold zone, which second condenser is configured to cool the heat transfer fluid in said cold zone. • The first condenser is a hydrocondenser, and the second condenser is an air cooler. Presentation of figures

[0013] Other characteristics and advantages of the invention will emerge clearly from the description given below, for information purposes only and in no way limiting, with reference to the appended figures, among which:

[0014] [Fig-1] [Fig.l] represents a schematic view of the operating cycle of the cogeneration installation of the invention;

[0015] [Fig.2] [Fig.2] represents a schematic view of a part of the installation during the cooling stage of the heat transfer circuit of the condenser;

[0016] [Fig.3] [Fig.3] represents a schematic view of a part of the installation during the stage of heating the heat transfer fluid of the stratified accumulator. Detailed description of the invention

[0017] It is first of all specified that in the figures, the same references designate the same elements regardless of the figure in which they appear and regardless of the form of representation of these elements. Similarly, if elements are not specifically referenced in one of the figures, their references can be easily found by referring to another figure.

[0018] It is also specified that the figures essentially represent an embodiment of the subject of the invention but that there may be other embodiments which meet the definition of the invention.

[0019] The invention relates to a cogeneration installation with optimized efficiency by controlling a stratified accumulator 6. The heart of this installation is formed by a closed primary heat transfer circuit 1a in which circulates a primary heat transfer fluid heated by a hot source and cooled by a cold source. The installation further comprises a pump 12 ensuring the circulation of the primary heat transfer fluid in the heat circuit 1a.

[0020] With reference to [Fig.l], the installation comprises a steam boiler 1 - which forms the heat source of the installation - which ensures the supply of thermal energy (i.e. heat) to the thermodynamic operating cycle of the installation by cogeneration, i.e. which ensures the heating of the primary heat transfer fluid circulating in the primary heat transfer circuit 1a of the installation. The heat generated by the boiler 1 may be of thermal or nuclear origin, or of any other origin capable of producing heat industrially. The primary heat transfer fluid of the installation is generally water in liquid form transformed into steam.

[0021] The boiler 1 is configured to vaporize the water in the primary heat transfer circuit passing it through the boiler 1. The steam outlet of the boiler is connected to the inlet of a turbine 2 in which the water vapor leaving the boiler 1 is expanded. In a known manner, the turbine 2 is connected to an alternator 3 which transforms the mechanical energy from the rotation of the blades of the turbine 2 into electrical energy.

[0022] The turbine 2 also comprises an outlet 2s called low pressure steam. By low pressure, we mean a steam pressure lower than atmospheric pressure, typically between a few tens of millibars and 500 millibars. Furthermore, the temperature of this low pressure steam varies between 35 and 82°C when the pressure is of the order of 100 millibars and of the order of 45° and 82°C when the pressure is around 500 millibars. The temperature and pressure of the low pressure steam are measured via sensors connected to control means of the cogeneration installation.

[0023] The cogeneration installation further comprises, at the outlet 2s of the turbine 2, a condenser 5 forming the cold source of the installation and configured to cool and condense the steam coming from the low pressure outlet 2s of the turbine 2 and circulating in the primary heat transfer circuit 1a.

[0024] The condenser 5 is a hydrocondenser whose outlet is connected to the inlet of the boiler 1, and whose function is to cool and condense the steam in the primary heat transfer circuit 1a.

[0025] This cooling, causing the condensation of the steam in the primary circuit 1a, is achieved by means of a secondary heat transfer circuit 5a passing through the hydrocondenser 5 and in which a secondary heat transfer fluid circulates, gener- water rattle.

[0026] This secondary heat transfer fluid comes from a stratified heat accumulator 6 to which the secondary heat transfer circuit 5a of the hydrocondenser 5 is connected, which stratified accumulator 6 is configured to recover the heat from the secondary heat transfer circuit 5a of the hydrocondenser 5, and therefore to cool the hydrocondenser 5 and the primary heat transfer fluid passing through the hydrocondenser 5 and returning to the boiler 1. This stratified accumulator 6 is a hydro-accumulator, and the heat transfer fluid stored in this hydro-accumulator 6 is in liquid form, and is typically water in the liquid state.

[0027] The heat transfer fluid in this stratified hydro-accumulator 6 is subjected to a temperature gradient. Indeed, the stratified hydro-accumulator 6 is divided into three zones, respectively a lower zone of minimum temperature of the heat transfer fluid called cold zone 8, an upper zone of maximum temperature of the heat transfer fluid called hot zone 9, and a zone of variable intermediate temperature of the heat transfer fluid called intermediate zone 7. Furthermore, this intermediate zone 7 is divided into at least two intermediate sub-zones, respectively a cold intermediate sub-zone 7a adjacent to the cold zone 8 and a hot intermediate sub-zone 7b adjacent to the hot zone 9.

[0028] Thus, the heat transfer fluid in the stratified hydro-accumulator 6 has a temperature gradient between the minimum temperature of the cold zone 8 and the maximum temperature of the hot zone 9. Since the density of the heat transfer fluids, and in particular of the heat transfer fluid in the stratified hydro-accumulator 6, depends on its temperature, the temperature gradient is directed along a vertical axis, and the hot zone 9 is located at the top of the stratified hydro-accumulator 6 while the cold zone 8 is located at the base of the stratified hydro-accumulator 6. Thus, the higher the temperature of the heat transfer fluid in the stratified hydro-accumulator 6, the higher its altitude level in said hydro-accumulator 6.

[0029] The temperature of the heat transfer fluid of the hydro-accumulator 6, measured by sensors installed over the entire height of said stratified hydro-accumulator 6 and connected to the control means, varies between approximately 30°C at the base of the cold zone 8 up to approximately 97°C at the top of the hot zone 9 of the stratified accumulator 6.

[0030] The stratified hydro-accumulator 6 has, for example and in a non-limiting manner, a heat transfer fluid volume of 2000 m3, which corresponds to a maximum thermal energy reserve of 100 MWh thermal.

[0031] The secondary heat transfer circuit 5a at the outlet of the hydrocondenser 5 opens at the inlet 13a of a first three-way valve 13 controlled by the control means of the installation, which first valve 13 comprises a first outlet 13b connected to the hot intermediate sub-zone 7b of the stratified hydro-accumulator 6 and a second output 13c connected to cold zone 8 of stratified hydro-accumulator 6.

[0032] Furthermore, the secondary heat transfer circuit 5a comprises, upstream of the inlet of the hydrocondenser 5, a second three-way valve 14 controlled by the control means of the installation and comprising a single outlet 14c fluidically connected to the inlet of said hydrocondenser 5. The second valve 14 further comprises a first inlet 14a connected to the cold intermediate sub-zone 7a of the stratified hydro-accumulator 6 and a second inlet 14b connected to the cold zone 8 of the stratified hydro-accumulator 6.

[0033] With reference to [Fig.l], the fluid connection to the stratified hydro-accumulator 6 at the first inlet 14a of the second valve 14 is arranged above the fluid connection to the stratified hydro-accumulator 6 of the second outlet 13c of the first valve 13, said fluid connection of the second outlet 13c of the first valve 13 itself being arranged above the fluid connection to the stratified hydro-accumulator 6 at the second inlet 14b of the second valve 14. In other words, the temperature of the secondary heat transfer fluid likely to enter the second valve 14 through its first inlet 14a is higher than the temperature of the secondary heat transfer fluid leaving the first valve 13 through its second outlet 13c, and the temperature of the secondary heat transfer fluid leaving through the second outlet 13c of the first valve 13 is higher than the temperature of the secondary heat transfer fluid entering the second valve 14 by its second inlet 14b.

[0034] The cogeneration installation also comprises a second condenser 11, typically a hybrid air cooler, comprising a tertiary heat transfer circuit 11a connected to the cold zone 8 of the stratified hydro-accumulator 6. More precisely, the connection between the stratified hydro-accumulator 6 and the inlet of the hybrid air cooler 11 is located at the same level as the connection between the stratified hydro-accumulator 6 and the second outlet 13c of the first valve 13 of the secondary heat transfer circuit 5a of the hydrocondenser 5. Furthermore, the connection between the stratified hydro-accumulator 6 and the outlet of the hybrid air cooler 11 is located at the same level as the connection between the stratified hydro-accumulator 6 and the second inlet 14b of the second valve 14 of the secondary heat transfer circuit 5a of the hydrocondenser 5.The role of this hybrid air cooler 11 is to further cool the secondary heat transfer fluid circulating in the secondary heat transfer circuit 5a of the hydrocondenser 5, in order to ultimately optimize the cooling of the primary heat transfer fluid passing through the hydrocondenser 5 via the primary heat transfer circuit 1a. According to an alternative embodiment, any other system or device capable of further cooling the secondary heat transfer fluid circulating in the secondary heat transfer circuit 5a of the hydrocondenser 5 can be adopted in place of the air cooler 11 without departing from the scope of the invention.

[0035] Finally, the stratified hydro-accumulator 6, the main role of which is to distribute thermal energy, is connected to at least one heat utilization system 10 stored in the stratified hydro-accumulator 6. Each utilization system 10 can be connected to the stratified hydro-accumulator 6 at different levels, depending on the quantity of heat required: the greater the quantity of heat required, the closer the level of the connection to the inlet of the heat utilization system 10 will be to the top of the hydro-accumulator 6. Furthermore, the same heat utilization system 10 can have several inlets located at different levels of the stratified hydro-accumulator 6, depending on the heat requirements (see [Fig.2]).

[0036] As an example shown in [Fig. 1], the stratified hydro-accumulator 6 can be connected to a medium-temperature heat utilization system 10 - for example for domestic heating or hot water requirements - the inlet of which is connected to an outlet 15c of a three-way controlled valve 15, the other two ways being first 15a and second 15b inlets of the valve 15, the first 15a connected to the hot zone 9 of the hydro-accumulator 6, and the second 15b connected to the hot intermediate sub-zone 7b of said hydro-accumulator 6. The outlet of the heat utilization system 10 is connected to the cold intermediate sub-zone 7a of the stratified hydro-accumulator 6.

[0037] Depending on the thermal energy required (for example depending on the season), the heat utilization system 10 can be supplied either via the first inlet 15a of the valve 15 with heat fluid coming from the hot zone 9 of the stratified hydro-accumulator 6, or via the second inlet 15b of the valve 15 with heat fluid coming from the hot intermediate sub-zone 7b of the hydro-accumulator 6.

[0038] The stratified hydro-accumulator 6 can also be connected to a low-temperature heat utilization system (not shown), for example for heating swimming pools, for drying sewage sludge in digesters in sewage treatment plants or for market garden greenhouses. The inlet of such a low-temperature system is connected to the cold intermediate sub-zone 7a of the stratified hydro-accumulator 6 while the outlet of said low-temperature system is connected to the cold zone 8 of the stratified hydro-accumulator 6.

[0039] According to the invention, a cogeneration method implemented by the cogeneration installation of the invention will now be described with reference to Figures 1 to 3.

[0040] The cogeneration installation is configured to operate in two different modes, depending on the quantity of thermal energy present in the stratified hydro-accumulator 6 and depending on the electricity requirements.

[0041] With reference to [Fig.2], if the temperature of the hot zone 9 of said accumulator 6 is lower than a first determined threshold, for example 50°C, that is to say if the quantity of thermal energy present in the stratified accumulator is lower than a first determined threshold fraction of the maximum quantity of energy that can be stored in said hydro-accumulator 6, then the installation is in a mode known as recharging with thermal energy of the stratified hydro-accumulator 6. In this operating mode, the heat transfer fluid circulates in the secondary heat transfer circuit 5a, between the valves 13, 14 and the stratified hydro-accumulator 6, according to the dotted arrows shown in [Fig.l].

[0042] To recharge the stratified hydro-accumulator 6 with thermal energy, the pressure and temperature of the low-pressure steam at the outlet 2s of the turbine 2 is increased to two first determined values, typically of the order of 500 millibars and of the order of 81°C. The control means control: • The opening of the inlet 13a and the first outlet 13b of the first valve 13 connected to the outlet of the hydrocondenser 5, and the closing of the second outlet 13c of said first valve 13; • The opening of the outlet 14c and the first inlet 14a of the second valve 14 connected to the inlet of the hydrocondenser 5, and the closing of the second inlet 14b of said second valve 14; • Stopping the circulation of the heat transfer fluid from the stratified hydro-accumulator 6 in the heat utilization system(s) 10; • If necessary, stop the circulation of the heat transfer fluid from the stratified hydro-accumulator 6 in the tertiary heat transfer circuit 11a of the air cooler IL

[0043] In this operating mode, the hydrocondenser 5 heats the heat transfer fluid of the stratified hydroaccumulator 6 circulating in the secondary heat transfer circuit 5a from a temperature of the order of 65°C to a temperature of the order of 80°C. This operating mode is advantageously selected when the electricity requirements are not preponderant, in particular because the efficiency of the installation with respect to the production of electricity is lower.

[0044] In a particularly advantageous manner, it is possible to increase the temperature of the heat transfer fluid of the hydro-accumulator 6 circulating in the secondary heat transfer circuit 5a at the outlet of the hydrocondenser 5 up to a temperature of the order of 97°C. To do this, an additional heat source such as a thermo-compressor or a steam superheater (not shown) is integrated into the primary heat transfer circuit 1a of the cogeneration installation between the low pressure outlet 2s of the turbine 2 and the hydrocondenser 5. This thermo-compressor raises the temperature of the low pressure steam to a value of the order of 100°C.

[0045] With reference to [Fig. 3], if the temperature of the hot zone 9 of said stratified hydroaccumulator 6 is greater than or equal to a second determined threshold, for example 55°C, that is to say if the quantity of thermal energy present in the stratified hydro-accumulator 6 is greater than or equal to a second variable threshold fraction of the maximum quantity of energy that can be stored in said hydro-accumulator 6, then the cogeneration installation is in a mode called cooling of the hydrocondenser 5 by the heat transfer fluid coming from the cold zone 8 of the stratified hydro-accumulator 6 and passing through the hydrocondenser 5 via the heat transfer circuit 5a. In this operating mode, the heat transfer fluid circulates in the secondary heat transfer circuit 5a, between the valves 13, 14 and the stratified hydro-accumulator 6, according to the solid arrows shown in [Fig.l].

[0046] Advantageously, in order to avoid too frequent changes from one operating mode to the other, the first and second temperature thresholds are different, as are the first and second threshold fractions. In particular, the temperature value corresponding to the second threshold is greater than the temperature value corresponding to the first threshold, and the second threshold fraction is greater than the first threshold fraction

[0047] By way of non-limiting example, the first temperature threshold is equal to 80°C, the second temperature threshold is equal to 50°C, the first threshold fraction represents 80% of the maximum amount of energy that can be stored in the stratified hydro-accumulator 6, and the second threshold fraction represents 50% of the maximum amount of energy that can be stored in the stratified hydro-accumulator 6.

[0048] To cool the heat transfer fluid passing through the hydrocondenser 5 via the secondary heat transfer circuit 5a, the pressure and temperature of the low pressure steam at the outlet 2s of the turbine 2 is reduced to two second determined values, typically of the order of 80 to 100 millibars and of the order of 45°C. The control means control: • Maintaining the opening of the inlet 13a of the first valve 13 connected to the outlet of the hydrocondenser 5, closing the first outlet 13b and opening the second outlet 13c of said first valve 13; • Maintaining the opening of the outlet 14c of the second valve 14 connected to the inlet of the hydrocondenser 5, closing the first inlet 14a and opening the second inlet 14b of said second valve 14; • Actuation of the circulation of the heat transfer fluid from the stratified hydro-accumulator 6 in the hybrid air cooler 11, which ensures the cooling of said heat transfer fluid in the cold zone 8 of the stratified hydro-accumulator 6; • Resumption of circulation of the heat transfer fluid from the stratified hydro-accumulator 6 in the heat utilization system(s) 10.

[0049] In this mode of operation, the secondary heat transfer fluid circulating in the heat transfer circuit 5a of the hydrocondenser 5 is cooled by the hybrid air cooler 11 via the cold zone 8 of the stratified hydroaccumulator 6. In the operating mode of [Fig.3], the inlet of the secondary heat transfer circuit 5a of the hydrocondenser 5 in the cold zone 8 of the hydroaccumulator 6 is at the same level as the outlet of the tertiary heat transfer circuit 11a of the hybrid air cooler 11 outside the cold zone 8, and the outlet of the secondary heat transfer circuit 5a of the hydrocondenser 5 outside the cold zone 8 is at the same level as the inlet of the tertiary heat transfer circuit 11a of the hybrid air cooler 11 in the cold zone 8.

[0050] Typically, the heat transfer fluid circulating in the hydrocondenser 5 leaves the cold zone 8 of the stratified hydroaccumulator 6 at approximately 30°C, circulates via the secondary heat transfer circuit 5a in the hydrocondenser 5 to cool it and leaves the latter at a temperature of the order of 40°C. In parallel, the heat transfer fluid circulating in the hybrid air cooler 11 leaves the cold zone at 40°C, circulates in the hybrid air cooler 11 via the tertiary heat transfer circuit 11a to be cooled there and re-enters the cold zone 8 of the stratified hydroaccumulator 6 at 30°C.

[0051] This operating mode is advantageously selected when the electricity requirements are predominant: the hydrocondenser 5 is cooled to the maximum to ensure a maximum drop in the temperature of the primary heat transfer fluid circulating in the primary heat transfer circuit 1a in the direction of the hot source 1, which allows a substantial increase in the efficiency of the cogeneration installation.

[0052] The cogeneration installation of the invention therefore makes it possible either to maximize the production of electricity and therefore to have an optimal efficiency of transformation of heat into electrical energy, or to recharge the stratified hydro-accumulator 6 with thermal energy. Thus, whatever the pressure of the steam at the low pressure outlet 2s of the turbine 2, the loss of thermal energy is minimized.

Claims

Claims

1. Method of cogeneration by a cogeneration installation comprising a hot source (1) producing expanded steam in a turbine (2) of which a so-called low pressure steam outlet (2s) is connected to the inlet of a condenser (5) forming a cold source, the hot source (1) being connected to the outlet of the condenser (5), the installation further comprising a stratified thermal accumulator (6) connected to a heat transfer circuit (5a) of the condenser (5), which accumulator (6) comprises a heat transfer fluid having a temperature gradient between a minimum temperature zone called the cold zone (8) of the accumulator (6) and a maximum temperature zone called the hot zone (9) of the accumulator (6), which method comprises a step of periodically measuring the temperature of the hot zone (9) of the stratified accumulator,followed by the selective steps of: • Heating by the condenser (5) of the heat transfer fluid of the stratified accumulator (6) when the temperature of said heat transfer fluid in the hot zone (9) is lower than a first determined threshold, by increasing the pressure and the temperature of the steam at the outlet (2s) of the turbine (2) up to two first determined values of pressure and temperature respectively; • Reducing the pressure and the temperature of the steam at the outlet (2s) of the turbine (2) up to two second determined values of pressure and temperature respectively, and cooling the heat transfer circuit (5a) of the condenser (5) by the heat transfer fluid coming from the cold zone (8) of the stratified accumulator (6) when the temperature of said heat transfer fluid in the hot zone (9) is higher than a second determined threshold.,

2. Method according to the preceding claim, characterized in that the stratified accumulator (6) is a hydro-accumulator which comprises an intermediate zone (7) between the hot zone (9) and the cold zone (8), in that the heat transfer fluid of the stratified accumulator (6) circulates in the heat transfer circuit (5a) of the first condenser (5) between the cold zone (8) and the intermediate zone (7) or the hot zone (9) of the accumulator (6) during the step of heating said heat transfer fluid, and in that the heat transfer fluid of the stratified accumulator (6) circulates in the heat transfer circuit (5a) of the condenser (5) at the level of the cold zone (8) of the accumulator (6) during the step of cooling said heat transfer fluid.

3. Method according to claim 1 or 2, characterized in that the temperature value corresponding to the second threshold is greater than the temperature value corresponding to the first threshold.

4. Method according to any one of the preceding claims, characterized in that the installation comprises a third second condenser (11) connected to the stratified accumulator (6) at its cold zone (8) and configured to cool the heat transfer fluid in said cold zone (8), which method comprises a step of cooling the heat transfer fluid in the cold zone (8) if the temperature of said heat transfer fluid in the hot zone (9) is higher than the second determined threshold.

5. Method according to any one of the preceding claims, characterized in that the first temperature threshold is between 50 and 80°C, and in that the second temperature threshold is between 30 and 45°C.

6. Method according to any one of the preceding claims, characterized in that the first two values respectively of pressure and temperature of the steam at the outlet (2s) of the turbine (2) are respectively between 300 and 500 millibars and between 70 and 80°C, and in that the second two values respectively of pressure and temperature of the steam at the outlet (2s) of the turbine (2) are respectively less than or equal to 80 millibars and greater than or equal to 45°C.

7. Cogeneration installation capable of implementing the cogeneration method according to any one of claims 1 to 6, comprising: • a hot source (1) capable of producing expanded steam in a turbine (2) whose so-called low pressure steam outlet (2s) is connected to the inlet of a condenser (5) forming a cold source, the hot source (1) being further connected to the outlet of the condenser (5), • a stratified thermal accumulator (6) connected to a heat transfer circuit (5a) of the condenser (5) and comprising a heat transfer fluid carrier having a temperature gradient between a minimum temperature zone called cold zone (8) of the accumulator (6), and a maximum temperature zone called hot zone (9) of the accumulator (6), which stratified accumulator (6) is configured to distribute thermal energy in the form of heat to a heat utilization system (10), • means for circulating low pressure steam arranged at the inlet of the condenser (5) and controlled by control means of the installation, • means for measuring the temperature of the low pressure steam at the inlet of the condenser (5) which are connected to the control means, and • means for measuring the temperature of the heat transfer fluid in the hot zone (9) of the stratified accumulator (6) which are connected to the control means.

8. Installation according to claim 7, characterized in that it comprises a second condenser (11) connected to the stratified accumulator (6) at its cold zone (8), which second condenser (11) is configured to cool the heat transfer fluid in said cold zone (8).

9. Installation according to the preceding claim, characterized in that the first condenser (5) is a hydrocondenser, and in that the second condenser (11) is an air cooler.

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