EP3015660A1 - Device and method for operating a thermodynamic cycle process - Google Patents

Abstract

The invention relates to an apparatus for operating a thermodynamic cycle, in particular an ORC process, comprising: a feed pump for conveying liquid working fluid under pressure increase to an evaporator; the evaporator for evaporation and optionally additional overheating of the working medium with the supply of heat; an expansion machine for generating mechanical energy by relaxing the vaporized working medium; and at least two capacitors connected in parallel between the expander and the feed pump for condensing and optionally additional subcooling the relaxed working medium. Furthermore, the invention relates to a corresponding method for operating a thermodynamic cycle.

Description

Field of the invention

The invention relates to an apparatus and a method for operating a thermodynamic cycle, in particular an ORC process.

State of the art

An exemplary system for recovering electrical energy from thermal energy consists of the following main components: a feed pump, which conveys liquid working fluid under pressure to an evaporator, the evaporator itself, in which the working fluid is preheated with the supply of heat, evaporated and optionally additionally superheated, an expansion machine in which the highly pressurized vaporized working fluid is expanded, thereby generating mechanical energy, which can be converted, for example via a generator into electrical energy, and a condenser in which the low-pressure steam (relaxed working medium) from the expansion machine and de-liquefied liquefied becomes. From the condenser, the liquid working medium returns to the feed pump of the system, whereby the thermodynamic cycle is closed. If the working medium is an organic working medium, it is an Organic Rankine Cycle as a thermodynamic cycle (ORC system).

To avoid cavitation in the feed pump, the liquid working medium is subcooled, that is cooled to a temperature below the condensation temperature (equivalent to the boiling temperature) at the condensation pressure. In this way, the NPSH value required for the pump (Net Positive Suction Head) is achieved.

In principle, there are two possibilities for carrying out the condenser of a thermodynamic cycle (in particular an ORC system). On the one hand, the condensation of the working medium against liquid (for example water) can take place or, on the other hand, the condensation can take place against air. Condensation against water has the advantage that the heat of condensation can be fed into a heating circuit and is thus available to heat consumers (for example a stable, a building heater, a fermenter, etc.). Are no heat consumers available only a condensation against air is possible, but this is the personal use of a fan at the expense of electrical efficiency.

There are also applications in which a heat loss is desired only for a limited time in the year. If, however, the use of heat and power generation by the ORC is still to be allowed, then in the period of the year when no heat is used, the excess heat must be removed, e.g. be discharged via the emergency cooler of a combined heat and power plant. However, this is associated with a high power consumption and thus with increased costs.

In principle, two capacitors can be connected together (according to the applicant's internal, unpublished state of the art) in order to enable both modes of operation (cooling against air and cooling against a liquid, in particular water). However, the difficulties here are to regulate the distribution of the mass flows of the working medium in the respective capacitors and thus the heat output. The aim is to allow the largest possible or defined usable amount of heat in a condenser, which is integrated into a heating circuit.

Mechanical valves such as shut-off valves could be used to control the mass flows. However, this involves the problem that different pressure levels are present in both capacitors. This can lead to the return flow of condensed fluid into the condenser with the lower pressure, to the point of full running of this condenser. The valves to be installed, however, the complexity of the system and the susceptibility to errors is increased because the correct valve positions must be maintained for the correct operating modes.

Description of the invention

The object of the invention is to overcome the disadvantages mentioned at least partially.

This object is achieved by a device according to claim 1.

The device according to the invention for operating a thermodynamic cycle, in particular an ORC process, comprises: a feed pump for conveying liquid working fluid under pressure increase to an evaporator; the evaporator for preheating, evaporation and optionally additional overheating of the working medium under the supply of heat; an expansion machine for generating mechanical energy by relaxing the vaporized working medium; and at least two capacitors connected in parallel between the expander and the feed pump for defrosting, condensing and optionally additional subcooling of the relaxed working medium. This has the advantage that, for example, in a heating circuit which can be supplied with heat via one of the capacitors, heat which is not required can be dissipated via the other condenser (s). On the other hand, two capacitors can be operated at different temperature levels, for example, to supply heat to different heating circuits. In this way, the heat distribution can be flexibly regulated.

The device according to the invention can be further developed such that the at least two capacitors comprise a liquid condenser and an air condenser. By liquid condenser is meant that a liquid flows through the condenser, which can absorb heat from the working medium also flowing through the condenser. In contrast, in the case of an air condenser, the air flowing through the condenser (or along its contact surfaces) is the heat-absorbing fluid.

Another development consists in that the liquid condenser is provided in a liquid circuit, in particular a heating circuit, with a pump and / or wherein the air condenser comprises a fan. With the pump and / or the fan, a heat dissipation in the liquid circuit can be controlled, in particular switched on or off and with the fan cooling of the working medium can be controlled against air, especially switched on or off.

According to another embodiment, the fan and / or the pump can be regulated, in particular the speed of the fan or the pumped by the pump mass flow of the liquid. The mass flow, which is conveyed by the pump, can be done for example via a speed control of the pump or via a balancing valve.

Another development is that each capacitor can be connected via a siphon to the feed pump, wherein a minimum filling level of the condensed working medium is determined in the condenser by the apex of the siphon. With the help of a siphon in the condensate line, the liquid level in the condenser is always as high as the height of the siphon. This also ensures a defined minimum subcooling.

According to another embodiment may further be provided between the capacitors and the feed pump, a pressure-tight container. A container between the condensers and the pump ensures that always liquid working fluid flows to the pump. If it comes to operating conditions in which one of the capacitors runs empty and thus gaseous working fluid flows in the direction of the pump, this is deposited in the container. Even with the liquid working fluid flowing gas bubbles, which could cause (partial) cavitation on the feed pump, are deposited in the container. If the container is not completely filled and a liquid level is established, the working fluid in the container tends to saturate. This results in two possible cases: If the working medium is colder than the environment, it evaporates and an equilibrium state between the liquid phase and the vapor phase sets in. However, if the working fluid in the container is warmer than the ambient temperature, heat is released to the environment and condensation takes place in the container. This causes the liquid level to rise until the container is full. By an additional partial pressure is applied to the liquid level in the container, for example by means of a non-condensing gas, sufficient subcooling (distance between boiling temperature and actual temperature) can be ensured and the condensation in the container can be prevented. In other words, such a gas provides a sufficient flow height for the feed pump.

Another development consists in that, for each of the capacitors connected in parallel, a check valve is provided between the respective capacitor and the feed pump and / or between the expander and the respective condenser, each check valve allowing only a flow in the direction of the feed pump. In this way, an undesirable natural circulation between the capacitors can be prevented.

According to another development, the device may further comprise: a temperature sensor for measuring the temperature of a liquid / heating circuit return, and / or a temperature sensor for measuring the temperature of a liquid / heating circuit flow and / or a temperature sensor for measuring the ambient temperature; and a control device for adjusting a rotational speed of the fan and / or for adjusting a pumped through the pump mass flow of the liquid based on the measured temperature or the measured temperatures, in particular for limiting the return temperature to a maximum value and / or for setting a constant flow temperature , Thus, e.g. It is to be avoided that emergency cooling units in a combined heat and power plant (CHP) switch on when the return temperature to the CHP becomes too high. On the other hand, for example, heating networks can be operated, which require a constant flow temperature at different Wäredarfen.

The object according to the invention is furthermore achieved by a method according to claim 9.

The method according to the invention for operating a thermodynamic cycle, in particular an ORC process, comprises during normal operation the following steps: conveying liquid working medium under pressure increase to an evaporator with a feed pump; Preheat, evaporate and optionally additional overheating of the working medium under Supplying heat in the evaporator; Relaxing the vaporized working medium in an expansion machine; De-icing, condensing and optionally additional subcooling of the relaxed working medium with at least two capacitors connected in parallel between the expander and the feed pump.

The advantages of the method and its developments correspond - unless otherwise stated - those of the device according to the invention.

According to a development of the method according to the invention, a mass flow of the expanded working medium can be distributed by the expansion machine in a self-regulating manner through a pressure equilibrium between the condensers into mass flows of the expanded working medium into the respective condensers.

Another development consists in that the at least two capacitors comprise an air condenser with a fan and / or a liquid condenser in a liquid circuit with a pump, and wherein the method comprises the following further step: setting a speed of the fan and / or adjusting a through the pump pumped mass flow of the liquid. By adjusting the speed of the fan and / or the pumped through the pump mass flow, a sliding control of the condensation components in the air condenser or in the liquid condenser, in particular by switching off the fan little or no condensation of the working medium takes place in the air condenser, preferably while the pump is running , or wherein by switching off the pump little or no condensation takes place in the liquid condenser, preferably with the fan running. In this way, for example, a load change between the capacitors involved take place.

According to another embodiment, the following further steps can be carried out during a start-up operation carried out before normal operation: provision of a sufficient flow height of liquid working medium in front of the feed pump in order to avoid cavitation in the feed pump; Start the thermodynamic cycle with the condenser in which the lowest condensation pressure is present; and connecting the further capacitors in the order of increasing condensation pressure. Therefore, at the beginning of the starting process, a minimum feed-forward height NPSH _{r is} ensured. Furthermore, a start without cavitation is ensured at the feed pump, since the pressure in front of the pump increases monotonically during the starting process.

Another development is that the step of starting with the fan running of the air condenser and shut off pump of the liquid circuit is performed, and wherein the step of connecting the liquid condenser by switching on or increasing the delivered mass flow of the pump.

The cited developments can be used individually or combined as claimed suitable.

Further features and exemplary embodiments and advantages of the present invention will be explained in more detail with reference to the drawings. It is understood that the embodiments do not exhaust the scope of the present invention. It is further understood that some or all of the features described below may be combined with each other in other ways.

drawings

Fig. 1

schematically shows a first embodiment of the device according to the invention.

Fig. 2

shows the course of the condensate temperature during startup.

Fig. 3

shows the filling level in the air and in the heating condenser.

Fig. 4

shows altitude and level of the capacitors.

Fig. 5

illustrates the change in the decoupled in the heating condenser heat quantity without regulating the heating water circulation pump and thus the change in the flow temperature in the heating water.

Fig. 6

illustrates the change in the decoupled in the heating condenser heat while maintaining the same flow temperature in the heating water with regulation of the heating water circulating pump.

Fig. 7

shows further embodiments of the device according to the invention, in particular with a siphon ( Fig. 7a ), and / or a container ( Fig. 7b ), and / or with non-return valves ( Fig. 7c ).

Fig. 8

shows the formation of a natural circulation when heating the unused capacitor. 3

embodiments

When operating an ORC system with two parallel capacitors, there are different operating states, for each of which certain operating parameters must be ensured. The operating states to be considered are: start-up, stationary operation, load change between heating condenser and air condenser operation, and parallel operation of heating condenser and air condenser.

The operating parameters to be ensured are: Suitable fluid distribution in each case for the load cases 100% air condenser operation, 100% condenser operation and parallel operation, as well as a sufficient flow height for the feed pump in the various operating modes.

In the simplest embodiment of the ORC system, the necessary operating parameters can be achieved in all different operating modes via control engineering methods as well as a suitable arrangement of components and a corresponding filling quantity with working medium. Additional components, such as valves, etc. are not required. In the following, the devices and methods are described with which the operating parameters can be met in the simplest embodiment.

Fig. 1 shows simplified the standard connection of the system. The liquid working fluid is in the heat exchanger (evaporator) 1 under heat preheated, evaporated and then expanded in an expansion machine 2 (eg screw expander, turbine). Downstream of the expansion machine, the distribution of the working medium mass flow to the liquid condenser (heating condenser) 3 and the air condenser 4 (with a fan 7) takes place. In the liquefaction of the working fluid in the heating condenser heat is released from the working fluid to the heating water network, the heating water is circulated by a pump 6. The circuit is closed by a feed pump 5 increases the pressure of the working fluid to the evaporation pressure and promotes it again in the evaporator 1. In the interconnection, the flow of the working medium or the distribution of the working medium is not controlled by valves, but is purely driven by thermal.

1. Approach

It is important to ensure a reliable system startup when operating an ORC system with two capacitors. In order to ensure a safe start without cavitation on the feed pump, it is necessary to let the pressure in front of the pump increase monotonically during the starting process, moreover, a minimum flow height NPSH _{r must} be ensured at the beginning of the starting process.

When the cold system is switched off, a low condensation pressure with a low condensation temperature is established. Even with a warm heating condenser, the condensation pressure due to the heat transfer to the environment via the air condenser will assume the saturation pressure at ambient temperature. During the start-up process, the condensation pressure increases, which also increases the condensation temperature. If the pressure were to drop, heated working fluid at a lower pressure would be present in front of the pump. Thus, the present subcooling of the working medium decreases, which can cause cavitation in the pump. It must therefore be ensured that there is always sufficient subcooling during the starting process. This can be achieved by two ways. On the one hand, the fill level and fluid distribution in the condensers must ensure subcooling, which allows pressure fluctuations without the risk of cavitation. On the other hand, the regulation can ensure that the condensation pressure increases monotonically during the starting process. This can be done be achieved that the system is started in the air condenser operation. Thus, the plant starts its operation at low pressure. Subsequently, the system flows smoothly into the heating condenser operation. If the temperature of the heating condenser is higher than the ambient temperature (which is almost always true), the condensation pressure will slowly increase monotonically. Table 1 (startup process): phase heating capacitor air condenser condensing pressure Location of working medium 1. Plant shut off warm, because of heating water to temperature cold, since cooled by ambient air low (saturation at ambient temperature) in the air condenser Second Plant start (start) warm cold, gets warmer increases still in the air condenser, since heating condenser temp. even higher than the condensation temperature, which is defined by the air condenser Third Plant start (advanced) warm warm further increased divided into air condenser and heating condenser depending on the state of equilibrium 4th Plant start (completed) warm warmer than a heating condenser high Working medium mainly in the heating condenser

Table 1 shows the procedure of the boot process. In phase 1 the system is shut down. The condensate temperature and thus the condensation pressure are low (see Fig. 2 ). The condensate temperature T _kond is equal to the temperature of the ambient _air T _L. In phase two, the system is started, the condensation pressure rises slowly. It fluid begins to shift into the heating condenser (see Fig. 3 ). The filling level L _HK in the heating condenser increases. The condensate temperature rises up to the temperature T _{VL of} the flow in the heating circuit. From the condensate temperature, which allows condensation in the heating condenser (phase 3) is significantly condensed in the heating condenser. The filling level L _LK in the air condenser reduces in this phase. The condensate temperature approaches the temperature T _{RL of} the return in the heating circuit. In phase 4 the start is completed and a pure condenser operation is active.

2. Stationary operation

In stationary operation, the working medium will always flow into the colder condenser, since there is lower pressure. Due to the self-regulating system, the colder capacitor is the one in which condensing is to take place. In air condenser operation, the air condenser is flowed through with cold outside air, while the heating condenser assumes the temperature of the exhaust steam in the stationary state. As a result, a lower pressure is established in the air condenser and the fluid (working medium) flows through the air condenser for condensation. The condensation heat is released to the ambient air. In heating condenser operation, the heating condenser is flowed through by the return of the heating water. This is colder than the evaporation temperature. Since the air condenser assumes a temperature close to the temperature of the exhaust steam when the fans are switched off, the condensation takes place in the colder heating condenser.

100% Condenser or 100% Air Condenser operation:

The 100% operating cases are each achieved by switching off or reducing the power of the fans, or the heating water circulating pump, so that in one of the capacitors no heat can be dissipated. Since the condensers on the side of the working medium are not separated from each other by valves, always a small part of the exhaust steam flows through the unused capacitor and is cooled by natural convection or heat conduction.

The sufficient flow height of the working medium in front of the feed pump is adjusted by the capacity and the geodetic height of the liquid column above the pump. The geometric relationships between the heating condenser and the air condenser are chosen so that with the same capacity and operation of one capacitor so much working fluid in the condenser is that a sufficient supercooling is achieved. On the required flow height in parallel operation of both capacitors will be discussed in more detail in the following section.

Self-stabilizing process:

$${\mathit{p}}_{\mathit{ges}}={\mathit{p}}_{\mathit{kond}}+\Delta p_{\mathit{geod}}$$

The process described here stabilizes itself. This means that always the condenser with the larger heat output also has the highest level. This is due to the fluidic distribution of the fluids. There is always a state of equilibrium where there are no pressure differences between the two capacitors. The total pressure p _ges to be considered is composed of the respectively prevailing condensation _pressure p _kond and the geodetic pressure Δp _geod which is established via the filling level Δh. $$\Delta p_{\mathit{geod}}=\rho \cdot G\cdot \Delta H$$

$${\mathit{p}}_{\mathit{ges}}={\mathit{p}}_{\mathit{cond}}+\Delta p_{\mathit{geod}}$$

Assuming by way of example that more heat is dissipated in condenser b than in condenser a, the following table applies with respect to the process parameters (for illustrative purposes see FIG Fig. 4 ): Table 2 (process parameters in Fig. 4): position parameter 1 V_dot, p a = b 2 V_dot a <b 3 p_kond a> b 4 p_geod. a <b 5 V_dot, p a = b H a <b Q_dot a <b

In the table, the process parameters V_dot denote the volume flow, p_kond the condensation pressure, p_geod. the geodetic pressure, h the filling level and Q_dot the heat flow. The positions 1 to 5 correspond to the respective condenser a and b: after the expansion machine and before dividing the total mass flow V_dot, p (position 1), after splitting and before entering the condenser (position 2), in the condenser (FIG. Position 3), after the condenser and before the merging of the partial mass flows (position 4), after the merging and before the feed pump (position 5). The comparison relates to the respective process parameters with respect to the two capacitors a and b.

Due to the higher volume flow in the direction of the condenser b, there are higher pressure losses than in the condenser a (path 1 to 3a / b). Due to the higher pressure loss, the condensation pressure in the condenser b must be smaller than in the condenser a. Since the two capacitors are connected to each other, there is a pressure equalization over the geodetic pressure. This causes the level in capacitor b to rise until there is no pressure difference between the capacitors at point 5. The higher filling level ensures that sufficient condenser cooling of the working medium flow is achieved in the condenser in which more heat is released, in which the larger part of the exhaust steam is condensed, thus ensuring a sufficient flow height in front of the pump.

To ensure stable operation, the capacity of the system must be such that none of the two capacitors runs idle during operation. Ideally, the filling quantity and the constructive height of the capacitors interact with one another in such a way that there is currently no or only minimal fluid in the respectively unused capacitor (100% heating capacitor or 100% air condenser). This reduces heat loss and helps to save fluid.

3. Load change between the heating condenser and air condenser

By the self-regulating principle of the load change is achieved by by adjusting the speed of the fan and / or funded by the pump mass flow, a sliding control of the condensation components in the air condenser or takes place in the liquid condenser, in particular by each fans or heating pump are turned off. This increases the pressure in the unused capacitor and the condensation takes place in the other condenser in which a lower pressure prevails.

4. Parallel operation between heating condenser and air condenser

If the full heat output is not required in the heating network, only part of the heat emitted by the ORC system can be condensed into the heating network. The other part is then removed via the air condenser. Both capacitors are in parallel operation. The parallel operation is achieved, for example, by operating the fans of the air condenser in partial load. Control parameters can be, for example, a maximum temperature of the heating circuit return. If too much heat is introduced into the heating network by the ORC, the temperature of the return to the combined heat and power plant (CHP) can increase. If this exceeds a certain maximum value, the emergency cooler switches on to dissipate the excess heat from the system. To avoid this, the ORC system has to reduce the coupled thermal power at an early stage.

Another control parameter may be the desired flow temperature for the heating network. By reducing the fan speed less heat is dissipated in the air condenser. As a result, the condensation pressure of p ₁ to p _{2 increases} and a part of the exhaust steam flows into the heating condenser, where it increases the heat dissipation in the heating network. With the same water volume flow (uncontrolled operation of the heating water circulating pump), the outlet temperature (= flow temperature T _VL ) of the heating water rises from T _{VL, 1} to T _{VL, 2} (see Fig. 5 ). This allows the system to respond to changing customer heat demand and inject more heat into the heating network when needed. Equally, however, an excessively large heat input is prevented. If the heat customer does not absorb the heat, the return temperature rises (coming from the heating network) and thus also the flow temperature. If a limit temperature is reached here, the system regulates this and couples more heat through the air condenser by increasing the fan speed again.

Additionally or alternatively, the heating water circulating pump can be regulated, which allows a constant flow temperature T _VL in the heating network (see Fig. 6 ). Thus, heating networks can be operated, which require a constant flow temperature at different heat demands (for example, for temperature-sensitive processes, or for a sanitation, etc.). By controlling the heating water circulating pump, the power of the pump can be adapted to the actual heat requirement and thus the efficiency of the system can be increased.

The sufficient flow height by appropriate supercooling of the fluid (working medium) is ensured by the self-regulating principle described in point 2. It must be ensured by a sufficient filling quantity with working medium that there is sufficient subcooling even when the working medium is divided between the two condensers.

The simple ORC system with two capacitors can be improved by various variations of the interconnection, so that the required operating parameters can be maintained more safely (see Fig. 7 ).

1. Installation of a siphon (FIG. 7a)

With the help of a siphon 8 in the condensate line, a defined minimum filling level can be defined in the condenser 3, 4, since the liquid level in the condenser must always be as high as the height of the siphon. This also ensures a defined minimum subcooling.

2. Container (Fig. 7b)

A container 9 between the capacitors 3, 4 and the feed pump 5 ensures that always liquid working fluid flows to the pump. If it comes to operating conditions in which one of the capacitors runs empty and thus gaseous working fluid flows in the direction of the pump, this is deposited in the container. Even with the liquid working fluid flowing gas bubbles, which could cause (partial) cavitation on the feed pump, are deposited in the container. If the container is not completely filled and a Liquid level sets, the working fluid in the container tends to a saturated state. This results in two possible cases: If the working medium is colder than the environment, it evaporates and an equilibrium state between the liquid phase and the vapor phase is established. However, if the working fluid in the container is warmer than the ambient temperature, heat is released to the environment and condensation takes place in the container. This causes the liquid level to rise until the container is full. By an additional pressure on the liquid level is impressed in the container, for example by means of a non-condensing gas (see, for example, patent DE 10 2009 053 390 B3 for cavitation avoidance), a sufficient supercooling is generated.

3. Check Valves (Fig. 7c)

In certain cases, there may be undesirable natural circulation between the heating condenser 3 and the air condenser 4 (see Fig. 8 ). If the unused capacitor 3 still heated, for example, flows through with warm heating water, it comes to this in the evaporation. The resulting level would bring the pressure balance of condensation pressure and geodetic pressure due to different filling heights out of balance. To obtain this equilibrium, condensed working medium flows out of the condenser 1. By incorporating check valves 10 in either the exhaust or condensate lines, this phenomenon is prevented.

The illustrated embodiments are merely exemplary and the full scope of the present invention is defined by the claims.

Claims (13)

Apparatus (100) for operating a thermodynamic cycle, in particular an ORC process, comprising: a feed pump (5) for conveying liquid working fluid under pressure increase to an evaporator (1); the evaporator (1) for preheating, evaporation and optionally additional overheating of the working medium with the supply of heat; an expansion machine (2) for generating mechanical energy by relaxing the vaporized working medium; and at least two capacitors (3, 4) connected in parallel between the expander and the feed pump for defrosting, condensing and optionally additional subcooling of the expanded working medium. Apparatus according to claim 1, wherein the at least two capacitors (3, 4) comprise a liquid condenser (3) and an air condenser (4). Apparatus according to claim 2, wherein the liquid condenser (3) is provided in a liquid circuit, in particular a heating circuit, with a pump (6) and / or wherein the air condenser comprises a fan (7). Apparatus according to claim 3, wherein the fan and / or the pump are controllable, in particular the rotational speed of the fan or the pumped by the pump mass flow of the liquid. Device according to one of claims 1 to 4, wherein each condenser is additionally connected via a siphon (8) to the feed pump, wherein a minimum filling level of the condensed working medium in the condenser is determined by the vertex of the siphon. Device according to one of claims 1 to 5, wherein further between the capacitors and the feed pump, a pressure-tight container (9) is provided. Device according to one of claims 1 to 6, wherein for each of the capacitors connected in parallel, a check valve between the respective capacitor and the feed pump and / or between the expander and the respective capacitor is provided, each check valve allows only a flow in the direction of the feed pump. Device according to one of claims 1 to 7 in combination with claim 4, further comprising: a temperature sensor for measuring the temperature of a liquid / heating circuit return, and / or a temperature sensor for measuring the temperature of a liquid / heating circuit flow; and a control device for setting a rotational speed of the fan and / or for adjusting a pumped through the pump mass flow of the liquid based on the measured temperature or the measured temperatures, in particular for limiting the return temperature to a maximum value and / or setting a desired flow temperature, in particular a constant flow temperature. Method for operating a thermodynamic cycle, in particular an ORC process, wherein during normal operation the method comprises the following steps: Conveying liquid working fluid under pressure increase to an evaporator (1) with a feed pump (5); Preheating, evaporation and optionally additional overheating of the working medium with the supply of heat in the evaporator (1); Relaxing the vaporized working medium in an expansion machine (2); De-icing, condensing and optionally additional subcooling of the relaxed working medium with at least two capacitors (3, 4) connected in parallel between the expander and the feed pump. The method of claim 9, wherein a mass flow of the expanded working medium from the expansion machine is self-regulating divided by a between the condensers adjusting pressure balance in mass flows of the expanded working medium into the respective capacitors. The method of claim 9 or 10, wherein the at least two capacitors comprises an air condenser with a fan and / or a liquid condenser in a liquid circuit with a pump, and wherein the method comprises the following further step: Adjusting a speed of the fan and / or adjusting a pumped through the pump mass flow of the liquid, in particular wherein no condensation of the working medium takes place in the air condenser by switching off the fan, preferably with the pump running, or wherein no condensation takes place in the liquid condenser by switching off the pump, preferably with the fan running. Method according to one of claims 9 to 11, wherein during a start-up operation carried out before the normal operation, the following further steps are performed: Providing a sufficient flow height of liquid working fluid in front of the feed pump to avoid cavitation in the feed pump; Starting the thermodynamic cycle with the condenser in which the lowest condensation pressure is present; Connecting the other capacitors in the order of increasing condensation pressure. The method of claim 12 in combination with claim 11, wherein the step of starting with the fan of the air condenser and shut off pump of the liquid circuit takes place, and wherein the step of connecting the liquid condenser by switching on or increasing the delivered mass flow of the pump.

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