KR20170008808A - System for controlling a rankine cycle - Google Patents

Abstract

The present invention relates to an electric production system comprising a closed heat transfer fluid circuit wherein the closed heat transfer fluid circuit comprises an evaporator (1), an expansion member (2), a condenser (3) and a circulation pump (4) A liquid-vapor separator (6) having a generator (5) coupled to the expansion member (2) and provided with a liquid reservoir (12) between the evaporator (1) and the expansion member (2) And the electric production system is further provided with a control device (15) configured to empty the liquid reservoir (12) when the liquid level of the liquid reservoir reaches a maximum threshold (13).

Description

SYSTEM FOR CONTROLLING A RANKINE CYCLE [0002]

The present invention relates to a control system of a Rankine cycle and an electric production method that can be implemented using the control system.

The Rankine cycle is a system that allows thermal energy to be converted to electrical energy. The recovered heat is used to heat and then vaporize the heat transfer fluid, whereupon the heat transfer fluid is expanded in an expansion member, typically a turbine, that powers the generator. The fluid is then condensed so that the cycle can be resumed.

Rankine cycles are used for electricity production, especially in, for example, electric power plants. These cycles typically use water as the heat transfer fluid.

Organic Rankine cycles (or ORCs) use organic products instead of water. This reduces the scale of the facilities and allows for the construction of low-power facilities.

At present, the cost of these facilities is still high due to the technologies required to control these facilities, which slows the development of this technology for current applications.

The presence of liquid particles at the inlet of the expansion member (turbine) causes corrosion and erosion of the expansion member and generates mechanical stresses that are liable to damage or destroy the expansion member.

Thus, the heat transfer fluid generally must be in a vapor state before the heat transfer fluid enters the expansion member. It is a well known practice to place the liquid-vapor separator between the evaporator and the turbine to prevent liquid from entering the expansion member.

Thus, publication US 7,841,306 discloses a Rankine cycle that includes a liquid-vapor separator between an evaporator and a turbine and allows liquid droplets present in the stream exiting the evaporator to be recovered and returned to the liquid reservoir located at the outlet of the condenser.

In addition, publication DE 10 2011 009 280 discloses a liquid-vapor separator connected to a pipe returning to an evaporator.

Publication No. WO 2007/104970 discloses a known Rankine cycle comprising a liquid-vapor separator between an evaporator and a turbine, with reference to FIG. 1 of the above publication. The pipe is provided to recycle the liquid from the separator to the evaporator. In addition, depending on the demand for electrical energy, the liquid level of the separator is determined and measured to control the circuit pump. If the liquid level in the separator increases, the delivery rate of the pump is reduced and vice versa. Thus, this publication proposes to distinguish itself from this known system by allowing the fraction of liquid to enter the expansion member and by controlling this fraction using a complex control system.

Publication No. WO 2012/130421 discloses a facility suitable for recovering heat from several distinct sources. The facility includes a common liquid-vapor separator and a common turbine, and some evaporators and pumps corresponding to various sources. Since the liquid-vapor separator is also fed with the liquid coming out of the condenser, the liquid-vapor separator serves as a facility liquid reservoir.

The publication FR 2976136 teaches a facility based on the Rankine cycle provided with bypass valves to bypass the turbine.

Therefore, there is a need to provide an electrical production system that relies on Rankine cycles that can operate with organic heat transfer fluids, where the expansion member is protected from any damage in a simple and economical manner.

The present invention firstly relates to an electric production system comprising a closed heat transfer fluid circuit, wherein the closed heat transfer fluid circuit comprises an evaporator, an expansion member, a condenser and a circulation pump, the generator being coupled to the expansion member , A liquid-vapor separator provided with a liquid reservoir between the evaporator and the expansion member is located, and the electric production system includes a control device configured to empty the liquid reservoir when the liquid level of the liquid reservoir reaches a maximum threshold It is additionally provided.

According to one embodiment, the heat transfer fluid is organic.

According to one embodiment, the emptying of the reservoir is carried out by a liquid recycle line fed into the evaporator.

According to one embodiment, the control device is configured to reduce the delivery rate of the circulation pump when the liquid level of the reservoir reaches a maximum threshold.

According to one embodiment, the liquid level of the reservoir is maintained between a minimum threshold and a maximum threshold.

According to one embodiment, the control device is configured to stop the emptying of the reservoir when the liquid level of the reservoir reaches a minimum threshold.

According to one embodiment, the control device is configured to increase the delivery rate of the circulation pump when the liquid level of the reservoir reaches a minimum threshold.

The invention also relates to the following co-occurring steps:

Heating and evaporating the heat transfer fluid using a heat source;

- separating the vaporized heat transfer fluid into a liquid phase and a vapor phase, said liquid phase being stored in a liquid reservoir;

- inflating said vapor phase to allow generation of an electric current;

Condensing the swelled vapor phase; And

- pumping the condensed phase;

And

- monitoring the liquid level of the liquid reservoir; And

- emptying the liquid reservoir when the liquid level of the liquid reservoir reaches a maximum threshold.

According to one embodiment, the heat transfer fluid is organic.

According to one embodiment, the emptied liquid is recycled to the heating and evaporating steps.

According to one embodiment, the delivery rate at which the condensed phase is pumped when the liquid level of the liquid reservoir reaches the maximum threshold is reduced.

According to one embodiment, the liquid level of the liquid reservoir is always maintained between a minimum threshold and a maximum threshold.

According to one embodiment, the step of emptying the liquid reservoir is stopped when the liquid level of the liquid reservoir reaches the minimum threshold.

According to one embodiment, the delivery rate at which the condensed phase is pumped is increased when the liquid level of the liquid reservoir reaches the minimum threshold.

The present invention makes it possible to overcome the disadvantages of the prior art. More particularly, the present invention provides an electrical production system that relies on Rankine cycles that can operate with organic heat transfer fluids, wherein the expansion member is protected from any damage in a simple and economical manner.

This is achieved by the use of a liquid-vapor separator provided with a liquid reservoir at the outlet of the evaporator, and the liquid reservoir is coupled to a control device capable of controlling the liquid level of the liquid reservoir.

Figure 1 schematically illustrates a Rankine cycle that can be used to implement the present invention.
Figures 2-5 schematically illustrate a portion of a system according to an embodiment of the present invention in various operating phases.

The present invention will now be described in more detail and in a limited manner in the following description.

1, an electric production system according to the present invention relies on a Rankine cycle including an evaporator 1, an expansion member 2, a condenser 3 and a circulation pump 4.

The Rankine cycle comprises a heat transfer fluid, which is preferably an organic compound, such as a hydrocarbon or hydrofluorocarbon or hydrofluoro olefin, or a mixture of several such compounds.

Preferred compounds are HFC-134a (1,1,1,2-tetrafluoroethane), HFC-32 (difluoromethane), HFC-125 (pentafluoroethane), HFC- Fluoroethane), HFC-134 (1,1,2,2-tetrafluoroethane), HFC-161 (fluoroethane), HFO-1234yf (2,3,3,3-tetrafluoropropene) , HFO-1234ze (1,3,3,3-tetrafluoropropene), HFO-1233zd (1-chloro-3,3,3-trifluoropropene), HFO-1336mzz , 4,4,4-hexafluorobutene (E or Z form), HC-600 (butane), HC-600a (2-methylpropane) and HC-290 (propane).

The evaporator 1 is coupled to a heat source.

The generator (5) is coupled to the expansion member (2). The generator provides current as an output from the system.

The heat transfer fluid receives heat from the heat source in the evaporator (1). Thus, the heat transfer fluid is heated, evaporated, and possibly overheated. The energy thus accumulated in the fluid is restored as mechanical work by expanding the fluid in the expansion member 2. This mechanical work is converted into current in the generator 5 in a manner known per se.

The expanded heat transfer fluid is condensed in the condenser (3) and then returned to the evaporator (1) by the pump (4).

Although only one element in each category is shown in Figure 1, it is possible to provide several such elements, for example several evaporators and / or some expansion members and / or some pumps and / or some condensers And these elements are in series and / or in parallel.

Here, the term "evaporator" is used in a generally accepted meaning. The evaporator represents a heat exchanger designed to heat, vaporize, and possibly overheat the fluid. Thus, the evaporator may comprise different sections, for example a heating section, a vaporizing section, and possibly an overheating section. The evaporator may be a boiler or may include the boiler.

The evaporator can be used as a heat source, for example, as a hot liquid source (geothermal source), an industrial stream (e.g., a combustion gas), or even other thermal equipment (such as a cooling or air conditioning plant , A combustion engine, etc.) can be used.

The heat source can either heat-exchange directly with the heat transfer fluid in the evaporator (1), or exchange heat with the heat transfer fluid by means of an intermediate heat transfer fluid circuit.

Likewise, in the condenser 3, the heat transfer fluid transfers heat to the cold source, which may be air or water, for example, from the environment, either directly or through an intermediate heat transfer fluid circuit.

The expansion member 2 is preferably a turbine, in particular a centrifugal, screw type, piston type or rotary (scroll type) turbine.

2 to 5, the present invention provides a liquid-vapor separation device 6 between an evaporator 1 and an expansion member 2. This liquid-vapor separation device causes the heated and evaporated (and possibly superheated) fluid to separate into a vapor phase (theoretically predominant or at a very broad prevalence rate) and possibly a liquid phase. The liquid phase is collected in the reservoir 12 where the liquid phase is accumulated.

Preferably, the liquid-vapor separator 6 comprises a reservoir 12, an immersion tube connected to the outlet of the evaporator 1 immersed in the liquid contained in the reservoir 12, Simply comprises a gas outlet connected to the inlet of the expansion member 2 arranged upwards.

Alternatively, the liquid-vapor separator 6 may comprise a cyclone or a fused membrane or any other separation device, wherein the reservoir 12 is intended to collect a previously separated liquid phase.

In the illustrated embodiment, the liquid recycle line 9 is connected to the outlet of the reservoir 12, and advantageously the valve 10 is fitted in the liquid recycle line. The liquid recycle line 9 may in particular be supplied to the evaporator 1. For example, the liquid recycle line may be connected to a pipe 7 located between the pump 4 and the evaporator 1. Alternatively, the pipe 7 may be fed directly to the evaporator 1 at its inlet or at some intermediate point.

Alternatively, the liquid recycle line 9 may be connected between the expansion member 2 and the condenser 3, or between the condenser 3 and the pump 4.

In the illustrated embodiment, one or more liquid level sensors are provided to the storage 12 to detect when the liquid level reaches the maximum liquid threshold 13 and the minimum liquid threshold 14 in the reservoir 12 do. These liquid level sensors are connected to the control device 15.

Preferably, the maximum liquid level 13 is located below the upper end of the reservoir 12 and the minimum liquid threshold 14 is below the upper end of the reservoir 12 to prevent the possibility of the reservoir 12 being completely emptied or completely filled. (12).

The control device 15 advantageously controls the valve 10 and the pump 4.

When the liquid level of the reservoir reaches the maximum threshold 13, the control device 15 empties the reservoir 12. This makes it possible to avoid the risk of the liquid being sucked into the expansion member 2.

The term "emptying " means an action involving complete or partial emptying of the liquid reservoir 12. Preferably, the emptying is only a partial one.

Emptying of the reservoir is carried out by opening the valve 10. In the case where the reservoir 12 is located above the evaporator 1, the emptying of the reservoir can be accomplished simply under the influence of gravity. Alternatively, if necessary, the liquid recycle line 9 may also provide an additional pump controlled by the control device 15.

Preferably, upon opening of the valve 10, the control device 15 acts on the pump 4 to reduce the delivery rate of the pump. The decrease in delivery rate is performed to a value other than zero or zero. In the former case, reducing the delivery rate means stopping the fluid stream through the pump 4. It should be understood that the same function may be performed by the control device 15 controlling the valves located upstream or downstream of the pump 4.

Conversely, when the liquid level of the reservoir reaches the minimum threshold 14, the control device 15 is designed to stop the emptying of the reservoir 12, The amount ensures that the liquid-vapor separator is sufficient to allow its function to perform correctly, and also allows the system to return to its normal operating mode. The termination of the evacuation is carried out by closing the valve 10. Preferably, at the same time, the control device 15 acts on the pump 4 to increase the delivery rate of the pump (which means that the pump 4 is switched on again if the pump 4 was previously switched off) box).

Figures 2-5 illustrate the system of the present invention in various configurations.

In Figure 2, the pump 4 pumps the liquid, and the valve 10 is closed. The liquid level in the reservoir 12 is between the minimum level 14 and the maximum level 13. This liquid level tends to rise over time as the liquid phase present at the evaporator outlet is progressively collected in the liquid-vapor separator 6.

3, the liquid level in the reservoir 12 reaches the maximum threshold value 13. In response, the control device 15 stops the pump 4 (or reduces its delivery rate to a non-zero value) and opens the valve 10. [

In Fig. 4, the liquid from the reservoir is emptied by the liquid recycle line 9 (for example under the influence of gravity). This liquid is heated in the evaporator 1, evaporated and, if appropriate, superheated, so that the system operates continuously and produces a current during this emptying step. The liquid level in the reservoir 12 is lowered during the emptying step.

In Figure 5, the liquid level in the reservoir 12 reaches the minimum threshold 14. In response, the control device 15 initiates the pump 4 (or increases the delivery rate of the pump if this pump was not previously switched off), and closes the valve 10. Thus, the system returns to the state of FIG.

Instead of opening and closing the valve 10, it is also possible to provide a flow of non-zero liquid to the liquid recycle line 9, in addition to the steps being emptied. In this case, the control device 15 makes it possible to increase the flow rate in the liquid recycle line 9 during the emptying steps. This alternative form can prove advantageous when a substantial proportion of the liquid is present at the outlet of the evaporator 1.

The embodiments illustrated in Figures 2-5 provide the advantage that they are particularly simple in design and implementation. However, it is also possible to provide a more complex system that can adapt more closely to changes in usage conditions, for example by providing thresholds of different levels other than the maximum threshold 13 and the minimum threshold 14, The control device 15 is designed to regulate the rate at which the pump 4 is delivered and / or the rate at which liquid from the reservoir 12 is recirculated in accordance with the level of liquid in the reservoir 12.

Claims (14)

An electrical production system, comprising an enclosed heat transfer fluid circuit,
The closed-loop heat transfer fluid circuit comprises an evaporator (1), an expansion member (2), a condenser (3) and a circulation pump (4)
The generator 5 is coupled to the expansion member 2,
A liquid-vapor separator (6) provided with a liquid reservoir (12) is positioned between the evaporator (1) and the expansion member (2)
Wherein the electric production system is further provided with a control device (15) configured to empty the liquid reservoir (12) when the liquid level of the liquid reservoir reaches a maximum threshold (13). The method according to claim 1,
Wherein the heat transfer fluid is organic. 3. The method according to claim 1 or 2,
Wherein the emptying of the liquid reservoir (12) is carried out by a liquid recycle line (9) fed into the evaporator (1). 4. The method according to any one of claims 1 to 3,
Wherein the control device (15) is configured to reduce the delivery rate of the circulation pump (4) when the liquid level of the liquid reservoir reaches a maximum threshold (13). 5. The method according to any one of claims 1 to 4,
Wherein the liquid level of the liquid reservoir (12) is maintained between a minimum threshold (14) and a maximum threshold (13). 6. The method of claim 5,
Wherein the control device (15) is configured to stop the emptying of the liquid reservoir (12) when the liquid level of the liquid reservoir reaches the minimum threshold (14). The method according to claim 5 or 6,
Wherein the control device (15) is configured to increase the delivery rate of the circulation pump (4) when the liquid level of the liquid reservoir reaches the minimum threshold (14). The following concurrent steps:
Heating and evaporating the heat transfer fluid using a heat source;
- separating the vaporized heat transfer fluid into a liquid phase and a vapor phase, said liquid phase being stored in a liquid reservoir;
- inflating said vapor phase to allow generation of an electric current;
Condensing the swelled vapor phase; And
- pumping the condensed phase; And
- monitoring the liquid level of the liquid reservoir; And
- emptying the liquid reservoir when the liquid level of the liquid reservoir reaches a maximum threshold. 9. The method of claim 8,
Wherein the heat transfer fluid is organic. 10. The method according to claim 8 or 9,
And the emptied liquid is recycled to the heating and evaporating step. 11. The method according to one of claims 8 to 10,
Wherein the dispensing rate at which the condensed phase is pumped is reduced when the liquid level of the liquid reservoir reaches a maximum threshold. 12. The method according to one of claims 8 to 11,
Wherein the liquid level of the liquid reservoir is always maintained between a minimum threshold and a maximum threshold. 13. The method of claim 12,
Wherein the step of emptying the liquid reservoir is stopped when the liquid level of the liquid reservoir reaches a minimum threshold. The method according to claim 12 or 13,
Wherein the dispensing rate at which the condensed phase is pumped is increased when the liquid level of the liquid reservoir reaches a minimum threshold.

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