DE102016004402A1 - Device for converting thermal energy - Google Patents

Abstract

The present invention relates to a device (12) for converting thermal energy from a heat source (14) into mechanical energy by means of a thermodynamic cycle (16) with a working medium and an expansion device for expanding the working medium, in which the expansion device is connected to a displacement machine (56 ), wherein the device comprises at least one means (70) for condensing and wherein before the means (70) for condensing a control unit (R) is arranged, which is designed so that a relaxation by the expansion device is not in the wet steam area.

Description

The invention relates to a device for converting thermal energy from a heat source into mechanical energy by means of a thermodynamic cyclic process with a working medium and an expansion device for expanding the working medium. Furthermore, the invention relates to a method for converting thermal energy with expanding the pressure of the working medium.

A thermodynamic cycle is generally a process in which a working medium undergoes periodic changes in its thermodynamic state variables such as pressure and temperature, repeatedly reaching its initial state. Depending on the change of these state variables, the working medium absorbs energy or releases energy.

In such thermodynamic cycle processes, the expansion device is an integral part of the device for converting thermal energy. By means of the expansion device or the expander, thermal energy is ultimately converted into mechanical energy. For this purpose, the working medium is initially placed in a cyclic process under an increased pressure and isobarically evaporated by transferring thermal energy and preferably superheated. The compressed working medium vapor thus produced is subsequently expanded in the expansion device. During expansion, the pressure and the temperature of the working medium vapor decrease, so that the transferred thermal energy is partially released. Part of this released thermal energy is converted into mechanical energy. This mechanical energy is preferably used for generating kinetic energy, in particular for driving a rotating shaft. Particularly preferably, the rotating shaft drives a generator which generates electrical energy.

To generate electrical energy, the classic Clausius-Rankine process in steam power plants is carried out on a large scale as a thermodynamic cycle. There, water serves as a working medium, which is heated to about 600 ° C by means of high temperature heat sources, such as coal, natural gas, petroleum and nuclear energy. If at least one organic working medium is used instead of water, this is referred to as the so-called ORC (Organic Rankine Cycle) process. Suitable organic working media have a much lower boiling point than water and thus in particular more favorable evaporation properties at lower temperatures. Therefore, ORC processes are used to recycle thermal energy from low temperature heat sources. Low-temperature heat sources include, for example, solar thermal or geothermal sources as well as previously unused waste heat from engines, industrial production processes and biogas plants. A benefit of this waste heat is economically and ecologically of great importance.

The invention preferably but not exclusively relates to such ORC processes.

In a known ORC method, as this example. In the DE 10 2012 024 031 A1 is described, the working fluid or fluid is placed under an increased pressure during the cycle. By isobaric transfer of thermal energy of the heat source to the working medium under elevated pressure, this is evaporated and preferably superheated. Subsequently, the thus produced, under the increased pressure working medium vapor is passed in at least one volume through the displacement machine. When passing through the individual volume forms a largely closed space, which increases. The volume of the volume of fluid passed through in this way increases, whereby the pressure of the working medium is lowered and the working medium expands. The working medium is under a lower pressure after expansion.

During expansion, the fluid is used, for example, to move a reciprocating piston to perform mechanical work.

Preferably, in such devices ammonia (NH3) is used as a working medium, which is particularly suitable as a working medium for a positive displacement machine as an expander due to its physical, chemical and thermodynamic properties. Thus, the very low absolute molecular weight of ammonia causes an expansion in which operates largely independently of the mass of the working medium particles. In addition, the intermolecular-acting, relatively stable hydrogen bonds of ammonia lead to a high enthalpy of enthalpy of vaporization. This means, on the one hand, that comparatively much thermal energy has to be expended in order to transfer a certain amount of ammonia from its liquid to its gaseous state of aggregation. This energy is stored, so to speak, in the formed, pressurized ammonia vapor until the steam is expanded. This releases a great deal of energy, so that a correspondingly high proportion can be used as mechanical energy. Because of the high evaporation enthalpy of ammonia, the pressure difference between evaporation and liquefaction is particularly large. With the big one Pressure difference is performed on the positive displacement machine advantageously a particularly high volume change work or expansion work. This makes a significant contribution to a particularly high yield of mechanical energy. In addition, ammonia occurs in nature, is biodegradable and participates in the natural nitrogen cycle of the biosphere. This ammonia is a natural working medium. In addition, ammonia does not have a carcinogenic effect.

However, u. a. in the previously described device of the prior art, which uses ammonia as the working medium, as well as other, similarly designed systems in practice, often the problem that relaxation or expansion to a certain extent always uncontrolled from equip, and beyond often takes place in the wet steam area.

This can lead to an interruption of the thermal energy conversion process.

Furthermore, as a result of this, partially liquid ammonia can again be formed on components in the apparatus which are neither designed for process engineering nor material technology, for example on expanders, oil pumps, oil separators or the like. Damage to components is preprogrammed, so that such systems must be regularly subjected to costly maintenance. Also, the conversion process can operate only partially economically, since it is not continuously feasible due to the failures.

Proceeding from this, the object of the invention is to provide a device for a thermodynamic cyclic process for converting thermal energy into mechanical energy, with which the thermodynamic cycle is optimized, in particular, can be operated continuously and damage to components is largely avoided.

This object is achieved with a device for converting thermal energy according to claim 1 and with a method according to claim 6.

The invention accordingly relates to a device for converting thermal energy from a heat source into mechanical energy by means of a thermodynamic cycle with a working medium and an expansion device for expanding the working medium, in which the expansion device is coupled to a displacement machine, wherein the device comprises at least one means for condensing and wherein before the means for condensing a control unit is arranged, which is designed so that a relaxation by the expansion device does not take place in the wet steam area.

According to the invention, the control unit has at least one pressure sensor and at least one temperature sensor. These sensors interact with an external control unit. Furthermore, a controllable valve is provided in the supply line to the means for condensing, wherein before the valve, a temperature sensor and after the valve, a pressure sensor and, if necessary. Yet another temperature sensor can be located.

The sensors are designed together with the external control unit to control the control behavior of the valve, individually, preferably by a fixed or variable program, or, for example, by means of a PLC control.

The control valve can preferably be a motor-controlled valve or a valve which can be activated by a form of external energy, for example a valve which can be activated by means of compressed air. However, it is also conceivable a valve type, which works similar to a heating thermostatic valve.

This control behavior can be used to specifically influence the subsequent expansion behavior of the working medium.

Moreover, the invention relates to a method for converting thermal energy from a heat source into mechanical energy by means of a thermodynamic cycle process in one operation, comprising the step of expanding the working fluid from an elevated pressure to a lower pressure, wherein the expanding does not occur in the for the Circular process defined wet steam area is done.

Further features and advantages of the invention will become apparent from the embodiment illustrated in the accompanying drawings. Show it:

1 an example of a simplified process diagram of a known device from the prior art;

2 a schematic pressure (log) enthalpy diagram of the thermodynamic cycle of the in the 1 shown method;

3 an example of a simplified process diagram of a part of a device according to the invention;

4 a schematic pressure (log) enthalpy diagram of the thermodynamic cycle of the in the 3 shown method.

5 an example of a process scheme in which a control unit according to the invention is used.

In the 1 and the 2 is an example of a known from the prior art method 10 and a known device 12 for converting thermal energy from a heat source 14 represented, as this example. In the above already mentioned DE 10 2012 024 031 A1 is described, the disclosure of which is expressly incorporated herein by reference.

The device 12 forms a closed system of a process plant in which a thermodynamic cycle 16 (S. 2 ) is carried out. This thermodynamic cycle 16 is intended to represent a modified Organic Rankine cycle process in which anhydrous ammonia (NH3, R717) can be used, for example, in a concentration of more than 99.8 mass percent as a working medium. The anhydrous ammonia may be in the form of a pressure-liquefied gas at a temperature of 25 ° C under a lower pressure 18 be provided as a lower pressure level of about 10 bar. For this purpose, in the embodiment shown, a collection container 20 intended.

This liquid ammonia is taken from the sump 20 through a pipe 22 to a pressure increasing device 24 guided. With the pressure booster 24 the pressure of the ammonia is in a first step 26 (S. 2 ) of the pressure increase or compression in the thermodynamic cycle 16 from the lower pressure 18 to an increased pressure 28 increased as the upper pressure level of about 37 bar.

From the pressure booster 24 is the liquid ammonia that is under increased pressure 28 stands, through a pipe 30 to a heat transfer device 32 pumped to transfer thermal energy to the ammonia.

The heat transfer device 32 includes a first heat exchanger 34 , a series-connected second heat exchanger 36 and an intervening separator 38 with an upper room area 40 and a lower room area 42 , The administration 30 leads into the upper room area 40 , In addition leads from the first heat exchanger 34 a line 44 in the upper room area 40 of the separator 38 , From the separator 38 leads a line 45 from the lower room area 42 in the first heat exchanger 34 , From the upper room area 40 leads a line 46 in the second heat exchanger 36 ,

Thus, the liquid ammonia is first designed via the line 30 in the upper room area 40 of the separator 38 pumped. The liquid ammonia separates from any existing gaseous ammonia and sinks into the lower space 42 , From there, the liquid ammonia passes over the line 45 from the separator 38 in the first heat exchanger 34 which serves as an evaporator. There, the liquid ammonia is in a second step 48 (S. 2 ) of preheating in the thermodynamic cycle 16 isobar warmed up and in a third step 50 evaporation largely evaporated. In the third step 50 (S. 2 ), the majority of the thermal energy or heat energy is supplied. For this purpose, the temperature of the ammonia is increased by means of a first transfer of thermal energy to about 75 ° C. This temperature of about 75 ° C corresponds to the existing elevated pressure 28 at about 37 bar the evaporation temperature of ammonia, so that ammonia evaporates. The ammonia vapor formed is a wet steam. This means that even small drops and finely divided liquid ammonia are present as condensate in the gaseous ammonia. The formed wet steam passes over the pipe 44 in the upper room area 40 of the separator 38 , The drops and the finely divided liquid ammonia sink into the lower room area 42 and accumulate there as liquid, while in the upper room area 40 only gaseous ammonia remains. The liquid ammonia passes over the line 45 back to the first heat exchanger 34 for reheating.

With the separator 38 , the wires 30 and 44 as well as the line 45 are prerequisites for a thermo siphon principle created. This principle is based on the fact that during evaporation in the first heat exchanger 34 reduces the density of the ammonia located there due to the wet steam formed. Due to the reduced density, the wet steam is forced through the pipe 44 in the separator 38 , Furthermore, always just as much liquid ammonia flows out of the lower room area 42 of the separator 38 through the pipe 45 in the heat exchanger 34 which is just needed for evaporation. In the separator 38 is a non-illustrated level controller provided. The level controller pumps the pressure booster 24 so regulated that only so much ammonia towards heat transfer device 32 pumped, which can also be evaporated.

From the separator 38 The gaseous ammonia comes from the upper space area 40 over the line 46 in the second heat exchanger 36 , This second heat exchanger 36 serves as a superheater. There, the gaseous ammonia is in a fourth step 52 (S. 2 ) of overheating in the thermodynamic cycle 16 Isobar is overheated by a second transfer of thermal energy. The temperature of the ammonia vapor is increased isobarically to about 125 ° C and generated superheated ammonia gas.

The superheated ammonia gas is via a line 54 passed into an expansion device, which in the present case with a displacement machine 56 is designed. There, the superheated ammonia gas in a fifth step 58 (S. 2 ) of expanding in the thermodynamic cycle 16 at least largely free of condensate from the increased pressure 28 to the lower pressure 18 expanded, which simultaneously reduces the temperature of the ammonia. This points in the positive displacement machine 56 entering ammonia a pressure of about 37 bar and a temperature of about 125 ° C and that from the positive displacement machine 56 exiting ammonia to a pressure of about 10 bar and a temperature of about 30 ° C. This means that part of the thermal energy of the ammonia during the step 58 becomes free. This released thermal energy is using the positive displacement machine 56 , at the same time as a drive unit for a generator coupled thereto 60 serves, used in mechanical work for generating electrical energy.

In the device 12 leads in the direction of flow after the displacement machine 56 a line 68 as steam outlet or exhaust steam line from the displacement machine 56 out and into a medium 70 for condensing. This will be the result of the displacement machine 56 exiting gaseous ammonia into the agent 70 passed, cooled and isobar in a sixth step 72 (S. 2 ) of the thermodynamic cycle 16 condensed. With the sixth step 72 Condensation is the thermodynamic cycle 16 closed, so again with the first step 26 of increasing the pressure of ammonia can be started.

The middle 70 for condensing may be formed as a condenser heat exchanger or cooler with an air cooler, in particular a Evaporativkühlturm so that the ammonia is cooled with air.

About one from the middle 70 leading out lead 74 the condensed ammonia is again, in particular continuously in repeating steps 26 . 48 . 50 . 52 . 58 and 72 through the device 12 pumped.

For supplying oil to the working medium, the device has 12 at the displacement machine 56 via an oil supply device 76 , This oil supply device 76 includes an oil supply means 77 for supplying oil to ammonia and an oil laxative 78 for removing oil from the ammonia. The oil supply agent 77 leads as a line directly into the positive displacement machine 56 so that oil is directed into the expander. In the displacement machine 56 Oil can get into the expanding ammonia. The resulting ammonia-oil mixture becomes the oil with the oil laxative 78 discharged again after expansion. This is the oil removal agent 78 in the flow direction after the displacement machine 56 positioned and includes a separator 79 as well as a heater 80 ,

The separating element 79 is present in the line 68 provided and formed with an oil separator, which mechanically separates the liquid ammonia-oil mixture from the gaseous ammonia. The gaseous ammonia then continues in the line 68 to the middle 70 led to condensation, while the separated liquid ammonia-oil mixture into the heater 80 is directed.

The heater 80 is formed with a container whose interior by means of a heating circuit 81 is heated. Initiated there, the ammonia-oil mixture is heated until the ammonia is almost completely evaporated from the oil or expelled. The resulting ammonia vapor is via a steam line 82 from the heater 80 back to the line 68 and thus in the thermodynamic cycle 16 guided.

The separated oil is mixed with the oil transfer agent 84 in the form of a line back to the oil supply 77 guided and again for lubrication and sealing in the positive displacement machine 56 directed. In the present case this is done by means of an oil pump 86 ,

Furthermore, the heating circuit 81 with the heat source 14 heat transfer coupled, so that the thermal energy of the heat source 14 is particularly well exploited. In addition, the heating circuit 81 in the flow direction after the heater 80 with the first heat exchanger 34 or evaporator heat-transmitting coupled. In this way, the thermal energy remaining in the heating circuit after heating is coupled 81 used at least partially in addition to the evaporation of ammonia and recycled particularly well.

In the above-described device of the prior art and in the method performed by them, the practical application showed that the step 58 the expansion actually not directly on the tau line (s. 2 ), but in some circumstances even directly in the Wet steam area may end, but this is not desirable because it brings the disadvantages shown above.

3 shows, therefore, by way of example a part of a device with the additional features according to the invention, which part can be integrated in devices such as the device described above or in principle in ORC processes in a corresponding manner so as to prevent the method carried out by these devices that eventually liquid ammonia on critical components, such as. The oil pump, the expanders and oil separators produced; and so that these processes can be carried out continuously.

In the lead before the middle 70 for condensing a control unit R is arranged, which is designed according to the invention that a relaxation of the working medium by the expansion device is no longer in the wet steam area.

For this purpose, the control unit R at least one pressure sensor PIC and at least one temperature sensor TIC1, which cooperate with each other.

Between these is a motorized valve 100 is provided whose control behavior can be determined by the recorded by the sensors PIC and TIC1 pressure or temperature values via an external control.

Behind the motorized valve 100 Yet another temperature sensor TIC2 is provided so that the temperature values before and after the valve 100 are measurable.

This through the control unit for the motorized valve 100 provided control scheme depending on the measured temperatures and / or pressure affects the in the agent 70 for condensing introduced working fluid, ie, the gaseous ammonia so, in accordance with the invention so that for a method such as. By the in the 5 can always be ensured that in the subsequent expansion steps an expansion outside the wet steam area is carried out, as shown in the 4 is illustrated.

In the 5 By way of example, a process diagram of a device with an integrated control unit R according to the invention is shown. The components, lines and components shown therein are marked with customary symbols and therefore comprehensible to the person skilled in the art.

As in the 3 and 5 can be seen in each case, is in the line after the separating element 79 and before the agent 70 for condensing the control unit R integrated with the above-described components.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102012024031 A1 [0006, 0026]

Claims (6)

Contraption ( 12 ) for converting thermal energy from a heat source ( 14 ) into mechanical energy by means of a thermodynamic cycle ( 16 ) with a working medium and an expansion device for expanding the working medium, in which the expansion device with a displacement machine ( 56 ), the device having at least one means ( 70 ) condensing and wherein before the agent ( 70 ) for condensing a control unit (R) is arranged, which is designed so that a relaxation by the expansion device does not take place in the wet steam area. Apparatus according to claim 1, wherein the control unit (R) comprises at least one pressure sensor (PIC) and one temperature sensor (TIC). Apparatus according to claim 1 or 2, wherein the control unit (R) at least one controllable valve ( 100 ) having. Device according to Claim 3, in which the valve is a motor-controlled valve ( 100 ). Device according to claim 3 or 4, in which a control unit is provided, which controls the control behavior of the controllable valve ( 100 ) certainly. Method for converting thermal energy from a heat source ( 14 ) into mechanical energy by means of a thermodynamic cycle ( 16 ) with one step, with the step ( 58 ): Expanding the working fluid from an elevated pressure ( 28 ) to a lower pressure ( 18 ), wherein the expansion does not take place in the wet steam region defined for the cycle.

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