EP4283098A1 - Heat engine - Google Patents

Abstract

A heat engine (1) for low-temperature operation for utilizing solar heat or waste heat from biological or industrial processes has at least one cylinder/piston unit (2 - 5), the cylinder (6) of which is designed to receive an expansion fluid (8), which is in Temperature change changes its volume and so moves the piston in the cylinder (6), and means (33) for supplying heat to the expansion fluid (8) in the cylinder (6), the piston being a plunger (24) which is round in the cylinder (6). leaves an annular space (26) around its displacement (25), in which the heat supply means (33) are arranged.

Description

The present invention relates to a heat engine, in particular for low-temperature operation for the utilization of solar heat or waste heat from biological or industrial processes, with at least one cylinder/piston unit, the cylinder of which is designed to accommodate an expansion fluid, which changes its volume when the temperature changes and so on Piston moves in the cylinder, and with means for supplying heat to the expansion fluid in the cylinder, the piston being a plunger which leaves an annular space in the cylinder around its displacement, in which the heat supply means are arranged, and the heat supply means being a pipe coil through which a heat transfer medium can flow have, which is arranged in at least one helical winding around the displacement of the plunger.

Such a heat engine is from AT 510 459 A1 known.

Heat engines for low-temperature operation, for example also from the EP 2 238 318 B1 , EP 2 668 374 B1 , US 2011/0100002 A1 or US 10 975 697 B2 known, use liquid or supercritical carbon dioxide (sCO ₂ ) as the expansion fluid. From a pressure of approx. 60 - 70 bar, carbon dioxide shows a volume expansion of around 2.2 times when heated from just 20 °C to 30 °C and is therefore particularly suitable for carrying out mechanical work from low-temperature heat transfer media.

In the known heat engines there is still a need for improvement with regard to the heat input into the expansion fluid when it expands.

The aim of the invention is to create a heat engine with improved efficiency.

This goal is achieved with a heat engine of the type mentioned in the introduction, which is characterized according to the invention in that the pipe coil is in at least two of each other radially spaced helical windings are arranged around the displacement of the plunger.

By using at least two helical windings, which are arranged at a mutual radial distance from one another in the area around the displacement of the plunger, a particularly intimate heat exchange is achieved between a flowable heat transfer medium, e.g. wastewater from an industrial plant, hot water from a solar system, etc. and the expansion fluid . As a result, a significantly improved efficiency of the heat engine can be achieved.

The invention is based on the knowledge that the heat input into the expansion fluid suffers in the known designs with an in-cylinder heat exchanger because the expansion fluid, as it expands, moves progressively further away from the cylinder base and thus the heat exchanger arranged there and therefore heats up increasingly poorly. In contrast, in the invention, by using a plunger, the annular space remaining around the plunger is used for the arrangement of the heat supply means. During its expansion, when it displaces the plunger from the cylinder, the expansion fluid is always in contact with the heat supply means over the same axial length of the cylinder, regardless of the retracted and extended positions of the plunger. This results in a heat input into the expansion fluid that is largely independent of the piston position and thus an overall improved efficiency.

It is particularly favorable if the heat supply means extend over more than half, preferably more than two thirds, of the axial length of the annular space. This ensures good contact between the heat supply means and the expansion fluid in every phase of the retraction and extension movement of the plunger and thus a high level of efficiency overall.

The heat engine according to the invention is suitable for use with a wide variety of expansion fluids, for example mixtures of carbon dioxide and other gases. Particularly advantageous is when - as is known from the literature references mentioned above - the cylinder is filled with carbon dioxide as an expansion fluid and a biasing fluid acts on the plunger opposite to the expansion fluid, which puts the carbon dioxide under a biasing pressure that is above the liquefaction pressure of carbon dioxide. This means that carbon dioxide can be used in the liquid or supercritical state, which has a particularly high coefficient of thermal expansion.

According to an advantageous feature, the plunger is axially guided in a front stuffing box of the cylinder, which contains at least one sealing ring made of CO ₂ -resistant plastic and at least one slide ring based on graphite, preferably made of PTFE-graphite. This achieves a particularly low-friction and at the same time durable sealing of the plunger.

The preload pressure required for some expansion fluids, such as carbon dioxide, can also be achieved in a variety of ways. For example, the plunger could be preloaded against the expansion fluid by means of an auxiliary piston that is acted upon by a preloading fluid, or the load that drives the plunger applies this counterforce. In a first preferred embodiment of the invention, the heat engine comprises at least two cylinder/piston units of the type mentioned, which are arranged opposite one another and whose plungers are rigidly connected to one another. If the cylinders of the two cylinder/piston units are fixed to the floor or to each other, for example, then one piston applies the preload pressure for the expansion fluid of the other cylinder/piston unit.

In a second preferred embodiment, the plungers of at least two cylinder/piston units are acted upon by a common biasing fluid in order to exert a common biasing pressure on the expansion fluids in the cylinders, as is apparent from the EP 2 238 318 B1 or the EP 2 668 374 B1 is known. One can use the heat supply means Control device connected to a pressure gauge for the preload pressure controls the heating and cooling phases of the expansion fluids of the individual cylinder/piston units depending on the measured preload pressure so that it is kept within a predetermined range.

The common biasing fluid can simultaneously be used as a working fluid for operating a hydraulic load by being guided from the cylinder/piston units via first check valves to an inlet and via oppositely directed second check valves to an outlet of a hydraulic load.

• Fig. 1 eine Wärmekraftmaschine mit vier Zylinder/KolbenEinheiten nach dem Stand der Technik in einem Prinzipschaltbild;
• Fig. 2 eine erste Ausführungsform der Wärmekraftmaschine gemäß der Erfindung mit einer einzigen Zylinder/Kolben-Einheit in einem Längsschnitt;
• Fig. 3 ein Detail der Wärmekraftmaschine von Fig. 2 in einer perspektivischen Explosionsdarstellung; und
• Fig. 4 eine zweite Ausführungsform der Wärmekraftmaschine der Erfindung mit zwei gegenläufigen Zylinder/Kolben-Einheiten in einem perspektivischen Längsschnitt.

The invention is explained in more detail below using exemplary embodiments shown in the accompanying drawings. In the drawings shows:

• Fig. 1 a heat engine with four cylinder/piston units according to the prior art in a schematic diagram;
• Fig. 2 a first embodiment of the heat engine according to the invention with a single cylinder/piston unit in a longitudinal section;
• Fig. 3 a detail of the heat engine from Fig. 2 in a perspective exploded view; and
• Fig. 4 a second embodiment of the heat engine of the invention with two opposing cylinder/piston units in a perspective longitudinal section.

Fig. 1 shows a heat engine 1 'according to the prior art, as shown, for example, in EP 2 668 374 B1 is described. The heat engine 1 'has one or more (here: four) cylinder/piston units 2 - 5. Each cylinder/piston unit 2 - 5 has a cylinder 6 in which a piston 7 (here: a disk piston) is located between one retracted position (shown at 2) and an extended position (shown at 5).

The space 6 'in the cylinder 6 to the left side of each piston 7 is completely occupied by an expansion fluid 8. The Expansion fluid 8 has a high coefficient of thermal expansion and expands when heated to move the piston 7 from the retracted to the extended position, or contracts when cooled to move the piston 7 back again.

In the example shown, the expansion fluid 8 is liquid carbon dioxide (CO ₂ ), which has a liquefaction pressure of approximately 65 bar at room temperature. In the supercritical state, which is reached above 73.8 bar and above 31 °C, carbon dioxide shows a thermal expansion of around 2.2 times with a temperature change of, for example, 10 °C. Instead of pure carbon dioxide, mixtures of liquid carbon dioxide with other substances could also be used as expansion fluid 8.

In order to keep the CO ₂ as expansion fluid 8 in its liquid state, the piston 7 is acted upon or biased with a preload pressure greater than or equal to the liquefaction pressure in the direction of the expansion fluid 8. For the supercritical condition, the preload pressure is selected correspondingly higher.

The preload pressure is exerted by a preload fluid 9, which acts in the space 6" to the right side of each piston 7, ie on the side of each piston 7 facing away from the expansion fluid 8. The preload fluid 9 - preferably a hydraulic oil - circulates in all cylinders/pistons -Units 2 - 5 common hydraulic circuit, which contains a hydraulic load 10. The hydraulic load 10 is, for example, a hydraulic motor with an input 11 'and an output 11", through which the preload fluid 9 flows and the pressure energy or kinetic energy of the preload fluid 9 is converted into mechanical work for an output shaft 11‴. A pressure drop Δp occurs between the input 11' and the output 11" of the load 10. Instead of a hydraulic motor, any other type of hydraulic load 10 could also be used, which can be driven with a pressure drop Δp, as is known in the art.

The biasing fluid 9 is led from the cylinder/piston units 2 - 5 via a set of first check valves 12' and a first manifold 13' to the inlet 11' of the load 10, and from its outlet 11" via a second manifold 13" and a Set of second check valves 12" back to the cylinder spaces 6" of the cylinder/piston units 2 - 5. Each individual cylinder/piston unit 2 - 5 is therefore a first one that opens and in the direction from the space 6" to the entrance 11' assigned to a check valve 12' which blocks in the opposite direction, as well as a second check valve 12' which opens from the outlet 11" to the space 6" and blocks in the opposite direction.

When a piston 7 is extended (arrow 14'), the biasing fluid 9 thus establishes a first pressure level p ₁ at the inlet 11' of the load 10 (inlet pressure) via the first check valves 12' and the first manifold 13' - as a "working fluid", so to speak. When the piston 7 retracts (arrow 14"), the respective first check valve 12' closes and the respective second check valve 12" opens, so that the second pressure level p ₂ , reduced by the pressure drop Δp, from the outlet 11" of the load 10 ("output pressure") via the second manifold 13" in the respective cylinder/piston units 2 - 5 and the expansion fluid 8 is biased.

The pressure of the preload fluid 9 in the spaces 6" of the cylinder/piston units 2 - 5 therefore oscillates between the inlet pressure (upper level) p ₁ when extending (arrow 14 ') and the outlet pressure (lower level) p ₂ when retracting (arrow 14"). As will be explained in more detail later, appropriate pressure measuring and control devices ensure that the lower pressure level, the initial pressure p ₂ , of the biasing fluid 9 does not exceed the necessary operating pressure for the biasing fluid 9, for example, in any phase of the movement 14', 14". falls below the liquefaction pressure of liquid CO ₂ and at the same time the desired or required pressure difference Δp = p ₁ - p ₂ at the load 10 is maintained.

A first elastic buffer 15' can be connected to the inlet 11' or the collecting line 13', for example a pressure vessel filled with gas and/or with an elastic membrane 15, in order to buffer short-term pressure fluctuations. Alternatively or additionally, a second such elastic buffer 15" can also be connected to the output 11" or the collecting line 13".

The expansion fluids 8 in the cylinder/piston units 2 - 5 are heated using controllable heat supply means 16 - 20. In the example shown, the heat supply means 16 - 20 include a heat exchanger 16 for each cylinder/piston unit 2 - 5, which contacts the expansion fluid 8 in a heat-conducting manner and in which a heat transfer medium 17 circulates. The heat transfer medium 17 is heated, for example, by a solar panel 18 in a heat transfer circuit 19 (return lines in Fig. 1 not shown for clarity).

Each heat exchanger 16 is provided with a controllable check valve 20. The check valves 20 are opened alternately and intermittently by a central control device 21 in order to alternately heat and cool each cylinder/piston unit 2-5, thereby alternatingly expanding and contracting the expansion fluids 8 in the cylinders 6 and thus ultimately the pistons 7 to move back and forth. The piston movements are synchronized via the preload fluid 9 circulating in the hydraulic circuit 10 - 13, in that the preload fluid 9 flowing back from the outlet 11 'via the second check valves 12" supports and forcibly couples the retraction movement (arrow 14").

The control device 21 actuates the check valves 20 depending on measured values of the input pressure p ₁ and preferably also of the output pressure p ₂ , which it receives from corresponding pressure gauges 22 ', 22 ", which are connected to the inputs 11 ', 11" or their manifolds 13 ' , 13" are connected. A first, primary control goal of the control device 21 is to keep the output pressure p ₂ within a first predetermined range p _2,min , p _2,max , which is determined in particular by the minimum preload pressure for the expansion fluid 8, for example (depending on temperature) approx. 50 - 60 bar for liquid carbon dioxide in the temperature range 20 - 50 ° C. In particular, the lower limit p _2,min of the first range is determined by the required minimum preload pressure.

Further control objectives of the control device 21 can be to simultaneously ensure that the input pressure p ₁ lies within a predetermined (second) range p _1,min , p _1,max . The first and second areas may be i-dent or partially overlap or directly adjoin each other or be spaced apart, in which latter case the output pressure p ₂ in a lower area (pressure band) and the input pressure p ₁ in an upper area (pressure band ) lies. With the latter embodiment, a minimum pressure difference or a minimum pressure drop Δp - p ₁ - p ₂ can also be set at the load 10 if such a difference is required for the proper operation of the load 10, or the pressure difference for the load 10 varies optionally to specify or control their energy consumption, for example.

If the pressure drop Δp across the load 10 is adjustable, ie the work of the load 10 can be controlled, the control device 21 can also control the pressure drop Δp of the load 10 in further control objectives, see optional control line e ₁ . For example, the pressure ranges of inlet and outlet pressure p ₁ , p ₂ that can be achieved based on the current temperature conditions can be used to calculate a usable pressure difference p ₁ - p ₂ and to set this as a specification for the pressure drop Δp at the load 10.

The stated control objectives of the control device 21 are achieved, for example, by controlling the number of those cylinder/piston units 2 - 5 which are currently in the heating phase at a certain point in time, in relation to the number of those other cylinder/piston units 2 - 5 which yourself to this The point at which we are currently in the cooling phase is reached, as in the EP 2 668 374 B1 is described.

In the Fig. 1 Cylinder/piston units 2 - 5 shown with disc pistons 7, which move away from the heat exchangers 16 arranged on the cylinder bases 6‴ during the expansion of the expansion fluid 8, have the disadvantage that as the expansion fluid 8 continues to expand, it becomes less and less separated from the heat exchanger 16 is achieved, see for example the maximum extended position of the cylinder/piston unit 5. This deteriorates the heat transfer from the heat exchanger 16 to the expansion fluid 8, especially in the area of the displacement 23, which each piston 7 in the cylinder 6 sweeps over. The ones in the Fig. 2 - 4 Illustrated embodiments of the invention overcome this problem.

In the Fig. 2 - 4 The same reference numerals denote the same parts as in Fig. 1 , and the following will only focus on the differences compared to the embodiment of Fig. 1 received.

Fig. 2 shows a first embodiment of a heat engine 1 according to the invention with a single cylinder/piston unit 2. It is understood that the heat engine 1 of Fig. 2 could also have more than one cylinder/piston unit 2, for example two, three or more cylinder/piston units 2 - 5, all like those in Fig. 2 Cylinder/piston unit 2 shown are designed and as in Fig. 1 can be interconnected via a common biasing fluid 9, which can simultaneously serve as the working fluid of a load 10.

According to Fig. 2 the piston 7 of the cylinder/piston unit 2 is designed as a plunger piston 24. In contrast to a disc piston, the plunger 24 does not seal against the inner peripheral wall of the cylinder 6, but leaves an annular space 26 around its displacement 25. The displacement 25 is the volume that the plunger 24 has in its fully retracted position (in Fig. 2 and on the left cylinder/piston unit 2 of Fig. 4 shown) and in its fully extended position (on the right cylinder/piston unit 3 of Fig. 4 shown) in cylinder 6 releases.

The plunger 24 is designed, for example, in the form of a cylindrical rod and is axially guided in a stuffing box 27, which is inserted into an end face 28 of the cylinder 6, ie the plunger 24 passes through the end face 28 of the cylinder 6 there and extends there. The extending end 29 of the plunger 24 can enter there as a working piston surface in an auxiliary cylinder 30, which contains the preload and working fluid 9, for example. The stuffing box 27 is equipped with at least one sealing ring 31, for example made of CO ₂ -resistant plastic, and/or at least one slide ring 32, for example based on graphite, preferably made of PTFE-graphite.

Heat supply means 33 for heating the expansion fluid 8 are arranged in the annular space 26 around the displacement 25 of the plunger 24. The heat supply means 33 can be, for example, an electrical heating coil. In the example shown, the heat supply means 33 are a heat exchanger for the heat transfer medium 17, in particular a pipe coil 34 for the flow of the heat transfer medium 17, which is heated by the solar panel 18.

The heat supply means 33 or (here:) the pipe coil 34 extend over a substantial part of the axial length L of the annular space 26, in particular over at least half of the axial length L, preferably over at least two thirds of the axial length L. As a result, the expansion fluid 8 remains over one Larger part of the longitudinal extent of the cylinder 6 is in thermal contact with the heat supply means 33, regardless of the retracted and extended position of the plunger 24. In the example shown, the pipe coil 34 forming the heat supply means 33 is in the form of two coaxial, axially largely overlapping helical windings 35, 36 arranged around the displacement 25 of the plunger 24.

Fig. 3 shows the double-helical coil 34 in detail with the plunger 24 partially extended. It is understood that the pipe coil 34 can also run in one or more than two windings 35, 36 and/or can be composed of partial pipe coils 34. The one or more windings 35, 36 of the pipe coil 34 are spaced radially from the outer circumference of the plunger 24, from the inner circumference of the cylinder 6 and from each other in order to enable the pipe joint 34 to be flushed with expansion fluid 8 from all sides.

In the case of two or more windings 35, 36, flow flows through them in particular in opposite directions. For example, the winding direction of the inner winding 35 is opposite to the winding direction of the outer winding 36 and the two windings 35, 36 are connected together at one end.

Fig. 4 shows an alternative embodiment of the heat engine 1 with two cylinder/piston units 2, 3, each as in the Fig. 2 and 3 are constructed as shown. The two cylinder/piston units 2, 3 are arranged here coaxially and axially one behind the other and in opposite directions to one another. The two cylinders 6 of the cylinder/piston unit 2, 3 are rigidly connected to one another via the intermediate auxiliary cylinder 30, and the two plungers 24 are rigidly connected to one another at their respective ends 29 at 37.

At their connection point 37, the two plungers 24 can carry a double-acting disc piston 38, which moves back and forth in the auxiliary cylinder 30 and forms two cylinder chambers 39, 40 in which the preload and / or working fluid 9 can be operated. The preload pressure for the expansion fluids 8 in the cylinders 6 of the two cylinder/piston units 2, 3 is achieved by appropriately dimensioning the lengths of the cylinders 6, 30 and the plunger pistons 24.

The invention is not limited to the illustrated embodiments, but includes all variants and modifications and combinations that fall within the scope of the appended claims.

Claims (8)

Heat engine, in particular for low-temperature operation for the utilization of solar heat or waste heat from biological or industrial processes, with at least one cylinder/piston unit (2 - 5), the cylinder (6) of which is designed to receive an expansion fluid (8), which when the temperature changes its volume changes and so moves the piston in the cylinder (6), and with means (33) for supplying heat to the expansion fluid (8) in the cylinder (6), the piston being a plunger (24) which is round in the cylinder (6). leaves an annular space (26) around its displacement (25), in which the heat supply means (33) are arranged, and wherein the heat supply means (33) have a pipe coil (34) through which a heat transfer medium can flow, which is in at least one helical winding (35, 36) is arranged around the displacement (25) of the plunger (24), characterized in that the tubular coil (34) in at least two radially spaced helical windings (35, 36) around the displacement (25) of the plunger (24) is arranged around. Heat engine according to claim 1, characterized in that the heat supply means (33) extend over more than half, preferably more than two thirds, of the axial length (L) of the annular space (26). Heat engine according to claim 1 or 2, characterized in that the cylinder (6) is filled with carbon dioxide as an expansion fluid (8) and a biasing fluid (9) acts on the plunger (24) opposite to the expansion fluid (8), which submerges the carbon dioxide Preload pressure sets that is above the liquefaction pressure of carbon dioxide. Heat engine according to one of claims 1 to 3, characterized in that the plunger (24) is axially guided in a front stuffing box (27) of the cylinder (6), which has at least one sealing ring (31) made of CO ₂ -resistant Plastic and at least one slide ring (32) based on graphite, preferably made of PTFE-graphite. Heat engine according to one of claims 1 to 4, characterized by at least two cylinder/piston units (2, 3) of the type mentioned, which are arranged opposite one another and whose plungers (24) are rigidly connected to one another. Heat engine according to one of claims 1 to 4, characterized by at least two cylinder/piston units (2 - 5) of the type mentioned, the plunger pistons (24) of which are acted upon by a common preload fluid (9) in order to apply a common preload pressure to the expansion fluids ( 8) in the cylinders (6). Heat engine according to claim 6, characterized by a control device (21) which controls the heat supply means (33) and is connected to a pressure gauge (22', 22") for the preload pressure and is designed to control the heating and cooling phases of the expansion fluids (8). to control individual cylinder/piston units (2 - 5) depending on the measured preload pressure (p ₁ , p ₂ ) in order to keep this within a predetermined range. Heat engine according to claim 6 or 7, characterized in that the biasing fluid (9) from the cylinder/piston units (2 - 5) via first check valves (12') to an inlet (11') and via oppositely directed second check valves (12 ") is led to an output (11") of a hydraulic load (10).

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