Screw expander and apparatus for generating electrical energy from heat with a screw expander

Abstract

In order to adapt a screw expander comprising an expander housing with a screw rotor chamber arranged therein, two screw rotors arranged in the screw rotor chamber and rotatably mounted in the expander housing, which interlock with their screw contours to receive working medium supplied via a high-pressure chamber arranged in the expander housing and discharge it in the area of ​​a low-pressure chamber arranged in the expander housing, and a generator driven by the screw rotors to different operating conditions, it is proposed that the screw expander has at least one control valve arranged in a slide channel of the expander housing and adjacent to both screw rotors with slide wall surfaces, which is movable in a displacement direction parallel to the screw rotor axes and is thereby designed to influence the final volume and / or the initial volume.and that a slide valve drive is provided for moving the control slide valve to different slide valve positions.

Description

[0001] The invention relates to a screw expander comprising an expander housing with a screw rotor chamber arranged therein, two screw rotors arranged in the screw rotor chamber and each rotatably mounted in the expander housing about a screw rotor axis, the screw rotors interlocking with their screw contours and each cooperating with wall surfaces adjacent to and partially enclosing these, in order to receive a working medium, in particular a gaseous working medium, supplied via a high-pressure chamber arranged in the expander housing and to discharge it in the area of ​​a low-pressure chamber arranged in the expander housing, wherein the working medium, in particular a gaseous working medium, is enclosed at high pressure with an initial volume in expansion chambers formed between the screw contours and wall surfaces adjacent to these and is expanded to a final volume at low pressure, and a generator, in particular an electric generator, driven by the screw rotors.

[0002] The problem with such screw expanders is to adapt the volume ratio defined by the initial volume and the final volume to different operating conditions.

[0003] This problem is solved by a screw expander according to claim 1.

[0004] The advantage of the solution according to the invention is therefore that the volume ratio of the screw expander can be adapted to different operating conditions when using it, for example in a cycle of the working medium in a cyclic process.

[0005] In principle, such a screw expander works with a control slide that can be moved in the direction of travel, with which the different slide positions and thus different volume ratios can be adjusted.

[0006] Alternatively, it is preferably provided that the screw expander has two control slides, wherein a first control slide is designed to influence the initial volume and a second control slide is designed to influence the final volume.

[0007] An expander used according to the invention is, for example, an open expander with an externally connected generator or a semi-hermetic expander with an integrated generator.

[0008] Furthermore, according to the invention, a control system is provided which controls the slide drive for the respective control slide to adjust a volume ratio suitable for the expansion of the working medium, formed from final volume divided by initial volume.

[0009] The control system can operate according to different specifications.

[0010] The invention provides that the control system detects the high pressure and the low pressure by means of a sensor arranged on the high-pressure side and a low-pressure side of a system for the expansion of working medium or an expander, for example, a high-pressure connection on the expander side and a low-pressure connection, and determines a pressure ratio of high pressure to low pressure from this.

[0011] Even when determining the pressure ratio of high pressure to low pressure, sufficient adjustments of the valve positions of at least one control valve or both control valves can be achieved by means of the control system.

[0012] The control system can operate according to different criteria.

[0013] The invention provides that the control system, by actuating the respective slide valve drive, positions the respective control slide valve according to whether at least one predetermined limit value for the pressure ratio of high pressure to low pressure is exceeded or fallen below.

[0014] This means that even with a predefined limit value, it is possible to move the control valves to different valve positions using the control system.

[0015] In particular, it is provided that if at least one limit value is undershot, the control system moves at least one control valve into a position with a reduced volume ratio of the final volume to the initial volume.

[0016] Furthermore, it is preferably provided that, when at least one limit value is exceeded, the control system moves at least one control slide to a position with a larger volume ratio of the final volume to the initial volume.

[0017] In the simplest case, one slide position corresponds to a larger, for example maximum, volume ratio and another slide position to a smaller, for example reduced, in particular a minimum, volume ratio, whereby the slide position for the larger volume ratio is used for pressure ratio values ​​that are above the specified limit value and the slide position for the smaller volume ratio or even the minimum ratio is used for pressure ratio values ​​that are below the limit value.

[0018] However, it is even more advantageous if the control system positions the control valve according to whether several limit values ​​for the pressure ratio are exceeded or fallen below.

[0019] In this case, it is possible to define an initial limit value for the pressure ratio, above which the slide position for the maximum volume ratio is set, and below which slide positions for reduced volume ratios are set, whereby further differentiation between different reduced volume ratios is also possible through further limit values ​​for the pressure ratio, so that, for example, with at least one further limit value for the pressure ratio, a differentiation between a slide position for a higher reduced volume ratio as opposed to a slide position for the lowest reduced volume ratio is possible.

[0020] Regarding the further function of the control system, a wide variety of possibilities are conceivable.

[0021] One simple solution involves the control system moving the respective control valve to corresponding valve positions within predefined volume ratios.

[0022] These can be two different predefined slider positions or multiple predefined slider positions.

[0023] In this solution, predefined, i.e. predetermined, slider positions are assumed and then held by the control system in conjunction with the respective slider drive.

[0024] Alternatively, it is provided that the control system moves the respective control slide in a position-controlled manner, i.e., can move it to any slide positions that are achievable by the screw expander, so that optimal utilization of the expansion possibilities of the screw expander is ensured within the scope of its design possibilities.

[0025] In particular, the solution according to the invention provides that the control system determines the positions of the control slides taking into account at least one or more of the following parameters, such as pressure level at low pressure, pressure level at high pressure, temperature of the gaseous medium at high and low pressure, rotational speed of the screw rotors, power consumption parameters of the gaseous working medium, in particular the refrigerant, and operating limits of the screw expander.

[0026] Furthermore, in the solution according to the invention, a position detection unit for the at least one control slide is preferably provided.

[0027] For example, the position detection unit comprises a position indicator element coupled to the positions of the at least one control slide, wherein the at least one position indicator element interacts with a detector element, and wherein the detector element is coupled to an evaluation unit that detects the positions of the position indicator element.

[0028] In the simplest case, it is provided that the at least one position indicator element is movable parallel to the displacement direction of the at least one control slide together with it, in particular that it is rigidly coupled to the control slide.

[0029] In the case of two control slides, it is preferably provided that the position detection unit for the two control slides comprises a first position indicator element coupled to the first control slide and a second position indicator element coupled to the second control slide, and that both position indicator elements interact with a common detector element.

[0030] In this case, the common detector element with the evaluation unit is able to detect the positions of both position indicator elements.

[0031] An advantageous solution provides that the detector element extends parallel to the displacement direction of the at least one control slide, along which the position indicator element is movable.

[0032] Particularly in the case of two control slides, it is provided that the detector element extends parallel to the displacement direction of the first and second control slides and along which the position indicator elements can be moved when the control slides are moved.

[0033] No further details have yet been provided regarding the arrangement of the position detection unit.

[0034] One advantageous solution provides that the position detection unit is arranged in a detector channel running parallel to the direction of displacement within the expander housing.

[0035] Furthermore, it is also provided that the respective position indicator element is arranged in the detector channel.

[0036] One particularly advantageous solution involves the respective position indicator element interacting with the detector element without contact.

[0037] To determine the position of at least one control valve, it is also conceivable, for example, if it is driven by a spindle drive with an electric motor, to record the rotational positions and / or revolutions of the electric motor during the positioning of the control valve and to determine the position of the control valve from these.

[0038] No further details have yet been provided regarding the design of the screw expander, particularly in the case of two control valves.

[0039] It is preferably provided that the first control valve and the second control valve are arranged one behind the other in the direction of their displacement.

[0040] Furthermore, it is expedient that the first control valve and the second control valve have an identical outer contour.

[0041] Furthermore, it is advantageously provided that the first control valve and the second control valve can be positioned directly adjacent to each other in a combined position and can be moved together in the direction of displacement.

[0042] Furthermore, it is provided that the first and second control slides can be positioned at a distance from each other in a separating position, forming an intermediate space.

[0043] No further details were provided regarding the design of the respective valve drive for the control valve in connection with the previous explanations.

[0044] It is preferably provided that the first control valve is rigidly connected to a piston of a cylinder arrangement forming the first valve drive for the movement of the control valve.

[0045] Furthermore, an advantageous solution provides that the second control valve is rigidly coupled to a piston of a cylinder arrangement forming the second valve drive for the movement of the second control valve.

[0046] As an alternative to using cylinder arrangements as a slide valve drive, another advantageous solution provides for a spindle drive driven by a motor, in particular an electric motor, as a slide valve drive.

[0047] It is advantageous for the electric motor to be supplied, for example, by the generator intended to generate the electrical energy or by an auxiliary generator coupled to one of the screw rotors.

[0048] However, it is also conceivable to power the electric motor from the grid into which the energy generated by the electric generator is coupled.

[0049] Furthermore, the invention relates to a system for generating electrical energy from heat, comprising a cyclic process in which a working medium circulated in a loop is compressed starting from the condensed state, evaporated by the supply of heat, expanded in an expansion system and subsequently condensed by the removal of heat, wherein the expansion system for expanding the working medium comprises at least one screw expander according to one of the preceding features.

[0050] Further features and advantages of the invention are the subject of the following description and the graphic representation of some exemplary embodiments.

[0051] The drawing shows: Fig. 1 a perspective view of a first embodiment of a screw expander according to the invention; Fig. 2 a section along line 2-2 in Fig. 1 Fig. 3 shows a section along line 3-3 in the area of ​​a position detection unit; Fig. 4 shows an enlarged section similar to the above. Fig. 2 in the area of ​​the position detection unit and the control valve at maximum power and smallest volume ratio; Fig. 5 a representation similar to Fig. 4 at maximum delivery volume and largest volume ratio; Fig. 6 a representation similar to Fig. 4 at approximately three-quarters of the power; Fig. 7 a representation similar Fig. 4 at approximately half power; Fig. 8 a similar representation Fig. 4 at approximately one quarter of the power; Fig. 9 an enlarged view of the position detection unit and the position indicator elements in conjunction with the control slide; Fig. 10 an enlarged perspective view of a position indicator element of the position detection unit; Fig. 11 a schematic representation of the second embodiment of the screw expander according to the invention with only one control slide similar to Fig. 5 at the largest volume ratio and highest power output; Fig. 12 a representation similar to Fig. 8 with reduced volume ratio and lowest power output; Fig. 13 a similar representation Fig. 4 with the smallest volume ratio and greatest performance; Fig. 14 a schematic representation of a third embodiment of the screw expander according to the invention, similar Fig. 11 and Fig. 15 a schematic representation of a system for generating electrical energy from heat with a cyclic process using a screw expander according to the invention.

[0052] A in Fig. 1 The illustrated embodiment of a screw expander 10 according to the invention comprises an expander housing designated as a whole by 12, which has an outlet port 14, through which an expanded gaseous medium, in particular refrigerant, exits and an inlet port 16, through which a gaseous medium under high pressure, in particular the refrigerant, enters.

[0053] As in Fig. 2 and 3As shown, in a screw rotor chamber 18 of the expander housing 12, two screw rotors 26, 28, each rotatable about a screw rotor axis 22, 24 and coupled to a generator 30, are provided, which interlock with their screw contours 32 and 34 and cooperate with wall surfaces 36 and 38 of the screw rotor chamber 18 adjacent to these circumferentially, in order to receive gaseous medium supplied in a high pressure chamber 44 adjacent to the screw contours 32, 34, expand it and release it into a low pressure chamber 42 in the expander housing 12 at low pressure.

[0054] In this process, the gaseous medium, in particular refrigerant, is enclosed in an initial volume at high pressure in expansion chambers formed between the screw contours 32, 34 and the wall surfaces 36, 38 adjacent to these, and expanded to a final volume at low pressure.

[0055] To adapt the screw expander 10, for example to the operating conditions required in an expansion circuit, the operating state of the screw expander 10 is adjusted firstly with regard to the volume ratio, which indicates the relationship between the maximum enclosed initial volume and the extended final volume, and secondly with regard to the expander power, which indicates the proportion of the volume flow actually expanded by the screw expander in relation to the maximum volume flow that can be expanded by the screw expander 10.

[0056] To adjust the operating state, during an initial, in the Fig. 2 bis Fig. 8 In the illustrated embodiment, a first control slide 52 and a second control slide 54 are arranged one behind the other in a slide channel 56 provided in the expander housing 12, wherein the slide channel 56 runs parallel to the screw rotor axes 22, 24 and guides the first control slide 52 and the second control slide 54 in the area of ​​their guide circumferential surface 58 which does not adjoin the screw rotors 26, 28.

[0057] The first control valve 52 faces the high-pressure chamber 44 and is therefore located on the high-pressure side, and the second control valve 54 is located on the low-pressure side relative to the first control valve 52.

[0058] Each of the two control slides 52 and 54 also has a slide wall surface 62 adjacent to the screw runner 26 and a slide wall surface 64 adjacent to the screw runner 28, which represent partial surfaces of the wall surfaces 36 and 38, and housing wall surfaces 66 and 68 formed by the expander housing 12, which also represent partial surfaces of the wall surfaces 36 and 38, and which complement the housing wall surfaces to form the wall surfaces 36 and 38, which together with the screw contours 32 and 34 contribute to the formation of the expansion chambers.

[0059] The first control valve 52 and the second control valve 54 are, as in Fig. 2 as well as 4 to 8, designed in such a way that they are identical insofar as they form the slide wall surfaces 62 and 64 and the guide circumferential surface 58 and can therefore be guided displaceably in a displacement direction 72 parallel to the screw runner axes 22, 24 in the slide channel 56 of the expander housing 12.

[0060] The first control slide 52 forms an inlet edge 82 facing the high-pressure chamber 44, which determines the initial volume of the expansion chambers, and which can be moved in the direction of movement 72 by moving the first control slide 52 and which, through its position relative to a high-pressure-side end surface 84 of the screw rotor chamber 18, co-determines the initial volume of the expansion chambers formed and thus the volume ratio.

[0061] As in the Fig. 2 and 4 bis 8 As shown, the first control valve 52 and the second control valve 54 have mutually facing end faces 86 and 88, with which they, as for example in Fig. 4 and Fig. 5 shown, so that they can be placed next to each other, so that the slide wall surfaces 62 and 64 of the first control slide 52 and the second control slide 54 merge into each other.

[0062] Furthermore, the first control valve 52 and the second control valve 54 are guided relative to each other by a telescopic guide 92 in addition to the valve channel 56, which has an inner guide body 94 and a guide receptacle 96, wherein the guide receptacle 96 is provided in the first control valve 52 and the guide body 94 is held on the second control valve 54 and projects beyond its end face 88, so that it can engage in the guide receptacle 96 in the first control valve 52.

[0063] Furthermore, a compression spring 104 is preferably provided in an interior space 102 of the second control slide 54 surrounding the guide body 94, which serves to act on the first control slide 52 relative to the second control slide 54 in such a way that the end faces 86 and 88 can be moved away from each other.

[0064] To move the first control slide 52, as described in Fig. 2 As shown, a cylinder arrangement 112 is provided as the first valve drive, comprising a cylinder chamber 114 and a piston 116, wherein the piston 116 is connected to a piston rod 118, which establishes a connection to the first control valve 52, for example with an extension 122 of the first control valve 52, which is arranged, for example, on one side of the same opposite the end face 86.

[0065] Furthermore, the cylinder arrangement 112 is located in particular on a side of the first control valve 52 opposite the second control valve 54, preferably in a high-pressure-side housing section 124 of the expander housing 12, which is arranged following the valve channel 56 and following the high-pressure chamber 44 and thus on a side of the expander housing 12 opposite the low-pressure chamber 42.

[0066] The second control valve 54 is displaceable by a cylinder arrangement 132 forming a second valve drive, which includes a piston 136 movable in a cylinder chamber 134, wherein the cylinder chamber 134 extends in particular in continuation of the valve channel 56 in a low-pressure-side housing section 142, in which drive-side bearing units for the screw rotors 26 and 28 are arranged, which can be driven, for example, via an output shaft 144.

[0067] In particular, the piston 136 is integrally formed with the second control valve 54 and has a piston area that corresponds at least to the cross-sectional area of ​​the second control valve 54.

[0068] The low-pressure side housing section 142, which accommodates the cylinder chamber 134 for the cylinder arrangement 132 for moving the second control valve 54, is located in a region of the expander housing 12 which is arranged opposite the high-pressure side housing section 124 for accommodating the cylinder chamber 114 for the cylinder arrangement 112.

[0069] The cylinder arrangements 112 and 132, for example, can be operated by means of pressurized oil, which is already present in the expander for lubricating the screw rotors 26, 28.

[0070] Furthermore, different piston positions can be set in such cylinder arrangements, as described for example in EP 1 072 796 A1, to which reference is hereby made.

[0071] The first control valve 52 and the second control valve 54 can be pushed together by the cylinder arrangements 112 and 132 to such an extent that the end faces 86 and 88 abut each other in a combined position, and the two control valves 52, 54 can also be moved together in the combined position as a single control valve, which extends from the low-pressure-side end surface 126 towards the high-pressure-side end surface 84 and whose inlet edge 82 contributes to determining the volume ratio, wherein, as in Fig. 4 As shown, the screw expander 10 always delivers the maximum volume flow in this combined position.

[0072] Depending on the position of the inlet edge 82 relative to the end surface 84, the volume ratio can be adjusted, increasing with the decreasing distance of the inlet edge 82 from the end surface 84 and reaching its maximum value when the inlet edge 82 has the smallest distance from the end surface 84 required to minimize the initial volume, as for example in Fig. 5 depicted.

[0073] If the expander performance, i.e., the actual volume flow rate, is to be varied additionally, this is done, as for example in Fig. 6 The diagram shows the separation of the end faces 86 and 88 by moving the control slides 52 and 54 apart into a separation position. In the separation position, the second control slide 54 is ineffective, and thus the position of the end face 86 of the first control slide 52 determines the final volume.

[0074] However, as long as the inlet edge 82 is not in a position in which it specifies the minimum possible initial volume, the ratio of the final volume, specified by the front surface 86, to the initial volume, specified by the inlet edge 82, is not variable.

[0075] However, if the first control slide is 52, as in Fig. 7 As shown, the inlet edge 82 is moved so far towards the high-pressure chamber 44 that it has the minimum distance from the end surface 84 or is even moved beyond it into an inlet chamber 146 enclosed by the high-pressure chamber 44 for the first control valve 52, a variation of the final volume by the position of the end surface 86 is possible without changing the initial volume, since this then always remains minimal.

[0076] To eliminate the effect of the second control valve 54 in the separation position, it is retracted into the housing section 142, in particular by means of the cylinder arrangement 132, wherein the cylinder chamber 134 is dimensioned such that it simultaneously includes a retraction space 148 for the second control valve 54 and thus makes it possible to move the second control valve 54 so far away from the first control valve 52 that the end face 88 no longer influences the final volume.

[0077] The second control slide 54 thus allows the final volume to be influenced by either having its end face 88 rest against the end face 86 of the first control slide 52 to form the combined position of the control slides 52, 54, thereby maximizing the final volume, or by having its own end face 88 move so far away from the end face 86 of the first control slide 52 that the final volume is no longer influenced by the second control slide 54, but is instead determined by the end face 86.

[0078] To detect the positions of the first control slide 52 and the second control slide 54, a position detection unit designated as a whole by 152 is provided, which comprises a detector element 154 extending parallel to the displacement direction 72 of the control slides 52, 54 and thus parallel to the screw rotor axes 22, 24, which is able to detect the positions of position indicator elements 156 and 158.

[0079] The position indicator element 156 is rigidly coupled to the first control valve 52, specifically to an end region 162 of the first control valve 52 adjoining the end face 86, and the position indicator element 158 ​​is coupled to the second control valve 54, specifically to an end region 164 of the same adjoining the end face 88, as shown in particular in Fig. 9 depicted.

[0080] As in Fig. 10 As shown, each of these position indicator elements 156 or 158 comprises a fork body designated as a whole by 174, which, with its two fork arms 176 and 178, defines an intermediate space 182 through which the elongated detector element 154 extends. Each of these fork bodies 174 is coupled to the corresponding control slide 52, 54 via a connecting body 172 connected to the respective end region 162 or 164.

[0081] Preferably, the fork legs 176 and 178 carry magnets 184 and 186 respectively, whose magnetic field permeates the detector element 154 at the location of the magnets 184, 186.

[0082] The detector element 154 is made of a magnetostrictive material, so that the respective location 188 of the magnetic flux of the detector element 154 by the magnets 184, 186 can be determined by means of an evaluation device designated as a whole by 192, wherein the evaluation device 192 generates sound waves, for example, in the magnetostrictive detector element 154, which experience a back reflection at the locations 188 through which the magnetic fields of the magnets 184, 186 are permeated, so that the evaluation device 192 can determine the location of the locations 188 in which the magnetic flux of the magnetostrictive detector element 154 takes place, based on the travel time of the reflected sound waves.

[0083] The connecting bodies 172, which are held at the respective end regions 162, 164 of the control valves 52, 54, extend through an elongated, slot-shaped passage 194, which is formed in a housing wall 196 forming the valve channel 56 and has a length which, in the separation position, allows the second control valve 54 to be fully retracted into the insertion chamber 148 and the first control valve 52 to be positioned at minimum initial volume, i.e., a position corresponding to Fig. 8 , and allows a position of the first control valve 52 at minimum volume ratio, i.e. maximum distance of the inlet edge 82 from the pressure-side end surface 84, and also allows a position of the second control valve 54 with the first control valve 52 in the combined position at maximum volume ratio ( Fig. 5 ) and minimum volume ratio ( Fig. 4 ) allows.

[0084] Each connecting body 172 connected to the respective end region 162 and 164 of the corresponding control slide 52 or 54, together with the slot-shaped passage 194, forms an anti-rotation device for the respective control slide 52, 54 similar to a guide by a T-nut and a groove, thus eliminating the need to provide grooves in the control slides 52, 54 that interact with T-nuts projecting into the slide channel 56.

[0085] The passage 194 is always maintained at the pressure in the low-pressure chamber 42 and thus also serves to keep the control valves 52, 54 with their guide circumferential surface 58 in contact with the valve channel 56, so that the control valves 52, 54 cannot press against the screw rotors 26, 28 with the valve wall surfaces 62, 64 due to the high pressure forming between the valve channel 56 and the guide circumferential surface 58.

[0086] The passage 194 is sealed against higher pressures, especially high pressure, by the narrowly tolerable gap between the valve channel 56 and the guide circumferential surface 58 of the control valves 52, 54.

[0087] To accommodate the fork bodies 174 and the detector element 154, a recess 204 is provided on a side of a wall 196 of a housing base body 198 opposite the slide channel 56. This recess 204 is covered by a lid 212, which in turn has a recess 214 facing the recess 204, so that the recesses 204 and 214 complement each other and, for example, form an elongated detector channel 216 running parallel to the direction of movement 72. The detector element 154 extends in this channel, and the fork bodies 174 are movable in this channel. Their fork legs 176, 178 encircle the detector element 154 on both sides and position the magnets 184, 186 such that their magnetic field passes through the detector element 154 at a specific location 188.

[0088] Preferably the cover 212 is designed such that the detector element 154 lies in its recess 214, so that the detector element 154 together with the evaluation device 192 is held exclusively on the cover 212 and can be removed with it, while the fork bodies 174 extend in the detector channel 216, in particular both in the recess 198 and in the recess 204.

[0089] In a second simplified embodiment of a screw expander according to the invention, as shown in Fig. 11 bis 14 As shown, only the first control slide 52' is provided.

[0090] In particular, the same components as in the first embodiment are provided with the same reference numeral, but are indicated by a ', so that with regard to the description of the same in detail, insofar as no further description is given, reference is made to the explanations and also in particular to Fig. 1 and Fig. 3 Reference is made to the first embodiment.

[0091] In this second embodiment, the first control slide 52' lies in the slide channel 56' and is guided therein by its guide circumferential surface 58'. Furthermore, the first control slide 52' forms outer slide wall surfaces 62' 1 and 64' 1, which directly adjoin the housing wall surfaces 66' and 68', with the slide wall surface 62' 1 adjoining the screw rotor 26' and the slide wall surface 64' 1 adjoining the screw rotor 28'.

[0092] The first control valve 52' also forms the inlet edge 82', which is arranged facing the high-pressure chamber 44' and which determines the initial volume by its distance from the end surface 84' in a comparable manner to the first embodiment.

[0093] Furthermore, the first control slide 52' forms an outlet edge 86' which determines the final volume, wherein the first control slide 52' has such an extension parallel to the screw rotor axes 22, 24 that, firstly, the maximum volume ratio V i can be set with it when the inlet edge 82' has the smallest possible distance from the end surface 84' and the outlet edge 86' has not yet reached the end surface 126', but is located in a space 135' in the low-pressure-side housing section 142', and secondly, a reduced volume ratio V i, for example with the minimum initial volume, can be set when the first control slide 52' with the inlet edge 82' is moved into the high-pressure space 44' and the outlet edge 86' determines the final volume ( Fig. 12 ).

[0094] However, it would also be possible to set a reduced volume ratio V i by retracting the first control slide 52' with the outlet edge 86' into the space 135' in the low-pressure side housing section 142', so that the initial volume for the expansion is determined through the inlet edge 82' along the screw rotors 26', 28' and at a distance from the end surface 84', in order to specify a larger initial volume ( Fig. 13 ).

[0095] However, in this case, the volume flow rate is higher due to the larger initial volume.

[0096] To detect the position of the first control slide 52', a position detection unit 152' is also provided, which has a position indicator element 156' coupled to the first slide 52', which extends, for example as a wedge body, along the first control slide 52' and interacts with a detector element 154', both of which are arranged in a detector channel 216 in the expander housing 12'.

[0097] In a third embodiment, shown in Fig. 14 , which represents a modification of the second embodiment, instead of the slide valve drive designed as a cylinder arrangement, a slide valve drive designed as a spindle drive 113 is provided, which has an electric drive motor 115 with which a spindle 117 can be driven, wherein the spindle 117 engages in an internal thread 119 of the slide 52', so that when the spindle 117 is driven by the drive motor 115, the slide 52' can be moved in the displacement direction 72 and into the respective intended positions, analogous to a spindle nut, wherein the spindle 117 can also be designed to be self-locking, and thus holds the control slide 52' in the respective position.

[0098] The drive motor 115 can be powered either by the generator 30' or by a separate generator 121 integrated into the expander 10 or by an external network.

[0099] Furthermore, a rotary encoder with a position indicator element 156" and a detector element 154" and an evaluation unit 192" is provided as a position detection unit 152", which detects rotational positions of the drive motor 115, from which a conclusion can be drawn about the position of the control slide 52' specified by the spindle 117.

[0100] Regarding the further development and features of the third embodiment, full reference is made to the explanations of the first and second embodiments.

[0101] Furthermore, those elements of the third embodiment are provided with the same reference numerals as the first and second embodiments, so that reference is made to them.

[0102] In both the first and the second and third embodiments, the control slides 52, 52' and 54 are moved into their designated positions as shown in Fig. 2 As shown, a control unit 218 is provided which, by means of the connection with the position detection unit 152, 152', 152" is able to determine the actual positions of the control slides 52, 52', 54.

[0103] With the 218 control unit, as in Fig. 1 and 2 The respective slide valve drives, for example the cylinder arrangements 112, 112' and 132 or the spindle drive 113, can be controlled to position the respective control slide valves 52, 52', 54.

[0104] For this purpose, for example solenoid valves ML1 and ML2 can be controlled to control the oil supply to the cylinder arrangement 112, 112' for the first control valve 52, 52', and solenoid valves MV1 and MV2 can be controlled to control the oil supply to the cylinder arrangement 132 for the second control valve 54, or the drive motor 115 can be controlled.

[0105] In all embodiments, the control unit 218 uses a pressure sensor SPH to detect pressure ( Fig. 2 , Fig. 11 , Fig. 14 ) the high pressure PH and with a pressure sensor SPN ( Fig. 2 , Fig. 11 and Fig. 14 ) the low pressure PN resulting after the expansion and controls, for example, the positions of the first control valve 52 and the second control valve 54 in the first embodiment or only the position of the first control valve 52' in the second embodiment based on a detected pressure ratio PV = PH / PN by comparison with at least one first limit value G 1 .

[0106] If the pressure ratio PV is greater than the limit value G 1, a maximum volume ratio V i is set, and if the pressure ratio PV is less than the limit value G 1, a reduced volume ratio is set.

[0107] In the first embodiment, a maximum volume ratio is achieved at a position of the first and second control valves 52, 54 according to Fig. 5 before and a reduced volume ratio at a position of the first and second control valve 52, 54 according to Fig. 4 at maximum volume flow or, for example, according to Fig. 6 , 7 at reduced volume flow or 8 at minimum volume flow.

[0108] In the second and third embodiments, a maximum volume ratio V i is achieved at a position of the first control valve 52' according to Fig. 11 or Fig. 14 or a reduced volume ratio in a position according to Fig. 12 or 13 at the same volume flow rate.

[0109] Since several slide positions are possible with reduced volume ratios, it is also possible to switch between the slide positions for reduced volume ratios, for example by setting further limit values ​​G w, whereby a transition to a larger reduced volume ratio V i or to a smaller reduced volume ratio is carried out by the control 218 when such a further limit value G w is exceeded or fallen below.

[0110] The control unit 218 can be further optimized with regard to its function if it detects the positions of the control valves 52, 54 or 52' ​​with the described position detection unit 152, 152', 152" and controls the respective valve drive, for example by pulsed operation of the solenoid valves ML1 and ML2 and optionally MV1 and MV2, controls the cylinder arrangements 112, 112' and optionally 132 or suitable operation of the drive motor 115, in order to, for example, approach predefined positions of the control valves 52, 52' and 54 to set predefined volume ratios V i.

[0111] In particular, it is also possible to position the control valves 52, 52', 54 with the control 218 in a position-controlled manner, that is, for example, to move and hold the positions of these control valves 52, 52', 54 exactly as determined by an expander control program and possible within the scope of the displacement of the control valve.

[0112] Such an expander control program runs, for example, on a higher-level expander control system.

[0113] In the illustrated embodiments, this expander control program is integrated in particular into the control unit 218, wherein in particular the operating limits of the screw expander 10 and the parameters of the gaseous working medium, i.e. in particular the refrigerant, are known, and is recorded, for example, via the pressure sensor SPN ( Fig. 2 , 11 , 14 ) the low pressure, via the SPH pressure sensor ( Fig. 2 , 11 , 14 ) the high pressure, and via a temperature sensor STH the temperature of the working medium on the high pressure side ( Fig. 2 ) and via a temperature sensor STN the temperature of the working medium on the low-pressure side.

[0114] In addition, the control unit 218 can also be used to record operating parameters of an electric generator 30 with regard to speed, power consumption, voltage and temperature.

[0115] Furthermore, the control unit 218 can also detect lubricant pressure, lubricant flow, lubricant level and lubricant temperature.

[0116] Furthermore, the required expander power, for example for an expansion circuit in which the screw expander 10 operates, is specified to the control unit 218 by means of an external signal.

[0117] From some selected of these values, in particular from the information about the working medium, e.g. about the refrigerant, about pressure and temperature on the high-pressure side and the low-pressure side, as well as about the rotational speed of the screw rotors 26, 28, or from other values ​​mentioned above, the control unit 218 with the expander control program can determine and adjust an optimal position of the control slides 52, 52', 54 for the respective operating condition.

[0118] One in Fig. 14 The depicted system for generating electrical energy from heat, in particular for generating electrical energy from waste heat, comprises a Fig. 15 depicted cycle process, in particular a cycle process operating with a Rankine cycle, in which a working medium guided in a circuit 240 is compressed from the condensed state by a compressor 242, which is driven by a motor 244.

[0119] In a subsequent heat exchanger 246, the working medium is evaporated by supplying heat from a heat stream 248.

[0120] For example, heat is supplied by the heat flow 248 via a hot water circuit 250, which flows through the heat exchanger 246 and in which a hot water pump 252 is arranged to circulate the hot water in the hot water circuit 250, which in turn is driven by a motor 254.

[0121] The working medium evaporated by the supply of the heat flow 248 in the heat exchanger 246 is supplied to an expansion system 260 arranged downstream of the heat exchanger 246 in the circuit 240, which in particular includes one of the screw expanders 10 described above, which drive a generator 30 for power generation.

[0122] After passing through the screw expander 10, the working medium is fed into the circuit 250 to a heat exchanger 262, in which the working medium condenses, whereby a heat flow 264 is removed through the heat exchanger 262.

[0123] For this purpose, a cold water circuit 270 is provided in particular, which also passes through the heat exchanger 262, wherein a cold water pump 272 is arranged in the cold water circuit 270, which is driven by a motor 274.

[0124] In particular, the compressor 242 performs an isentropic, preferably an ideal isentropic, compression of a liquid saturated condensate of the working medium produced by the heat exchanger 262, and in the heat exchanger 246 an essentially isobaric evaporation of the subcooled system takes place until the vapor saturated state is reached, in which the working medium is then supplied to an expansion system 260, whereby mechanical work is generated in the screw expander 10 by expansion, by which the generator 30 is driven.

[0125] In the heat exchanger 262, an isobaric, in particular a complete isobaric, condensation of the working medium takes place by removing the heat flow 264, so that a liquid saturated condensate can then be supplied to the compressor 242.

[0126] Organic working media, such as R245fa, R1224yd(z), R1336mzz(Z), R1336mzz(E), R1233zd, R1234ze, R1234yf, R134a, R513a, R245fa and mixtures thereof or similar media, are used as working media.

[0127] Preferably, such a cycle process serves to utilize industrial waste heat, which is generated, for example, in the range between 85°C and 700°C, whereby this waste heat can be optimally converted into electrical energy by the cycle process described above.

[0128] Since the heat flow 248 and the heat flow 264 both change during the cycle, the high pressure PH and low pressure PN at the screw expander 10, which are detected by the sensors SPH and SPN, also change, and thus the pressure ratio PV also changes, so that an adjustment of the screw expander 10 to changed pressure conditions is advantageous in order to prevent overexpansion on the one hand and underexpansion on the other, which would each lead to the screw expander 10 not being able to convert the separate energy provided in the cycle 240 into electrical energy with the generator 30.

[0129] This adaptation to different pressure conditions is made possible by the screw expanders 10 described above with the different positions of the control slides 52, 52', 54, which can be realized by the various described possibilities of the control 218 of the same.

Claims

1. A screw expander (10) comprising an expander housing (12) with a screw rotor chamber (18) arranged therein, two screw rotors (26, 28) arranged in the screw rotor chamber (18) and rotatably mounted in the expander housing (12) in each case about a screw rotor axis (22, 24), the screw rotors engaging into each other with their screw contours (32, 34) and in each case co-operating with wall surfaces (36, 38) which adjoin them and partly surround them, in order to receive a working medium supplied via a high pressure chamber (44) arranged in the expander housing (12) and supply it in the region of a low pressure chamber (42) arranged in the expander housing (12), wherein the gaseous working medium is enclosed in expansion chambers formed between the screw contours (32, 34) and the wall surfaces (36, 38) adjoining them at high pressure (PH) with an initial volume and is expanded to a final volume at low pressure (PN), and a generator (30) driven by the screw rotors (26, 28), wherein the screw expander (10) has at least one control slide (52, 52', 54) which is arranged in a slide channel (56) of the expander housing (12) and adjoins both screw rotors (26, 28) with slide wall surfaces (62, 64), the control slide being movable in a direction of displacement (72) parallel to the screw rotor axes (22, 24) thereby to affect the final volume, wherein a slide drive (112, 132, 113) is provided for the movement of the control slide (52, 52', 54) into differing slide positions, characterised in that there is provided a control device (218), which controls the screw drive (112, 132) for the control slide (52, 52', 54) for adjusting a volume ratio (Vi) appropriate for the expansion of the working medium, formed from end volume divided by initial volume, in that the control device (218) detects the high pressure (PH) and the low pressure (PN) by means of a respective sensor (SPH, SPN) arranged at the high pressure side and at the low pressure side and determines therefrom a pressure ratio (PV) of high pressure (PH) to low pressure (PN), and in that the control device (218), by controlling the slide drive (112, 132, 113), positions the control slide (52, 52', 54) corresponding to the exceeding or falling below of at least one predetermined limit value (G1) for the pressure ratio (PV) of high pressure (PH) to low pressure (PN).

2. A screw expander according to claim 1, characterised in that the screw expander (10) has two control slides (52, 54), wherein a first control slide (52) is configured to affect the initial volume and a second control slide (54) is configured to affect the final volume.

3. A screw expander according to claim 1, characterised in that the control device (218), upon falling below of the at least one limit value (G1), moves the at least one control slide (52, 52', 54) into a position with a smaller volume ratio (V1) of the final volume relative to the initial volume and / or in that in particular the control device (218), upon falling below the at least one limit value (G1), moves the at least one control slide (52, 52', 54) into a position with a larger volume ratio (Vi) of the final volume relative to the initial volume, in that in particular the control device (218) positions the control slide (52, 52', 54) corresponding to the exceeding or the falling below of a plurality of limit values (G1, Gw) for the pressure ratio (PV).

4. A screw expander according to any of the preceding claims, characterised in that the control device (218) moves the respective control slide (52, 52', 54) in slide positions corresponding to predefined volume ratios (Vi).

5. A screw expander according to any of the preceding claims, characterised in that the control device (218) positions the respective control slide (52, 52', 54) under closed-loop control.

6. A screw expander according to any of the preceding claims, characterised in that the control device (218) determines the positions of the control slide (52, 52', 54) taking into account at least one or more of the parameters such as pressure level (PN) at low pressure, pressure level (PH) at high pressure, temperature of the gaseous working medium at high pressure and low pressure (PN), rotary speed of the screw rotors (26, 28), power consumption of a generator (30), parameters of the gaseous working medium, in particular the refrigerant, and application limit values of the screw expander (12).

7. A screw expander according to any of the preceding claims, characterised in that there is provided a position detecting unit (152, 152', 152") for the at least one control slide (52, 52', 54), that in particular the position detecting unit (152) has a position indicating element (156, 156', 156", 158) coupled with the position of the at least one control slide (52, 52', 54), in that the at least one position indicating element (156, 156', 156", 158) co-operates with a detector element (154), and in that the detector element (154) is coupled with an evaluation unit (192, 192', 192"), which detects the positions of the position indicating element (156, 156', 156", 158), in that in particular the at least one position indicating element (156, 156', 158) is movable parallel to the direction of displacement (72) of the at least one control slide (52, 52', 54) and together therewith, in that in particular the detector element (154) extends parallel to the direction of displacement (72) of the at least control slide (52, 54), along which the position indicating element (156, 158) is movable.

8. A screw expander according to claim 7, characterised in that there is provided for both the control slides (52, 54) a position detection unit (152), which comprises a first position indicating element (156) coupled to the first control slide (52) and a second position indicating element (158) coupled to the second control slide (54), and in that both position indicating elements (156, 158) co-operate with a common detector element (154), in that in particular the detector element (154) extends parallel to the direction of displacement (72) of the first and second control slides (52, 54) along which the position indicating elements (156, 156', 158) are movable during the movement of the control slides (52, 52', 54).

9. A screw expander according to claim 7 or 8, characterised in that the position detection unit (152, 152') is arranged in a detector channel (216) running within the expander housing (12) parallel to the direction of displacement (72), in that in particular the respective position indicating element (156, 156', 158) is arranged in the detector channel (216).

10. A screw expander according to any of the preceding claims, characterised in that the respective position indicating element (156, 156', 156", 158) co-operates with the detector element (154) in contactless manner.

11. A screw expander according to any of claims 2 to 10, characterised in that the first control slide (52) and the second control slide (54) are arranged one behind the other in the direction of displacement (72) thereof, in that in particular the first control slide (52) and the second control slide (54) have an identical outer contour, in that in particular the first control slide (52) and the second control slide (54) can be positioned in a combined disposition directly adjacent to each other and are movable together in the direction of displacement (72), in that in particular the first and the second control slides (52, 54) can be positioned in a separated disposition at a spacing from each other with the formation of an intermediate space.

12. A screw expander according to any of the preceding claims, characterised in that the first control slide (52) is connected rigidly with a piston (118) of a cylinder arrangement (112) forming the first slide drive for movement of the first control slide (52).

13. A screw expander according to any of the preceding claims, characterised in that the second control slide (54) is coupled rigidly with a piston (136) of a cylinder arrangement (132) forming the second slide drive for movement of the second control slide (54).

14. A screw expander according to any of claims 1 to 13, characterised in that the at least one control slide (52') is driven by means of a spindle drive (113), in that in particular the spindle drive (113) is driven by an electric drive motor (115).

15. A facility for obtaining electrical energy from heat, involving a cycle, in which, starting from a condensed state, a working medium in a circulatory system (240) is compressed, is evaporated by the supply of heat, is expanded in an expansion apparatus (260) and is subsequently condensed by the removal of heat, characterised in that the expansion apparatus (260) has a screw expander (10) according to any of the preceding claims for expansion of the working medium.

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