DE102017121954A1 - Screw expanders and methods for generating mechanical energy by expanding a working fluid - Google Patents

Abstract

The invention relates to a screw expander (6) for generating mechanical energy by expanding a working fluid comprising at least one housing (12), at least two screws (13, 14) or at least one pair of screws (13, 14) at least partially in said housing (12), at least one output shaft (7) which is connected to at least one of the screws (13), so that the output shaft (7) can be driven by a rotational movement of the at least one screw (13, 14), at least one working fluid inlet (5 ) to the housing (12) disposed at an inlet end of the screws (13, 14) and at least one working fluid outlet (9) connected to an outlet end of the screws (13, 14) opposite to the inlet end Screws (13, 14) is arranged along, wherein the two screws (13, 14) are engaged with each other, that the two screws (13, 14) and the housing (12) at least one expansion chamber (22), in particular e define a plurality of separate expansion chambers (22) along the screws (13, 14), the expansion chamber (13, 14) being adapted to be in a receiving position of the screws (13, 14) at an inlet end of the screws (13, 14) Working fluid from the working fluid inlet (5), wherein the expansion chamber (22) is adapted, in an outlet position of the screws (13, 14) at an outlet end of the screws (13, 14) to discharge working fluid to the working fluid outlet (9), wherein the expansion chamber ( 14) is adapted to be transported by moving the screws (13, 14) from the inlet end to the outlet end, whereby the volume of the expansion chamber (22) increases.

Description

The invention relates to a screw expander for generating mechanical energy by expanding a working fluid. The invention further relates to a station for reducing the working fluid pressure comprising such a screw expander. Moreover, the invention relates to a method for generating mechanical energy by expanding a working fluid in at least one such screw expander.

Despite the significant advances that have been made in many non-thermal heat generation technologies, global energy production still relies on the use of heat to convert water into steam. The main fuel for heat production is coal. However, it also uses atomic energy, various forms of biomass, waste and concentrated infrared radiation from the sun. Waste heat from hot air is also often used to generate steam in steam boilers.

On a global scale, most of the energy is currently being produced by dry steam turbines that power electric generators. Dry steam can be generated by nuclear reactors or by burning fossil fuels, such as coal and natural gas. Although this process has become relatively effective, this process still has some disadvantages. The turbine blades rotate at a very high speed and as a result are very sensitive. The dry steam used must be extremely clean to prevent damage to the turbine blades. For similar reasons neither wet steam nor water can be used. In many cases, such restrictions hinder the use of these turbines. Geothermal applications are particularly problematic in terms of electricity generation. Currently, heat exchangers are used to heat clean water from geothermal water before the water can be converted to dry steam. This process is inefficient and it is difficult to effectively apply this technology to smaller machines.

It is therefore an object of the invention to provide a screw expander, a station for reducing working fluid pressure, and a method respectively as described above, which enables the generation of mechanical energy by directly using a working fluid without using a dry steam turbine.

This object is achieved according to claim 1 by a screw expander for generating mechanical energy by expanding a working fluid, the at least one housing, at least two screws or at least one pair of screws, at least partially in said housing, at least one output shaft with at least one of the screws is connected so that the output shaft can be driven by a rotational movement of the at least one screw, at least one working fluid inlet to the housing, which is arranged at an inlet end of the screws, and at least one Arbeitsfluidauslass disposed at an outlet end of the screws along the screws Inlet inlet opposite has, wherein the two screws are engaged with each other so that the two screws and the housing along the screws define at least one expansion chamber, in particular a plurality of separate expansion chambers, wherein the expansion chamber for is configured to receive working fluid from the working fluid inlet in an accommodating position of the screws at an inlet end of the screws, the expansion chamber being adapted to discharge working fluid to the working fluid outlet at an outlet end of the screws at an outlet end of the screws, the expansion chamber being adapted to move by moving the screws Screws are transported from the inlet end to the outlet end, whereby the volume of the expansion chamber increases.

This object is further achieved according to claim 9 by a station for reducing working fluid pressure, in particular a station for reducing gas pressure, especially a station for reducing natural gas pressure comprising at least one screw expander according to any one of claims 1 to 8 to the pressure of the working gas to be reduced during transport from the working gas inlet to the working gas outlet of the screw expander.

Moreover, the subject matter of claim 10 is achieved by a method of generating mechanical energy by expanding a working fluid in at least one screw expander according to any one of claims 1 to 8.

The screw expander provides mechanical energy, which can then be converted into electrical energy by driving a generator. The mechanical energy generated by the expander can also be used to drive other machines. The expansion can take place in several stages or only in one stage.

Screw expanders use two helical screws, also called rotors, which are engaged with each other, an engaging and a receiving screw, for expanding the working fluid. Therefore, only compressible fluids can be working fluids within the meaning of the invention. Furthermore, control gears can ensure that the engaging and retaining screws keep their exact alignment. In an oil-immersed screw expander, the space between the screws is bridged by lubricating oil, which provides both hydraulic sealing and mechanical energy transfer between the screws. Working fluid enters the high pressure side and moves through the screw threads as the screws rotate. The working fluid, due to its high pressure, forces the way along the screws that are engaged with each other, forcing the screws to rotate. Due to the rotation of the screws, the working fluid travels from the inlet side to the outlet side along the screw expander as the volume of the expansion chambers between the screws increases, so that the working fluid expands as it forces its way along the screw expander. The effectiveness of this mechanism depends on accurate installation spaces between the screws on the one hand and between the screws and the housing enclosing the screws on the other.

The engaging and receiving screws have different profiles. The engagement screw has convex helices which engage the concave cavities between the helices of the locating screws. The space between each two consecutive coils of each screw and its surrounding housing forms a separate expansion chamber. The volume of the expansion chamber increases as the rotation progresses due to the displacement of the contact line between the two screws. The rotation is caused by the working fluid expanding with the expanding expansion chamber. The volume of the expansion chamber is at a minimum of full engagement with the screws on the side of the inlet end to a minimum and at a maximum when approximately the entire length between the coils is not blocked by engagement with the other screw. Preferably, the expansion chamber is in fluid communication with the working fluid inlet when its volume is at a minimum and in fluid communication with the working fluid outlet when the volume is at a maximum. It is also preferred that the expansion chamber is at least substantially closed by a helix of the engagement screw at one end and by one end side of the housing at the opposite end of the expansion chamber.

The working fluid increases its volume in the screw expander steadily. Further, in operation, a plurality of expansion chambers are provided between the screws and the housing. Preferably, the expansion chambers each have different volumes. Consequently, the screw expander releases at least substantially continuously expanded working fluid. The pressure drop depends on the increase in the volume of the expansion chambers.

An efficient screw compressor requires a screw profile that has a large flow area and a short seal line. The larger the cross section, the higher the flow for the same screw sizes and screw speeds. Shorter sealing lines reduce leaks. Preferably, the engagement screw has less helix than the take-up screw, so it rotates faster. It is further preferred that the screws are constructed asymmetrically. The screw expander may have a four-screw engagement screw and a six-screw take-up screw, both of which have the same outside diameter. Other configurations, such as five / six and five / seven and four / five and three / five coils, are also possible. In addition, different outer diameters can be provided. The selection of the helical ratio may depend on the pressure of the working fluid in the working fluid inlet and the desired pressure of the working fluid in the working fluid outlet.

An advantage of the invention is that the pressure of a working fluid withdrawn from a gas line is used directly. Therefore, this invention can be effectively used at pressure reduction stations under various pressure, temperature and flow conditions. This is of particular interest because billions of cubic meters of natural gas flow through millions of gas pressure reduction stations worldwide. Natural gas is transported under high pressure over long distances through pipelines. High gas pressure is reduced to a lower pressure by means of gas pressure reduction stations. At normal stations, the pressure is usually reduced from 16 to 40 bar to less than 5 bar. At present, natural gas pressure is reduced by throttle valves, whereby isenthalpic expansion takes place without using energy but dissipating a large amount of energy, but dissipating a large amount of energy.

During gas expansion gases are cooled (Joule-Thomson effect). The natural gas temperature drop is about 0.5 ° C per 1 bar, depending on the composition of the gas and its properties. Replacing the gas pressure control process by screw expanders that allow the natural gas pressure to be converted to mechanical energy that can be transferred to a load-receiving device, such as an electric generator, thus generating electricity from a previously unused source; is of particular interest to the invention.

The screw expander may preferably be heated externally and / or designed for operation as a compressed-gas-operated turbomachine. Due to its construction, the machine is relatively immune to dirt and particles which could cause erosion on metal vanes of conventional turbines. Further, the screw expander requires much lower investment costs than a conventional multi-blade turbine designed for low pressure gas operation.

If appropriate, multiple screw expanders may be connected in series and / or in parallel with respect to the flow of working fluid. Alternatively or additionally, multi-screw expanders can be connected to each other and to a common output shaft so that respective screw expanders drive the common output shaft together. In this way, higher speeds and / or torques can be applied to the output shaft. The output shaft may drive a power generator or other device based on the difference in potential energy of the working fluid between the working fluid inlet and the working fluid outlet.

Steam has already been used in expanders to generate mechanical energy. This does not apply to compressed gas, especially compressed natural gas, as a working fluid for driving z. B. a power generator. Preferably, the screw expander is driven by compressed gas. Further, it is desirable to generate electricity by driving a power generator with the output shaft of the screw expander. Gas pressure reduction stations worldwide constitute a huge source of energy for generating electricity or driving certain devices.

In a particularly preferred embodiment of the screw expander, the at least one expansion chamber is designed so that the pressure exerted by the working fluid against the screws, which together with the housing surround the expansion chamber, results in a resultant force that moves the screws. The screws therefore rotate so that the expansion chamber is moved from the inlet end and along the screws to the outlet end. Consequently, mechanical energy can be provided very easily and reliably.

Alternatively or additionally, the at least two screws or the at least one pair of screws may have different numbers of intermeshing helical turns. In a particularly preferred embodiment, a screw, in particular an engagement screw, four Schraubenwendelungen and another screw, in particular a receiving screw has six Schraubenwendelungen which are engaged with each other. This can provide a very efficient process.

When at least two screws engaged with each other are synchronized so that the screws do not contact each other while moving the at least one expansion chamber from an inlet end to an outlet end of the screws, a highly reliable process can be provided. In addition, it can be ensured that only very thin gaps exist between the screws and / or between the screws and the inner wall of the housing. Consequently, only a very small amount of working fluid can pass through these gaps without driving the screws.

It is efficient and reliable if at least two screws engaged with each other are synchronized by a connecting and / or synchronizing means, in particular a chain, a belt and / or meshing pinions of the shafts of the screws which engage with each other Are engaged, which connect the waves. Alternatively or additionally, the chain or belt is engaged with pinions of the shafts of the screws which engage with each other, which is preferred in many cases.

For equalizing the temperature drop of the working fluid due to the volume increase of the working fluid, at least one heating means for heating the working gas in the at least one expansion chamber due to indirect heat transfer may be provided. In this regard, it is preferred to install said heating means in the housing. Alternatively or additionally, means for heating the working fluid prior to entering the expansion chamber may be provided, which would be a very simple and reliable method of heating the working fluid.

For electricity generation, it is preferred that the output shaft is connected to a power generator. If this connection is provided via a transmission, the speed can be varied and / or regulated.

It is also preferred that the screw expander be configured as a one-step screw expander that expands the working fluid in a single stage between the working fluid inlet and the working fluid outlet of the screw expander. The screw expander can then be designed less complex.

In a preferred embodiment of the method, working fluid is in the form of a gas used, which is preferably at least substantially free of steam and / or free of water. Alternatively, or moreover, the working fluid used is natural gas. This allows a very efficient and advantageous use of the method.

When the expansion of the working fluid is performed in a single stage while the gas is being transported along the screw expander from the working fluid inlet to the working fluid outlet, the process is very simple and reliable.

The advantages can be achieved especially if it is provided that the working fluid is expanded from a pressure of more than 16 bar, in particular more than 23 bar, especially more than 30 bar, and / or if it is provided that the working fluid to a pressure under 10 bar, especially below 7 bar, especially under 3 bar is expanded.

Alternatively or additionally, the advantages can be utilized in an efficient and preferred manner when the expansion of the working fluid is performed in a station for reducing the working fluid pressure according to claim 8.

• 1 ist ein Schema eines Elektrizitätserzeugungssystems, das einen Schraubenexpander und/oder eine Station zum Reduzieren von Arbeitsfluiddruck, jeweils gemäß der Erfindung, aufweist,
• 2 ist eine Seitenansicht eines Details des Elektrizitätserzeugungssystems von 1,
• 3 ist der Schraubenexpander von 2 in einer vertikalen Querschnittsansicht in der Längserstreckung des Schraubenexpanders,
• 4 ist der Schraubenexpander von 2 in einer vertikalen Querschnittsansicht in der Orthogonalen zur Längserstreckung des Schraubenexpanders und
• 5 ist der Schraubenexpander von 2 in einer horizontalen Querschnittsansicht in der Längserstreckung des Schraubenexpanders.

The invention will be described in more detail based on the attached drawings which show only a preferred embodiment of the invention.

• 1 Figure 11 is a schematic of an electricity generating system having a screw expander and / or a station for reducing working fluid pressure, according to the invention;
• 2 FIG. 10 is a side view of a detail of the electricity generating system of FIG 1 .
• 3 is the screw expander of 2 in a vertical cross-sectional view in the longitudinal extension of the screw expander,
• 4 is the screw expander of 2 in a vertical cross-sectional view in the orthogonal to the longitudinal extent of the screw expander and
• 5 is the screw expander of 2 in a horizontal cross-sectional view in the longitudinal extension of the screw expander.

The electricity generating system, which may be a station for reducing natural gas pressure, has a feed pipe 1 on, the compressed working fluid through a filter 2 , a shut-off device 3 and a check valve 4 if appropriate, a working fluid inlet 5 a screw expander 6 supplies. The screw expander 6 drives an output shaft 7 An electricity generator 8th drives. The check valve 4 if present, allows control of the mass flow of working fluid through the screw expander 6 , In order to at least partially compensate for the cooling of the working fluid due to the expansion of the working fluid, at least one heat exchanger or heat transfer unit may be provided in the feed pipe 1 provided and / or in the screw expander 6 be installed. The in the screw expander 6 expanded working fluid leaves the screw expander 6 through a working fluid outlet 9 in a low pressure tube. The working fluid is preferably filtered at a higher pressure level and the screw expander 6 supplied, in which the expansion of the working fluid is performed, and discharged at a lower pressure level in the low-pressure tube.

In 2 is a detail of the device according to 1 shown. The screw expander 6 is for controlling the speed of the generator 8th over the output shaft 7 mechanically with a gearbox 11 connected. The gear 11 is mechanical with the power generator 8th connected to generate electricity.

In 3 becomes the screw expander 6 shown in detail. The screw expander 6 has a housing 12 on which a pair of screws 13 . 14 which are engaged with each other, is arranged. One of the screws 13 forms the output shaft 7 as an extension of the respective propeller shaft 15 , The waves 15 . 16 the screws 13 . 14 are using respective bearings 17 in the case 12 assembled.

In 4 and 5 becomes the engaged pair of screws 13 . 14 shown in various cross-sectional views. A screw 13 is as an engagement screw 13 with four coils 18 designed while the other screw 14 as a pickup screw 14 with six coils 19 is designed. The helix 18 . 19 the engagement screw 13 and the pickup screw 14 engage each other so that the cavities between two adjacent coils of the receiving screw 14 each at least one of the two opposite ends through the helix 18 the engagement screw 13 getting closed. Consequently, along the pickup screw 14 Several cavities are provided through in the receiving screw 14 engaging helix 18 the engagement screw 13 be separated from each other.

The maximum length of the cavities is therefore smaller than the length of a circumference of a helix 19 the pickup screw 14 , Furthermore, the separate cavities have a different length because at least some of the cavities are at end surfaces 20 . 21 the housing of the mounting screw 14 ending at the working fluid inlet 5 adjacent or to the working fluid outlet 9 adjoin. Because the screws 13 . 14 in a suitable manner in the housing 12 are arranged, form the cavities together with the housing 12 expansion chambers 22 from the work intake 5 to the work outlet 9 grow. The expansion chambers 22 be due to the rotation of the screws 13 . 14 continue on the screw expander 6 transported along. At the same time, the volume of the expansion chambers decreases 22 to. Due to the working fluid pressure, the screws are 13 . 14 driven by therein as well as thereby expanding working fluid. The potential energy of the working fluid is converted into mechanical energy, which is the waves 15 . 16 the screws 13 . 14 drives. The total mechanical energy depends on the enthalpy difference of the working fluid at the working fluid inlet 5 and at the working fluid outlet 9 , the mass flow of the working fluid through the screw expander 6 and the thermodynamic efficiency of the screw expander.

Sprockets can with the waves 15 . 16 the screws 13 . 14 be connected to the speed of the screws 13 . 14 to synchronize. But there are also other synchronization means possible. Due to the synchronization of the waves 15 . 16 the screws 13 . 14 touch the coil 18 . 19 the screws 13 . 14 not mutually, but are separated by a very thin gap. Furthermore, touch the coil 18 . 19 the screws 13 . 14 not the case 12 but are due to very thin gaps from the inner wall of the housing 12 separated. In addition, the screw expander shown is 6 a one-step screw expander 6 because the expansion takes place in just one step. The screw expander 6 but could also be used as a multi-stage screw expander 6 be designed.

It is also preferred that the temperature and / or pressure of the working fluid be prior to entering the expansion chambers 22 and / or after discharge from the expansion chambers 22 is measured. For example, based on the respective temperature and / or pressure values, a controller may check whether the working fluid should be heated and determine the required heat. Thus, the control unit may provide the appropriate heating based on the measured temperature and / or pressure values. If appropriate, the mass flow of the working fluid may also be measured to increase the efficiency of the control process.

Claims (14)

A screw expander (6) for generating mechanical energy by expanding a working fluid comprising at least one housing (12), at least two screws (13, 14) or at least one pair of screws (13, 14) at least partially in said housing (12), at least one output shaft (7) connected to at least one of the screws (13) so that the output shaft (7) can be driven by rotational movement of the at least one screw (13, 14), at least one working fluid inlet (5) to the housing (12) disposed at an inlet end of the screws (13, 14) and at least one working fluid outlet (9) located at an outlet end of the screws (13, 14) along the screws (13, 14) opposite to the inlet end wherein the two screws (13, 14) are engaged with each other such that the two screws (13, 14) and the housing (12) comprise at least one expansion chamber (22), in particular a plurality of separate expansion chambers (22), along the screws (13, 14), the expansion chamber (13, 14) being adapted to receive working fluid from the working fluid inlet (5) at an inlet end of the screws (13, 14) in a receiving position of the screws (13, 14); wherein the expansion chamber (22) is adapted to discharge working fluid to the working fluid outlet (9) at an outlet end of the screws (13, 14) at an outlet position of the screws (13, 14), the expansion chamber (14) being adapted to move the screws (13, 14) to be transported from the inlet end to the outlet end, whereby the volume of the expansion chamber (22) increases. Screw expander after Claim 1 , characterized in that the at least one expansion chamber (22) is designed so that the pressure exerted by the working fluid against the screws (13, 14) which together with the housing (12) define the expansion chamber (22) results in a resultant force which moves the screws (13, 14) so as to move the expansion chamber (22) along the screws (13, 14) towards the outlet end. Screw expander after Claim 1 or 2 , characterized in that the at least two screws (13, 14) or the at least one pair of screws (13, 14) have different numbers of intermeshing screw threads and in particular one screw (13) has four screw threads and another screw (14) has six screw threads has engaged with each other. Screw expander after one of Claims 1 to 3 , characterized in that the at least two Screws (13, 14) engaged with each other are synchronized so that the screws (13, 14) do not contact each other while moving the at least one expansion chamber (22) from an inlet end to an outlet end of the screws (13, 14) move. Screw expander after Claim 4 , characterized in that the at least two screws (13, 14) engaged with each other are synchronized by a connecting and / or synchronizing means, in particular a chain, a belt and / or pinions of the shafts of the screws engaged with each other (13, 14) which engage with each other connecting the shafts (15, 16) and in particular the chain or belt with pinions of the shafts (15, 16) of the screws (13, 14) engaged with each other are engaged. Screw expander after one of Claims 1 to 5 characterized in that heating means are provided for heating the working gas in the at least one expansion chamber (22) due to indirect heat transfer, in particular in the housing (12), and / or means for heating the working fluid prior to entering the expansion chamber ( 22). Screw expander after one of Claims 1 to 6 , characterized in that the output shaft (7) is connected to a power generator (8), in particular via a transmission (11). Screw expander after one of Claims 1 to 6 characterized in that the screw expander (6) is designed as a single stage screw expander (6) which expands the working fluid in a single stage between the working fluid inlet (5) and the working fluid outlet (9) of the screw expander. Station for reducing working fluid pressure, in particular station for reducing gas pressure, especially station for reducing natural gas pressure, the at least one screw expander (6) according to one of Claims 1 to 8th to reduce the pressure of the working gas during transport from the working gas inlet (5) to the working gas outlet (9) of the screw expander (6). A method for generating mechanical energy by expanding a working fluid in at least one screw expander (6) according to any one of Claims 1 to 8th , Method according to Claim 10 wherein the working fluid is a gas that is at least substantially free of steam and / or free of water and / or wherein the working fluid is natural gas. Method according to Claim 10 or 11 wherein the working fluid expands in a single stage as the gas is transported along the screw expander (6) from the working fluid inlet (5) to the working fluid outlet (9). Method according to one of Claims 10 to 12 , wherein it is provided that the working fluid expands from a pressure of more than 16 bar, in particular more than 23 bar, especially more than 30 bar, and / or wherein it is provided that the working fluid to a pressure below 10 bar, in particular below 7 bar, especially under 3 bar expanded. Method according to one of Claims 10 to 13 wherein it is provided that the working fluid in a station for reducing the working fluid pressure after Claim 8 expanded.

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