Method and screw spindle pump for delivering a gas/liquid mixture

Abstract

Method for delivering a gas/liquid mixture fluid via a screw spindle pump that has a housing in which a drive spindle and a running spindle are accommodated. The spindles delimit together with the housing multiple pump chambers. A respective one of the pump chambers that is initially open toward the respective fluid inlet is closed off. The resulting closed-off pump chamber is moved axially toward the fluid outlet and, there, upon attainment of an opening rotation angle, is opened toward the fluid outlet. The drive spindle is driven so that the pressure in the respective pump chamber prior to and/or upon attainment of the opening rotation angle is increased in relation to the suction pressure of the screw spindle pump by at most 20% or by at most 10% of a difference in pressure between the suction pressure and the pressure in the region of the fluid outlet.

Claims

1. A method for delivering a fluid which is a gas/liquid mixture by way of a screw spindle pump, said screw spindle pump having a housing which forms at least one fluid inlet and one fluid outlet and in which at least one drive spindle and at least one running spindle, coupled in terms of rotation to the latter, of the screw spindle pump are accommodated, which spindles, in each rotation position of the drive spindle, delimit together with the housing multiple pump chambers, wherein the drive spindle is rotated by a drive in a drive direction, whereby a respective one of the pump chambers that is initially open toward the respective fluid inlet is closed off, the resulting closed-off pump chamber is moved axially toward the fluid outlet and, there, upon attainment of an opening rotation angle, is opened toward the fluid outlet, wherein the drive spindle is driven in such a manner that, for a given pump geometry of the screw spindle pump, the pressure in the respective pump chamber prior to and/or upon attainment of the opening rotation angle is increased in relation to the suction pressure of the screw spindle pump, which prevails in the region of the respective fluid inlet, by at most 20% or by at most 10% of a difference in pressure between the suction pressure and the pressure in the region of the fluid outlet.

2. The method according to claim 1, wherein the screw profiles of the respective drive spindle and running spindle are selected in such a way that the mean value of the number of pump chambers per drive spindle and running spindle that are closed off both with respect to the fluid inlet and with respect to the fluid outlet is at most 1.5 over a rotation angle of the drive spindle of 360°.

3. The method according to claim 1, wherein, in the context of the method, during at least one time interval, a gas/liquid mixture with a gas proportion of at least 90% is delivered, and/or in that, in the context of the method, during at least one further time interval, a gas/liquid mixture with a liquid proportion of at least 70% is delivered.

4. The method according to claim 1, wherein the pump geometry and the rotational speed of the screw spindle pump used are selected in such a way that the axial speed of the respective pump chamber during the axial movement toward the fluid outlet is at least 4 m/s.

5. The method according to claim 1, wherein the pump geometry of the screw spindle pump used is selected in such a way that the inner diameter of the screw profile of the drive spindle or of at least one of the drive spindles and/or of the running spindle or of at least one of the running spindles is less than 0.7 times the outer diameter of the respective screw profile.

6. The method according to claim 1, wherein the pump geometry of the screw spindle pump used is selected in such a way that the mean circumferential gap between the outer edge of the screw profile of the drive spindle or of at least one of the drive spindles and/or of the running spindle or of at least one of the running spindles and the housing is less than 0.002 times the outer diameter of the respective screw profile.

7. The method according to claim 1, wherein the pump geometry and the rotational speed of the screw spindle pump used are selected in such a way that the circumferential speed at the profile outer diameter of the drive spindle or of at least one of the drive spindles and/or of the running spindle or of at least one of the running spindles is at least 15 m/s.

8. A screw spindle pump for delivering a fluid which is a gas/liquid mixture, wherein the screw spindle pump has a housing which forms at least one fluid inlet and one fluid outlet and in which at least one drive spindle and at least one running spindle, coupled in terms of rotation to the latter, of the screw spindle pump are accommodated, which spindles, in each rotation position of the drive spindle, delimit together with the housing multiple pump chambers, wherein the screw spindle pump has a drive which is configured to rotate the drive spindle in a drive direction, whereby a respective one of the pump chambers that is initially open toward the respective fluid inlet is closed off, the resulting closed-off pump chamber is moved axially toward the fluid outlet and, there, upon attainment of an opening rotation angle, is opened toward the fluid outlet, wherein the screw profiles of the respective drive spindle and running spindle are selected in such a way that the mean value of the number of pump chambers per drive spindle and running spindle that are closed off both with respect to the fluid inlet and with respect to the fluid outlet is at most 1.5 over a rotation angle of the drive spindle of 360°, wherein the drive or a control device controlling the drive may be configured in such a way that, in at least one operating state of the screw spindle pump, the drive spindle is operated at least at a minimum rotational speed at which the pressure in the respective pump chamber prior to and/or upon attainment of the opening rotation angle is increased in relation to the suction pressure of the screw spindle pump, which prevails in the region of the respective fluid inlet, by at most 20% or by at most 10% of a difference in pressure between the suction pressure and the pressure in the region of the fluid outlet.

9. The screw spindle pump according to claim 8, wherein the inner diameter of the screw profile of the drive spindle or of at least one of the drive spindles and/or of the running spindle or of at least one of the running spindles is less than 0.7 times the outer diameter of the respective screw profile.

10. The screw spindle pump according to claim 8, wherein the mean circumferential gap between the outer edge of the screw profile of the drive spindle or of at least one of the drive spindles and/or of the running spindle or of at least one of the running spindles and the housing is less than 0.002 times the outer diameter of the respective screw profile.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In the drawing:

(2) FIGS. 1 to 3 show various detail views of an exemplary embodiment of a screw spindle pump according to the invention, by way of which an exemplary embodiment of the method according to the invention is carried out,

(3) FIGS. 4 to 7 show an illustration of the change in the geometry of the pump chamber when being opened toward the fluid outlet in the exemplary embodiment of the method according to the invention, and

(4) FIG. 8 shows test measurements concerning the effect of large gas proportions on the required drive power.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIGS. 1, 2 and 3 show various detail views of a screw spindle pump which serves for delivery of a fluid that is a gas/liquid mixture. Here, FIG. 1 schematically shows a perspective view of the drive spindle 5 and the running spindle 6 of the screw spindle pump 1, wherein, for reasons of clarity, the housing 2 is not illustrated in FIG. 1. FIG. 1 illustrates in particular the shape of the screw profiles of the drive spindle 5 and the running spindle 6, and also the interengagement thereof.

(6) FIG. 2 shows a face section, in which there can be seen in particular the interaction of the drive spindle 5 and the running spindle 6 with the housing 2 for forming multiple separate pump chambers 7, 8, 9, which are in turn indicated in FIG. 1 since they extend beyond the section plane shown in FIG. 2.

(7) For illustrating the transport of fluid from a fluid inlet 3, formed by the housing 2, to a fluid outlet 4, formed by the housing 2, by way of operation of the drive spindle 5 and the running spindle 6, FIG. 3 moreover illustrates a section perpendicular to the axial direction and to the plane in which the axes of rotation of the drive spindle 5 and the running spindle 6 lie.

(8) The running spindle 6 is coupled in terms of rotation to the drive spindle 5 by a coupling device (not illustrated), wherein a 1:1 transmission ratio is assumed in the example.

(9) Consequently, when the drive shaft 5 is driven by the drive 10 in the drive direction 11, the running spindle 6 is rotated in the opposite direction of rotation 12 and at the same rotational speed. The rotational speed of the drive spindle 5 and thus also of the running spindle 6 can be predefined by a control device 32 of the drive 10.

(10) The interengagement of the screw profiles of the drive spindle 5 and the running spindle 6 results in the fluid situated in the housing 2 being received in multiple pump chambers 7, 8, 9 which are separated from one another. The separation or closure of the pump chambers 7, 8, 9, owing to the radial gap 25 between housing 2 and drive spindle 5 or running spindle 6 and owing to remaining axial gaps between the interengaging screw profiles, is not completely tight, but rather allows a certain exchange of fluid between the pump chambers 7, 8, 9, which may also be regarded as leakage.

(11) In the rotation position shown in FIG. 1 of the drive spindle 5 and of the running spindle 6, the pump chamber 7 is open toward the fluid inlet 3 since the free end 13 of the wall 17 of the screw thread of the drive spindle 5 is directed upward in FIG. 1, whereby a gap remains between said free end 13 and the running spindle 6 in a circumferential direction, through which the fluid can flow between the pump chamber 7 and the fluid inlet 3. Correspondingly, the pump chamber 8, which is highlighted by dots on its outer surface in FIG. 1, is open toward the fluid outlet 4, since the free end 14 of the wall 17 delimiting said pump chamber, owing to the rotation position, is in turn spaced apart from the running spindle 6 and thus forms a radial gap through which the fluid can flow. The pump chamber 9 is closed off both with respect to the fluid inlet 3 and with respect to the fluid outlet 4.

(12) When the drive spindle 5 is driven in the drive direction 11, firstly the free end 13 of the wall 17 is moved to the running bobbin 6 and the initially open pump chamber 7 is thereby closed off. Further rotation then leads to the displacement of the closed-off pump chamber toward the fluid outlet 4. Upon attainment of a certain opening rotation angle, the pump chamber is then opened toward the fluid outlet 4, wherein, upon further rotation through 90° after attainment of the opening rotation angle, the result is the arrangement as is illustrated for the pump chamber 8 in FIG. 1, in which there is already a resulting gap in a circumferential direction that has a certain width between the free end 14 and the running bobbin 6.

(13) The procedure described for transporting liquids or else gas/liquid mixtures through a screw spindle pump 1 is known per se in the prior art. Consequently, further details and possible modifications, for example the use of multiple fluid inlets or multiple running spindles, shall not be discussed in any more detail.

(14) Screw spindle pumps are commonly used in areas in which significant differences in pressure of for example 5 to 50 bar between the fluid inlet 3 and the fluid outlet 4 can occur. If, in this case, a gas/liquid mixture is delivered, the result here is a compression of the gas proportion. Conventional screw spindle pumps are in this case designed in such a way that a relatively large number of pump chambers closed off with respect to one another, for example five to ten pump chambers closed off with respect to one another, in an axial direction is the result. The compression of the gas is realized here in the individual pump chambers in that liquid flows back from the pump chamber which is in each case adjacent in the direction of the fluid outlet, in which pump chamber a relatively high pressure already prevails, and thereby reduces the volume in the pump chamber that is available for the gas, which leads to compression of the gas. As already discussed in the general part of the description, such a compression of the gas proportion does however lead to the power requirement of the screw spindle pump, in the case of large gas proportions, being relatively high, specifically approximately as high as in the case of liquid delivery.

(15) It has been found that the power consumption in the case of delivery of gas/liquid mixtures with a large gas proportion can be reduced significantly if gas compression by such a backflow of liquid is largely avoided and thus the compression of the gas and thus also the increase of pressure in the pump chambers 7, 8, 9 is realized substantially only after the pump chamber 8 is opened toward the fluid outlet 4. This is achieved in the screw spindle pump illustrated in FIGS. 1 to 3 through selection of a suitable pump geometry, on the one hand, and through use of a sufficiently high rotational speed, on the other hand. In this way, it can be achieved that, in relation to the suction pressure of the screw spindle pump 1, which prevails in the region of the fluid inlet 3, the pressure in the respective pump chamber 7, 8, 9 prior to and/or upon attainment of the opening rotation angle is increased by only a few percent of the difference in pressure between the suction pressure and the pressure in the region of the fluid outlet 4. For example, the pressure in the pump chamber when being opened can be above the suction pressure by at most 10% or at most 20% of the difference in pressure.

(16) If it is then approximately assumed that only a negligible part of the fluid 23, in particular of the liquid proportion of the fluid 23, flows from the region of the fluid outlet 4 back into the open pump chamber 8, then this corresponds approximately to a compression of the fluid in the chamber 8 against a stationary fluid wall 33 in the region of the fluid outlet 4. The rotation of the drive spindle 5 in the drive direction 11, as will be explained in more detail below with reference to FIGS. 4 to 7, leads in this case to a reduction in the volume of the pump chamber 8 and thus to a compression of the gas proportion and an increase in pressure. It is thus possible to achieve degrees of efficiency similar to those in the case of gas compressors, which implement compression of gas through delivery against a rigid wall. At the same time, however, liquids with a large liquid proportion can still be delivered, which would not be possible with conventional gas compressors.

(17) At a point in time prior to the point in time shown in FIG. 1, at which the drive spindle 5, in comparison with the position illustrated in FIG. 1, is rotated through 90° counter to the drive direction 11, the the pump chamber 8 is just closed off and has the shape shown in FIG. 4. This position corresponds to the opening rotation angle, since an infinitesimal rotation in the drive direction 11 from this position opens the pump chamber 8.

(18) With the pump chamber 8 closed, the outer surface 24 of the pump chamber 8 is delimited by the housing 2, the inner surface 18 is delimited by the inner diameter 19 of the drive spindle 5, the face surface 16 is delimited by the wall 17 of the thread of the screw spindle 5 forming the pump chamber 8, and the concealed surfaces 20, 21 are delimited by the running spindle 6.

(19) When the drive shaft 5 is rotated in the drive direction 11, the pump chamber 8 is opened in that the free end with respect to the pump chamber 8 is displaced into the position 34 shown in FIG. 5. Consequently, the wall 17 no longer delimits the pump chamber toward the fluid outlet 4 over the entire surface of the pump chamber, but rather the surface portion 22 is exposed or is delimited by the fluid wall 33. If the fluid wall 33, as explained above, is approximately assumed to be rigid, this leads to a compression of the gas in the pump chamber 8 due to a reduction in the volume of the pump chamber 8.

(20) Further rotation of the drive spindle 5 in the drive direction 11 through 90° leads to the shape of the pump chamber 8 illustrated in FIG. 6 and thus to a further compression.

(21) FIG. 7 shows a further state of rotation with even greater compression.

(22) The behavior described could in principle also be achieved with conventional pump geometries solely through selection of a sufficiently high rotational speed, wherein, under some circumstances, the required high rotational speeds can lead to high loading or a high level of wear of the pump. The screw spindle pump 1 therefore uses a specific pump geometry, with which the described behavior can be achieved even at relatively low rotational speeds, for example even at 1000 revolutions per minute or 1800 revolutions per minute. In particular, instead of the use of a multiplicity of pump chambers which follow one after the other in an axial direction, said use being customary in screw spindle pumps, relatively few pump chambers or turns of the screw threads of the drive spindle 5 and of the running spindle 6 are used. In the rotation position shown in FIG. 1, only exactly one pump chamber 9 is closed off both with respect to the fluid inlet 3 and with respect to the fluid outlet 4. Dependent on the specific geometrical configuration of the free ends 13, 14 of the wall 17, the result in this case, in the example shown, can be at most one or at most two simultaneously closed-off pump chambers irrespective of the state of rotation of the drive spindle 5 and of the running spindle 6. The suitable maximum number of pump chambers which can be simultaneously closed off scales with the number of fluid inlets, so that, in the case of a two-channel pump, typically twice as many pump chambers can be simultaneously closed off than in the case of a single-channel pump. Moreover, the maximum number of pump chambers which are simultaneously closed off can scale with the number of running spindles and/or drive spindles used.

(23) The use of relatively few pump chambers following one after the other in an axial direction and thus of relatively few pump chambers which can be maximally closed off simultaneously allows axially relatively long pump chambers and thus pump chambers with a relatively large volume to be realized, whereby the same amount of a liquid flowing back into the pump chamber through gaps has a smaller influence on the pressure in the pump chamber.

(24) Furthermore, for achieving a large volume of the pump chambers 7 to 9, it is advantageous for the inner diameter 19 of the screw profile of the drive and running spindles 5, 6, as can be clearly seen in particular in FIG. 2, to be significantly smaller, smaller approximately by a factor of 2 in the example, than the outer diameter 24 of the respective spindle.

(25) For the purpose of avoiding excessive compression and thus an excessive increase in pressure prior to the opening of the respective pump chamber 7, 8, 9, it is also expedient to minimize the backflow of liquid into the respective pump chamber through use of narrow gaps in the screw spindle pump 1. In particular, the radial gap 25 between the housing 2 and the respective outer diameter 24 of the drive spindle 5 or of the running spindle 6 can be narrower than two thousandths of the outer diameter 24.

(26) As explained, the pump geometry of the screw spindle pump 1 and a sufficiently high rotational speed interact to achieve the effects mentioned above. Here, for a given pump geometry, the rotational speed should be selected in such a way that the axial speed of the movement of the respective pump chamber 7, 8, 9 toward the fluid outlet 4 is at least four meters per second, and/or that the circumferential speed at the profile outer diameter 24 of the drive spindle 5 or the running spindle 6 is at least 15 meters per second.

(27) FIG. 8 shows for test measurements on a prototype the relationship between the difference in pressure between the suction pressure of the screw spindle pump and the pressure in the region of the fluid outlet, which is plotted on the X-axis 26, and the drive power required for achieving said difference in pressure, which is indicated on the Y-axis. Here, the curves 28, 29 show this relationship for a rotational speed of 1000 revolutions per minute, wherein the relationship as per curve 28 is the result in the case of transport of liquid only and the relationship as per curve 29 is the result in the case of a gas proportion of 95% of the fluid delivered. As can be clearly seen in FIG. 8, the required drive powers in the two cases are very similar, that is to say, at a rotational speed of 1000 revolutions per minute, the prototype still exhibits the behavior of conventional screw spindle pumps.

(28) The curves 30, 31 show the same relationship for a rotational speed of 1800 revolutions per minute. Here, the curve 30 relates to the transport of a pure liquid, and the curve 31 relates to the transport of a fluid with a gas proportion of 95%. Through selection of a sufficiently high rotational speed, it is achieved here that, in the case of a large gas proportion in the delivered fluid, during the opening of the respective pump chamber, the pressure therein is only slightly above the suction pressure, whereby considerably less drive power is required for delivered fluid with a large gas proportion than for delivery of liquids. In the example shown, approximately 25% less power is required for operating the screw spindle pump. As mentioned above, this effect can be achieved even at lower rotational speeds through suitable modification of the pump geometry.

(29) While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.