Method for conveying a working medium

Abstract

A method for conveying a working medium within a supply line (2), wherein a pig package (48) is moved into the supply line (2) by means of a pushing medium conveyed by a first pump (40) to a proximal end of the supply line (2), is intended to enable TPS operation in a manner that is as technically simple as possible. To this end, a first conveying quantity of the pushing medium is determined by means of a first flow-measuring cell (44) associated with the proximal end, wherein a position of the pig package (48) in the supply line (2) is determined from the first conveying quantity and information about the cross-section of the supply line (2).

Claims

1. A method for conveying a working medium within a supply line (2), wherein a pig package (48) is moved into the supply line (2) by means of a pushing medium conveyed by a first pump (40) to a proximal end of the supply line (2), wherein a first conveying quantity of the pushing medium is determined by means of a first flow-measuring cell (44) associated with the proximal end, and wherein a position of the pig package (48) in the supply line (2) is determined from the first conveying quantity and information about the cross-section of the supply line (2).

2. The method according to claim 1, in which a targeted change in position of the pig package (48) is effected by controlling the first pump (40).

3. The method according to claim 1, wherein the pig package (48) consists of at least two pigs (50, 52), wherein by means of a feed line (14, 18) leading to the interspace (54) between two pigs and arranged on the supply line (2), the working medium is introduced into the interspace (54) or discharged therefrom, wherein the supply line (2) is filled with pushing medium on both sides of the pig package (48), wherein a second conveying quantity of the pushing medium is determined by means of a second flow-measuring cell (46) associated with a distal end of the supply line (2), and wherein a volume of the working medium introduced into the interspace (54) or discharged therefrom is determined from the first and second conveying quantity and information about the cross-section of the supply line (2).

4. The method according to claim 3, in which a pushing medium is conveyed into the distal end of the supply line (2) by a second pump (42).

5. The method according to claim 4, in which a targeted change in position of the pig package (48) is effected by controlling the second pump (42).

6. The method according to any of claim 3, in which by controlling the first and/or the second pump (40, 42) a change in position of the pig package (48) is effected in such a way that the feed line (14, 18) opens into the interspace (54).

7. The method according to claim 2, in which the change in position is effected with variable speed.

8. The method according to claim 1, in which the working medium is a coating material.

9. A control device for a system (1) for conveying a working medium within a supply line (2), designed to carry out the method according to claim 1.

10. A system (1) comprising a supply line, a first pump, (40) associated with a proximal end of the supply line (2), for a pushing medium for moving a pig package (48) into the supply line (2), further comprising a flow-measuring cell (44) associated with the proximal end, designed to determine a first conveying quantity of the pushing medium, and a control device designed to determine a position of the pig package (48) in the supply line (2) from the first conveying quantity and information about the cross-section of the supply line (2).

11. The system (1) according to claim 10, in which the control device is further designed to effect a targeted change in position of the pig package (48) by controlling the first pump (40).

12. The system (1) according to claim 10, wherein the pig package (48) consists of at least two pigs (50, 52), wherein on the supply line (2) there is a feed line (14, 18) for introducing or discharging the working medium into the interspace (54) between the two pigs (50, 52), wherein the supply line (2) is filled with pushing medium on both sides of the pig package (48), further comprising a second flow-measuring cell (46) associated with the distal end, designed to determine a second conveying quantity of the pushing medium, the control device being further designed to determine a volume of the working medium introduced into the interspace (54) or discharged therefrom from the first and second conveying quantity and information about the cross-section of the supply line (2).

13. The system (1) according to claim 12, further comprising a second pump (42) associated with the distal end of the supply line (2) for conveying pushing medium into the distal end of the supply line (2).

14. The system (1) according to claim 13, in which the control device is further designed to effect a targeted change in position of the pig package (48) by controlling the second pump (42).

15. The system (1) according to claim 12, in which the control device is further designed to effect a change in the position of the pig package (48) by controlling the first and/or the second pump (40, 42) in such a way that the feed line (14, 18) opens into the interspace (54).

16. The system (1) according to claim 11, comprising a flow control device, associated with the proximal and/or the distal end of the supply line (2), for the pushing medium for varying the speed of the position change.

17. The system (1) according to claim 9, in which the working medium is a coating material.

Description

[0024] An exemplary embodiment of the invention is explained in more detail by means of drawings. They show:

[0025] FIG. 1 a schematic diagram of a system with a supply line for paint according to the prior art, and

[0026] FIGS. 2 to 5 steps of a method for conveying paint through the supply line.

[0027] Identical parts are marked with the same reference signs in all drawings.

[0028] FIG. 1 shows a schematic diagram of a known system 1 with a supply line 2 for conveying a working medium, which in the exemplary embodiments described here is paint. Such a system 1 is used, for example, in a painting plant. It connects various paint reservoirs 4, 6 of different paint colors with points of consumption 8, 10, 12, each of which comprise an applicator for paint. Paint reservoirs 4, 6 as well as points of consumption 8, 10, 12 are each connected to the inside of the supply line via a feed line 14, 16, 18, 20, 22. In the feed lines 14, 16 in FIG. 1, pumps 24, 26 are shown for conveying the paint from the paint reservoir 4, 6. In principle, all feed lines 14, 16, 18, 20, 22 can contain such pumps or valves to shut off the feed line 14, 16, 18, 20, 22; however, these are not shown in FIG. 1.

[0029] The transport of the different coating agents or paints through the supply line 2 and the separation of different paints as well as of paint and pushing medium is done by means of pigs not shown in FIG. 1. A pig is an approximately circular-cylindrical object, waisted in the middle, which tightly fills the cross-section of the line and is pressed through the supply line 2 by means of a pushing medium and pushes the medium to be pushed out in front of it. For this purpose, system 1 has pig stations 28, 30 at the beginning and end of the supply line, which serve as sluices through which the pig can be inserted and removed from supply line 2.

[0030] The system 1 shown in FIG. 1 is designed for the paint recovery technique suitable for frequently used paints. For this purpose, the supply line 2 is filled with the corresponding paint from one of the paint reservoirs 4, 6, and after completion of the painting process, the paint quantity still in the supply line 2 is returned to the corresponding paint reservoir 4, 6 by means of the pigging technique described. The pushing medium used in the exemplary embodiments is a liquid cleaning agent, which is applied to the pig on the other side.

[0031] If, however, less frequently used special colors are to be used, the TPS process (tracking paint supply) should be applied for this purpose, in which only the exact amount of paint is filled in as is required at the points of consumption 8, 10, 12 to be supplied. The upgrading of system 1 for the TPS method and the implementation of the method is shown in FIGS. 2 to 5.

[0032] FIG. 2 shows the correspondingly modified system 1, although for reasons of clarity the pig stations 28, 30 are not shown. In addition, only one paint reservoir 4 with pump 24 and feed line 14 and a point of consumption 8 with feed line 18 is shown in each case, although there are actually several in each case, as described for FIG. 1.

[0033] The supply line 2 has at both ends a symmetrically designed pushing medium feed line 32, 34, which leads from a pushing medium reservoir 36, 38 into the respective end of the supply line 2. Each of the pushing medium feed lines 32, 34 has a pump 40, 42 and a flow-measuring cell 44, 46, which measures the volume flow, i.e. the volume of pushing medium flowing through per time unit. The pumps 40, 42 and flow-measuring cells 44, 46 are connected on the data side to a control device, not shown in detail, which analyzes the information from the flow-measuring cells 44, 46 and controls the pumps 40, 42. The control unit also stores precise information about the cross-sectional profile of the pushing medium feed lines 32, 34 and the supply line 2.

[0034] In the first step of the method shown in FIG. 2, a pig package 48, consisting of two pigs 50, 52 in contact with each other, is moved into the supply line 2. At least one of the pigs 50, 52 has a protrusion on the side facing the other pig 50, 52, so that a gap 54 remains between them. In the exemplary embodiment shown here both pigs 50, 52 have such protrusions. The position of the pig package 48 is determined and changed indirectly via the measurements in the flow-measuring cells 44, 46. Since the exact volume of pushing medium introduced into or discharged from the supply line 2 by means of the pumps 40, 42 can be determined and, in addition, the cross-sectional profile of the pushing medium feed lines 32, 34 and the supply line 2 is known, the control device can determine the exact longitudinal extension of the pushing medium column on both sides of the pig package 48 and from this the position of the pig package 48. Accordingly, the control unit can also control the pumps 40, 42 accordingly to achieve a targeted change of position.

[0035] This change in position is effected by the force of the pushing medium acting on one side of the pig package 48. By means of the force exerted, said package is moved, wherein the sealing element of each pig 50, 52 provides a contact surface for the pushing medium. Thus, on the one side of the pig package 48, the pushing medium exerts a force on the contact surface of the sealing element provided there, whereby as a result of the forces exerted on its contact surfaces, it is pressed against the inner wall of the supply line 2. The sealing elements of the pigs 50, 52 are thereby dimensioned in such a way that they already lie sealingly against the inner wall of the supply line 2, even if the pig 50, 52 is not moved in it. When the pig is driven inside the supply line 2, the sealing elements move along the inner wall of the supply line 2, by means of which liquid medium adhering to the inner wall is drawn off and pushed in front of the pig 50, 52 in the direction of movement of the pig.

[0036] By appropriately controlling the pumps 40, 42, the pig package 48 in the supply line 2 is displaced in the step shown in FIG. 2 such that the interspace 54 is arranged in such a way that the feed line 14 leads from the paint reservoir 4 into the interspace 54.

[0037] In the next step, shown in FIG. 3, the control unit controls the pump 24 for the paint from the paint reservoir 4. The pig 50 is thereby kept in a constant position by the corresponding closing the supply line 2 on the left side of FIG. 3, for example by a valve not shown in detail. By conveying paint through the pump 24 into the interspace 54, a force is exerted on the pig 52 on the right side in FIG. 3, so that it is pushed further along in the supply line 2 and pushing medium is supplied into the pushing medium reservoir 38. The exact quantity of the displaced pushing medium is recorded in the flow-measuring cell 46. It corresponds exactly to the quantity of paint introduced into the interspace 54, so that the control deviceagain indirectlyknows exactly the quantity of paint introduced and stops the paint supply by means of the pump 24, as soon as a sufficient quantity of paint is contained in the interspace 54.

[0038] In the next step, shown in FIG. 4, the pig package 48, which now transports the defined quantity of paint in its interspace 54 between the pigs 50, 52, is moved on in the feed line 2 by controlling the pumps 40, 42 while monitoring the position by means of the flow-measuring devices 44, 46, until the interspace 54 containing the paint is positioned in such a way that the feed line 28 to the point of consumption 8 opens into the interspace 54. The pumps 40, 42 are hereby designed in such a way that their speed is variable. They are therefore also suitable for variably controlling the flow of pushing medium. In the exemplary embodiment, this is used to accelerate the speed of the pig package 48 during transport to the target position on the feed line 28. In the vicinity of the feed line 28, the speed of movement is reduced for fine adjustment. In alternative, not shown exemplary embodiments, this can also be achieved by separate proportional valves or variable orifices in the area of the pumps 40, 42.

[0039] At the target point, a valve not shown in detail in feed line 28 is opened. Now the pig 52 on the right side in FIG. 4 is kept in a constant position by correspondingly closing the supply line 2 on the right side in FIG. 4, for example by a valve not shown in detail. The pump 40 is actuated by the control unit so that the interspace 54 is compressed. In this way, the paint is transported into the feed line 18. The thereby introduced volume of pushing medium measured at the flow-measuring cell thereby corresponds to the volume of paint introduced into the feed line 18.

[0040] Lastly, FIG. 5 shows the situation after the required quantity has been fed into the point of consumption 8. The quantity of paint in the interspace 54 is reduced accordingly. Now the valve, which is not shown in detail, in feed line 18 is closed. Subsequently, the pig package 48 with the paint still contained in it can be fed to the other points of consumption 10, 12, which are not shown in FIGS. 2 to 5. The positioning and determination of the position of the pig package 48 as well as the determination of the volume of paint in the pig package 48 is carried out as described above.

REFERENCE SIGN LIST

[0041] 1 System [0042] 2 Supply line [0043] 4, 6 Paint reservoir [0044] 8, 10 [0045] 12 Point of consumption [0046] 14, 16, [0047] 18, 20, [0048] 22 Feed line [0049] 24, 26 Pump [0050] 28, 30 Pig station [0051] 32, 34 Pushing medium feed line [0052] 36, 38 Pushing medium reservoir [0053] 40, 42 Pump [0054] 44, 46 Flow-measuring cell [0055] 48 Pig package [0056] 50, 52 Pig [0057] 54 Interspace