METHOD FOR DRAINING WATER FROM A TANK

Abstract

The invention relates to a method for draining water from a tank (22), more particularly a clarification tank, wherein water is optionally drained via a draining apparatus while maintaining a substantially constant liquid level (23).

Claims

1. A method for draining water from a tank (22), in particular from a clarification tank, wherein the water is optionally drained via a draining apparatus while maintaining a substantially constant liquid level (23), wherein the drainage is controlled by a selective supply of compressed air into a blocking volume (24) which is provided above at least one drainage opening (3) of a discharge device (1) firmly fixed in the tank.

2. The method according to claim 1, wherein the drainage of water is interrupted by introducing sufficient compressed air into the blocking volume (24) in order to lower the liquid level (23) in the blocking volume (24) to a level below the drainage opening (3).

3. The method according to claim 1, wherein the drainage is triggered by discharging compressed air from the blocking volume (24) in order to raise the liquid level (23) in the blocking volume (24) to a level above the discharge opening (3).

4. The method according to claim 1, wherein the drained water is allowed to flow into an overflow space (25) with an overflow weir (10), via which the water can flow off freely.

5. The method according to claim 1, wherein the compressed air is fed into a drainage pipe, inside which the blocking volume (24) is provided, and that the drainage of water takes place via at least one drainage opening (3), which is arranged in a lower region of the drainage pipe (1).

6. A draining apparatus for draining water from a tank (22), in particular from a clarification tank, comprising a discharge device (1) immersed in the tank (22) and having at least one drainage opening (3) which opens into the tank (22), wherein a device is provided for selectively supplying compressed air into the blocking volume (24), wherein the draining apparatus is fixedly mounted in the tank (22).

7. The draining apparatus according to claim 6, wherein the discharge device (1) is closed upwards by a cover (2) in order to form the blocking volume (24) between the discharge device (1) and the cover (2).

8. The draining apparatus according to claim 6, wherein the discharge device is designed as a horizontally disposed drainage pipe (1), and that the drainage opening (3) is preferably arranged on the upper side thereof.

9. The draining apparatus according to claim 6, wherein the cover (2) is formed as a concentric body in relation to the drainage pipe (1), which body has on its underside at least one draining edge (27), and that an annular space (29) of substantially uniform thickness is preferably formed between the drainage pipe (1) and the body.

10. The draining apparatus according to claim 6, wherein the drainage opening (3) is arranged below a liquid level (23) which is to be kept constant.

11. The draining apparatus according to claim 6, wherein the discharge device (1) is connected via a siphon bow (4) to an overflow space (25) which is sealed by an overflow weir.

12. The draining apparatus according to claim 6, wherein the cover (2) is designed to be liftable or removable.

13. The draining apparatus according to claim 6, wherein the discharge device is formed as a horizontally disposed drainage pipe (1), and that the drainage opening (3) is arranged on the underside thereof, so that the blocking volume is arranged in the interior of the drainage pipe (1).

14. The draining apparatus according to claim 6, wherein a bleed valve (7) is provided for venting the blocking volume (24).

15. The draining apparatus according to claim 6, wherein a three-way valve is provided for introducing, venting or maintaining the compressed air in the blocking volume (24).

16. The draining apparatus according to claim 6, wherein two mutually parallel draining edges are provided, which are preferably arranged at the same height.

17. The draining apparatus according to claim 6, wherein a plurality of discharge devices (1) are provided, which preferably form a linear structure.

18. The draining apparatus according to claim 6, wherein a plurality of discharge devices (1) are provided, which preferably form an annular structure.

19. The draining apparatus according to claim 6, wherein a pressure wind vessel (8) is provided.

20. The draining apparatus according to claim 6, wherein the distance between an overflow weir and the apex of a siphon bow (4) is at least as great as the distance between the drainage edge and the maximum water level.

21. The draining apparatus according to claim 6, wherein a threshold in the drainage pipe (1) is at least as high as the pressure level fluctuations to be expected in the tank (22).

22. The draining apparatus according to claim 6, wherein a uniform drawing-in of the liquid into the draining apparatus is achieved by an expansion of the distances (19) of the drainage openings (3) in the flow direction in the drainage pipe (1) or by reducing the opening widths of the drainage openings (3) in the direction of flow in the drainage pipe (1).

Description

[0023] The present invention is explained in more detail below with reference to the exemplary embodiments shown in the schematic drawings, wherein:

[0024] FIG. 1 shows a sectional view of a drainage apparatus according to the invention;

[0025] FIG. 2 shows the drainage apparatus of FIG. 1 in a top view;

[0026] FIG. 3 shows an alternative embodiment in a plan view;

[0027] FIG. 4 shows a detail of FIG. 1;

[0028] FIG. 5 shows a view corresponding to FIG. 1, explaining the propagation of the air cushion when the blocking volume is filled;

[0029] FIG. 6 shows a view corresponding to FIG. 1, explaining the achievement of the pressure equilibrium after filling of the blocking volume;

[0030] FIG. 7 shows an alternative embodiment without cover;

[0031] FIG. 8 shows the embodiment variant of FIG. 7 with an air cushion in the drainage pipe and siphon bow at maximum filling level in the tank;

[0032] FIG. 9 shows the embodiment variant of FIG. 7 in longitudinal section with a threshold and staggered distances of the drainage openings.

[0033] The draining apparatus of FIG. 1 and FIG. 2 consists of a discharge device in the form of a drainage pipe 1 with a horizontal axis which is arranged completely below the liquid level in a tank 22 on a fixed console 5. A plurality of drainage openings 3 are provided on the top side of the drainage pipe 1. The drainage pipe 1 is concentrically covered by a cover 2 in the form of a pipe half-shell, so that an annular space is produced between the drainage pipe 1 and the cover 2.

[0034] The water which has penetrated the drainage pipe 1 is supplied via a pressure line and siphon bow 4 connected to the drainage pipe 1 into an overflow space 25, which is terminated by an overflow weir 10.

[0035] Compressed air can be introduced into the annular space via a compressed air line 6, wherein the compressed air is generated by a compressor 9, which is connected to a pressure wind vessel 8. Valves 7 control the supply and discharge of compressed air.

[0036] If the draining weir is set too low, the water level 23 can drop to the height of the drainage openings 3. A further sinking is not possible with the opened air discharge valve, since no vacuum can build up due to the venting of the high point and therefore the vessel cannot be emptied further according to the lifter principle. An increase in the water level 23 above the level of the inflow openings is then only possible if the compressed air cushion in the annular space again drops below the level of the inflow openings and the hydrostatic pressure on both sides of the pressure sensor is the same. This means that the difference in the water level between the tank water level 23 and the lower edge of the air cushion in the annular space is equal to the water level difference on the outlet side between the water level in the drainage shaft and the water level in the drainage pipe. This means that as the water level 23 rises in the tank 22, the water level difference on the outlet side must be correspondingly increased by means of an additional air inlet into the region of the drainage pipe 1, or the draining weir can be increased.

[0037] The drainage apparatus is best suited for cyclic waste water treatment processes with a largely constant water level. In particular, the invention relates to methods in which the feed is conducted alternately between parallel tanks, and this feed displaces the supernatant water from the tank at approximately constant water level.

[0038] FIG. 3 shows a variant with an annular arrangement of drainage pipes 1, which are connected to one another by means of corresponding connecting pieces 10.

[0039] FIG. 4 shows in detail the connection of the pressure pipe 4 in the region of a connecting piece 11 between two drainage pipes 1.

[0040] FIG. 5 shows the dynamics during the filling of the blocking volume 24: The following differences in height are presented for explanation: [0041] 14: Difference in height between the water level 20 in the overflow space 25 and the water level 23 in the tank 22. [0042] 15: Difference in height between the water level 26 in the pipe 1 and the water level 20 in the overflow space 25. [0043] 16: Difference in height between the water level 28 in the annular space 29 and the water level 23 in the tank 22. [0044] 17: Difference in height between the water level 26 in the pipe 1 and the water level 28 in the annular space 29.

[0045] During the drainage of the liquid, the water level 20 during the weir overflow is lower than in the tank 22 due to the friction losses in the draining apparatus. Then the blocking volume 24 is filled with pressure (p.sub.com) via the compressed air line 6 at the top of the cover. The air cushion propagates from there and reaches the drainage openings and prevents further inflow of the liquid. It forms an equilibrium between the hydrostatic head 15 (p.sub.in=.sub.w*g*h.sub.in) on the air cushion from the inside of siphon bow 4 and the pressure head 16 (p.sub.ex=.sub.w*g*h.sub.ex) on the air cushion from the outside of the tank. The two hydrostatic pressures are therefore equally large by disregarding the weight of the air cushion and the overpressure of the compressed air must overcome this back pressure. The height difference 17 of these two hydrostatic pressure surfaces corresponds to the height difference 14 between the tank water level 23 and the overflow height 20. Similarly, the elevation differences 15 and 16 are also equal.

[0046] FIG. 6 shows the attainment of a stationary pressure equilibrium. The air cushion extends on the outer side to the draining edges and excess air rises to the surface of the tank. On the inside, the air cushion extends so far into the drainage pipe or into the siphon bow 4, so that the pressure level 15 also corresponds here to the overflow height 20 of the height difference 16 between draining edge 27 and tank water level 23.

[0047] FIG. 7 shows a variant without cover. In this case, the compressed air is directly pressed into the apex of the drainage pipe 1, and the air cushion then reaches as far as the drainage openings 3 attached to the underside of the pipe and excess compressed air escapes through these drainage openings 3.

[0048] FIG. 8 shows the maximum possible tank filling height at given siphon and overflow heights. The maximum tank water level sensor presses the filled blocking volume 24 until the minimum through-flow height of the siphon bow 4 is reached and additional compressed air can escape in the direction of overflow.

[0049] In FIG. 9, a longitudinal section through the draining apparatus without cover (see FIG. 7 and FIG. 8) is shown. By the arrangement of a threshold with the height 18, water inlets due to pressure fluctuations by ventilation in the tank for example are prevented. The staggered distances 19 of the drainage openings 3 are intended to make the liquid intake uniform as the inlet speed increases along the longitudinal axis of the draining apparatus.

[0050] The present invention makes it possible to robustly control the drainage of water from clarification tanks or the like in a very simple manner.