Pressure dew point-controlled purge air regulating unit

Abstract

A purge air regulating unit for a drying device for compressed air, the purge air regulating unit being connectable to a housing in which a membrane filter, such as a bundle of hollow fiber membranes, is arranged such that a sub-flow of dried compressed air flowing out of the housing from an outlet channel can be conducted back to the hollow fiber membranes as purge air by the purge air regulating unit. A method for regulating the flow of dried compressed air flowing out of a membrane dryer back into a housing of the membrane dryer, the membrane dryer being equipped with a membrane filter, such as a bundle of hollow fiber membranes, is also provided.

Claims

1. A purge air regulating unit for a drying device for compressed air, comprising: a regulator configured to calculate a pressure dew point of dried compressed air, comprising a dew point sensor configured to detect a dew point of the dried compressed air and a temperature sensor configured to detect a temperature of the dried compressed air; and a control valve which is regulated by the regulator and at least partially opens or closes a purge air channel based on the pressure dew point of the dried compressed air; wherein the purge air regulating unit is connectable to a housing including a membrane filter therein, such that a sub-flow of dried compressed air flowing out of the housing from an outlet channel thereof is conductible back to the membrane filter as purge air by the purge air regulating unit.

2. The purge air regulating unit according to claim 1, wherein the dew point sensor is located in the purge air channel.

3. The purge air regulating unit according to claim 1, wherein the dew point sensor is located in the outlet channel of the housing.

4. The purge air regulating unit according to claim 1, further including a creep air channel configured so that dried compressed air flows continuously back into the housing as creep air, even when the control valve is closed.

5. The purge air regulating unit according to claim 4, wherein the creep air channel branches off behind the dew point sensor in a direction of flow.

6. The purge air regulating unit according to claim 1, wherein the control valve is a motorized valve.

7. The purge air regulating unit according to claim 1, wherein the control valve includes a solenoid valve.

8. The purge air regulating unit according to claim 1, wherein the control valve includes a valve plunger configured to close and open the purge air channel, and an actuator valve plunger, configured to close and open an actuator channel.

9. The purge air regulating unit according to claim 8, wherein the valve plunger opens the purge air channel when the actuator valve plunger closes the actuator channel.

10. The purge air regulating unit according to claim 8, wherein the valve plunger is configured such that the purge air presses the valve plunger into an open position when the actuator valve plunger closes the actuator channel.

11. The purge air regulating unit according to claims 8, further including an energizing magnetic coil configured to move the actuator valve plunger.

12. A method for regulating the flow of dried compressed air flowing out of a membrane dryer back into a housing of the membrane dryer having a membrane filter therein, comprising: ascertaining a pressure dew point of dried compressed air flowing out of the membrane dryer; and regulating said flow by, based on the ascertained pressure dew point, opening or closing a control valve located in a purge air channel configured to conduct dried compressed air back to the membrane dryer as purge air when the control valve is open.

13. The method according to claim 12, further comprising comparing the ascertained pressure dew point with a target value and, when there is a deviation from the target value, cyclically opening and closing the control valve until the target value is reached.

14. The method according to claim 13, further comprising continuously opening the control valve when the target value is not reached by said cyclic opening and closing of the control valve after a predefined time period.

15. The purge air regulating unit according to claim 1, wherein the membrane filter comprises a bundle of hollow fiber membranes.

16. The method according to claim 12, wherein the membrane filter comprises a bundle of hollow fiber membranes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the basic principle of the purge air regulating unit in a simplified schematic diagram,

(2) FIG. 2 shows a preferred variant of the invention in cross-section, with the purge air channel open,

(3) FIG. 3 shows the preferred variant of FIG. 2 with the purge air channel closed.

DETAILED DESCRIPTION OF EMBODIMENTS

(4) FIG. 1 shows the function of a purge air regulating unit 20 according to the invention. Some of the fluid flows are indicated by arrows, moist air being marked A, dry compressed air being marked B, purge air being marked C and creep air being marked D.

(5) The arrows illustrate the flow path of the compressed air inside the membrane dryer 22. The compressed air is conducted through an inlet 24 of a housing head 26 into the membrane dryer 22, passes through an inner tube into an exit space and flows from there through an annular housing space through membrane fibres 28 (hollow fibre membrane) back to the housing head and back out through an outlet 30 as dried compressed air B or useful air. When flow passes through the membrane fibres 28, the moisture in the compressed air diffuses outwards through the hollow fibre walls as water vapour 32.

(6) A sub-flow of the dried compressed air B is diverted relatively shortly before the outlet 30, expanded and conducted as purge air C into the outer space of the hollow fibres, absorbs the diffused water vapour 32 there and then conducts it through a purge air output 34 into the environment.

(7) According to the invention, the purge air regulating unit 20 is placed on the membrane dryer 22 and has two connections that are connected to the purge air channel, so that the purge air C flows through the purge air regulating unit 20 before flowing back to the membrane fibres 28.

(8) The purge air regulating unit 20 has a dew point sensor 36 for detecting the dew point of the dried compressed air B, a temperature sensor (not shown) for detecting the temperature of the dried compressed air B and a control valve 38.

(9) Further parts of the purge air regulating unit 20 are a control printed circuit board 40, a display 42, connections 44 for transferring data and signals, and a housing 46. The display 42 is optional and can in particular serve not only as a display means but also as an operation unit.

(10) FIGS. 2 and 3 show a first variant according to the invention of the purge air regulating unit 20 in cross-section. FIG. 2 shows the situation when the control valve 38 is open, FIG. 3 shows the situation when the control valve 38 is closed.

(11) It can be seen that the dew point sensor 36 is connected to the regulating unit 35 via electrical lines (data lines) 74 and the regulating unit 35 is in turn connected to the magnetic coil 68 via data lines 74. The electrical lines 74 primarily serve for signal transmission between the dew point sensor 36 and the control unit 35, and primarily for energy transmission between the magnetic coil 68 and the regulating unit 35.

(12) An outlet channel 48, from which a purge air channel 50 branches off, can be seen. The purge air channel 50 branches into a first portion 52, which ends at a valve plunger seat 54, and a second portion 56, which ends at an actuator valve plunger seat 58. The valve plunger seat 54 bounds a valve plunger space 60, in which a valve plunger 62 is situated, and the actuator valve plunger seat 58 bounds an actuator valve plunger space 64, in which an actuator valve plunger 66 is situated. The actuator valve plunger 66 is surrounded by a magnetic coil 68 and can be moved by the latter.

(13) The actuator valve plunger space 64 is connected to the valve plunger space 60 via a connecting channel 70. The connecting channel 70 opens into the valve plunger space 60 on the side opposite the valve plunger seat 54, so that the valve plunger 62 is arranged between the valve plunger seat 54 and the connecting channel 70 or the opening thereof.

(14) Furthermore, a creep air channel 72 can be seen, which connects the valve plunger space 60 to the purge air channel 50 and opens into the latter behind the control valve 38 in the direction of flow.

(15) FIG. 2 shows that the pressure of the dried compressed air B is present below the valve plunger 62, as a result of which the latter is lifted. Therefore, purge air C can flow through the valve plunger seat 54, along the purge air channel 50 to the membrane fibres 28. In the process, the actuator valve plunger 66 closes the actuator valve plunger seat 58, so that the second portion 56 is closed.

(16) FIG. 3 shows the state in which the magnetic coil 68 has attracted the actuator valve plunger 66. The second portion 56 is opened thereby, since the actuator valve plunger 66 has opened the actuator valve plunger seat 58. Via the pressure of the dried compressed air B, sufficient pressure builds up in the valve plunger space 60 to press the valve plunger 62 onto the valve plunger seat 54, as a result of which the first portion 52 is closed and purge air C can no longer flow through the purge air channel 50.

(17) It can also be seen that only creep air D can flow through the creep air channel 72 out of the valve plunger space 60 into the purge air channel 50.

(18) The valve plunger 62 can be assisted in its movement by a spring (not shown).

(19) In this variant, the purge air channel 50 is therefore open when the magnetic coil 68 is in the non-energised state, so that purge air C can flow in particular even in the event of a power failure or malfunction.

(20) In the exemplary embodiment shown, the dew point sensor 36 is in the purge air channel 50. Alternatively, it can also be arranged in the outlet channel 48.

(21) Capacitive sensors or else mirror-type dew point sensors, for example, can be used as the dew point sensor 36.

(22) The invention is not limited to the exemplary embodiments shown but also includes further variants that can be implemented on the basis of the explained invention.