DE102017116266A1 - Compressed air membrane dryer with mixed air control - Google Patents

Abstract

The invention relates to a compressed air membrane dryer (20) with a housing (22) in which a membrane filter (24), preferably a bundle of hollow fiber membranes, is arranged and a housing head (26) with an inlet channel (30) through which a humid total air pressure flow flows and a Outlet channel (32), which opens into an outlet (34) through which dried useful air flows. This is characterized in that a bypass channel (40) is provided, which connects the input channel (30) with the output channel (32), wherein a first partial air flow (36) of the total compressed air flow passed through the hollow fiber module, dried therein and in the output channel (32 ),
- A first partial air flow (36) of the total compressed air flow through the membrane filter (24) passed and dried the output channel (32) is supplied, wherein the first partial air flow (36) and the second partial air flow (38) in the output channel (32) to a dried Nutzluftstrom mix.
- A second partial air flow (38) of the total air flow through the bypass channel (40) is supplied undried to the output channel (32), wherein the first partial air flow (36) and the second partial air flow (38) in the output channel (32) to a dried Nutzluftstrom mix.

Description

The invention relates to a compressed air membrane dryer for compressed gas, in particular compressed air, in which a membrane filter, preferably a bundle of hollow-fiber membranes, is arranged.

When using compressed air, for example in industrial technology or medical technology, moisture in the network and at the points of consumption is a quality problem. An important task is therefore always the drying of the compressed air. For this purpose, membrane filters are used, which are selectively permeable to water vapor. In the filter housing a bundle of highly selective hollow fiber membranes is arranged (membrane fibers) through which humid compressed air flows. The moist compressed air is preferably filtered, so that even contained in it dirt particles, oil mist and condensate are retained, so do not clog the hollow fiber membranes. Water vapor diffuses outwards through the hollow-fiber membranes. At the outlet for dried compressed air, a small partial flow of compressed air is diverted and used after expansion as purge air. The purge air is conducted in countercurrent to the compressed air via the outside of the hollow fibers. Due to the difference in the water vapor concentration, a constant migration of the water molecules from the compressed air is achieved in the purge air. Thus, the commonly used term membrane filter is at least ambiguous because a membrane filter separates not mechanically, but by diffusion. For the sake of simplicity, this term will nevertheless be used within the scope of the invention.

This process is continuous. The scavenging air constantly dries the incoming, moist compressed air. Only water molecules can penetrate the membranes of the hollow fibers. The composition of the dried compressed air remains unchanged. The result is pure, dry compressed air with a low pressure dew point.

Often, compressed air membrane dryers for compressed gas used in machines basically only have the task of preventing postcondensation, since downstream pneumatic components are very sensitive to condensate. In many cases, lowering the pressure dew point by 5 Kelvin is sufficient to avoid postcondensation.

Depending on the desired degree of drying, a corresponding membrane surface is required, which is realized in the membrane filter essentially by the number of hollow fibers with a defined length. In pneumatic applications with compressed air usually only a small reduction in the degree of humidity or the dew point at the end user point is sufficient to ensure a trouble-free compressed air application. Thus, a small hollow fiber membrane area is needed for the drying of a defined compressed air flow per unit time. At the same time, however, a sufficiently large inflow area is required to keep energy losses in the form of pressure losses low. Accordingly, hollow fiber modules have a short length with large module diameters. This results in cost disadvantages, because the costs increase disproportionately with increasing component diameter. At the same time adapters for size adaptation are necessary for performance attachments such as compressed air filter.

On this basis, the invention has the task of creating an improved compressed air membrane dryer for compressed gas. In particular, a reliable drying should be possible, which works just when a slight reduction in the degree of humidity or the temperature or the pressure dew point, with simple means reliably. The compressed air membrane dryer should be as compact as possible and inexpensive to produce. Another object of the invention is to provide a corresponding method for drying the compressed air.

According to the invention the object is achieved by a compressed air membrane dryer for compressed gas with the features of claim 1 and with the method steps of the independent method claim.

The invention is based on the idea to dry only a partial air flow of the total compressed air flow and to mix with the non-dried second partial air flow, so that the total desired degree of drying is achieved. The first partial air flow to be dried can be dried relatively strongly in order to achieve a correspondingly low humidity of the compressed air flowing out of the outlet channel of the housing after mixing with the second partial air flow. On the degree of drying of the partial air flow to be dried thus the degree of dryness of the outflowing dried compressed air is adjustable.

For example, it may be useful to dry only 30% of the original total compressed air flow while passing 70% of the original total compressed air flow without drying. Due to the different degrees of saturation results after mixing of the two partial air flows a pressure dew point, which is sufficient to prevent the post-condensation.

The invention has the significant advantage that the required hollow fiber membrane surface can be significantly reduced. As a result, the use of a membrane filter or a hollow fiber module with small diameter or shorter length possible. These can be designed to match corresponding compressed air filters. They are advantageously easy to adapt in a modular system.

The invention thus makes it possible to significantly reduce the necessary size of the compressed air membrane dryer. This not only saves manufacturing costs, there are also advantages in the installation of the compressed air membrane dryer on site or in a machine.

The mixture of the two partial air streams can be constant, adjustable or regulated.

According to the invention, provision can be made for throttling the second, non-drying partial air flow somewhat.

In order to achieve the separation according to the invention of the two partial air streams, a bypass channel is provided, which connects an input channel with an output channel of the housing head. The resulting second partial air flow can be adjusted and regulated according to the invention by a change in diameter of the bypass channel. A control is possible for example via a valve control, in particular depending on the desired pressure dew point of the compressed air. According to the invention, further integrated components and functions, such as non-return devices and the like may be provided.

In a particularly simple embodiment, the bypass channel is designed as an unlocked channel, in the simplest case as a hole. But the bypass channel can also be closed and opened by a valve, which is designed in particular as a check valve. It has proved to be particularly advantageous if this example is spring loaded and then opens when a request for compressed air is pending at the end user. As already described, however, the valve can also be controlled electronically, for example as a function of the pressure dew point.

The valve may according to the invention comprise a closure body which is movably guided in a valve housing. A spring element is arranged between the closure body and a rear wall of the valve housing, wherein in the valve housing an opening is provided which forms the bypass channel and which is then released and allows a flow with the drying partial air flow then when the closure body due to differential pressure against a spring force of the spring element in the direction of the rear wall shifts. The differential pressure results from the pressure loss of the volume flow through the membrane filter. As the volume flow increases, the differential pressure also increases, so that the opening on the closing body increases in relation to the spring pressure and regulates an increasing partial flow.

The valve housing is arranged as a unit in the bypass channel of the housing of the compressed air membrane dryer. The bypass channel preferably has a maximum diameter which is smaller than the diameter of the input channel. This ensures that the valve housing can be inserted through the inlet channel. Alternatively, the exit channel may have a larger diameter than the valve housing to allow insertion through the exit channel.

The exit channel opens into an outlet of the housing head through which the dried useful air is supplied to the end use point. The mixing of the two partial air flows according to the invention before the outlet, preferably in the output channel, but can alternatively be done after the occasion.

The control based on the pressure dew point is based on the idea of using a peculiarity of membrane dryers with regulated or uncontrolled purging air, namely, that the lowering of the pressure dew point has an almost constant, constant value. With changing pressure dew points in the inlet of a membrane dryer, the pressure dew point at the outlet also changes accordingly. This is also desired in many applications. For others, however, it is important to achieve a certain pressure dew point in the outlet, regardless of the pressure dew point in the inlet. This is often the case, for example, due to normative specifications in the medical field, for example in the generation of breathing air. About the pressure dew point of the dried compressed air at the outlet can be derived directly whether the purging air fed back into the housing is sufficient or whether the drying performance of the membrane dryer is satisfactory.

Thus, an optimal control of the volume flow of the non-dried second partial air flow by detecting the desired pressure dew point is possible. Depending on the desired pressure dew point, according to the invention, the valve for the bypass of undried compressed air can be regulated. In addition to an electronic control unit with a dew point sensor and a temperature sensor for this purpose, a control valve is still provided in the purge air duct.

Regardless of this, in addition, a pressure dew-point-dependent control of the purge air flow is also possible, which also leads to significant advantages.

By means of the determined values of the dew point sensor, which finally determines the degree of humidity of the dried compressed air, and the temperature sensor, the pressure dew point of the dried compressed air can be calculated. The values determined are forwarded to the electronic control unit in which the calculation is made. The volume distribution of the partial air flows and / or the degree of drying of the partial air flow to be dried can be regulated accordingly on this basis.

It is possible to use two separate sensors, ie a dew point sensor and a temperature sensor, but preferably a single sensor element is used, which can determine both values.

The electronic control unit has a control board with a computer processor, electrical connections for power supply, as well as the usual data and signal transmission to the operator. Preferably, but not necessarily, a display allows the display of the current state and the setting of desired states. The input can be made via the display itself (touch screen) or an additional keyboard. Alternatively, an externally arranged input device and / or display can be used according to the invention. The data transmission to the control unit can be done wirelessly or wired.

According to the invention, the desired pressure dew point is stored as a setpoint in the control unit in a control based on the pressure dew point. It is also conceivable to store a range of values in which the pressure dew point of the dried compressed air is to fall. The control unit compares the determined or calculated pressure dew point of the dried compressed air with the desired value or the desired value range and regulates the volume of the non-dried second partial air flow and, if necessary. Also the volume of the purge air flow as a function of the result.

This can be done according to the invention in cycles, so with a certain number of opening and closing operations. Once the setpoint has been reached, no further cycles are carried out. If the setpoint is not reached even after a preset time, the valve is permanently opened. The cycles are variably definable, ie with different opening and closing times. Equally variable is the timing to permanent valve actuation. With this method, it is possible to use a valve in the form of a simple solenoid valve with valve piston. This technique is very simple, inexpensive, operates reliably and requires little maintenance over long periods of operation.

Alternatively, the valve can also be designed with a motor operated valve or with a proportional valve or other variants. The bypass channel can also only partially, so not be opened or closed over its entire cross-section. The valve can also open or close the bypass channel continuously, depending on the volume requirement.

The control unit has all the modern interfaces of data communication or can be equipped with it. Measured values (pressure dew point, temperature) can be forwarded as well as service conditions, for example necessary replacement of wearing parts, operating hours or similar. It is also possible to issue an alarm if the setpoint is not or not permanently reached.

In addition to the mentioned temperature and dew point detection, additional data acquisitions with sensors, e.g. possible for pressure or volume flow measurement.

• - Aufteilen des feuchten Gesamtdruckluftstroms in den ersten Teilluftstrom und den zweiten Teilluftstrom,
• - Durchleiten des ersten Teilluftstroms durch einen Membranfilter des Druckluftmembrantrockners zu einem Ausgangskanal,
• - Durchleiten des zweiten Teilluftstroms durch einen Bypasskanal ungetrocknet zum Ausgangskanal,
• - Vermischen der beiden Teilluftströme im Ausgangskanal.

The process according to the invention comprises the following process steps:

• Splitting the moist total compressed air flow into the first partial air flow and the second partial air flow,
• Passing the first partial air flow through a membrane filter of the compressed air membrane dryer to an outlet channel,
• Passing the second partial air stream through a bypass channel undried to the outlet channel,
• - Mixing of the two partial air streams in the output channel.

• 1: einen erfindungsgemäßen Druckluftmembrantrockner im Schnitt,
• 2: eine Ausschnittvergrößerung aus 1
• 3: ein erfindungsgemäßes Ventilgehäuse in perspektivischer Darstellung
• 4: das Ventilgehäuse aus 3 im Schnitt

The invention will be explained in more detail with reference to the following figures. These are not intended to be limiting, but merely show schematic representations of the invention. Show it:

• 1 : a sectional compressed air membrane dryer according to the invention,
• 2 : a cut-out enlargement 1
• 3 a valve housing according to the invention in a perspective view
• 4 : the valve body off 3 on average

1 shows a Durckluftmembrantrockner invention 20 on average. This has a housing 22 in which a membrane filter 24 , preferably a bundle of hollow fiber membranes, and a housing head 26 on.

Through an inlet 28 flows a total air pressure flow in an input channel 30 in the housing head 26 into it. The housing head 26 also has an output channel 32 who is in an outlet 34 opens up.

It can be seen that a first partial air flow 36 the incoming total air pressure flow through the membrane filter 24 and from there to the exit channel 32 and finally to the outlet 34 is directed. A second partial airflow 38 flows through a bypass channel 40 immediately undried in the exit channel 32 , In the output channel 32 the first partial air flow mix 36 and the second partial airflow 38 together and flow as dried useful air from the outlet 34 out.

The bypass channel 40 is in the embodiment shown as an opening or channel 42 in the entrance channel 30 executed.

Especially 2 shows a valve housing according to the invention 44 that has latching arms 46 in the channel 42 is engaged. A maximum diameter of the valve body 44 is less than a minimum diameter of the output channel 32 so that the valve body 44 also in retrospect through the output channel 32 introduced and in the canal 42 can be locked.

The valve housing 44 has a closure body 48 on, which is designed in the embodiment shown as a disc whose diameter is greater than the diameter of the channel 42 is and then closes it when the closure body 48 at the opening or at the channel 42 is applied.

The closure body 48 is in the illustrated embodiment by a spring element 50 spring loaded, wherein the spring element 50 on a back wall 52 of the valve housing 44 supported. The spring element 50 causes the closure body 48 against the entrance channel 30 or the channel 42 is pressed and this closes in the idle state.

The valve housing 44 So represents a kind of check valve, which is the channel 42 then releases when the pressure difference, which is dependent on the decrease in the useful air, is large enough.

The 3 and 4 show the valve housing according to the invention 44 in perspective or in section.

The invention is not limited to the embodiment shown, but also includes other variants that can be realized on the basis of the illustrative invention.

LIST OF REFERENCE NUMBERS

20

Compressed air membrane dryers

22

casing

24

membrane filter

26

housing head

28

inlet

30

input channel

32

output channel

34

outlet

36

first partial airflow

38

second partial air flow

40

bypass channel

42

channel

44

valve housing

46

detent arm

48

closure body

50

spring element

52

rear wall

Claims (12)

Compressed-air membrane dryer (20) with a housing (22) in which a membrane filter (24), preferably a bundle of hollow-fiber membranes, is arranged, and a housing head (26) having an inlet channel (30) through which a moist total air pressure flow flows in and an outlet channel (32) opening into an outlet (34) through which dried useful air flows, characterized in that a bypass channel (40) is provided which connects the inlet channel (30) to the outlet channel (32), wherein - a first partial air stream (36) the total compressed air flow through the membrane filter (24) passed and dried the output channel (32) is fed, wherein the first partial air flow (36) and the second partial air flow (38) in the output channel (32) mix to a dried Nutzluftstrom. - A second partial air flow (38) of the total air flow through the bypass channel (40) is supplied undried to the output channel (32), wherein the first partial air flow (36) and the second partial air flow (38) in the output channel (32) to a dried Nutzluftstrom mix. Compressed air membrane dryer (20) after Claim 1 , characterized in that the bypass channel (40) is designed as an unlocked channel (42). Compressed air membrane dryer (20) after Claim 1 , characterized in that a valve is arranged in the bypass channel (40), Compressed air membrane dryer (20) after Claim 3 , characterized in that the valve is designed as a check valve. Compressed air membrane dryer (20) after Claim 4 , characterized in that the check valve is designed to be spring-loaded, and in response to a resulting differential pressure by a pressure drop of a volume flow through the membrane filter (24), wherein the differential pressure increases with increasing volume flow, whereby the closure body (48) the channel (30 ) increasingly releases against a spring force of the spring element (50). Compressed air membrane dryer (20) after Claim 3 , characterized in that the valve is adjustable. Compressed air membrane dryer (20) after Claim 6 , characterized in that the valve is controllable in dependence on the determined pressure dew point. Compressed air membrane dryer (20) according to one of Claims 3 - 7 characterized in that the valve comprises a closure body (48) which is movably guided in a valve housing (44), wherein in the valve housing (44) an opening is provided which can be closed and released by the valve, wherein the valve housing (44 ) is arranged in the bypass channel (40). Compressed air membrane dryer (20) after Claim 8 characterized in that a spring element (50) is disposed between the valve body and a rear wall of the valve housing (44) and the opening is released when the valve body shifts towards the rear wall due to differential pressure against a spring force of the spring element (50) , Compressed air membrane dryer (20) according to one of Claims 1 to 9 , characterized in that the bypass passage (40) has a maximum diameter which is smaller than the diameter of the inlet channel (30). Method for drying compressed air by means of a compressed air membrane dryer (20), characterized by the method steps: - splitting a moist total air flow into a first partial air flow (36) and a second partial air flow (38), - passing the first partial air flow (36) through a membrane filter ( 24) of the compressed-air membrane dryer (20) to an outlet channel (32), passing the second partial air stream (38) through a bypass channel (40) undried to the outlet channel (32), mixing the two partial air streams (36, 38) in the outlet channel (32) , Method for drying compressed air, characterized in that the compressed air membrane dryer (20) according to the Claims 1 to 10 is executed.

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