WO1995028626A1

WO1995028626A1 - Device for extracting the gases in liquids with subsequent detection, and its use

Info

Publication number: WO1995028626A1
Application number: PCT/DE1995/000495
Authority: WO
Inventors: Alfred MÜHLWITZ; Hans-Jochen Rindfleisch; Fred Schaffarzik
Original assignee: Medium - Sensor Gmbh
Priority date: 1994-04-14
Filing date: 1995-04-10
Publication date: 1995-10-26
Also published as: DE19580326D2; AU2253995A

Abstract

Liquids of various kinds, e.g. water, waste water or transformer oil, may contain dissolved gases in various concentrations which may be a considerable source of danger or be significant in undesirable phenomena. The invention is intended to permit the virtually continuous and rapid extraction of these gases by means of the permeation method in order, in an immediately subsequent detection process, to detect or signal the development of damage or undesirable phenomena in good time or immediately. According to the invention, extraction is operated by a device consisting of two permeation foils (1) with a gastight joint between them at their edges and at least one tubular output line or hose (3). To safeguard the space between the permeation foils (1) forming the gas chamber (2), either a supporting layer (6) can be fitted or the space can be maintained magnetically or electrostatically. The size of the space is inversely proportional to the thickness of the permeation foils (1) and can be elastically reversibly reduced to at least 50 % of its initial value by the exertion of a force. The collected gas is driven out by widely varying forms of pressure with subsequent detection in a measuring cell (9).

Description

Extraction device with subsequent detection of the gases contained in liquids and their use

T e c h n i s c h e s G e b i e t d e r E r f i n d u n

The extraction of gases contained in liquids is used in many fields of technology. However, the preferred area of application is analysis for the qualitative and quantitative detection of the extracted gases. The gases contained in the liquid can allow conclusions to be drawn about their condition. In the presence of certain gases, disturbances or environmental pollution can be signaled.

State of the art

It is known to use vacuum technology to extract the gases dissolved in the oil. According to DE-AS 21 43 045, a cylinder-piston arrangement is used for quickly changing the volume of an enclosed liquid sample and for expelling the gas released in the process.

Disadvantages are the sealing problems of the vacuum and the incomplete degassing, which is not completely definable due to absorption of the gas when the gas sample is pressed out. Furthermore, according to DD - PS 2 38 115 it is known to use the stripping technique. In this case, a carrier gas, for example air, is passed through the liquid in bubble form, gas exchange taking place between the carrier gas phase and the gas dissolved in the liquid. If the exchange distance is sufficiently long, a defined partial pressure equilibrium is established, so that analytically reproducible results are achieved.

The disadvantage here is that this technique can only be used for large volumes of liquid which are already almost saturated with carrier gas or after very long operating times. On the other hand, there is a risk of carrier gas Dissolution if only a limited amount of it is used, for example in discontinuous operation or in the case of a shock injection.

If a continuous exchange process with carrier gas and liquid is carried out in countercurrent, the speeds of the two streams must be exactly matched to one another. It is necessary to regulate the flows to compensate for the viscosity fluctuations due to changing temperature or to keep the temperature constant along the length of the gas exchange path.

The use of permeation technology is also known. The liquid space and the gas space are separated by a disk-shaped, gas-permeable membrane, gas exchange taking place as a result of the partial pressure difference through the membrane. According to the company brochure "HYDRAN Gas in Oil Analyzers" from Syprotec, West Chazy, N.Y. 12992, USA, the permeation current of the hydrogen to be detected is measured. The disadvantage is that gases with high solubility and in low concentrations cannot be detected in the liquid, since the permeation current of these gases is too low. Furthermore, the permeation current is strongly dependent on the temperature, which means that either a computational correction or a constant temperature in the area of the membrane is required. In the solution cited, the temperature of the entire measuring cell is required.

DE 28 04 367 AI describes a method and a device for removing and analyzing a gas carried in a liquid volume. The liquid is circulated using the density at different temperatures.

Here, the oil taken from a transformer housing is cooled by a temperature of 80 to 85 C in a tube with cooling plates designed as a cooling device by 10 to 20 ° C and then returned to the housing. In the part of the tube provided with cooling plates, a gas separation cell is arranged, which consists of a porous carrier tube and a semipermeable membrane. The gas that accumulates in the cell is transported into the gas detector / analyzer unit with the aid of a carrier gas. One disadvantage is the use of a carrier gas and on the other hand, the restriction of gas detection to gases with a low molecular weight, for example hydrogen, carbon monoxide and carbon dioxide.

Increasing the detection sensitivity for gases with high solubility is possible by increasing the membrane area and reducing the membrane thickness, but there are limits due to the bursting strength of the membrane, so that the measures required do not make the required detection sensitivity for gases with high solubility can be significantly increased.

The detection of the gas concentrations in the liquid can also be achieved in known ways in that it is not the permeation gas flow of the respective gas component but its concentration in the gas space that is determined after the partial pressure equilibrium has been set. The time that the compensation process takes also depends on the membrane area, the membrane thickness and the volume of the gas space with respect to the membrane area and thickness, but in the inverse ratio to the permeation gas flow. This means that in practical cases this time with a disk-shaped membrane and a measuring cell arranged behind it cannot be reduced to below the values available for recording damage-relevant processes. This means that the speed of the gas measurement is too low in comparison to the speed of the concentration changes in the transformer oil in order to be able to detect damage processes at an early stage.

D a r s t e l u n g e r e r f i n d u n g

The invention is based on the problem of effectively carrying out a quasi-continuous and rapid extraction of gases of high solubility and low concentration from liquids with the aid of permeation technology, in order to recognize damage development or disturbance within a few hours in an immediately subsequent analysis and to signalize. According to the invention, the distance between two permeation foils, which are connected to one another in a gas-tight manner, is inversely proportional in size to the thickness of the permeation foils. The distance should preferably be less than 400 μm with a permeation film thickness of 10 μm. The distance between the permeation foils must be able to be reversibly reduced to at least 50% of its initial value by the action of a force.

To maintain the distance between the permeation foils, either an elastic, gas-conducting support layer is required, or the permeation foils are kept at a distance magnetically or electrostatically.

From the gas space of the permeation foils, at least one tubular or tubular discharge leads to the measuring cell. If a support layer is arranged in the gas space, it can be advantageous for the diversion to continue in the form of a channel into the support layer. Spacers made of pressure-resistant and gas-conducting material can also ensure the necessary maintenance of the distance.

The edges of the permeation foils are connected using known techniques. It may be advantageous to metallize these edges beforehand.

Either mechanical or physical means can be used to discharge the gas collected in the gas space by permeation.

For the successful implementation of the invention, it is important that, after the partial pressure equilibrium with the surrounding liquid has been set, the gas separated from the liquid by permeation is displaced from the space between the two gas-permeable foils, an internal pressure gradient building up towards the outlets and thus a rapid outflow of the gas from the gap-shaped gas space is achieved. The time for the removal of the gas is determined solely by the speed at which the displacement front which arises as a result of the progressive reduction in volume moves toward the diversions which are under normal pressure. The resulting internal pressure leads to an expansion of the gap-shaped gas space due to the elastic expansion of the permeation foils, whereby the flow resistance is reduced and the rapid removal of the gas additionally is supported.

The removal of the gas can also be accelerated according to the invention in that a pressure is built up in the liquid container, which acts on the permeation foils and compresses the gas-conducting support layer in the gas space.

The device according to the invention is particularly suitable for monitoring water or waste water for gases which cause damage in the context of environmental protection and for timely detection of disturbances in oil-filled high-voltage devices, in particular transformers. The device can be arranged inside the medium to be examined or outside in a circuit.

B e s c h e i b u n g d e r Z e i c h n u n e n

The drawings represent various options for realizing the invention.

In FIG. 1, the permeation foils 1, which are connected to one another in a gas-tight manner at their edges 5, are kept approximately parallel at a distance by means of an elastic, gas-conducting support layer 6, so that a gas space 2 is formed between the permeation foils 1 and extends via tubular or tubular discharges 3 and a shut-off valve 20 is connected to a measuring cell 9. The device is enclosed by a pressure-resistant container 15, which is connected via the inlet 22 and the outlet 23 to the liquid 4 to be examined, so that the liquid 4 completely fills the container 15.

FIG. 2 shows a very similar device. Here, however, the permeation foils 1 are coated with a gas-permeable layer made of permanently magnetic material 7, the opposite layers being magnetized in opposite directions to one another. As a result, the permeation foils 1 are kept at a distance.

The gas-permeable layer made of permanent magnetic material 7 can also be replaced by a protective grid 16. This is said to cause undesired balloon-like inflation of the permeation films 1 Prevent during permeation.

According to FIG. 2, a hydraulic container 13 can also be used.

In FIG. 3, the permeation foils 1 are surrounded by a gas-permeable metallization layer, which represents the counterelectrode 12. The capacitor plates serving as the electrode 11 are arranged in a cylinder shape around the permeation films 1. To prevent contact between electrode 11 and counter electrode 12, spacer strips 14 are provided.

A direct voltage of 10 KV is applied to the electrode 11. The counter electrode 12 is grounded. As a result, the permeation films 1 are kept at a distance, so that a support layer 6 is omitted.

FIG. 4 shows a further variant of the device according to the invention. Between the permeation foils 1, strip-shaped spacers 8 made of pressure-resistant and gas-conducting material, which run towards the outlet 3, are arranged within the elastic, gas-conducting support layer 6, which simultaneously function as channels.

Section A - A shows a section through the permeation films 1 before the permeable gas is discharged. Section A ,. - A_, after that.

The device according to the invention is embodied in the form of a band in accordance with FIG. 5 and is attached to a hub 24 with its side facing away from the diversion 3, is additionally fixed by a pressure roller 25 and is held taut by a spring 26. The left picture in FIG. 5 shows a side view, on the right a front view is shown.

B e s t e W e g u z A u s f u h u u d e r E r f i n d u n g

example 1

The structure of the device is shown in Figure 1. By means of pump 17 there is a constant flow through the container 15 with the liquid 4 to be examined. To carry out of the first measuring cycle, valve 18 is closed and valve 20 is opened. The valve 19 in the drain line 23 is closed, as a result of which the pump 17 builds up a pressure in the container 15, which acts on the permeation films 1, compresses the gas-conducting support layer 6 and the gas located in the gas space 2 between the permeation films 1 into the measuring cell 9 presses where the detection is performed.

After the transfer, valve 20 is closed and valve 18 is opened. By subsequently opening the valve 19, the pressure prevailing in the container 15 is reduced, the gas-conducting support layer 6 erecting itself when the valve 18 is still open and outside air which is under normal pressure is sucked into the gas space 2 between the permeation films 1. The next measuring cycle begins when the partial pressure equilibrium with the surrounding liquid 4 has been established again in the gas space 2 between the two permeation foils 1.

Example 2

According to FIG. 2, the liquid 4 to be examined is pumped into the container 15 by the pump 17. Both a continuous and a cyclical mode of operation are possible. The valves 18, 20 and 21 are closed. In a continuous mode of operation, valve 19 is open, otherwise closed. After the partial pressure equilibrium has been reached, valve 20 is opened, as a result of which the permeable gas is led to the measuring cell 9 under the application of pressure and is detected there. The pressure can be applied by mechanical means, shown in other examples, or with compressed air.

Example 3

According to FIG. 2, the permeation foils 1 are located in a hydraulic container 13, which is arranged outside the liquid 4 to be examined. After filling, the valves 18, 19, 20 and 21 are initially closed. A defined volume, for example 35 cm, is now removed from the hydraulic container 13 via valve 21. It can be advantageous to install a capillary in the discharge line 3, which ensures pressure equalization with the outside atmosphere during the process. After reaching the partial pressure equilibrium, the mene amount of liquid 4 supplied again or there is a complete exchange and refill. The permeable gas is discharged and detected in the measuring cell 9.

Example 4

The gas space 2 of permeation foils 1 according to FIG. 3 arranged between capacitor plates can be emptied after the partial pressure equilibrium has been reached by switching off the current.

This principle does not require a support layer 6 in the gas space 2.

Example 5

The permeation foils 1 provided with bar-shaped spacers 8 and a support layer 6 are located in a closed container 15. By increasing the liquid pressure after the permeation, the volume in the gas space 2 is reduced, with the channels formed by the spacers 8 and those in the edge zones of the spacers 8 resulting gusset 10 is followed by the removal of the displaced gas.

Example 6

According to FIG. 5, the permeable gas is discharged from the gas space 2 exclusively by mechanical means. When the band-shaped permeation foils 1 are wound onto a hub 24, the elastic support layer 6 is pressed together with the valve 20 and the valve 18 open, whereby the gas is pressed into the measuring cell 9. When the processing films 1 are unwound, the support layer 6 straightens up again, whereby air which is under normal pressure is sucked into the support layer 6 of the gas space 2 when the valve 18 is open and the valve 20 is closed. Valve 18 is then closed. After the partial pressure equilibrium with the surrounding liquid 4 has re-established in the support layer 6, the next measuring cycle begins with the opening of the valve 20 and the winding of the permeation foils 1 onto the hub 24. The gas can be expelled from the support layer 6 are supported by a pressure roller 25. Commercial applicability

The invention can be used commercially in all fields in which gases dissolved in liquids are extracted and then examined qualitatively or quantitatively. The results obtained allow conclusions to be drawn about the state of the liquid. A preferred area of application is environmental protection when monitoring water or waste water. Likewise, the invention enables the operating state of oil-filled high-voltage devices to be monitored, in which damage processes are to be expected and which must be recognized in good time.

Claims

1. Device for extraction with subsequent quantitative detection of the gases contained in liquids using the permeation technique with gas space surrounded on all sides by gas and gas sensor detection in a measuring cell, characterized in that the gas space (2) from two to their The edges (5) of gas-tight permeation foils (1) are formed, the distance between the permeation foils (1) forming the gas space (2) being inversely proportional to the thickness of the permeation foils (1) and smaller than 400 μm at one The thickness of the permeation films (1) is 10 μm and can be reversibly reduced to at least 50% of its initial value by the action of a force, at least one tubular or tubular one, which, depending on the operating state, is effectively sealed with the measuring cell (9) or external atmosphere capable of equalizing connected outlets line (3).

2. Apparatus according to claim 1, characterized in that the permeation foils (1) are coated with a gas-permeable layer made of permanently magnetic material (7), the opposing layers being magnetized in opposite directions to one another.

3. Apparatus according to claim 1, characterized in that the permeation films (1) with a gas-permeable Metalli¬ sierungsschicht as a counter electrode (12) between electrodes (11) are arranged.

4. The device according to claim 1, characterized in that the permeation foils (1) are metallized at their edges (5).

5. The device according to claim 1, characterized in that between the permeation films (1) an elastic, gaslei¬ supporting layer (6) is arranged.

6. The device according to claim 5, characterized in that the support layer (6) in the direction of the diversion (3) has an increasing thickness and / or decreasing compressibility.

7. The device according to claim 5, characterized in that the diversion (3) in the support layer (6) continues in a channel shape.

8. The device according to claim 5, characterized in that in the support layer (6) at least one leisteπför-shaped spacer (8) made of pressure-resistant and gas-conducting material is angeord¬ net.

9. The device according to claim 1, characterized in that the permeation foils (1) are arranged between two scissor-like movable plates, the common pivot point of which is located at the point of the rejection (3) opposite the permeation foils (1).

10. The device according to claim 1, characterized in that the permeation films (1) are arranged between rotatably mounted rollers.

11. The device according to claim 1, characterized in that the permeation foils (1) at their end provided with a diversion (3) under tension on a spring (26) and opposite to a hub (24), optionally with an An¬ pressure roller (25) are arranged.

12. The apparatus according to claim 1, characterized in that the permeation foils (1) are designed in the form of clockwork spiral springs and the diversion (3) is located at the outer end.

13. Use of the device according to claim 1 to 12 for monitoring water or waste water for gases causing damage.

14. Use of the device according to claim 1 to 12 for the timely detection of disturbances in oil-filled high-voltage devices, in particular transformers.