Patent Application
20130126405
The invention relates to an oil/water separating device.
Oil/water separating devices are frequently used in connection with air compressors. Air compressors produce compressed air by sucking in and compressing ambient air. The air humidity contained accumulates as condensate due to physical reasons and due to the compressed air being dried. This condensate is waste water which, owing to the introduction of lubricants by the air compressor, most frequently is not permitted to be discharged into the public sewer because it exceeds the hydrocarbon concentration limits.
Given a volume flow of 60 m3/h sucked-in air, a mostly discontinuous condensate flow of 1.6 l/h charged with 300 mg/h oil may be produced; this corresponds to 190 ppm.
Depending on the climatic conditions (ambient temperature and humidity), the type of oil used, design and operation of the compressor etc., these values may fluctuate.
The bond between water and the lubricant also varies and ranges from mixtures of oil and water over dispersions to emulsions. Admissible values for discharge into the sanitary sewer are 20, or 10, in part 5 ppm (parts per million). Thus, a special waste is produced which has to be expensively disposed of by a waste disposal company, even though 99.5% percent of it is water from ambient air humidity.
The object of commercially available oil/water separating devices is to process the condensate on-site so that it can be discharged, i.e. to remove the oil contents from the water in a cost-effective manner. Known apparatuses of this design usually employ several separating stages in order to achieve the desired purity.
The condensate is discharged slowly and thus, with little turbulence, via a pressure relief element into a preseparator. The latter works according to the principle of gravity separation and provides for the deposition of heavy, sedimentary contaminants (density greater than 1 kg/dm3) and the floating of free oil contents (density lower than 1 kg/dm3), which then flow into a receiving container. In a second stage, fine oil droplets are separated from the condensate by means of adsorption filters, which are mostly based on oleophilic material and active carbon with a very large internal surface.
In another design according to the prior art, the condensate, together with the free oil contents, is fed through the adsorption filter, which in turn floats on the condensate surface and soaks up oil contents that deposit here (density greater than 1 kg/dm3). The construction works according to the principle of the corresponding water column; processed condensate leaves the apparatus at the treated-water outlet in the direction towards the sewer in the same extent that new condensate flows in.
The collected free oils and the oil-saturated filters are usually thermally utilized, but may also be treated.
Strongly dispersed or even emulsified condensates cannot be treated in these apparatuses and are usually treated by more complex methods, e.g. by membrane, evaporation or decomposition processes.
In practical use, there is occasionally the problem of filters or oil/water separating devices becoming blocked without the corresponding entry of oil, i.e. by additional foreign materials. The reason for this is the existence of bacteria, algae or fungi in the condensate. This is frequently caused by the installation conditions for the systems, e.g. in fruit juice companies, or the operating conditions, e.g. a high machine capacity utilization. An important cause also includes the lubricating oils and their use; modern lubricating oils for air compressors are used for very much longer and contain fewer and fewer bactericidal additives such as, e.g. softeners.
Due to the operational residence time in the oil/water separating devices, bacteria, algae and fungi produce a slime that partially deposits on the water surface, but also sinks and sediments or remains suspended. When flowing through the filtration stages, it can deposit on their surfaces and then leads to a blocking which, due to the operationally low admission pressure, no longer permits condensate to pass through. The apparatus then runs over, and the operating life of the filters is thus unacceptably reduced, e.g. from at least 6 months to 6 weeks.
An exemplary embodiment of the present invention to provides an oil/water separating device which has a long operating time even when slime-like substances accumulate in the mixture to be separated. At the same time, the oil/water separating device is supposed to have a simple design and be cost-effective to produce.
An exemplary embodiment of the invention achieves desirable results via an oil/water separating device which is characterized by an additional mechanical separating device for separating slime-like substances from an oil/water mixture.
For the purpose of simplification, the term oil/water mixture will be used below for the liquid that is conducted through the separating device, irrespective of the content of oil or the oil constituents in the liquid. Thus, the term also relates to the liquid behind the filter elements in the flow direction.
An exemplary embodiment of the invention is based on the insight that a bactericidal treatment of the condensate, which at first appears obvious and even advantageous, is disadvantageous for several reasons. The introduction of additional harmful substances into the condensate, i.e. into the waste water, leads to a load on downstream sewage plants. Moreover, defining a suitable agent is difficult because the conditions of every application are different. A complete elimination is also difficult; due to the subsequent residence times in the oil/water separating devices, the residues of bacteria, fungi or algae will again grow to problematic magnitudes. Furthermore, such methods most frequently require a more complex plant technology, e.g. for backwashing, which then would be disproportionate to the simplicity of commercially available oil/water separating devices.
In an exemplary embodiment, the invention advantageously prevents the development of slime-like substances, but rather in designing the oil/water separating device in such a way that it is capable of compensating for or withstanding the development or an increased accumulation of slime-like substances without the operating time being substantially limited. This solution contradicts the common prejudice that a mechanical separation of such substances is hardly possible, or possible only with an increased effort.
According to an exemplary embodiment of the invention, the separating device for separating the slime-like substances from the oil/water mixture can be formed by different systems.
The following embodiments have proven particularly advantageous:
All embodiments have in common that the slime entering the separating device is filtered and retained.
The advantage of an upstream filter element, i.e. a filter element disposed outside the housing of a main filter, lies in the fact that it can be cleaned and replaced independently from the separating device or the main container.
In all the embodiments, the filtration or separation of the slime serves for keeping clear or slowing down the blocking of the main filter which separates the oil from the oil/water mixture. For this reason, the separation of the slime always takes place prior to the separation of the oil or the oil-containing components from the oil/water mixture.
The utilization of a sucking or pressing pump as a flow regulator in connection with a slime filter has the great advantage that the blocking of the filter elements is hardly possible or is slowed down significantly. In any way, the aim is to always maintain the flow-through of oil/water mixture given for the conventional oil/water separator, which is why the pump is considered a flow regulator. This results in significantly higher operating lives for the separating device. This is particularly advantageous in cases where regular maintenance intervals are scheduled and a replacement of the filter elements is to be avoided in between the scheduled maintenance dates. The pump can be level-controlled or time-controlled. Level control means that the pump switches on if a corresponding filling quantity is reached in the separating device. Alternatively, and in particular in the case of a regular feed into the separating device, the pump can also be switched on after certain intervals. A combination of the two options is also conceivable.
Another essential advantage owed to the use of the pump lies in the fact that the pump is able to deliver in the reverse direction and that thus, the separating device can be cleaned by backwashing.
A nonwoven fabric is particularly suitable as a filter material because it has only a very low flow resistance while having a large surface area at the same time.
The integration of ventilation means that a gas is supplied which moves or entrains sediments in the direction opposite to the flow direction of the oil/water mixture. It is thus avoided that the main filter, which is supposed to remove the oil-containing constituents from the oil/water mixture, becomes clogged with sediment; at least the blocking of the main filter is slowed down. In addition to the ventilation, special sediment spaces can be provided in which sediment can settle. A combination of nonwoven fabric, ventilation and sediment space is also possible.
Various exemplary embodiments are explained below with reference to the following description of the figures.
In the figures:
The following Figures show different variants of an oil/water separating device 20 according to an exemplary embodiment of the invention. It has a housing 23.
In a first embodiment according to an exemplary embodiment of the invention, a filter element 22 which removes slime-like substances from an oil/water mixture is provided in the feed of a commercially available oil/water separating device 20, or of the housing 21 thereof. It was found that such a filter element 22 can preferably be formed of an aluminum foam coated with nanosilver; however, it can basically be formed of, or at least include, any material that has germicidal properties. For example, the filter element 22 can consist of a housing in which D45 discs are disposed in a stack and which has a volume of 0.2 to 0.5 liters. The mixture is fed under pressure and at an increased speed, whereby the filter element 22 remains clear and is not clogged over a long period of time owing to the only short residence time of the mixture within the filter element 22.
The pre-cleaned liquid exits the pre-filter 26 through pre-filter openings 31 and enters a main filter 30 which is separated from the pre-filter 26 by one or more spacers 28. The spacer(s) 28, among other things, cause the pre-cleaned liquid to collect and settle prior to entry into the main filter 30. Oil separation then takes place in the subsequent main filter 30. The cleaned liquid is conducted out of the oil/water separating device 20 via a riser 33.
Alternatively, it is also possible according to an exemplary embodiment of the invention to control or regulate the pump 36 in a time-dependent manner. This is possible without any trouble particularly if the feed quantity into the oil/water separating device 20 per unit of time is known. The level detecting device 32 can still be provided as a back-up system; in a simple variant, however, the level detecting device 32 can be omitted completely.
A substantial advantage of using the pump 36 lies in the fact that its capacity can be adapted to different conditions on-site or to contaminations of the liquid. By using the pump 36, it is possible, without any problems, to overcome the flow resistance resulting from the filter(s) 26, 30. Due to this mode of operation, the same amount of oil/water mixture per unit of time is treated as in a simple oil/water separator of identical capacity. Thus, the load, design and mode of operation of the apparatus remains the same; the pump thus merely works as a flow regulator in the case of an impairment by slime-like substances.
In another alternative embodiment, a pressing pump 36, which is then disposed before the filters 26, 30, seen in the flow direction, can be used instead of a sucking pump 36.
According to an exemplary embodiment of the invention, it is also possible to use the embodiment according to
In the embodiment according to an exemplary embodiment of the invention in accordance with
In the embodiment according to
Finally,
Advantageously, the main filter 30 can also be of a multi-stage design in all of the above-described embodiments;
The two filter stages can be realized separately from each another; however, they can also be combined with each other in a single filter stage. In the latter variant, the two filtration processes take place within a single filter stage. If two filter stages are realized, then they can be immediately adjacent to each other, i.e. be in contact with each other; however, they can also be separated from each other by a screen-like layer. Such a screen can consist of any suitable material. In a particularly advantageous embodiment, the various filter stages can also be replaced independently from one another, which is also facilitated by a screen located between them. The multi-stage construction of the main filter 30 is particularly suitable for use with a sucking or pressing pump because the latter pulls or presses the oil/water mixture through the main filter even if that is blocked by, for example, bacteria on its outer face.
The invention is not limited to the embodiments shown but also includes, in particular, combinations of the different possibilities for the separation and deposition of the slime-like substances.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2010 002 431.7 | Feb 2010 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP11/52857 | 2/25/2011 | WO | 00 | 8/17/2012 |
