عدد المساهمات : 3533
تاريخ التسجيل : 15/09/2009
العمر : 49
الموقع : مصر
|موضوع: مبادئ فصل الزيوت السبت مارس 31, 2012 2:16 am|| |
Oil separation in general.
Oil/water separation, and anything that compares to that, is a complicated process. It may be useful to learn more about this and get a better understanding on what is going on in your tank, bath or installation. Subjects that are discussed in this section are:
Oil/water separation; the basics.
Oil/water separation; beyond the theory.
Oil separation and aqueous cleaning.
Solids in oil/water separation.
What Suparator® is.
A simple, passive, construction! No controls, no instruments, no moving parts. Just making the laws of physics work for you. That's all, but it means everything in the separation of oil from water.
The Suparator® principle is a patented solution for the removal of floating substances, like oil, from water or other aqueous media. Initially developed for oil spill recovery applications, the principle has shown to be incomparably effective in the removal of any amount of floating matter.
The three-step separation principle.
The key to the Suparator® technology is the patented principle which is explained below. Unique about this principle is the three-step separation mechanism; collect -- concentrate -- separate. This enables separating even the smallest traces of oil, without a drop of water. All with a simple, passive construction.
The sketch at the left shows a channel in cross-sectional view. Through this channel flows, from left to right, an aqueous fluid (colored blue) with oil (colored red).
A number of valves are mounted across the channel, such that the major part of the flow passes underneath (under flow) and a smaller portion passes overhead (upper flow).
Click here for a video of the plexiglass model.
The principle functions as follows:
The numbers in the following explanation relate to the numbers shown in the sketch above and the photos to the right and below.
The upper fraction of the flow is separated from the rest.
This fraction passes overhead and carries along all the oil, regardless the amount.
Oil and oil traces are collected(step 1).
Water and oil (traces) are carried into the first compartment. Through the opening at the bottom, water only is sucked out of this compartment.
Oil is being concentrated(step 2).
The oil, with still fairly high concentrations of water and chemicals, is concentrated into a floating layer of considerable thickness. Water and chemicals migrate towards the interface and reenter the water flow.
Oil is being separated(step 3).
The upper fraction of the accumulated floating layer is skimmed off: pure oil is being separated.
And how it looks in an actual unit.
The photo to the left shows an 86/320 tank in use, viewed from above, right at the Suparator® construction.
The numbers refer to the explanation above. It is clearly visible how the traces of oil on the surface are carried into the Suparator® construction where they are collected, concentrated and subsequently separated.
At 4., in front of the final oil weir, there is already an accumulation of oil visible. This picture was taken shortly after the unit was taken into service.
How the performs in practice.
A Suparator unit in use.
Suparator® systems have been used for over a decade now. Everything that is explained about the technology and its advantages in these pages has become clear from the experience that was gained.
Suparator® proved to perform better than expected, in that it:
Makes any oil/water separator work better and achieves a level of performance that was considered impossible with physical separation only.
Can eliminate problems associated with oil water separation, like rag-layer build up, separator blow-through and equipment malfunctioning.
Is a really great tool for saving money since it reduces maintenance and waste disposal cost to a fraction of what it was.
Is a great companion to newly acquired technologies like membrane filtration and modern cleaning technology.
Cut cost; extend functionality.
More often oil separation is about sludge, grease, froth etc. than it is about oil.
Oil, grease, solids, chemicals, and what other substances found in the process, interact to form floating substances that are far from the nice, fluid, substance we think off when we say oil. A common way to deal with this is to regularly clean the installation: not just the oil separator but the washer, the cleaning bath, the pit or what ever. For Suparator® there is a more intelligent way to deal with this!
To help remove the non-oil substances, and to minimize operational and maintenance cost, a number of extensions have been developed for Suparator®. These include:
Flush headers are used to wash away the material that would otherwise accumulate and cause a Suparator® unit to need cleaning. Typically flushing is done during normal operation, using small amounts of fresh water.
Flush headers, mounted in crucial area's in a system, and designed to generate the required flow conditions, "stir up" the dirt and accumulated materials and cause it to be carried off with the flow.
A function which can easily be automated, practically eliminating the need for cleaning of the unit.
The animation on the right gives a good impression of what we are talking about. The froth that is removed here is a bio-mass which is formed in the installation, due to the combination of substances and the right temperature.
The flush headers are activated at the start of the sequence. The material on the surface accumulated before that, over a period of 8 to 10 hours. All material is washed away with the oil (a colorless, transparent solvent), into the oil trough.
As a result of installing the flush headers, the installation, shown in this animation, has not been cleaned for over a year now, where prior to this, cleaning was necessary every 2 weeks!
Some floating matter tends to build up and will not go over the oil weir. As a result it builds up in time and inhibits liquid oil from being separated as well. Manually removing the accumulated material at given times is a solution, but may not be very practical. A rake skimmer is the intelligent way to address the problem.
The idea is to sweep the surface in such a way that material that otherwise would accumulate, and which would not go over the valve tops or the oil weir, is pushed towards the oil weir and over it. There is no need for a full surface sweep or a multiple rake sweeping device; the Suparator® construction already takes care of cleaning the surface and accumulating any floating material.
See this video. A single rake, moving slowly and wiping the surface at the Suparator® construction does all the work. It is possible to have the rake follow a straight track, just wiping the tops of the valves, or to have it go up and down, scooping the material from all the compartments as shown in this demonstration video. What is preferred depends on the application.
The flexible part.
Suparskim® skimmers are used to take off the top layer of fluid from a tank, bath or pit. They are not an oil separation device by themselves but are an essential component in the Skim & Treat® method.
Suparskim® skimmers come in fixed-mounted and floating versions to accommodate for any level variation.
The variety in oil/water separation applications is enormous. Not only in the nature of the oil/water mixture, but also in the variations in shape, size and dimensions of the installations the mixture is to be found or treated. Washers, cleaning baths, coolant sumps, API separators, sewer systems etc..
To connect to this variety of installations in the right way, flexibility is a key issue. Suparskim® provides this flexibility. Typically one of the many Suparskim® models is mounted inside the tank, bath, pit or other and takes out the oil/water mixture for further processing.
How Suparskim® functions.
Suparskim® skimmers make use of a simple and reliable principle.
The skimmer automatically seeks a position whereby the same amount of liquid flows into the trough as is being evacuated. This way the skimmer responds to both changes in the liquid level and in the amount of liquid being evacuated. Its range is limited by the construction of the skimmer.
Suparskim® skimmers support optimal separation performance and eliminate problems with floating layers from oil, grease or other light substances. By continuously removing the top layer from a bath or tank, and separating the oil from this fluid, an optimal result is achieved. Floating layers can no longer be formed; Suparskim® skimmers don't even leave an oil film behind!
The sketches above show a skimmer trough in cross sectional view, partly submerged in a liquid.
When the liquid level (1) is high enough relative to the nose (2) of the skimmer, the trough will fill up with liquid.
The weight of the liquid (3) in the trough changes the balance and will cause the trough to tilt backwards (4).
If the liquid is evacuated from the skimmer (5) the level in the trough will drop (6).
The balance is again disturbed but now in the opposite direction (7) and the nose of the skimmer will drop below the liquid level (8) allowing more liquid to flow into the trough.
To skim off the top layer from a body of liquid continuously, Suparskim® skimmers must follow the liquid level.
The level variation a Suparskim® skimmer can accept is limited by the dimensions and construction of the skimmer. For level variations beyond 90 mm, floating versions are used, whereby one or more Suparskim® troughs are mounted to one or more floats. The float will cause the skimmer to follow the liquid level. The skimmer trough, exactly as with fixed mounted versions, takes care of skimming off the top layer only.
Oil/water separation particulars.
The separation of oil from water or aqueous fluids is one of the most common problems throughout the industry.
Many devices, systems and solutions have been developed over many years, some with success, most with little to no results. Many physical principles have been put to use, like adhesion, gravity separation, absorbance, membrane filtration, but also chemical and biological technologies.
The Suparator® technology concerns a physical separation technique, but one that is often just as effective, sometimes even more effective, than chemical or chemical/physical separation.
Characteristics of the problem
Distinctive for oil/water mixtures is that we have two immiscible fluids which, given time, will separate spontaneously.
A mixture that is not (completely) separated yet is called an emulsion. Oil is not dissolved in the water phase but is dispersed throughout the water phase as very fine droplets. The individual droplets are not visible with the naked eye, but the oil causes the water to be turbid. The more oil, the more turbid the water will be, from a very light haze to a milky, translucent, liquid. Depending on the color of the oil, the mixture will get a yellowish to brown coloring as well. Read more about it here .....
Free floating oil
It seems simple to remove a layer of oil from water, but it is not. Compare it with removing the floating grease bubbles from your soup with a spoon. No matter how hard you try, you will always get more soup than grease.
That is why many oil separation devices, as a compromise, settle for removing only the surplus of oil, leaving a more or less thick oil layer behind in the separator all the time. This is a very common situation in oil/water separators everywhere. Read more about it here .....
The thin film approach
Thin film refers to the removal of even very thin layers of oil. Any device, capable of removing even a thin film of oil, without removing water, will thereby remove all the dirt in the oil, and inhibit the build up of floating layers with the unavoidable interface layers.
Thin film oil removal has proven to bring unexpected improvements in the overall separation of oil from aqueous media. More than anywhere else, the principle of thin film removal proves itself when applied to valuable production fluids like aqueous cleaners and machine coolant. Read more about it here
The characteristics of oil/water separation
Distinctive for oil/water mixtures is that we have two immiscible fluids which, given time, will separate spontaneously. Under the influence of gravity the oil will rise to the surface and form a layer on top of the water phase. This is what is called gravity separation.
A mixture that is not (completely) separated yet is called an emulsion. Oil is not dissolved in the water phase but is dispersed throughout the water phase as very fine droplets. The oil "emulsifies"; oil and water build an emulsion. Depending on the characteristics, an emulsion will be more or less stable. The smaller the droplets, the longer it will take for the emulsion to separate under normal gravity conditions. Intensive mixing, which breaks up the oil and creates small oil droplets, will cause the oil to emulsify and separate less readily from the aqueous medium. That is why pumping and transferring oil/water mixtures can have an adverse effect on separation.
Other factors that negatively influence the separation (or de-emulsification) are the presence of other pollutants or chemicals in the mixture. In particular emulsifiers (surfactants, tensides) that are used abundantly in cleaners, metal working fluids and in food stuff, are known for their negative effect on oil/water separation.
Removal of floating oil
In the separation of oil from water, some devices target the removal of the floating oil, some the removal of the dispersed oil. Although some of the technologies for oil removal claim to target both, they often require pre-separation of the free (floating) oil for economical or technical reasons.
There are a number of reasons why it is not possible to "scoop off" an oil layer with a bucket or a weir, but there is one obvious one. Compare the oil layer with a piece of wood. As the wood, the oil layer "sinks" partially into the water. How deep it sinks depends on how thick the oil layer (the piece of wood) is, and how heavy the oil is (what density it has).
When removing floating oil with a simple overflow weir, initially pure oil is separated. This will cause the oil layer to get thinner and the interface between oil and water to move upwards, towards the top of the weir.
Even before the oil is completely gone, water will start spilling over the weir. Any over flow weir construction will result in high to excessive amounts of water, being separated with the oil, unless a relatively thick oil layer is allowed to sit on the surface all the time.
Why this situation is undesirable is explained here. The Suparator® thin-film technology overcomes these problems all the way, offering many advantages.
There have been many attempts to automatically adjust the position of skimming buckets or weirs, all without little to no success. The reason is that there are other factors influencing the skimming process. One is that, due to its lower viscosity, water will more readily flow towards a skimming device than oil. The skimming device quickly creates a hole in the oil layer and starts to remove more water than oil.
Many oil separation devices, as a compromise, settle for removing only the surplus of oil, leaving a more or less thick oil layer behind in the separator all the time. As a result a dirty, messy layer is formed at the interface between oil and water. As nothing gets removed, except for the nice top oil layer, in time more and more dirt accumulates at the interface and gets re-entrained in the water phase. This mechanism causes the performance of oil/water separators to deteriorate in time.
Gravity separator basics.
Gravity separation is a very simple principle, and most people have a basic understanding of it. However, there are a number of aspects that people are seldom aware of, and very frequently basic rules are violated.
This, by means of a series of animations, explains oil separation in a simple tank, in a classic separator, in a separator with baffles and in a Suparator® separation system.
The information in this section allows the reader to compare oil separators of various constructions and clearly shows how conditions improve when using the Suparator® technology.
About density, gravity and flow.
Typically, oil, and comparable substances, have a lower density than water, and gravity will cause the lighter oil to rise to the surface and float on top of the water. That's what gravity separation is.
Ideally, for an oil water mixture to separate, there should be no flow or agitation at all. That is what settling tanks are about. Normally though, the amount of fluid to be treated dictates flowing it through a device to separate the oil.
In that case the flow inside the separation device should be horizontal and laminar. Horizontal so that the direction of the flow is perpendicular to the direction of the gravity forces; the flow does not interfere with the upward traveling of oil drops. Laminar to avoid re-mixing of oil and water.
Oil separation in a simple tank.
When feeding an oil/water mixture through a tank or separator, oil, due to its lower density, will tend to rise to the surface and accumulate on top. This is what is called gravity separation.
Important thereby is the flow in the separator. A strong turbulent flow will mix oil and water; the oil can not escape to the surface. A horizontal laminar flow is ideal as this gives the oil the best change to reach the surface.
Observe the flow through the tank in the sketch at the left. The inlet is on the left, the outlet on the right. In the middle of the tank, the flow uses the full height of the tank and, provided the flow rate is not too high, the flow pattern will be laminar.
Notice that the corner sections of the tank do not really participate. There is no flow through the corners, which reduces the effective space and thereby the performance.
Click the image to let the oil in. In a simple tank, little will happen at the entrance side. The flow will push the oil layer towards the outlet side, and the downward flow at the end will pull along oil and dirt.
Oil separation in a classic separator.
To improve the design, the separator on the left is provide with a baffle at the inlet side, to divert the flow, and with under and over flow weirs at the right end to maintain a constant high level and minimize the oil that escapes.
The available space is used more effectively and with a laminar flow pattern the oil will rise to the surface well enough. To create a laminar flow, the separator should be dimensioned correctly ( L x W = 2 : 1 and a height of 80 to 100 cm) and the flow rate must not be too high for the size separator.
Click the image to let the oil in. The standard separator arrangement is a significant improvement. Most of the tank is used and less oil can be pulled down, below the underflow weir. The floating oil will initially be pushed towards the underflow weir, but as the layer gets thicker, it will cover the entire surface of the separator.
Putting baffles in an oil separator.
There are many oil separators on the market that have all kinds of baffling inside. The idea is to force the flow to follow a certain path making the oil/water mixture stay inside the separator longer. Unfortunately the result is the opposite of what one is trying to achieve. The path may be longer, but the velocity of the flow increases significantly. The result is a turbulent flow and "dead zones" where no flow occurs and which do not contribute to the separation.
Look at the image on the left. In the middle of the separator is a baffle plate with an opening near the bottom. See how the flow is forced to follow a path that leaves large sections of the tank unused. This single baffle plate has a very strong negative effect on the separation.
What is true for the single baffle plate is true for any construction that prevents or interferes with a horizontal, laminar flow. Even coalescing plates, often installed to improve separation, can have a negative effect on the flow pattern.
Click the image again. See what the effect of the baffle is. Only large oil drops will succeed in reaching the surface and getting out of the flow. The unfavorable flow pattern and the high velocity underneath the baffle make is impossible for the finer oil drops to escape. A lot of oil is carried off with the effluent.
Adding Supartor® to an oil separator.
Now look at the tank shown at the left. The box, shown inside the tank, represents a Suparator® unit.
Part of the total flow will pass through this unit and the result is a significant improvement of the flow pattern. There are hardly any dead zones in the separator now and a laminar flow is achieved over practically the full length of the tank.
The amount of oil that can escape via the underflow weir in reduced to an absolute minimum which is a big improvement compared to any other type of gravity separator.
Click the image for oil. Using the Suparator® technology changes the entire picture. There are no floating layers; oil can not accumulate as it is removed instantly by the Suparator® unit. And with the oil, all the dirt is carried off and removed.
Notice how the flow creates optimal conditions for all the oil to be captured and carried into the Suparator® unit.
Suparator® separation systems perform better than any other oil separation device, simply by creating optimal conditions for oil separation.
"Thin-film" oil separation.
Thin film separation refers to separation technologies that are capable of removing even a thin oil film from water. This approach eliminates the build up of a dirt or rag layer, common to two phase separation, at the interface between oil and water. The dirt gets removed with the oil.
Suparator® thin-film separation.
The Suparator® technology uses a unique principle to remove every trace of oil on the surface, without any water. Unlike any other oil separation technology or device, it functions independent from the amount of oil and the oil layer thickness. It removes the thinnest possible oil film, even sheen, without any water, and at the same time has a higher removal rate than any comparable device.
To achieve this, the Suparator® principle applies a three-step approach. It gathers all the oil, even traces, collects and concentrates the oil in the second step and only than removes it in the third step.
This active removal of all oil, without leaving any floating matter behind, has very significant advantages over alternatives methods and devices. It gives optimal control over all the pollution in the aqueous medium and is capable of removing even emulsified oil by means of induced coalescing.
Solids and thin film separation.
Using the Suparator® thin-film separation technology has a significant impact on the solids concentration in the aqueous medium. Typically heavier particles will settle to the bottom of a tank or bath, separating it from the fluid, and will be removed as sludge periodically. Finer materials however tend to remain suspended in the fluid, more so because they are associated with the oil which prevents settling or even makes this material float to the surface. Thin-film removal will separate this material with the oil.
Observe the two samples to the right, both pure floating matter, removed with a Suparator® separation system, without any water.