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Frequently
Asked MSR Oil and Water Separator QuestionsThe
first thing to do is to make very sure you know all of the possible inlet situations
- maximum flow rate, minimum temperature and oil types and concentrations that
may occur in the inlet. Make a schematic flow diagram of the system and identify
possible pressure drop causing equipment such as pumps and valves.With this information,
MSR can estimate the oil droplet sizes that are likely to be present in the inlet
water. We use this information in our proprietary computer program to predict
operations of the system. We estimate a separator size and configuration and do
a simulation calculation to see if the performance will meet the required effluent
concentration. We then adjust the size larger or smaller to ensure a proper fit.Because
the separation depends on Stokes's Law and we are careful to ensure (in the separator
design) that the conditions of this physical principle are met, the final design
system will meet the required effluent. We try to be very conservative in estimating
the droplet sizes so that the final design will be conservative and capable of
handling variations in flow and other conditions. The physics work and Sir Isaac
Newton's gravity can be trusted to operate correctly and predictably every time.A
very convenient property of coalescing plate separators not shared by some types
of oil-water separators is that at flow rates lower than the design flow they
just work better!
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Why is
it better to direct the flow into a separator by gravity flow than pumped flow?
Anything that decreases the average droplet size in the inlet of a
separator will decrease the performance of the separator. The type of equipment
that decreases droplet size is anything that causes shear in the inlet stream.
This includes pumps, especially centrifugal pumps, valves, especially globe and
other control valves, small or rough piping and undue amounts of elbows or other
fittings in the inlet pipe.If I have to pump into a separator, what is the best
kind of pump to use?The best type of pump to use is a positive displacement pump
such as a diaphragm pump or screw pump. The worst are centrifugal pumps.
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What
information do I need to gather for designing an effective, reliable separator?
Numerous factors must be considered in the selection and design of oil-water separation
system. Among these are:
1. Flow rate and conditions
2. Degree of separation
required - effluent quality
3. Amount of oil in the water
4. Existing
equipment
5. Emulsification of the oil
6. Treated water facilities
7. Recovered oil disposal method For industrial and some municipal applications,
flow rate, amount of oil, flowing temperature, and other conditions affecting
separation such as whether flow is laminar or turbulent may be easily determined.
For stormwater applications, however, it may be necessary to estimate water flows.
The degree of separation required is usually a matter of statutory or regulatory
requirements, but if the water is discharged to a sanitary or industrial treatment
plant it may be negotiable. The amount of oil in the water may be known, especially
in industrial applications, but it will often be necessary to estimate the quantity
in stormwater applications. MSR can provide guidance about quantities to be expected,
and some information has been published about stormwater quality Existing equipment
such as API separators may affect the design of equipment to be used. Often it
is possible to retrofit existing equipment with more sophisticated internals to
enhance separation quality. It is necessary to ensure that adequate size piping
is provided for downstream treated water removal to avoid flooding the separator
and perhaps filling the oil reservoir with water. A downstream test point should
be provided to allow for effluent testing. Adequate storage facilities for the
removed oil should be provided and means for recycling the oil included. Careful
records of removed and recycled oil should be kept to avoid possible future regulatory
problems.
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Can
I use soaps and detergents and still have my separator work well?
Soaps and detergents (known collective as surfactants, which is a contraction
of surface active agent) can cause emulsions that are very difficult to remove.
Without careful attention to the amount and type of soaps and detergents used
it is likely that a system will NOT operate satisfactorily if they are used. The
degree of emulsification of the oil is difficult to assess, but steps can be taken
to discourage the formation of emulsions and encourage the breakup of emulsions
that are inadvertently created. It may be necessary to substitute quick-break
detergents for conventional detergents that are also emulsion causing. Quick-break
detergents are those detergents designed to remove the oil (or grease) from the
item to be cleaned and then quickly dissociate again from the oil, leaving the
oil as free hydrocarbon droplets in the water. MSR will be glad to make design
suggestions and / or send our list of acceptable quick-break detergents.Note:
the small amount of detergents in detergent motor oils will not cause problems
with the operations of oil water separators.
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I
have dirt and / or grit in my flow stream - what will that do to the system? Small
quantities of dirt and grit will not harm the operations of the separator; they
will only cause some eventual plugging that must be removed periodically. If large
quantities of solid particles are expected, it is wise to provide a grit removal
chamber before the separator. These chambers should be designed according to normal
design parameters for grit removal as used in sanitary sewer plant design. MSR
will be glad to offer suggestions on this design.
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What
is the benefit of using separators over absorbents? The biggest
problem with the use of absorbents is that they are quickly used up, and since
there no way to determine if they are exhausted without laboratory testing, they
are often left in place long after their useful life is done. The used absorbents
are sometimes hazardous waste and will certainly cause a disposal cost.
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What can
I do about dissolved hydrocarbons? In general, hydrocarbons are only
marginally soluble with the notable exception of Benzene and some other aromatic
hydrocarbons. Even these are removable using coalescing plate separators or other
physical means so long as they are either removed so quickly there is not time
for the dissolution to occur or if they are present in concentrations greater
than the solubility.Dissolved hydrocarbons are, strictly speaking, not covered
by the Clean Water Act since they do not cause a sheen on the water. Many analysis
methods will detect dissolved hydrocarbons and some jurisdictions are concerned
about them, so it may be necessary in some cases to treat for their removal. Physical
methods such as coalescing plate separators will not remove dissolved hydrocarbons
and other methods such as biological treatment or absorbents are required.
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What
can I do with the oil recovered in a separator? Removing the
oil from the separators is not enough to protect the environment, it must also
be re- cycled to ensure that it is disposed of properly. Current U.S. law can
hold the owner of the oil-water separator responsible if this oil is not properly
disposed of, even if the owner has paid for proper disposal. There are many local
firms involved in recycling hydrocarbons. Most will be able to tell you what the
local regulations are and usually offer a pick-up service.
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What
are the ideal inlet conditions for an oil water separator? I'd like to make it
work as well as possible. Ideal inlet conditions for an oil-water
separator are:
1. Gravity flow (not pumped) in the inlet piping
2. Inlet
piping sized for minimum pressure drop
3. Inlet piping straight for at least
ten pipe diameters upstream of the separator (directly into nozzle)
4. Inlet
piping containing a minimum of elbows, tees, valves, and other fittings.
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