Treating Oily Water Condensate
A compressed air system will produce condensation which is the moisture that drops out of a compressed air flow as it cools.
The liquids drained from the system will contain oil if the compressors have lubrication in the compression chamber. This includes oil flooded rotary screw compressors and reciprocating compressors with lubricated cylinders.
This oily water mixture causes an environmental concern. There are regulations limiting the amount of lubricants that can be dumped on the ground, drained into surface waters or poured into local sewer systems.
There are several methods for handling the oily water mixture. However, the producer of the oily water is ultimately responsible for complying with environmental regulations.
It may take a little research, but you can find the regulations that apply to your situation. Then, you can choose the best way to handle the oily water mixture for your facility.
Some industrial companies collect the oily water mixture and pay an outside vendor to haul the mixture offsite for disposal. This is expensive when you consider the following:
a) Compressor condensate is mostly water. A rule of thumb is to expect a 50 to 1 ratio, 50 parts water to 1 part oil. This means there is approximately 1 gallon of oil in every 55 gallon drum of oily water condensate.
b) Air systems produce an enormous amount of condensate every day. A 100 horse power compressor operating in a climate of 70 degrees F with 80% humidity will generate approximately 2 gallons of condensate each hour of operation.
c) Disposal companies charge between $150 to $250 to dispose of a 55 gallon drum of compressor condensate.
The savings are considerable if you properly separate your condensate, and only pay to dispose of the oil.
If you use the numbers above, a 100 HP compressor, operating 24 hours, will produce a minimum of 48 gallons of condensate a day and only 0.96 gallons of this is oil. It will take you 57 days to accumulate a 55 gallon drum of oil with a minimum disposal cost of $150.
In that same 57 days, without separation, you will accumulate almost 50 drums of condensate with a minimum disposal cost of $7,500. That saves you over $7,000 in disposal cost during 2 months of operating at the conditions of this illustration.
There are several products being used to separate the oil from the water. Here are a few points to consider about 3 of these devices.
An Oily Water Filter
A new product uses a polypropylene filter bag to absorb
the oil as it moves though a housing.
This treatment works by exposing the oily water mixture to a continuing low level heat. The heat vaporizes the water into steam, but remains below the vaporization point of the oil.
The water is driven off to atmosphere in the form of vapor. The remaining oil is now ready for removal and disposal.
There are no filters to monitor or replace, but a distillation unit will have a higher initial cost and a constant operating energy cost.
A gravity separator is essentially a holding basins that allow for natural separation of oil and water. The separated water is usually passed through an activated carbon filter before draining.
This type of product will not work on all types of compressor lubrication because some oils do not readily separate from the water in the reservoirs. And, the large settling reservoirs have been known to stimulate bacteria growth and odor.
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