Liquid purification or separation – Processes – Separating
Patent
1998-09-24
2000-06-06
Popovics, Robert J.
Liquid purification or separation
Processes
Separating
210800, 210801, 210805, 210320, 210187, 210175, 210519, 2105321, 210538, 210540, B01D 1702
Patent
active
060714204
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for separation of water and oil or water and liquid that is not soluble in water, and to an apparatus for carrying out the method.
Oil, such as fuel oil, propellants like bunker oil from ships, return oil and waste oil, often contains large quantities of water. A load of waste oil, for example, often contains water in the amount of 95% or more, in addition to a number of particles that are generally found in the water. The return oil may be sold with concession from SFT (Statens Forurensingstilsyn [National Pollution Control Authority]) to special receivers who use it as a replacement for heating oil. These recipients have, however, set a maximum limit of 5% (in certain cases 10%) of water in the oil. In the meantime, the oil having a higher water content has little economic value, but can constitute a major environmental problem. The water content therefore must be reduced.
When bunker oil for ships is received, it also often contains excessively large quantities of water, in certain cases more than 5-10%. This water may create problems during the operation of the ship and must therefore be separated out from the bunker oil. First, with some types of oil it may be very difficult to separate out the water with the equipment available on board. Moreover, the customer is probably not interested in this water, which again produces an environmental problem since it will always be contaminated to some degree by oil.
Oil products and water normally have different densities, with the oil normally having a density lower than that of the water. Water and oil can create relatively stable emulsions, however, where small water drops are dispersed in oil, or where small oil drops are dispersed in water. These emulsions are often very difficult to separate, not least when the oil phase is relatively high-molecular and viscous at the temperature of the mixture.
There are known a majority of methods for separating oil and water that are based on this density difference. The simplest apparatus of this type is a tank where water and oil, after standing for a relatively long period of time, are separated into a water phase at the bottom of the tank and an oil phase at the top. Between these two "pure" phases will be a layer that does not lend itself to separation, consisting of water in oil or oil in water, the so-called "interface." Some of the lighter components in the oil are easily separated from water by this means, while some of the heavier and/or polar components cannot be separated from the water, with the result that this interface constitutes the major portion of the volume of the tank, even after a prolonged period. This interface is not a homogeneous mixture, either, but it will also adjust itself here so that the lightest oils containing the least water are on the top, while the heaviest oils and the mixture having the highest water content settle near the bottom. This solution thus requires large tanks, takes a long time, and provides for an inadequate separation of water and some of the components of the oil.
By heating the contents of the tank, however, the density difference between the water and oil is increased, and with increased temperature are also increasingly heavier components likely to separate from the water. The heat in such tanks is supplied by heating elements warmed by hot water, steam or electrical heating elements at the bottom of the tank, or the tank may be heated by means of a heating jacket surrounding all or parts of the tank.
Oil is difficult to heat by means of such heating elements, however, and when electrical heating or steam is used, some heat degradation and carbonization of oil products on the heating elements occurs, making the transfer of heat even less satisfactory. Moreover, this type of heating process will generate currents of heated water and oil that will rise within the tank, while cold components will sink, thereby creating eddies which will work against the separation of the phases. In practice, the
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Hoppin Ralph F.
Lipsitz Barry R.
Popovics Robert J.
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