The present invention relates to a method and apparatus for removing suspended matter from liquid. The method and apparatus of the present invention have utility, for example, in separating suspended contaminants and/or oil from water.
In many industries, including oil, paper and pulp, textile, electricity generating and food processing, there is an ever present problem of contaminated water as a by-product of various processes. In particular, water is often used to aid in the production of oil and gas on offshore platforms. This water is usually pumped into formation in order to be able to pump oil out. As a result, the water becomes contaminated with oil and solids encountered in the formation, and therefore cannot be disposed of simply by dumping it into the surrounding water.
Accordingly, numerous methods and systems have been devised to reduce the contaminant content of this water to a level which allows discharge of the water into the sea.
One such system, disclosed in U.S. Pat. No. 4,255,262, comprises a device which mixes and disperses gas in the form of fine bubbles in liquid in the tank in an attempt to remove contaminants from the liquid flowing through the tank. The gas is induced from the upper section of the tank downward into the liquid in the tank via a draft tube. The gas induction occurs as a portion of the liquid contained in the vessel is recirculated back through the individual cells or compartments using a centrifugal pump. The apparatus uses an electrically driven mechanical skimmer assembly, which serves to remove contaminant-laden froth which accumulates above the liquid level section of the tank.
U.S. Pat. No. 4,564,457 discloses another system for separating suspended matter from fluid. The device comprises a cylindrical tank, having an inlet chamber, a plurality of gasification chambers, and a quiescent outlet chamber. A skim trough is disposed near the top of the tank and extends the length of the gasification chambers into the outer chamber. Vertical baffles which separate the individual chambers extend downwardly and are spaced from the bottom of the tank, allowing fluid to flow through the bottom of the tank from the inlet chamber to the outlet chamber. Each gasification chamber is equipped with an eductor nozzle assembly positioned centrally in the lower portion thereof. The nozzle assembly provides for recirculation of fluid pumped from the outlet chamber. However, this system suffers from a number of drawbacks, one of them being failure to recognize the fact that the liquid in various chambers has different specific gravity, which prevented successful skim collection through the single trough.
Additionally, the system of '457 patent cannot be utilized in applications, wherein space requirements prevent installation of multi-cell flotation units.
The present invention contemplates elimination of the drawbacks associated with previous systems known to the applicant.