Measuring and testing – Volume or rate of flow – By measuring thrust or drag forces
Reexamination Certificate
1999-12-10
2001-12-11
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring thrust or drag forces
Reexamination Certificate
active
06327916
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally directed to the measurement of process parameters, and is more specifically directed to a device for measuring the flow rate of a slurry discharged from equipment such as flotation cells.
BACKGROUND OF THE INVENTION
Flotation cells are commonly employed to separate solid material from a slurry typically composed of liquids and solids in varying proportions. An impeller located in the flotation cell agitates the slurry dispersing entrapped gas, thereby causing the formation of gas bubbles. Particulate solid material adheres to the surface of the gas bubbles and rises there with to the slurry surface forming a froth that has a higher concentration of the floatable material, as compared to the starting slurry.
The froth, which is a combination of liquid, solid particles, and gas is removed from the flotation cell for further processing. In order to optimize the operation of the flotation cell, it is important to remove the froth at an appropriate rate. Where several flotation cells are operating at one time it is desirable to synchronize their operation, thereby simplifying the control of the individual cells.
A problem often encountered in flotation cell control is due to the non-homogeneous composition of the froth. It is difficult to accurately ascertain the rate at which the froth is being removed from the flotation cell. In the past, ultrasonic level sensors, and magnetic flow meters have been employed, however, the presence of the gaseous phase and the inability of these sensors to detect it has made the readings obtained from these instruments unreliable. Video cameras have also been utilized with little success in an effort to track the speed at which the froth moves toward a peripheral edge of the flotation cell.
Based on the foregoing, it is the general object of the present invention to provide a device for monitoring the rate of froth removal from a flotation cell, that overcomes the problems and drawbacks associated with prior art measurement instruments.
It is a more specific object of the present invention to provide such a device that is capable of measuring froth rate removal and is not affected by the presence of the gaseous phase.
SUMMARY OF THE PRESENT INVENTION
The present invention is directed to an apparatus for measuring the flow characteristics of a liquid/solid/gas slurry discharged from a flotation cell that includes, a metering flange coupled to the flotation cell. The metering flange includes at least one flange wall that defines an interior area having a central axis. An inlet section is provided and is coaxial with the central axis and in fluid communication with the slurry discharged from the flotation cell. An outlet coaxial with the inlet section allows the slurry to flow through the interior area of the metering flange. An impingement plate is positioned in the interior area and defines an impingement surface that is acted upon by the slurry flowing through the metering flange. A load cell measures the force exerted on the impingement plate by the slurry and therefrom via transfer means coupling the load cell and impingement plate together.
In the preferred embodiment of the present invention a support mechanism locates and maintains the position of the impingement plate relative to the inlet section in such a manner that the impingement surface extends approximately symmetrically about the central axis of the metering flange.
Preferably, the transfer means includes a flexible member coupled at a first end to the load cell, and at a second end to the impingement plate. The impingement plate being movable relative to the flange along the central axis such that the force exerted by the slurry against the impingement surface creates tension in the flexible member that in turn is measured by the load cell.
In an alternate embodiment of the present invention, the load cell is positioned to detect and measure compressive forces. To accomplish this, the load cell is secured to a mounting flange that in turn is attached to the metering flange adjacent to the outlet. The transfer means includes an actuating member extending from an underside of the impingement plate at one end and engaging the load cell at an appropriate end. During operation, the force exerted on the impingement surface by the slurry is transferred through the actuating member to the load cell, and from the load cell to a controller that determines the mass flow rate of the slurry. A bellows encompasses and seals the load cell from ingress of the slurry thereby preventing the load cell from being damaged.
In addition to mass flow rate measurements, the present invention can also be used to measure volumetric flow. Since the inlet section defines a known orifice diameter, a level sensor is positioned above the inlet section and the corresponding fluid level above the orifice can be measured. Volumetric flow can then be determined following well-developed flow equations.
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Engquist Kenneth D.
Kallioinen Jouko
Monchak Daniel P.
Probst Alexander C.
Schwartz William F.
Fuller Benjamin R.
GL&V Dorr-Oliver Inc.
McCormick Paulding & Huber LLP
Thompson Jewel V.
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