QVA Products
Teetered Bed Separators (TBS)
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Process Description
The TBS Hydrosizer is a hindered settling Classifier, which is used to separate mineral particles into two groups either by size or where there is a mixture of relative densities, by specific gravity.
It uses an upward current of water to create a 'column of teeter' within the vessel.
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The condition of 'teeter' is created when particles fall through a current of water passing upwards through a vessel, those particles with a free settling rate equal to the velocity of the upward current water are arrested and held in a state of 'teeter'. This in turn creates the condition of 'hindered settling' because a bed or layer of similar-sized particles is held in suspension within the vessel. This bed or layer becomes in effect a dense-medium using the natural material within the Hydrosizer. We refer to this bed of material as the teeter column.
Therefore, where the feed material consists of two or more specific gravities (e.g. a mixture of coal/shale), the particles with the greater mass will create the teeter column. The coarser, heavier material will penetrate the zone of teeter and report to the discharge spigot. The lighter material (including the fine heavier material) will be buoyed to the overflow.
The upward current water is introduced into the pressure box from where it is evenly distributed into the settling chamber through the teeter plate.
During the process of separation, the controls sense the condition of the teeter column within the vessel and as the quantity of similar sized particles builds up the density of the pulp within the vessel increases. The variation in density is measured using a hydro-static density probe which is immersed into the teeter column and sends a signal to the electronic controller. Any increase/decrease of the hydrostatic head is converted into a signal to the discharge valve to open/close proportionately. This automatic electronic control system is able to accurately maintain a preset condition regardless of the variation in the feed rate and provide a very accurate and consistent separation.
A further Screening/Dewatering function maybe required to remove the fine heavy particles that report to the overflow of the Hydrosizer.
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Pictue Gallery
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Upward Current water
The upward current water supply must be from a dedicated source and at a constant pressure (75-100 kPa). It is essential that this water be from a pipe large enough to prevent a significant loss of flow by friction.
The design of a pumped feed pipe system should include a non-return device such as a "Swan neck" with an air relief valve to prevent syphoning of the water and solids back through the teeter plate causing unnecessary wear to the Hydrosizer, flow meter and pump.
The volume of water required by a machine in continuous production can only be determined after a close study of the duty required. This will depend on various factors and is quoted for each application.
A flow meter and valve should be installed to indicate and adjust the flow rate of upward current water, this can be adjusted manually or using a PID function in conjunction with an electrically controlled valve.
Feed
The slurry feed should ideally be 50% solids by weight.
Control Function
The Hydro-static level sensor is positioned at a fixed height within the Hydrosizer vessel, the sensor in the probe requires a two wire 24 V dc power supply which is calibrated during commissioning. The probe provides a 4-20ma input into a PID loop (PV) which in turn provides a 4-20MA output to the three Electro Hydraulic Actuators in order to maintain the desired set point. The actuators modulate and adjust the rate of refuse discharge to maintain the process variable at the set point.
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