optimisation of the slurry density helps to reduce negative environmental impacts through leaching at the dams . Bed mass is calculated based on the total volume of combined water and solids in the tank and the total hydrostatic pressure measured near the bottom of the tank . As the speci c gravity of water is a known constant , the mass of the solid content can be calculated .
Volumetric measurement of the
thickener ' s in ow : Accurate volumetric measurement of the thickener ' s in ow is vital to ensure the clarity of the recovered process water . Essentially the in feed ow rate can be controlled based on high clarity of the over ow . So the clearer the out ow , the faster the in ow feed rate which leads to optimised thickener throughput . Combined with the mass ow measurement of the occulent , precise ratio control of the occulent dosing is achieved . �is enables automated , continuous occulent dosing which further increases process efficiency and reduces costs when compared to semibatch type operation .
Mass ow measurement of occulent :
Flocculants are used in most thickeners to obtain concentrations of over ow solids that will allow water to be reused or to comply with government regulations if the over ow is to be discharged . Recycled water containing 200 mg / L to 1 % solids is generally acceptable . Most thickeners can achieve this level of concentration by using a occulant . Although occulants are used in relatively small quantities , they are expensive . �e accurate measurement of occulant mass ow allows precise dosing pump control . Combined with other system parameters , the use of ' just enough ' occulant can be ensured minimising occulant usage and optimising process costs . Depending on the process this measurement can be made using high accuracy Coriolis mass ow instruments , or more economical volumetric electromagnetic ow meters .
Out ow density and volumetric measurement : Constant out ow density and volumetric ow measurements are important parameters which can be fed back to the variable speed drive controlling the out ow pump , optimising pump speeds , reducing wasted energy and improving efficiency . �e combination of density and volumetric ow rate provides an integrated mass ow rate which is useful for accounting of mineral recovery as well as waste .
Accurate measurement of all of these important parameters allows precise thickener process control which can lead to signi cant increases in thickener efficiency . �ese efficiency gains translate directly into overall re ning process cost reductions and increased pro tability . Enquiries : Susan Buitendag Industry Manager – Primaries
Endress + Hauser ( Pty ) Ltd Tel : ( 011 ) 262 8000 Fax : ( 011 ) 262 8062 info @ za . endress . com
Endress + Hauser People for Process Automation
Page18 | May - June 2016
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