The design of mixing tanks which produce adequate mixing of dose and influent components are a key element of industrial and water treatment process requirements. If the dose is not adequately mixed with the influent, then the required reactions cannot take place on the designed timescales (e.g. flocculation). If the system passes the dose forward too rapidly, then not all the influent will be exposed to the dose, again compromising the operational efficiency of subsequent flocculation & separation processes and ultimately significantly reducing the performance of the whole plant.
We have used CFD analysis to study the residence time of many chambers and mixers in practical engineering projects and have been able to generate novel and inexpensive solutions to many of these problems.
The mixing tank shown (above) was one in a series of three at a plant using magnetite as the dose material. The magnetite was recovered and re-used in the system, but initial design short comings and field experience had suggested short-circuiting was a potential problem.
Original proposals were for baffles between tanks costing the local equivalent of around $18,000 US. A CFD analysis project costing just a small fraction of this quickly identified the short-circuiting mechanism and our novel solution was a simple remediation to an inlet arrangement and relocation of the dosing pipe. Following the works upgrade through the use of CFD, the site showed a significant increase in capture efficiency at minimal cost in remediation.