The design of mixing tanks which produce adequate mixing of dose and influent components are a key element of industrial and water treatment process engineering 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 operation of subsequent flocculation and separation processes.
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 had suggest short-circuiting was a problem.
Original proposals were for baffles between tanks costing of the local equivalent of around 18,000 US dollars. A CFD analysis project costing just a small fraction of this identified the short-circuiting mechanism and our novel solution was a simple remediation to an inlet arrangement and relocation of the dosing pipe, costing a few hundreds of dollars. Following the works upgrade, the site showed a significant increase in capture efficiency.