A multi-stage static mixer is the perfect solution when a small flow of additives needs to be mixed into a main flow that has a (very) large turn-down ratio. In practice this often means for example adding just a few litres of additives into a main flow that can vary from 10 - 100% of the normal turn down ratio.
Maximum performance within the entire `operating envelope´ and 100% uptime
When designing a mixer for such or similar applications the greatest challenge is to create a set up that performs to the maximum across the entire range, the "operating envelope", without creating excessive pressure drops. As many of these mixes take place in a continuous process with a 100% uptime, it is often desirable to create a double or exchangeable configuration to be able to accommodate maintenance or unexpected situations. Consider for example water company substations.
The design of the multi-stage static mixer
A multi-stage static mixer configuration consists of a main mixer and a by-pass mixer. This means that the dosage flow becomes controllable and is accurately pre-mixed in the bypass mixer. This mixer works with a constant flow of liquids that are fed from the main pipe, with the help of a pump placed at an earlier stage in the process. The diameter of the bypass mixer is smaller in comparison and fully geared to the homogenisation of the dosage flow. The dosage flow is injected into the main stream through a special injector, just before the mixing elements of the main mixer. This allows the dosage flow to be optimally distributed across the diameter of the pipe, even at the lowest flow level within the turn-down ratio. This results in a controllable, homogeneous mixing in the main stream and a low pressure drop across the entire lay-out This is something that would not be feasible in this situation with a single mixer, or an alternative mixing configuration.
Materials Static Mixer
PRIMIX provides a great diversity of static mixer solutions and depending on the application can be produced, for example, in PVC, HDPE, PTFE, stainless steel, low temperature carbon steel or GRP. The choice of materials for the housing, mixer elements and injectors is often dependant on the use, and the reactivity of the medium You can read more about the material possibilities here.
More information - Case Study sheet “Multi stage in-line Dosage System”
Contact your local PRIMIX partner for further information about the possibilities with the PRIMIX multi-stage static mixer configuration. One situation in which a multi-stage static mixer has provided an adequate solution is described on PRIMIX Case Study sheet #57. This Case Study describes the process at a Dutch producer of drinking water who wanted to mix a limited amount of lye, just a few litres, into a DN500 main flow. The challenge was the large turn-down ratio of the main flow which varied in capacity between 10 - 100%. Read more about the solution that was offered on the Case Study sheet Multi stage in-line dosage System.