There are two main mixing systems in stirred services. An open system with a hydrofoil propeller or draft tube is used. Mechanimix offers high efficiency solutions that are not limited to the propeller itself.

Crystallization is a process step in a wide variety of applications and industries, such as chemicals, API production, food production, and precipitation of ores. Depending on the process requirements, cooling, evaporation, or precipitation are chosen to form crystals. Accordingly, the variety of machines applied is wide.

Cycling Crystallizers are often called Forced Circulation (FC) Crystallizers because the solution is forced to flow by a pump while crystallization into layers is a static process. There are two main mixing systems in stirred services. An open system with a hydrofoil impeller or draft tube is used. Mechanimix offers high efficiency solutions that are not limited to the propeller itself.

Examples for crystallization products

• Potash
• Sugar
• APIs

Mechanimix is happy to assist you throughout the entire project, from initial estimation to detail engineering, manufacturing and operation. Mechanimix not only has excellent experience in the design of mixers, but can also help with its expertise in vessel design and process know-how. We can also provide support with CFD simulations and trials in our laboratory or field.

It is common for crystallizations to be carried out in batch units using a hydrofoil propeller. In general, cooling is a method of achieving supersaturation in batch mode. In rare cases, evaporation is also used. Batch processing is extremely flexible, meaning changes in raw material can be easily accommodated. Often even multiple products can be processed without major changes to the mixer. Usually the only parameter to adjust is the shaft speed. There are some important parameters that need to be taken into consideration to achieve an efficient and high-quality process. First of all, the mixer must be designed to best suit the process.

Besides the basic mixing tasks of mixing and suspending solids, heat transfer is also an important parameter. For shear-sensitive crystals, a low shear system should be chosen. The design of the ship and its interiors has the potential for further improvements. Chamber geometry and the use of optimized chamber interiors can significantly affect product quality. An adapted operating mode completes the design. The cooling strategy, which includes cooling ramps and trapping points, can increase the size of crystals and at the same time narrow the particle size distribution. Seeding with selected crystal sizes can provide further improvements. Narrow particle size distribution with small amounts of fine particles increases efficiency and is beneficial for subsequent filtration and drying steps.

Continuously operated crystallizers are usually equipped with a draw tube. These units are called Draft Tube Oriented Crystallizers or DTBs. The impeller is located inside the draft tube and applies a directed axial flow with minimal turbulence.

The advantages of continuous operation are mainly for high-capacity production of a single product. For example, potash is commonly processed at a WMA. In addition to a high flow rate, a constant product quality and gradual separation of crystals are required. Smaller particles must remain in the process until a certain size is reached.

Mechanimix has developed the HWM, a three-blade draft tube circulator, with the aim of significantly increasing efficiency. By observing the entire system, including the draft tube geometry and specially designed straightening vanes, the ratio of axial flow to turbulent flow can be significantly increased. Therefore, less energy is required to reach a given flow rate. This affects both investment and operating costs. As a side effect, crystals are protected because less turbulence means fewer collisions and therefore less breakage.

To ensure safe and long-term operation, it would be useful to control stresses by finite element analysis (FEA) and frequencies by modal analysis at the design stage, as DTBs are subjected to high mechanical loads and vibrations.