Haoran Machinery: A specialized manufacturer of stainless steel vessels.
08
2022
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06
General principles of mixing and blending tank equipment
General Principles of Mixing Vessel Equipment: Structural Principles and Selection of Mixing Tanks and Vacuum Mixers. Stirred tanks, vacuum stirred tanks, and stainless steel stirred tanks are classified as agitated vessels. They are widely used in the dairy, pharmaceutical, chemical, and other industries for liquid–liquid and liquid–solid mixing, achieving effective agitation to produce qualified products that meet technical specifications. A stirring tank comprises a vessel body and various attachments welded onto it. The most common type of stirred vessel is a vertical cylindrical container, featuring a top cover, a cylindrical body, and a bottom. The vessel is mounted on a foundation or platform via supports. Under specified operating temperature and pressure conditions, the mixing tank provides the necessary space for the blending process. To accommodate diverse process requirements or due to structural needs, the tank interior is equipped with various components serving different purposes. For example, since reactions often involve thermal effects—requiring heat input or removal—a set of water jackets or coil tubes is installed within the vessel. To connect the reducer and shaft seal, the top cover is welded to the base. Manholes, handholes, and various nozzles are also required to facilitate maintenance and arrangement of internal components.
To monitor and control the temperature, pressure, and level of materials during operation, thermometers, pressure gauges, level indicators, sight glasses, and discharge devices should be installed. Sometimes, to alter the flow pattern of the material, increase mixing intensity, and enhance mass and heat transfer, baffles and guide tubes are welded inside the vessel. However, as the number of components increases, this often creates significant challenges in manufacturing and maintenance, raising equipment costs. Therefore, when determining the design of a stirred tank, a comprehensive approach is required to ensure the equipment meets process requirements, achieves economic efficiency, and attains an optimal design.
Key design considerations for mixing tanks are as follows: The tank’s length-to-diameter ratio and load capacity. To determine the appropriate volume of material in the mixer, select a suitable length-to-diameter ratio (H/D) and load capacity to establish the cylinder’s diameter and height. The length-to-diameter ratio of the mixing tank is more critical than its reaction requirements, as it affects mixing efficiency, effectiveness, and process demands. Mixing tanks primarily involve three aspects: 1) the mixing vessel itself; 2) the mixing power and impeller configuration; and 3) the intrinsic mixing and reaction characteristics of the material. When designing a mixing vessel, appropriately select the charge quantity, filling coefficient, and mixing method to maximize equipment utilization. Commonly used filling coefficients range from 0.6 to 0.85. If foaming or boiling occurs during the reaction, a coefficient of 0.6 to 0.7 is recommended. For relatively stable material responses, use a coefficient of 0.8 to 0.85 (particularly when dealing with high-viscosity materials).
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