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Centrifugation is a necessary step in many pharmaceutical and chemical production processes. These guidelines will help chemical engineers better understand the process of centrifuge selection.
Solid-liquid separation through centrifugation is often a crucial step to obtain the desired product after precipitation or crystallization. There are two types of centrifugation (also called dewatering or deliquoring): filtering and sedimenting. This guide focuses mainly on filtering centrifugation because it is the more common type of solid-liquid separation in chemical and pharmaceutical production applications.
Three steps to centrifuge selection
This three-step process for choosing the best centrifuge for a specific application evaluates the process characteristics, the product properties, and the numerous design options that should be considered to determine the optimal centrifuge to fit process requirements (Figure 1).
The selection of a centrifuge is governed by a myriad of factors. First, it is important to know whether the reaction is crystallization or precipitation, because reaction type greatly influences the morphology of the solid particles, which, in turn, has a direct bearing on the filterability of the slurry. It is also beneficial to determine the temperature, pH, and flowrates or batch sizes generated by the reaction. Some of the process and operational parameters that influence the selection criteria include: containment and washing requirements, vessel size, and batch cycle times. Particle characteristics such as size and shape, porosity, hardness, density, and concentration are also important. After the process and product parameters have been considered, centrifuges can be evaluated based on their size, automation and containment capabilities, and typical applications of a similar nature.
Step 1: Selection by process and application
The first step in centrifuge selection is to determine whether filtering or sedimenting centrifugation will be used. A filtering centrifuge is a batch-operated machine that uses a filter media to capture and collect a filter cake inside a rotating basket; a sedimenting centrifuge is usually continuous, and uses high rotational velocities to produce very high gravitational forces (i.e., g-forces) inside a solid bowl that separates the liquid from the solid (or liquid from another liquid) based on specific gravities. Some of the criteria used to select the most appropriate type of centrifugation are listed in Table 1.
Particle size affects cake porosity and filterability, which, in turn, influence the selection...