ChemScale: Optimum Turbine Agitator Selection
The ChemScale design procedure was developed to provide a logic for customers to quantify and define the agitation problem, specify required information for the design of an agitator, provide a communication tool for the customer and vendor to select a turbine agitator, and to optimize the agitator for the specific process at hand.
Applications of turbine agitators in the CPI (Chemical Process Industry) involve one or more of the following objectives: Combining process liquids of dissimilar composition and properties (Bulk Mixing), distributing reactants and products to promote desired reactions (Chemical Reaction), increasing convective motions adjacent to the transport surfaces (Heat Transfer), promoting contact between separate phases and different compositions (Mass Transfer), and dispersing immiscible liquids, suspending solids, or dispersing gases (Phase Interaction).
All the applications above involve the requirement for generating fluid motion to contact liquids, solids, or gases in a continuous liquid phase. These phases present in the liquid to agitate provides the means for the three main classifications of agitation problems:
Blending and Motion: Liquid in contact with another liquid
Solids Suspension: Solids in contact with a liquid
Gas Dispersion: Gas in contact with a liquid
In simple steps, the ChemScale design procedure involves: Classification of the Problem, Determine Size and Difficulty, and Determine the Process Result.
The Size of the problem is the “Equivalent Volume” and is calculated by the actual volume mixed in the vessel multiplied by the Specific Gravity of the liquid. Each Classifications has a separate “Difficulty” parameter as follows:
|Blending & Motion||Maximum viscosity of the liquid phase to be agitated|
|Solids Suspension||Settling rate of the solids particles|
|Gas Dispersion||Superficial gas velocity which is the volumetric flow rate of the gas divided by the cross sectional area of the tank|
The final step involves the selection of the required process result (or ChemScale). Each classification has a separate “ChemScale” parameter as follows:
|Blending & Motion||Bulk fluid velocity|
|Solids Suspension||Level of suspension|
|Gas Dispersion||Degree of gas dispersion|
Steps to determine the Process Result and ultimately the agitator size can be found on each of the Classification pages: Blending and Motion, Solids Suspension, and Gas Dispersion.
There are applications which may have all three phases (liquid, solids, and gas) in contact with another liquid. In these cases, the ChemScale design procedure can still be utilized for each category and it will normally establish the most difficult, and therefore controlling, problem to use for equipment selection.