Scale Up Flashcards
Process Safety Tests
- Chemical Hazard Evaluation
- Thermal Stability of Materials
- Reaction Calorimetry
- Risk ASsessment
Semi Batch vs Batch
Semi Batch Preferred
Semi Batch:
- At least one reagent added over time
- Reactive inventory is minimised
- Rate of reaction can be controlled by rate of addition
- Easy process control
Batch is the opposite
4 Safety Steps
- Substitute
- Minimise
- Moderate
- Simplify
Detrimental effects of scale up
- Poorer reaction conversion
- Rheological changes
- poorer Filtration separations
- Slower Phase Separations
- Lower Yield
Scale invariance definition
The geomertrical space and dimensionless numbers necessary to describe them have the same numerical value
Kinematic Similarity
- Velocitites at geometrically similar positions remain constant
- Constant speed tip
- Constant Superficial gas velocity
- Constant Maximum liquid velocity
Dynamic Similarity
- Ratio of forces remains constant at different scales
e. g. constant Froude Number
Scale up Problems
- Physical Operations take longer
- Heat transfer is poorer as vessel (A/V) is reduced
- Mixing more difficult to achieve
- Distillations are less efficient and take longer
When do N*D^m scale up rules apply?
- Geometrically similar vessels
- Turbulent Regime
Fast Reaction scale up rule
Equal Mixing Time
m = 0
Therefore:
N = Constant
Solid Distribution scale up rule
Equal energy input]
P/V = eps
m = 0.67
Therefore:
N*D^0.67 = Constant
Gas-Liquid Process scale up rule
Equal Mass Transfer
kla = eps
m=0.67
Therefore:
N*D^0.67 = Constant
Solid Suspension scale up rule
Zwietering Rule
m=0.85
Therefore:
Njs * D^0.85 = constant
Liquid Blending scale up rule
Equal tip speed U
m =1
Therefore:
N*D = constant
Heat transfer scale up rule
Equal (Constant) Re
m = 2
Therefore:
N*D^2 = Constant
