Lecture 2 Flashcards
Components of a batch reactor
- lid
- agitator and motor
- baffles
- base
- jackets
- Fabrication materials (MOCs)
- seals
- probes
The lid of a batch reactor
- configurable
- many ports but finite amount
- motor assembly can cause space issues
- access can be problematic
Agitator and motor of batch reactors
Drive system comprises
- drive assembly: motor, speed reducer and shaft support
- Wetted parts: impeller, shaft and seal
devices used to restrain the flow of a fluid, gas, etc
Baffles
Batch reactors - shapes of the base
- rectangular
- hemispherical
- torispherical
- conical
impellor type causes flow in the vessel to move the contents from top to bottom
axial flow impellors
impellor type causes flow to be pushed against walls and then move either up or down
radial flow impellors
Sucessful scale up of liquid mixing processes in tank reactors rely upon
- similar geometry of the large and small vessel
- the application of constant power per unit volume
Issues with CFD
- Grid design
- how to model rotating impeller
- turbulence models
CFD
Computational fluid dynamics (CFD)
Reynolds Number specific to tanks
Re = ρ N D^2 / μ
Power number
Po = P/ ρ N^3 D^5
Analogous to a friction factor
Proportional to the drag force per unit area of the impeller and the inertial stressed generated
depedent on the impeller type, dimensions, position and liquid properties
strong dependence of power input on N and D
Power number
Ratio of inertial forces to viscous forces
Comprises of a phyical properties component, a velocity and a characteristic dimension
Reynolds number
must be known for sizing the motor and drive. Large power
demands generally means a large drive
Power draw (P)
Power draw
P = 2πNΛ
Knowing the power dissipated into the liquid by the impellor is CRITICAL for predicting reactor performance
- micing time
- mass transfer
Torque measured at small scale
- mount vessel or motor on frictionless bearing and measure torque using a lead cell dynamometer
- use a commerical torque meter
- use a modified rheometer
Torque measured at large scale
- strain gauges can be used
- electrical current can be used by is subject to many errors as estimates of losses in the gearbox and bearing required
time taken to achieve desired homogeneity in the vessel
mixing time
implies not all parts of the tank are at the same concentration at all times, especially at the start of the reaction
A series of conductivity probes all on one probe. The probe can act as the vessel baffle. Much more data can be obtained than a single probe.
Electrical resistance tomography (ERT)
Accumulation equation
In – Out ± Reaction = Accumulation
Total batch time is the sum of:
- charging
- dissolution
- heating to reaction temperature
- reaction
- cooling batch
- discharge of contents
- cleaning in place
time required to complete all of the operations required to create one batch of product materials
batch time
minimum time needed to complete all of the operations required to create a batch of product
cycle time
series of operations that must occur in sequence
batch production
Considered as the time required to complete one whole batch
batch time
minimum time needed for all operations to occur
cycle time
how high impellor sits within a vessel
clearance
how much reactant is converted to any product
yield
how much reactant is converted to desired products
selectivity
Yield equation
moles A reacted / total moles A in feed
Selectivity equation
moles A reacted to desired product/ total moles reacted
Design criteria for the scale up of liquid blending processes in a reaction vessel
(N^3D^2)large=(N^3D^2)small
Design criteria for the scale up of liquid blending processes in a reaction vessel assumptions
- constant power number between scales
- constant physical properties between scales
- similar geometry between scales
- constant power per unit volume between scales
