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6.4 Constant flux reactor systems
Description
Chapter 6
The concept of ‘constant flux’ can be applied to most heat transfer devices and reactor designs
(batch, semi-continuous and continuous). However, constant flux has seen its most advanced
development in its application to the continuously stirred tank reactor – the most common type
of process equipment to be found in a modern fine chemical/pharmaceutical manufacturing
plant.
Constant flux stirred tank reactors use a fundamentally different temperature control
philosophy. Whereas conventional stirred tank reactors control process temperatures by
regulating the temperature of the heating/cooling jacket, constant flux stirred tank reactors have
variable heat transfer areas (see Figure 6.1 below). In the Figure, q = U . A . LMTD is the heat
transfer equation, where q = heat added or removed by the heat-exchanger (W), U = heat
transfer coefficient (W m -2 K -1 ), A = heat transfer area (m 2 ) and LMTD = mean temperature
difference between jacket and process (K).
TC
Conventional control
0ºC
q = U.A.LMTD
-20ºC
-5ºC
Tp
Regulation of the jacket
temperature (LMTD) controls
the process temperature
Constant Flux control
q = U.A.LMTD
Tp TC
Regulation of the effective
jacket area (A) controls the
process temperature
Figure 6.1: Comparison of conventional temperature control and constant flux control
The variable area surface is created by breaking the jacket up into multiple independently
controlled heat transfer elements. (The feed and return pipes to the individual jacket elements
are connected to common manifolds). The outlet manifold is fitted with a motorised piston
which is used to regulate the number of heat transfer elements in service.
The use of the area as the primary control parameter together with the use of small heat transfer
elements delivers some unique performance capabilities:
• process monitoring of unprecedented accuracy using heat balance calorimetry
• process temperature control that is more accurate, faster and more stable than conventional
techniques
• improved process conditions within the vessel
• more efficient utilisation of heat transfer fluid.
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