Large Reactor Temperature Control
Large Reactor Temperature Control
Scale up of processes from 50 L to 200 L presents an interesting problem for temperature control in glass reaction vessels. Factors that must be considered include:
Operating Temperature Range
- Achieving desired temperatures in small reaction vessels (<20 L) can be relatively easy with mid-sized refrigerated / heating circulators. Temperature control power requirements for larger vessels increase quickly given the decrease in reactor surface area to volume ratio.
Time to Temperature
- Combined with the operating temperature range the cooling or heating power needed to reach temperature within a specific time contributes greatly to the necessary heating and cooling power.
Process Heat Flow (exotherm / endotherm)
- For safety these values must be known to prevent unwanted events. The circulator must have enough cooling or heating power to overcome an exotherm / exotherm.
- Glass reactors typically have a jacket pressure limit <10 psi. Check with the reactor manufacturer for this value. The circulator pumps of the temperature control unit must operate below that pressure limit.
Thermal Stress - Maximum Temperature Difference Between Reactor Contents and Jacket
- Check with the reactor manufacturer for this value; deltas vary by manufacturer from 50 K to 180 K across the inner glass jacket. Using a band limit setting on the circulator will ensure that this value will not be exceeded.
- Given the pressure limit restrictions of a glass vessel the temperature control unit fluid pump must have a good flow rate throughout the operating temperature range. Centrifugal pumps decrease in efficiency as the bath fluid viscosity increases, particularly at low temperatures.
Fluid Expansion Volume
- Silicon fluids used in these applications have a thermal expansion value of 12% for every 100 K delta. Make sure that the temperature control unit has enough internal tank volume to accommodate for this volume change.
The new large Presto® W91 and W92 systems from Julabo accommodate a wide range of applications and reactor sizes with configuration flexibility to meet operational demands. The Presto W91 provides an operating range from -91 to +250 °C while the Presto W92 offers -92 to +250 °C. These Presto highly dynamic temperature control systems utilize unique engineering which eliminates atmospheric moisture condensation in the bath fluid when operating below ambient temperature and safely extends the upper operating limit above the fluid flash point. As a result extremely wide temperature ranges can be achieved with one bath fluid: Julabo Thermal P60 (-60…+250 °C) or Thermal P90 (-90…+170 °C).
The Presto W91 and W92 provide 12, 24 or 36 kW heating power options to meet the most demanding applications. The Presto W91 cooling power ranges from 11 kW from 200 °C to 20 °C with 6.5 kW at -60 °C and 1.5 kW at -80 °C. The Presto W92 design cranks the cooling power up to 31 kW at 200 °C, 29 kW at 100 °C, 19 kW at 20 °C while matching the Presto W91 capacity at -60 and -80 °C.
Pressure Under Control
All Presto W91 and W92 systems can operate under pressure control. This will keep the bath fluid below the pressure threshold limit of the glass vessel and offers peace of mind to the operator.
With the Presto operating in external mode (internal reactor temperature control via Pt100 sensor) a band limit can be set to the reactor manufacturer value. This will ensure that the internal reactor temperature and the jacket bath fluid temperature never exceed the specified delta K.
Centrifugal and gear pump options provide powerful fluid flow. The Presto W91 and W92 centrifugal pump fluid has flow rates between 26 and 80 L/min. The optional gear pump fluid flow rates range from 18 to 70 L/min. Gear pumps are not susceptible to changes in fluid viscosity and thereby supply a uniform flow rate across the entire temperature range.
Capacity for Expansion
The Presto W91 and W92 have 40 L internal expansion reservoirs. This large internal volume accommodates thermal fluid expansion across the wide operating range.
The photograph illustrates operation of the Presto W91t (24 kW heater, centrifugal pump) with a 100 L glass reactor containing 75 L of ethanol at -55 °C.
Presto® is a registered trademark of Julabo GmbH.
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