Many reactors handle heat well, but not pressure. In a jacketed or glass-lined reactor, excess pressure in the jacket doesn't just ruin the batch: it puts the equipment itself at risk. Therefore, controlling the temperature of a reactor without monitoring the pressure is half a solution. Here we explain why and how both are controlled at the same time.
The limit that cannot be seen: the maximum allowable pressure
Jacketed and glass reactors have a maximum allowable pressure in the jacket. Exceeding it, even for a moment, can damage the coating or the shirt itself. The limit is not set by the process: it is set by the container. And that limit is non-negotiable.
Where does that pressure come from? It is set by the temperature control unit
In these systems, a thermal fluid is pumped through the jacket from a temperature control unit (the temperaturer or TCU). The pressure seen by the reactor is the sum of three factors: the pump drive, the resistance to the passage of the fluid through the circuit and the thermal expansion of the fluid when heated. In other words: the temperature control unit not only sets the temperature of the process, it also sets the pressure at which the reactor works.
The danger is dynamic: be careful with the spikes
In stable regime, staying below the limit is easy. The problem is the transients. A sudden closing of a valve, a pump starting at full power or a cold and viscous fluid can cause a pressure peak well above the stable value. And to compromise the reactor, just one moment above the limit is enough.
What overpressure costs
A single overpressure can be very expensive:
- Cracked liner: glass reactors fail under overpressure.
- Jacket leak: deformed welds and escaping thermal fluid.
- Lost batch: scrap, contamination and reprocessing.
- Production stoppage: repair, requalification and lost production.
A damaged container costs much more than the control system that would have protected it.
The balance: sufficient flow, within limits
Here is the real challenge. Flow rate is needed to transfer heat efficiently, but the pressure must remain below the reactor limit. Low flow means poor heat transfer; too much pressure, reactor at risk. The system has to sustain both conditions at the same time and stay in the safe window.
How we control it
To keep the jacket within its safe window, both in steady state and during transients, we combine several technologies that work together:
- Pump with frequency converter, regulated to a pressure setpoint.
- Expansion vessel, which absorbs thermal expansion and cushions the circuit.
- High-efficiency automatic air vents, which eliminate gas pockets that destabilize pressure.
- Pre-set static pressure: the circuit is loaded at a defined static pressure.
Depending on the process, the solution can rely on pressurized water or in high temperature thermal oil.
Regulate the pump by pressure, not by flow
The same pump can be regulated in four ways: by pressure, by flow, by ΔT (the difference between flow and return) or at a fixed percentage of speed. For a pressure sensitive reactor the choice is clear: regulate the pump by pressure. Thus the system protects the container first, without sacrificing process control.
The result: protected reactor, batch after batch
With this approach, the reactor is protected in each batch, the temperature remains stable at its setpoint, the batches are repeatable and qualifiable, and the useful life of the reactor is lengthened. It stops being a variable and becomes a certainty.
In short: control both, pressure and temperature
A pressure-sensitive reactor requires both: precise temperature control for the process and pressure maintained below the vessel limit. The right thermal system offers both, without compromises. At MARSE we have been designing thermal control systems that do exactly that since 1978.
Frequently asked questions
Why is the pressure in a jacketed reactor dangerous?
Because the jacket (and, in glass reactors, the lining) has a maximum allowable pressure. Exceeding it can crack the glass or warp the jacket, damaging the container, not just the batch.
Where does the pressure in the shirt come from?
From the combination of the pump drive, the resistance of the circuit and the thermal expansion of the fluid. The temperature control unit that circulates the fluid is what, in practice, sets that pressure.
What causes pressure spikes?
Transients such as the sudden closing of a valve, the pump starting at full power or a cold and viscous fluid. An instant above the limit is enough to cause damage.
How do you control pressure without losing heat transfer?
Keeping the system in a safe window: enough flow to transfer heat, but with the pressure below the limit. It is achieved with a pressure-regulated pump, expansion vessel, automatic drains and a defined static pressure.
Why regulate the pump by pressure and not by flow?
Because in a pressure-sensitive reactor the priority is to protect the vessel. Regulating by pressure, the system adjusts the pump to never exceed the limit, while maintaining control of the process.