A MINOR TEMPERATURE CONTROL INCIDENT
When operating in relatively new plant, a hydrocarbon solvent was being heated to reflux in a Hastelloy vessel by setting the jacket temperature 30°C above the boiling point, a typical setting for many solvents in glass lined vessels. In the vent, the temperature overshot the set point and the contents boiled vigorously.
The following factors contributed to the incident:
- The increased heat transfer coefficient in a Hastelloy vessel
- The low heat capacity of the solvent
- The low heat of evaporation of the solvent
- The tuning parameters had been chosen to give good control of the temperature of the vessel contents at the expense of control of the jacket temperature
- Heating in difference mode (jacket temperature controlled at 30°C (or less) above temperature of vessel contents) may have been more appropriate
- Lack of experience, both with the specific plant and with the variables that may affect heat transfer.
The incident was of no consequence; nevertheless flammable solvents present a fire risk and any loss of containment presents a risk.