In a chemical plant, an electric furnace used to produce hot air, injected into a dryer by atomisation, was severely damaged as a result of overheating. The flange connecting the hot air outlet line to the electric oven had been heated red. Some of the furnace’s heating elements were severely burnt.
Analysis of the accident showed that, as a result of vibrations and airflow, the dryer’s air distribution plates had become loose and the dryer became less efficient. The dryer’s bottom outlet pipe was then clogged with pieces of wet cake. As air could no longer circulate, the dryer’s temperature began to drop. The operator then manually increased the temperature of the furnace to compensate for this drop. Since the furnace’s high-temperature control was not installed, the automatic heater shut-off could not function.
The operations crew was aware that this automatic control was not installed, but this lack of control had not been formalised as a safety review and was not performed before the installation of this new electric furnace had begun. The risk analysis conducted on the installation did not identify the consequences in the event a dryer outlet line became clogged. A check of the tightness of the diffuser’s plates was not included in the periodic inspection of the dryer. As no adequate training was provided, the operator was unaware of the consequences of the decreased airflow and therefore aggravated the situation.