ATEX and Solvent Extraction: Classifying the Area Around Your SX Circuit
Solvent extraction uses a flammable diluent — usually kerosene-type — and that makes the area around settlers and mixers a potentially explosive atmosphere. Under ATEX, the operator classifies the area and the equipment must match the zone.
How the classification is made
The starting point is the flash point of the diluent and its process temperature. A liquid handled below its flash point produces far less vapour than one handled above it. The classification also depends on the expected release frequency: continuous release gives Zone 0 or 1, occasional release Zone 2, and no expected release is unclassified.
| Zone | Atmosphere present | Equipment category |
|---|---|---|
| Zone 0 | Continuously or for long periods | Category 1G |
| Zone 1 | Occasionally during normal operation | Category 2G |
| Zone 2 | Rarely, and only briefly | Category 3G |
| Unclassified | Not expected | Standard industrial equipment |
What changes in practice
Motors and instruments. Mixer drives in a zoned area need Ex-rated motors, and the motor is often the single largest cost increase. Level and flow instruments need suitable protection concepts.
Electrical installation. Cabling, glands, junction boxes and earthing all change. Bonding of the skid and grounding of the organic circuit are mandatory, not optional.
Ventilation. Good ventilation can reduce the extent of a zone, and it is often cheaper than upgrading every component — but it must be engineered and documented, not assumed.
The operator’s responsibility
Under the ATEX workplace directive (1999/92/EC), the operator prepares the explosion protection document and classifies the zones. Equipment suppliers then supply equipment suitable for the stated zone. A supplier cannot classify your plant for you, though they can advise on typical practice.
Practical advice for buyers
Decide the zone map before requesting quotations. Otherwise you will receive three offers on three different assumptions and the comparison is meaningless. Ask each supplier to state the zone they have assumed and the Ex marking on the motors and instruments.
Send your diluent flash point, process temperature and area layout, and we will advise on the equipment protection level that follows.