SPEC was asked to do a project that included a pelletizer, an extrusion based machine with a rotating blade that would make pellets out of a viscous fluid stream. The client’s process was set up such that either of two reactors could empty their process fluid into the pelletizer. Once the batch had completed, the client would run a cleaning cycle. The cleaning cycle involved adding a Class IIIB chemical to the reactors, heating it up and swirling it around the vessel until any leftover process residue was dissolved. Then the cleaning solution (while still heated) was emptied into the pelletizer and collected in a drum-off station.
Class IIIB chemicals are non-hazardous (and do not require electrical area classifications) at room temperature, however, this property changes once they are heated above their flashpoint. Above their flashpoint, Class IIIB chemicals become hazardous as they are capable of forming combustible mixtures. We discovered that the users were heating the cleaning solution well above the flashpoint, and therefore making the chemical hazardous.
When encountering flammable liquids in a process environment, we typically employ electrical area classification (installing tested and labeled equipment with appropriate wiring methods) to eliminate ignition sources. This particular installation did not lend itself to such a solution. The pelletizer was a packaged vendor skid built to non-rated (NEMA 1) standards. Swapping out the non-rated components would have violated the manufacturer’s warrantee, and procuring an electrically classified skid would have been prohibitively time consuming and expensive.
Instead, we found a different solution, by monitoring the temperature of the cleaning solution and shunt-tripping all power in the area. We installed intrinsically safe temperature switches inside the reactors (with their barrier counterparts installed in a different control panel than the pelletizer). The switches were designed to close when the temperature reached 20% of the flashpoint. We also swapped out the main breaker feeding the pelletizer control panel with a shunt-trip capable equivalent. The temperature switches were tied to the main breaker’s shunt-trip so that at 20% of flashpoint, all power and controls associated with the pelletizer were de-energized. If the cleaning solution were to ever be released to the surrounding atmosphere, it would not encounter any potential ignition sources. Once the cleaning cycle finished and temperatures dropped back down to ambient, the shunt-trip would return power to the pelletizer.
This solution allowed the users to continue with their cleaning procedures with minimal interruption. Also, it avoided having to install expensive rated equipment for a Class IIIB chemical or voiding the manufacturer’s warrantee.
Andrew has been with SPEC since 2004 and has been SPEC's Sr. Electrical Engineer since 2008. He has been involved in a multitude of projects ranging from Class 100 cleanrooms, to food processing plants, to petro-chemical facilities. He has significant experience in developing and implementing electrical hazardous area classifications for various flammable materials.