Fire in cyclone

The accident occurred on the hopper for fine powders from a pair of cyclones (the hopper is the bottom conical part of the cyclone collecting the powder/dust separated from gas phase).

A burst disc ruptured on the hopper, releasing ethylene and hydrogen gases, followed by a flash and explosion. Two men were injured.

bursting disc, hopper, cyclone

Although not mentioned by the source of this event, the process to which the cyclone/hopper belonged to was the production of polyethylene production. Iits high-pressure separation system requires a cyclone to separate solid particles (dust/fine catalysts/oligomers) from a gas stream containing hydrogen and ethylene.

DESCRIPTION OF A HOPPER
A cyclone hopper is a cone-shaped collector located at the bottom of a centrifugal separator (cyclone) that gathers separated dust, powder, or material, ensuring high-efficiency particle discharge. It serves as a crucial component for particulate removal, with specialized designs often used in food-grade or industrial bulk handling for dust reduction

Safety systems mitigating explosions
There are basically two ways to mitigate the effect of an explosive combustion inside a hopper:
(1) explosion relief venting: a burst disc which ruptures at a pre-determined pressure to relieve pressure caused by a explosion and vent it through a vent pipe. This is applicable when the hopper is ‘external’ to other structure and can vent outside structure or building.
(2) Explosion suppression system. Detectors mounted on the collector detect the initial pressure excursion from an incipient explosion. A signal to a control panel triggers high-rate discharge extinguishers and shuts down the process. This option is necessary when no external venting is not possible.

[Palmer, Explosion protection of a dust extraction system, ICHEME, https://www.icheme.org/media/12193/v-paper-17.pdf
https://www.ieptechnologies.com/wheres-the-hazard/process-equipment-at-risk/dust-collectors#:~:text=Protection%20System%20Description,the%20Vented%20Dust%20Collector%20Datasheet]

Two men received 2nd degree burns over 25% body surface.

According to the ICHEME report (see references), the recommendations/ issued were:
1. Fit a "stack" to the disc stub, to direct any emission away from personnel.
2. Automate operations as far as practicable to minimise operator/equipment interaction.