Hi everyone, I would like to share some quick questions and notes, I made during a HAZOP (Hazard Operability) safety study for a reactor producing chemicals for the agriculture industry.
Powders and liquids are handled in a mixing process, that consists
of a bag tipping station, transfer conveyors, a ribbon mixer, liquid drum pumping
system, a product collection container and an extraction system.
Like my other posts, questions here can be asked for any
generic process plants.
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| Photograph 1: Generic Production Plant |
Powder handling system:
1.
Does a high flow rate of powder through an insulating discharge
hose cause the potential for propagating brush discharges?
(1)
Is there a potential for an explosion to occur?
(2)
Could you install earthing reinforced wires into
the discharge hose (coils)?
(3)
BUT ironically, earthing an insulting hose, can actually
create the potential for propagating brush, therefore it is better to use
static dissipative hoses
(4)
Could you use an orifice plate to slow down the powder
flow at the discharge?
2.
For the extraction for the bag tip station - Is
there an alarm for low flow, due to a blocked filter?
(1)
Could you install a simple (more practical) ribbon
hanging down on the bag tip station? - this is to show air flow is operating
correctly?
(2)
This is an alternative to differential pressure
gauge!
(3)
Is there a precheck of the filters before each
batch operation? is an inspection regime needed?
3. If the extraction fan is not ATEX rated, and there is a single layer filter, could you install another ‘pre-filter’ cartridge on the suction line, to stop flammable atmospheres entering into the unsuitable filter & extraction fan?
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| Photograph 2: Generic Dust Collector |
4. If a knife is dropped into tipping station can this cause sparks? Could you make the knife tied to station or make the knife too big for it to pass by the mesh?
Liquid Transfer
System:
5.
Can the liquid containers be warmed to make
pumping easier?
(1)
Check material properties for issues first
(2)
Can the liquid cool and crystallise?
(3)
If this is an issue, could you install a temperature
alarm for the room as well? This is because the external container body or transfer
pipes will usually freeze before the liquid inside does.
6.
Is there a potential for the air pumps to leaks?
- Can you enclose the pump station with protections against splashes?
Mixer unit
7. Can the inspection hatch of the mixer, be left open when the mixer is running?
(1)
Dust can be let out and accumulate at high levels,
thus become a secondary dust explosion risk
(2)
Could you install a timer to shut the mixer when
the hatch is open or after set period of time?
8.
Can the couplings between the agitator shaft and
motor become disconnected during operation?
(1)
Can you put dot of paint on non-driven end of
shaft and check if it is moving?
(2)
If it is a noisy operation, then this may not be
required
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| Photograph 3: Generic Mixer Vessel |
9. Could a wrong collection bag on the mixer discharge outlet, overfill?
(1)
Could you link the weigh scale underneath the
collection bag, to automatically shut the mixer discharge valve?
(2)
Ensure this discharge valve shuts close upon
loss of power as well.
(3)
Ensure material packed are no less dense than
water – so 1 tonne is a collection bag is full or less, but never more
10.
Is there a safe method of cleaning the mixer
unit? Is a confined space entry permit needed?
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Hope you have enjoyed reading this
Chiraq
#HAZOP #ProcessSafety
