Hi everyone, I would like to share some notes and questions I
made during a HAZOP (Hazard Operability) safety study of an Ammonia Refrigeration
Plant Room.
Ammonia is used to chill water in a heat exchanger system. The system consist of compressors, chillers, heat exchangers, liquid receiver vessels, gas detection, etc.
Like my other posts, questions here can be asked for any
generic process plants.
Please comment, like and subscribe.
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| Photograph 1: Generic refrigeration pipework |
1.
Is there mandatory gas monitor (RPE) requirements
for personnel entering the plant room?
(1)
Is there signage requiring gas monitors present?
(2)
Is it included in contractor rules / induction?
(3)
Can a radio system be used to inform a person
the actual ammonia concentration prior to entering in the room?
(4)
Are isolation valves readily visible, operatable
and indicated on a P&IDs, and on display on the wall of the room?
2.
Inadequate isolation procedures - Is there
double isolation on maintenance lines handling ammonia?
(1)
Can you consider relying on double isolation of
charging of ammonia
(2)
This should stop the plant but does not remove
the ammonia system – e.g. compressors, evaporators and condensers
(3)
Or is complete removal of ammonia needed? e.g.
from liquid receivers and/or spray chillers
3.
Can a leak in ammonia cause lighting to be
switched off by alarm activation at high level?
(1)
Can you consider temporary solution of leaving
access door open when someone is in ammonia room?
(2)
Is there painted hand rail/floor as guide to
emergency exit?
4.
Is there any fire extinguishers in ammonia plant
room? - This should be removed as temptation to tackle fire may expose an
operator to toxic ammonia releases
5.
Can you have extract fans running permanently at
low speeds – so they are ready to start when required? E.g. activation from a
gas detector, etc.
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| Photograph 2: Extraction fan in ammonia plant room |
Chiller & evaporator system:
6.
Is there any consequence for ammonia leaking
into water tubes of a chiller system?
(1)
Alkaline water in chilling process…
(2)
Mixing usually creates a vacuum – Is chiller
vessel rated for full vacuum?
(3)
Sampling taken by lab technician and potential
exposure?
7.
Is failure of electrical trace heating an issue?
(1)
Lack of heating oil and oil cools, thus ammonia
is not evaporated efficiently
(2)
Could you install stick-on digital temperature
indicators? to put on to the vessel
(3)
Include checking as part of daily walk through
by operator
8.
Are heat exchangers subject to the statutory
inspection under the Pressure System Safety Regulations (PSSR)? If so then undertake
inspection and implement the findings
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| Photograph 3: Generic compressors for ammonia circulation |
Compressor
9.
For the compressor outlet valve, can you cap the
valve stem, as a safeguard? Therefore only tools would be required to close
valve – thus prevent inadvertent closing of the valve.
10.
Does a failure in oil heater element, due to
high temperature trip - have a ‘fail off’ or ‘fail on’ mode? Could the oil heater stay
on, in a failure mode (high temperature)?
11.
Can the lube oil separator fail on start-up –
leading to low temperature? Is there automated shut off system and manual daily
oil level checks undertaken for this?
Pressure relief
12.
Can you add a manifold (multiple) of the
pressure relief valve lines? Should there be separate lines to atmosphere? (for
multiple PSVs)?
13.
Can you install a sight glass after a pressure
relief valve – if it is blocked or fails to open?
Thank you for reading, please comment, like and subscribe to this blog
Hope you have enjoyed reading this
Chiraq
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