Hi everyone, I would like to share some notes and questions I made during a HAZOP (Hazard Operability) safety study for a batch chemical reactor and its abatement system.
Its been a long time coming and well anticipated :)
Like my other posts, questions here can be asked for any generic process plants.
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| Photograph 1 - Reactor Units |
Storage containers (IBC)
1. Is contamination an issue, e.g. moisture, can it lead to over pressure within an IBC?
2. Is there a suitable SOP for IBC reuse? Are IBC labelled like with bar codes? Also account for IBC being pierced, impacted, - safe movement
3. Is there a Tri-clamp/cap for IBC when it is not ready to receive materials (non return flap)
4. For drum and IBC swapping tasks – are there risk assessed – e.g. lightweight blanks, mechanical aids, lifting, etc.
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| Photograph 2 - Generic IBC storage containers |
Liquid/vacuum Pumps
5. Is there a Non return valve (NRV - check valve) – to prevent back flow? Does it allow for flushing and draining of lines
6. Does pump filters have local pressure gauges?
7. Is maximum head pressure of pump below the design pressure of reactor/vessel
8. Is thermal expansion credible as block cold material warms up?
9. Where is location of local pump controls – can you minimise potential for operator exposure in case of leaks/releases. May also need weather protection if outdoors.
10. For variable speed drive pump (VSD) – is limit on pump speed needed? Can torque/current draw on the control system (DCS) be used for pump health indication
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| Photograph 3 - Typical vacuum pump |
Reactor system
11. For transfer lines & pipework
1.1. Is there procedure (SOPs) in place for isolation, flushing, purging, testing, drying, drainage, etc. for all the equipment, like pump, heat exchangers, check valves,
1.2. Is there sections of pipework where dead legs can occur? Is lagging/heat tracing needed, e.g. waste route drains, etc.
1.3. Is insulation/lagging or heat tracing needed for valves carrying out important safety functions?
1.4. Has pipe stress analysis been undertaken for stressed joints, e.g. thermal effects, is heat tracing needed to be extended, including thermal expansion joints?
1.5. Is a keyed interlock needed for manual valves to prevent closure leading to backpressure?
12. Is there a potential for accidental extraction (vacuum (known as bumping)) of process vessel during vessel use/filling?
12.1. There could be risk of rapid boiling under low pressure – thus material entering vacuum system, contacting liquid rings, and caustic of scrubber.
12.2. Is rate of pressure change in reactor controlled? Can pressure ramp function be used to prevent bumping during charging reactor with pressure?
13. Sampling of reactor
13.1. Does sample valve have a spring return? Can it also have a local enclosure?
13.2. Are calibration connections/flanges small bore? This is to reduce the risk of asphyxiation to operators
13.3. Is there a strategy for alarm response for instruments under fault conditions? E.g. DCS suppression, log and simulation, etc.
13.4. Can sampling be performed by one operator? E.g. one hand for valve and one hand for sampler
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| Photograph 3 - Generic Reactor (Vessel) |
14. Once mixing of product is complete - What inhibition is needed for mixed products for maintenance, visual inspection, operator exposure?
14.1. Is addition of inhibitor chemicals needed?
14.2. Does it need to be at a certain pressure, temperature, level, etc?
14.3. Is agitation needed? Is it continuous or linked to conditions like temperature, etc.
15. Should heating reactor be stopped if high temperature detected in vent header? Can vacuum be removed as low pressures can lead to boiling easier, (more heat into vent)?
16. Inerting - nitrogen line to reactor
16.1. Does the nitrogen control valve need a minimum stop to allow a small flow of nitrogen into header/reactor – in case there is a loss of actuated air for the valves?
16.2. For the nitrogen purge line, the safe valve (PSV) is it set below the design pressure of the line, vessel and system, ensure it is the lowest of the system?
16.3. Are nitrogen connection ports are dissimilar to compressed air and have labelled differently?
17. Is alarm system in line with industry standards - EEMUA Publication 191 Alarm systems - a guide to design, management and procurement
Gas cleaning abatement - Scrubber
18. Power failure of abatement
18.1. How should abatement system function on power failure?
18.2. High venting rates (e.g. from fail open valves) – is restriction orifices needed to prevent reaching design pressure
18.3. Can alternative safeguards be used like PSVs – pressure safety valves on vent header?
18.4. Can you install warning signs around vent area to limit personal access?
19. Is there an issue with solvent carry over from reactor – leading to layering of scrubber content & reducing efficiency?
19.1. This may not be detected in sampling or level gauge.
19.2. But usually have condenser and guards condensers to minimise solvent carry over)
19.3. Is there any issue with overfilled reactor producing extra gases into scrubber and incompatibility with caustic in scrubber? There shouldn’t be large volume in abatement (should be reacted) - check abatement operating envelope, material compatibility, engineering change (MoC), etc.
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| Photograph 5 - Generic control system for a abatement system |
20. Scrubber
20.1. Is leakage of caustic in heat exchanger with cooling water an issue? What is the likely leakage direction?
20.2. Is biofouling an issue within demister of column? This can be solved by spraying or by design (chevron v mesh)
20.3. For high temperature of gases in scrubber – does scrubbing liquid provide a suitable heat sink - e.g. pipework, venturi, packed vessel, cooler, etc. - Would a temperature gauge before a heat exchanger allow for better temperature monitoring and troubleshooting?
21. For inadvertent gases like hydrogen entering the abatement – is positive isolation needed? E.g. removable spool, updated SOPs procedures.
22. For the charging of the scrubber – Is an interlock needed between online temperature monitoring and charging pump to prevent temperature rise?
Thank you for reading, please comment, like and subscribe to this blog
Hope you have enjoyed reading this.
Chiraq
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