HAZOP of a Diesel Storage System

Hi everyone, I would like to share some notes and questions I made during a HAZOP (Hazard Operability) safety study for a diesel storage system for a typical generator. 

Like my other posts, questions here can be asked for any generic process plants.

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Photograph 1: Typical Road tanker filling for a Diesel Storage System

 

 Road tanker filling of storage tank:

1. Could the fast opening and closing of valves (during tank filling) lead to hammering effect, and thus a potential for ruptures or leaks?

 

2. For impact from vehicles – are bollards/high kerbs/fences in place?

 

3. Are flexibles piping & connections, within double containment? e.g. Pipe in pipe

 

4. Is there a potential for residual fuel in the flexibles – if is there a procedure for blowdown of the flexible line connected to the truck after filling activity

 

5. For power loss of tanker pump/valves

5.1.   Is there Overfill Protection Valve (OFPV)? – is it spring closed? Will all remaining actuated valves will fail to last position?

5.2.   Is there redundancy for power supply? Is a battery backup (UPS) system needed?

Figure 1: Generic overfill protection for a road tanker

Diesel day tank (Belly Tank)

6. If there is a blockage in the transfer lines

6.1. Is there a y-type strainer filter? Is this strainer a part of the site maintenance schedule?

6.2. Is there an emergency foot valve to stop operations?

6.2.1.Is it removable via an oversight flange on the tank manway?

6.2.2.BUT foot valve can fail stuck place due to debris or loss of spring! – there is potential for airlock in the generator and operational delay to start the generator due to lack of priming – therefore add foot valve to PPM

6.2.3.Can you Investigate the need for foot valve or alternative design to prevent the scenario (failed spring/debris)?

6.3. Is there a mobile fuel polisher in place at the belly tank to prevent potential blockages?

 

7. If pipe extends into the belly tank – is siphoning possible?

7.1. Is the return line from the generator to belly tank is below the fuel level in the belly tank?

7.2. Is there a need for anti-siphon hole at the top and inside of the tank?

 

Figure 2: Typical fuel polisher flow diagram

 

 8. Blocked tank vents – overpressure

8.1. Are two vents in place? Is there potential for rain ingress/birds nest?

8.2. Is there option for another tank to be selected to release/divert the pressure build up?

8.3. Is vents to a safe location?

 

9. Cold weather can lower freezing point of diesel – thus wax and blockages – is there a procedure to ensure that diesel type supplied during cold weather is of lower freezing point than the ambient

 

10. For overfilling of tank – Level switches….

10.1. If a level transmitter fails – is there spares on site? Is there a need for visual/hydrostatic gauge at the belly tank during manual filling?

10.2. Can you use a dedicated vibration level switch? Instead of a float, capacity or ultrasonic switch?

10.3. Vibrating switch is more sensitive for low density diesel, as floats may struggle with small level changes

10.4. Vibrating switches are not affected by foam, bubbles, or fuel viscosity. They are maintenance free as there are no moving parts.

10.5. Level switch types:

10.5.1. Float Switches: Use a buoyant float that moves up or down with the liquid level.

10.5.2. Capacitive Switches: Detect changes in capacitance when liquid is present.

10.5.3. Ultrasonic Switches: Use sound waves to detect liquid levels

Figure 3: Generic level detection for a storage tank

  

11. Is splash filling an issue? Electrostatic dicharges (potential Ignition)

11.1. Filling should be via a dip pipe below the diesel liquid level

11.2. Speeds should be limited 1 to 7m/s if flammable liquids in place (but not important as diesel is high flashpoint - for the UK but an issue in the Middle East)

 

12. Sampling of diesel tank

12.1. Is there a potential to drop object into the tank leading to operational delay? (should have safe system of work in place)

12.2. Can you carry out sampling with an extension tube to the bottom of the belly for the extraction of fuel oil sample?

 

13. Corrosion

13.1. Is there a painting specification philosophy - to match environmental condition (pipe and external of tank?

13.2. Is there a need for the entire or some part of the inner section to be painted or lined with corrosion protection coating?

13.3. Is propagating brush discharges an issue?

13.4. Is the basin of the belly tank to be coated or painted? There is a difference!

13.4.1. Paint: Typically consists of pigments, binders, solvents, and additives for colour and surface enhancement. Generally thinner compared to coating

13.4.2. Coating: Includes specialised resins, polymers, or metal layers designed for strength, durability, and specific industrial applications

 

Thank you for reading, please comment, like and subscribe to this blog

Hope you have enjoyed reading this.

Chiraq

HAZOP of a Chemical Reactor

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.

Please comment, like and subscribe.

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.

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

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

 

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.

 

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