Hi everyone,
I would like to share some notes and questions I made during a HAZOP (Hazard Operability) safety study for a natural gas fired furnace system.
Like my other posts, questions here can be asked for any generic process plants.
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| Photograph 1: Industrial Furnace |
Natural Gas
1. For the alarm of a blocked valve – does it operates on loss of compressed air and loss of electrical supply?
1.1. Confirm failure position of control valves
1.2. Is the furnace completely sealed? – if not, typically the billet entry and exit point may allow some pressure relief from blockages
1.3. Is further training provisions needed for operators?
2. Is impact damage to gas lines in particular by cranes credible? Is further protection needed - e.g. barriers, supports and signage, etc. ?
3. Is thermal shock on the refractory credible - leading to potential equipment damage?
3.1. Does the furnace requires gradual lowering of combustion air fan to limit thermal shock?
3.2. Is there a procedures for shut-down - one for long maintenance periods (forced cooling) and another for short maintenance activities?
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| Photograph 2: Refractory lining within furnace (failed) |
Combustion air
4. For NO FLOW – combustion air fan failure
4.1. Do you need running speed indication on the control system? Or other indications, e.g. power amperage, on/off power indication, etc.
4.2. Is there a Backup drive system, spare fan and motor(s) available should there be a failure of the fan system?
5. Is the pre heated air - Dew point downstream of the recuperator (preheated/waste heat recovery HEX) an issue – Is there a potential to generate and significant corrosion products with natural gas fired burners?
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| Figure 1: Simple diagram of a recuperator (Waste heat exchanger) |
Waste Gas
6. Is it credible that gusts of wind could be such that they prevent adequate venting of waste gases?
6.1. Is there a potential loss of containment of hot gases from the furnace?
6.2. Note High winds (venturi effect). Increased draw on the furnace. Decrease in furnace pressure leading to air ingress and cooling of the furnace. Increased gas consumption and inefficient operation
7. For sampling failure of CO, or black smoke – is there procedures on the sampling, e.g. Action in event of black smoke, calibration, servicing with third party, etc.
8. Mis-operation – Is ineffective pressure control possible e.g. putting pressure loop into manual control e.g. to affect processing speed.
8.1. Potential backpressure leading to over pressurising of the furnace. Potential Loss of containment of hot gases from the furnace.
8.2. Should combustion in the furnace be affected then is there a potential for increased smoke and CO generation?
8.3. Should access to the furnace (scale door) be attempted then is there a potential for operator to be hit by exiting hot gases?
8.4. Solution
8.4.1.Review means of data entry for control parameter entry to prevent inadvertent mis-entering information.
8.4.2.Determine what means are available for limiting non-furnace operator access to manual/auto selections, setpoint choice.
8.4.3.Ensure operators are aware of what actions may constitute a near-miss.
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| Figure 2: Typical Piping and Instrumentation diagram (P&ID) of a furnace - showing control logic |
Cooling Water system
9. Is there a history of excess scaling/blockages in the water lines? Is pipe thickness inspections undertaken regularly?
10. For hot water pipe leaks
10.1. Does pipework outside furnace need to be lagged/insulated for personnel protection?
10.2. Do you need to review sizing of towns water makeup capacity based on potential leak sizes?
11. Is air ingress and accumulation an issue in the water system?
11.1. Does bleeding of the system takes place following maintenance activities that can introduce air into the system?
11.2. Can all equipment in the system be adequately accessed, drained, vented and isolated?
Thank you for reading, please comment, like and subscribe to this blog
Hope you have enjoyed reading this
Chiraq
