Hi everyone, I would like to share some notes and questions I made during a HAZOP (Hazard Operability) safety study for a gas turbine unit.
The gas turbine has separate systems for the fuel gas & oil,
lubrication oil and a turbine washing section that was considered during the
study.
Like my other posts, questions here can be asked for any
generic process plants.
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| Photograph 1: Generic power plant station |
1. For high temperature feed gas into the burner - Can the blades of the turbine damage due to heat cycling of high temperature?
(1)
Can the blade shed, leading to mechanical
sparking downstream, if possible?
(2)
Is there exhaust temperature thermocouple,
monitoring, alarm and heat detectors externally?
(3)
Can loss of multiple thermocouples in an
inter-stage, fool the control system into thinking a deviation has occurred? E.g.
Spurious shutdown
2.
Can the drain valve of the turbine enclosure
fail to close upon start up?
(1)
Potential for combustion gases to enter turbine
house, cause asphyxiation, hot gases & flammable atmospheres
(2)
Unfiltered air could also be drawn into the
turbine enclosure, via open drain
(3)
There will be natural forced air external of
enclosure to dilute potential leaks via the drains
3.
Does the flame detection within the turbine enclosure
detect both oil and gas fires?
(1)
Is there emergency procedures for an external fire
to a fuel oil pump line & tank system?
(2)
Can you install a remote / automatic isolation
valve to the gas oil tanks that isolates the tanks during a fire scenario?
4.
Can fuel oil carry over into the feed fuel gas
line?
(1)
Oil can enter gas burner – carbonise and
potential to block burners & possible loss of power
(2)
Is there a demister (knock out KO :) vessel?
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| Photograph 2: Generic Fuel gas separator KO vessels |
5.
Can the float valve on the gas demister fail
open?, thus gas enters the liquid tank & sump
(1)
Is there annual maintenance on the float valve
(safeguard)
(2)
Is a review of the drainage arrange of gas
demisters needed to prevent it contaminating the drains?
(3)
To prevent gas ingress – is there leak testing
prior to start up?
6.
Combustion air inlet - Can the air filter block
due to icing? Thus potential carry over of debris into the turbine.
7.
Can vehicles strike and ruptured gas pipes? Is there
a vehicle protection systems for gas/oil lines?
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| Figure 1: Schematic of turbine with lube oil system |
8.
Can the waste heat boiler exhaust dampeners fail
close?
(1)
This can cause blockages of exhaust – leading to
high pressures
(2)
Is there duct pressure monitoring, alarm and
trips?
(3)
Could you have mechanical coupling on dampeners
to prevent both closing at the same time
9.
Can the diverter valve returning lube oil line
into the heat, fail close and heater remain on?
(1)
High temperature can degrade the lubrication properties
of the oil and thus cause bearing and turbine damage?
(2)
If lube oil was inadvertently cooled in the
cooler - Oil viscosity increases if cooled, and reduces efficiency of the
lubrication
(3)
Is there immersion heaters within the lube oil coolers?
10.
Lube oil filling – could the wrong oil be
filled? Is the correct oil drum kept nearby on a spill pallet & spill kit?
11.
Can the fuel oil nozzle within the burner fall
off? Is it constructed to minimise such failures?
12.
For turbine washing - Can you overheating the
wash fluid on cold days, change properties of fluid such that splashing during
filling could occur? Thus potential burns to operators
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Hope you have enjoyed reading this
Chiraq
