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Risk analysis

Risk analysis. Risks and possible consequences Martin Doubek. The risk analysis. This presentation describes possible failure scenarios, their consequences and actions that will be taken after the failure.

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Risk analysis

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  1. Risk analysis Risks and possible consequences Martin Doubek

  2. The risk analysis This presentation describes possible failure scenarios, their consequences and actions that will be taken after the failure. • When an critical alarm is triggered during the Thermosiphon run an automatic swap to compressor plant will be carried out. • Threshold values of the alarms stated in this presentation are open for discussion. Thermosiphon commissioning

  3. Thermosiphon redundancy Selected Thermosiphon redundant: • Water pumps • Brine pumps • Heaters Vital components can be switched to UPS and backup power: • Brine pumps • Thermosiphon liquid heater • All controls Thermosiphon commissioning

  4. Component cascade C3F8 side Water Chiller Brine C3F8 circuit Consequences of the: • Brine trip • R404 chiller trip • R23 chiller, Water trip Are the same: The Thermosiphon condenser pressure will start to increase R404 R23 Balcony unit Condenser Liquid heater Dummy load Evaporative connection Thermosiphon commissioning

  5. Critical parameters There are four critical parameters to be monitored when the Thermosiphon is cooling the detector: • Vapor pressure • Liquid temperature • Liquid pressure • Condenser level Thermosiphon commissioning

  6. Alarms on existing systems Liquid(Temp) High: - Low: 15°C Liquid High: 17.8 bara Low: - Liquid High: 16 bara Low: - Vapor High: 4 bara Low: - Vapor High: 4 bara Low: - Thermosiphon commissioning

  7. Possible trip scenarios • Brine trip • C3F8 flow remains stable • vapor pressure will start to increase • R404 chiller trip • C3F8flow remains stable • vapor pressure will start to increase • R23 chiller, Water trip • C3F8flow remains stable • vapor pressure will start to increase • Thermosiphon trip (liquid column, liquid heater) • Liquid C3F8flow STOPs • The vapor pressure remains stable (chiller continues to cool the condenser) • Passing valve • Fluid level in condensers will start to increase/decrease Thermosiphon commissioning

  8. Chiller/Brine trip Immediate consequences: The heat is no longer being removed from the Thermosiphon condenser. The vapor pressure will start to rise. When the pressure reaches 1.4 bara an automatic swap to the compressor plant will be triggered. • When the chiller stops and the brine continues to circulate the thermal inertia of the brine circuits limits the speed of the condenser warming. Pressure rise: 40 minutes to get from 1.3 to 4 bara @ 1.1 kg/s • When the brine circuits stops, which is much less likely than the chiller trip, the condenser starts to warm quickly. Pressure rise: 2 minutes to get from 1.3 to 4 bara @ 1.1 kg/s Thermosiphon commissioning

  9. Chiller/Brine trip dynamics The automatic swap to compressor plant will be triggered when 1.4 baravapor pressure is reached Thermosiphon commissioning

  10. Brine trip • Brine trip – worst case scenario • Heating rate ~2.7 bar/15min @ 1.1 kg/s ALARM Thermosiphon commissioning

  11. Liquid heater trip Scenario: The liquid heater in the balcony unit stops working. Immediate consequences: The temperature of the C3F8 liquid at the exit of the heater will drop to -14°C. This might happen gradually or quickly depending on the failure mode. Causes Circuit breaker malfunction, heater element failure • In case of power cut the liquid heater is on backup power • Two out of three heater elements are sufficient to keep the C3F8 liquid temperature at +20°C Thermosiphon commissioning

  12. Liquid heater trip Two heaters are enough to keep outlet temperature stable at 20°C -14°C -14°C +22°C +22°C Interlocks Thermosiphon commissioning

  13. Passing valve Scenario: A valve that separates the compressor plant from the Thermosiphon is passing. Consequences: The liquid level in the compressor plant condenser will be slowly increasing/decreasing issuing a warning. There is a manual valves in series with all the actuated valves involved in the separation of the two systems. Thermosiphon commissioning

  14. Passing valve We have to rely mainly on the more sensitive compressor plant level measurement to detect possible fluid migration Compressor plant condenser level monitoring: • Scale sensitivity: 0.10 kg • Normal level oscillation: approx. 10 kg • Alarm level: ±40 kg Thermosiphon commissioning

  15. Conclusions • Pumps for the water and brine are doubled, the liquid heater is redundant. • The brine pumps and liquid heater are on backup power. • The compressor plant PLC will be in charge of closing the Thermosiphon liquid and vapor lines in case alarm is triggered. • The alarm limits for the Thermosiphon vapor pressure will be very strict during the test. • The C3F8 vapor pressure will increase at steady rate after a chiller trip since the cold condenser and/or the brine thermal inertia will continue to condensate returning vapor. • The compressor plant coolant level will be monitored during the Thermosiphon test to detect possible fluid migration Thermosiphon commissioning

  16. Thank you for your attention Thermosiphon commissioning

  17. Backup slides Thermosiphon commissioning

  18. Passing valve The stability of the liquid level (weight in kg) in the Thermosiphon condenser has been evaluated during the run with dummy load. The results provide base for setting the leak detection alarm limits and to estimate the detection sensitivity. Weight measurement fluctuations during stable run Thermosiphon condenser Thermosiphon commissioning

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