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USE OF PSA FOR DESIGN OF EMERGENCY MITIGATION SYSTEMS IN A HYDROGEN PRODUCTION PLANT
Figure 7: Importance measures in original system
The process of reconfiguring the system was made in five iterations with minor changes at each
stage, as shown in Table 4. It should be noted that the number of iterations can be reduced if major
changes are made, however, in this way the effects of individual modifications could be hidden.
Table 4: Reconfiguration stages
Stage
Frequency
year-1
Original 5.29 E-09
Flushing system is removed 4.79 E-08
A new redundant valve is added to V51 5.48 E-09
Check valve is removed from Tank T01 5.43 E-09
Valve V53 is removed 5.46 E-09
A new diesel generator is placed in the neutralisation system 8.46 E-10
In the first stage, the EFS was eliminated to assess their importance in the overall level of safety
(given the disadvantages of its use), and although there was an increase of almost 10 times the critical
frequency of the final state, it was appreciated that minor modifications in valves could return the
initial value of event frequency.
Subsequent amendments were made to provide more certainty in the system, placing a redundant
valve to the V51, and removing the redundant valve V53, which was placed to isolate the E-207 reactor.
It should be noted that this change produces a significant savings, adding a valve specified at low
temperature and removing the other whose specification was high temperature (considerably more
expensive).
Changes in the neutralisation system consisted of adding a second back-up power generator and
removing the suction valve V01, located in the suction tank, by changing the geometry of the system
(pump below minimum level of the tank).
At the final stage, the mitigation system is composed of an isolation system and a system for
neutralisation (both with changes to the originally proposed).
The new system provides optimum configuration, saving space and money, in addition to raising
the safety level of the original system, even with the elimination of a complete flushing system.
For this process, a sensitivity analysis was performed at each stage. It should be noted that
although the order of implementation of changes will not alter the final frequency, it affects decision
making, therefore it should be done with the greatest caution possible.
Conclusions
The design of safety systems supported by PSA provides efficient designs at a lower cost than those
based solely on engineering criteria, guaranteeing a priori an adequate level of safety with a
predetermined risk acceptance. It is also a useful tool for appropriate location of isolation valves.
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