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USE OF PSA FOR DESIGN OF EMERGENCY MITIGATION SYSTEMS IN A HYDROGEN PRODUCTION PLANT
Methodology for PSA-aided design
The methodology for design of mitigation systems, which is proposed in this paper, is a simple
combination of existing techniques, based on the dynamic feedback of process engineering and
probabilistic safety assessment, which aims to develop reliable and effective systems in mitigation of
unwanted consequences to events, using a lesser amount of calculations and iterations through a
sequential process.
The system design follows a logical sequence, which starts with hazard identification from a
process flow sheet, goes through the initial proposal of the protection system, and culminates in the
final design of the system, as shown in Figure 1. It should be noted that this process covers all the
mitigation systems in the plant; however, this study only presents a case for an acid leak in Section II
of the General Atomics SI process. This danger was identified in a previous qualitative analysis, in
which Hazop was used (Mendoza, 2009).
In this paper, we show a simple case starting from the preliminary design structure, which was
postulated by following the steps shown in Figure 1. It should be noted that this case relates to risks
during operation and does not cover other states such as shutdown and start-up.
Figure 1: Process for PSA-aided design
Physical demarcation of the analysis area
Although the sulphuric acid achieves a final concentration of 90% in the distillation column bottoms,
the negative pressure in the tower minimises the possibility of leaks in this equipment.
The region which is considered in the analysis lies between the column bottoms pumping system
and the chemical reactor E207, due to the severe conditions of acidity pressure and temperature in
this part of the SI cycle (90% ac., T 1 100 K and up to 7 bar) (Brown, 2003).
Figure 2 shows, framed in a box (at the bottom left), the mechanical equipment that will be
covered by the emergency mitigation system designed in this paper.
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