Concept design for overfill protection at a tanker loading bay
Process safety
By combining process knowledge with E&I, Prohead succeeds in turning PHA recommendations into fully worked-out measures.
About the case
Context:
During a periodic HAZOP/LOPA review of an industrial site, it was found that the risk of overfilling tank trucks with formaldehyde solution was insufficiently covered. The existing protection system consisted of a bubbling tube and procedural checks by the operator and driver. However, the LOPA showed that an additional independent protection layer was needed to achieve the required risk reduction.
Approach:
Prohead Engineering developed a concept design comparing three possible solutions:
- Concept A – Stand-alone system: addition of an independent measuring system (vibrating fork) linked to an extra shut-off valve. This system operates independently of the existing bubbling tube and can be developed up to SIL 2.
- Concept B – New safety PLC system: implementation of the same detection (vibrating fork + shut-off valve), but integrated into a new safety PLC with remote I/O. This offers the most flexibility for future expansions and allows standard interfacing with the existing process PLC.
- Concept C – Upgrade of the current system: modernising the bubbling tube to SIL 2 level. However, analysis showed that this was not economically feasible due to the lack of SIL certificates and failure data for the current components.
In addition to the concept choice, the file contained:
- a comparison of the advantages and disadvantages of each concept,
- a high-level requirement list for engineering and commissioning,
- recommendations for the link with the existing BPCS,
- advice on fail-safe implementation and testability of the functions.
Result:
The study showed that upgrading the existing system (concept C) was not realistic. Both concept A (compact and independent) and concept B (with safety PLC and expansion options) offered a robust solution. This enabled the client to make a well-founded decision on which direction to develop further in basic engineering.
Added value:
By combining HAZOP/LOPA results with a concrete concept design, the site was able to demonstrate that the risk of overfilling is structurally controlled. The approach also provided a clear roadmap towards a SIL-compliant implementation, aligned with the existing installations and operational needs.