Reliability analysis and assessment of the explosion risk in a hybrid collector

Dust removal from a gas stream is a common problem in many industrial processes (e.g. power, cement, steel plants, etc.). In the last decades, plant managers more and more often have had to face the necessity of improving de-dusting systems in order to meet more stringent law requirements, inspired by the principle of the “maximum safety technologically feasible”, but also pushed by the increased penetration of environmental issues into public opinion, and its meaning in terms of company image. Budgets for these improvements play a role in a general asset management strategy: de-dusting, being often an operation having low influence on production performances, is seen more as a “necessary cost” than a profit generator. The trend for companies, especially in the actual economical scenario, is to reuse existing de-dusting plants, enhancing their efficiencies rather than install new plants that would involve costs for the decommissioning of obsolete equipment. The obvious economic benefits of retrofits are counterbalanced by technical disadvantages. In particular, a systematic assessment of safety issues is required, not limited to the safety-oriented design of new machines, but extended in the evaluation of the impact that changes in process conditions (induced by the new equipment) can have on the existing ones. In this work, explosion problems in the de-dusting section of a cement plant have been considered. Particularly, using fault tree analysis, it has been evaluated the changing in the overall risk (considering one year of mission time) of explosion referring to a hybrid-like collector realised by introducing a Fabric Filter (FF) downstream with respect to an Electrostatic Precipitator (ESP). Results have shown that a chain of failures in the FF section may affect relevantly the risk of explosions occurrence in the collector leading to the unavoidable need for the introduction of mitigation actions into the system.