Charging powders in vessels with flammable vapour atmospheres. An industrial approach

Abstract

Hazards linked to the operation of powder charging in vessels containing flammable vapour atmospheres are well known. As well, several industrial solutions exist to avoid these hazards and perform such operations in a safe way, meaning that electrostatic ignition sources are reliably avoided.However, in some industrial situations, the proposed solutions are difficult to implement due to the characteristics of the vessels, for instance not tight enough to implement a reliable inerting strategy; the layout of the location, for instance not enough room to install additional equipment; or services available at site level, for instance lack of vacuum or nitrogen supply in some plants.For these reasons, a detailed assessment has been performed focusing in the following points as those linked to the generation of effective electrostatic ignition sources:1. Nature of the liquid generating the flammable vapours.2. Characteristics and use of bags containing powders being charged.3. Powder falling into the vessel.4. Powder clouds in the vessel.5. Powder layers generated on top of the liquid.The assessment included a theoretical approach confirmed by experimental tests in site and lab.The paper will describe the detailed assessment performed in each of the identified points, present the experimental results and describe the final proposed solutions to ensure safety during powder charging to vessels containing flammable vapour atmospheres. Current situation requires adding powders from bags through manholes, which is considered as a non-acceptable practice from a risk assessment point of view.