Abstract
Each industry in which flammable gas and liquids are handled has the problem to collect in a safe way the vent of the equipments to a suitable emission treatment unit (thermal oxidizer, cryogenic condenser, scrubber).
Historically, a lot of accidents happened inside emission collecting systems of batch plants because of the contemporary presence of flammable vapours, air, and effective ignition sources in operations such as: Liquid transfer by pump or nitrogen/air pressure, Vent of equipment due to heating, distilling or gas release during reactionsIn the first part of this paper two accidents happened inside emissions collecting systems will be analyzed in order to define consequences and typical causes.
In order to avoid these accidents two different ways of safety design are usually proposed: Diluted emissions collecting systems, Inerted emissions collecting systems. The emissions systems in dilution are more common. The basis of safety, in this case, is to have flammable vapours concentration inside pipelines and manifolds below Lower Explosive Limit (LEL). This, normally, is guaranteed by an additional air stream given by a fan or a blower.
In the second system the basis of safety against explosion is given by assuring an atmosphere with oxygen content lower than Limiting Oxidant Concentration (LOC) of the flammable vapours. In the paper we will show the reasons why the use of inerted emissions collecting systems should be preferred.
High emissions flows are dangerous both for explosion risk and for ambient pollution and economically expensive thus this section will be followed by suggestions on emission flow optimization and reduction.
In conclusion, for both type of collecting system, some recommendations about avoidance of ignition sources and guidelines for safe connection of process equipments to emission ducts will be presented.
