RECENT TRENDS IN NCG DISPOSAL SYSTEM-DESIGN

The past public acceptance of kraft mill odor has been replaced with a more active, community concern for mills to clean up their emissions. Often this new attitude has been the driving force for more stringent environmental standards. The major source of these odors are from tot al reduced sulphur gases (TRS), namely hydrogen sulphide (H2S), methyl mercaptan (CH3SH), dimethyl sulphide (CH3SSCH3). TRS combined with ai r and water, plus varying amounts of vaporous methanol and turpentine are collectively known as noncondensable gases (NCG). The ''ro ten egg '' odor emanating from the kraft process is objectionable and is often more a nuisance than a safety hazard. However, as these gases are hig hly toxic, very corrosive and potentially explosive, careful considera tion must be given to the design of an NCG disposal system. This paper features the safety aspects of NCG disposal in the context of public issues and mill operation while focussing on the safety considerations involved with NCG equipment and system design.