The plant (2) has a pressure discharge line (10) including an inlet opening (22), which is arranged above a group by catalytic elements (34) and below an upper inflow and outflow opening (32) in an outer surface (28) so that a gas mixture provided in a containment shell (4) flows through a flow channel (26) from downwards to upwards according to a nature convection principle in a convection operation. The mixture flows into the channel from downwards and upwards according to a forced flow principle in a discharge operation, and disperses above the discharge line as a pressure discharge flow. The containment shell is designed as a sectionally viewable dome shaped steel casing.
