Primary Air Port Tube Integrity - A Critical Review of Primary Air Port Design and the Effect of Boiler Design Parameters, 2002 Fall Technical Conference

Cracking of stainless steel/carbon steel composite tubes in the primary air ports of black liquor recovery boilers has been reported repeatedly in the past few years, and is of special concern in several mills. Intensive studies have been conducted by various research groups to promote the understanding of air port cracking, by focusing on operating conditions, design and fabrication of the air ports, thermal properties of the system, and air port tube materials.

Primary air port cracking appears to be affected by many variables including air port design and fabrication. Kvaerner has two designs for its primary air ports: the casting design and the non-welded insert design. This paper discusses both of these designs and their performance in the recovery boilers.

Primary air port cracking might also be affected by water circulation, combustion air system, black liquor firing system, and char bed consistency and dynamics. This paper discusses the possible effect of these variables on primary air port tube performance and reviews the design of these various systems in a recovery boiler.