Black liquor is a mixture of organic matter and inorganic chemicals that result from the pulping process. The black liquor recovery boiler is designed to burn the volatile organic material in black liquor for its heating value and to allow the inorganic chemicals to collect on the floor of the boiler in a molten bed referred to as smelt. The inorganic chemicals present in smelt can be reclaimed and used to regenerate white cooking liquor, essential to the pulping process.

The most important criteria when selecting refractories for the black liquor recovery boiler is their resistance to the process smelt. The molten smelt that collects at the bottom of the boiler is extremely high in soda. These sodium compounds can attack alumina-silica systems in refractories to cause low-melting and/or expansive phases.

HarbisonWalker International maintains a comprehensive portfolio of monolithic refractories to address all areas of this corrosive application. High-alumina products like GREENCAST^® -94 PLUS, HP-CAST^® MAXIMA, and HWI’s newest product for this application, GREENCAST^® -90 RB ON-LINE^®, have all been used with success. Other options include magnesite-based products such as MAGSHOT^® and chrome-containing plastics from the PLASTECH^® RUBY^® family. Other applications such as doors may require brick, for which KORUNDAL XD^® and MAGNEL^® RS can be used for reliable service. Upper sections of the recovery boiler, including the penthouse, do not require as much smelt resistance. HWI products like the PLASTECH^® line of phos-bonded plastics, GREENCAST^®-12 GR PLUS, KS-4V^® PLUS, and TUFSHOT^® LI PLUS have all proved successful in this application.

Product choice depends heavily on specific operating conditions and past product performance. Please contact your local HWI representative for additional consultation.