A Historical Look At The Development Of Alternative Black Liquor Recovery Technologies And The Evolution Of Black Liquor Gasifier Designs, 2004 International Chemical Recovery Conference

Ever since the introduction of the Tomlinson recovery boiler, industrial and academic groups have worked on developing alternative recovery technologies that promise safer operation, higher efficiencies and more flexible processing options. The variety of proposed approaches is remarkable, but most—particularly those developed in the past 30 years—center on black liquor gasification. The gasification technologies are roughly evenly split between low temperature, operating below the melting point of the inorganic compounds (ash), and high temperature or smelt-phase systems. The fact that no commercial alternative to the recovery boiler is yet available is testament to the challenges associated with black liquor recovery. This paper reviews nearly two dozen of these alternative technologies, describing the processes and identifying why development was ultimately abandoned. Common threads are recognized: low temperature processes have problems achieving good conversion while avoiding ash agglomeration; high temperature processes suffer material problems caused by extremely corrosive conditions. In nearly all cases, funding has been unstable or withdrawn before the technical hurdles were overcome. The two gasification processes now under development are approaching commercial viability. Consequently, funding is shifting away from development of new recovery process concepts and towards improvement of these two technologies.