Recovery Of Kraft Black Liquor With Direct Causticization Using Titanates PDF Download

MTCI/StoneChem developed a steam reforming, fluidized bed gasification technology for biomass. DOE supported the demonstration of this technology for gasification of spent wood pulping liquor (or 'black liquor') at Georgia-Pacific's Big Island, Virginia mill. The present pre-commercial R & D project addressed the opportunities as well as identified negative aspects when the MTCI/StoneChem gasification technology is integrated in a pulp mill production facility. The opportunities arise because black liquor gasification produces sulfur (as H2S) and sodium (as Na2CO3) in separate streams which may be used beneficially for improved pulp yield and properties. The negative aspect of kraft black liquor gasification is that the amount of Na2CO3 which must be converted to NaOH (the so called causticizing requirement) is increased. This arises because sulfur is released as Na2S during conventional kraft black liquor recovery, while during gasification the sodium associated Na2S is partly or fully converted to Na2CO3. The causticizing requirement can be eliminated by including a TiO2 based cyclic process called direct causticization. In this process black liquor is gasified in the presence of (low sodium content) titanates which convert Na2CO3 to (high sodium content) titanates. NaOH is formed when contacting the latter titanates with water, thereby eliminating the causticizing requirement entirely. The leached and low sodium titanates are returned to the gasification process. The project team comprised the University of Maine (UM), North Carolina State University (NCSU) and MTCI/ThermoChem. NCSU and MTCI are subcontractors to UM. The principal organization for the contract is UM. NCSU investigated the techno-economics of using advanced pulping techniques which fully utilize the unique cooking liquors produced by steam reforming of black liquor (Task 1). UM studied the kinetics and agglomeration problems of the conversion of Na2CO3 to (high sodium) titanates during gasification of black liquor in the presence of (low sodium) titanates or TiO2 (Task 2). MTCI/ThermoChem tested the performance and operability of the combined technology of steam reforming and direct causticization in their Process Development Unit (PDU) (Task 3). The specific objectives were: (1) to investigate how split sulfidity and polysulfide (+ AQ) pulping can be used to increase pulp fiber yield and properties compared to conventional kraft pulping; (2) to determine the economics of black liquor gasification combined with these pulping technologies in comparison with conventional kraft pulping and black liquor recovery; (3) to determine the effect of operating conditions on the kinetics of the titanate-based direct causticization reaction during black liquor gasification at relatively low temperatures ((less-than or equal to) 750 C); (4) to determine the mechanism of particle agglomeration during gasification of black liquor in the presence of titanates at relatively low temperatures ((less-than or equal to) 750 C); and (5) to verify performance and operability of the combined technology of steam reforming and direct causticization of black liquor in a pilot scale fluidized bed test facility.