1 Modern Digester Configurations – LoSolids Pulping

2 Principles of modified cooking The concentration of dissolved lignin should be low especially at the end of the cook. The [OH-] should be low and uniform throughout the cook Concentration of [HS-] should be high, especially early in the cook Ionic strength of liquor should be low, especially at the end of the cook

3 STEAM H.P. FEEDE R IMPREG VESSEL W.L. SPLIT White Liquor L.P. steam Chips HEATHEAT HEATHEAT HEATHEAT COOK MCC WASH BLOW Black liquor Pulp Dilution TWO-VESSEL MCC TM DIGESTER

4 Modern Digester Configurations – LoSolids Pulping Principles Applied in MCC and EMCC Pulping Split white liquor additions for alkali profiling. Counter current cooking to minimize lignin concentration

5 Modern Digester Configurations – LoSolids Pulping Potential for improvement Pulping studies showed that presence of dissolved wood solids reduced pulp strength

6 Modern Digester Configurations – LoSolids Pulping How do you reduce dissolved solids in practice? Extract spent pulping liquors at various locations in the digester. Replace that spent liquor with water (to maintain hydraulic balance) and white liquor (to maintain pulping chemical strength)

7 Modern Digester Configurations – LoSolids Pulping

8 New dissolved concentration profiles are achieved

9 Modern Digester Configurations – LoSolids Pulping Higher Tear Strength at a given Tensile

10 Modern Digester Configurations – LoSolids Pulping Higher Pulp Viscosity – especially when temperature is lowered

11 Modern Digester Configurations – LoSolids Pulping Other potential benefits Easier bleaching (lower kappa factor). Better extraction in digester – easier washing Reduced scaling – calcium is extracted early from the digester Improved heat distribution – more radial flow through the digester