Freeze concentration recovery process for wood pulping
AssigneeWestvaco Corporation
InventorHong H. Lee
Life of this patent
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Abstract
Pulping liquor borne solids are concentrated within an aqueous solution by a successive plurality of freezing steps wherein a discrete quantity of the solution is crystallized in each step by freezing. The water crystals from each freezing step are subsequently separated from the remaining liquid solution by screening and applying axial pressure to the crystalline mass. Greater efficiencies may be obtained in some cases by mixing or reslurrying a pressed, crystalline mass and pressing a second time. Another auxiliary separation step comprises a quiescent thaw of the crystalline mass from the first two press steps to permit additional dissolved solids to be drained away from the purified water ice.
Claims11
A process for concentrating dissolved solids in a liquid solution of black liquor from a pulping digester comprising the steps of:
- A. crystallizing approximately 44 to 56 weight percentage of the total weight of solution of solution solvent from a black liquor solution comprising 10 to 18 weight percentage of solids by the removal of heat therefrom;
- B. separating crystals formed by said crystallizing step from remaining liquid thick phase solution by screening;
- C. first pressing said crystals in mass by axially applied pressure to express additional thick phase solution occluded between crystals;
- D. relieving the stress of said first pressing on the mass therefrom;
- E. isothermally mixing said stress relieved mass of pressed crystals to redistribute residual occluded thick phase solution without shearing the crystals;
- F. second pressing said crystals in mass by axially applied pressure to express additional thick phase solution occluded between crystals, there being no substantial addition or removal of heat relative to said mass between first and second pressing.
Dependencies are inferred from the claim text.