Recovery Process

There are variety of pumps used in the recovery process of a pulp mill. The type of pump recommended depends on the recovery step and the solids content of the product. Liquids moved in this section of the plant include black liquor‚ tall oil‚ white and green liquor, and liquid fuels.

In the recovery process‚ black liquor is evaporated multiple times to increase the solids content. In the first evaporation stage‚ black liquor soap rises to the surface and is skimmed off. This soap is further refined into tall oil.  Weak black liquor is further concentrated at the second evaporation stage. Evaporation occurs to raise the solids content producing heavy black liquor along with auxiliary liquid fuel or natural gas that is fed into the recovery boiler where it is burned. Progressing cavity pumps are commonly used in this section because of the solids content and abrasiveness heavy black liquor.

Tall oil is the processed rosin soap from black liquor. Typically‚ three screw and two screw pumps are used in this section of the process.

Green liquor is the resulting solution of sodium carbonate and sodium sulfide. This liquid is mixed with calcium oxide to regenerate the white liquor used in the pulping process. Because of the solids content and liquid abrasiveness‚ progressing cavity pumps are recommended for this section.

Following the transformation of green liquor to the white liquor‚ transfer pumps are used to move the white liquor back to the pulping process. Progressing cavity pumps are commonly used here.

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