SuperBatch

The typical SuperBatch tank farm also consists of three pressurized accumulators

and two atmospheric tanks (Fig. 4.132). Again, the liquor tanks are staged in temperature

and fresh alkali is supplied from the hot white liquor tank. Steam is used

for controlling the temperature of both hot white liquor and hot black liquor in

the tank farm, as well as for bringing the digester to cooking temperature.

The SuperBatch cooking cycle is shown schematically in Fig. 4.133. After chip

filling, impregnation liquor (i.e., black liquor of below 100 °C) is used for impregnation.

During the subsequent hot black liquor treatment, the impregnation

liquor is displaced from the digester back to the impregnation liquor tank. The

cooking liquor is then charged in the form of hot white liquor and hot black

liquor, and the digester is brought to cooking temperature by steam injection into

the circulation line. White liquor can be added during the cooking phase to control

the alkali balance. After cooking, wash filtrate displaces the hot black liquor

first into the primary hot black liquor accumulator and then into the secondary

accumulator. Eventually, the pulp is discharged by pumping [3].

4.2 Kraft Pulping Processes 373

HBL

I

HBL DIG WF

II

IL HWL

WHITE LIQUOR

CHIPS

PULP

BLACK

LIQUOR

WASH