Filtrate

WW

HW

STEAM

STEAM

Fig. 4.132 Simplified SuperBatch process flowsheet.

IL = impregnation liquor; HBL I/II = primary/secondary hot

black liquor; HWL= hot white liquor; DIG = digester;

WF = wash filtrate; WW = warm water; HW = hot water [3].

CHIPS

AIR

CHIP FILL

SUPERBATCH

COOKING

CYCLE

IMPREGNATION

HOT BLACK

LIQUOR

TREATMENT

HEATING

AND COOKING

COLD

DISPLACEMENT

PUMP

DISCHARGE

IL

HBL I

IL,

HBL II

WF

HBL I,

HBL II

PULP

WF

COOKING LIQUOR

CHARGE

HWL +

HBL I

HBL II

STEAM

Fig. 4.133 Steps of the SuperBatch cooking cycle [3].

374 4 Chemical Pulping Processes

Continuous Batch Cooking (CBC)

The CBC tank farm consists of two pressurized accumulators and two atmospheric

tanks (Fig. 4.134). There is no hot white liquor tank, and steam is used only for

heating of liquors in the tank farm. The temperatures and alkali concentrations of

the impregnation liquor and the cooking liquor are adjusted in the tank farm in

their respective tanks. There are also no digester circulation lines. During impregnation

and cooking, the liquor circulates from the tank to the digester and back to

the tank [4].

IL WBL CL DIG WF

WHITE

LIQUOR

CHIPS

PULP

BLACK

LIQUOR

WASH

FILTRATE

WW

HW

STEAM

Fig. 4.134 Simplified CBC process flowsheet.

IL = impregnation liquor; WBL= warm black liquor;

CL = cooking liquor; DIG = digester; WF = wash filtrate;

WW = warm water; HW = hot water [4].

After chip filling, impregnation liquor (IL) is charged to the digester. Once the

digester is hydraulically full, the liquor circulates back to the impregnation liquor

tank. Following the impregnation step, cooking liquor (CL) is pumped to the

digester and the displaced liquor first continues to return to the impregnation

liquor tank and then is switched to the warm black liquor tank (Fig. 4.135). All

heating of the digester contents is carried out by the supply of hot cooking liquor.

During cooking, the displaced liquor is returned to the cooking liquor tank. Subsequent

to cooking, the wash filtrate displaces hot black liquor first into the hot

black liquor accumulator and then to the warm black liquor accumulator. Eventually,

the pulp is discharged from the digester by pumping [4].

Since the CBC cook is controlled by alkali concentrations rather than by alkali

charges, the determination of chip weight in the digester is not an issue. With its

straightforward design, the CBC process features the least number of sequence

steps per cooking cycle, which makes its operation the easiest of all displacement

cooking processes.

4.2 Kraft Pulping Processes 375

PULP

WF

WF