|
HWL + HBL
BL, WBL
WBL
CHIPS
AIR
CHIP FILL
RDH
COOKING
CYCLE
IMPREGNATION
HOT
DISPLACEMENT
HEATING
AND COOKING
COLD
DISPLACEMENT
DISCHARGE
Fig. 4.131 Steps of the Rapid Displacement Heating (RDH) cooking cycle [1,2].
accumulator B. Eventually, the pulp is discharged from the digester by use of pressurized
air or by pumping [1,2].
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
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
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