US 4,537,655 AGranted

Process for producing and flash drying high yield mechanical cellulose pulp with steam and condensate recycle

AssigneeMoDo-Chemetics AB

InventorsSven-Erik D. Henriksson, Bo A. Ahrel, Claes G. S. Svensson, Torsten A. H. Franzen

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Abstract

A process is provided for inexpensively producing high yield mechanical cellulose pulp having good paper properties, which comprises preheating particulate lignocellulosic material; defibrating the preheated material under a superatmospheric steam pressure within the range from about 2 to about 4.5 bar above atmospheric pressure in a disc refiner under conditions such that steam is generated during the defibration; continuing the defibration until a cellulose pulp is obtained having a freeness within the range from about 300 to about 700 ml CSF; flash drying the defibrated cellulose pulp while maintaining a superatmospheric steam pressure within the said range during the drying; withdrawing steam generated during the defibration and passing it in indirect heat exchange with steam utilized in the flash drying, so as to utilize in the drying at least 30% of the heat content thereof; and then removing and baling the flash-dried cellulose pulp. Water vapor produced in the flash dryer is condensed and recycled to the disc refiner.

Claims7

Dependent claims

A process for inexpensively producing high yield mechanical cellulose pulp having good paper properties, which comprises

(1) preheating particulate lignocellulosic material;
(2) difibrating the preheated material under a steam pressure within the range from about 2 to about 4.5 bar above atmospheric pressure in a disc refiner under conditions such that steam is generated during the defibration;
(3) continuing the defibration until a cellulose pulp is obtained having a freeness within the range from about 300 to about 700 ml CSF;
(4) flash drying the defibrated cellulose pulp in a steam-heated flash dryer while maintaining a superatmospheric steam pressure within the said range during the drying;
(5) withdrawing steam generated during the defibration and passing it in indirect heat exchange with steam utilized in the flash drying, so as to utilize in the drying at least 30% of the heat content thereof;
and then
(6) removing and baling the flash-dried cellulose pulp;
(7) separating water vapor produced by evaporation in the steam-heated flash dryer and condensing the water vapor to water;
(8) recycling the water condensate for cooling and dilution to the disc refiner;
(9) vaporizing water condensate from the heating steam of the steam-heated flash dryer converting it to high pressure steam;
and then
(10) recycling the steam for heating to the steam-heated flash dryer.

9 more elements

Dependencies are inferred from the claim text.