Dissolved solids control in pulp production

A method of continuously producing chemical cellulose pulp using at least one screen assembly in a digester, comprising the steps of:

• (a) passing a liquid slurry of comminuted cellulosic fibrous material in a first direction to and past the screen assembly, the slurry having a first level of dissolved organic material therein;
• (b) withdrawing part of the liquid, having the first level of dissolved organic material, from the slurry at the screen assembly;
• (c) passing a first part of the liquid withdrawn in step (b) to recovery or other handling outside the digester;
• (d) recirculating a second part of the liquid withdrawn in step (b), in a recirculation loop, back to the digester at the approximate position of the screen assembly;
• (e) introducing cooking liquor into the recirculation loop;
• (f) introducing dilution liquid, having a second level of dissolved organic material significantly enough less than the first level to positively affect pulp strength, effective alkali consumed, H-factor, or bleachability, into the recirculation loop;
• and
• (g) heating the liquid in the recirculation loop before return of the liquid in the recirculation loop to the digester;
• and introducing the liquid in the recirculation loop back into the digester so that the liquid introduced from the recirculation loop has a third level of dissolved organic material therein significantly enough less than the first level to positively affect pulp strength, effective alkali consumed, H-factor, or bleachability.

A method of continuously producing kraft pulp using at least one screen assembly in a digester, comprising the steps of:

• (a) passing a liquid slurry of comminuted cellulosic fibrous material in a first direction to and past the screen assembly;
• (b) withdrawing part of the liquid, from the slurry at the screen assembly;
• (c) passing a first part of the liquid withdrawn in step (b) to recovery or other handling outside the digester;
• (d) recirculating a second part of the liquid withdrawn in step (b), in a recirculation loop, back to the digester at the approximate position of the screen assembly;
• (e) introducing cooking liquor into the recirculation loop;
• (f) introducing water, washer filtrate, or combinations of water and washer filtrate dilution liquid into the recirculation loop;
• and
• (g) heating the liquid in the recirculation loop before return of the liquid in the recirculation loop to the digester.

A method of continuously producing chemical cellulose pulp using at least first and second screen assemblies in a digester, spaced from each other in a first direction, comprising the steps of continuously:

• (a) passing a liquid slurry of comminuted cellulosic fibrous material in the first direction to and past the first screen assembly, the slurry having a first level of dissolved organic material therein;
• (b) withdrawing liquid, having the first level of dissolved organic material, from the slurry at the first screen assembly, and passing it to recovery or other handling outside the digester;
• (c) after steps (a) and (b) passing the slurry in the first direction to and past the second screen assembly;
• (d) at the second screen assembly withdrawing and recirculating in a recirculation loop, back to the digester at the approximate position of the second screen assembly, slurry liquid;
• (e) introducing cooking liquor into the recirculation loop;
• (f) introducing dilution liquid, having a second level of dissolved organic material significantly enough less than the first level to positively affect pulp strength, effective alkali consumed, H-factor, or bleachability, into the recirculation loop;
• and
• (g) heating the liquid in the recirculation loop before return of the liquid in the recirculation loop to the digester;
• and introducing the liquid in the recirculation loop back into the digester so that the liquid introduced from the recirculation loop has a third level of dissolved organic material therein significantly enough less than the first level to positively affect pulp strength, effective alkali consumed, H-factor, or bleachability.

A continuous digester having a top and a bottom, an inlet for cellulosic fibrous material to be digested at the top of the digester, and an outlet for digested pulp at the bottom of the digester;

• a top screen assembly for withdrawing liquid from the top of the digester;
• an extraction screen assembly below the top screen assembly;
• a cooking screen assembly between the extraction screen assembly and the bottom of the digester;
• means for withdrawing a first portion of the liquid passing through the cooking screen assembly and passing it to recovery, a second portion of the liquid passing through the cooking screen assembly remaining;
• means for adding low dissolved organic material liquid to said second portion to provide an augmented second portion;
• and means for recirculating said augmented second portion to the interior of the digester at about the level of said cooking screen assembly.

A continuous digester having a top and a bottom, comprising:

• an inlet for cellulose material to be digested at the top, and an outlet for digested pulp at the bottom;
• a top screen assembly;
• a trim circulation screen assembly below said top screen assembly;
• a first screen assembly below said trim circulation screen and having a first withdrawal conduit;
• a second screen assembly below said first screen assembly and having a second withdrawal conduit;
• said second withdrawal conduit operatively connected to a flash tank;
• means for adding low dissolved organic material liquid to said first withdrawal conduit;
• and means for recirculating liquid in said first withdrawal conduit with added low dissolved organic material liquid to the interior of the digester at about the level of the first screen assembly.