Desilication and manufacture of low carbon intensity chemi-mechanical non-wood pulp and co-products

Abstract

Systems and processes are described for producing pulp and other bioproducts from non-wood feedstock. Non-wood feedstock is screened, desilicated, impregnated, and mechanically refined to obtain a pulp stream which is then subjected to oxygen-alkali treatment. Lignin and silica are separated from the pulp stream to obtain the pulp. Desilication is performed at a first temperature with hot water, an alkaline solution, and/or an alkaline liquor having a low alkali charge to selectively separate silica from the non-wood feedstock. Impregnation may be performed at a second temperature with an alkaline solution having low alkali charge to selectively separate lignin from the non-wood feedstock and prepare the pulp for mechanical refining. The oxygen-alkali treatment is performed at a third temperature to separate more lignin from the pulp stream.

1 . A method for producing pulp from non-wood feedstock, the method comprising:
 desilicating the non-wood feedstock at a first temperature to selectively remove silica therefrom;   impregnating the desilicated non-wood feedstock at a second temperature with an alkaline solution having low alkali charge to selectively separate lignin from the desilicated non-wood feedstock;   mechanically refining the impregnated non-wood feedstock to obtain a pulp stream;   performing oxygen-alkali treatment on the pulp stream at a third temperature to separate lignin from the pulp stream; and   removing the lignin separated from the desilicated non-wood feedstock and the lignin separated from the pulp stream.   
     
     
         2 . The method of  claim 1 , wherein the non-wood feedstock is desilicated with a chemical compound solution. 
     
     
         3 . The method of  claim 2 , wherein the chemical compound solution comprises sodium carbonate, sodium hydroxide or potassium hydroxide. 
     
     
         4 . The method of  claim 1 , wherein the non-wood feedstock is mechanically desilicated with a mechanical pulper. 
     
     
         5 . The method of  claim 1 , wherein the first temperature is in the range of 50° C. to 100° C. 
     
     
         6 . The method of  claim 1 , wherein the second temperature is in the range of 100° C. to 130° C. 
     
     
         7 . The method of  claim 1 , wherein the third temperature is in the range of 95° C. to 130° C. 
     
     
         8 . The method of  claim 1 , wherein the second temperature is higher than the first temperature. 
     
     
         9 . The method of  claim 1 , wherein the third temperature is lower than the second temperature. 
     
     
         10 . The method of  claim 1 , wherein the third temperature is higher than the first temperature. 
     
     
         11 . The method of any one of  claim 1 , wherein the impregnated non-wood feedstock is mechanically refined at medium to high consistency. 
     
     
         12 . The method of  claim 11 , wherein the impregnated non-wood feedstock is mechanically refined at a consistency in the range of 8% to 40%. 
     
     
         13 . The method of any one of  claim 1 , comprising deconstructing the non-wood feedstock and cutting the deconstructed non-wood feedstock to a nominal length before desilicating the cut non-wood feedstock. 
     
     
         14 . The method of  claim 13 , wherein the nominal length is in the range of 40 mm to 100 mm. 
     
     
         15 . The method of  claim 13 , comprising screening the cut non-wood feedstock to remove fines before desilicating the screened non-wood feedstock. 
     
     
         16 . The method of  claim 15 , wherein the cut non-wood feedstock is screened by a primary screen and a secondary screen, the primary screen having a first set of slots interspaced between a first set of rolls and the secondary screen having a second set of slots interspaced between a second set of rolls, a width of each slot in the first set of slots defining a first internal roll opening and a width of each slot in the second set of slots defining a second internal roll opening. 
     
     
         17 . The method of  claim 16 , wherein the primary screen and the secondary screen are pyramid screens. 
     
     
         18 . The method of  claim 16 , wherein the first internal roll opening is about  1  mm, and wherein the second internal roll opening is about 2 mm. 
     
     
         19 . The method of  claim 15 , comprising washing the screened non-wood feedstock before desilicating the washed non-wood feedstock. 
     
     
         20 . The method of  claim 1 , comprising removing water from the pulp stream. 
     
     
         21 . The method of  claim 20 , comprising removing the water from the pulp stream by drying the pulp stream with superheated steam. 
     
     
         22 . A method for producing pulp from non-wood feedstock, the method comprising:
 chemically treating a stream of the non-wood feedstock with a first alkaline solution at a first temperature, the first alkaline solution selectively separating silica from the non-wood feedstock;   chemically treating the stream of desilicated non-wood feedstock with a second alkaline solution at a second temperature to separate lignin from the desilicated non-wood feedstock, wherein the second temperature is higher than the first temperature; and   removing the separated silica and the separated lignin from the stream.   
     
     
         23 . A system for producing pulp from non-wood feedstock, the system comprising:
 an apparatus for desilicating the non-wood feedstock at a first temperature to selectively remove silica therefrom;   an impregnation tube for impregnating the desilicated non-wood feedstock at a second temperature to selectively separate lignin therefrom;   a mechanical refiner for receiving the impregnated non-wood feedstock, and refining the impregnated non-wood feedstock into a pulp stream;   a reaction tower for receiving the pulp stream and configured to receive oxygen and steam to perform oxygen-alkali treatment on the pulp stream to separate lignin therefrom; and   a post-processing apparatus connected to the reaction tower to remove the separated lignin from the pulp stream.   
     
     
         24 . (canceled) 
     
     
         25 . (canceled)