That initial process,is called the digester,as it takes the raw pulp,and reduces it to a liquid![The same type process is used for regular paper production] The draining of water,and strangely the heating process,is also followed in Lithograph printing,and in newspaper production! Parallel operations,and each sort of plays follow the leader! Anyway,an interesting manufacturering technique! For reference,see the book,"The Way Things Work",which goes into sundry manufacturers of all kinds of materials,which are taken for granted! Thank you