Exothermic heat as a means of determining the degree of delignification

Claim 1

A continuous process for digesting cellulosic fibrous material in an elongated vertical continuous digester to provide pulp having a desired predetermined degree of delignification, comprising the steps of: continuously charging cellulosic fibrous material into the top of the digester at a substantially constant rate; impregnating the cellulosic fibrous material with digesting liquor; while maintaining substantially steady-state conditions, treating the material with heated digesting liquor while passing the material through a digesting stage of the digester so that the material undergoes a delignification reaction and so that the material is delignified; discharging the delignified material from the bottom of the digester at a substantially constant rate; continuously determining the exothermic heat of the delignification reaction in the digesting stage, and thereby determining the degree of delignification occuring in the digesting stage, by (i) determining the temperature rise occurring during the delignification reaction in the digesting stage, which step is accomplished by measuring the temperature of fibrous material and liquid generally adjacent the top of the digesting stage, and measuring the temperature of fibrous material and liquid generally adjacent the bottom of the digesting stage, and (ii) by determining the heat capacity of the cellulosic material and digesting liquor in the digesting stage; comparing the degree of delignification occurring in the digesting stage with the desired predetermined degree of delignification; and adjusting the amount of cellulosic fiber material continuously charged into the top of the digester to maintain the desired predetermined degree of delignification.