scope:

One of the objectives of the Process Engineering Committee is to provide information and instructions for the various pulp and paper making systems and equipment to assist management and the pulp and paper mill engineer in specification, evaluation and design of pulp and paper mill facilities. Particularly, such information will show the interrelationships within and between systems.

This TIP shows the material interrelationships within the recausticizing system as well as between it and the digester system. Specifically, it lists all the major material balance equations for the recausticizing system, starting with the smelt stream from the recovery furnace and continuing through the white liquor stream to the digester. All equations relate to only a few independent variables from the digester and recausticizing operations.

For each major press stream - recovery smelt, green liquor, raw white liquor, white liquor (clarified), lime mud and weak wash - equations are given for each of the following:

Overall material flow rates

Chemical component breakdown in Na₂O equivalents

Chemical component breakdown in actual chemical form

Overall water flow rate

Water content on each stream

In addition, for the raw white liquor and lime mud streams, the following equations are given:

Available lime and total lime flow rates

Total and net "grits" flow rate

Water consumed in slaking reaction

Total lime mud solids flow rate

The significance of this TIP is not that the equations are particularly new and different, but that they are presented in one concise set; and that they are in simple form and can be conveniently used by anyone be they engineer, designer, mill operator or whoever. Further, it is significant that the equations are based on only six digester variables and three recausticizing variables. Also, they are written such they can be conveniently used as a base for further mathematical manipulations.

Certain basic definitions, assumptions and derivatives are presented in the appendix. For the most part, derivatives for all equations are not given in order to keep the TIP as simple and direct as possible. The derivations are basically simple and the interested party can readily do their own.