Process to optimize brown stock washing unit operations

A system for controlling dosing of an additive to a brown stock washing process, comprising:

• a refractive index measurement device;
• a conductivity measurement device;
• a controller configured to receive data provided by the refractive index measurement device and the conductivity measurement device, and transform the data into additive addition output instructions, wherein the controller is configured to determine a total black liquor carryover in the brown stock based on a refractive index of the brown stock and a conductivity of the brown stock;
• and
• an additive delivery unit configured to receive and execute the additive addition output instructions from the controller after receiving data from the refractive index measurement device and the conductivity measurement device.

A method of treating brown stock in a brown stock washing process, comprising:

• measuring a refractive index of a brown stock;
• measuring a conductivity of the brown stock;
• determining an inorganic fraction and an organic fraction based on the refractive index of the brown stock and the conductivity of the brown stock, wherein a total black liquor carryover comprises the organic fraction and the inorganic fraction;
• and
• dosing an additive to the brown stock after measuring the refractive index and the conductivity of the brown stock.