Chlorination Process Control.

Pulp is treated in several stages during the bleaching process using a number of bleaching chemicals. The first stage is chlorination in which chlorine gas is mixed with a diluted pulp suspension in order to remove the lignin. The chlorination process is continuously monitored using a primary element which measures the available chlorine, and a control valve regulates the flow of chlorine on the basis of the measured value and a set value. The dynamics of the chlorination process and the measurement of the available chlorine are dealt with in the article, and an analysis of the control loop is performed in the normal manner with the aid of an open loop Bode diagram.