Cerlic optical sensors have been installed at the Billerud Karlsborg mill in Sweden, which produces white sack paper and white Kraft paper from the locally produced long fibre Kraft pulp.
Conventional equipment is used in the causticising operation for filtering and clarifying the green and white liquor. This process aims at producing good quality white liquor for the digester and also avoiding carry-over of dregs and lime mud that will upset the complete system.
Manual samples after the white liquor filter are analysed once a day. Normal lime mud content is 0-50 mg/l with an alarm level of 100 mg/l. Alarms are normally caused by holes in the filter felts that have to be quickly detected and repaired.
A Cerlic optical sensor has been used at the Karlsborg mill for many years for continuous monitoring of the white liquor preparation and measuring the suspended solids after the white liquor filter. The first sensor was installed in the mid-90s and exchanged in 2006 for the latest generation sensor, the CTX 20/25-K.
Installed on the pipe between the filter and the white liquor storage, the acid-proof sensor features Kalrez seals to cope with the aggressive liquor. The by-pass pipes to the sensor are insulated to maintain a high temperature (85-95°C), reducing deposits on the sensor windows. The sensor is removed once a month for manual cleaning with an acid solution.
Thanks to the continuous monitoring of the lime mud content by the Cerlic sensor after the white liquor filter, increased levels of solids due to damaged filter felts are quickly detected, allowing the problem to be fixed immediately while minimising the upset condition in the digester and chemical recovery system.
Cerlic optical sensors are available from Scandinavian Electronics Pty Ltd