Jan 8, 2016
The Anjalankoski Mill area is home to two of Stora Enso's production units, the Anjala Paper Mill, as well as the Inkeroinen Board Mill. Cooperative efforts between the mills cover raw materials, energy and power generation, as well as waste water treatment and resultant sludge drying and firing. The Anjala paper mill together with the wastewater treatment plant has a long history of equipment supplied by Valmet *) measuring sludge prior to drying and solids content of reject water. Earlier, the only possible reliable measurements were tedious laboratory tests unsuitable for real-time process control.
|The Anjalankoski mill area, Finland
|The specific need of the Anjalankoski mills was to get real-time information on flows from clarifiers and to sludge dewatering, as well reject water solids content from the belt press filter.
Valmet TS (Total Solids) *) transmitters measure the time of flight of a microwave signal through the sludge. Time of flight is dependent on the permittivity of the slurry which for organic substances is practically constant, whereas the permittivity of water is considerably different. The measured change in permittivity allows an accurate calculation of the total solids content in the slurry. The measured slurry consistency varies normally from 2 to 3 per cent.
The Valmet LS (Low Solids) *) - measuring system is designed to measure very low, 0 - 5000 mg/liter, solids content. The device utilizes two light sources in a sample measurement cell where absorption, scattering and depolarization signals are measured. The system also deaerates and filters the sample as well as self-cleaning the measurement optics at regular intervals.
The results have been compared to laboratory tests and match them perfectly. The transmitters are reliable and do not require much maintenance.
The LS-system helps avoid excessive solids content in the belt press reject water which would normally circulate unnecessarily over and over again through the plant. The online measurement allows accurate monitoring and the current target is to keep the solids content to less than 350 mg/liter, whereas earlier it was much higher.