Bleaching Process
Depending on the pulp density, the chemical pulp is transported via pumps, a flow distributor, or conveying spirals to the bleaching tower. The bleaching process then runs continuously at temperatures up to 203°F (95°C), with bleaching chemicals such as oxygen, ozone, or peroxide being added. The bleached pulp is discharged via feed screws. Similar processes are used for wood pulp bleaching and waste paper de-inking.
Level Measurement with the VEGAPULS 68 and VEGABAR 54
A constant level in the bleaching tower is important for the quality of the bleaching process. To ensure this, a continuous level measurement works in conjunction with a discharge control. The powerful radar sensor VEGAPULS 68 has special dynamics that ensure reliable measuring results even under the difficult conditions in the bleaching tower. The VEGABAR 54 pressure transmitter with ceramic CERTEC® measuring cell is integrated in a ball valve fitting to carry out the required measurement in the discharge area.
Overfill Protection with the VEGACAP 64
The VEGACAP 64 capacitive level switch is used as an additional protective measure to avoid overfilling the bleaching tower. The level switch prevents any spillage or blockage and the continuity of the process is ensured.
Chip Storage
Chips are the raw material for refined lignin and pulp. They are made from debarked logs or bought as waste from sawmills. They are transported via conveyor belts to large silos with a height of up to 82 ft (25 m) and, after screening, to a digester or a TMP plant (Thermo Mechanical Pulp). During storage, oxygen is consumed in the silo; the temperature then rises due to the exothermal reaction.
Level Measurement with the VEGAPULS 68
Chip silos must be filled and emptied in batches. During filling, a material cone is formed, large amounts of dust are generated, and material bridges collapse during emptying. The optimum solution for level measurement is the VEGAPULS 68 radar sensor for bulk solids. The VEGAPULS 68 is so powerful and has such a high dynamic range compared with conventional radar sensors, that measurement works reliably even during filling. Continuous recording, as well as reliable logistics planning are thus possible. Further application sites for the VEGAPULS 68 are the bark silos as well as the aeration tanks following the digester.
Indication and Adjustment with the VEGADIS 61
The VEGADIS 61 enables reliable and convenient indication and adjustment on site or remotely up to 82 ft (25 m) away.
