Density meter reduces costs and improves quality at paper mill
05 July 2011
Cartiere del Garda is using a Micro Motion density meter from Emerson Process Management to measure the concentration of kaolin and other additives in the coating process at its paper mill in Italy.
Cartiere del Garda operates one of the most modern paper mills in Italy, specialising in high quality coated papers. For many years, a Micro Motion Coriolis flowmeter was used to monitor the concentration of the paper coating mixture and this provided reliable and accurate results. However, because the recirculation system on the feeding tank generated entrained air, it was necessary to add expensive additives to the coating mixture to prevent quality problems.
Removing the additives would reduce production costs but would cause up to 20% air to be entrained in the coating mixture. The existing Coriolis flowmeter was not designed to provide the same degree of density measurement accuracy under these conditions, so an alternative solution was required. The company needed an on-line, solids concentration measurement of the coating solution, made directly at the film coater machine feed. A minimum accuracy of +/-1% of solids was required to guarantee the high quality of the paper being produced and avoid waste caused by out-of-specification batches.
Cartiere del Garda chose a Micro Motion 7845 density and concentration meter for this application. It specified the advanced electronics, entrained gas version, which is designed to accurately measure density in aerated liquids − providing a final accuracy of better than +/- 0.5 per cent with very high stability and repeatability. The 7845 provides a 4-20 mA signal to the control system, related to line density. Density is converted into percentage solids using a formula embedded into the control system.
The Micro Motion 7845 is a straight tube, liquid density meter that uses a vibrating tube to measure density. As the liquid density changes, it affects the vibrating mass of the density meter. The change in vibrating mass then affects the resonant frequency, which is inversely proportional to the density of the process fluid. By monitoring the resonant frequency and applying well-known conversions, the 7845 provides highly accurate in-line density data.
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