PNNL

Abstract

A novel sensor concept has been developed for measuring the consistency, the degree of refining, the water retention value (WRV), and the consistency of wood pulp during the refining process. The measurement time is less than 5 minutes and the sensor can operate in a slip-stream of the process line or as an at-line instrument. The consistency is obtained from a calibration, in which the attenuation of ultrasound through the pulp suspension is measured as a function of the solids weight percentage. The degree of refining and the WRV are determined from settling measurements. The settling of a pulp suspension (consistency less than 0.5 Wt%) is observed, after the mixer that keeps the pulp uniformly distributed is turned off. The attenuation of ultrasound as a function of time is recorded and these data show a peak, after a certain delay, defined as the “peak time.” The degree of refining increases with the peak time, as demonstrated by measuring pulp samples with different degrees of refining. The WRV can be determined using the relative peak time, defined as the ratio T2/T1, where T1 is an initial value of the peak time and T2 is the value after additional refining. This method offers an additional WRV test for the industry, because the freeness test is not specific for the WRV.