A preliminary measurement of fibres and fines in pulp suspensions by the scattering photoacoustic technique

Abstract

The consistency of fibres and concentration of fines need to be controlled during the production process in the paper industry. In paper pulp, fibre lengths range from less than a millimetre to several millimetres whereas fines particles have sizes of a few tens of micrometres. Therefore, the two fractions have different properties of optical scattering and acoustic attenuation, i.e., fibres produce more forward optical scattering and acoustic attenuation, while fines produce larger and more homogeneous scattering but less acoustic attenuation. Based on these facts, we specifically develop a new method, a scattering photoacoustic technique, to measure the consistency of fibres and concentration of fines simultaneously. It employs near-infrared light (1064 nm wavelength) to produce three acoustic waves with MHz frequencies. One piezoelectric transducer detects these waves, which are used to measure optical scattering and acoustic attenuation of pulp samples. The results indicate that our current apparatus successfully discerned the pure fibre and fines samples. It also proved capable of extracting the consistencies of fines and fibres in the studied samples that consisted of mixtures of fibre and fines. Finally, the scattering photoacoustic technique has a potential ability in online measurement of fibre and fines consistencies in pulp suspensions.

Backward-mode photoacoustic transducer for sensing optical scattering and ultrasonic attenuation: determining fraction consistencies in pulp suspensions

“…However, figure 3(c) indicates that, in the case of mixtures of TMP cellulose and fines, V r /V does not change with fines consistency. These results mean that long celluloses in pulp suspensions apparently generate acoustic attenuation, but fines do not, which is in agreement with our previous study [10,11].…”

“…In length, the celluloses ranged from sub-millimetres to several millimetres and their diameters were on the order of 10 μm. With sizes between 30 μm to 70 μm, the fines were made by filtering TMP pulp [10]. As diluting liquid, distilled water was used for the intralipid samples and tap water for all other samples.…”

“…Apparently, no single measurand, such as an optical, acoustic or a microwave signal, is capable of distinguishing and determining fractional consistencies in paper pulp; consequently, a practicable method of measuring fractional consistencies in a two-fractional suspension requires at least two independent signals. In our previous study, we developed a scattering PA (SPA) technique to simultaneously measure optical scattering and acoustic attenuation in paper [9,10]. The results showed that long celluloses are the predominant source of attenuation of ultrasonic waves, while fines particles are the predominant source of optical scattering.…”