Without particulate material collection

The measurement of particles or particle collections is achieved by one of two approaches (1) in situ, or quasi-in situ, continuous observation or (2) collection on a medium and subsequent laboratory investigation of the accumulated particulate material. No single method provides a self-consistent, complete physical picture of a particle suspension. For example, the first approach basically assumes that the particles can be treated as inert spheres during the measurement process. The second assumes the accumulation of material on a medium or substrate without modification of the particles. This is known to be a less than satisfactory assumption for particles reacting with the suspensing gas, but no better techniques have been developed. 

Particulate material can also be sampled from natural waters by direct collection onto vertical or horizontal plates (glass, Teflon, or other plastics) inserted for a while in the water column. Horizontal plates collect sedimenting particles without the drawbacks of conventional sediment traps (shifts in biological activity and redox conditions due to the absence of mixing at the bottom of the trap) vertical plates selectively collect those entities exhibiting a certain affinity for the plate (e.g., adhering bacteria, polysaccharides, Fe-oxyhydroxides). 

Particulate emissions can amount to as much as 0.25 tonne/tonne of pulp produced, particularly for an older pulp mill operating without controls (Table 15.13). Electrostatic precipitators, wet scrubbers, or occasionally both can achieve particulate containment of 95% or better [49]. The precipitator catch is returned to the black liquor stream for chemical recovery from the captured inorganic chemicals. Fumes lost from the dissolving tank vent are captured by demister pads or small low-energy scrubbers, which return the collected material to the green liquor circuit. Wet scrubbers are used for lime kiln dust containment. The waste liquor is used for slaking or other recycle functions in the lime circuit (Chap. 7), helping to decrease make-up chemical requirements and water emissions. 

The use of ultrasound has also enabled the development of a new, efficient method of separating particulate matter from a flowing material without the need for a filter membrane [80], One such process consists of a device comprised of two transducers set at a horizontal distance apart across the liquid-containing particles. If one transducer is activated and sets up a standing wave, then any particulate contaminant in the fluid is seen to collect rapidly in regions corresponding to 1/2 wavelength distances on the axis of the ultrasonic beam. If both transducers are... 

Typically the surface area of the product is very low 2 m and further work is underway to improve the porosity of these species. In an alternative procedure a pre-formed polybenzimidazole prepared in the presence of stabilising polymer to provide aliphatic hydrocarbon graft chains can be dissolved in cone. H2SO4 and the acid solution dispersed, without additional stabiliser, in paraffin oil. Slow addition of methanol to the suspension causes precipitation of the polybenzimidazole within the droplets and eventually solid particulates are formed. These can be collected, washed and dried in the usual way. Materials prepared by this method have better porosity and a surface area of 30 m g ... 

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