Flow measurement of pneumatically conveyed solids using intrusive electrostatic sensors

Particulate solids are commonly conveyed in industry by means of pneumatic pipelines. The particle flows often need to be controlled and maintained within certain bounds, but the development of instrumentation to monitor them remains a challenging area. A variety of techniques have been researched to measure various flow parameters. An overview of the existing technology is presented, along with advantages and limitations of each method.

A detailed investigation is conducted into the use of electrostatic sensors with intrusive electrodes to measure the velocity of pneumatic particle flows. Previous work has been reported on the use of non-intrusive ring electrodes, but few studies of intrusive electrodes have been undertaken to date. Modelling, based on the finite element method, is used to determine the characteristics of the charge induced by solid particle flows onto intrusive electrodes. These are then compared with the properties of non-intrusive circular ring electrode elements.

The effects of electrode intrusion depth are studied, and it is shown that whilst stability of the velocity measurements improves with intrusion depth, some types of flow are best measured using a particular intrusion that results in the most accurate average velocity reading. Electrode spacing, which must be close enough to allow a measurement to be taken but far enough to avoid unwanted interactive effects, is investigated, along with the effect of electrode cross sectional shape on sensor signals and the effect of common mode noise on cross correlation velocity measurement. This information is used in the development of a practical sensor system that uses embedded signal processing, which is then tested on laboratory and industrial flow rigs.

The results are used to characterise the features of intrusive electrostatic sensors and their response to different flow conditions. Most significantly, intrusive electrodes are shown to be sensitive to localised flow regimes. Finally, suggestions on aspects of electrostatic sensors that would benefit from further development are discussed.