Measurement of particulate velocity under stack-flow conditions

Electrostatic sensing technology in combination with cross-correlation signal processing techniques offers a promising and cost effective solution to the on-line continuous velocity measurement of particles in a stack. This paper presents the principle, design and evaluation of a novel instrumentation system, called `StackFlow 2000', which has recently been developed for the velocity measurement of particles in a stack. Experiments with aloxite, building plaster and icing sugar as test materials were conducted on a 300 mm bore stack-flow test facility over a velocity range of 2.5 to 22 m s-1 for particle-mass concentrations of between 0.1 and 10 mg m-3 . The performance of the system was quantified in terms of repeatability, linearity, response time and the lower limit of mass concentration. The accuracy of the system was studied by comparing the measured particle velocity to the air velocity in the duct. Effects of sensor contamination on the measurement and the suitability of the system for a wider range of stack sizes are also included. Results obtained from the test facility have demonstrated that the system is capable of providing highly repeatable velocity readings with nonlinearity no greater than ±1%, and a response time of less than 1 s.