Design and evaluation of electrostatic sensors for the measurement of velocity of pneumatically conveyed solids

Electrostatic sensing technology in combination with correlation signal processing offers a promising solution to the on-line continuous measurement of velocity of particulate solids in pneumatic pipelines. This paper describes the fundamental mechanism of the electrostatic sensing and identifies the important aspects of the design of constituent elements of the sensor including electrodes, amplifiers and sensing heads. Experimental evaluation of a prototype commercial product called V-TESS 500 was conducted on 36 min bore vertical and horizontal sections of a pneumatic conveyor circulating corn-flour and pulverised coal over a velocity range of 6 to 45 m/s for mass concentration of particles between 0.014 and 5.7 kg/m(3). The performance of the instrument was quantified in terms of repeatability, linearity and response time. The uncertainty of the system was studied by comparing the measured solids velocity to the superficial air velocity in the pipeline. Effects of particles' accretion on the inner surface of the pipe wall on the measurement are also included. Results obtained demonstrate that the system is capable of providing solids velocity measurements with repeatability better than +/-2% and response time less than 2.5 s. (C) 2000 Elsevier Science Ltd. All rights reserved.