Electrostatic probes for indicating instantaneous flow rate of pulverized coal suspension in a pipe were devised and tested. Experiments were performed on flow systems consisting of 2 and 5-in-ID pipes with mass flow ratios up to 0.66 lb of coal/lb of air at up to 115 fps air velocity. Calibrations were made with a differential isokinetic sampling technique. With accurate control of probe potential, consistent indication of electrostatic ball probes (1/4 to 1/2-in. dia) was at the 10−7 amp level and at 10−8 amp level with cylindrical probes (0.2-in. ID). Accuracy within 1 percent was demonstrated to be feasible. Since the probe output is an electrical signal, this device makes integrated control system including the coal line feasible. Further, instantaneous and accurate fuel adjustment into furnaces facilitates air-pollution control.

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