A novel capacitive system for the concentration measurement of pneumatically conveyed pulverized fuel at power stations

摘要

A novel capacitive system for the concentration measurement of gas-solid flow in pneumatically conveyed pulverized fuel at power stations has been developed. The capacitance sensor for measuring the concentration uses source-grid sensing electrodes. An active sensor and a dummy sensor are used to form a differential configuration, In order to eliminate baseline drift, to be immune to stray capacitance, and to ensure accurate measurement under very low solids/air mass flux ratio conditions, a correlated double sample (CDS) technique and lock-in detector with closed loop are used in the interface circuit. A laboratory scale pneumatically conveyed pulverized fuel loop system incorporating facilities for calibration has been fabricated for this purpose. The test section is a vertical ceramic tube of diameter 100 mm with an upward flow direction and pulverized fuel has been used as the solid phase. Results demonstrate that the system is capable of achieving linearity within ±5% at different temperatures or moisture content.