Measurement of fluidised bed dryer by different frequency and different normalisation methods with electrical capacitance tomography

An electrical capacitance tomography (ECT) sensor has been mounted near the bottom of a fluidised bed dryer. An ECT system based on an HP4128 impedance analyser has been used to measure capacitance and loss conductance between the electrode pairs in the sensor. It has been found that the capacitance depends on not only the particle moisture but also the frequency. With low moisture content, the relationship between capacitance and frequency is simple and linear. With high moisture content, however, the relationship becomes more complex and non-linear. For image reconstruction, different normalisation models have been used: series, parallel and Maxwell. The results show that with low moisture content, the three models give nearly the same image error. With the increase in moisture content, the difference between the three models becomes more and more obvious. With different gas-solids flow patterns, the three models also give slightly different images.