A Solid Concentration Measurement Method with Online Calibration of Solid Permittivity

Capacitive solid concentration measurement has been widely applied in gas-solid two-phase flow. In the existing method, the solid concentration measured from capacitance is based on a constant solid permittivity. However, due to factors such as the raw material ratio and moisture content, solid permittivity may vary during the measurement process, and in some cases even significantly. A novel concentration measurement method using a combination of capacitive sensors is proposed, in which a calibration sensor operating at a certain solid concentration provides solid permittivity information online, and then the output of the calibration sensor is used to correct the solid concentration in measurement sensor. An online calibration algorithm is presented based on the relationship between the outputs of two capacitive sensors, in which the solid permittivity information is given directly by the output of calibration sensor without the calculation of the solid permittivity. Moreover, it can obtain the relationship between the solid concentration and the output of the measurement sensor for the arbitrary solid permittivity over the working range. Static and dynamic experiments in the laboratory were carried out to verify the effectiveness of the proposed method. The average relative measurement error of average solid concentration was reduced from 34.07% to 6.68% when the solid permittivity information ranged from 2.09 to 5.46 in the dynamic experiments. The proposed method has been applied in the industrial tests of pulverized coal injection system of blast furnace, and the measured one-hour accumulated mass of pulverized coal can better agree with the true value.