(259b) A New System to Control Electrostatic Charge on Particles in Gas-Solids Pipe Flow

In industry, powders and other particulate solids are widely used as raw materials, intermediates, or final products. When handled in air, the surfaces become electrically charged and various phenomena occur. For example, the charged particles experience electrostatic forces, and thus tend to adhere to the walls or cohere to each other. If the particles are excessively charged, an electric discharge will occur, which can give rise to fire and explosion hazards. Various useful applications of particle charging have, however, emerged in recent years, e.g., electro-photography, powder coating, electrostatic separation, atomization, particle generation, manipulation, and measurement. To improve the performance of the applications, the measurement and control of the charge on particles are required. It is well known that particles are charged by contact with another material; however, there are still many unknowns and problems to solve. The mechanism for particle charging needs to be clarified. Contact charging depends on the surface materials. Hence, the chemical and electrical properties are important. In the present paper, particle charging in gas-solids pipe flow has been studied to control the electrostatic charge on particles. Micrometer-sized alumina particles were dispersed in airflow and pneumatically transported in dilute phase. Several different materials were used for the transport pipes, and the charge on particles was measured with an E-SPART analyzer. The experimental results were compared with the results calculated by the theoretical model presented by the authors, and it was confirmed that they were in good agreement with each other. On the basis of the above experimental and theoretical studies, a new system combined two different pipe materials is proposed to control the charge on particles. By changing the length of the pipes arrayed alternately in a line, the polarity and the amount of the particle charge can be controlled. In addition, the distribution of the particle charge can also be controlled by this method.