HHT analysis of electrostatic fluctuation signals in dense-phase pneumatic conveying of pulverized coal at high pressure

Particle charging generated by particle-wall, particle–particle and particle–gas contacts in pneumatic transport pipelines contain rich information on gas–solid flow hydrodynamics. In this paper, experiments were performed in a dense phase pneumatic conveying system, and electrostatic fluctuation signals were detected by a ring-shape electrostatic sensor that is based on electrostatic induction theory. Power spectrum analysis and Hilbert–Huang transform (HHT) were applied to the electrostatic fluctuations, namely outputs of the electrostatic sensor, to extract and characterize the intrinsic features of dense-phase gas–solid flow. Results show that the dominant peak of the power spectrum of the electrostatic fluctuations moves toward higher frequency with the increasing gas superficial velocity. The Hilbert–Huang transform reveals the non-linear and non-stationary intrinsic nature of the electrostatic fluctuations. By using the non-linear and non-stationary signal processing method (HHT), non-linear inter-modulation characteristics in the dense phase gas–solid flow were analyzed, and the relations between the energy distribution transmissions in intrinsic mode functions (IMFs) with different orders and the flow characterization of the dense phase gas–solid flow, was investigated as well, which can represent the behavior, stability and regime transitions of the gas–solid flow in the dense-phase pneumatic conveying system at high pressure.