Measurement of Particle Concentration by Multifrequency Ultrasound Attenuation in Liquid-Solid Dispersion.

Abstract

In mineral transportations, it is essential to measure the gas hydrate particle concentration to manage the risk of flowline blockage. Traditional single-frequency ultrasonic methods measure the particle concentration by treating the mixtures with an average particle size, which ignores the influence of the particle size distribution, and thus, measurement accuracy is limited. Therefore, this research studies the multifrequency ultrasound attenuation method to measure the particle concentration through the prior estimate of particle size distribution. First, considering the large particle size and low-density contrast characteristics of the hydrate-water dispersion, the influence of multiple scattering among particles cannot be ignored apart from the scattering attenuation caused by each particle, so the ultrasonic scattering attenuation mechanism considering multiple scattering effects is established to solve the attenuation prediction problem of the hydrate-water dispersion. Since the solution of the equation obtained by the ultrasonic attenuation model produces a Fredholm integral equation of the first kind, an inversion algorithm combining simulated annealing with genetic algorithm based on ultrasonic attenuation mechanism is proposed to solve the ill-posed problem in the inversion calculation of particle concentration. Finally, considering the characteristics of hydrate-water dispersion, the experiments were carried out with millimeter-sized acrylic spheres and saltwater as substitute materials of the hydrate-water dispersion. The results show that the method based on the multifrequency attenuation of ultrasound in the range 1-5 MHz has a good discrimination for the particle size, and the measurement error of particle concentration is less than 3% under different particle size distributions.