Approach for correcting particle size distribution measured by optical particle counter in high-pressure gas pipes

A set of online particle detection devices was developed for the quick and accurate assessment of particle size and concentration in high-pressure natural gas that can be applied at any pressure below 10 MPa. In actual site tests with P=3.42 and 2.36 MPa, the online tested results of particle size and concentration are generally smaller compared to those of the offline gathered under atmospheric conditions. That is mainly due to the detection performance degradation of an optical particle counter caused by gas pressure change leading to the refractive index change of the sounding medium with which the optical paths of the incident light and scattering light are altered. Aiming to solve this problem, an analysis of the dynamic change of optical measurement volume of the optical detection system with gas pressure was conducted based on the gas state parameters and geometric optics theory, and a dynamic model of both was established that can be accompanied by a particle size modification method based on light scattering theory. After a correction of tested results, the deviations in median diameter and concentration between the modified online and offline test results were within an acceptable range. Therefore, the proposed modification is a feasible and reliable approach to enhance online particle detection.