Mass flow measurement of bulk solids in pneumatic pipelines

Abstract

Many types of techniques for metering the mass flow rate of bulk solids in a pneumatic pipeline have been proposed and developed during the past 20 years. This paper presents a detailed and comprehensive review of the techniques and the current state of knowledge and experience. The techniques are classified under three main categories: direct measurement of solids mass flow rates, measurement of volumetric concentrations of solids and measurement of solids velocity. Future developments and possible trends in this field are also included.

Development of a Particulate Solids Thermal Mass Flowmeter

“…Two approaches are used; the first involves a measurement of temperature difference at sensors located before and after a heated region with a constant heat supplied to the system, while in the second method, a constant temperature difference is maintained within the heated region and the heat required to maintain this difference is measured (Zheng and Liu, 2011;Yan, 1996). The mass flow rate is deduced from the relationship between the rate of heat transferred, the measured temperatures, the heat transfer coefficient and the material's thermal conductivity.…”

“…The mass flow rate is deduced from the relationship between the rate of heat transferred, the measured temperatures, the heat transfer coefficient and the material's thermal conductivity. In his review of mass flow rate measurement methods, Yan (1996) stated that the problems with this method have been found to be poor repeatability of the instrument and a slow dynamic response time. Experiments conducted by Moriyama (1996) using three different measurement methods-cross-correlation, heat transfer and acoustic emission-showed the heat transfer method to have the highest time constant of the three methods.…”

“…The results showed a substantial increase in the gas-side heat transfer coefficient for the 30-micron particles, and no visible increase in the heat transfer coefficient for the 200-micron particles; showing that the heat transfer coefficient increased with decreasing particle size. This effect was explained as being due to the fact that increasing solids' sizes prolonged the thermal entry (Yan, 1996). length, with larger particle sizes having a longer thermal entry length approaching the tube length, therefore the thermal boundary layer was not fully developed within the tube length.…”

“…For a mass flow meter to be described as ideal it should have the following properties: it should be non-invasive so as not to disrupt the flow profile; it should be easily † Accepted: June 26, 2013 1 installed on the conveying line to provide on-line and continuous measurements; it should be able to provide a reliable and accurate indication of the mass flow rate regardless of the orientation of the measurement section, inhomogeneities in the solids' distribution, irregularities in the velocity profile, or variations in the particle size, moisture content and material properties (Yan, 1996;Arakaki et al, 2006). Finding all of these properties in one single instrument has not been achieved yet, but research is still ongoing.…”

“…A direct mass flow meter is one whose sensing element responds to the mass flow rate of solids passing through it, while an inferential mass flow meter obtains the mass flow rate from a calculation of velocity and concentration of solids measured by its sensor (Yan, 1996;Beck et al, 1987). A variety of methods exist for the measurement of solids' concentration and velocity using the inferential method (Carter et al, 2005;Arko et al, 1999;Hrach et al, 2008;Huang et al, 2001), as this has proved to be more easily achievable than obtaining a direct measurement of the mass flow rate.…”