Development of Electrostatic and Piezoelectric Sensor Arrays for Determining the Velocity and Concentration Profiles and Size Distribution of Pneumatically Conveyed Bulk Solids

One way countries around the world are increasing the proportion of renewable fuels for electricity generation is to convert coal fired power stations to co-fired (biomass/coal fired) or converting coal fired power stations to burn only biomass fuels. This however has led to measurement challenges monitoring the complex multi-phase flow of the pulverised fuels entering the furnace due to the complex shape of biomass particles.

To meet these measurement challenges a novel electrostatic sensor array and piezoelectric sensor array have been developed. The electrostatic sensor array consists of an array of electrostatic electrode pairs that span the diameter of the pipe. Consequently the electrostatic sensor array is capable of determining the particle velocity and concentration profiles as well as detecting specific flow regimes such as roping. The piezoelectric impact sensor array consists of an array of piezoelectric individual impact sensors that span the diameter of the pipe. The piezoelectric sensor array is capable of determining the particle concentration and size distribution profiles.

Experimentation has been carried out on laboratory scale pneumatic conveying systems using a variety of materials such as coal, biomass, coal/biomass blends and plastic shot. Experiments using the electrostatic sensor array have shown that it is indeed capable of determining the particle velocity and concentration profiles in both dilute developed and undeveloped flows. Analysis of the standard deviation of the velocity profiles as well as the correlation coefficient profiles have indicated that parts of the pipe cross section have a more stable flow compared to others. Data obtained through on-line and off-line experimentation using the piezoelectric sensor array has shown that through selective frequency filtering of the impact signal particle size can be determined assuming the particle velocity and the mechanical properties of the conveyed pulverised materials are known. By using a threshold voltage to determine when an impact has occurred on each element of the piezoelectric sensor array the particle concentration profile has been determined. The concentration profiles measured by the piezoelectric sensor array were verified using the electrostatic sensor array.