Concurrent Measurement of the Size Distribution and Velocity of Pneumatically Conveyed Biomass Solids Using Acoustic Emission and Electrostatic Sensors

In biomass-fired power plants, accurate measurement of the size distribution and velocity of biomass solids in pneumatic conveying pipelines feeding the burners is essential to maintain high combustion efficiency and reduce pollutant emissions. In this article, a new method for the size distribution and velocity concurrent measurement of biomass solids through acoustic emission (AE) detection and electrostatic sensing is proposed. When an AE waveguide protrudes into a biomass fuel pipe, an AE signal is generated due to the impact of biomass on the waveguide. In consideration of the inelastic and irregular characteristics of biomass fuels, the Stronge model is introduced to describe the inelastic impact process. The relationship between the statistical value of equivalent impact size and the shape characteristics of irregularly shaped solids is analyzed. Meanwhile, the velocity of biomass fuel is determined by processing the signals from arc-shaped electrostatic sensor arrays. The fusion of the peak amplitude of the AE signal and biomass velocity allows the measurement of biomass size distribution. Experimental tests with crushed wheat straw, sawdust, and corncob were conducted on a laboratory-scale pneumatic conveying test rig to assess the effectiveness of the size distribution measurement technique. The experimental results demonstrate that the measured biomass velocity varies with the air velocity and the transport capacity of the conveying air to biomass solids depends on factors such as shape and size distributions of biomass fuels. The relative error of the measured mean biomass size is within ±6.45% under all test conditions with a standard deviation within 2.15%.

I. Introduction

Biomass is an energy source with zero carbon emissions throughout its life cycle and its resource supply is stable, which makes biomass-fired power generation a low-carbon, efficient, and highly flexible way of producing electricity. In recent years, the installed capacity of biomass power plants has been increasing continuously [1], [2]. In biomass power plants, biomass materials such as sawdust, straw, and corncob are crushed and pneumatically conveyed to the boiler for combustion. The flow characteristic parameters of biomass solids, such as velocity and size distribution, have an important impact on the safety, efficiency, and emissions of the combustion process [3], [4].