Abstract

This investigation provides a comprehensive analysis of entrained-flow biomass combustion processes. Experimental and theoretical investigations indicate how particle shape and size influence biomass combustion rates. Experimental samples include flake-like, cylinder-like, and equant (nearly spherical) shapes with similar particle masses and volumes but different surface areas. Samples of small (less than 500 µm) particles were passed through a laboratory entrained-flow reactor in a nitrogen/air atmosphere and a maximum reactor wall temperature of 1600 K, while large samples were reacted in suspension in a single particle furnace operated at similar conditions as the entrained-flow reactor. A separately developed computer and image analysis system was used to determine particle surface-area-to-volume ratios based on three orthogonal particle silhouettes. Experimental data indicate that equant (spherical) particles react more slowly than the other shapes, with the conversion time ratio required for complete combustion becoming greater as particle mass increases and reaching a factor of two or more for particles larger than 1 mm in diameter (which includes most particles in commercial application). A color-band, non-contact pyrometer developed in this project measured particle surface temperatures and flame temperatures during pyrolysis and char burning processes. This technique employs widely available and relative inexpensive cameras and detectors. The camera-measured temperature data agree with black body calibration data within the accuracy of the data (± 20°C) and with thermocouple-measured data and model predictions within the repeatability of the data (± 50 °C) in most cases. A one-dimensional, transient particle combustion model simulates the drying, pyrolysis, and char oxidation and gasification processes of particles with different shapes. The model also predicts the shrinking/swelling and surrounding flame combustion behaviors of a single particle. Model simulations of the three shapes agree nearly within experimental uncertainty with the data. For biomass particle devolatilization processes, model predictions extended to a wider range of sizes predict the effects of shape and size on yields and overall mass conversion rates. The near-spherical particle loses mass most slowly and its conversion time significantly differs from those of flake-like particles and cylinder-like particles as particle equivalent diameter increases. Little difference exists between cylinder- and plate-like particles.

Degree

PhD

College and Department

Ira A. Fulton College of Engineering and Technology; Chemical Engineering

Rights

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