Development of a Drop Tube Furnace for Visualization of Combustion of Fuel Particles

Abstract

This thesis describes the development of a laboratory-scale burn simulator designed to maximize visualization capability in a combustion furnace with a high degree of control of temperature and particle presence. A specific research goal is to provide an understanding of combustion phenomena under conditions that simulate energy generation processing in cement production, such that alternative fuels can be evaluated as possible replacements for coal and other fossil fuels. The solid fuels used for this study were coal, wood chips and switch grass. The fuel particles used in the experiments were approximately 100 microns in size. Microscope and scanning electron microscope (SEM) devices were used to obtain images of the fuel particles to display their sizes and shapes. The thesis presents a description of a drop tube furnace and experiments that were conducted in it to observe and evaluate combustion characteristics and phenomena related to a high-temperature conversion of solid fuels. The design and operating conditions of the furnace were selected to evaluate the effectiveness of alternative fuels wood and switch grass in comparison to coal for application in cement production. A facility was designed and constructed for visualization of solid particles in a drop tube at laboratory room temperature and high temperatures (900 oC). Three visualization systems with different functions were applied to obtain images of particles in the furnace. The magnifications of different imaging systems were determined. The magnification for the images of combustion of particles in the furnace drop tube was 2.31 μm/pixel while the magnification of microscope images was 0.30 μm/pixel. The resolution of the combustion images in the vertical direction was 0.031 mm/cycle and 0.050 mm/cycle in the horizontal direction. A fuel particle injection system is described and shown to be effective at providing a controlled delivery of solid particles to the furnace drop tube. Particles were introduced via a vibrating syringe and flat-tip needle into a water-cooled injection nozzle to drop particles into the heated retort in the furnace. Dropping conditions were different for coal, wood and switch grass particles, and experiments determined that No. 21 gauge needles were best for coal particles while No. 20 gauge needles were best for wood particles and switch grass particles. Clear and highly resolved images of coal, wood, and switch grass particle undergoing combustion at 900 oC in air were obtained. SEM and microscope images were obtained of the fuel particles before and after combustion. Images of the burning particles revealed clarity and intensity contrast sufficient to estimate particle and flame size and shape. Particles were infrequently in the camera field of view at the highest magnifications because they meandered as they fell. Nevertheless, the capability of the furnace and imaging system was demonstrated, validating the potential of the system to provide color images for surface temperature measurement of solid particles undergoing combustion.