| The pyrolysis and ignition of coal, as initial steps of coal combustion, havesignificant effects on the subsequent processes such as char combustion,crushing, fine particle formation and emission of pollutants. Many of thequantitative investigations were unable to be done in the past. However, withthe continuous developments of new experimental methods and techniques, theyare being introduced into the investigations, and become a major driving forceto promote the development of coal pyrolysis and ignition research. Until now,most researchers only considered the process of coal particle pyrolysis andignition under the flameless, unstrained conditions. In fact, the coal particlescross the flame sheet frequently due to particle inertia. The ignition process ofprecipitating volatile gas phase can also be impacted by the strain rate of theflame. As a result, the ignition characteristics change. So far few literatureswere reported on the transport and combustion of pulverized coal aroundstrained flames. The aim of this work is to explore the behavior of dispersedcoal particles in gaseous strained flames by using several novel methods andtechniques.In this thesis, a novel counterflow flame apparatus that can meet therequirement of heterogeneous combustion of pulverized coal particles wasdeveloped and erected. The combustion chamber was designed to be heated upto1600K and at pressures from0.06MPa to1.50MPa. A new powder feedingsystem was developed based on the fundamental of collision theory, achieving aperfect dispersion of coal particles in carrier flows. The coal particle can becarried to the flames at a flow rate around50mg/min. The stability of the coalparticle introducing system is good during one hour even when the flow rate ofthe carrying gases change. This technology solved the problems of introducingthe pulverized coal to a specified position in the flame. A set of device formeasuring the normal direction of the temperature profile of flames was alsoestablished by using the thin-filament pyrometry technology with an error lessthan±30K. A data acquisition and control system was developed to monitor all the parameters to improve the safety and efficiency of the apparatus. Theconterflow flame experimental system can be started quickly and theexperimental condition can also be switched to another state within10s. Thissystem can be widely used to investigate the gas-solid phase reactions incounterflow flames.The experimental method and performance of each sub-system was studied.The effects of the coal particle seeder on the measurments were discussed. Themethod of ICCD optical technology and calculation theory were analyzed indetails. The proposed methods are significantly important in experimentalinvestigation of pulverized coal combustion in counterflow flames.An experiment of ignition temperature of different synthesis gases wasused to verify the reliability and accuracy of the counterflow flame system.Then the experimental research of the pulverized coal ignition in counterflowflames was carried out. The effects of the particle size and flame temperature onthe ignition characteristics were investigated. With the advanced ICCD opticaltechnology, the behavior of coal particles across the counterflow flame wasobserved. The flame structure, the particle pyrolysis and the ignition processwere also measured. Based on the results, an experimental method andevaluation guide line for pulverized coal combustion pyrolysis and ignitioncharacteristics in counterflow flames was proposed. A transient ignition modelof single coal particle in one-dimensional reaction zone of counterflow flamewas developed to calculate the particle temperature, density and productionchanges during across the flame. The effects on the pyrolysis mechanism wereanalyzed.In conclusion, the behavior of the coal particle across the gaseous strainedflame was studied on a coal combustion counterflow flame system. Thisresearch provides a new approach for the coal combustion investigation. |
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