Experimental Study On Characteristics In Circulating Fluidized Bed With Local Oxygen-enriched Combustion

Abstract:The method of using local oxygen-enriched combustion technology in the Back-Feeder is proposed to solve the problems of large oxygen consumption and high operating costs in the last CFB oxygen-enriched combustion technology. Meanwhile, some relative experimental researches are performed. The purpose of the study is to promote the development of the oxygen-enriched combustion technology, improve the practical application value and the economic application of the technology in CFB. Anyway, the research is of significance in the theoretical research and applied sciences.Bituminous coal, anthracite and coal gangue are tested to study the influence of the oxygen content on the combustion of different coals. Using nitrogen as the diluting gas to adjust oxygen volume content in combustion supporting gas, oxygen contents are21%,25%,30%,35%and40%, respectively.To make a further investigation on the effects of the oxygen volume content in the combustion improver to the combustion characteristics, the TG data of these coals are measured by thermal analyzer with5different kinds of combustion improvers. The ignition temperature, maximum combustion efficiency, indices of combustion characteristics, combustion characteristics of a comprehensive, activation energy and pre-exponential factor are obtained, and these combustion characteristics are analyzed. The results indicate that the oxygen volume content in the combustion improver influences the combustion characteristics of these kinds of coals. As the oxygen volume content in the combustion improver increasing, the ignition temperature of these coals decreased, especially the bituminous coal. And the ignition temperature of coal gangue fell the least. Meanwhile, the maximum combustion efficiency, the peak temperature, burning characteristics index, combustion characteristics of a comprehensive, activation energy and pre-exponential factor of the coals all increase, especially the bituminous coal, and the parameters corresponding to the coal gangue increase the least.A CFB experimental furnace with the0.3t/h steam output was designed and built out, to evaluate the effect of the oxygen content in the combustion improver on the combustion in the practical back feeder. To obtain the parameters of the working condition, resistance of distributor, critical fluidization velocity, the airflow of the returning wind are determined according to the results of the cold-state experiments first. Then series of thermal-state experiments are carried out. As a prerequisite of the comparison, the quantificationally maintain a constant value and fluidization wind speed keep in3.5m/s. The furnace temperature, unburned carbon in fly ash, the emissions of CO and SO2are assayed, when the oxygen contents are21%,25%,30%and35%, respectively in the thermal tests. The results indicate that the furnace temperature increases using different coals as the oxygen content increases. As the oxygen content in the atmosphere rise up to35%, the temperature in dense-phase zone of bituminous coal, anthracite coal and gangue increases by52℃,60℃,69℃, respectively, and in dilute phase zone it is increase by119℃and55℃,67℃. Obviously, the unburned carbon in fly ash decreases as the oxygen content increases. As the oxygen content in the atmosphere rise up to35%, the flying carbon contents of bituminous coal, anthracite and coal gangue reduced by30.93%,32.55%and29.7%, respectively.With the increase of oxygen concentration, the SO2emissions of bituminous coal, anthracite coal and gangue increase by95mg/m3,44mg/m3,263mg/m3, respectively, and the NO emissions increase by72mg/m3, and76mg/m3, and76mg/m3,respectively. No obvious regularity of CO emissions.The results of the experiments indicate that using the local oxygen-enriched combustion technology can be of benefit to improve the furnace temperature, ameliorate the temperature distribution and reduce the flying ash carbon content. Conversely, the emissions of NO and SO2increase as the local oxygen-enriched combustion technology are applied. And it has no no obvious regularity on the CO emissions.