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Experimental Research on Influence of Coal Reburning Reaction Conditions on NO_x Reduction by Non-Ca

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Tutor: QiuPengHua
School: Harbin Institute of Technology
Course: Thermal Power Engineering
Keywords: nitrogen oxides (NO_x),NO_x reduction,reburning,selective non-catalytic reductio
CLC: X701
Type: Master's thesis
Year:  2008
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Abstract:
NOx formed from coal combustion is one of the main pollutants in the air. All kinds of NOx reduction technologies have been investigated widely in our country. Advanced reburning integrated reburning with selective non-catalytic reduction (SNCR) has some advantages of low cost and high efficiency, which may become one of the optional NOx control technologies adapted to the situation of coal-fired plants.First of all, the background and present state of subject study were discussed. Then, the control technologies of NOx were introduced. Simultaneously, the principle and mechanism on NOx reduction during reburning, SNCR and advanced reburning process was explained. According to the study of domestic and foreign scholars’research methods on NOx reduction by advanced reburning, an experimental system had been developed which could simulate pulverized coal advanced reburning process, including two-stage reactor, sampling and analysis system, gas supply system, pulverized coal feeding system, preheating system, cooling system, temperature control system and blowdown system. And each of subsystem design and working principle was introduced in detail. On the basis of the research content of this paper, the experiments studying the NOx reduction characteristics of reburning, SNCR and advanced reburning were carried out on a 16 kW down-fired combustor including two series reactors, in which the upper is a coal reburning reactor, and the lower is an SNCR reactor. The effect of reburning coal fraction on NOx reduction was studied by the reburning system and the advanced reburning system at a reburning coal fraction from 15% to 25%. And the effects of NH3/NO molar ratio on NOx reduction was investigated by the SNCR system at a NH3/NO molar ratio ranged from 1.5 to 4.5.According to the results, following conclusions were observed: in reburning system, when the reburning zone temperature, the reburning zone residence time and the reburning coal quantity are invariant, NO reduction efficiency decreased with the increase of reburning coal fraction; in SNCR system, when the SNCR reaction temperature and the SNCR reaction residence time are constant, NO reduction efficiency increased with increasing the NH3/NO molar ratio; in advanced reburning system, when the reburning zone temperature, the SNCR reaction temperature, the NH3/NO molar ratio, the reaction residence time and the reburning coal quantity are hold in line, NO reduction efficiency increased with the increase of reburning coal fraction; NO emissions can be reduced by more than 80% by advanced reburning, which enable the efficiency of NO reduction to the maximum comparing with reburning and SNCR in the same condition. From the results of the experiment on advanced reburning, the most important conclusion was observed that there is the interaction between reburning and SNCR in the advanced reburning system.
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