| As the economic development level gradually increasing, the energyconsumption of our country is growing too. Apart from the thermal power industryand automobile exhaust, the cement industry is the third major source of nitrogenoxide emissions, which will pollute the air seriously and harm human health badly. Asa result, reducing nitrogen oxide emissions of the cement industry has becomeessential. The implementation of the new national cement industry NO_x emissionstandards and the exploitation of the new cement low NO_x calcined technology andequipment have become necessity. The calciner of cement kiln using the new dryprocess is the crucial equipment of the low NOXcalcined technology. In this paper,the selective non-catalytic reduction (SNCR) of nitrogen oxides removal in thecalciner has been done theory research, which has practical significance to reduce theNO_x emissions of the cement industry.The NO_x emissions and generation principle of the cement industry are analyzedintroduced in this paper. The application of SNCR technique in the calciner is alsointroduced and analyzed. Using the numerical simulation method of ComputationalFluid Dynamics (CFD) and basing on FLUENT software, the mathematical model ofthe5500t/d TTF calciner is established and then the appropriate numerical method isselected. We use Pro/E to establish the physical model of the calciner and use thepre-processing software Gambit of FLUENT to divide mesh of the physical model.Combined the pulverized coal combustion with the NO_x generation model in thecalciner, the pulverized coal combustion and the NO_x generation in the calciner arestudied by using the numerical simulation method using the nitrogen oxides model ofpollutants model combined with SNCR model to calculate the amount of nitrogenoxides generation and the denitration efficiency.The simulation results show that：After getting into the decomposition furnacefrom injection port, the pulverized coal dispersed the entire furnace and began theflameless combustion under the carrying capacity of the tertiary air. The maximumcombustion temperature appeared near the entrance of the tertiary air and the upperspace of the inlet of the pulverized coal. And the local high temperature didn’t appear.Due to the action of the combustion, nitrogen oxides generated in the calciner aremainly fuel NO_x which is mainly concentrated in the upper area of the calciner and show the characteristic of higher concentrations in the middle while less ones near thewall.Based on the combustion simulation in the calciner and the generation of NO_x,the numerical simulation about the removal process of NO_x using SNCR is carriedout. The ammonia injection rate and the installation height of the ammonia nozzle arethe optimized target by using SNCR. The rate of ammonia injection and the height ofammonia injection at different injection rates are carried out the further optimization.The following conclusions are drawn: the concentration of NO_x decreasessignificantly; the concentration of NO shows the characteristic of higherconcentrations in the middle while less ones near the sides; the rate of denitration canreach to87.9%in basic conditions. As to the ammonia injection rate neither the lowernor higher rate is conducive to the whole reaction process: The lower rate will lead tothe ammonia has not enough energy to mix with the flue gas thoroughly while thehigher rate will lead to the contact time of the reducing agent with the flue gas isshortened. As to the installation height of the reducing agent nozzle, with the heightbecoming bigger the concentration of NO and the leakage amount at the outlet willalso become bigger, which will reduce the rate of denitration. The conclusion drawnthrough the calculation is that the best installation height of the nozzle is h=36m.andthe best ammonia injection rate is60m/s, the best ammonia angulation is60°. |
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