Experimental And Modeling Study Of NO Formation And Reduction For Precalciner

In China, with the rapid development of cement industry, the total amount of NOx produced from the cement industry has been the third largest resources, besides the power plant and automobile. The precalciner technology(new type processing cement with daily output), in which precalciner is an important equipment for the reduction of NO emission, is the main technology for cement production in China now. Most of attentions about the researches of NOx emission in precalciner systems were paid to the actual results of NO reduction, however, the study of the mechanisms about NO formation and reduction in precalciner has been rarely concerned on up to now. Therefore, it is necessary and significant to study the conversion of NO for the reduction of NO emission from cement production.Therefore, the Characteristics of NO formation and reduction in precalciner and the NO distribution in 3-D precalciner have been studied with the methods of simulated experiments, theoretical analysis and CFD simulation. The researches have been carrid out mainly on the several following respects:A suit of equipment simulated the suspension and spray condition of precalciner was established in this dissertation, in which the experiments of NO fornation on different CO2 concentrations and with the catalysis of cement raw were carried out. It was shown that different types of raw meal had significant effect on the formation of NO. However, the catalytic capacity between different kinds of raw meal was almost the same. For different ingredients of cement raw meal, the catalysis of limestone on the formation of NO was the strongest. With the increase of CO2 concentration, the rate of NO emission and the total amount of NO emission during coal and char combustion decreased. The conversion of fuel-N and char-N to NO increased with the rise of temperature, however, the effect of temperature and cement raw meal on the NO emission reduced with the increase of CO2 concentration.The mechanism of NO reduction by coal and char in precalciner was discussed, and the effects of cement raw meal and CO2 concentration on the reduction of NO by coal and char at different temperatures were discussed, the mechanism of NO reduction by CO with the catalysis of char and cement raw meal was also concerned. It was found that the rates of NO reduction by volatiles was much higher while the reaction time of NO-C was longer. The amount of NO reduction by coal and char incresed with the addition of raw meal, which indicated that cement raw meal had positive catalysis on the reduction of NO. The catalysis of cement raw meal on the reduction of NO by higher volatile coal was more stronger, and the catalysis of the cement raw meal became stronger with the increase of the reaction temperature. With the increase of CO2 concentration, the NO recuciton capacity of coal and char became stronger. Char and cement raw meal could promote the reaction of CO and NO, however, the effect of cement raw meal decreased with the increase of CO2 concentration.The dynamic processes of NO reduction by coals and char at different O2 concentrations were firstly investigated on the suspension condition of precalciner. The effects of cement raw meal, temperature and O2 concentration on NO formation and reduction by coal and char were discussed. It was shown that there were two stages in NO reduction process at the presence of O2. The first stage was the early homogeneous NO reduction by volatiles, while the second one was the heterogeneous oxidation of char-N. Cement raw meal, temperature and O2 concentration could affect the dynamic processes of NO conversion by coals and char. The mechanism that lots of NO from kiln rotary was reduced in precalciner was revealed by the analysis of NO conversion with the presence of O2 in precalciner.The kinetics of NO formation during char combustion with raw meal presence in the suspension reactor was investigated. The influences of reaction conditions (species, temperature and cement raw meal) on the kinetics of NO formation during char combustion were discussed in this paper. The models and parameters have been applicated to the computer aided test platform for NO simulation in precalciner. The effect of cement raw meal on the kinetics of NO formation during char combustion as well as the correlation between the formation and reduction of NO during char combustion was also discussed.The emission of NO in precalciner was analyzed by numerical simulation, and the relevant mathematical models were developed. The numerical simulation method was combined to develop the computer aided test platform for NO simulation in precalciner, which could provide an experimental platform for design and development of low-NO precalciner. NO transformation and distribution in a 3 D-precalciner with the production capacity of 5000t/d was analyzed in this dissertation. The results indicated that the NO concentration on the top of the inlet of the tertiary air was the highest, and the distribution of NO in precalciner could be affected by temperature significantly. The emission of NO could be reduced by staged combustion effectively because of the reduction of O2 concentration in main combustion zone. It could be found that the platform was reliable through the comparison between the simulation results and the actual measurements.