| Ceramic output of our country ranks first in the world. However, compared withwestern developed countries, there exist higher energy consumption, lower energyefficiency and more pollution problems that hinder the sustainable development ofour ceramic industry. For this situation, it is urgent to achieve energy saving andemission reduction in the process of ceramic production. Oxy-fuel is considered as arelatively easy to implement energy-saving technology, which could speed up theburning, promote complete combustion of fuel, increase flame temperature, reducegas emission and save energy. Currently, oxy-fuel technology has been successfullyused in many fields such as glass, metallurgy. But it is not yet mature for the use ofceramic production, needed for further exploration and research.In the paper, two roller kilns of ceramics for daily use were researched.Three-dimensional geometric model of the combustion space was established andhexahedral mesh was generated. Then numerical simulation was preceded using CFDsoftware Fluent. The Realizable k-ε turbulence model, eddy dissipation model, DOradiation model, gray gas weighted average model (WSGGM) and NOxpollutantmodel were selected to calculate. The characteristics of oxygen enriched combustionwas researched and analyzed according to Fluent simulation results, which couldprovide the basis for the structural optimization of furnace and the promotion ofoxy-fuel technology. The results showed as follow:Oxygen-enriched combustion could improve the combustion temperature of naturalgas in roller kiln, but the flame was shorter and shrinking to the burner, causing thecoverage of flame smaller. Therefore diameter of the burner should be adjustedaccording to the oxygen concentration to improve the flow distribution to formeffective airflow circulation in roller kiln.The concentration of triatomic molecule such as CO2and H2O in flue gas increasedwith oxygen concentration raising, which not only improved the thermal radiation andheat efficiency in the furnace but also reduced the heat flux which was taken bynon-radiatived nitrogen. At the same time, the emission of NOxwas also increasedwith the added oxygen. In addition, thermal NOxwas the main type. The flame rigidity of natural gas combustion was improved after the optimizationof burner caliber on the basis of oxygen concentration. According to the furtheranalysis on the temperature field distribution, it was found that average temperatureof the firing zone was rising, and then failing, with the temperature uniformity ofcross section gradually getting worse. It may be due to a sharp drop of amount of gas,which made the stirred airflow weaker. Finally, given the comprehensive account,27%was the best oxygen concentration for2#roller kiln, correspondingly45mm wasthe best caliber.Under the optimal oxygen concentration of27%, the height between baffle andretaining wall which was located between preheating zone and firing zone wasadjusted. The simulation results show that after reducing the height by100mm, theairflow disturbance was enhanced, and that its intercepting had become more obvious,which could well prevent the high temperature flue of the firing zone unrestrictedmove to the preheating zone casing unnecessary heat loss.Finally, the effect of energy-saving and NOxemission were analyzed. The resultsshowed the reduction of fuel by10%,20%and30%could make the averagetemperature of the burning zone fall down. In order to meet the required firingtemperature, energy could be saved by20%at most when oxygen concentration wasadopted by27%in2#roller kiln. Based on this, it was found that the concentration ofNOxremained bigger than before. But it could still meet the pollutant NOxemissionrequirements of ceramic production. |
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