Numerical Simulation On Flow, Decomposition And Combustion In Precalciners Based On The One-dimension Furnace

As the leading technology of the cement production process, the precalciningtechnology emphasizes on enhancing the calcinations for the raw material, theburning of the fuel, and the heat transfer in the precalciner. Considering thecharacteristics of the precalciner, this paper firstly built the one-dimension furnace,which was verified as the proper equipment to obtain the decomposing kinetics ofcalcium carbonate via experiment research. On this basis, the Fluent software wasapplied to simulate the flow field and decomposition of calcium carbonate.Considering the simulation results, the kinetics of calcium carbonate was revised.Meanwhile, the rate exponent of each specie in the composition reaction was alsoacquired. On the basis of all the above research, a TSD type of precalciner wassimulated and results were according to the real station to a large extent. The mainconclusions were as follows.(1) A device named one-dimension furnace, was creatively designed and built todo research on the decomposition kinetics for calcium carbonate under hightemperature and suspension state. The one-dimension furnace was measured1,920mm by120mm, and the maximum temperature it could reach was1400℃. Besides,a tiny vibrator feeder and a digital mass flow controller were used to control thecalcium carbonate feed and the gas flow at a precise level.(2) The experiments to obtain the decomposition kinetics of calcium carbonatewere conducted in the one-dimension furnace. Results indicated that thedecomposition process under suspension state was in according with one step randomnucleation and growth mechanism, with apparent activation energy (Ea)67.24kJ/moland pre-exponential factor (A)65.51s-1. Its numerical simulation was also performedusing those data. However, the decomposition rates of simulation was far below theexperiment results. Considering the simulation results, the temperature and residencetime of the calcium carbonate particles were calculated again to revise the kineticsparameters. With the revised apparent activation energy (Ea)56.18kJ/mol andpre-exponential factor (A)61.87s-1, the simulation results were more closed toexperiment results.(3) Based on the simulation results from the one-dimension furnace, a series ofrate exponents for each species in the decomposition reaction were built according tothe characteristic of the power function. On this basis, the numerical simulation of theone-dimension furnace was used again to obtain the possible rate exponent for eachspecies, which demonstrated that the rate exponents for calcium carbonate, carbonoxide and calcium oxide were0.9,0.1and0respectively.(4) A precalciner used in a3200t/d line was simulated further. The results demonstrated that the flow field in the precalciner were complicated, which includedboth the spouting flow and rotation flow. The rotation flow was intensive in thepre-chamber, while the spouting flow in the main furnace was strong. Particles of bothcalcium carbonate and coal were filled well in the precalciner, and particle residencetime were4.6~10.5s and4.5~6.7s respectively. The combustion reaction was mainlycompleted in the prechamber, while the composition rate of the calcium carbonate onthe outlet of the prechamber were67.2%, and86.4%in the exit of the precalciner,which were close to the real stations.