Numerical Simulation Study On Coal Combustion In Decomposition Kiln In O₂/CO₂ Atmosphere

The cement industry is one of the main sources of CO2 and NOx and it has become the second largest emission source of CO2 and NOx after power industry,and it is of great significance to realize the reduction of CO2 and NOx emission in the cement industry.Based on a company's coal-fired decomposition kiln(rotary kiln and precalciner),the numerical simulation method is adopted in the paper to conduct further research on realizing CO2 and NOx emission reduction by using O2/CO2 flue gas circulation calcining cement technology,which provides technical support for the feasibility and application of adopting O2/CO2 combustion technology for calcining cement in decomposing kiln.The main research contents and conclusions are as follows:(1)The physical model and mathematical model of decomposition kiln are established.The process scheme for realizing the O2/CO2 combustion in the decomposition kiln system is determined.(2)The simulation results of the decomposition kiln under O2(0.21)/CO2(0.79)combustion atmosphere and air combustion(basic operating conditions)are compared and analyzed.The results show that the former compared to the latter,the burnout rates of pulverized coal in rotary kiln and precalciner are reduced by 3.16%and 3.61%,respectively,the decomposition rate of raw material in the precalciner is reduced by 4.22%,the CO2 concentration at the outlet of the precalciner rises from 32.13%to 95.25%which achieves the CO2 enrichment to reach the requirement of C recovery;the overall denitrification of the decomposition kiln is mainly the decrease of the production of NO in the rotary kiln and the overall denitrification rate is 56.1%.(3)In order to solve the problem of the burnout rate of pulverized coal and the decomposition rate of raw material are low under the combustion atmosphere of O2/CO2,the influence of four single factors namely particle size of pulverized coal,O2 concentration,tertiary air temperature,excess air coefficient on the combustion and decomposition in the furnace are evaluated,it is concluded that in the process of reducing the particle size of pulverized coal from 60?m to 20?m,the combustion of pulverized coal and the decomposition of raw material are significantly improved,and the concentration of NOx has increased slightly.When the O2 concentration increases from 21%to 37%,the combustion of pulverized coal and the decomposition of raw material are significantly improved,and the concentration of NOx has certain increases.When the tertiary air temperature increases from 1300 K to 1420 K,the combustion of pulverized coal has a certain improvement,the decomposition of raw material has better improvement,the NO concentration at the outlet decreases slightly.When the excess air coefficient increases from 1.15 to 1.31,the combustion of pulverized coal has a certain improvement,the decomposition of raw material increases slightly and then decreases,the NO flow at the outlet increases firstly and then decreases.(4)Based on the engineering application and economic perspective,a comprehensive evaluation of multiple factors is carried out,and the better scheme of particle size of pulverized coal is 60?m,excess air coefficient increases is 1.15 the tertiary air temperature is 1350 K,and O2 concentration is 31%is obtained.Under the optimal scheme,the burnout rate of pulverized coal is 97.26%,the decomposition of raw material is 95.12%,and the overall denitrification rate of the decomposition kiln is 52.93%,The concentration of NO at the exit is 293.8 mg/Nm-3.