Thermal Airflow Process Of Grate-Kiln System And FLUENT Simulation

Grate-kiln pellet production method has many advantages such as the adaptability of raw materials, large production capacity, roast evenly, pellets of high grade and recyclable waste heat, so it gets a rapid development in China in recent years. The main problems of current thermal airflow process for grate-kiln system: low temperature gas of grate-kiln system are discharged directly; the heat generated by the return section of the traveling grate is not recycled; the temperature of the recycling gas by annular cooler is not high. All those defects lead to inefficient recycling of waste heat and pollution. To this end, to carry out thermal airflow process improvement of grate-kiln system to further reduce emissions, improve heat recovery efficiency and achieve energy savings, eventually contributing greatly to the socio-economic development. Mainly task include three aspects.(1) Improved design on thermal airflow process of grate-kiln system. In light of existing defects of low efficiency for heat recovery and large emission, a heat recycling method through convection repeatedly is proposed and the design for thermal airflow process of grate-kiln system is improved on the basis of the analysis of current grate-kiln pellet manufacturing process and the thermal airflow process.(2) Theoretical analysis of heat recovery and structural design. On the one hand, according to the structure of the traveling grate and heat transfer theory, considering technology characteristics and technical requirements of the 2.4 million tons traveling grate, the appliance for traveling grate bed waste heat recovery is designed, and then a theoretical estimate of convective heat is made with a result of more than 60%; on the other hand, the structure and principle of the annular cooler are analysed, considering technical characteristic and requirements of 2.4 million tons annular cooler. theoretically estimate the amount of convective heat for the annular cooler are calculated. The result shows the new thermal airflow process for annular cooler has a higher exit gas temperature of 106℃,168℃,52℃or so than that of current thermal airflow process in the respective sections.(3) Computational fluid dynamics analysis of thermal airflow process. Based on computational fluid dynamics theory, the pre-processing software of GAMBIT and FLUENT are applied to analyze the traveling grate bed heat recovery unit and thermal airflow process of annular cooler. The simulation analysis shows that the outlet gas temperature of each section for the traveling grate bed were respectively 268℃,354℃and 427℃, consistent with the theoretical calculation of heat recovery efficiency; the increased values for the outlet gas temperature of each section under the new thermal airflow process for annular cooler coincident with the theoretical value. From the theoretical calculation and simulation analysis, the improved design of thermal airflow process for grate-kiln system is effective and workable, and may provide reference and guidance for practical application in the future.