| The grate-kiln pellets production process in iron and steel smelting industry can improve the pellet quality,save energy and protect environment.Grate is a thermal equipment for drying and preheating the pellets.Whether the temperature field inside the downdraft drying zone(DDD)of grate can achieve balance and stable control directly affects the mass production quality and reasonable utilization of heat energy.This paper focuses on the multi-physics coupling mechanism of the temperature field,airflow velocity field and gas pressure field of DDD and its influence on the pellet drying process,the multi-physics coupling modeling,simulation and experimental analysis are studied.1.According to the theory of porous media theory,CFD,heat transfer and drying kinetics theory,the multi-physics coupling mathematical model of temperature in the DDD of grate is established.The partial differential equations are used to describe the changes of key variables.The internal heat conduction of the pellet,the fluid-solid convection heat transfer,the moisture analysis during the pellet drying process,the airflow in the drying section of the grate,the heat exchange of the grate bed and the pressure loss of it are taken into consideration.2.A physical model of the drying section of the grate is established.The discretization of the region is performed and the numerical simulation calculation method is determined.Based on the FLUENT simulation software,the UDF and UDS are used to modify and define the source terms of the energy equation and the species transport equation.The multi-physics coupling model of the pellet drying process is numerically simulated.It is found that the temperature field of DDD has a temperature gradient in both the grate height direction and pellet bed process direction.3.The effects of the coupling between UDD and DDD on the multi-physics temperature distribution and pellet drying process were researched.Affected by the hot airflow of UDD,the local temperature of the temperature field in DDD is lower than expected,and the lowest is only 477 K.At the same time,the airflow velocity and pressure distribution in DDD are changed.Local temperature of the DDD changes sharply duo to the high temperature airflow in UDD.The local temperature in the upper part of the pellets layer is up to 565 K,which is much higher than the inlet airflow temperature(473K),and the temperature of the pellets layer can reach 492 K.It has a great influence on the drying process of pellets.Accordingly,it is proposed that the length of UDD can be appropriately shortened to reduce the drying time and increase the production of the pellets.4.A multi-physics distribution detection and dynamic coupling control test system is developed and produced.After designing the experiment program,the temperature multi-physics coupling experiment of the pellet drying was carried out.Combined numerical simulation with data measurement processes,with the comparison and analysis of numerical simulations and experiment results,the maximum calculation error is 9.3%,which can be applied to the actual control process after correction.The rationality of the mathematical model of temperature multi-physics coupling in DDD of the grate is verified through the study of the variation of temperature field distribution,the coupling mechanism of temperature multi-physics and the effect on the drying process of pellets.The study provides a theoretical basis for the control of the equilibrium and stability of the temperature field of DDD of the grate.It is of great significance to improve the comprehensive economic benefits of China's modern pellet production enterprises. |
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