Numerical method for predicting pellet drying process in grate blast drying section

Abstract

The invention discloses a numerical calculation method for predicting the pellet drying process of a grate blast drying section, which comprises the following steps: (1) establishing a two-dimensionalunsteady mathematical model of the pellet layer heat coupling process of the grate blast drying section; One-dimensional unsteady mathematical model of heat transfer in single pellet considering steam condensation as an important process of moisture transfer; (2) In order to improve the calculation speed, the drying process of grate blast drying section is simplified and assumed reasonably; (3) establishing mathematical model, including single pellet drying mathematical model, pellet bed drying mathematical model and so on; (4) calculating a model, according to the mathematical model, determining parameters of heat and mass transfer, geometry structure and the like, and simulating changes of drying process under different drying processes and control parameters of the grate blast drying section; (5) performing model verification, comparing with the actual pellet drying test results, to determine the value of empirical coefficients; (6) Simulation and optimization, adjusting the control and process parameters in the actual drying process, optimizing the pellet drying process.

Description

technical field [0001] The invention relates to the technical field of pellet sintering technology in iron and steel smelting, in particular to a numerical calculation method for predicting the drying process of pellets in the blast drying section of a grate machine. Background technique [0002] Grate machine is one of the key equipment for producing pelletized metallurgical materials, mainly used for drying and preheating green (wet) pellets from pelletizer. It distributes the raw (wet) pellets on the grate plate of the grate bed of the grate machine running at a slow speed through the distributing machine, and blasts the raw (wet) pellets by using the waste heat of the ring cooler and the hot air discharged from the rotary kiln. Drying, air drying and preheating oxidation, and after reaching sufficient compressive strength, it is directly sent to the rotary kiln for roasting to obtain pellets with reliable quality. [0003] The grate machine is composed of blast drying s...

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Problems solved by technology

Young et al. (Ironmaking&Steelmaking, 1979) established a mathematical model for the drying and preheating of pellets in the grate-rotary kiln-circular cooler, and calculated and analyzed the factors affecting the convective heat transfer of the pellets, but the author did not analyze the mathematical model In-depth analysis; Pan Shujing et al. (Steel Research, 2012) considered the mutual coupling effect among mass, energy and momentum in the pellet layer for the drying process of pellets in the blast drying section, and established the drying process The mathematical model of the multi-field coupling transfer process inside the pellet layer does not consider the internal heat conduction of the pellets, and does not study the entire drying process of the pellets; for the condensation of water vapor in the pellet layer, Cumming et al. (Ironmak.Steelmak., 1990 ) thinks that once the gas reaches saturation, water vapor begins to condense, but it ignores the mass transfer process; Dash et al. (Ironmaking steelmaking, 1978) believe that the condensation rate of water vapor is proportional to the difference between the gas humidity and the gas saturation humidity, and the model has certain experience

For the evaporation process of water in pellets, Patisson et al. (Metallurgical Transactions B, 1990) found that the evaporation rate of water in pellets consists of a constant speed section and a slowing speed section; Ljung et al. (SIMULATION, 2006) considered the pellet material layer as For porous media, the temperature distribution of the pellets was calculated by taking the porosity of the material layer into account, but it ignored the water evaporation of the pellets, and the parameters used were based on rough approximations, so there were large errors in the results; Tsukerman et al. (International journalof mineral processing, 2007) established a drying dynamics model of pellets. Through the research, it was found that the water on the surface of the pellets evaporated first, and then the evaporation front moved to the interior of the pellets, and the wet core of the pellets continued to shrink. However, this model did not consider water The effect of condensation on the water content of pellets

At present, most of the research work on pellet drying in the blast drying section of the grate machine focuses on the prediction and judgment of water evaporation rate and temperature, ignoring the condensation of water, which cannot truly reflect the water transfer mechanism of the pellet drying process, and cannot fully reflect Pellet Drying Process

[0007] The above calculation methods are mostly used for off-line operation analysis, and there are still limitations in industrial application. The main shortcomings are as follows: (1) Most models only consider gas-solid convective heat transfer, and basically do not involve the problem of pellet heat conduction; (2) ignore The water migration and condensation stage and the internal temperature gradient of the pellets cannot be truly and accurately reflected in the moisture transport mechanism of the pellet drying process; (3) the control equation is quite complicated, and the model solving time is long; (4) some main technical parameters in the model are selected too much Based on experience, its calculation accuracy cannot meet the requirements of industrial control, and its application range is narrow

[0008] From the above analysis, it can be seen that the pellet drying in the blast drying section of the grate machine is a complex heat and mass transfer process with many influencing factors, and it is difficult to establish a suitable mathematical model

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