| The energy consumption of sintering process accounts for 10 to 15 percent in the whole iron and steel making process, which is the second consumer in the energy using, following the ironmaking process. The heat resources in sintering process include the sensible heat of exhaust gas and heat from sinter ores, accounting for 20% and 45%, respectively, in total energy consumption in sintering process. The main purpose of current Annular Cooling Machine is cooling the sinter ores without revocering the heat of sinter ores, and this makes too large gas flow, too thin sintering layer, too rapid cooling and too serious air leakage is the drawbacks of Annular Cooling Machine, which unable to meet the high efficiency heat exchanger and heat removal requirements. In order to achieve both sinter cooling and waste heat recovering, structural design and thermal operation of Annular Cooling Machine should be reinvented. Inspired by the coke dry quenching technology (abbreviation CDQ), where a red hot sinter, pellets, are likely to intensify heat transfer enhancement as the CDQ with the way of gas-solid heat exchange, namely vertical-style equipment to replace the existing Annular Cooling Machine. The gas flow in the vertical-style equipment is the basis of the gas-solid heat exchange, so it is important to study on this gas flow in this paper. On the basis of the sinter cooling technology analysis and study of gas-solid moving bed, this paper mainly carried out the following studies:(1) Properties of sinter ores and grain size distribution experimentsDrum index and abrasion index of the sinter ores were obtained through drum tests, crushing performance of various sizes and the distribution ratios of different particle sizes were obtained through different continuous drum tests; Pulverization rate of various paritcle sizes was given by calculation and the bed permeability factor of sintering layer was analyzed on the above experiments. The results showed that:the larger the particles size is, the more easily broken the sinter ores is, and the greater the voidage of sintering layer is, the better the permeability of sintering layer is.(2) Distribution of sintering layer in the experimental equipmentsVoidage is considered as the key indicator for the distribution of sintering layer in the device, voidage along the height direction was measured by the cross-section image analysis method, radial voidage was calculated by dividing the annular regions artificially, and the voidage expression was obtained by the polynomial fitting method in Origin software. The results show that:the voidage increases as the particle size increases; voidage increases as the height of sintering layer increases when the height is below 0.5 m, and the voidage can be considered as a constant when the height is above 0.5 m; The radial voidage increases as the distance is away from the center of the sintering layer, its value is the largest near the wall of the vertical-equipment, and the wall effects become weaker as the bed to particle diameter ratios increases, it can be ignored when the D/dp>30. In the vertical-style equipment, increasing the particle size of sinter ores can enlarge the vodiage the sintering layer, so that the permeability of sinter ores can be improved.(3) Pressure drop of gas flow through the sintering layerExperimental data of the pressure drop of gas flow through the sintering layer was used for establish the correlation between Euler number and Reynolds number by dimensionless analysis and nonlinear fitting method according to the "self-modeling" feature of fluid. The fromula of pressure drop per unit under different particle sizes were obtained after the mathematical calculating for the above correlation. Then the pressure drop were compared with the Ergun equation, Yang’s equation and the result of numerical simulation, and it was found that the pressure drop in this paper was more reliable that the others. Two ways for decreasing the pressure drop of gas flow in the sintering layer were given:one was increasing the particle size of sinter ores in the vertical-style equipment and the other is decreasing the superficial velocity of cooling air in the euqipment, and the latter one can be realized by enlarge the diameter of the vertial-style equipment when designing in order to keeping the sas-solid water equivalent unchanged.(4) Design of vertical-style equipment and the analysis method of gas flow in itVoidage of the sintering layer and the pressure drop of gas flow through the sintering layer are considered as the basis of vertical-style equipment, considering the water equivalent of sinter ores and the cooling air, vertical-style equipment was designed combined with the convective heat, thermal conductivity and the heat balance equation. A design procedure based on the C language was developed to calculate the design of the vertical-style equipment instead of manual calculation which wasted lots of time; Take a sintering machine with capbility of 360 m2 for example, exact designing procedure was given in this paper. User-Defined Function (UDF) programs were written to represent the voidage distribution and their drag coefficients in the porous media, which replaced the real distribution of sintering layer in the vertical-style equipment; the control equations of gas flow in the equipment were established from the perspective of numerical analysis, and discretization and iterative solution were done by Gambit and Fluent software to get the simulation results. The key objects of gas flow in the vertical-style equipment were pointed out:the outlet temperature of cooling air, the pressure drop of gas flow and the streamline of gas flow. The outlet temperature represented the quality of the heat, the pressure drop of gas flow represented the economical of the vertical-style equipment, the streamline of gas flow represented the uniformity of the flow distribution, and the reliability of the equipment for recovering the heat of sinter ores could be represented.(5) Analysis of influencing factors of gas flow in the vertical-style equipmentThe gas flow in two designs of the vertical-style equipments was compared through the numerical simulation, and one design is determined as the vertical-style equipment of recovering the heat of sinter ores. Numerical simulation and the design program based on C language were combined to study the gas flow in the vertical-style equipment, and the design parameters’ impact on gas flow in the equipment was discussed. Changing the diameter of the equipment and keeping the height of sintering layer unchanged could change the uniformity of gas flow distribution, it was found that the gas flow distribution was uniform when the height to diameter ratio is between 1.2 and 1.6, which ensured the pressure drop of gas flow in the equipment was not large; gas flow distribution and pressure drop for center gas supply, surrounding gas supply and center and surrounding gas supply were compared, and different proportions of center and surrounding gas supply were analyzed; It is found that the uniformity of gas flow distribution can be improved by changing the shape of the material surface and the angle of the surface; the pressure drop of gas flow and the velocity of moving speed of sintering layer can be reduced through lowering the superficial velocity of gas flow, and the pulverization rate can be lowered accordingly; gas flow and pressure drop of different equivalent diameter of particle sizes in the vertical-style equipment were compared, and it was found that:larger particle size (35 mm)was suitable for filling in the equipment, UDF program could reflect the real gas flow distribution and the pressure drop compared with the uniform sintering layer. For the equipments with the diameter of 4 m,4.5 m and 5 m, the inlet temperature of cooling air was changed and the height of sintering layer, pressure drop of gas flow and height to diameter ratios were analyzed using the C program design procedure, then the final parameters of the vertical-style equipment were given based on the smaller pressure drop and the larger outlet temperature:the diameter is 5 m, the height of sintering layer is 6.2 m, inlet temperature of cooling air is 75℃, the superficial velocity of gas flow is 5.3 m/s, the moving speed of sintering layer is 1.6 mm/s, the total pressure drop is 15.4 kPa, and the pressure drop per unit is 2.6 kPa/m, the capability for a single vertical-style equipment is 350 t/h, the particle size of sinter ores in it is 35 mm, the cooling time of the sintering layer is 1.06 h, the waste heat from the equipment is 188.2 GJ/h, the required flow of cooling air is 378000 m3/h, and the gas to sinter ores ratio is 1080 m3/t. |
PDF Full Text Request