| The proven reserves of magnesite resources in Liaoning Province is about 2.57 billion tons,accounting for about 85%of the country’s total reserves and about 20%of the world’s total.Magnesite is mainly used for the production of refractory materials.Its main product forms are light-burned magnesium powder,sintered magnesia and fused magnesite,and its production ratio is 4:4:2.At present,the shaft furnace is the most important calcining furnace for sintered magnesia in China.There are still problems such as low single furnace output,high comprehensive energy consumption,and difficult to meet NOx emissions in flue gas.From a thermal point of view,the calcination shaft furnace is a gas-solid countercurrent vertical moving bed,which belongs to the category of large particle bulk bed.According to the relationship between the three types of variables of the kiln,the structure and operating parameters of the shaft furnace affect the flow and heat transfer thermal processes in the furnace,and then affect the shaft furnace output and product quality.Based on this,this paper relies on the key research and development plan project of Liaoning Province,"Research on Key Technologies for Preventing and Controlling Atmospheric Pollution during Sintering of Magnesia,Yingkou Company A 50,000 t/a re-fired sintered magnesia shaft furnace.The numerical calculation method is used to study the thermal behaviors such as the flow and heat transfer of the pellet layer of the shaft furnace,so as to find the existing problems or deficiencies of the shaft furnace,and then propose improvement suggestions to assist the subsequent efficient technological transformation.Main research contents and conclusions:(1)A small-scale test bed for the resistance characteristics of magnesite pellets was set up,and experiments such as edge effects within the pellet layer,flow regime determination,and correlation correction of resistance characteristics were carried out.The study shows that the pellet layer is in a sufficient turbulence zone;the correlation of the pellet layer resistance characteristics is:#12(2)Based on local thermal non-equilibrium theory and porous media model,fully consider the characteristics of lightly burned magnesia pellets such as drag characteristics and pellet down speed,a three-dimensional steady-state gas-solid flow heat transfer numerical calculation model.The calculation of the temperature,velocity,pressure and other fields of the research object was carried out,and compared with the actual measurement data of the research object,the reliability of the model was verified.(3)It can be known from numerical calculations:1)The temperature in the shaft furnace rises from top to bottom and then decreases to a multi-stage gradient distribution;There are multiple calcination air and single cooling air in the shaft furnace,which move from bottom to top;The pressure in the furnace is distributed in an inclined band;2)Under normal and stable working conditions at the production site,the calcination temperature is 1523K and the calcination time is 4h.The analysis shows that the shaft furnace calcination time is 4.6h,which meets the calcination requirements.The resistance of cooling air and calcined air through the material layer is about 1.65kPa and 0.70kPa,respectively.(4)It can be known from the numerical calculation analysis that the main factors affecting the gas-solid heat transfer in the shaft furnace are the calcination air volume,cooling air volume,preheating calcination section length and cooling section length.Within the adjustable range of production,as the calcination air volume increases,the cooling air volume decreases,the temperature of the shaft furnace section increases,and the pellet calcination time increases;as the preheating calcination section height increases,the outlet flue gas temperature decreases,and as the cooling section As the length increases,the export ore temperature decreases.For Yingkou Company A Shaft Furnace,with the increase of the calcination air volume by 10%,the temperature of the preheating section and the calcining section increased by 55℃ and 40℃,respectively,and the calcination time was extended by 40min.With the cooling air volume increasing by 10%,the temperature of the preheating section,the calcining section and the cooling section is reduced by about 50℃,30℃,and 80℃,respectively,and the calcination time is reduced by 20min.As the length of the preheating section increases by 5%,the outlet flue gas temperature decreases by 10℃.As the length of the cooling section increases by 5%,the outlet mine temperature decreases by 25℃.(5)At present,Yingkou Company a 50,000 t/a reburning shaft furnace data can basically meet the requirements of calcination temperature and time,but there are certain shortcomings.1)The current structure of the shaft furnace and the small cross-sectional area tend to cause the airflow to the central area of the shaft furnace,which leads to the heat input(ie,the fuel consumption per unit time)should not be too large,This slowed down the pellets(forced to match smaller heat input),which severely restricted the increase in production.2)Shaft furnace structure type,the cooling air volume at the bottom of the shaft furnace should not be too large,because the cooling air volume is too large,it will reduce the temperature of the calcination zone,making the pellet temperature at the shaft furnace outlet.3)The setting of the thermal parameters such as the size of the shaft furnace and the cooling air volume are not suitable,which also leads to a higher temperature of the pellets at the shaft furnace outlet,and the temperature of the flue gas at the shaft furnace outlet is lower,which is not conducive to the subsequent SCR denitration.Based on the actual arrangement of the project,suggestions for improving the original structure are given.The length of the cooling section is increased by 25%,and the cooling air volume is increased by 2.20%;the length of the preheating calcination section is reduced by 10.27%,and the calcination air volume is reduced by 17.80%.At this point,the pellet temperature at the shaft of the shaft furnace dropped to 283.44℃,Reduce energy consumption by 17.83%,and the temperature of the flue gas at the outlet rose to 346.91℃,which basically reached the appropriate denitration temperature for SCR. |
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