电弧炉烟气全余热回收装置的研究

Research on Total Waste Heat Recovery Device of EAF Flue Gas

目前国内大部分电弧炉都没有做到四孔烟气余热的全部回收。研发了电弧炉烟气全余热回收装置,在某钢厂110 t电弧炉上进行了中试,对烟气温度、烟气组成及换热情况进行了现场测试,并对测试结果进行分析,得到如下结论:兑铁水的比例从全废钢到质量分数为80%铁水,电弧炉烟气全余热回收装置出口的烟气温度均能控制在250℃以下,说明烟气全余热回收装置在变工况条件下能够回收电弧炉四孔烟气250~2100℃的全部余热。铁水加入量(质量分数)约50%的典型工况下,Ⅰ段烟道入口烟气最高温度可达1982℃。铁水加入量(质量分数)约50%的典型工况下,Ⅰ段烟道上半部分平均热流密度高达999.8 kW/m^2,传热系数高达657 W/(m^2·K);下半部分平均热流密度为327.2 kW/m^2,传热系数为277 W/(m^2·K),Ⅰ段烟道上半部分的平均热流密度为下半部分热流密度的3.06倍。一个冶炼周期内的烟气最大温差为1624℃。如此高的热流密度及温度交变,在Ⅰ段烟道设计时需充分考虑如此大幅波动的烟气温度所造成的汽化冷却烟道的疲劳问题。燃烧沉降室顶盖虽然采用了汽化冷却结构,但其换热量很小。由于燃烧沉降室四周及底部采用了耐火材料结构,具备很好的蓄热作用,减小了燃烧沉降室出口、Ⅱ段烟道及后续列管余热锅炉的温度波动,在冶炼初期还出现了燃烧沉降室加热烟气的情况。从冶炼周期烟气组成来看,由于漏风等原因,电弧炉第四孔出口到Ⅰ段烟道中部时烟气中的CO已经基本燃尽。主要原因可能是电弧炉的观火孔、电极孔等孔隙的漏风率已经很高,造成电弧炉内已经有大量CO燃烧。因此为了减少漏入空气量,保持合理的过剩空气系数,减小一次风机负荷,尽量多地回收烟气余热,此时水冷滑套的开度要尽可能小,同时应尽可能减少电弧炉孔隙的漏风量。

At present,most electric arc furnaces(EAFs)in China are not able to fully recover the waste heat of the fourth-hole flue gas.A total waste heat recovery device for EAF flue gas was developed.A pilot test was carried out on a 110 t EAF in a steel plant.The flue gas temperature,flue gas composition and heat transfer were tested on site,the test results were analyzed,and the following conclusions were obtained:The addition proportion of molten iron was from total scrap to 80%mass fraction.The flue gas temperature at the outlet of the total waste heat recovery device for EAF flue gas can be controlled to below 250℃,which indicates that the device can recover all the waste heat of the fourth-hole flue gas of EAF from 250 to 2100℃under variable working conditions.Under typical working condition where the molten iron charging(mass fraction)is about 50%,the maximum temperature of flue gas at the inlet of section I flue can reach 1982℃,the average heat flux in the upper half of the first section flue is as high as 999.8 kW/m^2,and the heat transfer coefficient is as high as 656.7 W/(m^2·K);the average heat flux in the lower half is 327.2 kW/m^2,and the heat transfer coefficient is 277 W/(m^2·K),the average heat flux in the upper half of the first section flue is 3.06 times of that in the lower half.The maximum temperature difference of flue gas in a smelting cycle is 1624℃.With such high heat flux and temperature alternating,the fatigue problem of vaporized cooling flue caused by such large fluctuation of flue gas temperature should be fully considered in the design of flue gas in first section.Although the top cover of the combustion settling chamber adopts vaporization cooling structure,its heat transfer is very small.Due to the refractory structure used around and at the bottom of the combustion settling chamber,it has a good heat storage effect,which reduces the temperature fluctuations at the outlet of the combustion settling chamber,second section flue and subsequent tube waste heat boilers,and at the early stage of smelting,the flue gas is heated by combustion settling chamber.From the composition of flue gas in smelting cycle,due to air leakage and other reasons,the CO in the flue gas from the fourth hole outlet of EAF to the middle of the first section flue is almost burned out.The main reason may be that the air leakage rate of the holes such as the observation hole and the electrode hole of EAF is very high,resulting in combustion of a large amount of CO in EAF.Therefore,in order to reduce the amount of air leakage,maintain reasonable excess air coefficient,reduce the load of primary air fan,and recover the waste heat of flue gas as much as possible,a t this time,the opening of water-cooled sliding sleeve should be as small as possible,and the air leakage of the holes of EAF should be reduced as much as possible.