基于离散单元法模拟引入AGD技术COREX竖炉物料运动行为

基于离散单元法,建立引入Areal Gas Distribution(AGD)技术COREX竖炉物料运动行为的DEM模型.模型计算结果与文献物理实验结果一致,证明模型的合理性.模拟结果显示,AGD竖炉内存在三种类型的流动区域:活塞流区、准停滞区及沟流区.物料运动流型呈现Flat→波浪→W的演变过程.AGD梁下方形成的三角形空隙是还原煤气导入竖炉中心的主要煤气通道.竖炉围管区域AGD梁的安装会影响该区域物料的均匀下降,局部区域的较大法向力可能导致物料的挤压黏结,诱发围管slot堵塞.     

COREX竖炉围管堵塞位置及其演变过程的物理模拟

建立COREX竖炉三维半周物理模型,模拟竖炉围管粉尘初始堵塞位置及其演变过程,考察鼓风量、排料速度、非工况排料等操作条件对围管粉尘堵塞的影响.模拟结果显示,COREX竖炉围管初始堵塞位置为AGD架梁圆管前方的8#~12#导气槽区域.当导气槽前端填充床内形成粉尘沉积区后,若沉积区向上发展速度大于其随物料向下运动速度,粉尘沉积区向围管方向发展,并逐步堵塞围管导气槽,进而在围管内形成粉尘堆积区.该堆积区在围管内继续发展,使得其堆脚向围管远端运动,从而逐步将远端导气槽堵塞.此外,模拟发现随着排料速度加快及鼓风量增加,围管内不易发生粉尘堵塞.当炉内非工况条件发生时,粉尘堆积的动态平衡被打破,易造成围管内粉尘的堆积堵塞.      

COREX熔化气化炉物料运动行为

基于离散元方法,建立了二维扁平熔化气化炉的离散元模型,应用此模型从颗粒尺度对物料运动流型、速度场以及空隙度分布进行了研究。结果表明:采用加入示踪颗粒的方法,对颗粒运动流型进行分析,示踪颗粒层逐渐由直线型变为两侧向下弯曲型;从物料速度场分布可以看出,炉内存在死料柱区、活塞流区以及管道流区等运动区域。回旋区对炉内竖直方向速度分布的影响限于距炉缸底部上方0.18m处,回旋区半径的减小导致炉内颗粒活跃区域缩小,死料柱区高度增加;炉内物料运动存在一定的偏析现象,该现象也可从空隙度分布看出。炉内死料柱区空隙度为0.37左右,回旋区处为0.65左右,位于自由空间下方和死料柱区以及回旋区之间的活塞流区空隙度在0.37~0.65之间。     

COREX预还原竖炉煤气停留时间分布的数值模拟

为研究COREX预还原竖炉内煤气流动特性,利用数值模拟方法研究了炉内煤气停留时间分布（RTD）,考察了AGD（Areal Gas Distribution）梁对COREX预还原竖炉炉内RTD的影响以及不同熔炼率下COREX预还原竖炉的RTD变化规律.模拟结果表明,随着2#COREX预还原竖炉AGD梁的安装,其整体时间密度分布函数变宽,平均停留时间变短,无量纲方差变大.AGD梁的安装增大了炉内的死区体积分数,2#COREX预还原竖炉炉内死区体积分数达到了26.81%.随着竖炉熔炼率的增加,炉内平均停留时间逐渐减小,无量纲方差逐渐增大.当熔炼率从150 t/h增长到180 t/h时,1#COREX竖炉死区体积分数降幅为68.1%,2#COREX竖炉降幅仅为15.52%.     

料斗倾角对气基竖炉布料过程中物料流动及分布的影响

球团矿离开料斗时的颗粒偏析会影响其在气基竖炉内的分布,分布不合理将影响还原气的利用率.建立20°～70°倾角的料斗、导料管、溜槽、气基竖炉三维模型,基于离散元法研究物料从料斗到气基竖炉布料过程中的流动和分布.结果表明：排料时,20°～25°倾角的料斗内炉料流型均为整体流,30°～55°倾角的料斗内炉料流型均为混合流,60°～70°倾角的料斗内炉料流型均为漏斗流;漏斗流促使料层形成快速流动的中心通道,大颗粒会更早地离开料斗进入炉内,在落点区域堆积,导致料斗内大颗粒负偏析、竖炉内落点区域大颗粒正偏析;20°～35°倾角的料斗布料后,炉内孔隙率偏差分布在0.003 83～0.004 68,倾角增大,孔隙率偏差增大;改变炉料-料斗静摩擦系数、炉料批重、料斗半径等参数,发现料斗倾角是影响布料过程和结果的主要因素,孔隙率偏差仍随料斗倾角的增大而增大.     

COREX竖炉炉料黏结的机理研究和影响因素分析

竖炉内炉料黏结是COREX炼铁工艺中的一个重大难题,国内外COREX生产操作都表明预还原竖炉内部的炉料容易黏结成块或黏结在竖炉的炉墙上,累积到一定程度后,会引起竖炉悬料,影响COREX还原煤气的利用和预还原竖炉的顺行,严重时甚至堵塞竖炉,使还原煤气难以接受或无法排料而被迫清空竖炉。在竖炉清空期间,对竖炉内黏结物进行了取样和分布情况调查,借助于化学成分检测、SEM和XRD等手段,分析了竖炉内黏结物形成的机理。在上述分析的基础上,通过实验室的试验研究考察了竖炉内炉料黏结的影响因素,结果表明,温度、金属化率、挤压时间、煤气成分等是黏结的主要影响因素。     

COREX预还原竖炉矿焦混合布料规律

 针对宝钢的COREX-3000预还原竖炉炉顶的万向节布料器矿焦混合布料过程进行了试验研究。基于量纲和谐原理推导了相似准数,并按照1∶5比例建立冷态模型装置,定量考察了物料混合比例对料流宽度、料面形状以及径向料堆结构的影响。研究表明：物料混合比例对料流宽度和料面形状的影响较小,对料堆结构影响显著,随着大颗粒质量分数的增加,料堆堆密度降低,料堆空隙率增大。研究结果对于指导COREX竖炉生产过程的布料规律具有参考价值。     

COREX CGD预还原竖炉内煤气停留时间分布的数值模拟

文章利用数值模拟方法研究了COREX预还原竖炉内煤气停留时间分布(RTD)特性,分析了CGD (central gas distribution)装置对炉内煤气RTD分布特性的影响,并对不同熔炼率下炉内煤气RTD规律进行了研究。模拟结果表明,安装CGD后,增加了竖炉底部中心供气,提高了煤气平均停留时间。此外,CGD的安装降低了炉内平均停留时间的无量纲方差,且有效减少了炉内死区体积分数,有利于炉内气固相间的还原反应及传质、传热。随着熔炼率增加,炉内煤气平均停留时间缩短,死区体积分数减小。     

宝钢2号COREX-3000工程的重大优化

宝钢1号COREX炉运行投产已近5年,在生产运行过程中暴露出金属化率低、下料管堵塞等诸多工艺及设备缺陷。针对这些问题,从生产运行、工程建设、技术改进角度分析了导致1号COREX炉出现问题的原因,如:竖炉煤气分布不均匀、炉缸位置耐材设计形式不合理等,在二期工程中累计提出增加竖炉煤气均布管道、修改炉缸耐材设计等优化项目400多项。同时,在2号COREX工程引进合同谈判、设计国产化、设备国产化方面以及2号COREX工程建设过程控制等方面都有了重大技术改进。     

优化COREX-3000竖炉布料的实践

根据COREX-3000投产后竖炉的生产实践,对COREX竖炉动态布料进行了分析和探索,总结了影响竖炉物料粒度分布不均或物料偏析的主要因素,并介绍四种典型竖炉布料模式,分析了不同炉况下布料模式的选择。动态布料器在布料模式和布料档位上的灵活性对疏导平衡还原煤气气流的分布起着决定性的作用。边缘和中心均衡发展的竖炉还原煤气流分布的煤气利用率最高,主要表现在金属化率高,热交换效率高两方面。     

Analyses of solid flow in COREX shaft furnace with AGD by discrete element method

COREX is an industrially and commercially proven smelting reduction process. The shaft furnace (SF) for the direct reduction of iron ore is one of the two major reactors of COREX. In the new design of COREX-3000 SF in Baosteel, China, a new technique called areal gas distribution (AGD) has been adopted. With the installation of two AGD beams, the cross-sectional area varies in a complicated manner, which will affect the burden descending behaviour. This work uses a slot model to investigate the solid flow behaviour in the SF by discrete element method. The applicability of the discrete element method model is validated. The results confirm that the flow profile in SF with AGD evolves from a flat to wave and finally to W profile as the solids descend. A triangle shaped free area is observed under the AGD beam, which is the main channel for gas flow into the shaft centre. Increasing the discharging rate has an effect of decreasing the quasi-stagnant zone size, but does not affect the macroscopic motion of particles and flow pattern above the bustle. The cross-section of AGD channel increase with the increase in the discharging rate. Under the asymmetric condition, the solid flow pattern is asymmetric. The influence of AGD on macro- and microscope properties of solid flow in SF is also evaluated. This investigation reveals that AGD beams affect the particle uniform descending in bustle zone and increase the complexity of normal force distribution.     

COREX竖炉内煤气流分布的三维数值模拟

通过基于有限体积法的竖炉内煤气流分布的混合两相流模型,对COREX竖炉安装AGD管道后的煤气流分布变化进行了三维数值模拟.模拟结果显示,安装AGD管道能降低竖炉的整体压差,提高竖炉的操作压力;增加竖炉下部煤气死区的体积,且并未改变竖炉上部中心1.0m半径范围内的煤气流速,仅提高了1/2半径处的煤气流速;AGD管道对煤气反窜有抑制效果,通过AGD管道进入竖炉的煤气约占56.88％;由围管导气孔进入的煤气主要集中在竖炉边缘及竖炉中心,AGD管道引入的煤气主要分布在其所在的垂直高度上,反窜煤气亦是通过竖炉中心上行.     

Influence of Cohesive Zone Shape on Solid Flow in COREX Melter Gasifier by Discrete Element Method

Based on the principle of discrete element method(DEM),a 2Dslot model of a COREX melter gasifier was established to analyze the influence of cohesive zone shape on solid flow,including mass distribution,velocity distribution,normal force distribution and porosity distribution at a microscopic level.The results show that the cohesive zone shape almost does not affect the particle movement in the upper shaft and deadman shape.The particles in the lower central bottom experience large normal force to support the particles above them,while particles around the raceway and in the fast flow zone exhibit weak force network.The porosity distribution was also examined under three kinds of cohesive zones.Like the velocity distribution,the whole packed bed can be divided into four main regions.With the increase of cohesive zone position,the low porosity region located in the root of cohesive zone increases.And the porosity distribution becomes asymmetric in the case of biased cohesive zone.     

布料模式对COREX预还原竖炉煤气流分布的影响

布料模式决定了炉料的空隙度,而炉料的空隙度分布决定了煤气流的第2次分布。采用三维竖炉数学模型,考察了单环布料情况下,挡位分别在竖炉炉顶直径的0.0、0.8、1.6、2.0、2.4、2.8 m时竖炉内煤气压差和煤气流的变化情况。结果表明：布料过程在料面上发生的炉料粒度偏析对煤气流分布的影响很大,料堆尖处煤气流速很低。随着布料档位外移,竖炉整体压差和围管压差呈现增加的趋势,而反窜煤气比例呈现先微弱降低后迅速增加的趋势,拐点出现在2.0 m布料档位。竖炉炉料布料方式对煤气流有再分配的作用,较为适宜的布料档位为1.6 m,不宜超过2.0 m。     

Influence of Screw Design on Burden Descending Velocity and Particle Segregation in COREX Shaft Furnace

COREX shaft furnace(SF)is an industrial system that employs screw feeders;thus,the burden descending velocity and particle segregation in the SF can be directly affected by the design of screw.A three-dimensional actual size model of COREX-3000 SF was established using the discrete element method.Four types of burdens,including pellet,ore,flux and coke,were considered in this model.With this consideration,the effect of screw design on solid flow was investigated.Results showed that,in the base case,burdens fell primarily down from the first flight of the screw.The burden descending velocities were nearly uniform in the peripheral direction and decreased along the radial direction.In addition,the normalized particle size increased in the center area and decreased in the wall area.Reducing the flight diameter of screw benefited an even flow pattern and restrained the rolling tendency of burden from the edge to center areas.An optimized case was also proposed,in which a uniform solid flow profile could be obtained and the evenness of descending velocity along the radius could be greatly improved.     

Experimental study and numerical simulation of dust accumulation in bustle pipe of COREX shaft furnace with areal gas distribution beams

ABSTRACT

The following study investigated the dust accumulation in the bustle pipe of the shaft furnace with Areal Gas Distribution (AGD) through physical and numerical simulations. Although the experimental and numerical results were obtained from different-sized furnaces, the results had a similar tendency, where an initial dust deposition zone formed in the packed bed located in front of slots 8–12. The growth velocity of the deposition zone became larger than the descending velocity. It then spread upwards, to plug the slots, until the dust accumulation was formed. The gas velocity in the bustle pipe decreased after passing the AGD beam due to nearly 60% gas that went into the furnace through the AGD inlet. This was the primary cause for the dust accumulation in slots 8–12. Both the physical and the numerical results showed that when the blast volume increased, it effectively reduced the dust flux in each slot and decreased the clogging effect.     

COREX熔化气化炉物料运动和气流分布

基于离散元数值计算方法(DEM),建立了熔化气化炉模型的离散元数学模型.应用此模型从颗粒尺度对气化炉3种软熔区域形状下的物料质量、运动速度、法向力、空隙度分布进行了研究.利用DEM计算空隙度数值,再结合计算流体力学软件对气化炉气流分布进行了计算.结果表明:软熔区域形状对气化炉料面形状和炉内下部法向力的分布影响很小,炉中...