【作者】 彭建平；

【导师】 冯乃祥；

【作者基本信息】 东北大学 ， 有色金属冶金， 2009， 博士

【摘要】 近年来,铝电解技术突飞猛进,铝电解槽容量从60年前的60kA发展到现在的500kA,电流效率达到95%,自动化水平和控制技术也得到提高。然而铝电解的电能消耗降低幅度不大,目前国内外电解槽直流电耗仍然徘徊在13000～13500kWh/T-Al,能量效率不足50%。因此降低铝电解的电能消耗成为国内外铝工业工作者关注的首要问题。大量研究表明通过改变电解槽结构实现大幅度降低铝电解电能消耗成为一种可能途径。论文对泄流式阴极电解槽进行两次半工业规模试验研究：1350A无烟煤基TiB2/C复合材料层泄流式阴极铝电解槽100 h电解试验和1850A石墨化基TiB2/G复合材料层泄流式阴极铝电解槽140 h电解试验。试验研究发现,泄流式试验电解槽从焙烧、启动到正常电解操作与传统电解槽无差别,泄流式电解槽槽电压和槽工作状态稳定,并获得较高的电流效率。泄流式阴极上制作的TiB2复合材料层腐蚀速度小,能有效地保护阴极基体,有利于延长电解槽寿命。利用铝参比电极由瞬时断电技术测得TiB2/G石墨化泄流式阴极电解槽的阳极过电压和阴极过电压分别与对应的电流密度遵循塔菲尔方程关系,其阳极过电压与传统工业电解槽相差无几,而其阴极过电压比工业电解槽高0.4 V左右,这是由于泄流式电解槽中不存在铝液波动,阴极表面附近的分子比比传统电解槽阴极表面电解质分子比高很多造成的。在重庆天泰铝业公司168kA系列上3台电解槽上进行工业试验,内容包括新型阴极结构电解槽的筑炉、焙烧、启动、正常电解生产过程。焙烧采用火焰一铝液二段焙烧新技术,其能耗仅为传统的铝液焙烧的1/4～1/3,焦粒焙烧的1/3,实现了节能的目的。到目前为止,3台新型阴极结构电解槽已稳定运行一年,一年的直流电耗平均为12100kWh/T-Al。最近半年3台新型阴极结构电解槽的槽电压平均为3.756V,阳极效应系数为0.063d-1,电流效率平均为93.3%,直流电耗平均约为12000kWh/T-Al,相比同系列127台传统电解槽阳极效应系数降低0.04d-1,电流效率提高1.9%,直流电耗降低约1370 kWh/T-Al,取得了大幅度降低铝电解电能消耗的效果。新型阴极结构实现高效节能的基本原理是：在新型阴极结构电解槽阴极表面有凸起,阴极铝液流速场被分割,铝液的流速大大降低,削弱了其对重力波的强化,使铝液的波动减少。同时这种凸起使阴极铝液内的电流分布更均匀,从而减少了诱发铝液流动的源泉。在凸起的表面所形成的较小水平电流围绕凸起形成铝液循环,可削减电解槽纵向方向波的功能。因此使得电解槽阴极铝液面的波峰高度大大降低,电解槽的有效极距加大,从而达到通过降低极距来降低槽电压的目的；新型槽的阴极表面具有凸起,电解时在凸起的表面形成适度的水平电流,并由此可围绕凸起形成铝液循环,这种循环铝液有利于氧化铝的溶解,可减少因为局部氧化铝浓度过低而发生阳极效应；新型阴极结构电解槽使铝液面波动减小,稳定性增强,并使阴极铝液面的有效面积减少,故减少了铝的二次溶解,提高了铝电解槽电流效率。通过对168kA新型阴极结构电解槽和传统电解槽的电热平衡研究表明：新型阴极结构电解槽的极距小,电解质电压降比传统电解槽的电解质电压降小；新型阴极结构电解槽可以在较低的槽电压,降低的能量输入下,通过侧部和底部加强保温,实现较低热损失,以达到电解槽的热平衡。试验表明,铝电解槽可以实现由散热型转变为保温型,从而提高能效。论文通过对168kA新型阴极结构电解槽阴极铝液面稳定性的测量与研究,发现：新型阴极高效节能铝电解槽,与对比同系列的传统电解槽一样,其阴极铝液面的波动具有相同的周期和频率,其周期在50s左右,其波动近似于正弦波；其不同点在于新型阴极高效节能铝电解槽,与对比的系列中的其它电解槽相比,具有较小的波幅,表明新型阴极高效节能铝电解槽的创新阴极结构设计,起到了减波(幅),稳定阴极铝液面的作用；当对比电解槽槽电压从4.10V降至3.95V时,阳极导杆内的等距离压降Ued的变化幅度由0.6 mV增大到1.1 mV,说明此时电解槽内铝液和电解质非常不稳定,波动增大,证明系列对比槽在3.95V的较低槽电压下不能正常工作；新型阴极结构电解槽在3.75V槽电压时24块阳极的电流分布标准偏差为0.589kA,比传统电解槽4.10V的24块阳极的电流分布标准偏差为0.829kA小,因此可以判定新型阴极结构铝电解试验槽3.75V电流分布比4.10V传统电解槽电流分布更均匀,槽内铝液更稳定。在实验室电解槽上对电解质和钠对阴极的腐蚀与渗透研究,结果表明：含TiB2/C阴极被电解质和钠渗透,电解质通过阴极孔隙渗透,金属钠既可通过孔隙渗透,也存在于通过碳晶格渗透,用EDS对电解2h后的TiB2/C阴极表面电解质的分析,可以观察到TiB2在电解质中有少量溶解；金属钠在TiB2/C阴极中的渗透符合菲克定律,其中含16%TiB2的阴极试样中钠渗透深度系数为1.42mm/min1、2。通过对TiB2/C复合材料阴极在铝电解过程中钠膨胀率的研究发现,TiB2/C阴极在铝电解过程中同样具有钠膨胀特性,但在相同实验条件下其膨胀率小于碳质阴极的钠膨胀率,且随着TiB2组份含量的增加,其膨胀率降低。通过无铝液存在条件下阴极受电解质腐蚀实验研究发现,电解后电解质熔体的渗透发生的钠的渗透之后,NaF渗透速度大于冰晶石熔体的渗透速度。在电解后电解质熔体导电性能发生改变,电解一段时间后,电解质熔体的电阻会比未电解前电解质熔体的电阻有很大的改变。更多还原

【Abstract】 In recent years, aluminum reduction technology by Hall-Heroult has made a big progress with the capacity increased from 60kA 60 years ago to the current 500kA and the Current Efficiency (CE) to 95% by advanced computer control. However, this has not changed the fact that 13000-13500 kWh/T-Al of Energy Consumption (EC) is still required to produce aluminum from alumina with poor Energy Efficiency (EE) below 50%. So it has become the most important task for aluminum industry experts to reduce the EC. It’s found that cell structural modification may be one way to realize this goal.As a newly structured cell, drained cathode cell is well considered to represent the direction of aluminum development. Two different tests on drained cell were also done to study its potentiality. One is electrolysis test of 1350A for 100h on drained anthracite based cathode cell with TiB2/C coating, and the other is 1850A for 140h on drained graphitized cathode with TiB2/G coating. It’s shown by the two tests that there are no big differences from traditional cells in preheating, start-up and operations. Drained cathode cell works stably and can get higher CE. The TiB2 coating can protect the cathode base because of its lower erosion rate. Moreover, the over-voltage at different current densities was measured with an aluminum reference electrode by interruption technique on the graphitized drained cathode cell. Both the anodic and cathodic over-voltages comply with the Tafel Equation. Furthermore, the anodic over-voltage.in the drained cell was close to that on industrial cells, while the cathodic over-voltage was much higher, reaching 0.5 V at around 1 A/cm2. This should be the reason that a stable molten Al layer and high molar ratio (CR) bath covering on the cathode.To overcome the very shortcoming of drained cathode cell, another newly structured cell is put forward in this thesis. The novel energy-saving technology is applied on three 168 kA cells in Chongqing Tiantai Aluminum Industry Co., Ltd. Gas-aluminum preheating method (GAP method), a special and effective preheating method for the three test cells, is also described here. After one year operation, an average EC of 12092 kWh/T-Al has been achieved on the three test cells. And in the last 6 months, the three test cells have been working steadily with cell voltage at 3.756 V, anode effects frequency (AEF) of 0.063, CE of 93.3% and EC of 12001 kWh/T-Al, compared with other 127 tradition cells in the line with cell voltage of 4.113V, AEF of 0.11, CE of 91.4% and EC of 13373 kWh/T-Al, respectively.It’s verified that because of the newly structure cathode that the cell voltage and Anode-Cathode Distance (ACD) in the test cells are decreased, and the flow velocity of metal pad is reduced consequently. During electrolysis, AE caused by local lower alumina concentration is decreased by moderate horizontal current to improve alumina solution rate in test cells. Moreover, higher CE is obtained because the weaker wave and more stable pad result in lower loss of aluminum.Voltage drop of molten bath in the test cells is lower than in traditional cells due to lower ACD. Enhanced insulation around the cell can decrease energy loss and achieve good energy balance under lower cell voltage, so the EE is increased.Measurement and study on the stability of metal pad in the 168kA test cells have shown that 50s of wave period is almost the same as that in traditional cells. However, the wave amplitude in the test cells is lower than that in traditional cells. When cell voltage of traditional cells decreases from 4.10V to 3.95V, variation amplitude of Voltage Drops(Equidistant (Ued)) measured in anode bars increases from 0.6 mV to 1.1 mV. This proves that the traditional cells cannot work normally below cell voltage of 3.95V. The anode current distribution in the test cell at 3.75V is more uniform than that in traditional cells at 4.10V because the former has lower anode current deviation (ADN).Upon study on cathode corrosion and penetration by molten bath and sodium in laboratory cell, it is found that bath penetrates predominantly into the pores of TiB2/C cathode, while sodium penetrates predominantly through the carbon lattice. Titanium in TiB2/C cathode can be dissolved into the bath. Sodium penetrates into the T16 cathode sample at 1.42mm/min1/2. Sodium expansion in TiB2/C composite cathode has the same characteristics as in those amorphous carbon cathodes during electrolysis, however, its expansion rate is smaller than in pure graphite cathode. And with the increasing of TiB2 content in TiB2/C composite cathode, the expansion rate decreases. Without aluminum, the cathode is penetrated by sodium first followed by bath, and the penetration of NaF is faster than bath.更多还原