冶炼有色金属使用的耐火材料工艺(四）

   炼锌用耐火材料炼锌用耐火材料有：炼锌焙烧炉，还原蒸馏炉和精馏设备用耐火材料。

  （1）焙烧炉，一般焙烧温度为1070~1120℃，一般用黏土砖和高铝砖即可满足要求。

  还原蒸馏炉，是生产金属锌或粗锌用的热工设备。先在焙砂中配入 29%~33%的优质焦煤，焙烧炉烟尘灰及适量的结合剂，经混合并压制成团块，然后在800℃的条件下，形成具有一定强度的团块，即为还原蒸馏炉的原料。

  竖罐蒸馏炉：由竖式蒸馏罐、燃烧室和空气道等部分组成。蒸馏罐一般由传热性能好和强度高的黏土结合碳化硅砖砌筑。我国葫芦岛锌厂采用碳化硅波纹砖砌筑蒸馏罐内壁，比用标型砖增加热辐射面18%左右，同时将砖砌成竖沟状，减弱了气流上升阻力，降低了炉内压力，加快了反应速度。当罐内壁蚀损较大，或局部出现孔洞，可用碳化硅质喷涂料进行热喷补。燃烧室工作温度为300~1360℃，工作层用硅砖砌筑，其余部位用黏土砖砌筑。冷凝器，水平底和边墙工作层用高铝砖砌筑，其他部位用黏土砖砌筑。冷凝器内装有转子，转子用轴由石墨质材料制作，用碳化硅材料能显著提高寿命。

  电热蒸馏炉：主要由圆筒形炉体，冷凝器和电极加热装置等部分组成。该炉易损部位的工作层用碳化硅砖砌筑，其余各部位工作层用黏土砖砌筑，非工作层用黏土隔热砖砌筑，使用寿命较高。

  （3）精馏设备，由熔化炉，精炼炉，燃烧室，精馏塔和冷凝器等组成。

  精馏塔中部，即蒸馏室两侧设有燃烧室和换热器，塔体上部设有冷凝器，借助通道与铅塔和镉塔及熔化炉相连。塔内一般安装40~60块塔盘，分为蒸馏盘和回流盘两种，均用碳化硅质材料制作，厚度为30~50mm，冷凝器和各种通道等部位工作层普遍用碳化硅砖砌筑；熔化炉，精炼炉，精馏塔的燃烧室及换热器和下延部等部位的工作层，一般用黏土砖砌筑，非工作层用漂珠砖等隔热砖砌筑，塔壁用碳化硅砖砌筑，粗锌连续精馏精炼设备的使用寿命，取决于碳化硅质塔盘的工作寿命，其损毁主要是温度波动及化学侵蚀所致，铅塔寿命一般为1~2年，镉塔寿命为2~3年。

  目前，有色冶金的发展趋势是不断采用新工艺和新技术，更新炉窑设备，强化冶炼操作，提高生产率。因此随着有色冶金炉窑大型化和高效化，使用的耐火材料品种扩大，质量提高，数量增大。

  一般情况下，有色冶金用耐火材料占耐火材料总消耗量的 2%~6%，其中黏土砖占25%，高铝砖占5%~16%，碱性砖占10%~17%。使用不定形耐火材料的比例在不断上升。

  有色金属炉衬的损毁机理，主要是熔融金属，金属氧化物或熔渣的浸透和温度应力作用造成的。在炉窑衬体中存在温度梯度，当熔融金属，氧化物或熔渣沿着衬体的缝隙或气孔渗透到纵深内部时，则发生3种情况：

  1）熔融金属发生氧化，还原或形成低熔点矿物，致使衬体遭到侵蚀，或产生龟裂剥落；

  2）熔融金属或氧化物发生沉积，造成衬体膨胀而塌落；

  3）强碱性熔融金属或熔渣流动性很强，对衬体的冲刷和侵蚀较为严重。

  铜的熔点为1083℃。在冶炼过程中，熔融金属铜向衬体内部渗透，发生氧化并伴随着体积膨胀。当铜氧化成CuO₂时，体积增大0.64倍，氧化成CuO时，则体积增大0.75 倍。由于体积的不同变化，致使内衬的组织结构产生龟裂、裂缝，甚至发生剥落。

  在一定的温度下，铜的氧化物能与耐火材料内衬的某些氧化物发生反应而生成液相，例如氧化铜与SiO₂的共熔点为1060℃，与MgO的共熔点为1135℃，与Cr₂O₃的共熔点为 1560℃以上。由于低熔物质的形成，破坏了炉衬的组织结构，并发生熔蚀现象，降低了使用寿命。另外，在有色金属冶炼过程中，熔渣里含有大量的铁硅酸盐，对镁砖侵蚀较严重，对含铬的尖晶石的镁铬砖侵蚀要轻一些，因此有色金属熔炼炉普遍使用镁铬砖做内衬。

  金属铜，锌，特别是铅，最容易渗透到砌体中，在氧分压较低的炉衬冷面不断发生沉积，使砌体向炉膛内鼓胀而损毁。如果炉衬损毁较严重时，熔融物的渗透可造成泄漏事故，直接影响生产。

  在冶炼过程中，由于炉内温度的骤然变化，可能使炉衬产生龟裂以及发生剥落。另外，在适当的温度下，废气中的 SO₂对碱性砖的方镁石相互发生作用，生成含镁的硫酸盐，使砌体的组织结构产生崩溃，降低使用寿命。在一般条件下，与金属熔液和熔渣接触的炉衬部位，目前普遍采用高级碱性砖，碳化硅砖，氮化硅砖或石英砖等材料砌筑，使用效果较好。

Refractory Materials for Smelting non-ferrous metals (4)

  Refractory materials for zinc smelting Refractory materials for zinc smelting include: refractory materials for zinc smelting baking furnace, reduction distillation furnace and rectification equipment.

  (1) Baking furnace, the general roasting temperature is 1070~1120℃, the general use of clay bricks and high aluminum bricks can meet the requirements.

  Reduction distillation furnace is a thermal equipment for the production of metal zinc or crude zinc. First, 29%~33% of high quality coking coal is added to calcine, calciner ash and an appropriate amount of binder are mixed and pressed into clumps, and then clumps with a certain strength are formed under the condition of 800℃, which is the raw material of the reduction distillation furnace.

  Vertical distillation furnace: consists of a vertical distillation tank, a combustion chamber and an air passage. The distillation tank is generally constructed of clay with good heat transfer performance and high strength combined with silicon carbide bricks. Huludao Zinc plant in China uses silicon carbide corrugated brick to build the inner wall of the distillation tank, which increases the thermal radiation surface by about 18% compared with the standard brick. At the same time, the brick is laid in the vertical groove, which reduces the resistance of the air flow rising, reduces the pressure in the furnace and speeds up the reaction speed. When the inner wall of the tank is corroded greatly, or there are local holes, silicon carbide spray coating can be used for hot spray repair. The working temperature of the combustion chamber is 300~1360℃, the working layer is built with silicon brick, and the rest is built with clay brick.

  The condenser, the horizontal bottom and the working layer of the side wall are laid with high aluminum bricks, and the other parts are laid with clay bricks. The condenser is equipped with a rotor, the rotor shaft is made of graphite material, the use of silicon carbide material can significantly improve the life.

  Electric distillation furnace: It is mainly composed of cylindrical furnace body, condenser and electrode heating device. The working layer of the vulnerable part of the furnace is built with silicon carbide brick, the other parts of the working layer is built with clay brick, and the non-working layer is built with clay heat insulation brick, which has a high service life.

  Rectification equipment, consisting of melting furnace, refining furnace, combustion chamber, rectification tower and condenser.

  The middle part of the distillation tower, that is, the combustion chamber and heat exchanger are provided on both sides of the distillation chamber, and the upper part of the tower is provided with a condenser, which is connected with the lead tower and cadmium tower and the melting furnace by means of a channel. Generally installed in the tower 40~60 tray, divided into two kinds of distillation tray and reflux tray, are made of silicon carbide materials, thickness of 30~50mm, condenser and various channels and other parts of the working layer is generally built with silicon carbide brick; The working layer of the combustion chamber and heat exchanger of the melting furnace and the lower extension part of the rectification tower is generally built with clay brick, the non-working layer is built with thermal insulation brick such as floating bead brick, and the tower wall is built with silicon carbide brick. The service life of the crude zinc continuous rectification and refining equipment depends on the working life of the silicon carbide tray, and the damage is mainly caused by temperature fluctuations and chemical erosion. Lead tower life is generally 1 to 2 years, cadmium tower life is 2 to 3 years.

  At present, the development trend of non-ferrous metallurgy is to constantly adopt new processes and new technologies, update furnace equipment, strengthen smelting operations, and improve productivity. Therefore, with the large-scale and high-efficiency of non-ferrous metallurgy furnaces, the variety of refractory materials used is expanded, the quality is improved, and the quantity is increased.

  Under normal circumstances, non-ferrous metallurgy refractories account for 2% to 6% of the total consumption of refractories, of which clay bricks account for 25%, high-aluminum bricks account for 5% to 16%, and alkaline bricks account for 10% to 17%. The proportion of amorphous refractories used is increasing.

  The damage mechanism of non-ferrous metal lining is mainly caused by the penetration of molten metal, metal oxide or slag and the action of temperature stress. There is a temperature gradient in the furnace lining, and when molten metal, oxide or slag permeates deep inside along the gaps or pores in the lining, three things happen:

  1) The molten metal oxidized, reduced or formed a low melting point mineral, resulting in erosion of the lining, or cracking and spalling;

  2) Molten metal or oxide deposition, causing the lining to expand and collapse;

  3) Strong alkaline molten metal or molten slag has strong fluidity, and the erosion and erosion of the lining are more serious.

  The melting point of copper is 1083℃. In the smelting process, the molten metal copper penetrates into the lining, and oxidation occurs along with volume expansion. When copper is oxidized to CuO₂, the volume increases by 0.64 times, and when oxidized to CuO, the volume increases by 0.75 times. Due to the different changes in volume, the structure of the lining cracks, cracks, and even spalling.

  At a certain temperature, copper oxides can react with some oxides of refractory lining to form a liquid phase, such as copper oxide and SIO2 eutectic point is 1060℃, eutectic point with MgO is 1135℃, and Cr₂O₃ eutectic point is more than 1560℃. Due to the formation of low melting material, the structure of the lining is destroyed, and the corrosion phenomenon occurs, and the service life is reduced. In addition, in the process of non-ferrous metal smelting, the slag contains a lot of iron silicate, the erosion of magnesia brick is more serious, and the erosion of magnesia chrome brick of spinel containing chromium is lighter, so the non-ferrous metal melting furnace generally uses magnesia chrome brick as the lining.

  Metal copper, zinc, especially lead, the most easy to penetrate into the masonry, in the low oxygen partial pressure of the furnace lining cold surface is constantly deposited, so2 that the masonry to the furnace swelling and damage. If the furnace lining is seriously damaged, the penetration of the melt can cause leakage accidents and directly affect the production.

  In the process of smelting, due to the sudden change of temperature in the furnace, the lining may crack and flake. In addition, at the appropriate temperature, SO₂ in the exhaust gas interacts with the cubic magnesite of the alkaline brick to generate magnesium sulfate, which causes the organizational structure of the masonry to collapse and reduces the service life. Under normal conditions, the lining parts that are in contact with metal molten liquid and molten slag are generally laid with materials such as advanced alkaline brick, silicon carbide brick, silicon nitride brick or quartz brick, and the use effect is good.