Refractories for lead blast furnaces

Lead smelting has two types of processes: first, lead and zinc are smelted separately as independent raw materials; Second, lead and zinc as co-ore, through smelting at the same time to obtain crude lead and crude zinc or coarse lead and high zinc soot (wet zinc extraction raw materials).

The methods of producing metal lead and zinc from ore or concentrate can be divided into pyrometallurgy and hydrometallurgy. The smelting of lead is almost all pyrometallurgy, and the hydrometallurgy is still in the trial stage. The traditional sintering roasting ---- blast furnace smelting process is widely used in pyrometallurgical lead smelting. This process accounts for about 85% of the world's lead production. The lead produced by lead-zinc closed blast furnace is about 10%, and the remaining 5% is obtained from the direct smelting of concentrate. The old methods of direct smelting include precipitation smelting and reaction smelting. These two smelting methods have low metal recovery rate, small output and bad working conditions, which are not used in large lead smelting plants. Since the 1980 s and began to direct lead smelting method of industrial applications mainly oxygen flash smelting Kivcet method and oxygen bottom blowing smelting QSL method, it will be the traditional sintering roasting - reduction smelting process of two method to merge in a device, improve the utilization rate of sulfur and heat and simplify the production process, improve the environment, other smelting method such as rich oxygen top-blown smelting method, SKS method is to simplify the process, improve the environment, but it is in the improvement of the industrial production or build a demonstration plant stage.

The traditional pyrometallurgical process of lead smelting is sintering - blast furnace reduction smelting. Almost all existing lead production plants in China adopt this traditional process. In this method, lead sulfide concentrate is roasted and quickly sintered, and then reduced and smelted in a blast furnace to produce crude lead.

Sintering - blast furnace lead smelting method has the advantages of stable and reliable technology, strong adaptability to raw materials and good economic effect. The disadvantage is that the concentration of SO2 in sintering flue gas is low, and it is difficult to realize the utilization of SO2 by conventional acid production process, which seriously pollutes the atmospheric environment. In addition, the heat generated in the sintering process can not be fully utilized, the dust points are scattered, and the working conditions are poor.

There are two kinds of blast furnaces for lead smelting: round furnace and rectangular furnace.

Lead blast furnace is composed of furnace base, furnace top, hearth, discharge product device, tuyerian device, water pipe system, etc., which is divided into two kinds of structure with hearth and without hearth. When the smelting products are separated in the furnace, the hearth is set; A hearth is not needed if the smelting product is separated by precipitation outside the furnace. The hearth is placed on the hearth base and constructed with refractory material.

The top temperature of the lead blast furnace is 400~500℃, mostly the closed top. The furnace is full water jacket, and the refractory material is only used in the throat and hearth. Fast lead concentrate sintering and coke, flux and other solid materials from the top to join, furnace body side tuyere drum into the high pressure air, and the materials are melted down, oxidation and reduction reaction, such as complete smelting process, liquid metal, matte, slag from the mouth or throat hearth bottom the stove, smoke, dust, etc. From the flue gas outlet.

The main components of slag are FeO, SiO2, CaO, and its typical slag composition is FeO39%, SiO2 27%, CaO14%, ZnO10%. Under the action of high temperature, the chemical erosion of slag on the throat and hearth is particularly serious. Therefore, the throat refractory materials mainly use magnesium brick, magnesium chrome brick, aluminum chrome brick, its slag resistance, anti-erosion performance is good, in the throat also has a special small water jacket to protect the part of the brick. The side wall of the hearth and the upper part of the hearth bottom are laid with magnesium brick, the outer side and the steel plate part of the hearth bottom are laid with clay brick, and the hearth bottom is laid with reverse arch.

As mentioned above, the smelting products of the blast furnace with hearth are mainly separated by precipitation in the furnace, but the discharged slag also contains a small amount of metal and matte particles, which need to be further separated and recovered. No hearth blast furnace, smelting products are separated outside the furnace, the separation equipment usually adopts electric heating front bed. The electric heating front bed is an important unit operation process in the lead smelting process of blast furnace. It is used to lead slag melt temperature, so that lead and slag can be clarified separation, improve the direct yield and recovery of metal is an important step.

Electric heating before bed is one of the types of ore heat furnace, much to oblong, in order to ensure the effective separation of lead slag and metal within the bed before and escape from the furnace slag, smoothly through the insert electrodes in the slag, relying on the electrode and slag formation of the micro arc boundary surface and the melt resistance of the dual role, make the electric energy into heat energy, the temperature of 1300 ℃, the heat preservation of lead slag and precipitation separation inside before bed, to ensure that the slag discharge temperature greater than 1150 ℃, temperature, discharge lead in 800 ~ 1000 ℃. Lead is released from the siphon port.

Electric heating before bed in operation, furnace slag convection movement caused by electric arc of high temperature molten slag slag flushing furnace wall, the slag slag line caused by volatility, making furnace mechanical erosion is serious, especially slag line parts bear the chemical erosion of alkaline slag, furnace wall damage soon, for lead slag notch and out of the mouth, except by the scouring effect, is better than the furnace wall materials were stronger oxidation and thermal stress. At present, most of the refractory materials used for the electric heating front bed of lead blast furnace are magnesia-chrome brick and chrome slag block, etc., and their service life can reach more than 1 year, and the use effect is quite good. The furnace wall of electric heating front bed in a nonferrous metal company is constructed by high chromium magnesium-chromium brick, and its service life is up to 2 years.