The main refractory of copper smelting is flotation concentrate, which is suitable for treatment in reverberatory furnace. Therefore, with the development of flotation method, reverberatory furnace has been widely used.
There are two methods for smelting matte in reverberatory furnace: raw Concentrate Smelting and calcine smelting.
① When copper sulfide concentrate is smelted directly in the reverberatory furnace, the basic process of smelting is sulfide melting and slagging of gangue. This smelting method is called raw Concentrate Smelting.
The advantages of smelting raw concentrate are that the roasting system is cancelled, the investment cost is reduced, the amount of smoke and dust is less, the copper content in slag is low, and the metal yield can be increased by 3% ~ 3.5%; The disadvantage is that because the concentrate contains water, it consumes more fuel during smelting and the melting speed is slow, so the productivity is low.
② When the matte grade obtained by direct smelting of copper sulfide concentrate is too low, such as less than 20%, it must be roasted in advance to convert it into calcine containing a certain amount of metal oxide. When calcine is added to the reverberatory furnace for smelting, in addition to sulfide melting out and gangue slagging, there is also the mutual reaction between sulfide and oxide. This smelting method is called calcine smelting.
Technological process and working characteristics of copper smelting in reverberatory furnace
In addition to desulfurization and removing some impurities, roasting can also make the charge well mixed and preheated in the roasting furnace, and all the water evaporates. Adding hot calcine into the reverberatory furnace can improve the smelting conditions of the reverberatory furnace. Therefore, the productivity of the reverberatory furnace for smelting calcine is higher than that of smelting raw concentrate. However, due to the development of beneficiation technology, the grade of copper concentrate is improved and the raw concentrate smelted in reverberatory furnace is increased.
The reverberatory furnace is lined with refractory bricks. There is a burner for heating at one end and a flue for discharging furnace gas at the other end. The mixed furnace charge composed of concentrate or calcine, return material and flux is added through the feeding ports on both sides of the furnace top to form a material slope in the furnace. The material slope is immersed in the molten pool and close to the inner surface of the furnace wall and bottom. The fuel burns on the surface of the furnace charge in the furnace, so as to heat, melt, slag and form matte.
The characteristics of matte smelting in reverberatory furnace are as follows.
① The charge immediately enters the high temperature zone of 1773 ~ 1823k and melts quickly at the place where it is added. Therefore, the charge should be mixed well in advance, with the particle size less than 3 ~ 5mm, so as to obtain good smelting technical and economic indicators.
② The furnace is in a slightly oxidizing or neutral atmosphere. In order to obtain higher temperature in the furnace, fuel combustion is carried out under limited excess air, which is 10% - 15%.
③ Low heat utilization. During the smelting of reverberatory furnace, the furnace gas does not pass through the charge, but only flows through the charge surface. Therefore, only a small part of the charge is in contact with the furnace gas, so that the utilization rate of heat is only 25% - 30%.
④ The oxygen content of furnace gas is small, generally less than 1.5%, and the contact with furnace charge is limited. Therefore, during smelting, there is no obvious chemical action between gas and charge, which is mainly the interaction between solid charge and liquid charge.
⑤ The furnace material forms a material slope along the side wall, so that the furnace wall is not corroded by slag.
Since the first matte smelting reverberatory furnace was completed and put into operation in 1899, it has gradually replaced the position of blast furnace in Pyrometallurgical copper smelting and become the main copper smelting method. Since then, the reverberatory furnace has dominated pyrometallurgical copper smelting for a long time. This situation is formed because the reverberatory furnace can basically meet the needs of production development.
The advantages of reverberatory furnace are solid and reliable, long service life, high productivity, easy operation and great adaptability to fuel and raw materials. The disadvantage is that the reverberatory furnace uses the radiant heat of high-temperature flame generated by fuel combustion for smelting, which has low thermal efficiency, high fuel consumption, large amount of flue gas, low S02 content in flue gas (about 1%), can not be recovered economically, and is discharged into the atmosphere, resulting in environmental pollution; In addition, the reverberatory furnace covers a large area and the construction cost is high.