First, the mixing smelting mechanism Mechanism smelting reduction mechanism comprises mixing bismuth oxide, bismuth sulfide substitution mechanism, melting the reaction mechanism. (1) Reduction mechanism of cerium oxide. Carbon monoxide is the only product of carbon combustion in the high temperature range of mixed smelting. Each metal oxide free enthalpy change with temperature relationship shown in Fig. Figure 1 Free map of metal oxides The stable order of each metal oxide in Fig. 1 is that the oxide having a low linear position is stable, and the linear position is unstable. At the same time, a metal oxide having a high linear position and a high linear position can be reduced, such as CO 2 to reduce Cu 2 O, Bi 2 O 3 , PbO, etc. The reduced metal impurities, into the thick part of bismuth, a portion of the copper sulfide into the ice, when the reducing agent is sufficient, the possibility of re-oxidation of the slag is very small. (2) The replacement mechanism of strontium sulfide. In the mixed smelting high temperature range, the relationship between the free enthalpy of various metal sulfides and temperature is shown in Fig. 2. Figure 2 Free stencil of metal sulfide As can be seen from Fig. 2, the order of stability of various metal sulfides at a given temperature is stable at a low linear position, and the metal sulfide having a high linear position can be replaced. Therefore, iron can replace Ag 2 S, Bi 2 S 3 , PbS, and the like. Since iron scrap is cheap and easy to obtain, iron scrap is used as a displacer, and the reaction is: When the amount of iron filings is insufficient, the replaced impurity metal can replace the strontium sulfide: Ferrous sulfide is the main component of the composition of matte, and other impurity metal sulfides are dissolved therein. (3) Reaction melting mechanism. Due to the presence of both strontium sulfide and strontium oxide in the charge, reaction smelting is inevitable: At the appropriate temperature, the reaction is accompanied by a small amount of basic barium sulfate: When the iron powder and blended with a sufficient amount of coal, melting the mixed precipitate predominantly smelting and reduction smelting, melting a small proportion of the reaction. This can be illustrated by the fact that smelting produces a large amount of ferrous sulfide-based matte and the sulfur dioxide concentration in the furnace gas is extremely low. Second, the thermal principle of mixed smelting The heat conduction in the metallurgical furnace includes physical heat sensible heat, chemical reaction heat between materials and combustion heat of the fuel. The physical sensible heat brought into the furnace with the charge and the chemical reaction heat between the components of the charge are not large, and the total heat income is Only 15% to 20% of the heat, and the remaining 80% to 85% of the heat comes from the burning of fuel. The combustion of the fuel produces a high temperature. When the hot gas flows in the furnace, the heat is directly transmitted to the charge, but the heat is indirectly transmitted to the charge through the hot roof and the furnace wall. In metallurgical furnaces, conduction, convection and radiant heat transfer often occur simultaneously, while radiation heat transfer is dominant. (1) Conducting heat transfer. Conductive heat transfer is calculated according to Fourier's law, namely: Where Q- heat flow in the x direction (joules per hour); F- heat transfer surface perpendicular to the heat flow (m 2 ); Λ-thermal conductivity, (Joules/m·hr·°C). The Fourier equation shows that the conduction heat transfer is related to the heat transfer surface and the temperature gradient. (2) Convective heat transfer. Convection heat transfer is expressed by Reynolds' law: Q pair = 523μC i w 0 (T 1 -T 2 )F (joules per hour) Where Q is - convective heat (Joules); --flow frictional resistance coefficient; C i - specific heat of the furnace gas (joules / gram · degrees); w 0 - furnace gas velocity (m/h) at 0 ° C and 1 atm (101,325 Pa); T 1 - furnace gas absolute temperature (K); T 2 - the absolute temperature (K) of the surface of the charge; F-charged surface area (m). (3) Radiation heat transfer. Radiation heat transfer is calculated according to the quadrilateral law: Where Q radiation - radiation heat (joules); C-radiation heat transfer coefficient; F-burner heated surface area (m 2 ); T 1 - furnace gas absolute temperature (K); T 2 - the absolute temperature of the surface of the charge (K); T-time (hours). It can be seen from the above formula that increasing the furnace gas temperature is a key factor in increasing the radiant heat. In fact, the loss of radiant heat should be considered in the radiation formula. The radiant heat loss through the metallurgical furnace door opening can be calculated by the following formula: Q loss - radiant heat loss (Joules): T-furnace gas absolute temperature (K); F-heated area (m 2 ). The fuel used in the refining and metallurgical furnace is mainly bituminous coal and heavy oil. The fixed carbon content in bituminous coal is 45%-65%, and its calorific value: The combustion process of bituminous coal in the metallurgical furnace can be discussed according to the Budor reaction. Budor passes the reaction CO 2 + C Table 1 Reaction CO 2 + C = 2CO gas equilibrium composition at high temperature It can be seen from Table 1 that in the metallurgical furnace smelting high temperature (1250 ° C), CO is the only product of carbon combustion, and when excess air is present, CO will continue to burn into CO 2 . The thermochemical equations for carbon combustion can be divided into incomplete combustion and complete combustion: The former formula is a reaction in which carbon and oxygen are incompletely combusted to form CO, and the latter formula is a reaction in which carbon and oxygen are completely combusted to form CO 2 . Comparing the above two equations, the thermal effect of complete combustion of carbon is more than three times that of the incomplete combustion of carbon. Therefore, in order to obtain a high temperature in a metallurgical furnace, complete combustion of carbon is required. Therefore, when air is blown in, the amount of excess air should be considered first to completely burn the carbon to obtain a high temperature. Compared with coal, the heavy oil has high calorific value, is easy to burn completely, has less ash and has high flame brightness. Therefore, liquid fuel is commonly used in metallurgical furnaces. The properties of heavy oil are listed in Table 2. Table 2 Properties of fuel heavy oil The approximate components of heavy oil are listed in Table 3. Table 3 Approximate composition of heavy oil (%) The thermal properties of heavy oil used in metallurgical furnaces for fuel are limited to 0.5%, 2.0% and 3.5% (low sulfur, sulfur and high sulfur heavy oil, respectively). The thermal properties are listed in Table 4. When heavy oil is used as fuel, atomization of fuel is important. Atomization is usually achieved by means of a nozzle. There are two explanations for the mechanism of liquid fuel atomization: capillary wave theory and cavitation theory. Table 4 Thermal properties of heavy oil The atomized capillary wave theory believes that ultrasonic waves are generated on the surface of the vibrating liquid, and the peak formed by the vibration amplitude is separated from the liquid surface by the droplet form. As the vibration frequency increases, the diameter of the fuel droplet decreases, and the ultrasonic wave Fuel droplets of several microns in diameter can be obtained. The atomization cavitation theory holds that in the thin layer of liquid fuel, bubbles filled by liquid vapor form cavitation, and the destruction of these bubbles forms a strong shock wave, which destroys the stability of the liquid fuel surface and causes it to atomize. Although heavy oil fuel is superior to solid fuel, it will also produce coking residue after combustion. Taking heavy oil No. 100 as an example, the residue rate after combustion can reach 19%, which will affect the fuel combustion process. The combustion of the atomized heavy oil can be decomposed into a complete combustion stage of the pre-fire preparation stage and the coke residue. The pre-fire preparation phase consists of heating the fuel droplets and starting to boil and evaporate until a fuel-air combustible mixture is formed and heated to the ignition temperature. It was determined that the preparation period of heavy oil before ignition was 60 microseconds. The complete combustion phase of the coke residue includes combustion of the fuel droplets, free carbon precipitation in the gas phase, and combustion of the carbon particles in the flame. The carbon residue generated by the combustion of the fuel mist is 25 to 150 micrometers in diameter, and the carbon black precipitated in the gaseous hydrocarbon is only about 0.01 to 0.05 micrometers in diameter, and the carbon black particle size formed by the mountain is very different. Therefore, thermal decomposition of the gas in the flame at the time of combustion is important. When heavy oil is burned, the degree of decomposition is 1% to 2%. The main measures to strengthen the combustion of heavy oil are as follows: Improve the atomization quality of the fuel and select the appropriate nozzle by calculation: The multi-stage combustion of the fuel is carried out, that is, the air is supplied in sections to ensure that the heavy oil can be completely burned after atomization: The high temperature gas is recycled, and the free radicals contained in the high temperature gas stream returning to the ignition zone of the fuel-air mixture interact with the hydrogenating agent and the hydrocarbon molecules to form a chain reaction active center, and the combustion products are recycled to the flame root. Not only strengthens the thermal process, but also stabilizes the flame; The strengthening of the mixture to achieve turbulence of the air or combustion product gas stream is an effective method for enhancing the mixing of fuel and air and enhancing combustion; Others, such as reverse flow combustion of fuels, etc., these measures to enhance the combustion of heavy oil should be considered in the design of metallurgical furnace heavy oil nozzles in order to explore potential and strengthen the combustion process. Return Rollers Return Rollers,Conveyor Belt Return Rollers,Return Rollers For Conveyors,Return Idler Roller SHIJIAZHUANG VITURE IMPORT AND EXPORT TRADING CO.,LTD , - Temperature gradient (°C/m):
2CO research found that the reaction is reversible, the direction of the reaction and the degree of equilibrium and stability are related to the equilibrium composition of the gas. Please refer to Table 1.