Application of Refractories in Heating Furnaces and Reflection Furnaces

Heating furnace and reverberatory furnace are high temperature equipment, lining masonry can not be separated from refractory materials, reverberatory furnace is a traditional equipment to heat the furnace materials or complete oxidation, reduction and other smelting operations.

The large continuous heating furnace is a high-temperature furnace used to heat billets. There are many varieties, but the structure of the furnace body is composed of several parts such as the furnace top, furnace wall, furnace bottom, flue, and heat exchanger. According to the heating system of the continuous heating furnace, the heating furnace can be divided into a preheating section of 800~ 900 ° C (1100~ 1400 ° C) and a soaking section (1100~ 1400 ° C). There are also differences in the refractory materials used for different segmented working temperatures.

Refractory for heating furnace

I. Stove top

The roof of medium and small heating furnaces is mostly arched structure. Large modern heating furnaces adopt hanging flat top structure. The top of the heating furnace is a weak link, and its life is a sign of the life of the furnace.

The temperature of the furnace is about 1400 ° C, so it is mostly made of clay refractory materials. It can be made of clay bricks or castables or plastics to make the overall furnace top. Only high-temperature key parts use high-alumina refractory materials such as high-alumina bricks or phosphate high-alumina castables. The life of the furnace top is generally 10 years. In order to reduce the loss, a layer of thermal insulation is laid on the furnace top. The anti-arch part of the furnace top is mainly subject to thermal stress and gas erosion, and is sometimes impacted by the arch body. Generally, hanging brick tops, refractory castables or plastic products are used.

II. Furnace wall

The furnace wall is divided into side wall and end wall. The working lining of the side wall is mainly clay bricks, and the non-working layer is mainly refractory bricks. The side wall working lining of a modern large heating furnace can use high-alumina bricks, the non-working layer is clay bricks, and the light brick insulation layer. In order to save investment, refractory segments can be selected according to the temperature.

In recent years, the world has widely promoted the application of refractory castables and plastic lining, which have high service life and good energy saving effect.

Third, the bottom of the furnace

The total effective area of the heated steel at the bottom of the furnace. The bottom of the heating furnace includes a soaking bed, a preheating section and a sliding rail support structure for the heating section. To withstand the load, friction and vibration of the billet. The high temperature section is also eroded by iron oxide.

The soaking bed is usually made of magnesia brick or high alumina brick, or more than 370% of Al2O370 molten casting material or Zr02-doped zirconium aluminum.

The working lining of the furnace bottom of the heating section is the same as that of the preheating section. Generally, the same or similar material as the side wall is used, usually clay bricks. Sometimes high aluminum bricks can also be used to heat. The furnace bottom is generally solid. The guide rail is silicon carbide or water-cooled pipe, or cast iron beam.

Iv. flue

Flue lining is generally clay brick or refractory castable block, plus clay brick arch, or cover made of refractory castable cover.

Reflective furnace refractory

First, the reverberation furnace is composed of refractory bricks and metal skeleton, and the high-temperature flue gas of pulverized coal or heavy oil used in the smelting operation is heated or completed such as redox and other smelting operations.

Existing types of reflective furnaces: 1. Small furnace capacity 10~ 50 tons, furnace width 23 meters, length 3~ 5m, aspect ratio 1.5~ 3, molten pool depth 0.4~ 0.6m. When burning coal or lump coal, a combustion chamber (or fire chamber) is set on the furnace head. A firewall is built between the combustion chamber and the molten pool, and the firewall is 200~ 300mm higher than the liquid level of the molten pool. 2. Large-scale refined reverberatory furnace with a capacity of 100~ 400t. Length 10~ 15m, width 3~ 5m. Large reverberatory furnace does not have a combustion chamber, and directly burns pulverized coal, heavy oil or natural gas with a nozzle.

Basic structure of reverberatory furnace The reverberatory furnace is a horizontal rectangular furnace body, which consists of furnace base, furnace bottom, furnace wall, furnace top and metal support. The following is the basic structure of the reverberatory furnace.

The working principle of the reverberatory furnace is to use a one-stage method to deal with the smelting of miscellaneous copper, which is generally carried out in a fixed reflection furnace, so in fact the reverberatory furnace is both smelting and refining. And the principle is the same as that of the pyrometallurgical copper smelting method, but due to the high content of crude copper impurities, it also has its own characteristics in operation. The reverberatory furnace handles miscellaneous copper, and the entire refining process includes melting, oxidation, reduction. Slag removal. Pouring and other operations. The core of this process is oxidation and reduction. In the whole melting process, the key to oxidation and reduction is fast, the impurities in the copper liquid are completely removed, and efforts should be made to strengthen the oxidation process so that the Cu2O content in copper reaches saturation. The main impurities are: iron. Nickel. Zinc. Lead. Arsenic (Sb) and so on.

The failure mechanism of refractories for reverberatory furnaces is an important indicator reflecting the age of the furnace. Stress occurs on the inner wall of the copper furnace during use, and the damage factors are mainly as follows: 1. Chemical factors: 1) erosion caused by melt infiltration; these substances are mainly derived from slag and also contain impurities in scrap copper; 2) due to Erosion caused by the diffusion of SO2 gas in copper; 3) Oxygen pressure change or redox effect caused by low oxygen partial pressure; 4) Special circumstances, such as using seminal ore or rebuilding with furnace lining. 2. Thermal factors: 1) The temperature value determined by the exothermic reaction during furnace heating and smelting; 2) Serious intermittent thermal shock caused by abnormal charging or furnace operation; 3) The infiltration of copper in the molten pool. 3. Mechanical factors: 1) Wear caused by the movement of materials in the furnace (such as metal, scrap copper, slag, charge, dust-filled exhaust gas, etc.). Smelting. Smelting. Wear caused by reduction; 2) Impact stress generated by filling; 3) Stress generated by improper lining construction. Again, because the reverberatory furnace is an indoor flame furnace, the heat transfer in the furnace not only depends on the reflection of the flame, but also mainly through the radiation heat transfer of the furnace top, the furnace wall and the hot gas. The temperature in the furnace is 1800 ° C and the molten pool temperature is 1350 ° C. Therefore, the above-mentioned damage mechanism of the reverberatory furnace refractory requires the reverberatory furnace refractory to have corrosion resistance, thermal shock resistance and high compressive strength.

Reflective furnace roof with refractory materials for each part: furnace roof masonry can currently be divided into two forms: vault roof and hanging roof. The hanging ceiling is further divided into the hanging roof of the simple hanging furnace. Compression beam thrust hanging furnace roof. Vertical bar thrust hanging furnace roof. Furnace top thickness: generally between 230 and 380mm; reinforcement brick thickness is 380mm-460mm. Vault masonry uses silicon refractory bricks. The ceiling is made of magnesia-aluminum refractory bricks, but there are magnesia-chrome bricks that are directly combined with magnesia-chrome bricks and phosphate abroad. Vault roof: the advantages of using siliceous refractory brick masonry: simple structure, less steel, convenient construction period is short. Disadvantages: 1. Poor structural stability, when the vault is stopped, it is necessary to often pay attention to adjusting the looseness of the tie rod, and the labor intensity is large; 2. The life of the furnace roof is short, and the general service life is about 3 months; 3. When the furnace roof is repaired, the working conditions are not good. Purpose: Suitable for reflector furnace, the road width is less than 5m. Ceiling Ceiling: Made of magnesia-aluminum brick and high-aluminum refractory brick masonry. Advantages: The advantage of the ceiling is that it can reduce the height of the furnace roof arch, which is conducive to strengthening the heat transfer of the furnace gas to the furnace material, reducing the pressure of the furnace roof on the furnace wall, simplifying the furnace roof structure, and will not collapse in a large area, which is beneficial to prolong the furnace age. Disadvantages: 1. High cost and large amount of steel;

3. The structure is complex, the installation and adjustment operation remains unchanged, the labor intensity is high, and it is inconvenient to clean the furnace roof. Purpose: Suitable for smelting large-scale molten copper reflector furnaces. Furnace wall: Most of the inner walls of the molten reflector furnace use magnesia bricks. Some important parts, such as copper melting furnace burners and slag scraping ports, are built with chrome-magnesia bricks in order to prolong the service life. The insulation layer is usually built with clay refractory bricks. Copper melt reflector wall masonry method: The thickness of the upper molten pool is generally between 460 and 690mm. In order to prolong the service life of the furnace wall, the lower part of the molten pool gradually adopts the method of split-layer thickening. The thickness of the furnace wall can reach 900~ 1290mm, and the thickness of the lower wall of the end wall can reach 10001400mm. Due to the large temperature fluctuation of the furnace for periodic operation, in order to improve the stability of the furnace wall, the furnace wall is often built into an arc to prevent the furnace wall from collapsing in the furnace. Schematic diagram of the furnace wall structure: directly masonry the copper molten copper reflective furnace bottom on the basis of heat-resistant concrete. The base requires a temperature above 850 ° C. The bottom of the furnace is the bottom of the entire sintering furnace. The bottom of the sintering furnace is generally composed of upper and lower layers, and the total thickness is generally between 1100 and 1400mm. (115m) Clay refractory brick layer (about 50mm) Asbestos board and quartz sand (about 50mm) Magnesium-aluminum brick layer (thickness 345-460mm) Sintering layer (thickness 200-500mm). Note: The material of the sintering layer can be quartz stone and magnesium iron respectively according to the composition of the slag. Slag scraping port: There is a slag scraping port on the other side or the other end of the furnace wall, 400 × 400mm in size, forming a molten pool around the furnace wall below the slag scraping port. The material is the same as the furnace wall material. Copper discharge port: The side wall or end wall of the molten pool is equipped with a copper discharge port. The outer copper discharge port is two layers inside and outside. The inner layer size is about 150 × 150mm and the depth is 360~ 400mm. The outer wall is a round hole, about 25~ 30mm, 200mm deep, the outer layer of the copper discharge outlet is detachable for easy maintenance. The entire copper discharge port can be built with magnesia-chrome brick.

Masonry requirements for reverberation furnace:

1. Furnace bottom and molten pool masonry 1) Furnace bottom anti-arch refractory brick masonry should be less than 1~ 1.5mm. 2) The furnace wall brick seam below the slag line should be within 1~ 1.5mm, and the furnace wall brick seam above the slag line should generally not exceed 1.5~ 2.5mm. 3) All holes in the molten pool (such as slurry port, metal discharge port, etc.) should be wetted according to a kind of masonry. 4) The lateral expansion joint of the molten pool anti-arch is usually left on both sides of the anti-arch according to the expansion amount. The shape of the expansion joint should be determined according to the actual situation, and it is advisable to be wide and narrow at the bottom. Reverse arch longitudinal expansion joints can be concentrated at both ends, and can be dispersed for furnaces with larger lengths (one for every three refractory bricks in the upper anti-arch, that is, an expansion joint is set every 115mm * 3 = 345mm, The second layer of anti-arch can be divided into four pieces to leave one.

5) The molten pool masonry shall not produce other through joints except for flat joints.

6) The bottom of the furnace should be dried before the magnesia brick is laid.

7) The anti-arch of magnesium bricks is generally dry masonry. After the masonry is completed, the brick joints are swept with magnesium powder, or the fine magnesium powder is swept with tung oil to fill the brick joints.

2. Furnace top masonry 1) The furnace top is generally wet, and the thickness of the brick joints does not exceed 2mm. In use) when dry laying (mostly used for ceiling) all the reserved holes on the furnace top (such as feeding holes, instrument holes and copper plate holes, etc.) are wet.

2) Metallurgical furnace roof masonry is usually divided into two types: ring masonry and staggered masonry. The annular structure is relatively simple to construct and easy to maintain, so ring masonry is used for smaller spans and hanging furnace roofs. However, the structural strength and air tightness of the ring vault are poor, so staggered masonry is usually used when the furnace span is large.

1). The small reflective furnace uses expansion joints to build longitudinal joints on the furnace top, and the longitudinal cracks of the furnace top are generally concentrated at both ends of the furnace top, as well as at the junction of the horizontal arch and the inclined arch of the furnace top. There are two types of centralized and decentralized longitudinal expansion joints in the large-diameter reflective furnace top. The centralized retention method is to divide the furnace top into several sections according to the furnace temperature distribution, so that the expansion of the masonry on each inner furnace top is concentrated in one expansion joint. The length of the arch section in the high temperature area is usually 2 to 3 mm, the length of the arch section in the low temperature area is usually 4 to 5 mm, and the width of the expansion joint between the two arch sections is generally 20 to 40 mm. In order to avoid the furnace gas from emerging from the expansion joint when the furnace is turned on, a layer of refractory bricks is covered on the straight-through expansion joint of the furnace top. The advantage of centralized directly buried expansion joints is that the construction is convenient, but the expansion is not good, which affects the air tightness of the furnace top and is also one of the first damaged parts of the furnace top. Decentralized reservation means that 2 to 4 mm expansion joints (clamping cardboard) are left every 1 to 2 bricks. The dispersed expansion joint expands well and improves the air tightness of the furnace top, but the construction is difficult.

2) The reserved reflective furnace brick vault with lateral expansion joints on the top of the furnace does not leave lateral expansion joints under normal circumstances, and the lateral expansion is adjusted by the elastic tie rod, so the thread length of the tie rod should leave a certain space to adapt to the needs of adjusting the tie rod. The top of the large reverberatory furnace is suspended, and a "radial" expansion joint is reserved on the top of the furnace, and cardboard is sandwiched between the two refractory bricks.

3. The distance between the tie rod on the furnace and the brick masonry on the furnace top should be less than 0.4mm. 2) The height of the civil foundation of the electric furnace should avoid forward errors. The side of the foundation should be flat, which is convenient for installing columns.

In order to improve the service life of the furnace, refractory materials should be reasonably selected according to the degree of local damage in the furnace.