The refractory bricks of the waste heat utilization equipment (represented by the regenerator) have a grid, a grate, the top of the regenerator, a side wall and a middle partition wall. The temperature of the brick body of the regenerator changes with time. The amplitude of temperature fluctuation is larger at the bottom of the grid body of the regenerator (300~500℃). The top layer of the lattice body is relatively small (150~300℃). The highest temperature of the brick body: about 1350℃ for the top layer of the lattice body and about 600℃ for the bottom layer of the lattice body.
The gases in contact with the refractory bricks in the regenerator include air, producer gas, natural gas and flue gas. The flue gas contains solid powder (such as alkali powder, borax, lead dust), batch decomposition products (such as the decomposition products of various salts, chlorides, and fluorides), coal particles, and fuel combustion products (including SO₂, V₂O₅ Corrosive gas) and so on.
According to the nature of the atmosphere, there are oxidizing and reducing. If the regenerator is operated with "anti-burning", the brick body will also directly contact the high-temperature flame.
Under the above-mentioned working conditions of the regenerator, the brick body is subjected to three functions: thermal, chemical and mechanical. The heat effect is high temperature burning and thermal shock, which causes the brick body to melt, soften and generate thermal stress, which causes the brick body to crack. The chemical action is the erosion of the above-mentioned solid powder and gas and the contact reaction between lattice bricks of different properties. These will cause the brick body to melt into a liquid phase, crystal growth, crystal form transformation, structural cracking and loosening, and even peeling. The chemical action will intensify under changes and atmosphere changes. The mechanical action is mechanical load. According to estimates, the total weight of a regenerator grid body is 40-50t, and the unit load of the bottom layer of the grid body is 8-10t/m². With electric melting, zirconium, alkaline, and high-density materials The expansion of the use of the brick will increase the load value, and the heavy load at a certain temperature will cause the brick body to deform, crack or even collapse.
Due to the difference in temperature at the height of the regenerator and the different working conditions caused by the temperature, in addition to the above three common functions at different heights of the regenerator, each has its own use characteristics. Usually, it is roughly divided into the upper part of the lattice body (1100~1300°C), the middle part of the lattice body (80~1100°C), the lower part of the lattice body (50~800°C), and 3 chrysanthemums.
The use characteristics of the upper part of the lattice body are: high temperature burning, erosion of solid powder, erosion of SO₂, V₂O₅ and other gases (formation of ettringate, etc.) and crystal growth (such as periclase, spinel recrystallization), etc. . It can make checker bricks melt, burn or burst.
The use characteristics of the middle part of the lattice body are: alkali, boron, fluorine and other volatile components solidify and deposit in the brick holes. The deposits such as (Na₂SO₄, NaF, etc.) strongly corrode the lattice bricks, and repeat solidification and melting (such as Na₂SO₄, NaF, etc.) with temperature fluctuations. The repeated solidification and liquefaction of Glauber's salt), it will loosen the internal structure of the checker brick, leading to cracks or cracks.
The common ones are: Alkaline powder and alumina-silica bricks generate nepheline phase (reaction formula: 3Al₂O₃·2SO₂+Na₂O→Na₂₂O·Al₂O₃·2SO₂[nepheline]+2Al₂O₃, Al₂O₃+2SO₂+Na₂O→Na₂O·Al₂O₃₂· 2SO₂[nepheline], the formation temperature of nepheline phase is above 730℃), the volume increases, causing the brick to crack or peel off. V₂O₅ acts as a catalyst at 950~1150℃ to oxidize SO₂ to SO₃, and react with periclase (MgO) to form MgSO4, causing bricks to expand, crack, and peel off. The Fe₂O₃ contained in the brick will change when the atmosphere properties change, causing the brick to crack and reduce its strength. In addition, it is necessary to pay due attention to the mechanical load at high temperature, because the bulk density of the currently used upper checker bricks is relatively large.
The use characteristics of the lower part of the lattice body are: the combustion-supporting air just enters, the temperature fluctuates greatly, and it bears almost all the weight of the checker bricks, and the mechanical load is large, which will cause the checker bricks to crack and deform. In addition, condensates of various salts (such as carbonates and sulfates) and compounds (such as fluorine and boron compounds) may deposit and block the grid pores. It will also generate nepheline, causing flaking.
The use characteristics of the regenerator wall are the same as that of the grid on the same horizontal plane. The intermediate partition wall, especially the intermediate partition wall between the air and gas regenerators is very important, and its use conditions are also heavy.
Choose the material according to the characteristics of use. It can be seen from the above analysis. The selection of materials for the regenerator can be attributed to the selection of checker bricks.
The general requirements for checker brick materials are: high temperature resistance, erosion resistance, thermal shock resistance, large heat capacity, and large thermal conductivity. The checker bricks of the upper, middle and lower parts are selected according to different usage characteristics.
In the past, the selection of checker bricks was high alumina bricks for the upper and middle parts, and clay bricks for the middle and lower parts. High alumina bricks can withstand high temperatures, and have general corrosion resistance and thermal shock resistance. The main disadvantage is that it is easy to form nepheline phase with alkali powder, causing swelling and cracking and peeling. It is better to use anti-stripping high alumina bricks. Clay bricks are inexpensive and have good thermal shock resistance, but they are not resistant to high temperatures, corrosion, and easy to burn, and nepheline phases are also formed. The service life of high alumina bricks and clay bricks is not long (no more than two years).
Currently, there are two major series of checker bricks.
One is the alkaline material series, which is highly regarded by Japan. Most of them use the upper, middle, and lower three-stage type (the so-called three-stage, that is, three different materials are used). The three-stage material is as follows. The upper part (accounting for 15%-20% of the height of the entire lattice body), contains MgO: 95%-98% high-purity magnesia bricks or fused spinel bricks. These materials have good corrosion resistance, good permeability resistance, thermal shock resistance and high temperature creep resistance, and can be used continuously for more than 4 to 5 years. The middle part (accounting for about 30%~35% of the height of the entire grid), containing MgO: more than 90% of magnesia bricks or magnesia alumina bricks and magnesia olivine bricks. These materials have strong corrosion resistance to alkaline coagulum and SO₂ and V₂O₅. However, the service life cannot match the upper material. For example, the liquefied Glauber's salt enters the brick hole and expands repeatedly, which will cause the magnesia brick to crack. The lower part (accounting for about 40%~45% of the height of the entire grid) is a high-quality clay brick with low porosity. It has strong resistance to high temperature creep and good thermal shock resistance. In order to prevent the contact reaction between the alkaline material and the clay brick, a transition layer (about 5% to 10% of the height of the entire grid) can be set between the middle and the lower part, and the anti-stripping high alumina brick is commonly used as the transition material.
The other is the zirconium series. This series is highly respected by France. The domestic light industry system uses more tank kilns. In the late 1970s, the French company SEPR (SEPR) introduced the same cross-shaped fused zirconia corundum checker brick (ER-1681) for the entire grid body. Formed grid holes like vertical wells, the surface of the bricks is smooth, no pores, no dust, no condensed gas absorption, no possibility of blockage. The brick thickness is reduced to 40mm or even 30mm, which can save energy by about 15%. The shape of the bricks is constantly improving, such as changing into a corrugated shape, which can improve the heat exchange effect and stability. The performance of this material is ideal in all aspects, and the service life can reach two kilns (more than 7 years). The disadvantage is the high price, but it can be made up for by its excellent performance. It should also be noted that it contains 17%-21% of the glass phase, which can be precipitated between 1380~1410℃. In view of the large investment in fused materials, sintered zirconium corundum cylindrical checker bricks are used in China. The cylindrical brick was introduced after the cross-shaped brick. Compared with the cross-shaped brick, it does not need matching brick shape, is convenient to stack, has good stability, and other properties are not inferior to the cross-shaped brick, so it is quickly promoted. The method of use is also divided into three parts (the height of each part is basically the same as that of the alkaline material). The upper part uses ZrO₂: 33% sintered zirconium corundum brick, and the middle part uses ZrO₂: about 18% sintered zirconium corundum brick ( Commonly known as semi-zirconia bricks), the lower part still uses low-porosity high-quality clay bricks. As long as the sintered AZS brick is sintered well and reaches the required mineral composition (especially the oblique zircon phase), its use effect is ideal.
The horizontal flame tank kiln has multiple pairs of regenerators, and the temperature and erosion conditions of each pair of regenerators are different. The materials can be selected separately, and there is no need to insist on the same.
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