1. Temperature and environmental conditions of the regenerator
When the total height H of the grid body and the upper and lower temperatures t1 and t0 in the regenerator structure and operating parameters are determined, the flue gas temperature ti at any level can be estimated according to the following formula, which can be used as one of the bases for selecting refractory materials.
Therefore, the selection of refractories materials for the regenerator should meet the following conditions:
(1) Temperature cycle changes;
(2) Oxidation/reduction effect;
(3) Solid fly erosion;
(4) The effect of volatile fly and condensate.
For the grid body refractories material, it is also necessary to have a good heat exchange value to meet the needs of the grid body thermal efficiency.
2. Reasonable selection of refractory materials
1. Grid body upper layer
The temperature drop per meter in the regenerator is generally 80-100℃, and the highest temperature at the top of the grid body reaches 1380-1400℃. In the upper layer of the lattice body at a temperature above 1300℃, it is advisable to use directly bonded high-purity magnesia bricks. This brick is fired at high temperature (1780-1800℃) with high-purity fused sand. The content of CaO, SiO2 and Fe2O3 is low, and periclase is directly bonded. It is difficult for the gas phase and liquid phase to enter the brick. The brick body has strong corrosion resistance and can reduce the capping phenomenon of surface bonding powder.
Since SiO2 in the flying material will gradually enter the cracks of the brick body and change the CaO/SiO2 ratio of the matrix part, low-melting phase diopside CMS2, magnesium scapolite C2MS2, forsterite M2S and magnesium rhodonite C3MS2 will be formed, resulting in a large volume effect. Periclite crystals can also gradually grow under the action of alkali vapor, causing the brick body to crack, break and peel off, shortening the service life of the brick body.
In a non-weak reducing atmosphere, calcium vanadate is in liquid phase, which penetrates into the brick to promote the growth of periclase crystals and also causes the brick body to deform.
2. Middle layer of the lattice
The temperature of the middle layer of the lattice is about 800-1100℃, and magnesia-chrome, forsterite and magnesia-alumina refractory materials can be selected. Magnesia-alumina materials have strong resistance to sulfate erosion, but are expensive. This type of refractories material has not yet been widely used in China. The use temperature of forsterite bricks should not exceed 1050℃, and they are used in the low temperature zone of the middle layer.
There is a phenomenon of repeated liquefaction and solidification of sulfate in the middle layer of the lattice. This is caused by the residual V2O5 carbon chain cracking catalyst in the heavy oil, which turns SO2 in the flue gas into SO3 and gradually corrodes the lattice refractories . Its solidification expansion can cause corresponding stress embrittlement damage to the brick structure.
Above 1000℃, sulfate will react with MgSO4 to form NaxMg(yS2O2)2, and the intensity of the reaction will increase with the increase of the Na2O/SO3 ratio. In order to improve the corrosion resistance of magnesia-chrome bricks, the Cr2O3 content should be increased as much as possible, and the degree of direct bonding of the mineral phase should be increased so that the chrome spinel wraps the periclase particles, which can extend its service life.
3. The lower layer of the lattice and other parts
The temperature of the lower layer of the lattice is below 800℃, and the chemical corrosion is weak, but the total weight of a regenerator lattice is at least 40-50t, and the unit load of the lower layer of the lattice is as high as 8-10t/m2. In addition, there is a need to use the flame method to melt and clean the lattice. Therefore, it is advisable to use high-quality low-porosity clay bricks with strong creep resistance and good thermal shock resistance. In order to prevent the contact reaction between alkaline bricks and clay bricks, high-alumina bricks can be used as a transition layer between the middle and lower layers of the lattice.
Other parts of the regenerator include the crown top, side walls and grate crown, where the refractory materials are relatively weak in erosion. Generally, the regenerator arch top is made of high-quality silica bricks, and the side walls are divided into three parts. The regenerator wall in the upper space of the lattice body is made of high-quality silica bricks, and the target wall can also be made of directly bonded magnesia-chrome bricks. From the part above the grate bar to the top surface of the grate body, the better solution is to use the same material as the grate body in the same height section, which can extend the service life of the wall. Another solution is to use alkaline bricks or directly bonded magnesia-chrome bricks that are one level lower than the corresponding grate body material in the upper section, directly bonded magnesia-chrome bricks in the middle section, low-porosity clay bricks in the lower section, and first-level clay bricks below the grate bar. The grate bar arch generally uses low-porosity clay bricks, and can also use fused cast AZS material with clay guard arches.
3. Structural form of the lattice body
In the glass melting furnace, the regenerator lattice body is usually arranged in Siemens and basket weaving styles with straight bricks. However, the lattice holes are often blocked. When the blockage is serious, measures such as hot repair and replacement of lattice bricks are taken. The hot repair conditions are very bad and the labor intensity is extremely high. Octagonal cylindrical bricks are used to replace the original straight bricks. The lattice is chimney-shaped and not easy to be blocked. No hot repair is required during the entire kiln period. Just check regularly. If there is a small amount of blockage, the lower part of the lattice can be cleaned by flame melting from bottom to top.
One of the important energy-saving technologies for large glass melting furnaces is to promote the use of cylindrical lattice bricks. Octagonal cylindrical lattice bricks retain the physical and chemical properties of the original straight bricks, and are easy to lay. The bricks are aligned up and down with basically no free hanging parts. The structure is stable, the heating area per unit volume of the lattice is high, and the service life is long, which is increasingly valued. The wall thickness of the cylindrical brick can be reduced to 40mm, which not only reduces the weight of the unit lattice, but also increases the thermal conductivity. The cost of the cylindrical lattice is about 15% higher than that of the basket lattice, and about 15% lower than that of the cross lattice. However, in terms of energy saving, the difference between the cylindrical lattice and the cross lattice is not much. The heat consumption of the basket lattice increases by 1% to 2% each year, and the heat consumption of the cylindrical lattice increases by about 0.5% each year. A lot of energy is saved due to the slowdown of "aging".
In the design of the regenerator structure, special attention should be paid to the connection method between the cylindrical lattice bricks and the grate arch. The Siemens arrangement of straight bricks should be used for transition between the cylindrical lattice bricks and the grate arch, with a height of about 1m. In this way, the lattice holes can be smoothly connected up and down, and the uniformity of the gas entering the cylindrical lattice can be improved, giving full play to the advantages of the cylindrical lattice bricks and improving the thermal efficiency of the glass melting furnace.
At present, the regenerator of the domestic glass melting furnace has gradually changed from the traditional ascending road structure to a box-shaped partitioned or connected structure. Further strengthening the research on the reasonable selection of refractory materials for the regenerator, the use of partitioned configurations, and the development of new varieties can meet the requirements of improving the efficiency and mission life of the regenerator. It is of great significance for the production of high-quality glass in domestic glass melting furnaces and the early realization of the development goals of low energy consumption, high thermal efficiency, large tonnage scale and long kiln life.
