03
A new refractory material for the wall brick of the melting part of the glass kiln
At present, the refractory materials used in glass kiln walls are usually cast AZS bricks. This is determined according to the use characteristics of the glass kiln pool wall. In the glass kiln, the pool wall is in contact with the glass liquid, and the contact surface is continuously scoured and thermally corroded by the flowing glass liquid. In addition, a part of the pool wall brick is exposed. Outside the molten glass, the temperature here can generally reach 1399-1454°C, while the maximum temperature of the material in the molten glass is only 1399°C. It can be seen from the above data that the pool wall bricks work in two different temperature environments. Due to the inconsistent expansion of the material body, there will be small gaps in the contact area between the bricks and the brick surface, and the flowing melt enters the material resistance through the gaps between the bricks. Less erosive areas erode material from the inside out.
Especially in melting furnaces producing photovoltaic ultra-clear rolled glass, the erosion of the pool wall bricks in the melting part by the molten glass is more serious. Due to the low iron content of ultra-clear glass (<200ppm), the thermal conductivity of the molten glass is very good, and the temperature of the molten glass is very high, especially the temperature rise of the vertical wall of the kiln wall and the bottom of the paving brick is the largest. In addition, the large temperature difference between the high temperature area and the low temperature area of the kiln promotes the convection velocity of the glass liquid. At the place, the resistance solution penetrates through the brick joint to cause erosion at the interface between the two bricks.
In order to improve the service life of ultra-white glass kiln refractories, refractory manufacturers add rare earth elements to fused cast AZS bricks to change the temperature of zirconia transformation and reduce expansion so that the brick joints can be better bridged to prevent the melt from penetrating into the brick joints . Through experiments, it is known that the expansion and shrinkage of the corrosion-resistant AZS material is small, and the joints of the brick body are well sealed, so it is beneficial to alleviate the erosion along the brick joints, prevent the glass from penetrating into the brick joints and cause serious erosion, and improve the quality of the bricks. The service life of the glass kiln wall bricks has avoided the accident of glass liquid leakage.
The emergence of this material will greatly prolong the service life of the glass furnace wall bricks, especially suitable for ultra-clear glass furnaces with high flow rate of glass melt and high working temperature. It effectively avoids the severe erosion caused by the glass melt intruding into the brick joints of the pool wall.
04
New chrome-free checker brick for regenerator
The refractory material used in the regenerator is mainly lattice body. If the checker brick is damaged, it will lead to the collapse of the masonry body, block the normal heat exchange channel, affect the normal thermal system of the glass kiln, and force hot repair or even cold repair. The main causes of corrosion are as follows: (1) high temperature; (2) pressure on the upper lattice body; (3) corrosion of the lattice structure by flying materials, alkali vapor and solidified sulfate; (4) oxidation Reduction produces a volume change in the material.
At present, the middle part of the regenerator mainly uses magnesia-chrome checker bricks, which can better resist the effects of mechanical stress, thermal stress and chemical erosion on the material in the regenerator. However, this material has a fatal flaw – hexavalent chromium emissions. It will cause great harm to the environment. At present, although the existing national standards do not have clear limits on chromium emissions from glass kilns, with the development of my country’s social economy and people’s increasing requirements for quality of life, the issue of chromium pollution in glass kilns will be put on the agenda.
4.1 Spinel lattice cross brick
For the erosion resistance of refractory materials, refractory manufacturers have developed a new type of spinel fused-cast checker brick. This new checker brick is composed of 100% magnesia-alumina spinel. The maximum use temperature of magnesia-alumina spinel can reach 2100℃, and its thermal expansion coefficient is also very small compared with other materials. Therefore, magnesium aluminum spinel has good high temperature performance. Magnesia-aluminum spinel and an internal phase that is easily corroded (such as a low-melting glass phase) are observed by scanning electron microscopy. The internal structure of this material only has spinel and holes. It is composed of pure spinel grains, and there are a certain number of holes in the grains. Coarse spinel grains endow the material with good high-temperature mechanical strength and thermal conductivity, while the holes in the grains endow this fused cast material with good thermal shock resistance. What’s more noteworthy is that since the material does not contain low melting point substances, the ability of the material to resist erosion and creep is greatly improved. For example, under alkaline conditions, the corrosion resistance of fused-cast spinel materials is far superior to existing sintered materials and general fused-cast materials.
This material is different from the AZS casting material, it does not contain acidic substances that react with alkali, so that the material will not produce a large amount of low-melting point compounds when it is in contact with alkaline substances. This can greatly enhance the performance and life of checker bricks in alkaline environments. Through the above introduction, we can get that due to its unique structure, the spinel checker brick still has high physical properties and chemical corrosion resistance under the environment of high temperature and saturated alkali steam. The use of this new material will greatly increase the service life of the checker bricks in the regenerator and reduce the probability of kiln shutdown due to the heat of the grid body collapse in the regenerator.
4.2 Magnesium-zirconium combined checker brick
The temperature in the regenerator area of the glass kiln varies from 700°C to 1100°C. The high-temperature corrosive gas flowing at high speed in the regenerator is constantly eroding the surface of the checker bricks. In order to improve the corrosion resistance of the checker bricks in the regenerator, glass kiln Magnesia bricks are used in the regenerator. However, due to the toxic hexavalent chromium produced during the use of magnesia-chrome bricks, it will cause serious harm to the environment. In order to protect the environment, magnesia-zirconium checker bricks have become an option to replace magnesia-chrome bricks.
In 1987, magnesia-zirconium checker bricks were developed and successfully used in the medium temperature zone of the regenerator of the glass kiln. When manufacturing magnesia-zirconia bricks, magnesia is used as aggregate, and magnesia and chrome powder are used as powder materials. During firing, the following chemical reaction occurs to form a forsterite-deleyite matrix: ZrSi0₄+2Mg0=Mg₂Si0₄+Zr0₂
When used in the middle of the regenerator of a glass kiln, magnesia-zirconium bricks exhibit high corrosion resistance. This erosion resistance is achieved by a special structure. Magnesia-zirconia bricks are composed of periclase aggregate + forsterite-decadeite composite matrix, the aggregate is the isolated phase, and the matrix is the continuous phase. Because forsterite has a better ability to resist S03 erosion, it alleviates the erosion of periclase particles caused by acidic substances. Due to the presence of oblerite, the erosion of the forsterite phase by alkaline substances is alleviated.
It can be said that this is an environmentally friendly lattice high-temperature material. Due to the presence of a matrix with high corrosion resistance, the corrosion resistance of the material is comparable to that of magnesium chromium materials. With the improvement of performance, it does not pollute the environment, which points out a development path for the glass industry to go chrome-free.
4.3 Forsterite checker brick
In order to solve the problem that the production cost of magnesia-zirconium bricks is too high to be widely promoted in the glass production industry, refractory manufacturers at home and abroad have developed a substitute for magnesia-chrome lattice bricks-magnesia olivine lattice bricks. Compared with the physical properties of magnesia-zirconium bricks, the physical properties of forsterite bricks are higher than the apparent porosity of the material, and other physical properties are higher than the performance indicators of magnesia-zirconium bricks.
The raw materials of forsterite are sintered magnesia and natural forsterite. Due to the wide distribution of forsterite raw materials, the cost of raw materials is low and there is no pollution to the environment. Some manufacturers select natural forsterite minerals with good sinterability and stable physical properties through selection of natural forsterite minerals. In the past, forsterite had poor thermal shock resistance and was not suitable for use in glass kiln regenerators; now, the modification of forsterite refractories has greatly improved its thermal shock resistance. However, the iron content of forsterite bricks is very high, which greatly affects the creep resistance of the material. Therefore, forsterite bricks may be suitable for places where the temperature is low and the erosion is not severe, such as wall bricks for regenerators.
05
epilogue
It can be seen from the above that refractory materials used in the glass industry are developing in the direction of long life, high performance and low pollution. The use of high and low glass phase infiltration fused cast bricks in the upper space of the glass kiln can effectively reduce the erosion of alkali vapor. The use of erosion-resistant casting AZS in the glass tank furnace can improve the erosion of molten glass along the brick joints. All of these are beneficial to prolong the service life of the glass kiln, reduce the pollution of the glass liquid caused by the refractory of the kiln, and improve the quality of glass products. The use of fused-cast spinel bricks, magnesia-zirconia bricks, and even forsterite bricks in the regenerator can reduce the use of traditional magnesia-chrome checker bricks. On the one hand, it reduces the pollution to the environment; on the other hand, it ensures the normal operation of the regenerator, saves a lot of fuel purchase expenses for the enterprise and reduces the maintenance cost of the kiln at the same time.