In recent years, the glass industry with high energy consumption and high pollution has been restricted by the national environmental protection policy. What is more worrying is that with the continuous expansion of glass production capacity, the relationship between the supply of glass products in the market is becoming more and more obvious. Many glass manufacturers are facing the pressure of declining market and declining profits. In order to change the current dilemma, it is necessary to do everything possible to reduce the operating cost of the glass kiln and reduce the pollution of the external environment in the glass production process. As a result, refractories for the traditional glass industry need to be able to better adapt to changes in glass furnace operating conditions. For example, in the process of changing from burning petroleum fuel to burning petroleum coke fuel, a large amount of S02, V205 and other impurities are introduced, and the erosion of refractory materials is intensified. Thus, it is necessary to take the corresponding kiln temperature increase, glass temperature rise, speed up the flow rate, strong scour the bottom of the pool, the pool wall refractory problem. For example, the glass kiln heat storage chamber is also widely used magnesium lattice brick, resulting in serious six valence Ming pollution problems. Therefore, the country may soon introduce mandatory regulations to restrict the use of magnesium refractory materials in the glass industry.

This paper mainly describes the main erosion faced by glass furnaces and introduces some new refractory materials developed for the key areas of glass furnaces. After using these materials, it is expected to extend the life of the furnace, improve the quality of glass, improve the efficiency of waste heat recovery, reduce the pollution to the environment, provide strong support for the technological upgrading of the glass industry, and contribute to the saving of expenditure and income, energy saving and emission reduction of glass enterprises.

1. Main structure and working environment of glass kiln

The main glass kiln is composed of three parts: the melting part, the cooling part and the heat storage chamber. Among them, the melting department is responsible for the melting, clarification and homogenization process of the batch materials. It consists of the upper structure of the melting section (big noise, breast wall, small furnace mouth, etc.) and the pool kiln (pool wall, pool bottom, etc.)

The flame from the small furnace fills the flame space in the superstructure, and the flame space has a very high working temperature, so that the batch material is forced to melt. In a soda-lime glass furnace, this temperature can reach 1649°C. Therefore, the refractory material used for the superstructure of the melting section must not only withstand higher operating temperatures, but also have the ability to resist alkali vapor, fly material erosion, and small furnace flame erosion of the material.

Generally, the material used for the superstructure is under the action of high temperature and the erosion of saturated alkali vapor, the glass phase in the refractory material will be precipitated from the tissue and enter the glass liquid. On the one hand, it leaves pores in the refractory material and becomes a channel for foreign substances to invade; on the other hand, defects such as stones, stripes and bubbles are formed, which seriously affect the quality of the glass. The pool wall bricks are in direct contact with the molten glass and are eroded by the molten glass. After being eroded, the surface of the fused cast refractory produces a high-viscosity liquid layer. At this time, the service life of the refractory material is closely related to the protective effect of the layer. For example, if there is an eddy current on the surface of the refractory material, the high-viscosity liquid phase layer will quickly be lost, exposing new surfaces of the refractory material, and the glass liquid will continue to attack these surfaces. Thus, the refractory material is quickly damaged. In contrast, pool wall bricks are more susceptible to glass erosion than pool bottom bricks. For example, the pool wall brick is most prone to erosion of the place is the glass "liquid surface line". This is located at the interface of the gas, liquid and solid phases. Because the protection of the high viscosity liquid phase flowing down from the upper part cannot be obtained, the erosion speed of this area is very fast, and it is often necessary to use cooling or brick binding methods to maintain life. After the glass liquid penetrates into the brick joint, it first erodes the area with weak resistance to erosion in the brick tissue. If the erosion product can not adhere to the brick seam, and the loss into the glass liquid, will produce serious erosion groove.

The cooling zone is the place where the glass liquid is cooled, and the glass liquid with gradually reduced temperature enters the tin bath through the lip brick. This area is subject to less chemical, thermal, and mechanical erosion than the melt. But. The glass liquid also has no ability to melt fine stones, stripes and other defects in the glass. Therefore, it is necessary to use "clean" refractory materials such as fused-cast alpha-beta alumina bricks and beta alumina bricks.

The regenerator is used in the glass kiln to recover the waste heat in the exhaust gas, preheat the combustion air and strengthen the combustion. The regenerator mainly relies on the lattice brick to undertake the function of heat exchange. When heated, the lattice brick cools the exhaust gas and is heated by itself; after the airflow is reversed, the lattice brick preheating exhaust gas itself is cooled. On the one hand, the lattice brick to frequently withstand the alternating changes of hot and cold; on the other hand, the lattice body not only withstand the impact and abrasion of high temperature exhaust gas, but also by the erosion of waste and alkali steam. In particular, after using petroleum coke as an alternative fuel, the content of harmful substances such as S02 and V205 in kiln gas and fly material increases greatly. These low melting point substances are enriched on the surface of the grid and react with the grid matrix, which greatly shortens the service life of the material.

In short, the glass kiln working environment is very harsh, so that the erosion of refractory materials is very serious. The key parts of the glass kiln, according to the erosion mechanism, targeted selection of new refractory materials with appropriate performance, so as to effectively extend the service life of the kiln.

2. A new type of fused cast refractory used in flame space-low glass phase exudate fused cast AZS refractory

The ambient temperature of the flame space of the glass furnace is relatively high. Excessive temperature will significantly reduce the service life of the materials in this area. According to the data, the service life of refractory materials will be shortened by 1/2 when the melting temperature in the kiln increases by 50 -60 ℃.

In order to improve the service life of glass furnaces, in the 1990 s, fused cast refractories were widely used in the superstructure of glass furnaces. The fused-cast AZS material is mainly composed of a clinochrome phase, a corundum phase, and a silicate glass phase. However, with the continuous improvement of the equipment level of China's glass industry and the full promotion of oxygen combustion technology, the melting temperature of the glass furnace is greatly increased compared with the traditional AZS casting material used in the upper structure of the glass furnace. Because it contains glass phase components with lower melting point, when the melting temperature exceeds the melting temperature of the glass phase, the glass phase will become liquid and carry finely divided clinochrome stone to exfiltrate into the brick surface. On the one hand, the refractory material produces a large number of pores, so that the erosion of the material intrusion, exacerbated the corrosion of the brick; on the other hand, the material in the glass phase drip into the glass solution, so that the production of glass has a large number of defects, affecting the quality of glass. Therefore, in order to adapt the material to this high temperature, high alkali environment, to ensure the normal operation of the furnace, improve the qualified rate of products, refractory workers for this phenomenon developed a low glass seepage AZS casting material.

The chemical composition of the material: the proportion of SiO2 is 13%, the proportion of ZrO2 is 17%, and the proportion of NaO2 is 1.7. It can be seen that the material contains high glass phase forming chemical components. In addition, the petrographic analysis also shows that the number of glass phase of the material has reached 21%, which is equivalent to the glass phase content of ordinary AZS fused cast brick. Therefore, the reason for the low glassy phase exudation of this material is not entirely due to the composition of the material, but also to the specific structure of the material.

Through a large number of experiments, it is concluded that the low glass phase material has the excellent characteristic of "zero" exudation at high temperature, which effectively solves the problem of glass liquid pollution caused by the exudation of glass phase from the casting material in the upper flame space in the high temperature environment, and because it contains lower glass phase composition, the material has higher creep resistance and can withstand higher working temperature, the high temperature performance of the material has been improved, and it is particularly suitable for use in the upper structure of the furnace charging area where erosion is more severe.

3, glass kiln melting pool wall brick new refractory material

At present, the refractory material used in the glass kiln wall is usually fused cast AZS brick. 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 washed and thermally corroded by the flowing glass liquid. In addition, part of the brick body of the pool wall brick is exposed to the glass molten liquid, and the temperature here can generally reach 1399-1454°C, while the highest temperature of the material in the glass liquid is only 1399°C. From the above data, it can be seen that the pool wall brick works in two different temperature environments. Due to the inconsistent expansion of the material body, small gaps will be generated in the contact area between the brick and the brick surface. The flowing molten liquid enters the area with weak erosion resistance of the material through the gaps between the brick joints to erode the material from inside to outside.

Especially in the production of photovoltaic ultra-white rolling glass furnace, glass liquid for the melting pool wall brick erosion is more serious. Due to the low iron content of ultra-white glass (<200ppm), the thermal conductivity of the glass melt is very good, and the temperature of the glass melt is very high, especially the temperature rise at the bottom of the kiln wall and 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 speed of the glass liquid to increase. Refractory materials should not only resist the erosion of the high-speed flowing glass liquid in the high temperature environment, but also resist the erosion caused by the penetration of the solution through the brick seam at the interface between the two bricks at the joint of the pool wall and the paving brick.

In order to improve the service life of ultra-white glass furnace refractories, refractory manufacturers add rare earth elements to cast AZS bricks to change the temperature of zirconia transformation and reduce the expansion so that the brick joints can be better bridged to prevent the melt from penetrating into the brick joints. Through the experiment, it is known that the expansion and contraction of the erosion-resistant AZS material is small, and the close degree of the brick joint is good, which is conducive to alleviating the erosion along the brick joint, preventing the glass from penetrating into the brick joint and causing serious erosion, improving the service life of the glass kiln pool wall brick, and avoiding the accident of glass liquid leakage.

The emergence of this material will greatly extend the service life of glass furnace pool wall bricks, especially suitable for ultra-white glass furnaces with large glass melt flow rate and high working temperature. Effectively avoid the glass melt into the pool wall brick joints and the emergence of serious erosion phenomenon.

4. New chromium-free lattice brick for regenerator

The refractory material used in the regenerator is mainly a lattice. If the lattice brick is damaged, it will lead to the collapse of the masonry, block the normal heat exchange channel, affect the normal thermal system of the glass kiln, and force the thermal repair or even the cold repair. The main reasons for the erosion are as follows:(1) high temperature effect;(2) the pressure of the upper grid;(3) the erosion of the grid structure by flying materials, alkali vapor and solidified sulfate;(4) the volume change of the material caused by oxidation reduction.

At present, the central part of the regenerator mainly uses magnesia chrome lattice brick, which can better resist the mechanical stress, thermal stress and chemical erosion 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 a clear limit on the emission of chromium from glass kilns, with the development of China's social economy and the increasing demand for quality of life, the problem of chromium pollution in glass kilns will be put on the agenda.

4.1 spinel lattice cross brick

In order to resist the erosion of refractory materials, refractory manufacturers have developed a new type of spinel fused-cast lattice brick. This new type of lattice brick is composed of 100% magnesium aluminate spinel, the maximum use temperature of magnesium aluminate spinel can reach 2100 ℃, and the thermal expansion coefficient value is very small compared to other materials. Therefore, magnesium aluminate spinel has good high temperature performance. Magnesium aluminum spinel and internal easily corroded internal phase (such as: low melting point glass phase) by scanning electron microscopy, the internal structure of this material only spinel and holes. Pure spinel grain composition, grain and grain there is a certain number of holes. The coarse spinel grains give the material good high temperature mechanical strength and thermal conductivity, while the holes in the grains give the cast material good thermal shock resistance. What is more noteworthy is that because 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 erosion resistance of fused cast spinel materials is far superior to existing sintered materials and fused cast materials in general.

This material, unlike AZS melt-cast material, does not contain an acidic substance that reacts with alkali, so that the material does not produce a large amount of low-melting compounds when contacted with an alkaline substance. This can greatly enhance the performance and life of the product in the alkaline environment. Through the above introduction, we can get spinel lattice brick due to its unique organizational structure, so that the brick body at high temperature, saturated alkali steam environment still has high physical properties and chemical erosion resistance. The use of this new material will greatly improve the service life of the regenerator lattice bricks and reduce the probability of kiln shutdown due to the collapse heat of the regenerator lattice.

4.2 magnesia-zirconium bonded lattice brick

The temperature of the glass kiln regenerator area varies from 700 ℃ to 1100 ℃. The high-temperature corrosive gas flowing at high speed in the regenerator continuously erodes the surface of the lattice brick. In order to improve the erosion resistance of the lattice brick in the regenerator, magnesium inscription brick has been widely used in the regenerator of the glass kiln. However, due to the use of magnesia chrome brick in the process will produce toxic hexavalent chromium, causing serious harm to the environment. In order to protect the environment, magnesia-zirconium lattice bricks become an alternative to magnesia-chrome bricks.

In 1987, magnesia-zirconium lattice bricks were developed and successfully used in the medium-temperature zone of the glass kiln regenerator. In the manufacture of magnesia-zirconium bricks, magnesia is used as aggregate, and magnesia and chromite powder are used as powder materials. During firing, the following chemical reactions occur to form a forsterite-clinoptilolite matrix:

　　ZrSi04 2Mg0=Mg2Si04 Zr02

When used in the middle of the regenerator chamber of the glass kiln, the magnesia-zirconium bricks show high corrosion resistance. This erosion resistance is obtained due to the special structure. Magnesia-zirconium brick is composed of periclase aggregate forsterite-clinoptilomircon composite matrix, the aggregate is isolated phase, and the matrix is 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 clinoptilolite, the erosion of the forsterite phase by alkaline substances is alleviated.

It can be said that this is an environmentally friendly high-temperature material. Due to the existence of a matrix with high erosion resistance, the erosion resistance of the material can be 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 move towards chromium-free.

4.3 forsterite check brick

In order to solve the problem that the production cost of magnesia-zirconium brick is too high to be widely promoted in the glass production industry, domestic and foreign refractory manufacturers have developed a substitute product of magnesia-chromium lattice brick-forsterite lattice brick. The physical properties of the forsterite brick are compared with the magnesia-zirconium brick, and we find that the apparent porosity of the material is higher, and other physical properties are higher than the performance index of the magnesia-zirconium brick.

The raw material of forsterite refractory is sintered magnesia and natural forsterite. Due to the wide distribution of forsterite raw materials, the raw material cost is low and there is no pollution to the environment. Some manufacturers have selected natural forsterite minerals with good sintering and stable physical properties by selecting natural forsterite minerals. In the past, the thermal shock resistance of forsterite was very poor, and it was not suitable for glass furnace regenerator; now, the modification of forsterite refractory 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. Thus, the forsterite brick may be suitable for use in areas where the temperature is low and the erosion is not severe, such as wall tiles for regenerator chambers.

5. Conclusion

It can be seen from the above that the 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 exudation fused-cast bricks in the upper space of the glass kiln can effectively reduce the erosion of alkali vapor on the refractory. The erosion of molten glass along brick joints can be improved by using erosion-resistant fused cast AZS in glass tank furnaces. All these are beneficial to prolong the service life of the glass kiln, reduce the pollution of the furnace refractory to the glass liquid, and improve the quality of the glass products. The use of fused-cast spinel bricks, magnesia-zirconium bricks, and even forsterite bricks in the regenerator can reduce the use of traditional magnesia-chrome lattice 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 procurement expenses for enterprises and reduces the cost of kiln maintenance.