Refractory selection for crowns of glass furnace regenerators must recognize both the functions of the refractories and the operating environment within the chambers.

The main function of crowns is to limit thermal losses. The main operating factors to be considered are temperature, repeated temperature cycling, airborne particulates, volatiles and load. Fuel and glass composition must also be considered when deriving the refractory specifications.

The main refractories for the crowns of glass furnace regenerators include basic refractories, silica brick, mullite brick and alumino silicates refractories. In making the choice, the resistance to creep and chemical attack must be taken into consideration.

The temperature is very important for the refractory choice. Basic refractories have limits in creep resistance. If the temperature is close to 1,500°C and the material is under a strong compression, life limiting creep will ensue. As a consequence, basic refractories can be used only if the operating temperature is lower than 1,500°C (1,460-1,480°C).

Considering only creep resistance, silica brick is the best refractory because of its lack of glassy phase and its different crystalline structure, which avoids plane slipping. Furthermore, creep starts only at temperatures close to 1700°C. Mullite brick is another quality suitable for the crowns for its excellent creep resistance.

Basic refractories have a very good chemical resistance to the alkaline gases coming from the glass furnace, but they are susceptible to carry-over enriched with silica and subsequent forsterite formation at the hot face. This chemical reaction increases volume and leads structure to a collapse.

Basic refractories can be used in the crowns temperatures lower than 1,500°C (1,460-1,480°C). Silica brick is not suggested for crowns because condensation of alkali in the colder zones of the masonry would lead to corrosion, loss of mass and also holes.

Mullite brick reacts with alkali and slags to form a series of layers which prevent alkali penetrating into the refractory and wear proceeds at a minimal rate while the thermo-mechanical properties are preserved. Mullite brick is a good choice for crowns but it must have high mullite content (95-97%).

Zhengzhou sunrise refractory Co., Ltd. is a refractory supplier from China, specializing in various refractories for glass furnaces, such as fused cast AZS block, magnesia bricks, silica brick and mullite bricks.

Ceramic fiber module is made of ceramic fiber blanket by folding and compressing. Currently, it gradually becomes the first choice for the thermal insulation of industrial furnace linings.

Ceramic fiber module has white color and regular size. It can be directly fixed to the anchor nail on the steel plate of the furnace shell. It has good insulation performance and can improve the integrity of the furnace. It simplifies and speeds up the construction of furnaces and promotes the masonry techniques of furnaces.

It has many advantages over the ceramic fiber blanket.
1) During installation, after releasing the tying, the folded blankets can generate a huge stress, which makes them crowded together tightly without gaps.
2) The flexibility of ceramic fiber blanket can compensate the deformation of the furnace shell and reduce the construction cost. At the same time, it can make up the gaps caused by the thermal changes of the different components.
3) Since it has light weight and low thermal capacity, it can significantly reduce the energy cost during the temperature operation.
4) Flexible ceramic fiber blanket can withstand external mechanical forces.
5) It has good resistance to thermal shock.
6) The ceramic fiber lining requires no drying and maintenance. It can be put into use immediately after the construction is completed.
7) It has stable chemical properties. It is not eroded by acids, bases, water, oil and vapor, except phosphoric acid, hydrofluoric acid and strong base.

It can be used for the furnace lining insulation in the petrochemical industry, metallurgical industry, ceramic industry, glass industry, heat treatment industry and other industries.

Zhengzhou Sunrise Refractory supplies various ceramic fiber products including ceramic fiber blanket, ceramic fiber board, ceramic fiber module, ceramic fiber vacuum formed shapes, calcium silicate board, ceramic millboard, ceramic fiber paper, ceramic fiber bulk, and ceramic fiber cloth tape, rope and yarn.

When selecting refractories for regenerator chambers serving natural gas fired furnaces producing soda lime glass, both the functions of the refractories and the operating conditions within the checkers should be taken into consideration.

As heat exchangers, checkers should have high thermal capacity and thermal conductivity. Basic refractories and fused cast refractories are the best solution.

However, refractory selection also depends on the operating conditions, while the operating conditions depend on the position. According to the temperature, checkers can be divided into four zones: Top zone (from the first row to 1,350℃), Mid zone (from 1,350℃ to 1,000℃), Condensation zone (from 1,000℃ to 700℃) and Lower zone (from 700℃ to rider arches).

Top Zone

High temperature and batches and dusts result in chemical attack and gradual corrosion of the basic refractory bricks. If refractories are magnesia bricks, the chemical attack is up to the CaO/SiO2 ratio in the waste gases. if the radio is low, forsterite (Mg2SiO4) will be formed, which results in fissures opening within the bricks. Subsequently, silica penetrates these fissures resulting in the familiar cubic breakdown of the upper checkers. If the CaO/SiO2 ratio in the waste gases is high, a liquid phase enters into the refractory causing deformation. The best solution is magnesia bricks with high Mg content, well developed MgO crystals and a direct bonded structure. Additionally, the refractories should have low iron to avoid FeO oxidation to Fe2O3 and vice versa (Fe2O3 reduction to FeO) with volume variations and resultant brick failure.

Fused cast refractories have no surface porosity thus they are resistant to the corrosive effects of waste gases and carryover and can be used in all the checker zones. Compared to sintered refractories they are more resistant to abrasion due to their dense and homogeneous structure thus they are suitable for the top zone where there is a strong carry-over. Fused cast alumina brick is recommended for its very limited glassy phase. No glassy phase means no exudation therefore no excessive bonding with carry-over thus minimizing the risk of blockages.

Mid Zone

This zone is protected by the top checker area and temperature level is lower, thus 96% MgO with low iron and fused cast AZS 33# are recommended.

Condensation Zone

This is another critical area. The waste gases contain alkaline sulphate and SO3 which will condense out in the 1,000-700℃ range. In presence of sodium sulphate, the predominance of Na2O or SO3 in the waste gases causes chemical attack. Periclase base refractories are not chemically attacked by sodium sulphate or sodium oxide but they strongly react with SO3 forming MgSO4 causing densification of the Structure.

The chemical attack, enhanced by the presence of vanadium pentoxide when using fuel oil, breaks up the refractory and the structure densification lowers thermal shock resistance. Viable substitutes for chrome bearing refractories, which have a high resistance to condensates but cannot be used for environmental reasons, are both the spinel (MgO·Al2O3) and refractories made by periclase (MgO) and zirconia (ZrO2) having good resistance against Na2O and SO3.

When firing with natural gas, since the SO3 quantity is low, basic refractories can be used. When fused cast material is used, fused cast AZS is recommended.

Low Zone

Super duty fire clay brick can be used in non severe working conditions. 90-92% magnesia brick is recommended when firing by natural gas. Fused cast AZS 33# is also used in this zone.