The grid design is an important part of the design of the entire glass melting furnace. A well-designed grid can fully increase the preheating temperature of the combustion air, so that the fuel produces a higher combustion temperature, which has a combustion and heat-supporting effect on the entire melting furnace. It can recover more flue gas waste heat and discharge exhaust gas at a lower temperature. It can reduce the amount of combustion exhaust gas, thereby reducing the emission of harmful substances such as nitrogen oxides, sulfur and its oxides, flue gas dust, etc., which has a relatively obvious effect on environmental protection.
The grid of the regenerator of the glass melting furnace is built with standard grid refractory bricks, with uniform brick size, low price and short delivery time. The refractory material used to produce grid bricks should have a high density and a large thermal conductivity so that the grid has sufficient heat storage and heat exchange capacity. Setting the combustion air preheating temperature and exhaust gas temperature is an important prerequisite for grid design.
The function of the regenerator is to exchange the flue gas waste heat discharged from the furnace of the melting zone of the glass melting furnace to the combustion air for waste heat recovery. The type, arrangement, aperture size, wall thickness (brick thickness) and material of the checker bricks all have an impact on the heat transfer performance of the checker. The type of fuel plays a big role in flue gas radiation and is also one of the factors affecting the heat transfer performance of the checker.
From the perspective of thermal technology, the aperture size of the checker has a direct impact on heat exchange, which is reflected in the fact that the smaller the aperture, the greater the unit heating area and heat exchange capacity of the checker. However, from the perspective of operation, the smaller the aperture, the greater the gas flow resistance, and the possibility of blockage due to ultrafine powder in the batch or dripping slag also increases, which will affect the heat exchange capacity of the checker.
Material selection of checker refractory bricks commonly used in glass melting furnace regenerators
Alkaline bricks have a large heat storage capacity and strong heat exchange capacity when used as checker materials. According to the different temperatures of different height areas of the checker, the dust flying in the flue gas, and the temperature cycle changes, different materials of refractory materials are selected.
Alkaline bricks can meet the increasingly high requirements of the working conditions of the regenerator of the glass melting furnace, so in recent years, alkaline bricks have been increasingly commonly used to build the regenerator of the glass melting furnace. In the high temperature section of the lattice body (1100-1450℃), low-iron fired magnesia bricks with better masonry structure are used, and the domestic brand is fused magnesia brick DMZ-97.
In the medium temperature section of the lattice body 800-1100℃ area, the lattice body magnesia bricks will be significantly chemically eroded by alkaline sulfates and SO3. Changes begin to occur on the surface of the brick body, and MgO and CaO will be diffused or volatilized. This erosion will reduce the wall thickness (brick thickness) of the lattice brick, and the development will endanger the safety and stability of the lattice body. In the upper half of this temperature range, domestic fused magnesia bricks DMZ-95 bricks can be used; in the lower half of this temperature range, domestic direct bonded magnesia chrome bricks DMC-12 bricks can be used.
In the low temperature section (below 800℃) of the lattice body, low-porosity clay bricks (ZGN-42 bricks, 42% AL 2O3) with good resistance to cold and heat shock are used, and the use is good.
Common checker brick types and arrangement methods for glass melting furnaces
There are many types of checker bricks in the regenerator, the most commonly used are strip refractory bricks (also called straight bricks), cylindrical bricks, and cross bricks; there are also uncommon I-shaped and [-shaped collection bricks, groove bricks, chimney bricks, etc. In the past, the most commonly used checker bricks in the regenerator of the glass melting furnace were mostly strip bricks, and the arrangement methods included: straight grate bar type, diagonal staggered grate bar type, basket type, and basket and grate bar combination arrangement. The thickness of strip brick is 65mm, the length of brick is 230～375mm, the height of brick is 114mm, the most commonly used grid aperture size is 165mm, the maximum error of brick height is ±0.5mm, and the large error of brick height will make the brick surface force uneven, even if the brick is precisely laid, the grid body will tilt and collapse. The commonly used aperture size of strip brick grid body is 150～200mm, and the glass melting furnace regenerator with a design life of 8～12 years is recommended to use strip brick grid brick.
The application of cylindrical grid brick (octagonal cylindrical brick) in domestic glass melting furnace is developing rapidly. The wall thickness of cylindrical grid brick is usually 40mm, with large unit heating area, strong heat exchange capacity, small grid body weight, large grid hole flow area, and good stability of the cylindrical structure. The common aperture size of cylindrical checker bricks is 140-170mm. It is recommended to use domestic cylindrical checker bricks for glass melting furnace regenerators with a design life of 5-8 years. This is because the wall thickness of cylindrical checker bricks with a wall thickness of 40mm will gradually decrease after being eroded, which will affect the heat exchange capacity and safety of the checker body.
Cross-shaped checker refractory bricks have been used in foreign glass melting furnaces for more than 40 years. The wall thickness of the cross-shaped checker brick is usually 38/40mm. The surface of the cross-shaped brick wing is smooth or corrugated, and the heat transfer coefficient of the unit volume of the checker body is large. The material of the checker brick is fused zirconium corundum brick (1682) and fused alumina brick (5312). It has excellent chemical corrosion resistance and cold and hot erosion resistance. The checker hole has a large flow area, the stability of the cross-shaped structure is also good, and the service life is the longest, which can be twice that of other bricks. The commonly used aperture size of cross checker bricks is 140/170mm. Cross checker bricks are recommended for glass melting furnace regenerators with a design life of 10 to 15 years.
