(1) Fabrication and installation of steel structure
The main function of the steel structure of the oxy-fuel furnace is to support and fix the refractory materials, which is not fundamentally different from the traditional air-fired kiln. It’s just that in the installation and adjustment of the big ballast foot, due to the characteristics of its large-size single-ring ballast non-bite masonry, there is usually a separately adjusted structure, and the steel structure treatment method of other parts of the kiln is basically the same.
(2) Masonry of the big block
Due to the fact that the large ballast of the oxy-fuel glass kiln mostly uses fused casting materials and dry masonry, it is quite different from the mud masonry of the existing silica brick ballast in masonry. The typical structure of the fused material Ballast is shown in Figure 1.
Fig.1. Typical structure of the electrofused material Ballast
In order to ensure consistency between each ring (radian, arch height, span), refractory manufacturers are required to pre-assemble in the factory and make the necessary corrections to the problems found during pre-assembly. After the design requirements are met, the joint mark is sprayed at the designated position of the brick, and the data record of the ballast assembly is made. Pre-assembly is very important and is generally done by experienced assemblers. Special tools should be used during assembly to avoid bumping of bricks during assembly. Pre-assembly is done on an assembly platform. The assembly platform shall have a platform, a clamping device, a support device, and an assembly tire. The ballast tire for assembly is an important tool for pre-assembly of refractory manufacturers, and it is also an important tool for large ballast masonry during engineering construction. Generally, the same set of ballast tires is used for assembly and masonry to avoid poor masonry consistency caused by different ballast tires. Common ballast tires include steel ballast tires, wooden ballast tires and earth and stone ballast tires. No matter what kind of ballast tire should ensure its reliability and stability. When the construction personnel are masonry, they should carry out masonry according to the pre-assembly data provided by the refractory manufacturer. The first step to ensure the quality of masonry is to install the ballast tires to ensure that they are horizontal and vertical. When installing the last lock brick of each ring, it is necessary to ensure that the clearance of each ring is the same, and the consistent height size (when the big block is built, the falling height of the big block arch height after the ballast tire is withdrawn) can ensure the consistency of the arch height. Fig. 2 is the description of the requirements for important dimensions when the masonry is built.
Fig.2 Description of the requirements for important dimensions during the construction of the large blockade 5
Roasting kiln for oxy-fuel furnaces
At present, the oxy-fuel furnace is mainly based on hot air baking kiln. Main equipment of hot air baking kiln: multiple kiln ovens; Supporting fan; control cabinets; Burner pre-gun components (regulator valves, ball valves, adjustment needle valves, check valves, flow meters); Supporting thermocouples and wires; portable kiln pressure measuring instrument; Hand-held infrared thermometer (one for high and one for low temperature); Mercury thermometer. Kiln tools: adjust the top wire, pull wrench (or pipe wrench); afterburner rod; Mallet; Lube; Flashlight; markers; Ruler; iron wire, iron chain; high-temperature blankets; Welder; gas cutting; Iron hooks. Hot air baking kiln layout diagram 3.
Fig.3 Schematic diagram of the layout of the hot air oven
(1) Adjustment of steel structure
Different from the traditional kiln, the adjustment of the steel structure is mainly concentrated in the steel structure part of the big ball, and the adjustment of the big block has two ways: tie bar tightness and jacking wire adjustment, which mainly depends on the column fastening method adopted by the kiln designer according to the size of the kiln span and the choice of materials. The adjustment of the steel structure should strictly implement the kiln plan, and adjust it according to the characteristics of different parts and different refractory materials combined with the heating curve. In principle, it is guaranteed that the adjustment is made frequently and the adjustment is reduced. Combined with the kiln worker’s experience in the tightness of the strand and jacking wire, the tightness of the steel structure is guaranteed to match the expansion amplitude of the refractory.
The adjustment of the steel structure of the big ballot should be adjusted in combination with the arch height data and the cracking degree of the upper part of the ballast to ensure that the final ballot brick is slightly open, and the opening width is best controlled at 0~3 mm. It should be noted that when the kiln heats up, the opening under the brick will cause the stress point of the ballast to be concentrated in the upper part, which is very easy to cause the collapse of the ballast block.
(2) Establishment of a temperature system
Depending on the choice of refractory material, a temperature rise curve is developed. Several nodes that need to be paid attention to: moisture removal stage, excessive fire stage, refractory shrinkage and steel structure finalization stage, etc. 1. About 200 °C is the stage of moisture removal, and the exclusion of internal moisture in the refractory is mainly considered to avoid the explosion of bricks when the temperature rises rapidly due to the accumulation of internal moisture. In the drainage stage, the holding time of 4~8 h is planned; 2. 1000 °C (±50 °C) is the conventional over-fire stage (also known as over-fire). It is the process of switching the heating of the hot air oven to the heating of the oxy-fuel burner, and the switching time of 4 h is generally considered. When switching, attention should be paid to the change of the atmosphere in the kiln after the flue gas volume drops significantly, and the operator should closely monitor the change of kiln pressure and adjust it in time. After switching the fire, due to the arrangement of the all-oxygen combustion guns, the balance of the kiln temperature should be considered as much as possible in the case of multiple firers, so as to avoid the local temperature being too high or too low, which will affect the overall expansion of the kiln; 3. 1300~1350 °C is the steel structure finalization and zirconium sealing material sintering stage (some fused casting materials have an obvious shrinkage stage during this period, and we must pay close attention to the steel structure adjustment). It is generally planned to keep warm for 8 h. After that, the steel structure is basically finalized, and the steel structure will no longer be adjusted except for individual parts; 4. 1350~1600 °C is the feeding stage (according to different products). In the early stage, broken glass feeding is adopted, and there are manual pushing and blowing modes. When the liquid level rises to 300 mm away from the production level, the feeder can be switched to feed and consider the batching mode of changing from full broken glass to broken glass powder, so as to produce normally as soon as possible. 5. Some kilns will be arranged for a certain period of time before they are put into production, usually about 8 h. There are also some manufacturers who do not go through the stuffing stage and directly discharge the production.
(3) The expansion characteristics of the main materials of the kiln need to be considered in the formulation of the heating rate.
At the key point, it is necessary to ensure the stability of the temperature rise, and leave sufficient time for the adjustment of the steel structure. When baking the kiln, the engineer on site should adjust the progress of the kiln in time according to the specific situation.
For oxy-fuel furnaces, the flame space is mostly made of cast refractory materials. Therefore, it puts forward higher requirements for the treatment of expansion joints and the adjustment of steel structure during the baking kiln. Although the hot air oven uses a large air volume to support combustion, the temperature inside the kiln will be relatively uniform. However, with the continuous development of special glass kilns, it puts forward higher requirements for kiln masonry and baking kiln technology.
(1) Arrange more kiln ovens According to the structure of the kiln, in order to obtain a more uniform temperature, more kiln ovens are usually installed in more parts of the kiln, and the kiln ovens are individually adjusted in combination with the information of the temperature measurement point, in order to obtain more uniform temperature rise data.
(2) The new kiln system of the automatic control system adopts more detection points (including denser thermocouples, kiln pressure, and optical pyrometers) to ensure the accuracy of the detection data. The automatic control system will automatically adjust the fuel consumption of the kiln at different locations and the air volume of the fan according to the data collected by the system of each part of the kiln. When the target temperature exceeds the set heating schedule, the system will send out an alarm and the on-site personnel will intervene.
(3) Application of electrode coating: The original molybdenum electrode usually starts to push the electrode into place after the glass level reaches a predetermined position. However, as a plate electrode and mushroom head electrode, it must be pre-installed inside the kiln or forehearth, and the previous practice is to cover it with glass fiber cloth and water glass, but this has certain risks. There are also projects that fill the kiln with broken glass before the kiln, which has the advantage of perfectly protecting the electrode from oxidation, but the disadvantage is that the kiln time is too long and the cost cannot be effectively controlled. With the advent of high-temperature coating technology, these problems are solved. At present, many domestic enterprises have mastered the high-temperature coating technology of electrodes, which provides more choices for the development of special glass furnaces.
(4) Application of refractory internal coating Kiln internal coating technology has been developed in recent years, mainly using nanomolecular materials to spray the inside of the kiln (mainly kiln flame space refractories), which plays the role of increasing heat reflection ability, increasing the surface density of refractory materials, reducing erosion rate and prolonging kiln life. At present, it is known that siliceous, corundum, zirconium corundum, and aluminum-silicon spraying materials are used in production practice. History is developing, technology is advancing. As more and more people of insight invest in the field of oxy-fuel combustion technology, oxy-fuel furnaces will develop faster in the glass industry, and more advanced technologies and equipment will be used. Lower energy consumption, lower emissions, better product quality, better economic benefits, longer kiln life, and more reasonable construction and operating expenses are the goals that the industry is constantly pursuing.
Post time: Sep-05-2024