As an important part of the glass melting furnace, the flame space formed by it, the breast wall and the front wall can absorb the heat released by fuel combustion and then radiate to the liquid surface of the glass. In the design, it is necessary to ensure the stability of the structure to extend the service life, and to reduce the heat loss and improve the energy-saving effect. Because of its light bulk density, high mechanical strength, and low production cost, silica brick is generally used as the material of choice for glass melting furnaces. Therefore, the refractory design composition of the large-scale glass furnace structure is shown in Figure 1. The flame-contacting space uses high-quality silica bricks, which meets the requirements of the silica brick GB/T2608-2012 standard, and the load softening temperature is not less than 1680°C. The temperature is not lower than 1710℃. Lay a layer of 50mm thick siliceous sealant on top of the silica brick. The siliceous sealant requires SiO2 mass fraction not less than 96%, load softening temperature not less than 1650℃, and refractoriness not less than 1710℃ . Lightweight silica bricks are used to lay an insulation layer on the sealing mud to achieve the effect of heat insulation and energy saving. Lightweight silica bricks require SiO2 mass fraction not less than 92%, load softening temperature not less than 1620℃, and refractoriness not less than 1700℃. The above 3 layers are cold masonry. After the kiln is baked, the thermal insulation coating is laid on the outermost surface. The thermal insulation coating can have a slightly lower refractoriness requirement.
Obviously, the requirements for the intermediate silicon sealant are relatively high, and if an improper sealant is used, it will bring serious consequences. A float glass melting furnace in a certain company has been in operation for just over half a year, and there have been problems.
Glass defect analysis
A float glass melting furnace has been in operation for more than half a year. Due to the problem of the water quality of the cooling circulating water, most of the bubblers were burned out and leaked. As a result, all the bubblers were withdrawn, and the temperature of the 3# and 4# small furnaces corresponding to the large furnace rose. Near 20°C, a large number of defects appear in the glass, about 6-10 per 10m2, the position is not fixed, and the edges are slightly more. For the defects in the glass, sampling and analysis were carried out. The defects were all transparent lumps (namely boils), and the deformation size was about 0.5-5mm.
The BM 2100 P0L polarizing microscope from Jiangnan Optical Instrument Factory was used to further observe the glass defects. There was no unmelted material and crystals inside and around the furuncle defect, but long glass bars were drawn at both ends of the furuncle. It shows that this defect has experienced high temperature, which may come from the upper space of the furnace.
Based on the MIRA 3 electron scanning microscope of TESCAN, the 9806A-3UUS-SN energy spectrometer of Thermo was used to analyze the components of boils. A total of 15 samples were analyzed, and the composition was basically the same.
Source analysis of glass defects
Based on the above analysis results, it is preliminarily judged that the defects of glass furuncle may originate from the upper space of the furnace, that is, the refractory material of the dome roof. Therefore, the dome roof insulation layer at the corresponding position of the 4# small furnace was opened for inspection. After the insulation layer was opened, it was found that the sealing mud was gone. Peel off the dome roof insulation layer at the corresponding position of the 5# small furnace. The result was that the sealing material was found It gradually becomes thinner from the edge to the inside, until it disappears. For the sampling and analysis of the remaining sealing mud, the chemical composition is shown in the composition of the siliceous sealing material 1# in Table 2, which is obviously far from the composition of the designed siliceous sealing material 2# (selection and sampling).
The main components of the actually used dome sealant are CaO, Al2O3 and SiO2. Referring to the phase diagram of the CaO-Al2O3-SiO2 system in Figure 5, the eutectic point of this component is marked below 1300°C. The temperature of the hot surface of the large wall inside the glass melting furnace is 1580 to 1590°C, and the interface temperature between the wall brick and the sealing mud is calculated to be 1301.69 to 1310.16°C, which is higher than the eutectic point of the sealing material used. Especially after the bubbler is stopped, the temperature of the dome top will further increase, so that the sealing material will melt, flow down along the expansion joints and masonry joints of the large dome bricks, and drip into the glass.
After analyzing the reasons, the process was adjusted: reducing the heat load in the front zone, adding to 5#, 6#, strengthening homogenization; reducing the temperature of the hot spot by 30°C. After taking this measure, the defects quickly reduced and gradually became normal.
After the defect was resolved, due to the failure to deal with the wrong sealing material in time, after the furnace was operated for a few months, the large chrysanthemum broke through fire. A high-temperature endoscope is used to inspect the large chrysalis. Rat holes have appeared. This is because the molten sealant flows down to form a larger gap, and the furnace gas (mainly alkali vapor) rises along the gap and is relatively hot. Condensation deposition in the lower part, with the participation of Na2O, reacts with silica bricks to form eutectic; when it reaches the sealing material position, it reacts with the sealing material, the large siliceous bricks and the lightweight insulation bricks, which intensifies the corrosion of the refractory materials.
Therefore, the glass melting furnace can no longer run with the wrong sealing mud material, and the external insulation is opened section by section to replace the sealing material, which fundamentally solves the problem.
in conclusion
Due to the incorrect use of the sealing mud between the large silica bricks and lightweight insulation bricks in the glass melting furnace, a eutectic with a melting point lower than the top temperature of the furnace was formed during the operation of the furnace, which caused glass furuncle defects at the same time, The erosion of the silica bricks on the roof of the dome was intensified, and rat holes appeared in the dome in a short period of time, which sounded the alarm for the masonry engineers of the glass melting furnace.
