Glass furnaces are the heart of glass factories, and their operating safety is extremely important. As a large-scale thermal complex, the maximum flame temperature of the furnace in its operating space is generally above 1600℃, and the maximum temperature of the glass liquid must reach above 1450℃. There will inevitably be some phenomena of high-temperature flame burning of the furnace body refractory materials and erosion of high-temperature glass liquid during production, which will affect the safe operation and service life of the glass furnace.

Before 2000, the production and operation cycle of the float glass furnace with the largest furnace tonnage (commonly known as "furnace age" in the industry) was mostly 5 to 8 years; with the improvement of the quality of the glass furnace main refractory materials and the advancement of glass furnace operation and maintenance technology, the operating life of glass furnaces is getting longer and longer. After 2000, the operating cycle of float glass furnaces, i.e., furnace age, generally reached more than 10 years, and the longest furnace age reached 15 years. The extension of glass furnace age can bring huge economic benefits to glass factories, and each enterprise is pursuing a longer glass furnace age under the premise of safety control.

 

The burning and erosion of the glass furnace during operation can be controlled and reduced through professional hot maintenance. The more common hot repair work includes side wall patching, side wall replacement, ceramic welding, nozzle brick replacement, chimney replacement, large arch and regenerator rat hole repair, regenerator wall tilt maintenance, etc.
The tuck stones under the flame nozzle are directly facing the flame impact. Although the most resistant to burning and erosion fused cast AZS blocks are used, there is also a situation of gradual burning. With the extension of the glass furnace age, the burning to a certain extent will expose the breast wall support plate of the lower part to the flame space, and even directly burn it by the impact of the flame airflow, which brings great hidden dangers to the safe operation and the lifespan of the glass furnace. Before 2000 AD, it was even the main factor that determined whether the glass furnace should end a furnace life cycle and shut down for cold repair.
In recent years, with the improvement of glass furnace maintenance technology, in the normal production and operation of the glass furnace, the replacement of the burned tuck stones under flame nozzle through hot maintenance has become a relatively mature glass furnace maintenance operation, which can effectively protect the breast wall support plate from burning and extend the safe use life of the glass furnace. In some glass furnaces, due to factors such as the quality of refractory materials or glass furnace operation flame control, the tuck stones are burned abnormally quickly. Hot replacement of some tuck stones plays a more important role.

 

1. Factors controlling the burning of tuck stones

2. Key points for controlling the hot replacement of tuck stones during production

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Factors controlling the burning of tuck stones

The horizontal flame regenerator air combustion furnace is the most common furnace type at present, as well as the end fired air combustion furnace in some light industries. Most of them use bottom-fired burners, and their flame nozzle structures are shown in Figures 1 and 2.

 

1. Schematic diagram of the cross section of the port flame nozzle

2. Photo of a newly built flame nozzle on a certain line

The inspection photos of the glass furnace after cold repair and the glass furnace inspection photos of the furnace in production show that the burnout of the blast hole is serious. In actual production, the hook bricks are seriously burned, or the breast wall support plate is burned and deformed after the hook head falls off, and the support plate sinks and deforms by as much as 5mm.

3.This is a photo of the tuck stones that are severely burned.

Factors that affect the burning of tuck stones or the breakage of tuck stone heads under the flame nozzle of the port:

⑴ Material and structural factors of tuck stones.

Choose AZS materials with good high temperature resistance and corrosion resistance and without shrinkage cavities by molten oxidation method. Clear standards are set for the quality indicators such as material composition, bulk density, and refractoriness.

The size and structure of the tuck stones should also be optimized to reduce the stress of the hook angle.

Especially the corner of the tuck stone head.
 

Tuck stone pictures before 2000

 

Improved tuck stone diagram in recent years

Figures 4 and 5 are two types of hook head corner structures. In comparison, the structure of Figure 4 is prone to cracks during the brick casting process, while the structure of Figure 5 is more conducive to reducing the stress of the brick manufacturing process, and the corresponding hook head will be less likely to burst during glass furnace operation.

⑵ The unreasonable flame angle and length in production will also aggravate the burning of tuck stones and nozzle bricks, especially in the early stage of production, the unreasonable flame angle may directly burn.

⑶ Too much flying materials in production and high sulfur content in fuel will adhere to the surface of bricks at the port , forming a fusion with the bricks, and the material pile will be skewed, which will erode the gap on the side wall and the tuck stones, and will also accelerate the burning.

⑷ The hook head of the tuck stones also broke due to unexpected factors such as sudden temperature changes and sudden furnace pressure changes in production.

For factors such as flames and flying materials in production, it is necessary to check, discover and correct them in a timely manner, and form a standardized operation system to improve the stability of glass furnace operation and reduce fluctuations.

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Key points for controlling the hot replacement of tuck stones during production

During the production and operation of glass furnaces, the port flame nozzle is the most severely burned part, especially for regenerative combustion furnaces. The flame nozzle is impacted and changed by the repeated circulation of airflow from the upper and lower fires, and is directly impacted by hot airflow or even flames on the lower fire side. Therefore, the tuck stones at the port are often severely burned. The tuck stones protect the steel structure breast wall support plate. When the tuck stones are burned and eroded to a certain extent, part of the breast wall support plate will be exposed to the flame space. The direct impact of the flame on the support plate will cause the support plate to deform and burn, which will cause hidden dangers to the structural safety of the breast wall.

During the operation of the glass furnace, it is necessary to conduct regular glass furnace inspections on the burning condition of the furnace body. Methods such as observation with a fire mirror, measurement with a ruler, temperature measurement, and endoscope photography are adopted to evaluate the burning condition of the tuck stones and determine whether maintenance is needed and when to repair. Hot maintenance and replacement of the tuck stones under the flame nozzle is a highly professional thermal maintenance operation, which is dangerous to the safety of the glass furnace and the safety of the operators, and requires a systematic plan and professional work.

The main steps of the operation process are as follows:

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Hot repair plan formulation, personnel division of labor, and material and tool preparation

Formulate a hot repair plan. Professional glass furnace inspection and maintenance personnel use professional furnace inspection tools, endoscopes, cameras, etc. to inspect and take pictures of the furnace burnout, determine the hot repair plan, and clarify which tuck stones to replace; The personnel have clear division of labor, including main operators, auxiliary personnel, and emergency safety supervisors; The corresponding hot work labor protection supplies are adequately prepared, and emergency water guns, air guns, shovels, temporary reinforcement steel, etc. are in place; In terms of hot repair brick preparation, the tuck stones under the flame nozzle, nozzle bricks and spacer bricks are replaced together. Considering the difficulty of hot replacement operation and the rapid heating of new bricks to avoid cracking, the new tuck stones are generally smaller in width, as shown in Figures 6 and 7.

 
Original tuck stone assembly diagram

 

Schematic diagram of hot replacement tuck stone

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Build a brick kiln and preheat the new bricks

According to the number of tuck stones and nozzle bricks to be replaced, the brick kiln is built and preheated using the brick kiln. As shown in Figures 8 and 9,

 

Brick kiln photos

Tuck stones and nozzle bricks in the brick kiln

 Generally, natural gas gun is used for heating. Before loading new tuck stones and nozzle bricks into the kiln, use a flashlight to check each brick. Only when there is no problem can it be put into the kiln. In order to prevent the tuck stones from exploding when heated, the nozzle bricks and the spacer are installed on the side of the fire channel, and the tuck stones are placed on the side away from the fire channel. After the brick kiln is built, the bricks are sealed and insulated after entering the kiln, and the burner and monitoring thermocouple are installed. The priority order of heating fuel is natural gas and liquefied gas. If diesel is used, pay attention to the uniformity of heating to avoid the flame directly burning the pre-heated bricks.

Develop a detailed heating plan. According to the hot repair plan time, start heating the brick kiln 3 days in advance. When the bricks are heated to above 800℃, keep them warm for about 8h before starting hot repair. The heating plan is as shown in the following table, refer to this heating rate. Generally, before heating, new bricks have been placed next to the furnace for 1-2 months to dry out moisture naturally; if new bricks have not been naturally baked next to the furnace, the heating rate will be adjusted accordingly, and the heating rate in the low temperature section will be slowed down. The commonly used heating rate table is shown in Table 1.

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Develop process adjustment plans during hot repair 

In order to regulate the replacement of the tuck stones of the port, there will be a certain impact on the flame burning of the port. It is necessary to formulate a melting process adjustment plan with a detailed operation plan and emergency plan to avoid the randomness of the process operation during the replacement process and avoid the impact on production caused by untimely process adjustments such as pulling amount and combustion. During the replacement of the tuck stones of the port, the main impact on the melting process is the adjustment of the burner, the temperature drop in the glass furnace and the distance of the material mountain. Therefore, the main direction of the process adjustment during the hot repair is to adjust the fuel distribution in time, increase the fuel amount of adjacent burner, and keep the temperature and material mountain stable.

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 Replace tuck stones and adjust port burner

• At the beginning of hot repair, the melting and fitter will remove the spray gun and gun holder corresponding to the tuck stones position on the side of the fire tip;
• then the furnace protection team will start to remove the old nozzle bricks, spacer bricks, tuck stones, and replace the tuck stones. During the removal process, pay attention to protecting the pallet, and control the broken bricks not to fall into the glass liquid in the glass furnace;
• note that the new tuck stones is smaller than the old tuck stones, and start the removal from the side of the port. After removing two tuck stones, install a new tuck stone in hot state;
• pay attention to the new bricks in the kiln. In the installation, use special tools to quickly take out the new bricks and put them in place on the pallet;
• try to remove bricks and other operations on the upper fire side, and do a good job of heat insulation cotton to block the fire when the fire is lowered. Consider a certain amount of new bricks for backup. When removing bricks, try to pry them from the left and right to reduce the number of direct knocks to prevent the iron plate from being driven;
• the temperature of the brick kiln drops relatively quickly during the process of taking new bricks, so it is necessary to pay attention to the insulation of the bricks;
• before installing new tuck stones, carefully check whether there are cracks, and bricks with cracks are not allowed to be used;
• after the installation of the new nozzle bricks is completed, the melting chemical and equipment fitter will restore the corresponding position of the spray gun and gun holder on the side of the fire tip;
• after the spray gun is restored to burn, the next spray gun can be removed. During the replacement operation of a port with 3 spray guns, at most one spray gun should be stopped to ensure that two guns are burning;
• a port with 2 spray guns needs to stop one gun during the hot repair process;

that is, during the hot repair process, try to keep it as long as possible to affect the burning of one gun, and a port should be hot-repaired in one day, and the normal combustion of the port should be restored during the night shift to reduce the impact on the normal process.

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Pulling amount and process control during hot repair

Before replacing the tuck stones, comprehensively evaluate the current load and the blockage of the regenerator, combined with the designed melting rate and clarification rate, to determine the reduction of the pulling amount before replacement (it can be reduced by 2% to 10% according to the evaluation situation);

During the replacement process, the pulling amount is dynamically controlled according to the working conditions in the glass furnace, that is, according to the changes in the flame combustion state, temperature, material pile, and bubble boundary in the glass furnace at different stages of construction, small adjustments are made to ensure the stability of production quality and the control of heat unit consumption;

After the replacement is completed, the pulling amount before the replacement is restored, and the restored amount should be ≤5t/d. Adjustment of the proportion of cullet: According to the inventory situation, under the premise that the quality of purchased cullet is controlled, it can be increased by 2% to 4%, and temporary adjustments can be made during the replacement process. After the replacement of the tuck stones is completed, it can be gradually reduced and restored in combination with the pulling amount, the working conditions in the glass furnace, and the quality of the glass.

►Adjustment of fuel and wind and fire volume:
The fuel volume of the hot repair furnace should be appropriately distributed to the adjacent furnaces. The specific allocation should be based on the flame combustion situation, and the combustion-supporting air volume should be adjusted accordingly to ensure that the total fuel volume and total heat in the glass furnace do not change much, and that the material mountain and temperature are controllable; fuel adjustment should ensure that the flame burns fully, stably, and has a certain degree of clarity; during the replacement process, pay close attention to the material mountain, bubble boundary, and material deviation. If abnormalities occur, adjust the pulling amount or feeding coefficient accordingly; the adjustment of fuel and combustion-supporting air needs to notify the environmental protection department to ensure that the environmental protection import data is controllable.

►Feeding control:
Before the formal hot repair and replacement, the feeder is switched to a one-to-one control mode on the left and right sides, which is convenient for the balance control of the material mountains on the left and right sides during the replacement process;

►Furnace pressure control:
It should be controlled within the normal furnace pressure index range as much as possible. The non-fire change fluctuation during the replacement process shall not exceed the normal furnace pressure setting value of 5Pa. If there are gaps in other parts of the furnace, they should be sealed in time and temporary sealing should be done; The top temperature of the furnace is controlled according to the working conditions in the glass furnace, and temporary temperature indicators are formulated to ensure the consistency and continuity of the team operation.

The plan for resuming production after the replacement of the tuck stones should comply with the following control principles:

♦ Control of the top temperature of the arch:
The top temperature and clarification temperature of the 1# port and the hot spot port should be restored to the normal temperature index before the replacement;

♦ Control of the position of the material pile:
During the process of increasing the pulling amount, the material pile should be controlled in front of the normal position; after the pulling amount is restored, the material pile should be restored to the normal position before the pulling amount is reduced;

♦ Control of the furnace pressure:
During the process of increasing the pulling amount, the furnace pressure is controlled according to the normal index;

♦ Control of the proportion of fuel in each port:
Restore the control of the heat load distribution ratio of each port before the replacement. If optimization is required, it should be further explored according to the actual situation after the pulling amount is in place;

♦ Control of combustion-supporting air:
It should be controlled according to the air-oil ratio index of the port before the replacement. The melting engineer needs to measure the O2 content and CO content in the exhaust gas, and measure the breast wall temperature of each port;

The process parameters not mentioned above should be restored with reference to the indicators during normal production; while resuming production, all the seals of the glass furnace should be quickly rectified and restored to avoid increased heat consumption.

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Safety Precautions

1. When heating bricks, heat them strictly according to the temperature rise curve, and arrange special personnel to guard the site for 24 hours; safety protection should be done in the aisle of the port and under the aisle.

2. During the hot repair period, the team should assign a special person to contact the fire change, and if necessary, manual fire change should be adopted to extend the burning time;

3. The installation of the spray gun, gun holder, and new tuck stones are all done on the fire root side, and the breast wall support plate should be well protected before the change;

4. When cutting bricks with oxygen melting rods, the iron filings produced cannot enter the glass furnace, and all old bricks should be removed as much as possible;

5. Use special tools to clean the attachments and scrape them as clean as possible. During the replacement, avoid knocking the tuck stones to produce debris falling into the glass furnace, which affects the quality of the glass;

6. Do a good job of labor protection. When replacing the tuck stones, the operator needs to wear labor protection supplies; avoid heat stroke and burns of on-site personnel.

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 Summary

The tuck stones under the flame nozzle are the parts directly impacted by the flames in the glass furnace. The tuck stones under the flame nozzle are similar to the tongues of early gas furnaces. Their burning will directly affect the operating life of the glass furnace. Selecting better fused cast AZS materials, optimizing the structure to reduce stress cracks at the corners of the tuck stones when the bricks are cast and formed, and controlling the flame, flying materials and temperature stability in the glass furnace operation can effectively slow down the burning of the tuck stones. Hot replacement of severely burned flame nozzle tuck stones is a highly professional hot work that has only been carried out in recent years. It can effectively extend the furnace lifespan of the glass furnace. Formulate a detailed replacement organization plan, build a special brick kiln for pre-heating, implement the hot repair work step by step according to the steps, and make a plan for the melting process control during the hot repair period.

It can achieve safe replacement of the tuck stones under the flame nozzle of the port, and ensure that the production during the hot repair period is basically not affected.

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Henan SNR Refractory Co., Ltd. has been specializing in the production of fused cast AZS blocks for about 25 years. We use high-quality raw materials and advanced fusion technology to provide customers with high-quality products. From raw material procurement to finished product delivery, every step is strictly quality inspected to ensure that every indicator meets the standards, so you can use it with confidence.

If you have any needs, you can contact me at any time.

Web:www.snr-azs.com

     Email:wendy@snrefractory.com