How Does A Clogged Glass Kiln Lattice Body Affect The Kiln?

The collapse of the heat storage chamber's refractory material, primarily in the upper high-temperature zone, causes part of the material to fall toward the middle and lower sections of the lattice. This collapse often occurs in the upper part of the lattice, resulting in a blockage located in the middle and upper portions of the lattice body. Such blockage can prevent proper smoke exhaust, disrupting the normal discharge of flue gas, and also affects the air inlet, hindering the normal entry of combustion air. As a result, this impacts the furnace in the following ways:

 01 branch flue temperature

When a blockage occurs in a lattice body, the resistance to exhaust gases increases, and a portion of the flue gases is discharged from the neighboring lattice body. This results in a reduction in the volume of flue gases flowing through the blocked lattice body. The decrease in flue gas volume causes the temperature of the lattice body to drop, while the temperature of the adjacent lattice body increases due to the higher flue gas volume.

As the temperature of the lattice body decreases, the volatiles in the flue gas condense more easily, worsening the blockage. This, in turn, causes more flue gas to flow through the other lattice body. This cycle leads to lattice temperature polarization. The higher temperature lattice body, although less prone to blocking, will experience increased ablation if the temperature becomes too high, which endangers safety. Once the lattice body temperature decreases, the heating effect on the combustion air weakens, lowering the combustion air temperature and reducing the corresponding flame temperature in the furnace. Additionally, the changes in hot air flow within the furnace lead to shifts in the temperature distribution, altering the temperature curve of the pool furnace.

To monitor the temperature of the lattice body, thermocouples are installed on the branch flue connected to the heat storage room. The temperature displayed by these thermocouples corresponds to the lattice body temperature. The temperature of the branch flue rises gradually during smoke exhaust and decreases gradually when combustion air is supplied. When both the air intake and exhaust smoke are stable, the temperature fluctuates within a certain range. The peak branch flue temperature reflects the heating effect of the flue gas on the lattice body. The branch flue temperature increases when the flue gas volume increases and decreases when the flue gas volume decreases. By recording and tracking the branch flue temperature, it is possible to monitor changes in hot gas flow and the blockage condition of the lattice body.

 02 Combustion state

In the initial and intermediate stages of lattice body blockage, although the blockage of the lattice holes affects the flow of gas, the combustion air flow can still generally meet the demand through the adjustment of the combustion air valve. In other words, the flame can maintain a normal combustion state. However, due to the decrease in lattice body temperature, the combustion air temperature also drops, resulting in a lower flame temperature.

Under normal conditions, the pressure at the observation hole of the slag chamber is negative. When the lattice body is severely blocked, although the combustion air flow appears normal, the pressure at the observation hole becomes positive, causing combustion air to overflow and preventing it from fully reaching the small furnace mouth. As a result, the flame becomes unstable, drifting, muddy, and smoky. This leads to a lower flame temperature, which, on one hand, lowers efficiency, and on the other hand, may affect the melting and clarification of the glass due to changes in the flame atmosphere.

 03 Kiln pressure output

When the lattice body becomes clogged, the resistance to flue gas discharge increases. To maintain kiln pressure, the regulating gate is opened wider to pump out the flue gas at a greater negative pressure. As the latticework becomes progressively clogged, the kiln pressure output increases. If the total blockage on both sides is approximately equal, the kiln pressure output will increase by about the same amount on both sides. However, if one side of the lattice is heavily clogged, the kiln pressure output will be higher on that side of the exhaust (i.e., the side opposite to the combustion).

Although the control system can store the kiln pressure output values for each side separately, significant differences in kiln pressure output between the two sides can make it difficult to match the kiln pressure with the desired output during the commutation process. This leads to large fluctuations in kiln pressure, which can affect the stability of the glass level.

Once the lattice body is unblocked, the kiln's processes can be restored: the flame in the small furnace becomes bright, and the normal rigidity is re-established. The skew of the material bed caused by the lattice blockage is corrected, the foam becomes thinner and shorter, and the liquid level in the clarification section becomes clean. Additionally, the energy consumption of the kiln unit decreases, the quality of the glass improves, and both the good-quality rate and the first-rate product rate increase. Table 1 shows a comparison of the data before and after unblocking at a certain time.

The latticework unclogging process causes significant changes in furnace temperature, pressure, and other factors. The kiln processes before and after the latticework is unblocked are quite different. Unlike the "gradual" changes caused by the clogging process, the changes that occur after unclogging are "abrupt." Both of these changes must be carefully adjusted to minimize their impact, as failure to do so may lead to fluctuations in glass quality.

 04 Combustion airflow and related changes

During the lattice body dredging and slagging process, the door of the slag chamber in the heat storage room must be opened. This allows a large amount of air to enter the furnace from the slag chamber through the heat storage room. The amount of air cannot be accurately measured or controlled, as it varies considerably due to the different degrees of blockage in the lattice body. The maximum estimated flow rate can exceed 10,000 Nm³/h, which is higher than the combustion air typically required for a single small furnace.

The significant increase in air volume can lead to several issues:

1.The changes in the flame atmosphere of the small furnace may cause the flame to become unstable, which affects the normal decomposition of nitrous oxide in the clarifier.

2.Excessive air entering the furnace can lead to the formation of nitrogen oxides (NOx) due to the high-temperature reaction between oxygen and nitrogen, increasing the concentration of NOx in the flue gas.

3.The increased amount of flue gas in the furnace will raise the kiln pressure output. If the EP system's pumping capacity is insufficient, this will further increase kiln pressure and cause fluctuations in the liquid level.

4.The increased flue gas volume will also carry away more heat from the furnace, lowering the furnace temperature.

To mitigate the adverse effects of increased air volume, several steps are taken:

1.The fuel of the furnace is increased before operation to maintain a stable temperature.

2.The flue gas treatment process is scheduled in advance to strengthen the monitoring of emission concentrations and take timely action to prevent excessive emissions.

3.During operation, the combustion air supplied to the corresponding small furnace is turned off. At the same time, based on kiln pressure output and flame changes, the combustion air to both sides of the small furnaces is appropriately reduced.

4.In response to changes in kiln pressure output and flame conditions, the combustion air volume for both small furnaces is adjusted to maintain a stable total combustion air volume.

5.Finally, if kiln pressure increases, the frequency of the EP fan is adjusted to ensure that kiln pressure remains under control.

 05 Kiln pressure output

Based on the discussion of the issues caused by the blockage, it can be observed that once the lattice body is unblocked, the kiln pressure output will decrease overall, and the difference between the two sides will also reduce. Figure 1 shows the change in kiln pressure output on both sides during the unblocking process.

Due to the lattice blockage, certain parameters were adjusted to reduce kiln pressure fluctuations during the commutation process. Therefore, during the dredging process, it is important to monitor the changes in kiln pressure output and the fluctuations in kiln pressure. The commutation control parameters should be restored in a timely manner to maintain stable kiln pressure.

 06 Branch flue temperature

Similarly, as the latticework is unblocked, the temperature of each branch flue changes significantly. Unblocking the latticework causes the temperature of the corresponding branch flue to increase, while the temperature of the adjacent branch flue decreases. The magnitude of this temperature change is related to the degree of unblocking: the greater the change in permeability, the larger the change in branch flue temperature. Figure 2 shows the temperature change curve of the branch flue on the south side during the latticework evacuation process.

Before the dredging process, the South 3# latticework was severely blocked, and its branch flue temperature was the lowest. In contrast, the temperature of the neighboring South 4# branch flue was close to 800℃, with a temperature difference of 450℃ between the two. The South 4# heat storage room also showed reddish discoloration of the corner bricks, with slag accumulation in the chipped lattice bricks.

As the dredging work progressed, the hot air flow in the furnace was redistributed, and the temperature difference between the branch flues gradually decreased. The temperature of the South 3# branch flue increased from 344℃ to 515℃, while the temperature of the South 4# branch flue decreased from 792℃ to 613℃.

Although the temperature changes in the branch flues during the dredging process are beneficial, the magnitude of these changes must be carefully controlled to avoid significant fluctuations in the over-temperature regime, which could affect the quality of the glass. Typically, a particular lattice body is evacuated while the branch flue gate is lowered to reduce the magnitude of the temperature increase. After the operation is completed, the gate is gradually raised, allowing the temperature to increase steadily to the target value.