Large-scale float kilns are still mainly air-fueled at present. They are generally regenerative cross-fired kilns. The weight of refractory materials for the construction of the regenerator accounts for 1/3 to 1/2 of the total kiln. The lattice body is used as the The main body of the regenerator, together with the small furnace, undertakes the functions of the furnace combustion, energy supply and waste heat recovery system. In order to improve the melting capacity of large melting furnaces, cylindrical bricks with high heat exchange efficiency are usually used as checker bricks.
Various reasons cause the checker block of the regenerator of the kiln to block the heat exchange efficiency, and even the checker body collapses, and the checker bricks have to be heated in advance. Occasionally, the kiln body is damaged due to excessive pressure of the kiln and improper handling. Seriously, the kiln is short and cold repaired in advance, which has a great impact on production stability and cost.
1 The reason for the blockage of the regenerator checker
1.1 Checkered brick structure is affected by
(1) There are defects in the manufacturing process of checker
refractory bricks, such as low grade of raw materials and low sintering degree, resulting in insufficient brick strength;
(2) Checker bricks with cracks cannot be picked out when damaged or masonry is impacted by external force during shipment, and the cracks intensify due to expansion during baking;
(3) Alkaline checker bricks are hydrolyzed by moisture due to being drenched in water or stored in a humid environment for a long time;
(4) The partition wall of the regenerator is skewed or collapsed (especially the siliceous partition wall), the bricks fall onto the lattice body, and the silica bricks and magnesia lattice bricks are eutectic;
(5) Improper design and control of expansion joints during kiln baking can damage the structure of the regenerator.
1.2 Design, process operation
(1) The distance between the front wall and the 1# small furnace is too small; the opening of the 1# small furnace branch flue gate is too large, resulting in increased flying materials and increased erosion
(2) The water content of the batch material is too low, the fine powder is too much, and a large amount of fly material enters the checker body of the regenerator, causing blockage;
(3) Abnormal combustion such as long flame, bad burner angle, improper setting of branch flue, etc. causes the flame to have an impact on the batch pile, especially the first and second pairs of small furnace flying materials in the front area of ??melting, resulting in checker Deposits on the top surface of the body;
(4) The setting of thermal parameters is unreasonable and the thermal repair is not timely, resulting in serious burning of the kiln body.
1.3 The V content in the fuel residue is too high (>100×10-6)
The V2O5 produced after combustion reacts with the CaO in the magnesia brick to produce 3CaO·V2O5. On the one hand, the ratio of CaO/SiO2 in the magnesia brick is changed and the composition of the binding phase is changed; on the other hand, the liquid 3CaO·V2O5 will also invade the magnesia brick. , To promote periclase recrystallization and growth, cracking and pulverizing the brick body.
1.4 Sulfate deposition
Because the batch materials and fuels contain sulfates and sulfides, the low-temperature region in the lattice body will inevitably lead to their deposition. When the Cl- content in soda ash is high, its volatility will increase the sulfate deposition effect. Cold repair and demolition of the checker body will find that the checker body (800~1 100 ℃) area in the medium and low temperature zone, that is, the height of the checker body starts from the bottom, the 15th to 25th floors, usually the sulfate deposition zone, and the air flow channel is obviously smaller or completely blocked. , Even glued together, it is difficult to remove.
2 Regenerator lattice structure
Existing float kiln large-scale melting kiln regenerator lattice body is usually box-shaped structure, generally using cylindrical bricks (the second generation, Chimney Block) as checker bricks, but also in the upper part of the regenerator, using fused cross AZS Brick (the third generation, Cruciform), although it has good corrosion resistance, is expensive and the heating area of ??its unit checker is not as good as that of cylindrical bricks. The replacement of cylindrical alkaline bricks can meet the requirements, except when there are special requirements for corrosion resistance. Adopted, strip bricks are only used for shorter kilns such as burning gas.
In order to achieve the need for controlling the combustion atmosphere of the kiln, the checkers are usually separated by a semi-connected manner. From the perspective of cost saving and improving the efficiency of flue gas heat recovery, there are 3 pairs of small furnaces connected in the front area, and the rear area is separated separately; or two-by-two partitions are used to construct the regenerator checker.
Cylindrical checker bricks are widely used: TL&TG 14/15 and 17/15. The dimensions of the corresponding checker holes are 140 mm×140 mm, 170 mm×170 mm; height and wall thickness. They are 150 mm and 40 mm respectively. The heating area of ??the lattice body is 15.97 m 2/m3 and 13.90 m 2/m3 respectively. Compared with the TG type, the TL has openings at the lower part of the four facades, which enhances the airflow disturbance and has a higher heat exchange efficiency. On the premise of not affecting the safety of the overall structure of the lattice body, the TL type cylindrical brick is used as much as possible.
3 checker maintenance and dredging method
The height of the top surface of the checker body of the regenerator is usually 100-120 mm higher than the liquid level of the glass, and the overall height is usually 8-9 m to maximize the heat transfer efficiency of the checker body and ensure that the air flow is relatively evenly distributed across the width of the checker body . There are basically four ways to dredge the lattice body, namely, the process dredging method, the artificial slagging method, the special burning gun slag method and the replacing lattice brick method.
3.1 Process dredging method
The so-called process dredging method is to increase the temperature of the lattice body in the regenerator by adjusting the process system, so that the sulphate in the lattice holes is melted and flows to the sediment chamber at the lower part of the regenerator, thereby achieving a method of dredging the lattice body. This method of operation is suitable for the unblocking of the regenerator checker when the checker body is initially clogged, but the checker body has just started to be clogged, but has not been completely clogged.
In the process of dredging method operation, first determine the clogged regenerator, install thermocouples in the parts that need to be monitored, and then increase the checker body by increasing the opening of the branch flue gate or increasing the heat load or extending the flame or extending the fire exchange time Temperature. When the temperature of the checker body reaches above the melting point of sulfate, the sulfate blocked in the checker body will flow to the slag chamber of the regenerator under the action of gravity, so that the checker body can be dredged.
When using the process dredging method, attention should be paid to the possible impact on the quality of the glass. In addition, special attention should be paid to the temperature of the grate wall to ensure the safety of the grate wall and the checker body.
3.2 Manually slagging method
The manual slagging method is a lattice body in which the kiln worker uses a pointed steel pipe to loosen the sulphate or other debris blocked in the lattice hole and make it fall to the bottom of the regenerator in the slag chamber of the regenerator. Unblock method. This method is mostly used to clean up the blockage of the middle and lower parts of the regenerator and the clogging of the fly material cap on the top of the checker.
In addition to special steel pipes, the tools used in the manual slagging method can also use orchid bamboo chips. Due to the better toughness of the orchid bamboo sheet, it can better protect the checker bricks from being damaged by external forces, but its use and operation method are more complicated than the use of steel pipes. The artificial slagging method to dredge the checker body of the regenerator does not need to increase the temperature of the checker body, which is safer for the grate slats, but if the operation is improper, the checker bricks may be damaged. In addition, the labor intensity is also greater. This method It should be used sparingly, but if this method is used in combination with the process dredging method, the effect will be better.
3.3 Special burning gun slag method
Burning gun slag method is to use a special burner to heat the slag in the checker hole, mainly sulfate, to the melting point, make it melt and flow to the slag chamber of the regenerator, so as to make the checker body dredge. There are three types of professional burning guns: natural gas guns, LPG air guns and diesel guns. Natural gas and LPG air guns are simple in structure and easy to control, while diesel guns are complicated in structure and relatively difficult to control.
When using the burner slag, the burner head can be made into several types. For furnaces with checker-burning holes reserved on the target wall, you can use an elbow burner to unblock the outside of the heat storage chamber. For furnaces without reserved holes, you can choose to open a hole at the ash-pumping door. , You can also choose to unblock the gun frame to the grate hole in the slag chamber. But no matter what kind of burning gun is used, pay attention to the flame temperature not to be too high, so as not to damage the checker bricks. As the number of burns increases, the frequency of dredging will continue to increase, and it is harder to burn each time. In the later stage of the furnace operation, more and more checker holes around the furnace will become dead holes, and the effect of the slag method will become less and less.
In addition, when the checker body is seriously blocked, consider using a special hot air generator, control the heating rate of the hot air generator to 10 ℃/min, monitor the temperature of the grate slats<1 000 ℃, and the temperature of other checker body sections should also be lower than safe In this way, the temperature of the entire regenerator is increased, so that all the clogging in the checker body is melted and flowed down. The advantage of this method is that it has high dredging efficiency, and it can dredge the corners and the thick and dense parts that are difficult to deal with by other methods; the disadvantage is that the dredging cost is high. If the dredging process is not properly controlled, the local temperature of the checker may be too high. If it is damaged, it may cause partial collapse of the checker after dredging.
What needs special reminder is that because the basic principle of the slag method is to forcibly melt sulfate at high temperature in a short time, it is inevitable that sulfate will be decomposed at high temperature to release SO2 gas, which will cause the SO2 gas content in the flue gas to increase sharply. Taking a 500 t/d ordinary natural gas float kiln as an example, using the slag method to dredge a single checker body, the SO2 gas content in the flue gas can be increased from
3.4 Replace the checker brick method
With the increase of the age of the kiln, the blockage of the checker body has become more and more serious. The checker brick itself has been partially damaged under the erosion of the furnace exhaust gas. In addition, the checker brick is unavoidable when the checker body is dredged, and the checker body may have partially collapsed. In some furnaces with unreasonable design or poor quality of brick materials, a large area collapse of the lattice body may even occur at a certain level, and the lattice body needs to be replaced at this time.
The replacement of checker bricks belongs to the category of kiln hot repair. When replacing the checker bricks, a water bag is used to block the hot air flow at the mouth of the small furnace, the branch flue gate is blocked, and the hot repair door is opened. After the temperature of the lattice body decreases, the hot repairer starts to replace the checker bricks. Replacing checkered bricks is difficult to operate and high maintenance costs, and it is generally not used until the end.
4 summary
Once the furnace is put into operation, the checker design, material selection, and masonry quality are a foregone conclusion and cannot be changed. However, for kilns of the same design, the actual operation of the blockage is often quite different, and different process control levels determine the sooner or later that the checker body will be blocked. There are many ways to deal with checker blockage, but the greater the number of dredging, the greater the damage to the checker brick itself. Therefore, during the production process, efforts should be made to control the level of process operation and strictly control the quality of raw materials. Find an optimal matching value in order to match the service life of the checker body with the overall design life of the furnace.
