I. Causes of bursting of refractory castables for cement kiln
1 Due to the heavy production tasks, most cement plants have to take time to pretend to be repaired. In order to open the kiln production as soon as possible, the curing and baking time of the castables has to be compressed.
2 At present, China's cement kiln refractory castable material is mainly SiO2, Al2O3 system, and its binder is fast-hardening early-strength cement based on aluminate cement. This requires that the castables have sufficient curing time and a reasonable baking system after construction, which takes a long time.
3 China's cement industry maintenance is basically commissioned by the furnace company, the professional level of the construction team, whether the construction is normative have a greater impact on the construction quality and use of refractory castables.
4 Some special parts of the cement kiln, such as the front kiln mouth, the kiln head cover, the top of the grate cooler and the side wall, etc., have the problem of difficulty in baking. For these parts, some cement companies do not need wood baking at all, and some enterprises only do baking for a short time. In the burner kiln stage, due to the control of the cement kiln process parameters, the hot gas flow propagates and radiates to the kiln tail system at a certain speed, while the kiln head cover and the grate cooler only have part of the radiated heat energy, which is insufficient in heat. In order to fully discharge the free water in the castable. At the beginning of the production, the hot air in the system returns to the kiln head in a short time; at the same time, the high temperature clinker (above 1300 °C) starts to accumulate at the bottom of the kiln cover, causing the temperature of the kiln head cover and the grate cooler to rise sharply. At this time, the phenomenon that the castable material bursts and falls off is most likely to occur.
2. Mechanism analysis of bursting of refractory castables for cement kiln
At present, the kiln head cover of the cement production line in China, the hot section of the grate cooler and the castable material of the front kiln mouth are prone to bursting. The reason is analyzed, mainly in the kiln stage, because the temperature rises too fast, the temperature in the kiln rises rapidly, the free water in the refractory material changes from liquid to gas in a short time, and forms a certain value as the lining temperature increases. Vapor pressure, when the water vapor inside the lining cannot be diffused in time, the pressure will increase. When the water vapor pressure inside the lining is out of balance, the phenomenon of peeling, peeling and even bursting of the castable will occur.
For the problem of cracking of castables, refractory manufacturers of cement kiln generally use 0.1% to 0.3% of organic fibers in the cement industry to prevent the occurrence of bursting. The organic fiber is melted or burned at about 160 ° C to form a fine and narrow pore that penetrates and evenly distributes. The formation of the organic fiber increases the gas permeability of the lining material, accelerates the drainage and buffers the water vapor pressure, and prevents baking and opening. The sudden temperature change in the kiln feeding stage causes the lining to burst. However, the use of organic fibers has problems in that the castable is not easily dispersed, the amount of addition is large, and the strength is affected.
3. Measures to solve the problem of bursting of refractory castables for cement kiln
1Because each cement production enterprise has the cross-operation of equipment maintenance, pouring material construction and other parties during the maintenance period, all departments must coordinate and do well the construction schedule of the pouring material in each part of the cement kiln. For some castable materials that are difficult to be baked (cold cooler, kiln hood and front kiln mouth), priority should be given to pouring construction, and sufficient curing time should be reserved; at the same time, supervision work of the construction unit should be done well, and mixing of castables should be done. The amount of water added, the formwork, and the maintenance should be strictly in accordance with the construction instructions.
2 When the kiln head cover is constructed, it is best to leave the vent hole. The specific punching requirements are: 300mm × 300mm, and embedded with φ5mm wood strip, the depth is half of the castable.
3 After the kiln cap casting hole is closed, keep 8 vent holes and waterproof. At the same time, in order to ensure that the refractory castable in the front kiln mouth does not burst during baking, it is better to use the φ3mm bamboo stick to keep the vent hole in the construction. The venting hole is arranged at 100 square meters per square meter.
4 For the repair and overhaul of the cement kiln, before using the burner oil-fired kiln, some special parts (kiln head cover, grate cooler, front kiln mouth) are best baked with wood, and the baking time is not lower than 12h. At the same time, in the process of drying the kiln, the heating rate should not be too fast. For the low-cement series refractory castables, when the thickness of the lining is within 200-400mm, the optimum heating rate is not more than 15 °C per hour. need.
5 In the emergency repair, accident shutdown kiln maintenance without baking time, phosphate-bonded refractory castables, such as PA-852 phosphate castables, can be used. These products have the advantage of no baking, and the strength increases as the temperature rises. However, it should be pointed out that this type of product also has its own weaknesses, such as poor wear resistance and short service life.
In short, the bursting problem of refractory castables for cement kiln is a complex problem, which is closely related to many factors, especially in winter construction. Adding 0.1% to 0.3% of explosion-proof fiber to the castable can improve the explosion-proof performance of the product. For the front kiln mouth, grate cooler, kiln hood, etc., where the pouring material is likely to burst, as long as the construction is reasonably arranged, the quality control of the construction link, the venting, the baking, etc., the refractory lining burst The phenomenon is completely avoidable.
