In metallurgical furnaces, the structure of the ignition and heat preservation furnace of the sintering machine is relatively simple, but as an important part of the sintering process, the ignition and heat preservation furnace of the sintering machine plays a vital role in the quality and energy consumption of the sintered ore.

The main purpose of the ignition holding furnace is to concentrate the flame ejected from the burner, improve the thermal strength in the furnace, improve the output and quality of sintered ore, and reduce the energy consumption of the sintering process. In order to improve the ignition work, the method of increasing the length of the igniter and adding a heat preservation section is often used to prolong the ignition time, make the ignition more uniform, and have a heat preservation effect. The surface temperature level of the sintered material is increased, and the high temperature operation time is prolonged, and sufficient heat can be obtained, which is conducive to the consolidation of the surface layer powder and improves the surface layer sinter strength and yield. However, the current problems of the above method are: the refractory material of the ignition holding furnace is seriously washed by air flow, the service life is short, and the construction time for dismantling and replacement is long, especially the oven time is long.

In order to shorten the production stop time, some researchers combined with the actual situation of production and construction, using a new material - sol combined corundum mullite castable to replace the traditional mullite castable. Its early strength is high, the curing and demoulding time is short, and the production can be resumed with only simple baking, which greatly shortens the construction period and has significant economic effects.

Project Overview

At present, the sintering area of a sintering machine in a factory is 435m2. Its ignition and holding furnace uses coke oven gas as fuel, and the burner adopts a double-inclined type (the width of the high-temperature flame band is suitable, the temperature is uniform, the high-temperature ignition time is well matched with the running speed of the trolley, and the flame Short, complete combustion, high ignition efficiency, low energy consumption), the process conditions of the sintering machine are: the thickness of the sintering machine material layer is 700mm; the output of the sintering machine is 562.5t; the gas type is coke oven gas, and the gas calorific value Q≥16.28MJ/ m3; gas pressure before burner ≥2000Pa; combustion-supporting air pressure before burner ≥3000Pa; ignition temperature is 1150℃±50℃; ignition time is 1 minute to 1.5 minutes.

Since the design life of the ignition holding furnace is 5 years, after the ignition holding furnace is used for 5 years, the top of the ignition section is seriously worn, and it is necessary to decide whether to dismantle and replace it. In view of the relatively intact insulation section, it was decided to keep it in this overhaul. Based on past experience, the researchers used traditional construction methods, using ordinary mullite refractory castables and thermal insulation products to suspend refractory bricks through heat-resistant anchors to form an integral composite refractory lining. Ordinary mullite castables have slow early strength, long demoulding time, and long oven time. Because the process requires segmented construction of furnace walls and furnace tops, the total construction period cannot meet production requirements. In order to minimize production downtime , decided to use a new material - sol combined with corundum mullite quick-drying castable. The sol corundum mullite quick-drying castable has high early strength and short demoulding time. In addition, the special sol is used to combine with less crystal water, so the oven time is greatly shortened.

Refractory Comparison

The design size of the ignition furnace in this factory is 5.32m×5.146m, of which the thickness of the furnace wall and furnace top working lining is 450mm to 310mm.

Usually, the ignition holding furnace adopts a composite refractory lining composed of mullite castables and thermal insulation products suspended by refractory bricks through heat-resistant anchors. Erosion and wear resistance. However, after it is stirred and vibrated with water, it must pass 24 hours before it can be demolded. After 48 hours of natural curing, it can be baked. The oven time is at least 72 hours to ensure that the water is discharged and does not burst. It takes at least 6 days from stirring, making and pouring, to mold removal and maintenance, and then to the oven. It does not include the removal of the original furnace body, the erection of scaffolding for mold making, the separate pouring and construction of the furnace wall and the furnace roof, and the removal of molds. The total construction period At least 15 days.

The advantages of the solvent sol combined corundum mullite castable are as follows: the sol combined corundum mullite castable chemically reacts with the silica sol and Al2O3, and at the same time covers the solid surface to promote the bonding and curing of the material, so its bonding strength is high, and the low temperature can be used. Produces high strength and can be demolded in a short time; the ionization of silica sol in water produces the same negative charge, which repel each other, so the material has good construction fluidity; the load softening temperature when the deformation amount is 0.6% under the load of 0.2MPa is ≥1550 ℃, the softening temperature is high, and the high temperature strength is high; because this material is bonded by sol, the moisture content of the material accounts for about 10% of the total material. During the low temperature baking process, the moisture can basically evaporate, and the thermal shock stability test is 1100 ℃ The number of water cooling is ≥34 times; adding steel fibers to the castable during construction can further enhance its thermal shock stability. The change rate fluctuates little, and the internal stress generated by the material is very small; the damage to the internal structure of the material is very small, and the mullite in the high temperature section is interwoven into a network of needle-like and column-like crystals, which reduces slip and enhances the toughness of the material. Earthly enhanced thermal shock stability. Although the initial investment cost of the sol combined corundum mullite castable is relatively high, it can save 8 days of construction period and generate considerable economic benefits of 3.6 million yuan.

Material selection

After many discussions and studies by the expert group, in order to ensure production and reduce downtime, and to ensure the integrity, wear resistance and durability of the furnace roof and furnace wall, it was decided to use a new material - sol corundum mullite quick-drying castable to replace the original mullite castables.

The main steps in the construction process are to first remove the furnace roof steel structure, then remove the furnace roof castables and slag; use a trolley to set up a furnace roof construction scaffold platform, and then arrange the furnace wall refractory material removal; welding furnace wall anchoring nails; furnace wall Molding and pouring sol combined with corundum-mullite castable, curing and demolding, installation of furnace top anchor bricks, furnace top molding and reserved temperature measuring holes, furnace top pouring sol combined with corundum-mullite castable, curing and demolding, The oven is then carried out, and through a reasonable optimization plan, it takes 7 days to complete. From this construction process, the castable has good fluidity and convenient construction. The strength of the castable in 12 hours at room temperature can reach about 20MPa, which is the condition for demoulding. After a 24-hour simple oven, it can be put into normal production. The above advantages have been fully reflected in practice. During the drying process, there is no furnace cracking and other phenomena, and there is no excessive temperature in the furnace hearth and furnace top. The thermal insulation effect is obvious. Item indicators are good.

Since the ignition furnace has reached its service life, it must be dismantled and replaced. In order to meet the production demand and shorten the downtime, the construction personnel boldly used the new material sol combined with corundum mullite castable. The sol combined corundum mullite castable has high early strength, which can reduce the demoulding time; its reburning line change rate is small, the flexural strength is high, the oven time is reduced, and the construction plan and process are adjusted reasonably, saving 8 days of construction period, produce good economic benefits. It has been put into production for more than a year, and all production indicators are good, meeting production needs.