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Technology of slag splashing in converter of automatic reheating furnace
Aug 03, 2018


At present, slag splashing technology is widely adopted in all major converter steelmaking plants in China. The slag splashing furnace means that the high pressure nitrogen is blown into the furnace by the top blowing gun, and the slag in the steelmaking process is splashed on the wall of the converter furnace, thus the purpose of repairing the furnace lining is achieved. When oxygen lance is blowing, steel slag is often adhered to the body of the lance. In general, steel slag is adhered thinly, and steel slag will fall off when the lance is lifted. However, once the converter slag is not good, the steel slag on the gun body will be thicker, stick very firmly, when lifting the gun will not fall off, resulting in sticky gun.

Past experience is to make slag so as not to stick to the gun, often need to add some fluorite, bauxite and other diluted slag to the furnace materials. Now slag splashing technology is not allowed to add fluorite and other diluted slag materials, and some steel plants even bauxite is not allowed to join. Therefore, in order to achieve good effect of slag splashing, the slag will have a certain viscosity in the steelmaking production, and the slag containing Magnesium Oxide and other materials with high melting point should be added to the slag. The slag has good slag adhering effect and can be blown to the converter lining to achieve the purpose of protecting the lining.

Frequent replacement of oxygen lance affects normal production

Because slag is sticky, the outer layer of oxygen lance will inevitably adhere to steel slag in the process of blowing. If it is not cleared in time, with the increase of the number of smelting furnace, the slag on the oxygen lance will be thicker and thicker like a snowball, which eventually leads to the replacement, and even the oxygen lance is too thick to lift the oxygen lance nitrogen vent. At this time, the only solution is to use the flame cutting gun to cut off the sticking part of the oxygen lance, put the oxygen lance out of the furnace, and replace the new oxygen lance.

According to statistics, the consumption of oxygen lance increased by 3~4 times after splashing slag protection technology. However, the biggest influence is not the increase of oxygen gun consumption, but the need to replace the oxygen lance frequently, the converter production is often forced to stop, making the steelmaking continuity affected, reducing the operation rate of the converter and disrupting the normal production rhythm.

At present, oxygen lance is a common problem in converter steelmaking, and it is not only slag on oxygen lance, but in most cases it is a kind of steel slag mixture.  It is not only disadvantageous to the labor protection of the converter workers, but it is very difficult to clear the slag mixture on the oxygen lance. When the sticky is thick, it needs to use oxygen to cut the steel slag out of the gap and then pry it out with a crowbar. A little carelessness can easily damage the oxygen lance body. At the same time, accidents such as toasting, scalding, and bruising often occur, and the work of sticking guns is dangerous.

The use of slag scraper is limited

The most common way to handle sticky guns is to install slag scraper. The 210 ton oxygen lance of converter imported from abroad in No. 2 Steel Works of Shougang has its own slag scraper, which is the earliest slag scraper used on oxygen lance in China. The slag scraper is shaped like a sluice, with a 2.5 circular blade with a sharp edge, which will hold the gun barrel tightly, and the blade is scraped off in time when the blade is put on the gun. Later, with the popularization of slag splashing technology, the phenomenon of oxygen lance sticking occurred frequently. Some domestic steel plants and design units have introduced slag scrapers. According to the structure of slag scraper, it can be divided into fixed slag scraper and movable slag scraper. The fixed slag scraper is easy to clamp oxygen lance, so it is not widely applied. The movable slag scraper is applied more flexibly and has been applied in some steel mills.

If the condition of sticking gun is not serious, the slag on the oxygen lance is slag, and it is effective to use oxygen scraper to remove the slag. If the surface of the gun is glued with steel, or a big stick is glued, the scraper can not be removed, still need to be flame cutting treatment. At the same time, another drawback of slag scraper is that it easily causes deformation of oxygen lance. The temperature of steel slag adhered on oxygen lance is very high. Although forced water cooling is used inside the oxygen lance, the surface temperature of the steel pipe in the outer layer of the oxygen lance is also above 600 degrees Celsius, some softer, and the strength of the slag scraper is very large, which is very easy to cause the deformation of the barrel.

Effectively reducing the phenomenon of sticky gun by the cone oxygen lance

The conical oxygen lance determines the length of the conical part according to the height of the sticking gun. The length of the conical tube is usually greater than the height of the sticking gun. The spatter height of large converter steel slag is usually about 5 meters, and the length of the cone part can be designed to be 6 meters. The spatter height of small converter steel slag is usually about 3 meters, and the length of the cone part can be designed to be 4 meters. The specific length of the cone part should be determined according to the actual situation of the production enterprise. The maximum outer diameter of the conical tube depends on the inner diameter of the nitrogen vent and the processing capacity of the cone tube.

The large head of the conical tube is connected with the barrel through the variable diameter pipe. In order to avoid the high splash of steel slag in a few cases, the steel slag can not fall off, and between the big head of the cone tube and the variable diameter tube, the 1 meter long straight pipe is designed, which makes the slag dropping more smoothly.

In order to ensure the water cooling strength of the cone oxygen lance, the middle tube of the cone part is also designed to be conical. In this way, the flow velocity of water is slow, but the gap of the backwater channel is the same as that of the original straight gun, but the flow velocity of backwater has not changed much.  When the inlet water slows down, the resistance of water flow decreases. When the pump capacity is surplus, the cooling water flow will increase and the water cooling strength is guaranteed. The maximum outer diameter of the middle cone pipe depends on the taper of the outer cone tube and the water cooling requirement of the lance body. Corresponding to the outer pyramidal tube, the middle cone tube has also designed a thick straight pipe and variable.

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