Treatment technology of stainless steel slag pot

Slag of ladle metallurgical furnace for steelmaking (LMF) and argon-oxygen decarbonization furnace for stainless steel steelmaking (AOD) is generally dumped on the ground and gradually cooled. When this data is cooled, phase transition and/or hydration reaction will occur, resulting in volume expansion and slag disintegration. Then dust occurs, dust slag makes data processing and metal recovery difficult, air atomization method is widely used to deal with arc slag and converter slag in the iron and steel industry, this paper introduces the mechanism of LMF and AOD dust composition. And how dry slag granulation overcomes the problem of dumping and slow cooling. The advantages of dry slag atomization include directly stabilizing slag, improving metal recovery rate, or making metal recovery simpler and achieving higher economic benefits.

Introduction

1.1 Slow cooling pulverization principle of AOD slag

AOD slag is produced in the process of stainless steel production, and ladle metallurgical slag (LMF) is produced in the secondary refining process. AOD slag and LMF slag generally contain dicalcium silicate Ca2SiO4 (C2S).Ca2SiO4 (C2S) exists in various forms in slag, such as α, α'H, α 'L, β and γ. In the traditional slow cooling process, α-C2s exhibits a variety of solid phase changes during 600-700℃.Become a beta C2S. Part or all of β-C2s changes into γ-C2s during 400-500℃. The difference of crystal structure and density between β-C2s and γ-C2s leads to the increase of internal stress, which simply makes the slag appear.Now pulverized into dust, together with about 10%-20% of the volume increase. After slow cooling and pulverizing, AOD slag forms many powders. In addition, tricalcium silicate (C3S) changes into dicalcium silicate and free calcium oxide.Is the cause of slag increased, the subsequent hydration effect also increase the volume(See Equations (1) and (2)), make material pulverization further addition polymerization.

3CaO·SiO2→2CaO·SiO2+CaO（1）

CaO+H2O→Ca（OH）2（2）

1.2 Traditional treatment of slag

AOD slag and ladle metallurgical slag pos are generally stacked on the ground and slowly cooled. The commonly used slag treatment method is a huge protective cover with gas treatment and dust collection system, which is costly. In order to reduce the area occupied by buildings, water cooling and other accelerated cooling methods are often used to suppress the occurrence of dust. Cooling with water in the slag and embedded metal area, there is a potential possibility of water-slag metal steam blasting, which has obvious safety risks.AOD slag and ladle metallurgical slag are especially high in metal content, and water cooling will be more unsafe.

1.3 Stainless Steel Slag Stabilization Additive

There are many ways to make stainless steel slag stable in industry. Boric acid treatment is a very useful way to stabilize steel slag. Borate can be combined with various slags, but the mechanism that can prevent slag pulverization is the combination of borate and C2S. Borate requirement accounts for 0.25% of slag weight. Although a small share, it is an important input for both steel producers and slag handlers.

In addition to borate, phosphate can also secure stainless steel slag, but the demand has increased substantially, accounting for about 2% of the slag weight. Another option for stable stainless steel slag is to add a lot of silicon and adjust the alkalinity of the slag to prevent the formation of C2S. Dissolving so much silicon in practical production requires other slag treatment processes. Contain residue or aluminum bauxite and alumina can be used to secure EAF furnace stainless steel slag, decline chromium leaching. BGH stainless steel plant in the production of aluminum spraying practice.

1.4 Rapid quenching of slag

Rapid quenching of slag can coagulate C3S and prevent the formation of C2S. And even the part that has now been changed to C2S can prevent the conversion from β Changes to the γ; , thus swelling and bursting are minimized. When slag is cooled rapidly, the area occupied by crystal decreases greatly, and the polycrystal of C2S β At low temperature is now stable, can restrain the volume swelling, will not burst into dust.

Quench with water and air to achieve rapid cooling. The commonly used treatment method of blast furnace slag is slag water quenching process.In this process, the molten slag is quickly cooled by water spraying to form non-crystalline slag with cement function.Furnace slag generally does not contain metal, and the water quenching process can be well controlled, with a safe prospect.However, AOD slag and ladle metallurgical slag are rich in metal, the content reaches 50% of the weight ratio, so the water quenching process is very dangerous, which is not a feasible method.

Air quenching has been studied for forty years by dispersing slag into the air or blowing it away with compressed air. Select spiral disc or spiral cup skills for centrifugal granulation. It is a dry granulation skill, which has been pilot-tested with blast furnace slag. In this way, slag is thrown into the center of a high-speed spinning disk and sprayed radially from the outside, forming small droplets. Despite the success of this approach in the laboratory, there are still many serious problems to be solved. The condensation of molten data on the rotating disc simply causes the rotating disc to lose balance, which is a practical problem faced by successive industrial production. Condensing slag hitting the rotating plate simply makes the plate lose stability, appear glued or damaged, in order to finish or replace the plate and so on, downtime problems occur. Therefore, although a lot of research work has been done, the investment is also very large, centrifugal granulation skills have never carried out large planning of industrial production.

Air atomization is a hardening skill to stabilize AOD slag and ladle metallurgical slag, which was developed for stable BOF slag in Asia 30 years ago. This skill consists of a slack progress in which air is forced through the slag stream. The molten slag released from the furnace is sent through the slag pot or slag pot to the slag feeder located in front of the atomizing chamber. The air spray gun of the atomizing granulator quenching the molten slag in the atomizing chamber. In the atomizing room, the blowing air causes the molten slag to be scattered into particles and blown together to the hot slag particles to cool the slag particles and get the thermal flow.The cooled and condensed residue can be collected regularly or transported consecutively to a collection room and then packaged for storage or sale. The recovered hot waste gas directly enters the waste gas treatment system or equipment so that the waste heat can be used.

1.5 Ecomaister-Hat Ch dry atomization process

Air atomization is a hardening skill to stabilize AOD slag and ladle metallurgical slag, which was developed for stable BOF slag in Asia 30 years ago.The skill consists of a distraction process in which air is forced through the slag stream.The slag released from the furnace is sent to the slag feeder located in front of the atomization chamber through the slag pot or slag pot, and the air spray gun of the atomization granulator quench the slag in the atomization chamber.In the atomizing room, the blowing air causes the molten slag to be scattered into particles and blown together to the hot slag particles to cool the slag particles and get the thermal flow.The cooled and condensed residue can be collected regularly or transported consecutively to a collection room and then packaged for storage or sale. The recovered hot waste gas directly enters the waste gas treatment system or equipment to make the waste heat used.

Because there is no machine and equipment in the production process and slag directly touch. Dry atomization process is relatively simple.The damage of slag flow or coagulated slag in the slag pot will not damage the machinery and equipment required by the process operation. This skill is therefore widely used for slag treatment in processes that contain iron (such as electric arc furnaces, converters and ladle furnaces) and in processes that do not contain iron (zinc and silicon-manganese).

The primary advantages of atomization skills include: slag treatment safety is improved, slag heat can be recovered, slag treatment costs are reduced, and most importantly, high value-added slag products can be stably produced.