ELECTRIC ARC FURNACE FLOWLINE: BRIEFLY EXPLAIN

By | August 8, 2016
electric arc

                                Fig 1. Electric arc furnace flowline

In order to ensure steel making more economically and environmentally sustainable and profitable, Electric arc furnace flowline process was introduced in the market. This process has become highly successful in reducing greenhouse effects by mitigating greenhouse gas emissions significantly.

However, this process needs more significant closures of basic oxygen furnace capacity. In this article, we shall discuss on electric arc furnace flowline process in details.

Furnace Operations

Furnace operations work, on the principle of batch melting process that produces batches of molten or liquid steel call “heats”.  The cyclic order of this operation is called the tap-to-tap cycle.

electric arc furnace

                      Fig 2. Electric arc furnace

 

Given below are the steps of operation that goes under tap-to-tap cycle:

  • Furnace charging
  • Melting
  • Refining
  • De-slagging
  • Tapping
  • Furnace turn-around

The cutting-edge tap-to-tap operation takes less time. It is lower than 60 minutes. Besides, there are some twin-shell-furnace operations that take 35 to 40 minutes As tap-to-tap times.

electrode

                                         Fig 3. Electrode

Furnace Charging

This is the first step in the production of any heat selected for making the grade of steel. Generally, a schedule or routine is developed. It is prior to each production shift. Therefore, the melter must know the schedule for his shiftin advance. The scrap yard operator prepares buckets of scrap depending on the needs of the melter.It is the first step towards Electric arc furnace flowline process .

At the first step of any tap-to-tap cycle, melter is to ensure the “charging” into the scrap. The roof and electrodes are raised. Now these are swung to the side of the furnace so that the scrap charging crane can move a full bucket of scrap into the place over the furnace. The bucket bottom is designed like a clamshell. The bucket opens up automatically with the reaction of two segments on the bottom of the bucket. Therefore, the scrap falls down into the furnace. Now scrap crane removes the scrap bucket. Once it is done, the roof and electrodes swing back into place over the furnace. At last, the roof is lowered and then the electrodes are done the same to strike an arc on the scrap. This helps to start the melting process of the cycle. Needless to say, the number of charge buckets of scrap depends on the needs. It varies on the necessity of heat production, the volume of the furnace and definitely the scrap density.

It is worthy to mention here that most advanced furnaces are developed to operate a minimum amount of back-charge.

Melting

 The melting period is the backbone of electric arc furnace operations. This step is conducted by supplying adequate energy to the interior for the furnace. This energy can be produced in an electrical or chemical way. Electrical energy is supplied through the graphite electrodes used as the largest contributor in the melting operation. Generally, an intermediate voltage tap is chosen until the electrodes bore into the scrap. The light scrap is placed on the top of the charge to accelerate bore-in. in this operation step nearly 15 % of the scrap. This happens during the initial bore-in period. Not more than five minutes, the electrodes penetrate the scrap sufficiently in a subtle way so that a long arc (high voltage) tap can be used without the fear of radiation damage to the roof. The long arc can maximize the power transfer to the scrap. After that a liquid, pool of metal is formed in the furnace hearth. At the very beginning, the melting the arc remains erratic and unstable.

 

Refining

 Refining operations in the electric arc are conducted for the removal of aluminum, silicon, sulfur, manganese, phosphorus, and carbon from the steel. In the modern times, dissolved gases, especially hydrogen and nitrogen are passed through it. In the past days, refining operations were conducted with a flat bath. These refining reactions are all dependent on the availability of oxygen. Oxygen was lanced at the end of meltdown to lower the bath carbon content to the desired level for tapping. Most of the compounds which are to be removed during refining have a higher affinity for oxygen that the carbon. Thus the oxygen will preferentially react with these elements to form oxides which float out of the steel and into the slag.

In modern EAF operations, especially those are operating with a “hot heel” of molten steel and slag retained from the prior heat, oxygen may be blown into the bath throughout most of the heat. As a result, a few melting and refining operations occur simultaneously.

As the consequences of reactions, Phosphorus and sulfur occur are produced in the furnace that makes the charge higher inside. Unfortunately, the conditions are not suitable for the removal of phosphorus. This is why all attempts are made to push it into the slag.Refining operation is an important part of electric arc furnace flowline process.

 

De-slagging

 De-slagging means removal of impurities from the furnace. The fact is that at the time of melting and refining operations, some undesirable materials are produced automatically in the bath. To remove this, oxygen is passed through melted materials in order to remove the slags. In this operation, phosphorus is pushed into the slag as much as possible and removed this. Sometimes carbon is added in order to reduce the preponderance of FeO in metallic iron.

 

Tapping

As soon as desired steel composition and needed temperature are achieved in the furnace, the tap-hole opens up automatically. After that, the steel is poured into a ladle for transferring it for the next batch operation. During the tapping process bulk alloy are added, depending on the bath analysis and the targeted steel grade.

De-oxidizers are sometimes added to the steel to lower the oxygen content if it is needed for further processing.

Furnace Turn-around

During this process, the electrodes and roof are raised. If needed, repairing works are made to the hearth, slag-line, tap-hole and spout. In the case of a bottom tapping furnace, the tap-hole is filled with sand. This reduces the power-off time for the EAF and maximizes furnace productivity.

Above we discussed are the electric arc furnace flowline process.

This method is the industrial steel making process. This is highly beneficial for both economy of a country and environmentally friendly.  This is most commonly used method in today’s steel manufacturing industries.

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