Analysis on the Reasons of Under-burning of Electrode Paste in Submerged Arc Furnace Smelting Nickel Pig Iron
I think the closed paste smelting of submerged arc furnace electrode paste depends on two major factors: process characteristics and parameter selection.
Process characteristics-According to the resistance characteristics of the smelting melt, select the appropriate smelting mode.
Parameter selection-according to process characteristics, flexible selection of appropriate electrical parameters.
Speaking of smelting modes, briefly introduce the three major smelting modes of electrode paste submerged arc furnace.
Submerged arc mode-requires energy to discharge the electrode paste electrode submerged arc and hot furnace mouth operation in the slag layer, such as: high-carbon ferrochrome, silico-manganese alloy.
Submerged arc mode-requires energy to be concentrated in the submerged arc and cold material surface operation in the reaction zone (note: it is different from the above), such as: ferrosilicon.
Resistance mode-such as: electrode paste ferro-tungsten smelting.
Arc shielding mode-requires energy to be released on the surface of the molten pool and hot furnace mouth operations, such as nickel-iron.
A friend asked, can’t the submerged arc mode be used in the high-standard closed paste smelting of ferronickel?
can.
1. Submerged arc mode-laterite ore-melt resistance characteristics (with limestone)-slag type (silica-calcium oxide-magnesia system, alkalinity is about 0.93)-ferronickel products (nickel group Low content, high iron content, containing 10%-11% nickel)
Electrical parameters-high current, low voltage-low power factor-easy to insert electrodes-easy to cut off or under load-high smelting temperature (above 2100 degrees on average)-serious corrosion of furnace bottom- High power consumption
2. Arc shielding mode-laterite ore-melt resistance characteristics (natural ore)-slag type (ferrous oxide-silica-magnesia system, alkalinity about 0.6)-ferronickel products (nickel component High, low iron content, containing 15%-20% nickel)
Electrical parameters-low current, high voltage-high power factor-electrode lift-low smelting temperature (melting slag is 1623-1703 degrees, alloy melting point is 1400-1493 degrees)-low power consumption
Through the comparison of the process and electrical parameters of the above two modes, it can be seen that the submerged arc mode furnace is deteriorated and difficult to operate, the content of nickel is low, the power consumption is high, and the electrode paste electrode consumption is also high; while the shielded arc mode has a great Advantages: stable furnace conditions, easy operation, high nickel content, low power consumption, and low electrode paste and electrode consumption.
This is the conclusion drawn by the production test of the smelter, not the result of imagination.
Therefore, the shielded arc mode is the preferred mode for most domestic and foreign electrode paste submerged arc furnace methods (that is, Elkem method) for smelting ferronickel.
Why choose a higher secondary voltage for the arc shielding mode?
First, the resistance characteristics of the nickel-iron melt are: the resistance is large, and the electrode is easy to be inserted.
The characteristic of shielded arc smelting is that the melting point of the slag is higher than the melting point of the alloy.
The reduction reaction of smelting is carried out at the interface of the nickel ore melt. The heat is mainly generated at the junction of the arc and the material layer and the slag layer. The temperature of the crucible area at the bottom of the electrode paste electrode is the highest, and the temperature field in the rest of the furnace is distributed in a layered manner.
In short, the heat is transferred through the slag to control the reduction of ferrous oxide. The selective reduction process is used to produce the charge, which is mainly made of nickel ore, and most of it is in a non-melted state in the furnace. When the electric charge is not molten or liquid, the material moves slowly. Therefore, the resistance of the charge is large, and the conductive medium in the furnace is greatly reduced after the slag iron is removed from the electric furnace.
If a low-voltage, high-current power supply system is adopted, the arc of the electrode terminal is short, and the current transmission in the furnace material with little melting is severely blocked, and it is easy to cause interruption or insufficient load.
Second, what are the benefits of high secondary voltage?
Increasing the secondary voltage can increase the arc power, the arc is elongated, the arc starts, the electrode rises, the high temperature area moves up, and the power factor is high.
It is consistent with the characteristics of the arc smelting process.
3. What are the factors for selecting high secondary voltage?
1. When the resistance is large, the voltage should be selected high (it is consistent with the resistance characteristics of the nickel-iron melt).
2. When the diameter of the pole center circle is larger, the secondary voltage should be larger.
3. When the inner diameter of the furnace is larger, the secondary voltage should be larger.
Most of the current ferronickel furnaces are modified by smelting other products. Judging from the available information, most of the furnace parameters are calculated by the Mikulinsky coefficient method.