Analysis of 6 Major Reasons for Short Service Life and Damage of Ferroalloy Electric Furnace Linings

Analysis of 6 Major Reasons for Short Service Life and Damage of Ferroalloy Electric Furnace Linings

An improper furnace drying process can damage the furnace lining.

Common furnace lining materials include not only carbonaceous materials but also clay bricks, high-alumina bricks, refractory granules, asbestos boards, filler paste, and binders. These materials all contain a certain amount of moisture, and the filler paste and binders contain a large amount of volatile matter. If prebaked carbon bricks are used, they contain even more volatile substances. Both water and volatile substances will turn into gases and be released when exposed to high temperatures.

An improper furnace drying process when a new furnace lining is first put into use can cause damage to the lining. If the furnace drying time is shortened, the temperature will rise too quickly. When the furnace temperature rises too quickly, a large amount of moisture and volatile gases in the newly laid carbon bricks and related materials will be rapidly discharged. Moreover, the energy released at this time is also very large. If this energy is not released slowly and fully, it will cause the carbon bricks at the bottom of the furnace to loosen, and a large number of vent holes will appear between the carbon bricks in the furnace lining. Liquid manganese silicon alloy will seep into the furnace lining through these vent holes, arching the carbon bricks at the bottom of the furnace, causing a certain degree of damage to the furnace bottom, and even leading to a furnace leakage accident.

Unreasonable Electricity Usage System

Since the transformer’s capacity is determined at the factory, the basic operating cost of the transformer borne by the manufacturing enterprise is fixed.

(1) Overload operation can achieve good economic benefits. If more electricity is consumed during production, the basic operating cost per kilowatt-hour will decrease, that is, the price of electricity per kilowatt-hour will decrease, so the electricity cost per ton of alloy product will decrease. With fixed parameters, the size of the electric furnace is also fixed. In this case, an increase in the amount of electricity input into the furnace raises the furnace temperature, speeds up the melting process, and increases the output. In recent years, in order to obtain higher output and better economic benefits, electric furnaces have generally been operating under overload conditions, with overloads ranging from 10% to 20% to 30% to 40%.

(2) Overload operation can cause damage to the furnace lining. Although overload operation brings great economic benefits to enterprises, excessive overload also causes great damage to the furnace lining. Overload is basically achieved by first exceeding the voltage and then the current. Excessive current requires deep electrode insertion. When the desired current cannot be achieved, the electrode must be released quickly. If the electrode release is not properly controlled, the working end of the electrode will be too long, which will damage the furnace bottom. Currently, no refractory material can withstand the temperature of the electrode arc. Over time, the carbon bricks below the electrode base are prone to floating up, causing damage to the top layer of carbon bricks.

Long-term water leakage inside the furnace

Water leakage inside the furnace poses a significant hazard to smelting production. When the equipment leaks severely, the electric furnace cannot operate at full capacity, easily leading to massive material collapse and endangering the safety of on-site operators. Furthermore, the evaporation and decomposition of leaking water require a large amount of heat, causing heat loss within the furnace and increasing alloy power consumption.

If liquid water encounters high temperatures, it will rapidly decompose into hydrogen and oxygen. When hot carbon bricks encounter oxygen, oxidation is very rapid, potentially causing a furnace leak. If the furnace walls are soaked with water, the moisture will vaporize at high temperatures, causing the furnace walls to expand rapidly. If the water cannot be drained in time, it will damage the furnace walls.

Poor furnace shell welding leads to air leakage.

Carbon furnace linings are neither acidic nor basic, therefore they are resistant to both acidic and basic slag corrosion. They also have high refractoriness and a high load softening temperature, so under normal circumstances, the high temperatures generated during smelting (not the high temperatures of arcing), erosion, and the acidity or alkalinity of the slag have little impact. From these aspects, carbon furnace linings are relatively ideal for ferroalloy smelting. However, their fatal weakness is their extremely poor high-temperature oxidation resistance.

If the furnace shell welding is poor, or if the welds crack over time, the carbon furnace lining will inevitably be exposed to air. During production, the temperature of the carbon bricks in the furnace wall can reach over 300℃, providing conditions for the carbon furnace lining to react with oxygen. The lining will rapidly oxidize to produce carbon dioxide, leading to corrosion and damage.

Practice has shown that the oxidation of the furnace lining by oxygen begins in the gaps between the carbon bricks and then spreads to both sides. The oxidized areas are relatively smooth, without obvious sharp edges, and can develop in depth. When repairing a leaking furnace, first clean the burned-through area, then seal it with electrode paste or plugging mud, ensuring that the welded joints of the furnace shell are airtight.

Damage to Furnace Lining by Heavy Metals

The main raw material for the production of silicon manganese alloy is manganese ore, which is generally associated with heavy metals, primarily lead, tin, and silver. Lead has a melting point of 327.5℃ and a specific gravity of 11.35 g/cm³; tin has a melting point of 231.89℃ and a specific gravity of 7.3 g/cm³; silver has a melting point of 962℃ and a specific gravity of 10.49 g/cm³. Siemens manganese alloy has a melting point of 1240–1300℃ and a specific gravity of 6.0–6.4 g/cm³. These heavy metals all have lower melting points and higher specific gravity than silicon manganese alloy. During high-temperature smelting, the lower-melting-point heavy metals are reduced before manganese and iron. Because these heavy metals, reduced to liquid form first, are heavier, they easily seep into the carbon bricks through the brick seams, causing the bricks to arch and damaging the furnace lining.

Damage to the furnace lining due to lack of regular maintenance

Under normal circumstances, the furnace lining should be shut down for maintenance after about one year of use, especially the taphole area, which will suffer more damage than other parts after prolonged exposure to high temperatures, erosion, and oxidation. If the electric arc furnace is operated for a long time without regular maintenance, the damage to the furnace lining will inevitably worsen, potentially leading to a furnace lining leak accident.