Reverberatory Furnace

In medieval times, metallurgists began to face a common problem: the use of direct flames for smelting impurified the metals that were intended to be purified. To tackle this issue, they developed a new model of metal furnace with an arched roof, now known as the reverberatory furnace, incorporating a few modifications. This revolutionary smelting tool was such a marvel that it is used in scores of metallurgy projects to this day, and it will be our topic of discussion today. So let’s begin! 

1.0Reverberatory Furnace Meaning

The reverberatory furnace's meaning lies in its name. The word reverberatory is derived from the term reverberate itself, which means “to reflect”. In this furnace, the heat produced by burning fuel in a separate room is reflected from the arched ceiling and sent down onto the material core in the hearth below. The fuel and the charge (the thing being heated) do not directly touch each other, unlike other furnaces, which require close contact with metal for smelting. This avoids contamination, which ultimately enables more controlled heating, a remarkable feature when handling metals such as copper, tin, or aluminium.

2.0Construction of Reverberatory Furnace

The structure and construction of a reverberatory furnace have evolved through history from its simple medieval version to the most advanced ones with a higher efficiency. While the working principle remains the same for both, medieval furnaces consisted of a hearth, an arched roof, a firebox, and a chimney with manual control, modern furnace consists of: 

1. Main Body – A refractory-lined rectangular box of steel that resists slag and heat corrosion.
2. Roof – Slightly arched and sloping towards the flue; constructed from the same refractory materials to reflect radiant heat effectively.
3. Burners – Situated on one side of the furnace to produce heat; can usually utilise oil, gas, or electricity.
4. Vertically Lifting Door – Provided at one end for charging and maintenance purposes.
5. A Pouring Spout – Placed opposite the burner to draw out molten metal.
6. Exhaust Gas Duct – Placed close to the pouring spout for efficient removal of waste gases.
7. Hearth – Constructed of robust, thick refractory material that can endure high temperatures and slag corrosion.
8. The Bridge Wall and Flue – Guides the flame and deflects it for maximum reverberation and uniform heating.
9. Heat Transfer – Primarily by radiation from hot refractory surfaces and direct flame reverberation.
10. Temperature Control – Modern furnaces incorporate sensors and automated systems for regular operation.
11. Tapping and Refining – Metal is tapped at regular intervals and passed on to be purified further.

3.0Working Principle of Reverberatory Furnace

The working principle of the reverberatory furnace is based on the process of indirect heating by means of an arched roof. This arched roof is the main component of this method, as this is the part of the furnace where the heat gets reflected after intersecting with the roof. Regardless of the metal that needs to be smelted and the type of furnace, the process in a reverberatory furnace remains the same, which is: 

• Charging the Hearth: In the first step, scrap metal or ore, also known as the charge, is placed in the hearth.
• Igniting the Firebox: Now, the fuel is combusted in another chamber, different from the charge chamber.
• Heat Transfer: Radiant heat and hot gases bounce off the arched ceiling onto the charge.
• Melting and Reactions: The metal is melted or reacts (e.g., smelting, oxidation).
• Slag Formation: Impurities float up to create slag, which is removed separately.
• Molten Metal Collection: The purified, molten metal accumulates in one part of the hearth.
• Tapping: The molten metal is tapped or drained from the furnace.
• Gas Exit: Waste gases are released through a flue or chimney after heat transmission is finished.

See the following reverberatory furnace diagram to get a better understanding of the working of this tool. 

4.0Applications of Reverberatory Furnace

As mentioned earlier, a reverberatory furnace is used for a wide range of metallurgical processes, which include: 

• The most common use of a reverberatory furnace is smelting of non-ferrous metals, like copper, tin, nickel, and lead. Smelting is the process of purifying an impure ore via heat and chemical reducing agents. 
• It is also used in refining projects in which impurity control is an important aspect. 
• A reverberatory furnace is also used to recycle and melt aluminium scrap or waste materials. 
• Owing to its unique construction design, the reverberatory furnace is ideal for treating metals that require the avoidance of direct flame contact. 

5.0Reverberatory Furnace vs Blast Furnace