Reverberatory furnaces, also known as open hearth furnaces, have been used for metal smelting since the 17th century. They are typically used to melt non-ferrous and softer-than-iron metals, relying on convection and radiation for heat transfer. While improvements have been made, they still have a limited temperature range and require more fuel than refractory furnaces. One common use is to smelt soft lead into pure lead, but there are concerns about environmental contamination.
A reverberatory furnace is a type of metal smelting or refining furnace that has been in use since the mid-17th century and is more commonly known as an open hearth furnace. Smelts metal-bearing ore by generating hot gases near the roof of the furnace without the metal ever coming into direct contact with the fuel source that is used to heat it. Because a reverberatory furnace is an age-old design and has a limited temperature range, it is usually used to melt non-ferrous and softer-than-iron metals, such as copper, aluminum, and tin. The furnace design has also been used to smelt nickel and more environmentally hazardous metals such as lead, which has given it a negative reputation for the amount of air pollution it can generate.
Industrial furnaces can have complex or simple designs based on the precise amount of temperature control they must have and the types of ore they process. The reverberatory furnace is a rather simple design that has a usually rectangular enclosed chamber with a depression in the lower center known as the hearth. Flames or hot gases are directed through the firebox from above and the flue gases are then vented out of the furnace through one or more ducts along the opposite side. As the hot gases and flames are drawn into the furnace chamber, the opposite wall acts as a baffle off which they bounce to continue circulating through the chamber. A major design requirement for a reverberatory furnace is that the path of the burning fuel be as long and unobstructed as possible, as this allows for more intense heating of the interior and rapid smelting of the ore.
While a metallurgical furnace can rely on any of three types of heat transfer to the molten ore, from conduction to convection and radiation, usually the conduction or transfer of heat from one solid surface to another is more efficient. The reverberatory furnace, in contrast, relies almost entirely on convection and radiation, where heat is transferred to the ore via the surrounding air. This means that a reverberatory furnace requires significantly more fuel to heat and smelt the ore than a refractory furnace which relies on the ambient heat held in the refractory bricks to melt the metal. Softer metals such as bronze or compounds such as glass are usually processed in a reverb furnace as they have lower melting points, although some reverb designs have also been used to process steel in special cases.
While improvements to the reverberatory furnace, such as making the roof structure out of firebricks to raise the heat level, made them a more versatile class of process furnaces, they kept much of their age-old design. The reverb’s name itself comes from the arched shape in the center of the roof that allows hot gases to flow upwards and then bounce back into the center of the furnace. The location of the flue or flues for the exhaust gases is generally at the lowest point of the roof, and the highest point of the arch of the roof is immediately above where the fire and hot gases are routed. These changes have increased the temperature range of the furnace reverberation, which can give the exterior roof structure a kind of oblong whale-like appearance.
The reverberatory furnace is a general form of the puddle furnace, using the same principle of heating by hot gases to smelt iron ore. A primary use for reverberatory furnaces as of 2011, however, is to smelt soft lead metal into pure lead. These furnaces have several potential weak spots where the surrounding environment can be contaminated with lead. These include the kiln operating under positive pressure, emissions caused by dust and fume losses as the kiln is not a fully sealed chamber, and lead emissions to the environment when ore is funneled into the kiln and slag or pure metal are removed.
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