Define Reverberatory Furnace?
A reverberatory furnace is a type of furnace primarily used for the extraction of copper, tin, nickel, and aluminium metals and in the production of certain types of cement and concrete. Mostly, the furnace can be used for refining and smelting these materials.
The early records of the reverberatory furnace used are primarily for melting bronze in the medieval period. They were largely used for smelting of lead and copper in the late 17th century. However, with every passing decade, the construction materials changed by yielding better production capacities, whereas the furnace was used for smelting several metals besides just copper.
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Construction and Operation
Nowadays, the reverberatory furnace mostly contains a rectangular steel box that is lined with castables processing refractory bricks or non-wetting properties. There is also a vertically lifting door at one end, and the burners are usually placed on the other side of the furnace. Towards the opposite side of the burners, there is an exhaust gas duct and pouring spout. On the other side, roofs are made of similar refractory brick, which is durable, and it further helps to generate higher temperatures, leading to faster refining. However, as the latest technical innovations continue to be forged, they are improving and changing the basic construction materials and including the production capacity of this furnace.
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According to the operation, in a reverberatory furnace, heat is passed generally over the hearth that consists of the ore mixture. The primary method of heat transfer is through the radiation using the refractory bricks that are present in the roof and walls. Additional heating can be supplied from the burner to the ore. The furnace’s roof is also arched slightly and remains slanted to the direction of the flues bridge that deflects the reverberation flame. The mixture can be continuously heated until it touches the melting point.
Meanwhile, the impure molten metal is collected in the hearth, which looks as thick and is made of a strong material that can resist any disintegration also by the slag. This process is further repeated in the furnace until the ore concentrate can be tapped at regular intervals. Then, the collected material is sent to a converter for the process of further refinement.
Comparison with Blast Furnace Applications
These types of device applications fall into 2 general categories, which are given as metallurgical melting furnaces and lower temperature processing furnaces, which can be typically used for metallic ores and other related minerals.
A reverberatory furnace falls at a disadvantage from the efficiency standpoint compared to a blast furnace because of the spatial separation of the subject material and burning fuel. It is also necessary to utilize both direct contacts and reflected radiant heat effectively with the exhaust gases (convection) to maximize the transfer of heat.
These furnaces have used solid fuel historically, and bituminous coal has been confirmed to be one of the best choices. The brightly visible flames (because of the substantial volatile component) produce more radiant heat transfer than anthracite charcoal or coal. In contact with the combustion products, which can add undesirable elements to the subject material, can be used to advantage in a few processes. Control of the air or fuel balance can change the exhaust gas chemistry toward either a reducing or an oxidizing mixture, hence altering the chemistry of the material being processed. As an example, cast iron is puddled in an oxidizing atmosphere to convert it to bar iron or lower-carbon mild steel. The Siemens-Martin oven present in the open hearth steelmaking can also be said to as a reverberatory furnace.
In this context, the reverberatory furnaces (usually called air furnaces) were also used formerly for melting bronze, pig iron, and brass for foundry work. At the time of the 20th century, for the first 75 years, they existed as the dominant smelting furnace, used in copper processing, treating as either raw copper sulphide concentrate or roasted calcine. At the same time, the reverberatory furnaces have been supplanted in this role, first by the flash furnaces and very recently also by the ISASMELT furnaces and Ausmelt, as they are most effective at slags production with fewer copper losses.
Advantages and Disadvantages
A few of the prominent advantages of reverberatory furnace can be low operating, high volume processing, and maintenance costs. On the other side, the disadvantages can be listed as high metal oxidation rates, low efficiencies, and usually, a large space is required.
Reverberatory Furnace vs. Blast Furnace
We know that in a reverberatory furnace, the fuel besides the combustion gauges can be actually separated from the processed material. Here, heat can be supplied through the convection of hot gases and reflection from the furnace's roof and sides and produced by refractory bricks. However, when a blast furnace exists, there is no separation of the burning fuel (otherwise coke) and the subject material.