Melting furnaces 

Melting furnaces for secondary aluminum

The first question, which occurs when selecting a melting furnace for aluminum - is its capacity. Small oven capacity 5 or even 10 t apply to small enterprises, or for any specific conditions. This applies to plavilьnыm pecam, and distributing stoves, and pecam-mikseram.

Melting furnaces for aluminum

The smaller capacity ovens, the greater the cost of its maintenance per ton of metal. Therefore, in the aluminum industry is currently dominated by the oven capacity 25 tons or more. This bath furnace vessel is considered to be optimal in terms of service and performance.

Another factor in choosing the furnace vessel can be a production delivery. Typically, the minimum aluminum party is 20 tonnes and one of the requirements of customers is, to all the metal was from the same heat.

An important factor when choosing a furnace is the convenience of its service. Dross, which is formed during the furnace operation - smelter, furnace mixer, holding furnace - it tends to build up on the oven walls or sink to the bottom, sometimes it gets even on the furnace roof. Even at the optimal design of the furnace can not be avoided on 100 %. Growth slag thickness on the walls of the furnace and the furnace hearth decreases its effectiveness. Therefore, the slag must be periodically cleaned off. This is especially important when changing alloy, which is melted in the furnace. Therefore, the structure of the furnace must always be capable of removing slag from the melt surface and convenient cleaning ovens.

However, the most important issue when choosing a furnace is the choice of type of energy, which will be fed into the furnace.

Fuel for melting furnaces

In furnaces for melting, holding and processing of aluminum, the following types of fossil fuels are used:

The choice of energy source depends on its availability in the place of production location. Natural gas is very suitable for application in the furnaces, but it can be applied, if there is a next available gas pipeline. If this is not possible, the used oil or diesel oil.

Diesel fuel is more convenient, than oil, but it has a high price. Fuel oil cheaper diesel, but its use is associated with certain difficulties.

Furnace gas, fuel oil and diesel fuels generally have the structure, which are variants conventional hearth furnaces, chill casting furnaces and rotary kilns. These furnaces are used most frequently in the aluminum industry and are characterized by good performance in respect of suitable metal yield and energy consumption. As used in these furnaces, direct radiation, the efficiency of the combustion system is very high and heat transfer to the metal very high.

Electric melting furnaces

The designs of electric furnaces for aluminum melting furnace divided into the resistance and induction furnaces. Electric heating may be more convenient than in some cases, for example, gas, but subject to the availability of cheap electric energy.

Application of the electric heating in furnaces in the production of primary aluminum is represented justifiable, at least because of the cheapness of electricity for such production. However, the cost of electricity may be quite different in the place, where is the production of secondary aluminum. No gas or other fuel combustion products in the processing of molten aluminum furnace provides low loss of metal from the oxidation of, and also eliminates the contamination of molten aluminum with hydrogen and other gases. From the point of view of ecology,, This oven cleaner.

Crucible induction furnace

Crucible induction furnace can be operated with a pure scrap, ingots or molten aluminum. Due to limitations in size induction furnaces have a maximum capacity 8-10 tonnes, that may be insufficient for large-scale production of secondary aluminum. Such large furnaces have a rather large diameter and loaded on top, that is increased danger to personnel. Typically, induction furnaces require a large capital investment and have high maintenance costs and labor. Therefore, in the secondary aluminum industry for the production of induction furnaces are used rarely and, primarily, remelting fine aluminum chips.

Channel induction furnaces

Channel induction furnaces are typically designed with a circular shape and charge load from above, but there are also rectangular oven. The capacity of such furnaces achieves induction 40 tonnes. These furnaces operate with a constant "swamp", that is ready to metal is not completely drained, and part of it remains in the furnace for the next melting. This complicates the use of such furnaces as both smelters, as mixers and holding furnaces. AND, of course, it's not the cheapest furnace.

Electric resistance furnaces

Resistance melting furnace design as stationary or tiltable reverberatory furnace. The heating elements are mounted on the roof of the furnace and heating of the metal takes place only by means of radiation energy. Operating temperature refractory materials for walls and roof aluminum melting furnace is about 1200 ° C, that is the limiting factor for this type of furnace. Energy, which comes from the body of radiation, effectively prevents the melting of solid charge materials. Therefore such furnaces are mainly used as a holding furnace and casting the metal. With no loss of metal in the furnace combustion products from the oxidation of very low. The initial cost and maintenance cost of such furnaces is quite high, but it must be assessed for each individual case. Usually this type of furnace is not used in the production of secondary aluminum.

Electric or gas oven for aluminum?

If we compare gas heated ovens with electric furnaces equivalent in capacity and performance only in terms of energy cost, the cost of gas is usually less, than the cost of electricity.

From the standpoint of ensuring the degree of purity of the melt, hydrogen content and the loss of metal from the burn electric ovens have obvious advantages.

From the standpoint of environmental advantage of electric furnaces is doubtful. Yes, furnace itself does not pollute the environment, but for her it makes power, from which it takes energy. If, of course, this is not the hydroelectric.

On thermal power to generate electricity, you must first work out the heat, and then to the turbines and generators transform it into electrical energy. The overall efficiency of this process is about 33 %. In the electric furnace, this energy is converted back into heat. Therefore, the overall efficiency of the energy chain are clearly below, something and, which is achieved by direct gas or fuel oil heating.

Account of all the circumstances leads to the conclusion, that gas or oil-diesel furnace capable of providing sufficiently high efficiency at the smelting furnace and the processing of aluminum in combination with a lower cost of maintenance. At least, in the production of secondary aluminum.

However, of course, there may be cases, advantageous when used with electrically heated ovens, especially induction furnace. This combination is often used: a gas melting furnace and an electric furnace for holding and distributing aluminum. There are even combination furnaces: they use gas to melt aluminum, and when exposed, hand - electricity.

Source: Ch. Schmitz, Handbook of Aluminium Recycling, Vulkan-Verlag GmbH, 2014.