The residues and by-products from metallurgical industry are typically difficult to process. As an example, let us point out the hydrometallurgical precipitates from zinc plants, such as jarosite, as well as the dust and scales from steel industry.

Usually the above mentioned materials represent a non-combustible, chemically inert material. Residues can be treated by smelting the waste material, by binding it in some other material and by utilizing it in some other process or product. The reactions of the solid waste particles do not produce heat, but when smelting the waste, all necessary energy must be brought in the form of external fuel. Thus the reactions are endothermic. Often the waste particles are agglomerated of many small particles, and therefore they are porous in structure.

According to the patent FI 91283, there is known a method and arrangement for raising the temperature and mixing efficiency of mainly non-combustible, pulverous solid particles so high that the desired smelting and volatilization is reached. The invention is characterized in that the heating and mixing are carried out in at least two steps. Into the reaction shaft, there is fed a mixture of fuel and oxygen or oxygen-enriched air, which mixture is ignited, and the non-combustible solid material is fed in the flame. The furnace is provided with various burners for producing heat in addition to the pulverous material and air/oxygen input. The reactions are arranged to take place in a suspension smelting furnace.

From the patents US 4,654, 077 and US 4,732, 368 there is known a method and arrangement for smelting residues and slags. Also in the arrangements according to these publications, fuel is fed together with oxygen or oxygen-enriched air to the reactor, and the feed to be smelted is fed in the reactor in a later step.

From the patent FI 108865 there is known a device for feeding finely divided sulfidic solids and oxygen bearing oxidizing gas to a suspension smelting furnace, so that a suspension is created of the solid material and the oxidizing gas in a separate suspension forming space before feeding them into the reaction space.

By means of the invention, the combustion of the feed material is made more homogeneous.

When using separate burners in the reaction space for producing energy, it is difficult to transfer heat from the flame to the material to be smelted. In addition, the thermal load of the reaction space walls is high and difficult to control, because part of the emission of the burner flames is directed to the walls, thus causing local overheating.

The object of the present invention is to introduce a novel arrangement for smelting inert material, such as residue, in a metallurgical temperature reactor. A particular object of the invention is to enhance the smelting of inert material in a temperature reactor by forming a suspension of at least the inert material, the fuel creating the combustion heat, as well as the oxidizing gas, already before they are brought in the temperature reactor.

The invention is characterized by what is set forth in the characterizing part of claim 1. Other preferred embodiments of the invention are characterized by what is set forth in the rest of the claims.

Remarkable advantages are achieved by the arrangement according to the invention. The invention relates to a method for smelting inert material, such as residue, in a metallurgical temperature reactor, so that at least the inert material is fed through a separate mixing space to the reaction space of the temperature reactor, in which case at least the inert material and the fuel are mixed with the oxidizing gas in the separate mixing space to form a suspension, essentially before feeding them in the reaction space of the temperature reactor. Moreover, according to the invention, the suspension is conducted to the reaction space of the preheated temperature reactor for igniting the suspension, and further to smelting the inert material. When the suspension is created before the fuel is ignited, the combustion takes place evenly in the suspension. When the inert material, the fuel and the oxidizing gas, i. e. oxygen or oxygen-enriched air, are fed in the temperature reactor already in the form of a suspension, the heat released in the combustion of the fuel particles is efficiently transferred to the inert particles, and the inert particles are smelted. When also the fuel is mixed in the suspension, heat transfer between the burning fuel particles and the inert particles to be smelted is extremely efficient in comparison with a situation where the fuel is fed in later.

The inert material fed in the temperature reactor is finely divided, so that the diameter of the particles is 0.2 millimeters at most. When the inert particles are small, they have more time to smelt properly in the temperature reactor.

According to a preferred embodiment of the invention, the employed fuel is gaseous fuel, such as natural gas. Further, according to another embodiment, the employed fuel is solid fuel, such as coal dust. When using solid fuel, the fuel can be mixed with the inert material already before feeding the mixture to the mixing space.

According to an embodiment of the invention, the dust and gases created during the smelting of the inert material are removed from the temperature reactor.

According to an embodiment of the invention, binding agent such as silicate is also added in the mixing space. According to an embodiment of the invention, the employed mixing space is a diffuser burner. The term'diffuser burner'means a device provided with a separate space for creating the suspension before feeding the suspension to the reactor. According to an embodiment of the invention, the employed metallurgical temperature reactor is a flash smelting furnace.

Owing to the reactions taking place in the suspension and to heat transfer, also the thermal load of the temperature reactor walls is well in control, and overheating does not occur. Thus the reaction temperature can be maintained very high, for instance by increasing oxygen-enrichment, without having to fear that the heat volume transferred to the smelting unit walls would be harmful for the reactor itself, and respectively the waste heat is low. The arrangement according to the invention can also be considered an economical and effective method for smelting residue or corresponding inert material. According to the invention, additional burners for bringing heat in the reactor are advantageously not needed. The burning of the suspension-form fuel maintains the temperature in the temperature reactor continuously so high that ignition takes place immediately when the suspension enters the reaction space.

The invention is illustrated below with reference to the drawing.

Figure 1 Practical application of a method according to the invention Figure 1 illustrates a method according to the invention for smelting inert material 1, such as residue, in a metallurgical temperature reactor 8. The inert material is fed through a separate mixing space 2 to the reaction space 3 of a preheated temperature reactor 8, and said inert material 1 and fuel 4, such as coal dust, is mixed with oxidizing gas 5 in the mixing space 2 to form a suspension 6 essentially before feeding the suspension into the reaction space 3 of the temperature reactor.

In the mixing space wall there is arranged a required amount of nozzles 7, through which the oxidizing gas 5 can be discharged into the mixing space at various locations. When a solid state fuel is used according to the example, the fuel can be mixed with the inert material to be smelted already before feeding them in the mixing space, such as a diffuser burner. When being discharged from the mixing space to the reaction space 3 of the temperature reactor 8, the fuel particles in suspension 6 are ignited, and heat is transferred from the particles to the inert particles, which are smelted owing to the heat. When the reacting substances are in suspension already before the fuel is ignited, the heat transfer between the burning fuel and the inert material to be smelted is efficient. The molten material is removed from the bottom of the temperature reactor through a tapping hole, and the material is processed further according to the needs of the situation. The dust and gas created in the smelting process are exhausted from the temperature reactor along with the combustion gases. Dust is separated from gas for example in a gas cleaning unit, and possibly recirculated to the temperature reactor along with the inert feed.

The invention is described in more detail below with reference to the appended example.

Example According to the example, the method of the invention is applied for smelting dust from an LD steel converter, classified as hazardous waste, to a practically usable form as bound to silicate. After being treated this way, said dust can be utilized for instance as construction material, or it can be stored in a dumping area.

The dust from an LD converter (content Fe 33%, CaO 28%, Si02 4%, C 2%, iron is contained in the dust as hematite) is fed 5 t/h (=tons/hour) to a metallurgical temperature reactor, such as a flash smelting furnace, through a diffuser burner as mixed in an appropriate amount of coal dust (content: C 72.2%, H 4.8%, 1.21 t/h) for creating smelting energy, and sand (content: Si02 90%) 2.1 t/h for forming silicate slag. The oxygen needed for burning the coal is fed in the same burner as oxygen-enriched air (oxygen 1710 Nm3/h and air 1127 Nm3/h).

The inert material (dust from an LD converter), silicate (sand) and coal are mixed together before feeding them into the diffuser burner. In the burner, the oxygen- enriched air is mixed with a solid substance mixture, which means that all of the four components (dust, sand, coal and oxygen) are in a homogeneous suspension when entering the reaction space. The reaction space is preheated, and its temperature remains high owing to the burning of the coal contained in the suspension. The inert dust particles and sand are heated up to the melting temperature when being in suspension in the reaction space, and react with each other forming on the bottom of the temperature reactor molten silicate slag, according to the example 6.8 t/h (content Fe 23.0%, Si02 30.0%, CaO 18.8%, temperature 1300° C). The molten material is tapped out of the tapping hole of the temperature reactor and cast into billets or granulated for example by water, depending on the target of use. In the temperature reactor, there also is created gas (3783 Nm3/h and temperature 1333° C).

For a man skilled in the art, it is obvious that the various embodiments of the invention are not restricted to the examples described above, but may vary within the scope of the appended claims.