Process and Apparatus for Melting a Furnace Charge

(a) Field of the Invention

The present invention concerns the melting of a charge in a furnace, for example an electrical furnace for melting scrap iron for the production of steel, of the type which uses an input of melting energy to the charge and with post-combustion of the smokes by injection of an oxygenated gas in the furnace space above the charge in the form of at least one first jet at a first horizontal level of the space and having at least one substantially tangential component with respect to a vertical axis of said space.

(b) Description of Prior Art

Such a process is described in EP-A-0.257.0450 or the equivalent U.S. Pat. No. 4,827,486, and simultaneously utilises a stirring of the bath and an injection of an oxygenated gas by means of fixedly mounted injectors located at a level at the top of the furnace.

The object of the present invention is to propose a process for the injection of an oxygen containing gas thereby improving, for example, for the post-combustion, the distribution of the oxygen containing gas with the combustion gases, and enabling to increase the duration of exchange between the oxygen containing gas and the combustion gases, for example CO and H.sub.2 which escape from the charge, to ensure a maximum transfer of the energy formed, towards the metallic charge.

For this purpose, according to a characteristic of the invention, the oxygen containing gas is injected in the form of at least one second jet having a main component which is substantially tangential to a second level of the space, the first and second jets being oriented so as to constitute two oppositely directed rotary currents around the axis of the space.

According to other characteristics of the invention:

the jets of oxygen containing gas of a stepped series of jets undergo cyclic variations of the flow of oxygen containing gas;

the cyclic variations of the flows of oxygen containing gas from a series of jets are synchronized with one another;

the variations of the flows are of the pulsating type between a minimum flow and a maximum flow (that is, the flow of the oxygen containing gas injected by the injectors is not constant but varies cyclically between a maximum flow and a minimum flow which, for example, may be almost zero);

the cyclic variations of the flow of oxygen containing gas from a stepped series of jets are carried out at the same frequency as the cyclic variations of flow of oxygen containing gas of the stepped series of jets which is immediately adjacent thereto;

the cyclic variations of the series of jets of a plurality of stepped series of jets are carried out in synchronism (that is, are performed at substantially the same time).

In this manner, an accentuated and controllable turbulence of the oxygen containing gas with the gaseous products originating from the charge is ensured, and it can be adjusted to an optimal value corresponding to the post-combustion reaction which is as complete as possible.

The invention also concerns an apparatus for carrying out such process of the type comprising a space overhanging a charge into which emerges at a first horizontal level of the space, at least a first injector of oxygen containing gas which is oriented to give a jet having at least one component which is substantially tangential with respect to the vertical axis of the space, characterized in that it comprises at least a second injector of oxygen containing gas emerging into the space at a second horizontal level and oriented to deliver a jet having a substantially tangential main component which is oppositely directed with respect to the jet of the first injector.

The characteristics and advantages of the invention will appear from the description which follows of a melting apparatus of the electrical furnace type, with reference of the annexed drawings in which:

FIG. 1 is a vertical cross-section of an electrical furnace;

FIG. 2 is a horizontal cross-section of the same furnace.

With reference to the annexed figures, an electrical furnace 1 has a hearth 2, a lateral partition 3 with a so-called cleaning door 4 and a pouring jet 5 for the molten product, as well as a vault 6 also forming the support of three electrodes 7, 8, 9 which are also distributed around a vertical axis X-Y.

The furnace 1 is provided with at least two stepped series of at least two, typically at least three injectors of oxygen containing gas, respectively 11a, 11b, 11c, and 12a, 12b, 12c, the first series of injectors 11a, 11b, 11c being located at a level N.sub.1 near half the height H between the lowest point 2' of the hearth 2 and the highest point 6' of the vault 6, while the second stepped series of injectors 12a, 12b, 12c is located at a level N.sub.2 which represents approximately 3/4 of this same height. The injectors 11a, 11b, 11c, on the one hand, 12a, 12b, 12c, on the other hand are therefore located in two stepped horizontal planes in which the vertical distance apart is of the order of one quarter of the maximum height H of the vault. Each injector is oriented so as to present a main tangential component and a radial centripetal component. The openings 11a, 11b, 11c, of the lower series of injectors at level N.sub.1 =H/2 are all oriented, as viewed from above, in the direction of the hands of a watch, so as to form a lower current of gas with rotary circulation F.sub.1 in the direction of the hands of a watch, the openings of the injectors 12a, 12b, 12c of the upper series of injectors at level N.sub.2 =3 H/4 being all oriented, as viewed from above, in the opposite direction to the direction of the hands of a watch so as to form an upper current of gas with rotary circulation F.sub.2 in a direction opposite to the direction of the hands of a watch.

The injectors at a same level (11a, 11b, 11c at level N.sub.1)(12a, 12b, 12c at level N.sub.2) are supplied by means of ducts 13a, 13b, 13c derived from a main duct 13, on the one hand, by means of ducts 14a, 14b, 14c derived from another duct 14 on the other hand so a to produce for example differences between cyclic flows of variations, for example pulsated flows, of the series of injectors 11a, 11b, 11c at level N.sub.1 with respect to the series of injectors 12a, 12b, 12c at level N.sub.2.

The process and apparatus described may be used not only in an electrical furnace for the production of steel but also for the production of ferro-alloys, in any melting or refining container for the production of metallic alloys and more generally in any container containing a liquid mass at high temperature producing gases which are not completely burned (metallurgy, glassware, cement manufacture).