Combined Installation of a Metal Production Unit and a Unit for the Separation of Air Gas

The present invention concerns a combined installation consisting of at least one unit for the production of at least one metal, comprising at least one device for the production or treatment of metal, and at least one unit for the separation of gas from the air, with at least one outlet for at least one air gas.

Metal production units, in particular for steel, at present integrate several metal production or treatment devices, if necessary regrouping them in a complete production line that extends from the treatment of the raw mineral to the production of finished products ready for marketing. Most of these metal production or treatment devices consume large quantities of compressed air (over 100 Nm.sup.3 of air per ton of metal) and/or gas from the air, notably oxygen (over 50 Nm.sup.3 per ton of metal) and/or a neutral gas (over 10 Nm.sup.3 per ton of metal). These air gases are generally supplied from liquefied gas containers or by gas pipelines. Besides, these air gases are produced by units for the separation of air gases, notably of the cryogenic type, which are also supplied with compressed air. Whether for the metal production or treatment devices or for the air gas separation units, the air compressors used are particularly heavy-duty items of equipment that consume a great deal of electrical energy, and because of this, considerably increase the production costs of such units.

The aim of the present invention is to propose a combined installation comprising at least one metal production unit and at least one unit for the separation of air gas, which will optimize the synergism between these units, notably by sharing a compressed air production unit and by the direct, on-site coupling of metal production or treatment units with the sources of air gas offered by the air gas separation unit.

To this end, in accordance with one characteristic of the invention, the combined installation comprises a compressed air production unit having at least one outlet connected to an air gas separation unit and to the said production or treatment unit, to supply these latter with air.

In accordance with another characteristic of the invention, the installation comprises at least one fluid pipeline connecting the outlet of the separation unit to the said device and supplying at least one air gas, in gaseous or liquid form, to the latter.

The present invention also aims to propose a combined installation of the above type which also makes use of the thermal synergism between the two units, notably the refrigeration power offered by a separation unit, in particular of the cryogenic type.

To this end, in accordance with a characteristic of the invention, the metal production or treatment unit comprises at least one cooling circuit, at least one part of which is functionally associated with at least one fluid circuit of the cryogenic air gas separation unit.

A further aim of the invention is the optimization of a cryogenic separation unit supplied with excess compressed air.

Other characteristics and advantages of the present invention will emerge from the following description of design options, which are presented for illustrative purposes but are in no way limiting, and which refer to the attached drawings, in which:

FIG. 1 is a schematic view of a design option for a combined installation according to the invention, which groups together a steel production line and a cryogenic air gas separation unit, and

FIG. 2 is a schematic view of a design option for a cryogenic air gas separation unit suitable for use in a combined installation according to the invention.

In the description that follows and in the drawings, identical or analogous elements are designated with the same reference numbers, if necessary indexed.

In the design option represented schematically in FIG. 1, three mutually cooperating main groups are shown, namely a high and medium pressure group for the production of compressed air I, a steel production line II, and a cryogenic air gas separation unit III, in this case of the cryogenic type.

In the example shown, the line II comprises a steel melting furnace 1, typically an EAF arc furnace or an EOF tuyere and burner-type furnace, whose molten metal is transferred to a converter-type device 2 for the treatment or composition adjustment of the molten steel, typically an AOD ("argon oxygen decarburization") or a BOF ("basic oxygen furnace"), which is then transferred via a continuous casting unit 3 and a continuous reheating furnace 4, to a rolling mill 5. The furnace 1 is charged with steel, either directly from a device 6 of the blast furnace, or COREX, or DRI direct reduction type for the reduction or pre-reduction of iron ore, or with scrap iron from a scrap sorting device 7. The cryogenic air gas separation unit III comprises typically at least one double-distillation column 9 which, as shown in FIG. 2, includes a medium-pressure column 10 and a low-pressure column 11 and, advantageously, an argon mixture column (not shown), which is supplied with compressed air under a pressure of at least 4.times.10.sup.5 Pa, typically between 6 and 35.times.10.sup.5 Pa, by a compressed air supply line 12 incorporating an adsorption-type purifier device 13. In the example shown, the separation unit comprises at least one pure oxygen outlet 14, an outlet for largely pure nitrogen 15, an outlet for largely pure argon 16, an outlet for residual gases 17 (generally impure nitrogen), and an additional outlet for cryogenic fluid 18, for example liquid or gaseous nitrogen or liquid air.

In accordance with one aspect of the invention, the groups II and III are supplied with compressed air by a common compressor group

I comprising a line of compressors 19 with several outlets, at least some of which are connected to an oil precipitation and drying group 20, which supplies at least compressed air at high pressure (typically in excess of 6.times.10.sup.5 Pa) to at least one pipeline 21, and advantageously at least air compressed to medium pressure (between 3 and 6.times.10.sup.5 Pa), to a series of pipelines 22. The pipeline 21 is directly connected to the pipeline 12, while the pipelines 22 are connected, via a control and if necessary a pressure reduction device 23, to the furnace 1 to feed its burners or tuyeres, to the molten steel treatment device 2 to feed its tuyeres or burners, to the reheating furnace 4 to feed its burners, and to the rolling line 5 to provide air for the vaporization of cooling water, and to supply all these devices with medium-pressure dry air known as "instrument air" for the protection or shielding of control and monitoring equipment associated with these devices, for example temperature probes or television cameras. Medium-pressure air is also fed to the sorting device 7 to supply its sorting air ejection nozzles. Medium-pressure and/or high-pressure air is also directed to the steel reduction or pre-reduction device 6, to supply its tuyeres or burners and/or as instrument air. Medium-pressure dry compressed air may also be supplied from an outlet 24 of the device 23, to a compressed air network for other equipment used in the installation or nearby.

Correlatively, in accordance with an aspect of the invention, the oxygen supplied by group III is directed to the reduction or pre-reduction device 6 to supply its burners or injectors, to furnace 1 to supply the post-combustion burners or tuyeres, to the molten steel treatment device 2 to supply its tuyeres or burners, and to the reheating furnace 4 to supply its burners. Similarly, nitrogen and/or argon are directed to device 1 to carry away carbon particles, to device 2 to produce bubbling, and to devices 3-5, to render them inert or to zone them.

From the above description it will be understood that the essential gases required for the operation of groups II and III are supplied from the compression group I, which in fact transforms the electrical energy brought in by a line 25, to pneumatic energy used in many ways, so permitting a reduction of the production costs with an advantageous electrical energy contract and a large-scale compression group whose yields are therefore higher than the yields of individual compression groups for each group or, as is often the case nowadays, for each of the devices in group II.

In accordance with another aspect of the invention, it is also possible to take advantage of the heat content or the saturable gases available in group III to cool the elements of groups II and if necessary I. As shown in FIG. 1, a cooling water inlet pipeline 26 acting as a direct or indirect heat exchanger is located within an exchanger 27, with a flow of residual or saturable gas available at outlet 17 and/or outlet 18 of the double column 9, and directed by a pipe 170, the water so cooled being directed to input A of the cooling water circuit of furnace 1, or to that part of the cooling circuit of furnace 1 which acts upon its hottest zones, to an input B of cooling water for at least one stage of the compressor line 19, and/or to an input C of cooling water for the reduction or pre-reduction device 6. Synergism between groups II and III may be improved still further by recovering the hot water or steam from water cooling circuit A of furnace 1, from circuit C of the device 6, and/or from cooling circuit B of the compressor line, and directing it to the purification device 13 in order to regenerate its absorption medium.

The hot water or steam emerging from the cooling circuits A to C, and/or the hot compressed air emerging from a stage of the compressor line 19 may also be utilized to vaporize a cryogenic liquid available at the outlet of the separation unit III or, notably in the case of argon not necessarily produced by unit III, supplied from a reservoir, the resultant gas being at least in part fed to the devices of unit II.

In accordance with another design option of the invention, the compressor line 19, at least in part, is of the compressed steam distillation type, the steam being advantageously provided by a steam network E, at least part of which exchanges heat with at least one of the devices 1-6 of the metal production unit II.

In this way, it is possible to make use of the energy produced by the said device (1-6) to form steam, in the classical way. To this end, the steam network E is more particularly connected to at least one among the metal melting furnace 1, the reheating furnace 4, and the ore reduction or pre-reduction device 6.

FIG. 2 shows a particular design option for group III, which makes use of the availability of large quantities of high-pressure air from the outlet of a compressor line of high capacity, used to produce oxygen and nitrogen at least at medium pressure and dried and purified air at least at medium pressure, to supply at least the various devices in group II. The figure shows the high-pressure air supply line 12 comprising, upstream from the purifier 13, a refrigeration group 28, of the mechanical or absorption type. The cooled and purified air is over-compressed by a fan 29 driven by an expansion turbine 30, known as a Claude turbine, which allows expansion of part of the over-compressed air, and is cooled in a first exchange line 31, then passed into the body of the medium-pressure column 10. Part of the over-compressed and cooled air is directed via a second cold exchange line 32 and an expansion valve to an intermediate level of the medium-pressure column and, having been under-cooled, to an upper level of the low-pressure column 11. In this design version, liquid oxygen is extracted at 33, from the body of the medium-pressure column 11, gaseous nitrogen is extracted at 36, at the head of the medium-pressure column 10, and liquid nitrogen is extracted at the head of the medium-pressure column 11. In accordance with one aspect of the invention, the expanded air, typically at a pressure between 5 and 7.times.10.sup.5 Pa at the outlet of the turbine 30, is collected and directed by a line 34 crossing the exchange lines 32 and 31, to the distribution device 23 or directly to some of the devices of group II. The expansion of this supplementary air not introduced into the double column 9 allows the production of additional cold, which is used to increase the production of the cryogenic liquids in the double column 9, and this, with notably less specific energy, by virtue of the provision of compressed air by the high-capacity compressor group I. As a result, besides the supplies of gases to the devices of unit II, the cryogenic unit III can, as shown by the network E in FIG. 1, supply at least part of these fluids to other areas where they are used, via pipelines after vaporization, or in bulk form. As a variant, and as also shown in FIG. 2, over-compressed air can also be tapped directly from the line connecting the compressor fan 29 to the expansion turbine 30, upstream from the exchange line 31, to provide a supply, via a line 35, to the distribution device 23 or directly to at least some of the devices of group II.

The installation according to the invention, apart from reducing energy, investment and operating costs, allows optimization within the metal production unit, of each of groups I, II and in such a way as to reduce the ground area occupied and decrease the level of nuisance, notably the overall noise level, produced by the installation. In fact, the installation of the invention permits group I, which is generally noisy, to be localized in a single and unique part of the site chosen for that purpose.

Though the present invention has been described in relation to particular design versions, it is not limited by these but on the contrary, can be modified and varied in any way deemed appropriate by the designer. Notably, the integration may be achieved in a similar way, alternatively, or additionally, with an air gas separation unit of the adsorption or permeation type, producing in this case essentially pure oxygen and/or essentially pure nitrogen instead of a cryogenic unit such as 9 or in parallel with the latter, the two separation units in the latter case being supplied from the same unit I, and with non-ferrous metal production units, notably for copper, nickel, zinc or lead. Similarly, other types of metal production or treatment units (1 to 6) may be incorporated, such as crucible furnaces, degassing units, surface treatments, and dephosphorization or desulfurization treatments.