Abstract:
The present invention relates to a method of operating a converter, in particular a Peirce-Smith converter or a converter with similar design or mode of operation, and to an apparatus, for instance a plant, for carrying out the method. The method comprises the step of:
       loading the converter with a starting material comprising said metal, the metal in the starting material being chemically bound at least in part to at least one compound substance, in particular sulphur;   maintaining a temperature within the converter interior space, which is above the melting temperature of the starting material; and   supplying an oxygen-containing process gas into the converter interior space through injection nozzles arranged in the wall of the converter,
 
the gas supplied through the injection nozzles comprising carbon dioxide, preferably very cold, technically pure carbon dioxide, as well as oxygen gas and/or air.

Description:
The present invention relates to a method of operating a converter, in particular a Peirce-Smith converter or a converter with similar design or mode of operation, and to an apparatus, for instance a plant, for carrying out the method. 
     PRIOR ART 
     Peirce-Smith converters (PSC) are horizontal converters which are used in the metallurgical production of copper. The starting material is the so-called copper matte which is obtained from a copper-bearing ore by means of preceding processing steps and comprises approximately 40% of copper. The copper matte contains, inter alia, iron sulfide and copper sulfide. In the Peirce-Smith converter, the sulphur is oxidized to give sulphur dioxide by injecting air into the glowing and liquid copper matte in a two-stage conversion process referred to as “fuming”, and is discharged in the exhaust gas. In the first step of slag blowing, iron is bound to form slag and is removed, in the second step of refining the crude copper, comprising more than 98% of copper and residues of base and noble metals, is produced and founded. 
     The Pierce-Smith process is similar to the Bessemer method in steel production; historically seen, it is derived from the Bessemer method via several intermediate steps. In contrast to the Bessemer method, the air is not blown in from the bottom, but from the side, and the shape of the Peirce-Smith converter is horizontally elongated. The basic principle of the Pierce-Smith converter has been given some further developments, resulting in the Hoboken converter, for example. 
     The converter comprises an opening at its top, which serves for charging the copper matte and founding the crude copper and is never completely closed in operation. This is why the amount of intake air corresponds approximately to the amount of produced exhaust gas. A further optimization of the covering with the aim to limit the amount of intake ambient air would require substantial modifications of the process design. 
     The converter is supplied with air at several places via special injection nozzles (Tuyeres). The air produces bubbles which result in scabs on the surface of the molten mass and on the walls, in particular in the area surrounding the opening. This is also the area where slag and dust are deposited. 
     On the one hand, the air serves for supplying oxygen and, on the other hand, for cooling purposes. In the conventional methods using air, the amount of air for cooling the PSC is so high that there is always a surplus of oxygen. 
     The exhaust gas of the converter contains sulphur dioxide. With conventional converters, a sulphuric acid production plant is arranged downstream to produce sulphuric acid from the sulphur dioxide. Through this, the emissions of sulphur dioxide are to be minimized (controlled). The sulphuric acid production plants are large-scale process plants. The market for sulphuric acid is a limited one. Thus, the main purpose of these sulphuric acid production plants is to remove the sulphur dioxide in a controlled manner. In the article “Peirce-Smith Converting—another 100 years?”, Thomas Price et al.; International Peirce-Smith Converting Centennial, TMS, 2009, a method is described on page 193 in which sulphur dioxide is operated in circulation in a Peirce-Smith converter plant. 
     The reactions proceeding in the converter are of exothermal nature. This is why the thermal load at the exit opening of the injection nozzles is high, and the thermal erosion of the refractory lining of the converter is particularly high in this area, compared to other areas. This might necessitate an early renewal of the lining. In the article “Operation of the Air Liquid Shrouded Injection (ALS™) Technology in a Hoboken Siphon Converter”, Romeo U. Pagador et al.; International Peirce-Smith Converting Centennial, TMS, 2009, pages 367 ff., the use of a jacketed nozzle is described in which air enriched with oxygen is blown into the converter in a sheathing nitrogen stream. 
     In normal operation, the injection nozzles get clogged. Until now, the injection nozzles are cleared by mechanical impact. This is performed manually. To this end, a ball valve is opened and a puncher is pushed through it to remove the crust agglomerating on the nozzle. 
     BRIEF SUMMARY OF THE INVENTION 
     It is the object of the present invention to avoid the disadvantages of the prior art. In particular, one object of the invention is to provide a method of operating a Peirce-Smith converter, which is more efficient and can be controlled in an easier way. 
     At least a part of the afore-mentioned objects is achieved by the features of the independent claims. Preferred embodiments and further developments of the invention, which solve special subtasks, are the subject-matters of the sub-claims. 
     According to one aspect of the present invention, a method of operating a converter, preferably a Peirce-Smith converter or the like, for obtaining a metal, preferably copper, iron, lead and/or zinc, comprises the steps of:
         loading the converter with a starting material comprising said metal, the metal in the starting material being chemically bound at least in part to at least one compound substance, in particular sulphur;   maintaining a temperature within the converter interior space, which is above the melting temperature of the starting material; and   supplying an oxygen-containing process gas into the converter interior space through injection nozzles arranged in the wall of the converter,
 
the gas supplied through the injection nozzles comprising carbon dioxide, preferably very cold, technically pure carbon dioxide, as well as oxygen gas and/or air.
       

     The heat capacity of CO 2  is much larger than that of air. Therefore, the cooling function of CO 2  is better than that of air. Due to the better cooling effect of CO 2 , a smaller amount of gas may be enough to cool the converter to a sufficient extent. A smaller amount of gas means fewer bubbles in the molten mass and hence fewer scabs. Moreover, the amount of oxygen can be reduced so that a surplus of oxygen can be reduced or even avoided. 
     Furthermore, pure oxygen is added to the CO 2  so that the oxygen demand of the copper matte can be covered in a particularly precise and effective manner. This does not exclude, however, that air is an additional constituent of the process gas. 
     Since the total amount of gas is substantially lower in the invention than in the prior art, the amount of oxygen in the gas is also higher than in the air. This is why oxygen is present with a higher partial pressure. This results in a better chemical conversion of the oxygen in the converter. 
     All in all, the Peirce-Smith converter exhibits a smaller amount of scabs, dust, bubbles and agglomerations around the opening. As the amount of supplied gas is smaller, the number of the injection nozzles (Tuyeres) can also be reduced. Moreover, the exhaust gas cleaning equipment can be made smaller. This effect is enhanced by the fact that the covering of the converter is not sealed which is why the amount of intake air corresponds approximately to the amount of produced exhaust gas. 
     CO 2  has a higher specific weight as compared with air. Despite of the lower amount, a higher impulse is maintained, alleviating or preventing a clogging of the injection nozzles. This applies, above all, in combination with a smaller number of injection nozzles. Due to the use of carbon dioxide gas and oxygen gas as the process gas, the need of a clearing process by mechanical impact can be reduced or even completely prevented. 
     Basically, the cooling effect in the Peirce-Smith converter represents the limiting factor. As the cooling performance is improved according to the invention, the production of the whole factory can be controlled in a better way. It is preferred that the CO 2  is very cold, i.e. as cold as technically feasible. The cooler the CO 2 , the more effective is the cooling effect on the converter wall and the lining, and the lower is the demand for cooling gas. 
     In a preferred design, the method is distinguished in that the carbon dioxide in the process gas originates at least in part from the exhaust gas of the converter. In this way, the consumption of liquid CO 2  can be diminished and the efficiency of the plant can be improved. 
     In a preferred embodiment, the method comprises the further steps of: vaporizing liquid carbon dioxide, preferably utilizing heat energy comprised in the exhaust gas; and using the obtained carbon dioxide gas as a constituent of the process gas. During the operation of the converter, the carbon dioxide gas as a constituent of the process gas is required in an amount which varies over time. Thus, it is advantageous if it is stored in compact, i.e. liquid form, and provided in gaseous form according to demand. The exhaust gas has to be cooled in the course of its treatment. This can be carried out e.g. with heat exchangers which are operated with air, for example. The heated cooling air can be used for its part for vaporizing liquid carbon dioxide. The same applies if the heat exchangers are operated with cooling water. The heat exchange can also take place between the exhaust gas and CO 2  in a direct manner without any connecting heat transmitting medium. The efficiency of the plant can be improved by utilizing the heat energy comprised in the exhaust gas. As no additional heating system is required (except for starting up the plant from cold state), the profitability of the plant can be improved. Since the heated cooling medium used in the exhaust gas heat exchanger is again cooled down during the vaporization of the liquid carbon dioxide, the environmental burden can be reduced when the heat transfer medium is released into the environment. 
     In a preferred embodiment, the method comprises the further steps of: collecting the exhaust gas in an extraction hood; cooling the exhaust gas; cleaning the exhaust gas, preferably by an electrostatic filtering process and/or wet washing; drying the exhaust gas, in particular by extracting water from the exhaust gas stream; and liquefying sulphur dioxide gas comprised in the exhaust gas, preferably by further cooling down the exhaust gas to a temperature which is below the boiling point of sulphur dioxide, and extracting as well as preferably collecting the liquid sulphur dioxide from the exhaust gas stream. The cooling and cleaning steps during the treatment of the exhaust gas allow to liquefy the SO 2  comprised in the exhaust gas and bring it to further use such as in the production of sulphuric acid. 
     In a preferred embodiment, the method comprises the further steps of: vaporizing liquid oxygen, preferably utilizing heat energy comprised in the exhaust gas; and using the obtained oxygen gas as a constituent of the process gas. The exhaust gas has to be cooled in the course of its treatment. The efficiency of the plant can be improved by utilizing the heat energy comprised in the exhaust gas in vaporizing the liquid oxygen. As no additional heating system is required (except for starting up the plant from cold state), the profitability of the plant can be improved. 
     In a preferred embodiment, the method comprises the further steps of: compressing the exhaust gas; and liquefying carbon dioxide gas comprised in the exhaust gas, the exhaust gas during the step of compressing being compressed to a pressure at which the carbon dioxide does not freeze during the subsequent liquefying process. These steps allow the utilization of the carbon dioxide comprised in the exhaust gas. This allows to improve the profitability of the plant and to reduce the CO 2  emissions. 
     In a preferred embodiment, the method comprises the further steps of: intermediately storing liquid carbon dioxide obtained in the liquefying step in a buffer reservoir; and gasifying the liquid carbon dioxide temporarily stored in the buffer reservoir in order to be supplied to the injection nozzles as carbon dioxide gas, the buffer tank being preferably supplied with liquid carbon dioxide from a carbon dioxide tank if the filling level falls below a threshold value. In this way, the demand for carbon dioxide as a constituent of the process gas can be largely met from the exhaust gas by filling an intermediate storage tank from which the liquid CO 2  is withdrawn for renewed vaporization. 
     In a preferred embodiment, the step of liquefying the carbon dioxide comprises the sub-steps of: cooling down the exhaust gas to a temperature which is below the boiling point of carbon dioxide, preferably using the cold energy of the liquid oxygen which is vaporized during this step, and separating the liquid carbon dioxide. In this way, it is possible to perform a direct heat exchange between the CO 2  to be cooled and the oxygen to be heated. Both processes can be combined in one component. This can further improve the efficiency and profitability of the plant. 
     In a preferred embodiment, the method is distinguished in that the oxygen gas is admixed to the carbon dioxide gas which has been obtained in the vaporizing step. This results in a process gas comprising a mixture of carbon dioxide and oxygen. The mixture can be supplied to the converter in a collecting line. 
     In a preferred embodiment, the method is distinguished in that the carbon dioxide is extracted from the exhaust gas by pressure swing adsorption. This means that cooling the exhaust gas for separating the carbon dioxide would be unnecessary; the separated CO 2  could be collected in a pressure tank and stored for further use. 
     In a preferred embodiment, the method is distinguished in that the exhaust gas is cooled by air, in particular by air originating at least in part from the exhaust gas after removal of the liquid carbon dioxide, the heat energy required in the step of vaporizing the liquid carbon dioxide being preferably taken at least in part from the air which was used before for the purpose of cooling the exhaust gas. In this way, the heat energy comprised in the exhaust gas can be effectively used, on the one hand, for vaporizing the liquid carbon dioxide. On the other hand, the exhaust air which is cold after the separation of the liquid CO 2  can be used once more. Through this, the efficiency of the plant can be further increased. 
     In a preferred embodiment, the method is distinguished in that comparatively cold air is admixed to the exhaust gas, preferably in the region of the extraction hood. In this way, the temperature of the exhaust gases can be lowered from the start of the exhaust gas branch. The thermal load of the materials and the heat emission of the exhaust gas ducts can be reduced. Cooling the extraction hood is also possible. Conventionally, the covering of a Peirce-Smith converter is cooled with water. If an air cooling system is provided, it can support the water cooling system or even completely replace it. 
     In a preferred embodiment, the method is distinguished in that the carbon dioxide gas and the oxygen gas are introduced into the converter interior space in separate gas streams, this process of introducing gas into the converter interior space preferably occurring in such a manner that the oxygen gas stream is shielded with a carbon dioxide gas stream in each case. With a sheathing stream of this type, oxygen can be blown into the converter interior space, on the one hand, and the direct vicinity of the oxygen jet can be cooled, on the other hand. This is why the thermal abrasion of a lining material of the converter can be counteracted, and the lifetime of a converter lining can be prolonged. Further, CO 2  has advantages in terms of the handling and recovering it from the exhaust gas as compared to other cooling media such as nitrogen, and has a higher specific gravity and hence a higher impulse than nitrogen. 
     In a preferred embodiment, the method is distinguished in that several converters are operated in parallel, the converters being operated on a cyclic basis and staggered in time. Usually, a converter is operated in a discontinuous manner. One cycle of the method may be seen, for instance, in filling the converter with molten copper matte, fuming, preferably in two stages (slag blowing and refining), discharging the slag and discharging the crude copper. In case several converters are operated in parallel and the converters are operated on a cyclic basis and staggered in time, the post-processing of the exhaust gases in the sulphuric acid production plant can be carried out almost in a continuous way. 
     According to a further aspect of the invention, provision is made for an apparatus for smelting metal, preferably copper, iron, lead and/or zinc, comprising a converter, preferably a Peirce-Smith converter or the like, the apparatus being designed and adapted to carry out the steps of the method suggested above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further aspects, advantages and features of the present invention will be apparent from the following description and the appended drawings of particularly preferred embodiments of the invention. 
         FIG. 1  is a schematic concept of a Peirce-Smith converter plant in a first embodiment of the invention. 
         FIG. 2  is a schematic concept of a process gas side of a Peirce-Smith converter plant in a second embodiment of the invention. 
         FIG. 3  is a schematic sectional view of a sheathing stream injection nozzle in operation in a third embodiment of the invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A first embodiment of the invention will be explained below with reference to  FIG. 1 .  FIG. 1  shows an exemplary embodiment of a converter plant according to the invention, with only one Peirce-Smith converter (PSC)  10  being schematically shown in the illustration. Further converters can be connected. 
     Provided in a side wall of the converter  10  is a series of injection nozzles in an injection nozzle arrangement  12 , which open towards the interior space of the converter  10 . Although not shown in the Figure, the wall of the converter  10  is provided with a refractory lining. Arranged above the converter  10  is an extraction hood  14  opening into an exhaust gas line  15 . The extraction hood  14  comprises a double wall through which air flows which is supplied to the lower region of the extraction hood  14  as an air curtain  16 . The air required for this purpose is introduced via a cooling air connection  18  in the upper area of the extraction hood  14 . Although not shown in more detail in the Figure, the extraction hood  14  is also capable of aspirating air from the environment. An additional water cooling system for the extraction hood  14  is conceivable, but not shown in more detail either. 
     The interior space of the converter (PSC)  10  is filled with a glowing and liquid copper-bearing copper matte in a discontinuous manner. The copper matte is obtained in foregoing steps from a copper-bearing ore and comprises, inter alia, iron sulfide and copper sulfide. 
     An oxygen-containing process gas is supplied to the interior space of the converter (PSC)  10  via the injection nozzle arrangement  12 , with the aid of which the copper matte is refined. During this operation, the sulphur is dissolved from copper and other metals such as iron and is oxidized to give sulphur dioxide (SO 2 ). The major part of the iron is bound in slag which is poured off. Crude copper remains, having a high copper content and residues of base and noble metals. 
     The process gas also contains carbon dioxide (CO 2 ). The carbon dioxide, preferably technically pure, very cold carbon dioxide, serves for cooling the converter. 
     In addition to air, the exhaust gas of the converter also comprises sulphur dioxide (SO 2 ) and carbon dioxide. Both gases are extracted from the exhaust gas by degrees, as will be explained in detail below. 
     The exhaust gas line  15  of the PSC  10  opens into an exhaust gas collecting line  20  to which further exhaust gas lines of other converters (not shown in more detail) are connected. The exhaust gas is first cooled in a heat exchanger  22  and freed from floating particles, dust etc. in an electrostatic filter  24 . Thereupon, the exhaust gas is cooled in a further heat exchanger  26  and washed in a water wall filter or wet filter  28 . The wet filter  28  is supplied with water via a water pump  29 . The collected waste water may be further used as a washing solution, or it can be discharged when harmful substances have been removed. 
     Depending on the gas composition, further cooling and/or cleaning stages can be provided which are, however, not shown in more detail here. 
     The pre-cooled and filtered exhaust gas is supplied to a drying apparatus  30  in which water is removed. As schematically outlined in the Figure, the drying apparatus  30  can be an adsorption-based dehumidifier, a device with another operating principle or a complex system with several stages. 
     Subsequently, the exhaust gas is cooled in an electric cooling unit  31  to such an extent that the SO 2  is liquefied (i.e. at least below the boiling point of SO 2  which is at −10° C.). The liquefied sulphur dioxide can be stripped in a separator  32  in a residue-free manner. The stripped liquid sulphur dioxide (LSO 2 =liquid SO 2 ) is collected in containers (not shown in more detail), or is put to further use through a pipeline, preferably in a plant for producing sulphuric acid, or is sold directly. 
     What is left is the exhaust gas consisting essentially of air and CO 2 . The residual exhaust gas is compressed by means of a compressor  34  so that liquid CO 2  is produced in the subsequent cooling process: Carbon dioxide snow would be the result without any cooling. The liquefaction is performed, for instance, by heat exchange. The liquefaction process can be carried out with the support of the liquid oxygen (LO 2 ) which extracts heat energy from the residual exhaust gas via a heat exchanger  36  and is vaporized in this process. Thus, the heat exchanger  36  acts, on the one hand, as a liquefying means for the CO 2  in the exhaust gas and, on the other hand, as a vaporizer unit for the liquid oxygen. The heat exchanger (CO 2 -liquefying means)  36  and the compressor  34  can be integrated in one apparatus. 
     The liquid oxygen is supplied to the heat exchanger  36  from an LO 2 -container  40  through an LO 2 -line  38 , is heated in the heat exchanger  36  at least to the boiling point of oxygen (−182.9° C.) and exits the heat exchanger  36  in the form of oxygen gas through an O 2  (gas) line which can be controlled by a valve (O 2  valve)  44 . The CO 2  which has been liquefied in the heat exchanger  36  is separated in a separator  46  and collected in an LCO 2 -buffer reservoir  50  via an LCO 2 -separator line  48 . 
     The cold air left in the CO 2  liquefying process is used for cooling purposes. That is to say, the cold air is supplied to the cooling air connection  18  of the extraction hood of the converter  10  and to the first heat exchanger  22  via a cooling air line  52 . Instead of branching to the cooling air connection  18  and the heat exchanger  22 , as illustrated in the Figure, the cooling air line  52  first can extend through the heat exchanger  22  and extend from there to the cooling air connection  18  of the converter  10 . 
     The filling level of the LCO 2 -buffer reservoir  50  is monitored by means of a filling level detector  54 . The filling height h can be determined indirectly, e.g. by weighing or other methods. When the filling level is low, the LCO 2 -buffer reservoir  50  can be supplied with liquid carbon dioxide (LCO 2 ) via a valve (LCO 2 -inflow valve)  56  from an LCO 2 -storage container  58 . For this, the filling level measured by the filling level detector  54  is fed to a controller which is coupled to the actuating element of the valve  56 . When the filling level is low, the valve  56  opens and makes liquid CO 2  flow from the storage container  58  into the buffer reservoir  50  until a prescribed target level is achieved. Such a phase of refilling may be required in particular during starting up the plant when carbon dioxide from the exhaust gas is not yet available. Possible losses in the process can be balanced in this way, too. 
     In case of need, the liquid carbon dioxide stored in the buffer reservoir  50  is withdrawn through an LCO 2 -line  60  which can be controlled by a valve (LCO 2 -valve)  62 , is vaporized by means of a CO 2 -vaporizer unit  64  and flows from the latter into a CO 2 -line  66  which can be controlled by a valve (CO 2 -valve)  68 . Downstream of the CO 2 -valve  68  and the O 2 -valve  44 , the CO 2 -line  66  and the O 2 -line  44  unite to a common process gas distribution line  69 . 
     The vaporization of the liquid carbon dioxide in the CO 2 -vaporizer unit  68  is carried out according to the heat exchange principle with warm air which is introduced via a hot air line  70  from the second (exhaust gas) heat exchanger  26 , after having cooled down the exhaust gas there. A blower  72  aspirates supply air through the CO 2 -vaporizer unit  64 , the hot air line  70  and the heat exchanger  26  and discharges it again into the environment as outlet air. Alternatively, the heat exchanger  26  and the CO 2 -vaporizer unit  64  can also be integrated in a single apparatus as is the case with the O 2 -vaporizer unit  36 . It is also possible to use a bypass flow of the exhaust gas for vaporizing the liquid carbon dioxide. 
     The volume flow in the process gas distribution line  69  is measured by a flow meter  74 . The opening state of the CO 2 -valve  68  is controlled as a function of the output signal of the flow meter  74 . Further, the gas composition in the process gas line  69 , i.e. the ratio of oxygen and carbon dioxide on a percentage basis, is determined by a gas analyzer  76 . The opening state of the O 2 -valve  44  is controlled as a function of the output signal of the gas analyzer  74 . In this way, the amount of gas and the gas composition can be automatically adjusted. 
     A process gas line  77  branches off from the process gas distribution line  69  and extends to the injection nozzle arrangement  12  of the Peirce-Smith converter  10 . The process gas distribution line  69  extends to further converters (not shown in more detail) in the plant. A temperature sensor  78  and a pressure gauge  80  are arranged in the process gas line  77 . In a control device which is not shown in more detail, the parameters of the process gas can be evaluated and used for determining target values for the volume flow and the composition of the process gas. In the example which is illustrated, the set-point values for the temperature and pressure of the process gas are at 0° C. and 10 bar (o), respectively, but can be adapted as required to the circumstances and specific conditions prevailing in each case. The process gas line  77  for the converter  10  can be shut off in a controlled manner by means of a valve  82 . 
     The state variables of the carbon dioxide, i.e. its purity, flow rate, pressure and temperature, require a close monitoring in order to prevent any condensation or resublimation in the pipe installation. 
     As already explained, several converters  10  are provided in the plant, but only one of them is shown. The converters operate in a discontinuous and cyclic manner. The procedure from filling in the glowing and liquid copper matte until founding the crude copper can be seen as one cycle of a converter  10 . Each converter  10  is cleaned and inspected between the cycles to be able e.g. to discover and repair a damaged refractory lining early enough. In order to allow a quasi-continuous operation of the plant, the cycles of the individual converters begin so as to be staggered in time. 
     In the exemplary embodiment illustrated above, the flow-measuring device (the flow meter)  74  and the gas analyzer  76  are provided in the process gas line so as to be shared for all converters in the plant. In this arrangement, the central control device (not shown in more detail) can determine target values on the basis of the total demand. The temperature sensor  78  and the pressure gauge  80  are, however, provided in the individual process gas line  77  of the converter  10  to take account of the individual conditions in the converter. It is conceivable to provide only one temperature sensor  78  and one pressure gauge  80  in the process gas distribution line  69 . 
     For the purpose of a finer and individual adjustment of the process gas for each converter provided in the plant, it is also possible that the O 2 -line  44  and the CO 2 -line  68  along with all mountings and measuring instruments are separately provided for each converter. Such an arrangement is shown as a second embodiment in  FIG. 2 . 
     In  FIG. 2 , only the process gas side of the plant is schematically illustrated; the exhaust gas side corresponds to the illustration of the first embodiment in  FIG. 1 . 
     According to the illustration in  FIG. 2 , several converters  10   a ,  10   b , . . . ,  10   n  are provided in a converter plant. Each of the converters has an individual process gas line  77   a ,  77   b , . . . ,  77   n  associated to it, in which a flow meter  74   a ,  74   b , . . . ,  74   n , a gas analyzer  76   a ,  76   b , . . . ,  76   n , a temperature sensor  78   a ,  78   b , . . . ,  78   n  and a pressure gauge  80   a ,  80   b , . . . ,  80   n  are provided in each case. 
     As in the first embodiment, an O 2 -vaporizer unit  36  and a CO 2 -vaporizer unit  64  are provided here, too. In this arrangement, however, an O 2 -distribution line  84  branches off from the O 2 -vaporizer unit  36 ; from this O 2 -distribution line, an O 2 -gas line  42   a ,  42   b , . . . ,  42   n , which can be individually controlled by a valve (O 2 -valve)  44   a ,  44   b , . . . ,  44   n , branches out for each converter  10   a ,  10   b , . . . ,  10   n . Similarly, a CO 2 -distribution line  86  extends from the CO 2 -vaporizer unit  64  and branches out into CO 2 -gas lines  66   a ,  66   b , . . . ,  66   n  which lead to one converter  10   a ,  10   b , . . . ,  10   n  each and can be individually controlled by a valve (CO 2 -valve)  68   a ,  68   b , . . . ,  68   n . The gas lines  42   a ,  42   b , . . . ,  42   n  and  66   a ,  66   b , . . . ,  66   n  merge in the process gas lines  77   a ,  77   b , . . . ,  77   n  in each case. The valves are driven individually for each leg on the basis of the criteria explained above with respect to the arrangement according to the first embodiment. 
     The other design of the plant, in particular the treatment of the exhaust gas and the overall process of the converter method, is equal to the first embodiment. A repeated explanation is omitted to avoid any repetitions. 
     In a modification, oxygen and carbon dioxide can be separately fed into the converter  10 . A particularly advantageous embodiment of this option is shown in  FIG. 3  as a third embodiment of the invention. In this third embodiment, the oxygen gas and carbon dioxide gas are separately fed into the converter interior space through jacketed nozzles in such a way that the oxygen gas is shielded by a sheathing of carbon dioxide.  FIG. 3  shows a jacketed nozzle in the longitudinal section in a portion of the converter wall, as well as its mode of operation. 
     According to the illustration in  FIG. 3 , the converter  10  comprises a wall  88  which is provided with a lining  90 . The lining  90  consists, for instance, of an arrangement of refractory bricks. The molten copper matte  92  is in the interior space of the converter which is confined by the lining  90 . 
     Inserted in the converter wall  88  is a plurality of sheathing flow injection nozzles  94 , one of these being shown in the Figure in longitudinal section with a portion of the converter wall  88 . The sheathing flow injection nozzle  94  extends through the converter wall  88  and the lining  90  and opens at the inner bordering thereof. The sheathing flow injection nozzle  94  comprises an inner tube  96  which is coupled to an oxygen gas port  98 . The oxygen gas (O 2 ) which is supplied enters the copper-matte molten mass  92  in the form of a jet  104  at the opening end, is distributed in this area and fulfils the functions according to the process. The inner tube  96  is surrounded by a jacketed tube  100  which is in connection with a carbon dioxide gas port  102 . The supplied carbon dioxide gas (CO 2 ) surrounds the O 2 -jet  104  in the form of a sheathing, enters the copper-matte molten mass  92  at the opening end and effectively cools the converter wall  88 , the lining  90  and hence at least indirectly the copper-matte molten mass  92  in the direct surrounding of the outlet opening of the sheathing flow injection nozzle  94  and is then mixed with the O 2 -jet  104 . A loose and porous agglomeration  106  of solidified, quasi foamed copper matte forms around the outlet opening, which in the region of the opening end of the nozzle  94  is blown away by the O 2 -jet  104  and the CO 2  contained therein, but deposits around the outlet opening of the nozzle  94  on the lining  90  and forms an additional protective layer which prevents a thermal erosion of the lining  90  at this particularly vulnerable spot. 
     The rear end of the sheathing flow injection nozzle  94  comprises a closure  108  which—if necessary—is removable and allows a cleaning of the nozzle by mechanical impact. Moreover, the closure  108  may comprise an inspection window for observation. Instead of the closure  108 , a ball valve can be provided which is cleaned by mechanical impact. 
     Preferred exemplary embodiments have been explained above on the basis of the Figures. Further modifications may relate to specific details of the method without relating to the gist and the applicability of the invention. 
     According to a deteriorated embodiment, CO 2 , oxygen and air can be supplied. The larger the amount of air, the larger the loss of efficiency. The supply of CO 2 , however, always results in an improvement with respect to conventional methods. 
     In a modification it is also possible to supply CO 2  and/or oxygen to the Peirce-Smith converter in liquid form. The vaporizer unit(s)  36 / 64  may be dispensed with in this case. 
     As the plant is usually operated with several converters on a cyclic basis and staggered in time, a sufficient amount of exhaust gas should also always circulate between the cycles of an individual converter to provide the required heat energy for vaporizing the oxygen and carbon dioxide in the vaporizer units  36  and  64 . If, however, the entire plant is to be started from full standstill, the vaporizer units  36  and  64  can comprise additional heating means such as an electric heating system or a hot water based heating system to produce the process gas in this phase. 
     In quasi-continuous operation and under full load, the buffer reservoir  50  may be bypassed in order to supply the CO 2 , taken from the exhaust gas stream, to the process in a direct manner. If too many converters are out of operation, the process of blowing in CO 2  via the valve  62  can be stopped and the buffer reservoir  50  can be filled with liquid CO 2 . Returning the medium from the buffer reservoir  50  to the storage container  58  is conceivable, too. In case the buffer reservoir  50  (and possibly the storage container  58 ) is full, the oxygen supply can be stopped so that air is only aspirated via the extraction hood  14 . In this case, the heat exchangers  36 ,  64  are deactivated and the exhaust gas is discharged into the environment through a chimney. 
     In case of a problem in the operation of the plant, the exhaust gas compressor can feed compressed air to the system to maintain an emergency operation without supplying CO 2 . In The CO 2 -liquefying means will be deactivated in this case. 
     The exhaust gas side branch up to the point of removing SO 2  is shown exemplarily and schematically to a great extent. The number of the cooling stages, the modalities in terms of the cleaning, filtering, cooling and drying means and the recovery of SO 2  and CO 2  from the exhaust gas are optional and can be modified on the basis of expert knowledge and skills. The storage, production, treatment and routing of the process gas and its components can be handled in different way, too. 
     It could be possible, for instance, to accumulate the CO 2  by means of pressure change adsorption (vacuum pressure change adsorption, if applicable) and to discharge the remaining air (adsorption). In this case, no further cooling process would be required, and no preceding compression either. As a cooling process by liquid oxygen would not be required, the oxygen could also be provided in gaseous state. The CO 2  required for the process would be provided in a second container (desorption). In this manner, desorption and adsorption could occur alternately. 
     It is also possible in the context of the invention to use a high-temperature membrane for separating CO 2  from the exhaust gas, instead of employing a pressure change adsorption method. 
     Cooling the extraction hood by the cold, compressed air as well as the use for cooling the exhaust gas are optional. 
     The invention is not only applicable to the conversion of copper-bearing copper matte and to a Peirce-Smith converter. Advantages may be offered by any application in which an oxygen-containing process gas is blown into a metal-bearing molten mass to oxidize disturbing components and remove them from the molten mass in this way. The method can be used in particular for metallurgical processes, especially conversion processes in the production of iron, lead or zinc. 
     List of Reference Numerals 
     
         
         
           
               10  converter ( 10   a ,  10   b , . . . ,  10   n ) 
               12  injection nozzle arrangement 
               14  extraction hood (covering) 
               15  exhaust gas line 
               16  air curtain 
               18  cooling air connection 
               20  exhaust gas collecting line 
               22  heat exchanger I 
               24  electrostatic filter 
               26  heat exchanger II 
               28  wet filter 
               29  water pump 
               30  drying apparatus 
               31  cooling unit 
               32  SO 2 -separator 
               34  compressor 
               36  O 2 -vaporizer unit 
               38  LO 2 -line 
               40  LO 2 -storage container 
               42  O 2 -line ( 42   a ,  42   b , . . . ,  42   n ) 
               44  O 2 -valve ( 44   a ,  44   b , . . . ,  44   n ) 
               46  CO 2 -separator 
               48  LCO 2 -separator line 
               50  LCO 2 -buffer reservoir 
               52  cooling air line 
               54  filling level detector 
               56  LCO 2 -inflow valve 
               58  LCO 2 -storage container 
               60  LCO 2 -line ( 60   a ,  60   b , . . . ,  60   n ) 
               62  LCO 2 -valve 
               64  CO 2 -vaporizer unit 
               66  CO 2 -line ( 66   a ,  66   b , . . . ,  66   n ) 
               68  CO 2 -valve ( 68   a ,  68   b , . . . ,  68   n ) 
               69  process gas collecting line 
               70  hot air line 
               72  blower 
               74  flow meter ( 74   a ,  74   b , . . . ,  74   n ) 
               76  gas analyzer ( 76   a ,  76   b , . . . ,  76   n ) 
               77  process gas line ( 77   a ,  77   b , . . . ,  77   n ) 
               78  temperature sensor ( 78   a ,  78   b , . . . ,  78   n ) 
               80  pressure gauge ( 80   a ,  80   b , . . . ,  80   n ) 
               82  cut-off valve 
               84  O 2 -distribution line 
               86  CO 2 -distribution line 
               88  converter wall 
               90  lining 
               92  copper matte-molten mass 
               94  jacketed injection nozzle 
               96  inner tube 
               98  O 2 -port 
               100  jacket tube 
               102  CO 2 -port 
               104  O 2 -jet 
               106  porous agglomerations 
               108  closure 
           
         
       
    
     Special reference is made to the fact that the above list of reference numerals forms an integral part of the description.