GB2103660A

GB2103660A - Copper-refining installation

Info

Publication number: GB2103660A
Application number: GB08218133A
Authority: GB
Inventors: Theodor Niess; Haribert Przybylla; Gunther Finger
Original assignee: Gottfried Bischoff Bau Kompl Gasreinigungs und Wasserrueckkehlanlagen GmbH and Co KG
Current assignee: Gottfried Bischoff Bau Kompl Gasreinigungs und Wasserrueckkehlanlagen GmbH and Co KG
Priority date: 1981-07-01
Filing date: 1982-06-23
Publication date: 1983-02-23
Also published as: CA1192411A; BE895252A; GB2103660B

Abstract

The invention relates to a copper- refining installation having a refining furnace, a crude gas duct extending mainly horizontally, a gas purification equipment and a pure gas duct with attached chimney stack, converter copper being introduced into the refining furnace, and the crude gas drawn off from the refining furnace conveyed to the chimney stack via the gas purification equipment and the pure gas duct. The gas purification equipment consists of a sulphur dioxide washing tower with a plurality of scrubbing jets for the introduction of a sulphur dioxide washing medium, and at least one differential-pressure washing appliance, there being an extraction fan located in the pure gas duct before the chimney stack by means of which the pure gas is exhausted from the washing tower and forced into the chimney stack. The refining furnace is constructed as a negative pressure furnace in which a negative pressure of 5 to 20 mm, water-column is maintained by means of the extraction fan, and a control circuit having equipment to measure the pressure in the negative furnace and/or in the crude gas duct.

Description

SPECIFICATION.

Copper-refining installation This invention relates to a copper-refining installation.

Such installations are known to have a refining furnace, a crude gas duct extending mainly horizontally, a gas purification equipment, and a pure gas duct with attached chimney stack, in which copper, produced in a copper extraction plant converter, can be introduced into the refining furnace, and the crude gas drawn off from the refining furnace can be conveyed to the chimney stack via the gas purification equipment and the pure gas duct. In such copper extraction plants usually copper matte, melted at high temperature in a cupola furnace or in an ore-slurry furnace, is charged into the converter. Air at a pressure of 1 bar is blown into the copper matte through the converter nozzles, by which the iron and sulphur in the copper matte are oxidized.The oxidized iron forms, together with fluxing material that is charged in the cold state, a highly fluid slag which is poured off after the end of the blowing process.

The oxidized sulphur escapes with the converter waste gases in the form of sulphur dioxide and sulphur trioxide, and the converter waste gases are normally subjected to sulphur purification.

After the converter blow, the converter copper is approximately 98% pure. The converter copper is refined in the refining installation. if it is not charged in the liquid state at high temperature it must be melted, and copper scrap can be charged with it. The refining furnace is fuelled by gas and/or oil and/or coal dust. The refining process is carried out at about 13000 C, initially under oxidizing conditions and subsequently under reducing conditions. The final product is firerefined copper. In order to obtain a maximum electrical conductivity, and in addition to extract the accompanying metals silver and gold, the firerefined copper is cast into anode plates which are submitted to final refining and extraction of the noble metals by electrolysis. For this reason such refining furnaces are sometimes described as anode furnaces.During furnace refining a slag is produced which absorbs the chemical impurities in the raw copper.

In installations of the above-described type, the gas-purification equipment is incorporated in a waste-heat boiler for the crude gas flowing out of the refining furnace. In the waste-heat boiler the dust in the stream of gas settles under the force of gravity and can be drawn off through dust pockets. The dust contains a considerable amount of copper, in fact approximately 50%. It can be conveyed back to the copper extraction plant or be introduced once more into the refining furnace, but in any event the dust is difficult to handle. If it is introduced into the refining furnace a great deal of it is carried away with the crude gas.

Sulphur dioxide is not removed from the crude gas. The concentration of sulphur dioxide in the crude gas is in fact relatively small because the crude gas carries with it a considerable amount of excess air. Removal of the sulphur dioxide would be rather expensive on account of its low concentration in the crude gas. On the other hand discharge into the atmosphere via the chimney stack of clean gas from which merely the dust has been removed, and that is still accompanied by sulphur dioxide even though at a low concentration, can on account of protection of the environment no longer be justified.

It is the object of the present invention to improve a copper-refining installation of the above kind so that the sulphur dioxide can be removed from the crude gas at small expense.

According to the present invention, a copperrefining installation comprises a refining furnace, a crude gas dust extending mainly horizontally, a gas purification equipment and a pure gas duct with attached chimney stack, in which converter copper produced in a copper extraction plant converter is introduced into the refining furnace, and the crude gas drawn off from the refining furnace is conveyed to the chimney stack via the gas purification equipment and the pure gas duct, the gas purification equipment consisting of a sulphur dioxide washing tower with a plurality of scrubbing jets for the introduction of a sulphur dioxide washing medium, and at least one differential-pressure washing appliance, the lower part of which has a washing tower sump with sludge withdrawal means, there being an extraction fan located in the pure gas duct before the chimney stack by means of which the pure gas is exhausted from the washing tower and forced into the chimney stack, and the refining furnace being constructed as a negative pressure furnace in which a negative pressure of 5 to 20 mm, water-column is maintained by means of the extraction fan, there being additionally a control circuit having equipment to measure the pressure in the negative pressure furnace and/or in the crude gas duct and by which, by means of pressure measurements, the extractor fan and/or the differential pressure washing appliance is controlled so that the crude gas exhausted is free from infiltrated air. The sludge from the sump of the washing tower can without difficulty be refined as copper. For this purpose it can be added to the copper ores or be introduced into the refining furnace.According to the construction and method of heating of the refining furnace the sludge also contains a considerable quantity of soot, but this burns off when the sludge is further processed to produce copper in the manner indicated.

The invention is based on the recognition that by suppressing the suction of infiltrated air, a crude gas is formed the concentration of sulphur dioxide in which is sufficiently high for an effective sulphur dioxide scrubbing to be possible by means of a washing tower and with the use of a differential-pressure washing appliance in the manner described. Thereby a gas is produced that is substantially free from sulphur dioxide. The sulphur trioxide contained in the crude gas is washed out at the same time. Simultaneously however effective dust removal from the crude gas takes place, in which valuable constituents are recovered not in the form of dust but as a sludge that can be handled, and consequently further processes to form copper can be carried out in relatively simple manner.Withdrawal by suction of crude gas without infiltrated air means that practically only those products that are formed in the refining furnace by the oxidizing or reducing treatments of the converter copper already described, are withdrawn from that furnace.

In order to suppress infiltration of air, the invention primarily teaches that the refining furnace is to be constructed as a negative pressure furnace. By this is meant a type of furnace, the furnace chamber of which is enclosed sufficiently for it to be possible to maintain the negative pressure required. The expenditure on control equipment necessary for this is small, the control circuit employed operates with normal constructional units. The static pressure measured in the crude gas can be directly related to a quantity of externai gas, and by pressure measurement the conditions can without difficulty be so arranged that the crude gas contains practically no external gas.The actual value of pressure is compared with the prescribed target value by a target value/actual value comparator, and either the extractor fan or the differentialpressure washing appliance adjusted according to the difference between the target value and the actual value. The possibility however also exists of adjusting them both together in proportion to the difference between the target value and the actual value. The differential-pressure washing appliance can be an annular gap washer, with a flow channel and with a venturi-like constriction and/or diffuser, and also an inserted body, adjustable in the flow channel, by which the annular gap length can be adjusted. The differential pressure can without difficulty be so adjusted that effective dust removal also takes place in the differential pressure washer.

It is within the scope of the invention to provide in the crude gas duct additional scrubbing jets for the introduction of the sulphur dioxide washing medium. Both the crude gas duct and also parts of the washing tower and the pure gas duct can be constructed as waste heat boilers. According to one proposal of the invention, soda lye is used as sulphur dioxide washing medium. This soda lye can be circulated in a closed path.

The process according to the invention can be further developed so that copper-containing deposits occurring in the washing process can be re-introduced into the refining process. Thus, water can be used as the sulphur dioxide washing medium, and a preparation equipment having a thickener and a settling tank attached to the sludge outlet of the washing tower. That the sludge from the thickener can be fed back into the settling tank and from the settling tank into the refining furnace, either indirectly (via a flash furnace) or directly. Return pipes can be attached to the thickener and to the settling tank by means of which overflow water can be led back into the gas purification equipment. It is to be understood that soda lye is added to the washing water, nevertheless in the following it is called washing water for brevity.

According to the preferred method of operation, the overflow water can be conducted on the one hand to the washing tower and on the other hand to the scrubbing jets in the crude gas duct. The thickener is expediently constructed as a laminated thickener by which the necessary thickening can be conducted in very small space.

According to the preferred form of construction of the invention, an intermediate container is associated with the thickener and can be equipped with a water-softening plant.

Two embodiments of the invention will now be described with reference to the accompanyina drawings, in which: Figure 1 is a side elevation of a copper-refining installation according to the invention; Figure 2 is an enlarged view of part of Figure 1, with further details; and Figure 3 shows another construction of copperrefining installation according to the invention.

The copper-refining installation shown in Figures 1 and 2 consists in its basic construction of a refining furnace 1, a crude gas duct 2 extending mainly horizontally, a gas purification equipment 3 and a pure gas duct 4. The pure gas duct 4 is attached to a chimney stack 5. Converter copper, produced in a converter of copper extraction plant, can be introduced into the refining furnace 1 with, if required, additional scrap. The crude gas drawn off from the refining furnace 1 is conveyed to the chimney stack 5 via the gas purification equipment 3 and the pure gas duct 4. As shown, particularly by Figure 2, the gas purification equipment 3 consists of a sulphur dioxide washing tower 6 with a plurality of scrubbing jets 7 for the introduction of a sulphur dioxide washing medium, and at least one differential pressure washing appliance 7.

Preferably the differential pressure washing appliance is an annular gap washer 8 with a venturi-like flow channel 9 with an inserted body 10 adjustable therein. In its lower portion the washing tower 6 has a washing tower sump 11 with a sludge outlet 12. An extractor fan 1 3 is located in the pure gas duct 4 before the chimney stack 5, and the pure gas is sucked out of washing tower 6 by means of an extractor fan 13 and forced into chimney stack 5. The refining furnace is constructed as a negative pressure furnace, and so arranged that a negative pressure of from 5 to 20 mm, preferably about 10 mm water-column, can be maintained in the negative pressure furnace 1 by means of the extractor fan 13. In addition a control circuit 14 is provided, as is illustrated in Figure 1 by a heavily traced chaindotted line. The constituent parts of control circuit 14 are pressure measurement devices 1 5 located in the crude gas duct 2 and in the negative pressure furnace 1. By the control circuit 14, the extractor fan 13 and/or the differential-pressure washing appliance 8 are controllable via the pressure measurement, to provide crude gas extraction which is free from infiltrated air. Thus, in practice, only the reaction products produced during the oxidizing or reducing treatment of the converter copper in the refining furnace 1 are drawn off. The sludge from washing tower sump 11 can be re-introduced into the refining furnace 1 , which is illustrated by a corresponding return pipe 17.In addition, the design is so arranged that additional scrubbing jets 1 6 are located in crude gas duct 2 to introduce the sulphur dioxide washing medium. The crude gas duct 2 and/or parts of the washing tower 6 and the pure gas duct 4 can be constructed as a waste-heat boiler.

The sulphur dioxide washing medium is for example soda lye. This can also be circulated in a closed circuit, in which however it is obvious that the lye that is consumed must be replaced.

A preparation plant is attached to the sludge outlet 12 of washing tower 6, which has a thickener 18 and a settling tank 19. The sludge from the thickener 1 8 is fed back into the settling tank 1 9 and from there into the refining furnace, this being either indirectly via a flash furnace or directly. Return pipes 20 are attached to the thickener 18 and to the settling tank 19, by means of which overflow water can be led back into gas purification equipment 3. It is obvious that the normal pumps 21 are located in the piping system. The overflow water can be conducted on the one hand to washing tower 6 and on the other hand to the scrubbing jets 1 6 in crude gas duct 2.

Thickener 1 8 is a laminated thickener, with which an intermediate container 22 is connected in series, and the intermediate container 22 is combined with a water-softening plant 23. The sludge 24, withdrawn through the thickener 1 8 and the settling tank 19, contains nearly 50% of metallic oxides, chiefly copper, and also free carbon.

The overflow water from the thjckener 1 8 flows through an intermediate container 22, in which a constant admixture of a water-softening medium takes place. From this intermediate container 22, which is equipped with a float valve for the addition of compensation water, the water passes via the return pipe 20 back to gas purification equipment 3. On account of the relatively high temperature of this return flow of water and its high pH value, deposits of calcium carbonate and magnesium can occur in jets 7 and 16. When this is the case, water-softening is carried out in the manner described. By water-softening the formation of such deposifs is avoided. The water flowing out of intermediate container 22 is returned to the gas purification equipment by two pumps 21. During the oxidation period, an addition of 30% lye is made in the clarified water pipe, which serves to absorb the large peaks of sulphur dioxide that occur particularly at the beginning of the oxidation process. The thickened sludge 24 which is drawn off from the lower portion of thickness 18 passes into two small drying tanks or settling tanks 1 9, whilst the dried sludge 24 is mechanically further processed or can be re-introduced into the refining process.

Claims

1. A copper-refining installation comprising a refining furnace, a crude gas duct extending mainly horizontally, a gas purification equipment and a pure gas duct with attached chimney stack, in which converter copper produced in a copper extraction plant converter is introduced into the refining furnace, and the crude gas drawn off from the refining furnace is conveyed to the chimney stack via the gas purification equipment and the pure gas duct, the gas purification equipment consisting of a sulphur dioxide washing tower with a plurality of scrubbing jets for the introduction of a sulphur dioxide washing medium, and at least one differential-pressure washing appliance, the lower part of which has a washing tower sump with sludge withdrawal means, there being an extraction fan located in the pure gas duct before the chimney stack by means of which the pure gas is exhausted from the washing tower and forced into the chimney stack, and the refining furnace being constructed as a negative pressure furnace in which a negative pressure of 5 to 20 mm, water-column is maintained by means of the extraction fan, there being additionally a control circuit having equipment to measure the pressure in the negative pressure furnace and/or in the crude gas duct and by which, by means of pressure measurements, the extractor fan and/or the differential pressure washing appliance is controlled so that the crude gas exhausted is free from infiltrated air.

2. An installation as in Claim 1 , wherein the sludge from the washing tower sump is reintroduced into the refining furnace.

3. An installation as in Claim 1 or Claim 2, wherein the crude gas duct has additional scrubbing jets for the introduction of the sulphur dioxide washing medium.

4. An installation as in any one of Claims 1 to 3, wherein the crude gas duct and/or parts of the washing tower and clean gas duct are constructed as a waste heat boiler.

5. An installation as in any one of Claims 1 to 4, wherein soda lye is used as sulphur dioxide washing medium.

6. An installation as in any one of Claims 1 to 4, wherein water is used as sulphur dioxide washing medium, and a preparation equipment having a thickener and a settling tank is attached to the sludge outlet of the washing tower, the sludge from the thickener being fed back into the settling tank and from the settling tank directly into the refining furnace, there being return pipes attached to the thickener and to the settling tank, by means of which overflow water can be led back into the gas purification equipment.

7. An installation as in Claim 6, wherein instead of being fed directly in the refining furnace, the thickener is fed indirectly via a flash furnace.

8. An installation as in Claim 6 or Claim 7, in the form of construction with additional scrubbing jets in the crude gas duct, wherein the overflow water is conducted on one hand to the washing tower and on the other hand to the scrubbing jets in the crude gas duct.

9. An installation as in any one of Claims 6 to 8, wherein the thickener is constructed as a laminated thickener, with which an intermediate container is connected in series, and the intermediate container is combined with a watersoftening plant.

10. A copper refining installation substantially as hereinbefore described with reference to Figures 1 and 2, or Figure 3 of the accompanying drawings.