APPLIED TECHNOLOGY _____ _

Flash Converting - Continuous Converting of Copper Mattes ___________ J. A. Asteljoki, L. K. Bailey, D. B. George and D. W. Rodolff

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SUMMARY

A new continuous process for conversion of copper mattes to blister copper has been successfully pilot-tested and is now ready for commercial application. The process, known as Kennecott-Outokumpu Flash Converting, involves reaction of solidified matte particles with industrial grade oxygen, in a flash furnace, to produce blister copper and a small quantity of slag which can be recycled to the primary smelting furnace. Production of low-volume high 802 content offgases, separation of smelting and converting operations to allow increased on-line availability, and simplified process control are the major benefits of the process which translate to reduced smelter capital and operating costs.

INTRODUCTION

Increasingly stringent environmental regulations combined with the high cost of gas cleaning and sulfuric acid plants have necessitated major ex­penditures by the copper industry to capture process gases from Peirce­Smith converters. Additional expenditures are being made in many U.S. and foreign plants to control fugitive emissions and improve in-plant hygiene. In visiting many modem smelting facilities, it is now difficult to tell whether the metal producing portion of the plant is supported by an auxiliary gas handling system or vice versa. Approximately 35% of a new smelter's capital cost is related to gas cleaning and sulfur fixing equipment.

The key factor in the size and cost of the gas handling equipment is the volume of gases which must be treated. While major advances have been made in reducing offgas volumes from primary smelting furnaces, principal­ly through the increased use of industrial 02, Peirce-Smith converters have remained relatively unchanged. Extensive dilution of process gases with nitrogen, intermittent operation, and high instantaneous gas volumes from the batch converters have prompted the industry to examine continuous converting options.

CONTINUOUS CONVERTING APPROACHES

Numerous proposals have been advanced for continuous converting and nearly all involve transport of molten matte to a furnace followed by oxidation with air or oxygen enriched air. Of these processes, the Mitsubishi converting or "C" furnace portion of the three step MI process is probably the best known, with two successful commercial applications. Contop, spray converting, Noranda batch converting, and other concepts are in varying stages of development but have not yet been commercialized. All of these systems, however, are limited in their ability to utilize high levels of oxygen enrichment, and hence to reduce gas volumes, by heat balance considerations. As shown in Figure 1, for Peirce-Smith converters, also applicable to continuous processes utilizing molten matte, nitrogen acts as a major means of dissipating the heat from exothermic process reactions. High levels of oxygen enrichment or, put another way, the exclusion of nitrogen from the systems, would result in severe overheating unless fur­nace heat losses are dramatically increased or another means of heat dissipation can be employed. Higher heat losses, however, would restrict tum down ratios and would require new furnace construction techniques.

FLASH CONVERTING

An alternative to increasing heat losses to allow high levels of oxygen enrichment is to utilize the matte fed to the converter as a coolant. By solidifying matte from primary smelting furnaces, heat balances can be maintained without the need for extensive nitrogen dilution (Figure 2). Transport of the matte would also be simplified since expensive hot metal cranes would .no longer be required in new smelters or many retrofit applications. A pictorial flowsheet of the Flash Converting process is shown in Figure 3. All of the required unit operations use demonstrated technology.

JOURNAL OF METALS· May 1985

REACTION HEAT

70 60 50

[MJ/h]=1000

HEAT LOSSES

60

BLISTER

70 Matte Grade %

[MJ/h]=1000

r-~r---------'---------~200------~--------~r-~

180

REACTION HEAT

70 60 50

160

BLISTER

60 70 Matte Grade %

Matte can be supplied from any type of furnace, though an Outokumpu flash smelting furnace is ideal. The molten matte would be tapped to a granulator where high pressure water jets would break up and cool the matte stream forming small easily dewatered granules. A stockpile of the granules would supply the converting operation. Alternatively, the matte could be solidifed in ladles or pits.

Prior to feeding to the flash converting furnace, the matte would be milled and dried. A grind of less than 80% minus 100 mesh is sufficient to allow complete combustion and milling costs are low. Drying to less than 0.5% H20 can be accomplished in simultaneous drying/grinding mills or standard rotary, flash, steam coil, or fluid bed driers. In the flash converting furnace, matte reacts with oxygen to form blister copper and slag. Oxygen efficiencies in the furnace are essentially 100%. Either silicate or lime­based slags can be utilized and two- or three-phase operation can be selected depending on the desired sulfur content of the blister copper. In treatment of mattes containing 55-78% copper, a relatively small quantity of slag would be produced, resulting in high first pass copper recoveries. This slag would be recycled to the primary smelting furnace.

PILOT TEST WORK

Following small scale (up to 50 lb.lhr.l tests by Kennecott, it was decided to confirm the flash converting process and develop commercial plant de­sign criteria on a pilot scale. Outokumpu Oy was selected as the firm best able to perform the work, and the tests were conducted during the last quarter of 1984.

JOURNAL OF METALS· May 1985

Figure 1. Heat balance of molten matte converting.

Figure 2. Heat balance of flash converting.

KENNECOTT·OUTOKUMPU FLASH CONVERTING

SLAG

BLISTER COPPER TO ANODE REFINING

HIGH STRENGTH SO, OFF·GASES

Figure 3. Kennecott-Outokumpu Flash Convert­ing.

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Over 600 tons of 55 and 70% Cu matte were combusted in the Outokumpu pilot plant at Pori, Finland. The 55% Cu matte was solidified in pits prior to crushing and grinding, while the 70% Cu material was granulated at the HaIjavaltasmelter and then milled. Feed rates to the pilot furnace were gen­erally about 2 mt.lhr., though higher rates were tested for short periods. Oxygen enrichment was varied between 75 and 100%.

The pilot tests successfully verified all expectations. A summary of the test results is presented in Table I. The process was easily controlled in either the two-phase (slag/metal) or three-phase (slag/matte/metal) modes. Two­phase operation provides more flexibility to produce lower sulfur levels in blister copper. Sulfur contents as low as 0.04% S were produced and process control was demonstrated to be relatively easy. While some test data are still being analyzed, minor element removal in Flash Converting appears similar to that in conventional converters.

Table I. Results of Flash Converting Tests in the Pilot Flash Smelting Furnace for Different Grades of Ground Matte and with Different Types of Slag

Ground matte Cu% 54.6 68.9 70.7 Oxygen enrichment O2% 75 94 100

Blister copper S% 0.7 0.6 1.0 Fe% 0.025 0.063 0.042

Slag Cu% 16.8 22.2 12.2 S% 0.06 0.08 0.13

Fe% 25.8 24.8 36.0 Fe30 4 % 32.2 31.0 35.0

Si02% 27.6 26.9 3.7 CaO% 1.5 1.0 20.1

First pass copper distribution into metal phase % 84.8 93.7 97.7

Note: Copper Distribution Assumes All Flue Dusts Are Recirculated.

When combined with data on matte granulation, milling, and Outokumpu's previous experience in designing flash furnaces, the furnace test work confirms that the Kennecott-Outokumpu Flash Converting proc­ess is ready for commercialization. All unit operations in the process are based on proven technology, making the concept both new and time-tested at the same time. Flash Converting will be marketed world-wide by Outo­kumpu Oy in full cooperation with Kennecott.

POTENTIAL BENEFITS OF FLASH CONVERTING

The ability of the Flash Converting process to produce a steady stream of low-volume high S02 concentration offgases dramatically reduces costs of gas handling and sulfur fixation equipment when compared with conven­tional batch converting technology. Fugitive emission control is also simpli­fied and ladle transfers of molten materials can be eliminated. These advantages, in turn, allow simplification in the design of smelters, with associated cost savings. Figure 4 compares a layout for a conventional flash smelter converter aisle with a design for a smelter utilizing flash converting. By granulating matte directly from the primary flash furnace and laundering copper from the flash converting furnace to the anode furnaces, all hot metal cranes are eliminated and the size of the smelter facility is decreased. The size of the gas handling equipment is also reduced, and the continuous flow of high strength S02 gas allows optimization of acid plant design. In a recent study for a smelter treating 500,000 mtpy of chalcopyrite concentrates, the gas cleaning plant would have to treat 60,000 SCFM (100,000 NM3/hr.) of process gases from a flash furnace and a Peirce-Smith converter. Using flash converting, the gas cleaning require­ment is reduced to 25,000 SCFM (43,000 NM3/hr.). Preliminary estimates indicate potential savings of up to 20% in both capital and operating costs for a "greenfied" smelting complex. Additional benefits include the possi­ble separation of smelting and converting operations either in "space" i.e., physical location, to simplify construction and allow centralized converting operation, or in "time" to avoid scheduling conflicts between smelting and converting furnaces, increasing overall plant ava,ilability. Simplified proc­ess control and amenability to control instrumentation are also beneficial.

JOURNAL OF METALS· May 1985

CONCLUSION

Continuous production of blister copper is becoming more attractive as environmental regulations increase pressure to control emissions from con­ventional converters. The Kennecott-Outokumpu Flash Converting process, which has been successfully pilot-tested and is now ready for commercial application, is not only continuous but can utilize industrial grade oxygen to minimize offgas volumes and costs. Heat balance considerations, which preclude ~se of oxygen in other processes, are overcome by utilizing solidi­fied matte as a coolant. The new process, which is being marketed world­wide, offers significant capital and operating cost benefits in addition to its unique ability to separate smelting and converting operations.

SLAG MILL

ACID PLANT

FLASH SMELTING AND PEIRCE SMITH CONVERTING LAY-OUT WITH HOT METAL CRANES

ACID PLANT

SLAG MILL

FLASH SMELTING AND FLASH CONVERTING LAY-OUT WITHOUT HOT METAL CRANES

JOURNAL OF METALS· May 1985

Figure 4. Comparison of conventional and flash converting smelter layouts.

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ABOUT THE AUTHORS __________ __

J.A. AstelJokl received his M.Sc. and D.Sc. degrees in process metallurgy from the Helsinki Institute of Technology. He is currently the Research Manager, Pyrometallurgy, at the Outokumpu Metallurgical Research Centre in Pori, Finland. Dr. Asteljoki is also a member of TMS-AIME.

L.K. Bailey received his M.A.Sc. and Ph.D. from the University of British Columbia, British Columbia, Val1couver, Canada. He is currently a Sr. PrinCipal Metallurgical Engineer for Kenne­cott Process Technology in Salt Lake City, Utah. Dr. Bailey is also a member of TMS­AIME.

D.B. George received his degree from the Uni­versity of Utah. He is currently Manager, Opera­tions, Pyrometallurgy for Kennecott in Salt Lake City, Utah. He is also a member of TMS-AIME.

D.W. Rodolff received his degree from the Uni­versity of Arizona. He 'is currently the North American representative for the Engineering Division of Outokumpu Oy, Finland and is Man­ager of Nonferrous Metallurgy for the U,S. sub­sidiary Outokumpu Engineering, Inc., in Denver, Colorado. He is also a member of TMS-AIME.

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