INSTALLATION FOR CONTINUOUS COPPER FIRE REFINING
BACKGROUND OF THE INVENTION
1. Field of the Invention: This invention relates to an apparatus for continuous fire refining of unrefined copper or scrap copper.
2. Description of the Prior Art: The melting of copper concentrates produces matte and slag. The copper matte is converted into unrefined copper in Peirce-Smith Hoboken converters, or continuous conversion processes such as Kennecott-Outokumpu or Mitsubishi. Unrefined copper is directed to a fire refining process before electrorefining. Fire refining of unrefined copper is carried out in fixed reverberatory or vascular furnaces called anodic furnaces due to the most common casting of refined copper in the form of anodes, which are transferred to electrolytic refining. The process of refining fire is a classic baking process consisting of four stages: loading, oxidation and slagging of impurities, reduction and anodic casting. The refining cycle time without the stage of
foundry varies from 6 to 14 hours. Oxidized copper after the oxidation stage contains from 5000 to 10,000 ppm of oxygen. Copper is reduced by a carbon or ammonia reducing agent. The most common reducing agent in use are petroleum or natural gas. The oil or natural gas is injected with air into the molten copper bath through a nozzle or nozzles. The copper reduction faces notable limitations · in the speed of the process and the efficiency of use of the reducing agent. The liquid copper charge reduction stage, which fluctuates from 150 to 400 t, varies in the range of 1.2 to 2.0 hours. The reported efficiency of the reducing agent is below 50%. The injection of the liquid or gaseous reducing agent into the copper produces black fumes in the gas discharge due to the thermal decomposition of the hydrocarbons. The partial use of coal in the reduction of oxygen from copper produces the presence of carbon particles in the reduction gases, which are partially burned if the flame of the burner is oxidized. The carbon particles are transferred to the gas discharge from the kiln, creating black fumes emitted through a chimney into the atmosphere. The reduction of liquid oxidized copper is practiced for centuries and was first described by Georgious Agricultural (G:
Agricultural: "De Re Metallica", translated from Latin, la. 1556 edition by Hebert C. Hoover and Lou H. Hoover, Dover Publications, 1950, 535-536). After the oxidation of the copper with air in an open hearth furnace and the removal of impurities, the copper was reduced with a wood. The reduction of copper with wood (tolerated) is still practiced in some smelting furnaces. L. Klein presented a new idea of the use of the gas reducing agent as a substitute for wood ("Gaseous reduction of oxygen-containing copper", J. of Metals, Vol. 13, No. 8, August 1961, 545-547 U.S. Patent No. 2,289,397, June 1961). The study showed that injecting natural gas with air provides a better solution than injecting only natural gas into a liquid copper. The copper deoxidation method with reformed natural gas and a related apparatus have been patented by Phelps Dodge Corporation in the United States and Canada. (C. Kuzell, M. Fowler, S. Davis and L. Klein: "Apparatus for reforming gases" US Patent No. 3,071,454, January 1963; "Gaseous reduction of oxygen containing copper", Canadian Patent No. 669,598, August 1963). R. Nenych, F. Kadkler and V. Sedlacek replaced conventional reduction with wood for ammonia, which allowed the production of high quality copper. The ammonia consumption is approximately 1 kg / t of copper, when the
Oxygen is reduced from 4000 to 1000 ppm. (R. Henych et al., "Copper refining by gaseous ammonia," J. of Metals, vol. 17, No. 4, April 1955). N. Themelis and P.Schmidt have patented the deoxidation of a liquid copper by injection of several reformed hydrocarbons (methane), ethane, butane) with steam, leading to the formation of the gas that contains carbon monoxide and hydrogen. The patented installation was based on the vascular furnace ("Apparatus and process for the gaseous deoxidisation of molten metal, Canadian Patent No. 827,066, November 1969) R.Beck, C.Anderse and M. Messner have patented the process for deoxidation of copper with the mixture of natural gas / air ("Process for deoxidising copper with natural gas-air mixture, US Patent No. 3,619,177, November 1971). Anaconda Company patented a process of copper deoxidation in a vascular furnace by injection through lancets of the mixture of natural gas or diesel and steam (W. Foard and R. Lear: "Refining copper" US Patent No. 3,529,956, September 1970). J. Henderson and W. Jonson have patented for ASARCO the copper reduction method in a vascular furnace by injection of natural gas through nozzles ("Gas poling of copper", North American Patent No. 3,623,863, November
1971). G. Mckerrow and D. Panlle reviewed the evolution of copper deoxidation methods in a "Gaseous deoxidization of copper at the Noranda smelter" Canadian Metallurgical Quarterly, Vol. 11, No. 4, 1972, 629-633. the Noranda melting furnace using natural gas injected through nozzles in a vascular furnace. J. Oudiz made a general review of copper reduction processes ("Poling processes for copper refining", J. of Metals, Vol. 25, December 1973, 35-38). Based on industrial data on the consumption of the reducing agent, benefits and problems related to the use of various reducing agents have been analyzed, reforming reactions and efficiency of the reducing agent. L. Lavrov ("Deoxidization of anode copper by natural gas and steam mixture", The Soviet Journal of Non-Ferrous Metals, Vol. No. 19, No. 5, translation in English, greater than 1978, 25-26) verified the Use of a mixture of leftover natural gas and steam injected through a lancet.
C. Toro and V. Paredes ("Partial replacement of diesel oil by Enap-6 as a reducing agent in the process of obtaining anodic copper in the Potrerillo smelter", 34th Annual IIMCh Convention, November 1983, Rancagua) developed on an industrial scale and demonstrated the possibilities of using heavy oil (ENAP-6), with
higher sulfur content and lower price, in copper reduction. J. Minoura ("Bunker fuel oil poling in the furnace at Kosaka smelter", 114th Annual Meeting, 1985, NY, USA) describes the reduction of copper with heavy oil (Bunker C), showing the advantages and low costs compared to the reduction of copper with ammonia practiced since 1967. References related to the use of porous plugs in copper fire refining are fragmentary since in the 1980s (P. Goyal, N. Themelis and W. Zanchuk, "Gaseous refining of anode copper ", J. of Metals, Vol 34, December 1982, 22-28, P. Goyal, S. Joshi and J. Wang" Porous plug injection in anode refining furnace ", J. of Metals, Vol 35 , December 1983, 52-58). The use of porous plugs was transferred from the iron metallurgy and developed immediately in the metallic casting area. Industrial applications in copper refining were first oriented to copper desulfurization by nitrogen agitation. The idea of reducing copper with hydrogen introduced through porous plugs was only investigated on a laboratory scale. The description of the industrial operation of porous plugs is presented in a letter from A, Rugby and M. Lanyi: "Porous plug in molten copper production and
refining ", CIM '96, August 1996, 393-403 The operational practice and the proposed methods of injection, bath agitation and type of reducing agent, highlight the problems existing in the removal of oxygen from a liquid copper, such as prolonged reduction time, low efficiency of the reducing agent and emission of gases with unburned particles.
COMPENDIUM OF THE INVENTION It is an object of the invention to provide a new copper continuous fire refining method. This method is achieved by a method, which uses additional solid flotation of the reducing agent on the surface of the copper with simultaneous agitation of the bath by the inert gas supplied by the porous plugs.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a drawing schematically illustrating the principle of continuous continuous fire refining of the unrefined copper supplied from the Mitsubishi continuous copper mat kiln conversion furnace.
DETAILED DESCRIPTION OF THE INVENTION This invention relates to a pyrometallurgical method of removing oxygen from a copper
liquid by the use of the solid carbonaceous reducing agent, loaded on the surface of the copper in addition to the injection of the reducing agent through nozzles or lancets and the simultaneous stirring of the copper bath with inert gas introduced through porous plugs. The method in which the carbonaceous reducing agent and the petroleum and natural gas hydrocarbons mixed with air or steam react with oxygen dissolved in copper results in a high rate of reduction, reduced time and increased efficiency of the reducing agent. Thus, the invention that leads to a method of extracting oxygen from a liquid copper consists of the following steps: a) Oxidation of copper bath at the level necessary for removal of impurities; b) Addition of the carbonaceous reducing agent on the copper surface, injection of the fuel reducing agent mixture through the nozzle (s) and agitation of the nitrogen bath through porous plugs; c) Continuation of oxygen extraction from a copper to the desired oxygen content. According to this invention, the reduction (4) of copper, after the oxidation and slagging of impurities, is carried out by injection of a liquid or gaseous reducing agent (petroleum, natural gas) (3) with simultaneous addition
of the solid reducing agent (5) on the surface (4) of the copper bath and the bath agitation with inert gas (1) through porous plugs (2). The injection of a liquid or gaseous reducing agent with deficient amount of air (3) into the copper (4) liquid produces chemical reactions in the gaseous stream from the nozzle and the generated gas bubbles (9) emerged: • Decomposition of hydrocarbons CnHm = > n C + m H2 • Partial combustion with air 2C + 02 = > 2 CO 2 H2 + 02 = ¾0 • Reduction of copper (0) Copper + C = > CO (0) copper + CO = > C02 (0) copper + ¾ = > H20 The addition of charcoal or other solid carbonaceous reducing agent on the surface of the copper bath initiates the reactions at the copper / carbon interface: (0) copper + C - = CO (0) copper + CO = C02 C02 + C = > 2 CO The injection of inert gas (1) through the porous plug (2) prevents the formation of the oxygen content gradient in the copper, decreasing the reaction rate. The continuous stirring of the copper bath in the total volume by inert gas (1) ensures the transfer of mass over the
Reaction surface (copper / charcoal). The simultaneous reduction of copper (4) by the injected reducing agent (oil, natural gas) and the floating bed of charcoal or coke significantly increases the total process speed, decreasing the reduction time and increasing the kiln productivity. The bed (5) of charcoal or floating coke on the copper surface (4) allows higher flexibility of operation of the burner. Even in the case of oxidant flame, charcoal (5) protects copper against oxidation, allowing more efficient use of fuel and better temperature control of copper. In addition, the excess oxygen in the burner allows the post-combustion of gases (7) of reduction leaving the bath that produces clean gases. The biggest problem in the reduction of copper (4) by injection of oil and natural gas (3) is the formation and emission of black smoke. The thermal decomposition of hydrocarbons produces hydrogen and elemental carbon (9). The carbon particles are partially reacted with oxygen from the copper, but partially rise inside the bubbles that are released from the melt. This part of coal can be partially burned on the smelter if there is sufficient oxygen supplied by the burner. But, the primary carbon monoxide is from reaction gases it burns. Finally, the remarkable part of the coal that is directed
The chimney is emitted into the atmosphere. According to the invention, the float bed of charcoal or coke on the copper surface acts as a filter for the carbon particles. The particles are trapped by a filter, sintered and the carbon is used as a reducing agent along with the charcoal. This leads to higher carbon utilization and higher efficiency of the reducing agent. This invention has the following advantages compared to traditional methods of copper reduction: a) The application of solid carbon addition combined with bath agitation by nitrogen introduced by porous plugs during the injection of the liquid or gaseous reducing agent remarkably shortening the time of reduction from 40 to 60% compared to the common reduction practice. b) The efficiency of the reducing agent (coal and hydrocarbons) is increased from 30 to 50% of the average values of traditional operation. c) The emission of gases with black fumes (carbon black) is drastically reduced, reducing the impact of the negative process on the environment. d) The higher efficiency of the reducing agent and the shorter reduction time results in the decrease
of the unitary reducing agent and the fuel consumption as well as in the increase of productivity of the furnace. e) The cost of applying the method is low. The necessary modifications of the refining furnace are minor. F)
EXAMPLE 1 The copper refining is carried out in a vascular anodic furnace with a capacity of 150 t of copper as illustrated schematically in Figure 1. Four porous plugs (2) are mounted in the lower part of the furnace. Nitrogen (1) is injected into the molten copper (4) through the porous plugs. The nitrogen flow rate varies from 40 to 120 Nm3 / h. The oxidation period ends when the slags are desescorded. The oxygen content in copper is at the 8000 ppm level. Then, 1.5 to 4 kg of charcoal (5) per ton of copper is loaded through the mouth onto the copper surface. The flow of oil through a nozzle is presented (approximately 4-8 kg / h per ton of copper) together with the air (4-8 Nm3 / h per ton of copper). The furnace is tilted and the nozzle is submerged to begin blowing into the copper. The flow velocity of the oil gradually increases to the point where black fumes are not emitted. Burner adjustment is changed. The
The flow rate of the oil through the burner is stopped and the air flow is maintained at the level of 3-20 Nm3 / h per ton of copper. The air introduced through the burner ensures effective post-combustion of reduction gases leaving the bath. The charcoal on the surface prevents copper from oxidation. The exhaust gases produced that leave the furnace to a chimney are clean and acceptable for emission. After 45 minutes of the injection of the reducing agent through the nozzle, the flow velocity of the oil gradually settles and the furnace tilts by placing the nozzle on the bath. Afterwards, the flow of oil and air stops. The oxygen content in copper is 400-800 ppm and the oven is prepared for anodic casting.
EXAMPLE 2 Copper refining is carried out in a stationary anodic furnace with a capacity of 300 tons of copper. Four porous plugs are installed in the lower part of the side wall against the wall with loading window. The flow rate of nitrogen through the porous plug is 0.3-1.0 Nm3 / h per ton of copper. After finishing the oxidation period and the desescorification of the slag refining, the portion of 1.3-4.0 kg of charcoal per tonne of copper is loaded through a window over the
copper surface. Then, the oil flow is presented through a lancet (2-5 kg / h per ton of copper) together with the air (2-5 Nm3 / h of ton per copper). The lancet is immersed inside the copper and brought to reduction. The burner is supplied by natural gas. The parameters of the burner are determined: 1-3 Nm3 / h of natural gas and 7-20 Nm3 / h of air per ton of copper. This ensures effective post-combustion of reduction gases and the emission of clean discharge gas to the atmosphere. After 100 minutes, the lancet is removed and the oil and air flowing stop. The oxygen content has been decreased from 6000-8000 ppm to approximately 400-800 ppm. Then, the anodic casting is continued.