Reductive smelting of sulfides and a burner therefor

Abstract

 A burner and method for smelting metallic sulfide concentrates in a reverberatory furnace. The concentrates are passed through a central feed bore (14) of a burner. A blanketing shield of fuel is fed through a conduit (18) and envelopes the feed and thereby separates it from an oxygen-containing gas fed through a further conduit (22) prior to combustion. By shielding the feed from the oxygen, oxidation of sulfidic sulfur to sulfur dioxide is minimized.

Description

TECHNICAL FIELD

[0001] The instant invention relates to the pyrometallurgical processing of metal sulfide ores or concentrates in general and, more particularly, to a more efficient method and burner apparatus that minimize the generation of sulfur dioxide (S0₂) in a reverberatory smelting vessel.

BACKGROUND ART

[0002] In the course of recovering nickel and/or copper from sulfidic materials such as concentrates containing chalcopyrite, pyrrhotite, pentlandite, etc. the first pyrometallurgical step is the oxidation of iron which ultimately leads to its extraction via slag removal. This process results in a matte rich in nickel, copper and other desired metallic values. One such smelting method that accomplishes this end. utilizes a reverberatory furnance.

[0003] Briefly, in current reverberatory furnaces, a fossil fuel (coal, oil or gas) is burned separately from the material being smelted. The furnace is a long rectangular structure with burners arranged at one end. Flames from the burners are played over the bottom of the furnace (hearth) wherein a large portion of the heat in the combustion gas radiates directly to the charge lying on the hearth below. Simultaneously, a remainder of the heat from the burners is radiated from and reflected off the roof and walls - hence it "reverberates" in the furnance. Although quite versatile, reverberatory smelting requires large quantities of fuel and results in the formation of nitrous oxides (^NOx)^. x

[0004] The charge fed into the furnace is the sulfide containing calcine feed eminating from a roaster. The charge is fed through a series of vertical fettling pipes that pass through the roof and dropped along the sides of the furnace. As it melts, the charge flows into the hearth and forms the characteristic slag and matte. A silicious flux to bind up the iron oxide (formed in the roaster) is added as necessary. The slag (rich in undesirable iron containing compounds) floats above the matte (rich in desirable nickel, copper and other metallic compounds). The slag and matte are separated by appropriate tapping procedures for further treatment in convertors.

[0005] An improved variation on this theme is the oxy-fuel reverb furnace. In this embodiment, a plurality of burners, essentially parallel to inner walls are mounted in the roof. Pure oxygen is mixed with-the fuel to cause combustion. The resultant flame impinges directly on the charge below. This configuration increases furnace throughput and decreases fuel consumption. The feed is independent of the burners.

[0006] A great difficulty posed by the pyrometallurgy of sulfide ores is that substantial quantities of sulfur dioxide are liberated as a by-product. In view of a heightened awareness concerning the release of sulfur dioxide, it has become imperative that sulfur dioxide emissions be subtantially reduced whenever and wherever possible. Accordingly, it is often desirable to produce sulfuric acid as a by-product. In any event, it is always desirable to improve furnace throughput, decrease expensive fuel consumption and reduce 8°2 emissions.

BUMMARY OF THE INVENTION

[0007] Accordingly, there is provided a process and a burner adapted therefor wherein a nickel and/or copper sulfide concentrate is passed through the central bore of a burner extending into a oxy-fuel reverberatory furnace and is contacted with a gaseous fuel rather than oxygen prior to combustion. More specifically, the sulfide concentrate may be a mixture of nickel or copper sulfide concentrate and roasted nickel or copper concentrate (calcines) or it may be partially roasted nickel or copper concentrate. This flame smelting technique minimizes the oxidation of sulfidic sulfur to S0₂ in the smelting vessel and improves fuel efficiencies and throughput without being deleterious to the refractories lining the vessel walls. In addition, NO_x formation is reduced.

BRIEF DESCRIPTION OF THE DRAWING

[0008] 

Figure 1 is a cross sectional elevation of an embodiment of the invention.

Figure 2 is a partial cross sectional view taken along line 2-2 in Figure 1.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

[0009] Referring to Figures 1 and 2 there is shown a burner 10 adapted for installation into a reverberatory furnace (not shown). The burner 10 includes feed inlet 12. The inlet 12 intersects central bore 14 which extends through the burner 10 to combustion zone 16. Fuel conduit 18 circumscribes the bore 14 and includes inlet 20. Oxygen conduit 22 circumscribes the fuel conduit 18 and includes inlet 24. Cooling jacket 26 circumscribes the oxygen conduit 22. Cooling fluid (usually water) is introduced through inlet 28 wherein it courses through the jacket 26 before exiting from outlet 30. Mounting plate 32 serves as a mounting surface to affix the burner 10 to the furnace. Inspection port 34 permits visual observation of the burner and flame. The burner 10 is ignited in a usual fashion.

[0010] It is proposed that flame smelting, that is, feeding the sulfide containing calcine material through the burner 10 into the flame increases the smelting efficiency of a reverberatory vessel. In this fashion, the individual particles are more fully exposed to the high temperature of the flame. The much impraved heat transfer conditions permit increased throughput without any detriment to refractory life. Moreover, the fuel itself partially acts as a temperature depressant by decreasing the flame temperature and thus reducing the formation of NO . x

[0011] It should be noted that by simply introducing the feed through the central bore 14 of the burner 10, excessive sulfur elimination as S0₂ would occur because the feed is not protected from the oxidizing ___ (oxygen) stream used for combusting the fuel. Therefore, the burner 10 initially reduces the exposure of the feed to the oxygen by channeling the fuel between the oxygen and the feed. The fuel shields and insulates the feed from the oxygen thus minimizing the oxidation of sulfudic sulfur to S0₂ in the furnace.

[0012] Protection of the sulfide containing calcine feed is particularly important in those cases in which smelting is preceeded by fluid bed roasting with the objective of capturing part of the sulfur of the metal concentrate in a continuous, strong gas stream which can be fed to an acid plant. Minimization of sulfur evolution as S0₂ in the smelting vessel permits maximizing sulfur elimination in the roaster. Optimum operating conditions towards this objective are proposed in the roast reduction smelting process described in Canadian Patent 1151430. In this process, the nickel concentrate is partially roasted and the calcine with a reductant are fed to an electric furnace. A sulfur deficient matte (all of the Fe and part of the Ni, Cu and Co in the matte are metallized) is produced, thus making sulfur elimination during the succeeding converting operation very small.

[0013] In view of the teaching in the aforesaid Canadian patent partial reduction smelting (mattes with only partial metallization of Fe) can also be practiced in a reverberatory furnace. Feeding of the partially roasted calcine and reductant through the burner 10 protects both the sulfide feed from excessive sulfur elimination as S0₂ and the solid reductant.

EXAMPLES

[0014] A small pilot plant electrical furnace 5 ft. (1.5 m) I.D. X 5 ft. (1.5 m) high was modified by removing the electrodes and inserting the burner 10. The feed was projected down the central bore 14 in both tests described hereafter. The results are given in Table I'below. In Run 1 the oxygen and fuel were dispatched through conduits 18 and 22 respectively whereas in Run 2 the fuel was injected into conduit 18 and the oxygen was fed into conduit 22.

[0015] The velocity of the feed and gas are on the order of 20-25 meters/second. This results in somewhat of a three ring concentric laminar flow as the various components emerge from the burner 10 into the combustion zone 16. The oxygen, shielded from the feed by the fuel, sees the fuel and is consumed during the resulting combustion reaction before it has the opportunity to oxidize the feed. The close proximity of the feed to the heat generated by the combustion reaction greatly increases the efficiency of the process while reducing the need for fuel. '

[0016] 

[0017] It should be noted in Run 2 more of the sulfur was fixed into the furnace matte. This shows that injecting the gas or other fuel next to the partially roasted concentrate helped prevent the oxidation of the sulfides by the oxygen used for the combustion and is a superior arrangement to achieve the desired objective. Note also that the combination of increased coke in the feed through the burner plus the natural gas injection next to it give a superior reduction of the slag, i.e. the nickel in the slag is substanially lower. Thus both the sulfuric sulfur and the coke were protected by the burner 10.

Claims

1) A burner for the reductive smelting of sulfide containing materials, the burner comprising a central feed bore, a fuel conduit circumscribing the bore, an oxidizing conduit circumscribing the fuel conduit, and means for cooling the burner.

2) The burner according to claim 1 wherein the bore, the fuel conduit and the oxidizing conduit define a combustion zone wherein the fuel minimizes contact between the feed and the oxidizer so as to reduce the oxidation of sulfidic sulfur to sulfur dioxide.

3) The burner according to claim 1 affixed to a reverberatory furnace.

4) The burner according to claim 1 wherein an inlet is affixed to the bore, the fuel conduit and the oxidizing conduit.

5) The burner according to claim 1 wherein the bore includes an inspection port.

6) A process for smelting sulfide containing materials, the process comprising introducing a sulfide containing concentrate into a burner, injecting an oxidizer about the concentrate, adjacently injecting fuel between the concentrate and the oxidizer, and then combusting the resultant combination.

7) The process according to claim 6 wherein the fuel shields the concentrate from excessive sulfur elimination as sulfur dioxide.

8) The process according to claim 6 wherein the concentrate is selected from the group consisting of nickel sulfide concentrate and copper sulfide concentrate and from the group consisting of roasted nickel concentrate and copper concentrate.

9. The process according to claim 6 wherein the concentrate is selected from the group consisting of partially roasted nickel concentrate and copper concentrate.

10. The process according to claim 6 wherein the concentrate is injected into a central burner bore, the fuel is injected into a first conduit circumscribing the bore, the oxidizer is injected into a second conduit circumscribing the first conduit, the concentrates, fuel and oxidizer emerging from the burner and being combusted, the fuel substantially interposed between the concentrates and the oxidizer, and/or wherein the process occurs in a reverberatory furnace, and/or wherein a reductant is introduced into the bore, and/or wherein the fuel is a gaseous hydrocarbon, and/or wherein the oxidizer is an oxygen containing gas, e.g. oxygen.

Drawing