A PROCESS FOR MANUFACTURING SELF-REDUCING PELLETS/BRIQUETTES FROM BAG HOUSE DUST MIXED WITH CARBON TO BE USED IN STEELMAKING FURNACES

Abstract

Bag house dust is combined with a carbon source and shaped into pellets or briquettes and used to recycle valuable metals present in the bag house dust.

Claims

1. A solid composition adapted for use as a feed stock in steel making furnaces comprising; (i) a baghouse dust comprising iron oxide and at least 1% zinc by weight; and (ii) a carbon source; wherein said solid composition is in the form of a briquette or pellet

2. The solid composition of claim 1, wherein the product does not comprise either or both of ferrous chloride and ferrous sulfate amount that alters the properties of the composition as a feed stock in steel making furnaces.

3. The solid composition of claim 1, wherein the carbon source comprises greater than 50% carbon by weight.

4. The solid composition of claim 1, wherein the carbon source comprises at least one member selected from the group consisting of anthracite, graphite, coal, coke, petcoke, coal tar pitch, tar, tar, molasses and decanter sludge.

5. The solid composition of claim 1, wherein the iron oxide is iron (II) oxide (FeO), iron (III) oxide (Fe.sub.2O.sub.3), iron (II,III) oxide (Fe.sub.3O.sub.4, Fe.sub.5O.sub.6, Fe.sub.5O.sub.7), or mixtures thereof.

6. The solid composition of claim 1, wherein the zinc is zinc oxide (ZnO), or any other zinc containing oxide, zinc ferrite, or mixtures thereof.

7. The solid composition of claim 1, further comprising from greater than 0% up to 15% by weight of an additive.

8. The solid composition of claim 7, wherein the additive comprises at least one member selected from the group consisting of lime, calcium chloride, silica, limestone, clay, iron grindings, steel grindings, iron borings, steel borings, iron turnings and steel turnings.

9. The solid composition of claim 1, wherein the baghouse dust comprises greater than 30% iron oxide by weight.

10. The solid composition of claim 1, wherein the baghouse dust comprises 30% to 70% iron oxide by weight.

11. A briquette or pellet adapted for use as a recycled feed stock in electric arc and/or basic oxygen furnaces, the briquette or pellet comprising; (i) 60 to 90% by weight of a bag house dust comprising iron oxide and zinc, wherein the iron oxide comprises 30 to 70% by weight of the bag house dust; (ii) 3 to 20% by weight of a carbon source; and (iii) 0 to 15% by weight additive.

12. The briquette or pellet of claim 11, wherein the product does not comprise either or both of ferrous chloride and ferrous sulfate.

13. The briquette or pellet of claim 11, wherein the carbon source comprises greater than 50% carbon by weight.

14. The briquette or pellet of claim 11, wherein the carbon source comprises at least one member selected from the group consisting of anthracite, graphite, coal, coke, petcoke, coal tar pitch, tar, tar, molasses and decanter sludge.

15. The briquette or pellet of claim 11, wherein the additive comprises at least one member selected from the group consisting of lime, calcium chloride, silica, limestone, clay, iron grindings, steel grindings, iron borings, steel borings, iron turnings and steel turnings.

16. The briquette or pellet of claim 11, wherein the iron oxide comprises at least one member selected from the group consisting of iron (II) oxide (FeO), iron (III) oxide (Fe.sub.2O.sub.3), and iron (II,III) oxide (Fe.sub.3O.sub.4, Fe.sub.5O.sub.6, Fe.sub.5O.sub.7).

17. The briquette or pellet of claim 11, wherein the zinc is zinc oxide (ZnO), or any other zinc-containing oxide, zinc ferrite, or mixtures thereof.

18. The briquette or pellet of claim 13, wherein the additive comprises at least one member selected from the group consisting of lime, calcium chloride, silica, limestone, clay, iron grindings, steel grindings, iron borings, steel borings, iron turnings and steel turnings.

19. The briquette or pellet of claim 13, wherein the iron oxide comprises at least one member selected from the group consisting of iron (II) oxide (FeO), iron (III) oxide (Fe.sub.2O.sub.3), and iron (II,III) oxide (Fe.sub.3O.sub.4, Fe.sub.5O.sub.6, Fe.sub.5O.sub.7).

20. The briquette or pellet of claim 13, wherein the zinc is zinc oxide (ZnO), or any other zinc-containing oxide, zinc ferrite, or mixtures thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0018] FIG. 1 is a graph of exhaust gas composition and furnace temperature during reduction as per Example 1.

[0019] FIG. 2 shows the XRD pattern of an unreduced briquette according to Example 1.

[0020] FIG. 3 shows the XRD pattern of a reduced briquette according to Example 1.

DETAILED DESCRIPTION

[0021] Various features and advantageous details are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions, and or rearrangements will become apparent to those of ordinary skill in the art from this disclosure.

[0022] In the following description, numerous specific details are provided to provide a thorough understanding of the disclosed embodiments. One of ordinary skill in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0023] The present disclosure provides methods and compositions that make use of the steel-making waste by-product, bag house dust. The bag house dust contains valuable materials such as iron and zinc, primarily in the form of oxides. High oxide content in the bag house dust oxide precludes direct use of bag house dust in industrial steel furnaces. In the methods and compositions disclosed herein, the bag house dust is combined with a carbon source and optionally an additive, and molded into briquettes or pellets. Without wishing to be bound by theory, the carbon source is believed to act as an in situ reducing agent that assists in transformation of metal oxides to useful metals. The briquettes or pellets may be employed as a source of iron, zinc, and/or carbon in iron, zinc, or steelmaking processes.

[0024] The bag house dust is mixed with, a carbon source and molded into briquettes or pellets. The carbon source carbon source may be anthracite, graphite, coal, coke, petcoke, coal tar pitch, tar, molasses, decanter sludge, or combinations thereof. In some aspects, the carbon source and bag house dust are combined in a weight ratio ranging from 0.03:1 to 0.18:1, with carbon as the major weight constituent of the carbon source. In one embodiment, the briquettes or pellets comprise a 0.06:1 weight ratio of carbon source to bag house dust.

[0025] One or more additives may optionally be included in the pellets or briquettes, including lime, calcium chloride, silica, limestone, day, iron and/or steel grindings, iron and/or steel borings, iron and/or steel turnings, and the like. The pellets or briquettes may include an optional binder. The pellets or briquettes may include one or more non-carbonaceous reducing agents. In preferred embodiments, non-carbonaceous reducing agents are excluded from the pellets or briquettes.

[0026] The pellets or briquettes may be employed in a steelmaking process wherein the bag house dust iron oxide is used as an iron source for the production of steel. The pellets or briquettes may be combined with recycled iron or steel, unrecycled iron, or a metal ore.

[0027] In a briquette or pellet-making process, bag house dust is combined with a carbon source and shaped into briquettes or pellets. The bag house dust, carbon source, optional additive, and optional binder are combined in a mixing apparatus. In some embodiments, the carbon source acts as a binder. The binder, if added, will be sufficient to bind together the carbon source and the BHD to be formed into briquettes via the chosen processing technique. Typically, the binder will be present in an amount of from 1 to 20% by weight of the mixture of BHD, carbon source and the binder. Preferred binders include hydrocarbon binders such as, e.g., corn starch, cellulose, and the like. Water may be optionally added to the mixture to create a slurry.

[0028] The relative amounts of bag house dust, carbon source, and optional components (additive, binder, and water) may be adjusted in order to improve the adherence of the mixture and/or the strength of the briquette or pellet product. The mixture may be mixed at room temperature, or it may be subjected to heating conditions.

[0029] The mixture is formed into briquettes or pellets using any molding or shaping method known in the art. Exemplary methods include extrusion and pelletizing. The shaped briquette or pellet may be further coated with additional bag house dust mixture and subsequently molded or shaped.

[0030] The shaped briquette or pellet may be heated in an oven. The oven may be used to remove water, increase binding, and/or cause at least a portion of the metal oxide content to be reduced. The oven may be provided with a stream of oxygen or an oxygen-containing gas or in inert atmosphere such as Ar and N. The briquettes or pellets may be used immediately or may be aged prior to using. Aging of the briquettes or pellets may be accomplished at ambient temperature or under elevated temperature.

[0031] The briquettes or pellets may be used in iron or steel-making furnaces. The briquettes or pellets may be used in other processes, for example, the briquettes or pellets may be used in a Midrex and HYL processes or any other reduction technology whereby the iron oxide is reduced in the absence of melting. The briquettes or pellets may be used as an aggregate and added to concrete. The briquettes or pellets may be used to enhance zinc content in zinc distillation or extraction methods. The recycling of bag house dust may provide financially advantageous environmental protection credits for waste reduction and/or recycling of iron and zinc oxides.

Example 1

Analysis of Self-Reducing Baghouse Dust (BHD) Briquettes

[0032] Baghouse dust (BHD) briquettes containing carbon as a reductant in briquettes containing carbon as a reductant in a 1.6:1 molar ratio of carbon to Fe.sub.2O.sub.3 The BHD briquettes were prepared by mixing 10 wt % carbon with 90 wt % BHD along with water. The wet mixture was then pressed into briquettes with a roller press cold briquetting machine. The BHD was provided by SABIC, and was obtained from an electric arc furnace. The chemical composition of an exemplary, non-limiting BHD analyzed by X-ray fluorescence spectrometry (XRF) used in accordance with the present invention is provided below in Table 1:

TABLE-US-00001 TABLE 1 Element Average weight (%) Aluminum (Al) 0.17 Calcium (Ca) 5.79 Iron (Fe) 29.44 Magnesium (Mg) 2.5 Manganese (Mn) 1.52 Lead (Pb) 1.8 Silicon (Si) 1.31 Zinc (Zn) 18.78 Potassium (K) 3.24 Sodium (Na) 0.88 Chloride (Cl) 2.25 Sulfur (S) 0.46 Phosphorus (P) 0.13 Copper (Cu) 0.13

[0033] The briquettes of Example 1 were subjected to reduction at 1100 C. and analyzed. Analysis of the as-received and reduced briquettes was performed by x-ray diffraction (XRD) for phase identification, and x-ray fluorescence (XRF) spectrometry to determine approximate elemental composition. The nominal compositions of the reduced BHD briquettes is summarized in the Table 2 below:

TABLE-US-00002 TABLE 2 Composition of reduced BHD briquettes (All constituents above 1% listed unless otherwise noted.) Element Concentration (wt. %) Zn 5-20 Ca 8-15 Fe 29-37 Pb 1-3 Mg 1-2 Al <1 Mn 1-2 Si 2-3 Na 2-3 K 1-2

[0034] Reduction of a sample briquette was carried out in a vertical tube furnace under flowing argon gas (flow rate of 150 mL/min). One briquette was weighed, and then suspended (using Kanthal wire) at the top of the furnace while the furnace was heating up. The furnace was taken from room temperature to 1100 C. at a rate of 5 C. per minute, where it was held for one hour, before being cooled to room temperature also at a rate of 5 C. per minute. Upon reaching 1100 C., the briquette was lowered into the hot zone of the furnace, and the exhaust gasses were directed to an infrared gas analyzer, which recorded the concentrations of CO, CO.sub.2, CH.sub.4, H.sub.2, and O.sub.2. After the furnace had fully cooled down, the briquette was removed from the furnace and weighed again.

[0035] XRD patterns were analyzed by using the QualX software package (See A. Altomare, N. Corriero, C. Cuocci, A. Falcicchio, A. Moliterni, and R. Rizzi, QUALX2.0: a qualitative phase analysis software using the freely available database POW_COD, J. Appl. Crystallogr., vol. 48, no. 2, pp. 598-603, April 2015). The patterns were filtered to remove the broad carbon peak present around 20=25, and major peaks were identified from the filtered pattern. The search-match database was restricted to elements listed in Table 1, in addition to carbon and oxygen in order to account for oxides and carbides that may have been present. The phases that best accounted for the peaks were selected manually.

Results

[0036] Data gathered from the infrared gas analyzer is plotted in FIG. 1. It shows a sudden increase in the CO generation rate, which peaks after approximately 10 minutes, then decays. Similar peaks are seen in the concentration of CO.sub.2 and H.sub.2. The presence of hydrogen gas indicates that the reductant is not pure carbon, but likely a pulverized coal. The long decay time is due to the residence time of the exhaust gasses in the furnace (caused by the low flow rate, 150 mL/minute); note that the rate of decay does not significantly change after the furnace begins to cool after the 1 hour dwell at 1100 C. Reduction was likely completed shortly after the peak in CO concentration was reached.

[0037] The data suggests that the rate of reduction is quite fast. The infrared (IR) spectrometer data is particularly useful for determining the total amount of CO, CO.sub.2, and H.sub.2 produced by integration of the curves.

[0038] The mass loss of the briquette was significant (initial mass=13.7 g, final=9.2 g). The inside surface of the furnace tube was also coated with a gray powder, which was analyzed by scanning electron microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) and found to zinc-contain primarily zinc. The XRF results (Table 3, which shows the approximate ratios of Ca, Fe, and Zn, normalized to 100%) show an almost complete loss of zinc in the final product.

TABLE-US-00003 TABLES 3a and 3b XRF analysis of samples before reduction (top) and after reduction (bottom) Element Concentration (wt. %) Table 3a Ca 21 Fe 65 Zn 14 Table 3b Ca 27 Fe 73 Zn <1

[0039] XRD of an unreduced ground briquette shows in FIG. 2 that the main crystalline phases are magnetite (Fe.sub.3O.sub.4, phase P.1 in FIG. 2), wustite (FeO, phase P.2), lime (CaO, phase P.3), zinc oxide (ZnO, phase P.4), and sodium and potassium oxides (Na.sub.2O and K.sub.2O, phases P.6 and P.5, respectively). The other constituents shown in the chemical analysis are not visible over the background, either because they are not present in significant enough concentrations or because they are not crystalline enough to generate a strong x-ray signal.

[0040] XRD on the reduced briquette as shown in FIG. 3 show a different set of peaks. First two phases of metallic iron are present, ferrite (phase P.1 in FIG. 3) and austenite (phase P.3). Lime (CaO, phase P.2) is still present, but peaks corresponding to a dicalcium silicate (Ca.sub.2SiO.sub.3, phase P.4) are now present. Zinc oxide is not present in the XRD pattern, as expected given the XRF data in Table 2.

[0041] This suggests that the briquette has been fully reduced by the reductant in about 1 hour or less at 1100 C. The presence of austenite is likely due to the presence of significant amounts of manganese. If all manganese was reduced as well, the resulting iron should contain 5 weight percent manganese given the composition in Table 1. Manganese is an ausenite stabilizer as can be seen from, e.g., the phase diagram in FIG. 4 of the ASM Handbook, Volume 3, Alloy Phase Diagrams (1998). It is believed, without being bound to any theory, that the presence of dicalcium silicate is likely due to interactions between the CaO and SiO.sub.2, as silica was not detected in the unreduced sample's XRD pattern because it was either not present in sufficient quantities or was amorphous.

[0042] From the data, it can be concluded that reduction was rapid at the tested furnace temperature of 1100 C., resulting in complete reduction of the iron and near-complete removal of zinc by reduction of zinc oxide to metallic zinc, that evaporated out of the briquette.

Example 2

[0043] The BHD of Example 1 having the composition shown in Table 1 above process was premixed with anthracite as a carbon source according to the procedure and ratios described in Example 1 above and shaped into pellets/briquettes using the method of Example 1.

[0044] Experiments were conducted to evaluate the use of BHD and the aforementioned carbon briquettes in the EAF. Different experiments were conducted with varying temperature and time. The summary of experimental result shown in table 1

[0045] Steps for conducting the experiment of Example 2 are described below in Table 3 with reference to Table 4:

TABLE-US-00004 TABLE 3 Method Using Box Furnace 1. Preheat the furnace to required temperature while empty crucible is inside 2. Alumina crucible was used to conduct experiment. 3. Open the furnace and put the sample 4. Close the furnace 5. Hold for the indicated time 6. Shut down the furnace, remove the sample and quench in water.

TABLE-US-00005 TABLE 4 Experimental results Temp. Time Mass Mass Fe Metallic Sample Materials ( C.) (min) before (g) after (g) Total (%) Fe % Metallization % A1 90% BHD + 1400 10 161.4 133.8 82.4 64.7 79.02 B1 10% Carbon 138.8 127.3 82.46 66.4 81.76 C1 158.2 118 82.42 65.6 80.19 A2 90% BHD + 1400 15 158.5 127 82.38 65.6 80.03 B2 10% Carbon 160.9 104.3 82.47 65.6 80.69 AA1 90% BHD + 1200 10 163 127.9 83.1 63.9 77.35 BB1 10% Carbon 160.9 137.4 82.9 63 76.55 CC1 163.3 136.9 82.4 63.1 76.65 AA2 90% BHD + 1200 15 142.1 125.9 82.7 65.9 79.79 BB2 10% Carbon 155.2 125.2 83.05 66.23 79.83 CC2 162.4 131.1 82.47 65.7 79.69

[0046] The results in Table 4 show that the four set of experiments conducted with varying temperature (1200 C. and 1400 C.) and holding time 10 and 15 min) result show that acceptable amounts of reduction occur in all cases (76.55 to 80.69% reduction).

[0047] At 1200 C. and 10 min holding time metallization varies from 76.55% to 77.35% whereas with 15 min holding time metallization varies from 79.69% to 79.83%.

[0048] In case of 1400 C. and 10 min holding time metallization varies from 79.02% to 81.76% whereas with 15 min holding time metallization varies from 80.03% to 80.69%.

[0049] The claims are not to be interpreted as including means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) means for or step for respectively.