Biomass Direct Reduced Iron

Abstract

A compacted ‘green’ briquette between 5 cm.sup.3 and 20 cm.sup.3 including, prior to reduction in a direct reduction process, a composition including at least 30% lignocellulosic biomass material by dry weight and at least 55% iron ore fines by weight, a density of between 1.4 g/cm.sup.3 and 2.0 g/cm.sup.3, and a compaction strength of at least 500N. A direct reduced iron briquette suitable for the production of iron and/or steel including at least 85% iron by weight and at least 1% fixed carbon by weight, and a volume of between 7.5 cm.sup.3 and 30 cm.sup.3, wherein the briquette has, prior to reduction (i.e. as a ‘green’ briquette), the above composition.

Claims

1. A compacted ‘green’ briquette that is suitable for a direct reduction process, the briquette being between 5 cm.sup.3 and 20 cm.sup.3 and including, prior to reduction in a direct reduction process, a composition of at least 30% lignocellulosic biomass material by dry weight and at least 55% iron ore fines by weight, a density of between 1.4 g/cm.sup.3 and 2.0 g/cm.sup.3, and a compaction strength of at least 500N.

2. A direct reduced iron briquette that is suitable for the production of iron and/or steel in a downstream ironmaking/steelmaking process including at least 85% iron by weight and at least 1% fixed carbon by weight, and having a volume of between 7.5 cm.sup.3 and 30 cm.sup.3, wherein the briquette has prior to reduction (i.e. as a ‘green’ briquette) a composition including at least 30% lignocellulosic biomass material by dry weight and at least 55% iron ore fines by weight.

3. A briquette according to claim 1 wherein the lignocellulosic biomass material is selected to flex around the iron ore fines during compaction of materials to form the ‘green’ briquette.

4. A briquette according to claim 1 wherein the ‘green’ briquette has a compaction strength of at least 850 N.

5. A briquette according to claim 1 wherein the lignocellulosic biomass material forms a majority of the surface area of the ‘green’ briquette prior to reduction.

6. A briquette according to claim 5 wherein the lignocellulosic biomass material includes dry tubular stalks of grasses.

7. A briquette according to claim 5 wherein the lignocellulosic biomass material includes wood saw dust.

8. A briquette according to claim 5 wherein the lignocellulosic biomass material includes dry tubular stalks of grasses and wood saw dust.

9. A briquette according to claim 2 wherein the briquette prior to reduction also contains non-volatile carbon material, said material not being lignocellulosic biomass material.

10. A briquette according to claim 2 wherein the briquette prior to reduction also contains no more than 5% non-volatile carbon material, said material not being lignocellulosic biomass material.

11. A briquette according to claim 9 wherein the amount of the non-volatile carbon material is selected so that the fixed carbon of the direct reduced iron briquette is at least 3% carbon by weight.

12. A briquette according to claim 9 wherein the amount of the non-volatile carbon material is selected so that the fixed carbon of the direct reduced iron briquette is at least 4% carbon by weight.

13. A briquette according to claim 9 wherein the non-volatile carbon material includes coal.

14. A briquette according to claim 9 wherein the non-volatile carbon material includes char, coke or carbon containing soot.

15. A briquette according to claim 1 in which a substantial amount of the iron ore fines is between 0.15 mm and 2.0 mm.

16. A briquette according to claim 2 including at least 1% by dry weight of a lime material for fluxing a slag from iron produced in downstream ironmaking/steelmaking processes.

17. A method of manufacturing the compacted ‘green’ briquette defined in claim 1 includes mixing together the lignocellulosic biomass material and the iron ore fines and compacting the mixture into the ‘green’ briquette.

18. A direct reduction process that includes reducing the ‘green’ briquette defined in claim 1 in a furnace and producing iron.

Description

BRIEF DESCRIPTION OF THE PHOTOGRAPH AND DRAWING

[0067] The present invention is described further by way of example with reference to the accompanying photograph and drawings, of which:

[0068] FIG. 1 is a photograph of one embodiment of a briquette for producing direct reduced iron (DRI) from iron ore and lignocellulosic biomass material in accordance with the invention; and

[0069] FIG. 2 is a flowsheet diagram illustrating an embodiment of a process and an apparatus for producing ‘green’ briquettes from iron ore and lignocellulosic biomass material in accordance with the invention for subsequent reduction to produce direct reduced iron (DRI).

DESCRIPTION OF EMBODIMENT OF BRIQUETTES ACCORDING TO THE INVENTION

[0070] FIG. 1 is a photograph of a section of one embodiment of a briquette in accordance with the invention.

[0071] The briquette shown in FIG. 1 consists of lignocellulosic biomass material and iron ore fines, with no binders.

[0072] The briquette was formed by mixing sized sugar cane bagasse and iron ore of the desired ratio in an Eirich horizontal intensive mixer, and then passing it through a Maschinenfabrik Köppern GmbH & Co. KG industrial-sized briquetting machine at the University of Freiberg in Germany.

[0073] It is noted that the invention is not confined to briquettes that only include lignocellulosic biomass material and iron ore fines. The invention extends to briquettes that include other materials, such as binders.

[0074] It is evident from FIG. 1 that the lignocellulosic biomass material (in this case bagasse of particle length 1 to 2 mm) has deformed in a plastic manner around the iron ore fines (<2 mm) to encase the ore fines intimately as well as form the majority of the surface area of the ‘green briquette’.

[0075] The inventor has found that the use of such lignocellulosic biomass material, such as tubular stalks of grasses, appears to trap the smaller fines (<1 mm) in the briquette ‘structure’ without leaving them exposed to the outer surface of the briquette, thus minimising dust make, while in a DRI reduction process allowing volatiles (generated during the heating phase between 100°−600° C. in producing a DRI briquette) a pathway to move through and escape the briquette, without undue breakdown of the briquette.

[0076] When ‘green’ briquettes according to the invention are reduced to DRI by way of example using the method described in the applicant's earlier International patent application PCT/AU2017/051163, they not only retain a good degree of compressive strength (particularly when cooled naturally) but have at least 85% iron and at least 1.0% fixed carbon by weight.

[0077] Having fixed carbon in reduced briquettes, as against having all the carbon consumed in the reduction process, can be desirable for downstream ironmaking or steelmaking process, where the briquette is required to be melted as part of the relevant process.

[0078] By way of example only, the Basic Oxygen Furnace (BOF) relies on carbon within molten iron to reconvert FeO formed by driving oxygen into the bath (effectively burning iron) to bring the temperature up to the melting point of steel, which can be above 1400° C. Having a DRI (in the form of HBI) with a fixed carbon above 2% potentially lowers the melting point of such feed material to around 1400° C., as against say pure iron with a melting point of 1538° C. Bringing the fixed carbon up to 4% lowers the melting point further to around 1200° C. While a BOF relies on its principal charge already being molten iron, it is supplemented (typically, up to 20% of the charge) by scrap steel, solid pig iron or DRI. Anything that reduces the energy needed to melt the supplemental material improves the efficiency of the process and effectively reduces the amount of FeO (arising from the fast combustion/melting process) that has to be reduced back to iron by reacting with dissolved carbon or that by default passes out of the process into the slag.

[0079] The production of HBI from hot DRI produced by a direct reduction processes is known within the iron industry and briquetting machines therefor are available throughout the world, such as from Maschinenfabrik Köppern GmbH & Co. KG in Germany.

Embodiment of Method of Manufacture of Embodiment Briqettes According to the Invention

[0080] As noted above, in broad terms, the present invention is based on forming a compacted ‘green’ briquette of between 5 cm.sup.3 and 20 cm.sup.3 (in matrix size) that has, prior to reduction in a direct reduction process, a composition of at least 30% lignocellulosic biomass material by dry weight and at least 55% iron ore fines by weight and a strength of at least 500 N.

[0081] FIG. 2 is a flowsheet diagram illustrating an embodiment of a process and an apparatus for producing ‘green’ briquettes from iron ore and lignocellulosic biomass material in accordance with the invention.

[0082] In FIG. 2, the apparatus includes a shredder/sizer 3 for reducing the size of a lignocellulosic biomass feed material 1, which may be any suitable lignocellulosic biomass, down to a preferred size below 6 mm.

[0083] The shredder/sizer 3 may take many forms, but for manufacturing the sample briquettes according to the invention for the Example, an industrial pin disk mill (exp. cap. 2 t/h) was used, with the material discharged through a perforated plate of either −4 mm or −1 mm and oversize material returned for further processing through the mill. All material processed through the mill was dry (as shipped).

[0084] While not shown in FIG. 2, the lignocellulosic biomass material may be pre-cut to a set size, such as 6 mm, for feeding into the shredder/sizer 3.

[0085] Once the lignocellulosic biomass material is sized, it is mixed in a mixer 5 thoroughly with iron ore fines 2 and other minor additives such as flux 20 and fixed carbon 30.

[0086] The mixer 5 may take many forms, but for the briquettes produced in test work of the inventor, an Eirich, 175 litre horizontal intensive mixer was used in batch mode with 90 seconds mixing time.

[0087] An important mixing requirement for the embodiment is that there be good mixing behaviour so that a homogenous mix is achieved with no segregation between ore and biomass. The mixing however is not for the purpose of agglomeration i.e. having the iron ore fines and lignocellulosic biomass form a dough that itself becomes a coherent mixture. The ratio of material fed to the mixer by weight is at least 55% iron ore fines and at least 30% lignocellulosic biomass material by weight (naturally dried). The balance of the mixture (other than those materials) in the case of the examples referenced in Table 1 in the Example is taken up by limestone or slaked lime (around 10 percent), which is a flux for the downstream reduction and/or smelting/melting processes i.e. to seek a basicity of about 1.2 (CaO/SiO.sub.2). Up to 5% primarily non-volatile carbon material (fixed carbon 30); like coke may also be added to the mix.

[0088] After appropriate mixing, the mixed material is fed into a screw feeder 7, which sits atop of a pair of counter-rotating briquetting rolls 9 which have suitable size and shape pockets machined/etched into the faces (not shown). In operation, the rolls are rotated in a synchronized manner such that the pockets align in a nip between the rolls. Typically, one roll may be fixed and the other roll floating and have a set force applied to it so that a relatively constant pressure is applied to the rolls and the material passing through the nip. The required pressure may be set as required, but generally the nip between the rolls should be minimised, while still allowing iron fine particles to pass between the rolls (in the non-pocketed spaces) without undue crushing/grinding occurring, i.e. the purpose of the rolls is not to crush or grind the iron ore particles, but to apply sufficient force so that the feed material will tend to flow into the pocket sections of the rolls.

[0089] Suitable suppliers of briquetting machines are available throughout the world, but for the briquettes produced for the test work in the Example, a machine with screw feeder from Maschinenfabrik Köppern GmbH & Co. KG in Germany was used.

[0090] After the mixture passed through the rolls, a fully form compacted ‘green’ briquette cake was observed. By this it is meant that briquettes of a size above the volume of the individual pockets (but no larger than twice the volume thereof) were observed.

[0091] Often the briquettes will be joined together by a relatively thin skirt of feed material between them. This arises because of the objectives of ensuring that there is always an excess of mixture to fill the pockets and that the briquettes have been properly compacted.

[0092] It is not unusual to observe some variation in density of individual briquettes across the rolls due to feeding variations between rolls during compression of the mixture passing between them, i.e. feed to the edges of the rolls can be lower in practice.

[0093] As the briquettes pass downwardly from the rolls, it is usual for the briquettes to break up and size towards their set matrix sizes, with the scraps from such breakup passing through a selected screen/sieve 13 and then fed back to the screw feeder. Alternatively, such scrapped material could be returned to the shredder/mixer 3. Simple dropping of the briquettes after compaction will usually achieve breakup with scrap material being produced.

[0094] It is noted that it is important that the compression strength of the briquettes be sufficient so as to able to bear the static weight load and drag effects that arise through downstream processing in a direct reduction plant, which typically will be of a fixed bed configuration, although the use of a rotary kiln is not precluded.

[0095] For the test sample results provided in Table 1 of the Example, 12 individual briquettes were tested and averaged after the maximum and minimum results were excluded.

[0096] It is also noted that it is important that the briquettes be capable of withstanding handling and transportation without undue shattering. To mimic this performance requirement, 2 kg of briquettes, of each test sample, were dropped four times from a height of 2 m, with the fines sieved therefrom after the 2.sup.nd and 4.sup.th drops.

Example—‘Green’ Briquettes in Accordance with an Embodiment of the Invention

[0097] The inventor directed extensive test work on: [0098] (a) forming ‘green’ briquettes of lignocellulosic biomass material and iron ore fines with different lignocellulosic biomass materials and different ratios of lignocellulosic biomass materials and iron ore fines; and [0099] (b) extensive test work on the ‘green’ briquettes.

[0100] The above description of FIG. 2 explains how the ‘green’ briquettes were formed and tested.

[0101] The photograph of FIG. 1 shows one such ‘green’ briquette.

[0102] Table 1 provides the compositions of a selection of the examples of compositions of ‘green’ briquettes of various lignocellulosic biomass material that were tested.

TABLE-US-00001 TABLE 1 T.01 T.02 T.04 Test Reference T.10 T.12 T.20 (2020) (2020) (2020) Biomass Wheat straw Sorghum Bagasse Spruce Spruce Spruce/coal Ore/Biomass (blend % by wt.) 65/35 65/35 60/40 60/40 60/40 60/30/10 Limestone % g wt. (with ref to ore) 9.0 9.0 9.0 12.5 12.5 12.5 Matrix size cm.sup.3 10 10 5 10 20 10 Actual volume cm.sup.3 17.97 20.00 9.85 17.4 28.3 18.6 Density g/cm.sup.3 1.48 1.43 1.43 1.64 1.5 1.80 Strength (N) 1814 1055 2084 877 657 1014 Integral briquette remaining after 85.68 83.21 83.38 84.3 67.5 79.0 shatter test wt. %. 20 mm

[0103] Table 1 also provides the properties (density and strength) and the performance (shatter test results) of the ‘green’ briquettes tested.

[0104] It is evident from Table 1 that suitable ‘green’ briquettes could be formed from a range of lignocellulosic biomass materials with different ratios of lignocellulosic biomass material and iron ore fines and, in the case of sample T.04, with coal as part of the mixture.

[0105] As noted above, the test work was conducted under the direction of the inventor. The experience of the inventor allows the inventor to extrapolate the results across the ranges of proportions of lignocellulosic and iron ore fines described in the specification.

[0106] Many modifications may be made to the embodiments described above without departing from the spirit and scope of the invention.