Description:TECHNICAL FIELD
The present disclosure relates to the field of metallurgy. Particularly, the disclosure relates to a method of preparing directly reduced iron briquette (DRI-B) from steel plant waste materials. The disclosure also relates to directly reduced iron briquettes (DRI-B) and a method of preparing briquette from steel plant waste materials.

BACKGROUND OF THE DISCLOSURE
In an integrated steel plant, variety of iron bearing solid wastes in the form of fines/sludge/dust/scales are being generated as a by-product and treated as a waste due to contamination with moisture, oil, grease, size fraction etc. Integrated steel plant data indicates that the generation of LD sludge is around 15 to 16 kg/ton whereas generation of mill scale represent about 2% of steel produced. The coke dry quenched (CDQ) fines/dust having size greater than 1mm are being generated during rapid quenching of coke and accounts to about 1.4 to 1.6% of total coal charged. It is noted that Mill scale is partially utilized in sinter making in an integrated steel plant, whereas LD sludge is being treated as waste. Consequently, it is either dumped or exported at lower price. However, major load of LD sludge remains unutilized in the plant heads.

Also, disposal of steel plant wastes such as mill scale, LD sludge, CDQ fines/dust etc possess environmental issues. Thus, there is a need to effectively utilize such steel plant waste materials so that there is no environmental hazard from the waste materials generated from steel industry.

Conventionally, the sponge iron, i.e., direct reduced iron is produced by employing binder materials to agglomerate the raw materials and involves curing or induration/pre-induration at a particular temperature for specific duration of time to increase the strength of the briquettes, which is known to increase process steps and overall production cost involved in the production of sponge iron. For instance, in the known processes, curing is carried for about 3 to 20days by exposing to an atmospheric air for about 10 to 14 hours for removal of moisture which is time consuming and increases the production cost. Further, curing/pre-induration of briquettes or pellets require additional supply of energy which again adds to the production cost.

It is reported that use of or mixing of binder with the raw materials to produce sponge iron increases the level of impurities in the produced sponge iron, as a result, increases the production cost associated with separating the impurities from the produced sponge iron. It is also reported that the produced sponge iron from the known or available process are prone to re-oxidation due to low metallization content.

Further, few of the processes available or known for producing sponge iron leads to sponge iron with high sulphur, phosphorous and gangue contents and low metallization.

Thus, there is a need for effective process for producing sponge iron which addresses the above-mentioned drawbacks.

In order to address the above noted drawbacks regarding the environmental issues caused by steel plant waste and the drawbacks in the production of direct reduced iron/sponge, the present disclosure describes an environmentally friendly and efficient process for using the steel plant waste material to produce improved direct reduced iron briquettes.

STATEMENT OF THE DISCLOSURE
Accordingly, the present disclosure describes an effective or efficient method for producing directly reduced iron briquettes from steel plant waste materials, such as LD sludge, BF sludge, mill scale, wherein the process is environmentally friendly, energy efficient and economical. The said method comprises- blending the steel plant waste and water and optimizing moisture content to obtain briquette, followed by drying; mixing the dried briquette with a mixture of reducing agent and desulphurizing agent, followed by heating; and cooling the heated briquette to obtain the DRI-B

The present disclosure further describes a directly reduced iron briquette having high metallization content and low sulphur content.

The present disclosure further describes an efficient method of producing briquettes from steel plant waste in absence of binder material. The said method comprises- blending the steel plant waste and water; and optimizing moisture content to the blend to obtain the briquette.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
In order that the present disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, where:

FIGURE 1: describes a flow chart capturing the steps in producing directly reduced briquettes from steel plant waste materials. The steps in the flow chart are for illustrative purpose only and they should not be construed to be limited. The detailed description provides the details of the steps involved in producing the directly reduced briquettes.

FIGURE 2 depicts Scanning electron microscopy with energy dispersive analysis of X-ray (SEM-EDAX) micrograph of reduced briquettes (DRI-B) containing about 80% LD sludge, about 10 % BF sludge and about 10% mill scale reduced with CDQ fines about 12500C for about 3 hours

DETAILED DESCRIPTION OF THE DISCLOSURE
With respect to the use of any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” or “containing” or “has” or “having” wherever used, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification may not necessarily all refer to the same embodiment. It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or in any suitable sub-combination.

The present disclosure describes a method for preparing directly reduced iron briquette (DRI-B) from steel plant waste. The said method is environmentally friendly, energy efficient and economical.

In an embodiment of the present disclosure, the method for preparing DRI-B from steel plant waste comprises- blending the steel plant waste and water and optimizing moisture content to obtain briquette followed by drying; mixing the dried briquette with a mixture of reducing agent and desulphurizing agent followed by heating; and cooling the heated briquette to obtain the DRI-B.

In an embodiment of the present disclosure, the blending of steel plant waste and water is carried out in absence of binder material.

In an embodiment of the present disclosure, the parameters during blending are optimized with respect to amount of steel plant waste including but not limited to LD sludge, BF sludge and mill scale. and moisture content to yield optimum green strength of the briquettes.

In an embodiment of the present disclosure, the LD sludge is in an amount ranging from about 60% to 100%.

In another embodiment of the present disclosure, the LD sludge is in an amount of about 60%, about 62%, about 64%, about 66%, about 68%, about 70%, about 72%, about 74%, about 76%, about 78%, about 80%, about 82%, about 84%, about 86%, about 88%, about 90%, about 92%, about 94%, about 96%, about 98% or about 100%.

In an embodiment of the present disclosure, the BF sludge is in an amount ranging from about 10% to 20%.

In another embodiment of the present disclosure, the BF sludge is in an amount of about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19% or about 20%.

In an embodiment of the present disclosure, the mill scale is in an amount ranging from about 0% to 20%.

In an embodiment of the present disclosure, the mill scale is in an amount of about 0%, about 1%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%,about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19% or about 20%.

In an embodiment of the present disclosure, moisture content of the blend of the steel plant waste and water is optimized to obtain briquettes having green strength ranging from about 18 N to 25 N per briquette. The moisture content of the briquette is optimized to a content ranging from about 2.5 % to 5.5 % depending upon the steel plant waste including but not limited to LD sludge, BF sludge and mill scale.

In another embodiment of the present disclosure, the blend of steel plant waste and water is optimized to obtain briquettes having green strength of about 18 N per briquette, about 19 N per briquette, about 20 N per briquette, about 21 N per briquette, about 22 N per briquette, about 23 N per briquette, about 24 N per briquette or about 25 N per briquette, wherein the moisture content of the blend is optimized to a content of about 2.5%, about 3.0%, about 3.5%, about 4.0%, about 5.0% or about 5.5%.

In an embodiment of the present disclosure, the briquettes obtained upon said blending and optimizing the moisture content has dimensions including but not limited to 51mm x 38mm x 18mm.

In an embodiment of the present disclosure, the briquettes obtained upon optimizing the moisture content is subjected to drying at a temperature ranging from about 20 ºC to 110 ºC for a duration ranging from about 2 hours to 48 hours.

In another embodiment of the present disclosure, the briquettes obtained upon optimizing the moisture content is subjected to drying at a temperature of about 20 ºC, about 30 ºC, about 40 ºC, about 50 ºC, about 60 ºC, about 70 ºC, about 80 ºC, about 90 ºC, about 100 ºC or about 110 ºC for a duration of about 2 hours, about 4 hours, about 6 hours, about 8hours, about 10 hours, about 12hours, about 14 hours, about 16 hours, about 18 hours, about 20 hours, about 22 hours, about 24 hours, about 26 hours, about 28 hours, about 30 hours, about 32 hours, about 34 hours, about 36 hours, about 38 hours, about 40 hours, about 42 hours, about 44 hours or about 48 hours.

In an embodiment of the present disclosure, the drying is carried out under normal atmosphere or by utilizing exhaust gases from tunnel kiln.

In an embodiment of the present disclosure, the dried briquette is mixed with the mixture of reducing agent and desulphurizing agent at a weight ratio ranging from about 1:0.4 to 1: 0.8.

In an embodiment of the present disclosure, the said weight ratio ranging from about 1:0.4 to 1:0.8 between dried briquettes and the mixture of reducing agent and desulphurizing agent is specifically optimized so that there is only required amount of coal for optimum reduction of briquettes during heating and that there is no impurities formed while obtaining DRI-B by the described process.

In an embodiment of the present disclosure, the reducing agent and the desulphurizing agent in the mixture is at a weight ratio ranging from about 1:0.05 to 1:0.15. The desulphurizing agent in the said mixture is ranging from about 5% to 15% of total weight of the reducing agent.

In another embodiment of the present disclosure, the desulphurizing agent in the said mixture is about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, or about 15% of total weight of the reducing agent.

In an embodiment of the present disclosure, the desulphurizing agent is employed in the said specific optimized range of about 5% to 15% of total weight of the reducing agent so that there is no sulphur pick in the produced DRI-B.

In an embodiment of the present disclosure, the desulphurizing agent has particle size ranging from about 70 mesh to 200 mesh.

In another embodiment of the present disclosure, the desulphurizing agent has particle size of about 70 mesh, about 75 mesh, about 80 mesh, about 85 mesh, about 90 mesh, about 95 mesh, about 100 mesh, about 105 mesh, about 110 mesh, about 115 mesh, about 120 mesh, about 125 mesh, about 130 mesh, about 135 mesh, about 140 mesh, about 145 mesh, about 150 mesh, about 155 mesh, about 160 mesh, about 165 mesh, about 170 mesh, about 175 mesh, about 180 mesh, about 185 mesh, about 190 mesh, about 195 mesh or about 200 mesh.

In an embodiment of the present disclosure, the heating is carried out under normal atmospheric pressure at a temperature ranging from 1000 ºC to 1350 ºC for a duration ranging from about 1 hour to 8 hours.

In another embodiment of the present disclosure, the heating is carried out under normal atmospheric pressure at a temperature of about 1000 ºC, about 1050 ºC, about 1100 ºC, about 1150 ºC, about 1200 ºC, about 1250 ºC, about 1300 ºC or about 1350 ºC for a duration of about 1 hour, about 2 hours, about 3 hours, about 4 hours, 5 hours, about 6 hours, about 7 about or about 8 hours.

In an embodiment of the present disclosure, the cooling is a multistep cooling comprising- cooing the heated briquette to a temperature ranging from about 500 ºC to 600 ºC, followed by cooling again to a temperature ranging from about 100 ºC to 150 ºC under atmospheric pressure.

In another embodiment of the present disclosure, the cooling is a multistep cooling comprising- cooling the heated briquette to a temperature of about 500 ºC, about 510 ºC , about 520 ºC, about 530 ºC , about 540 ºC, about 550 ºC, about 560 ºC, about 570 ºC, about 580 ºC, about 590 ºC or about 600 ºC, followed by cooling again to a temperature of about 100 ºC, about 110 ºC, about 120 ºC, about 130 ºC, about 140 ºC or about 150 ºC.

In an embodiment of the present disclosure, the said method additionally comprises separating the obtained DRI-B from the residues of mixture of reducing agent and desulphurizing agent.

In an embodiment of the present disclosure, the dried briquettes and the mixture of reducing agent and the desulphurizing agent are arranged alternatively, i.e., between two dried briquettes, mixture of reducing agent and desluphurizing agent is arranged for achieving effective reduction of the dried briquettes during heating.

In an embodiment of the present disclosure, the dried briquettes and the mixture of reducing agent and the desluphurizing agent are placed in the bed of CDQ fines during heating for effective reduction.

In an embodiment of the present disclosure, the steel plant waste is selected from a group comprising LD sludge, BF sludge, mill scale and a combination thereof.
In an embodiment of the present disclosure, the LD sludge comprises Fe2O3 ranging from about 26.7 % to 34.5 %, FeO ranging from about 61.4% to 68.6 %, FeT ranging from about 66.3 % to 71.1%, LOI ranging from about 0.01% to 0.05%, SiO2 ranging from about 2.0 to 6.0%, Al2O3 ranging from about 2.0 to 6.0%, P ranging from about 0.15 % to 2.0%, S ranging from about 0.08 to 0.1 %, C ranging from about 1.0 to 1.5%, CaO ranging from about 5.5% to 6.0%, MgO ranging from about 0.5 % to 0.9 % and moisture ranging from about 10% to 15%.

In another embodiment of the present disclosure, the LD sludge comprises Fe(T) of about 66.77%, Fe(MET) of about 0.5%, FeO of about 61.4%, Fe2O3 about 26.7%, CaO of about 5.79%, SiO2 about 1.49%, P2O5 of 0.35%, MgO of about 0.78 %, MnO of about 0.24%, Al2O3 of about 0.91%, C of about 1.23% and S of about 0.082%.

In another embodiment of the present disclosure, the LD sludge comprises Fe(T) of about 30.95%, FeO about 0.77%, Fe2O3 of about 43.39%, CaO of about 3.43%, SiO2 about 8.39%, P2O5 of 0.242%, MgO of about 1.77%, Al2O3 of about 3.87%, C of about 29.3% and S of about 0.355%.

In an embodiment of the present disclosure, the BF sludge comprises Fe2O3 ranging from about 40.1 % to 43.5 %, FeO ranging from about 0.5 % to 0.8 %, FeT ranging from about 30 % to 32.5%, LOI ranging from about 0.5% to 1%, SiO2 ranging from about 7.0 % to 8.5%, Al2O3 ranging from about 3 % to 3.9 %, P ranging from about 0.08 % to 0.12 % and S ranging from about 0.3 % to 0.4 %.

In an embodiment of the present disclosure, the mill scale comprises Fe2O3 ranging from about 62.5 % to 70 %, FeO ranging from about 25.0 % to 29 %, FeMet ranging from about 2.5 % to 3.8%, FeT ranging from about 66.2 % to 72.5%, LOI ranging from about 0.01% to 0.05%, SiO2 ranging from about 2.0 % to 0.5%, Al2O3 ranging from about 0.2 % to 0.06 %, P ranging from about 0.05 % to 0.08 % and S ranging from about 0.01 % to 0.06 %.

In an embodiment of the present disclosure, the reducing agent is selected from a group comprising coke dry quenched (CDQ), lean grade coking coal/fines, non-coking coal/fines, Jhama coal (partially oxidized coal) and a combination thereof.

In an embodiment of the present disclosure, the CDQ comprises fixed carbon ranging from about 80 % to 85%, ash ranging from about 13 % to 18 %, moisture ranging from about 0.5 % to 1.5% and volatile matter ranging from about 0.4 % to 0.6%.

In an embodiment of the present disclosure, the lead grade coking coal/fines, non-coking coal/fines, Jhama coal (partially oxidized coal) comprises filed carbon content ranging from about 28% to 45%, respectively.

In an embodiment of the present disclosure, the desulphurizing agent is selected from a group comprising dolomite, lime fines and a combination thereof.

In an embodiment of the present disclosure, the dolomite comprises MgO ranging from about 28 % to 40 %, CaO ranging from about 45 % to 55 %, Al2O3 ranging from about 2 % to 6 %, P ranging from about 0.5 % to 1.5 % and SiO2 ranging from about 1 % to 2 %.

In an exemplary embodiment of the present disclosure, the method of preparing directly reduced iron briquette (DRI-B) from steel plant waste comprises-
blending the steel plant steel plant waste with and water and optimizing the moisture content during briquetting to obtain briquettes having green strength of 18 N to 25 N per briquettes, wherein the blending is carried out in absence of binder material.
drying the briquettes at a temperature ranging from 20 ºC to 110 ºC for a duration ranging from about 2 hours to 48 hours.
mixing the dried briquettes with a mixture of reducing agent and desulphurizing agent in a weight ratio ranging from about 1:0.4 to 1:0.8.
heating the dried briquettes and the mixture of reducing agent and desluphurizing agent under normal atmospheric pressure at a temperature ranging from about 1000 ºC to 1350 ºC for a duration ranging from about 1 hour to 8 hours; and
cooling the briquettes in two steps- i. cooling the briquette to a temperature ranging from about 500 ºC to 600 ºC; and ii. cooling again to a temperature ranging from about 100 ºC to 150 ºC, under atmospheric pressure, to obtain directly reduced iron briquettes having high metallization content and low sulphur content.

In an embodiment of the present disclosure, the directly reduced iron briquette obtained by the method has high metallization content ranging from about 79% to 84%.

In another embodiment of the present disclosure, the directly reduced iron briquette obtained by the method has high metallization content of about 79%, about 80%, about 81%, about 82%, about 83% or about 84%.

In an embodiment of the present disclosure, the directly reduced iron briquette obtained by the method has low sulphur content ranging from about 0.009% to 0.018%.

In another embodiment of the present disclosure, the directly reduced iron briquette obtained by the method has low sulphur content of about 0.009%, about 0.01%, about 0.011%, about 0.012%, about 0.013%, about 0.014%, about 0.015, about 0.016%, about 0.017% or about 0.018%.

In an embodiment of the present disclosure, the directly reduced briquettes obtained by the method has cold crushing strength ranging from about 1800 N to 5500 N.

In another embodiment of the present disclosure, the directly reduced briquettes obtained by the method has cold crushing strength of about 1800 N, about 1900 N, about 2000 N, about 2100 N, about 2200 N, about 2300 N, about 2400 N, about 2500 N, about 2600 N, about 2700 N, about 2800 N, about 2900 N, 3000 N, about 3100 N, about 3200 N, about 3300 N, about 3400 N, about 3500 N, about 3600 N, about 3700 N, about 3800 N, about 3900 N, about 4000 N, about 4100 N, about 4200 N, about 4300 N, about 4400 N, about 4500 N, about 4600 N, about 4700 N, about 4800 N, about 4900 N, about 5000 N, about 5100 N, about 5200 N, about 5300 N, about 5400 N or about 5500 N.

In an embodiment of the present disclosure, the directly reduced briquettes obtained by the method has reduced melting time ranging from about 17% to 23%.

In another embodiment of the present disclosure, the directly reduced briquettes obtained by the method have reduced melting time, wherein the reduction observed is ranging from about 17% to23 %for the briquettes having metallization content ranging from about 79% to 84%.

The present disclosure further describes a directly reduced iron briquette (DRI-B).

In an embodiment of the present disclosure, the directly reduced iron briquette has high metallization content ranging from about 79% to 84%.

In another embodiment of the present disclosure, the directly reduced iron briquette has high metallization content of about 79%, about 80%, about 81%, about 82%, about 83% or about 84%.

In an embodiment of the present disclosure, the directly reduced iron briquette has low sulphur content ranging from about 0.009% to 0.018%.

In another embodiment of the present disclosure, the directly reduced iron briquette has low sulphur content of about 0.009%, about 0.01%, about 0.011%, about 0.012%, about 0.013%, about 0.014%, about 0.015, about 0.016%, about 0.017% or about 0.018%.

In an embodiment of the present disclosure, the directly reduced iron briquette has cold crushing strength ranging from about 1800 N to 5500 N.

In another embodiment of the present disclosure, the directly reduced iron briquette has cold crushing strength of about 1800 N, about 1900 N, about 2000 N, about 2100 N, about 2200 N, about 2300 N, about 2400 N, about 2500 N, about 2600 N, about 2700 N, about 2800 N, about 2900 N, 3000 N, about 3100 N, about 3200 N, about 3300 N, about 3400 N, about 3500 N, about 3600 N, about 3700 N, about 3800 N, about 3900 N, about 4000 N, about 4100 N, about 4200 N, about 4300 N, about 4400 N, about 4500 N, about 4600 N, about 4700 N, about 4800 N, about 4900 N, about 5000 N, about 5100 N, about 5200 N, about 5300 N, about 5400 N or about 5500 N.

In an embodiment of the present disclosure, the directly reduced briquettes has reduced melting time ranging from about 17% to 23%.

In another embodiment of the present disclosure, the directly reduced briquettes has reduced melting time of about 17%, about 18%, about 19%, about 20% about 21%, about 22% or about 23%.

The present disclosure further describes a method of preparing briquettes from steel plant waste.

In an embodiment of the present disclosure, the method of preparing briquettes is carried out in absence of binder material.

In an embodiment of the present disclosure, the method of preparing briquettes from steel plant waste comprises- blending the steel plant waste with water; and optimizing moisture content of the blend to obtain the briquette.

In an embodiment of the present disclosure, the method of preparing briquettes from steel plant waste optionally comprises the step of drying the briquette, wherein the drying is carried out at temperature ranging from about 20 ºC to 110 ºC for a duration ranging from about 2 hours to 48 hours.

In another embodiment of the present disclosure, drying of the briquette is carried out at a temperature of about 20 ºC, about 30 ºC, about 40 ºC, about 50 ºC, about 60 ºC, about 70 ºC, about 80 ºC, about 90 ºC, about 100 ºC or about 110 ºC for a duration of about 2 hours, about 4 hours, about 6 hours, about 8hours, about 10 hours, about 12hours, about 14 hours, about 16 hours, about 18 hours, about 20 hours, about 22 hours, about 24 hours, about 26 hours, about 28 hours, about 30 hours, about 32 hours, about 34 hours, about 36 hours, about 38 hours, about 40 hours, about 42 hours, about 44 hours or about 48 hours.

In an embodiment of the present disclosure, the moisture content is optimized to a content ranging from about 2.5% to 5.5% during the preparation of the briquettes.

In another embodiment of the present disclosure, the moisture content is optimized to a content of about 2.5%, about 3.0%, about 3.5%, about 4.0%, about 5.0% or about 5.5% during the preparation of the briquettes.

In an embodiment of the present disclosure, the briquette obtained by the method has green strength ranging from about 18 N to 25 N per briquette.

In another embodiment of the present disclosure, the briquette obtained by the method has green strength of about 18 N per briquette, about 19 N per briquette, about 20 N per briquette, about 21 N per briquette, about 22 N per briquette, about 23 N per briquette, about 24 N per briquette or about 25 N per briquette.

The advantages achieved by the method of preparing directly reduced iron briquettes of the present disclosure is highlighted below-
• the method employs the waste generated from the steel plant or beneficiation plant in as-received condition without any processing or beneficiation and converted into value added products, i.e., directly reduced iron briquettes.
• briquettes are obtained from the steel plant waste materials without application of binder material.
• the method requires very less green strength ranging from about 20N to 25 N and dry strength ranging from about 50N to 80N) compared to the conventional/available methods for making briquettes which require green strength ranging from about 40 N to 60 N and dry strength ranging from about 1000 N to 1500 N.
• the method does not subject the briquettes to curing or pre-induration prior to reduction. This significantly reduces energy and time consumed, as a result significantly reduces the production cost.
• the method does not cause re-oxidation of the obtained DRI-B. This is achieved by employing multi step cooling and also due to high metallization content in the DRI-B.
• The method provides an opportunity to partially recycle the char/residues of reducing agent and/or desulphurizing agent obtained during the method for next set of reduction.
• The directly reduced iron briquettes obtained by the method have high metallization content which makes it suitable as a feed for production of all grades of steel in Electric arc furnace (EAF), induction furnace (IF) and Basic oxygen steelmaking (BOF).
• Melting behaviour of the DRI-Bin an induction furnace is much superior than the conventionally known directly reduced iron pellets/lumps. Slag formed during melting is highly viscous and easily separable. Rate of dissolution of DRI briquettes of the present invention during melting was quite good leading to decrease in melting time.
• The overall power consumption for melting of the DRI-B is much lower than the conventional directly reduced iron pellets/lumps in an induction furnace.
• The obtained DRI-B has very low sulphur content which is achieved by employing specific optimized content of desulphurizing agent in the method.
• The method requires only little excess amount of carbon than the stoichiometric carbon required for reduction compared to the existing conventional process which requires 1: 0.9 to 1: 1.1 ore to coal ratio. In the present method, gasification of carbon during reduction is minimum, as a result of which less carbon content is utilized.

In the present disclosure, the steel plant waste including but not limited to LD sludge, BF sludge and mill scale would contain water content, i.e., by way of moisture absorption by the steel plant waste during storage. In the step of blending, the steel plant waste and water in the described method of producing directly reduced iron briquette, the water content is part of the steel plant waste, i.e., absorbed by the steel plant waste during storage or water is added tothe steel plant waste.

In the present disclosure, the term ‘reduced briquettes’ or ‘briquettes reduced’ described herein means directly reduced briquettes obtained by the method described herein.

In the present disclosure, the term ‘pellet/pellets’ means the pellet prepared from the directly reduced briquettes which are produced according to the method described herein.

The term “about” as used in the specification encompasses variations of +/-10% and preferably +/-5%. Such variation of+/-10%, preferably variation of +/-5% is appropriate for practicing the present invention and the same does not deviate from the scope intended and the results achieved.

It is to be understood that the foregoing descriptive matter is illustrative of the disclosure and not a limitation. While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.

Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above described embodiments, and in order to illustrate the embodiments of the present disclosure certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.

EXAMPLES

Example 1: Method of preparing briquettes
About 9.0 kg of LD sludge of composition: FeT: 71.55 %, SiO2: 0.38%, Al2O3: 0.3 and S: 0.033 were mixed homogeneously with about 1.0 kg (10 %) of mill scale of composition: FeT: 71.55 %, SiO2: 0.38%, Al2O3: 0.3 and S: 0.033. The homogeneous mixture was used to prepare green briquettes. About 2.0 kg of the said mixture was mixed with about 2% of water to get moisture contents sufficient to make the briquettes. This wet mixture was then fed to briquetting machine to get pillow shaped briquette having dimensions 51mm x 38mm x 18mm and stored with their identity number. The green briquettes were tested for their crushing strength within few minutes of their preparation to avoid moisture evaporation. The briquettes were tested with increasing moisture contents by about 2 wt. % till the briquetting was smooth and feasible without sticking due to excess moisture. The green strength of the LD sludge briquettes with different percentage of added water is described in Table1. It can be noted that the green compressive strength (Newton) of the briquettes first increases with moisture addition and then decreases. The optimum moisture for briquetting is considered where the maximum compressive strength starts falling.

Optimization of moisture for briquetting of LD sludge with 10% mill scale
Moisture (%) 0 2 4 6 8 10
Green Strength (N) 8 12 26 22 16 8
Table 1: Optimization of moisture for briquetting of LD sludge with 10% mill scale

Example 2: Method of Preparing Directly reduced iron briquettes
Sixty four sets of LD sludge of composition: FeT: 71.55 %, SiO2: 0.38%, Al2O3: 0.3 and S: 0.033 were mixed homogeneously with 10% mill scale of composition: FeT: 71.55 %, SiO2: 0.38%, Al2O3: 0.3 and S: 0.033. Pillow shaped briquettes were made with the homogeneous mixture of LD sludge and mill scale in presence of optimized amount of moisture in a briquetting machine as described in Example 1. Briquettes were air dried and mixed with the desulphurising agent and the CDQ, followed by placing the contents (dried briquettes, mixture of desulphurizing agent and CDQ) in the bed of CDQ fines in a sagger. Each sagger containing about 5.0 kg of briquettes were kept in the muffle furnace simulating tunnel kiln condition and reduced at a temperature of about 10000C, about 10500C, about 11000C, about 11500C, about 12000C, about 12500C, about 13000C and 13500C, respectively for varying reduction time of about 1 hour to 8 hours at an interval of one hour. After reduction of briquettes at different reduction temperature and time, saggers were removed from the furnace and allowed to cool from reduction temperature to room temperature in normal atmosphere. After cooling of saggers, reduced briquettes were separated from the residue of CDQ char by screening. The samples collected from different reduction temperature and time was characterized for their chemical composition, Optical, SEM-EDAX and XRD analysis. It was observed that more than 77% reduction was be achieved at 10500C in about 2 hours of reduction time whereas more than 90% of reduction was achieved in about 4 hours of reduction time at about 11000C. The percentage reduction and chemical composition of the reduced briquettes (DRI-B) is given Table 2 and Table 3, respectively. Table 3 describes that more than 77% of metallization can be achieved in about 3.0 hours of reduction time at about 11000C. However, the further enhancement of reduction time reveals decrease in percent metallization due to re-oxidation of reduced pellets.
Reduction time (hrs) 1 2 3 4 5 6 7 8
% Reduction 67 77.7 89.8 93.2 93.3 91.8 91.8 91.1
Table 2: Percentage reduction of briquettes of LD sludge containing 10% mill scale at 1100 0C

Reduction time FeM FeT FeO % Metallization (MZ)
1hour 51 79 33.3 64.5
3 hours 72.32 83 11.3 87.13
5 hours 78.7 89 6.2 88.4
Table 3: Chemical analysis of DRI-B obtained from LD sludge with 10% mill scale reduced at 1100 0C.

Example 3: Method of Preparing Directly reduced iron briquettes
Sixty four sets of LD sludge of composition: FeT: 71.55 %, SiO2: 0.38%, Al2O3: 0.3 and S: 0.033 was homogeneously mixed with 10% mill scale of composition: FeT: 71.55 %, SiO2: 0.38%, Al2O3: 0.3 and S: 0.033 and pillow shaped briquettes were made in presence of moisture in a briquetting machineas described in Example 1. Briquettes were air dried and mixed with the desulphurising agent and the CDQ, followed by placing the contents (dried briquettes, mixture of desulphurizing agent and CDQ) in the bed of CDQ fines in a sagger. Reduction experiments were carried out at different temperature and time as mentioned in Example 2. The samples (reduced briquettes) collected from different reduction temperature and time was characterized for their chemical composition, Optical, SEM-EDAX and XRD analysis. It is observed that at about 1200ºC, percent reduction of LD sludge briquettes is more than 93 % at all the reduction time starting from about 1.0 hour to 5.0 hours. Similar trends have been observed in the chemical analysis of the briquettes reduced at about 1200ºC as shown in Table 5.However, enhancement of reduction time more than 5.0 hours shows decrease in percent reduction as well as metallization due to re-oxidation of reduced briquettes as shown in Table 4. The re-oxidation of the pellets is due to holding at higher temperature after completion of reduction and or deficiency of carbon.

Reduction time (hrs) 1 2 3 4 5 6 7 8
% Reduction 94.6 96.1 96.2 93.2 93 91.4 91 91.1
Table 4: Percentage reduction of briquettes of LD sludge containing 10% mill scale at 1200 ºC

Reduction time FeM FeT FeO % Metallization (MZ)
1hour 73 86 12 84.9
3 hours 76 85 11 85
5 hours 78 88 7 88
Table 5: Chemical analysis of DRI-B obtained from LD sludge with 10% mill scale reduced at 1200 0C.

Example 4: Method of Preparing Directly reduced iron briquettes
About 80% LD sludge, about 10% BF sludge and about 10% mill scale were mixed homogenously to obtain a mixture. Pillow shaped briquettes were made with the said mixture in presence of optimized moisture content in briquetting machine as described in Example 1. The briquettes were air dried and mixed with the desulphurising agent and the CDQ, followed by placing the contents (dried briquettes, mixture of desulphurizing agent and CDQ) in the bed of CDQ fines in a sagger and subjected to reduction at a temperature of about 1250 ºC for about 3 hours. Figure 2 depicts the SEM-EDAX micrograph of the reduced briquette (DRI-B). From the said SEMEDAX micrograph, it can be observed that iron wiskers fuses at the said reduction temperature and forms a strong metallic bond. Due to optimum reduction and formation of metallic bond, ejection of gangue/slag phase can be observed (point 6 in the image). The formation of metallic bond in the reduced briquettes (DRI-B) leads to increased cold crushing strength of the pellets of the said DRI-B.

Example 5: Assessing cold crushing strength of the obtained DRI-B
Cold crushing strength (CCS) of briquettes reduced (DRI-B) at different reduction temperature and time as mentioned in Example 2, is described in Table 6. It is observed that cold crushing strength of the briquettes (DRI-B) is more than 300 kg above at about 1100°C above 3.0 hours of reduction time. The pellets reduced at about 1150°C having more than 400 kg strength. The enhancement in cold crushing strength of the pellets is due to high metallization leading to formation of metallic bond. The strength of reduced briquettes is ample to feed it in electric arc furnace as well as in BOF for steel making. Similar trend has been observed in 100% LD sludge briquette as shown in Table 7.

Reduction time (hrs) 1 2 3 4 5 6 7 8
% Reduction 4489 4728 4907 5717 6715 6710 6750 6690
Table 6: Cold crushing strength of DRI-B obtained from LD sludge with 10% mill scale, reduced at 1150 0C.

Reduction time (hrs) 1 2 3 4 5 6 7 8
% Reduction 4450 6674 8280 9238 9763 9710 9730 9720
Table 7: Cold crushing strength of DRI-B obtained from LD sludge, reduced at 1200 0C.

Claims:
WE CLAIM:
1. A method for preparing directly reduced iron briquette (DRI-B) from steel plant waste, comprising:
blending the steel plant waste and water and optimizing moisture content to obtain briquette, followed by drying;
mixing the dried briquette with a mixture of reducing agent and desulphurizing agent, followed by heating; and
cooling the heated briquette to obtain the directly reduced iron briquette,
wherein the directly reduced iron briquette has high metallization, and
wherein the steel plant waste is selected from a group comprising LD sludge, BF sludge, mill scale and combination thereof.

2. The method as claimed in claim 1, wherein the blend of the steel plant waste and water is optimized to have moisture content ranging from about 2.5% to 5.5%.

3. The method as claimed in claim 1, wherein the briquette obtained after optimizing the moisture content has green strength ranging from 18 N to 25 N per briquette.

4. The method as claimed in claim 1, wherein the drying is carried out at a temperature ranging from about 20 ºC to 1100C for a duration ranging from about 2hours to 48 hours under atmospheric pressure.

5. The method as claimed in claim 1, wherein the dried briquette is mixed with the mixture of reducing agent and desulphurizing agent at a weight ratio ranging from about 1:0.4 to 1:0.8.

6. The method as claimed in claim 5, wherein the reducing agent and the desulphurizing agent in the mixture is at a weight ratio ranging from about 1:0.05 to 1:0.15 and wherein the desulphurizing agent in the mixture is ranging from about 5% to 15 % of total weight of the reducing agent.

7. The method as claimed in claim 1, wherein the heating is carried out under normal atmosphere at a temperature ranging from about 1000 ºC to 1350 ºC for a duration ranging from about 1 hour to 8 hours.

8. The method as claimed in claim 1, wherein the cooling is a multistep cooling comprising cooling the heated briquette to a temperature ranging from about 500 ºC to 600 ºC, followed by cooling to a temperature ranging from about 100 ºC to 150 ºC under atmospheric pressure.

9. The method as claimed in claim 1, wherein the directly reduced iron briquette obtained by the method are separated from residues of the mixture of reducing agent and desulphurizing agent.

10. The method as claimed in claim 1, wherein the LD sludge comprises Fe2O3 ranging from about 26.7 % to 34.5 %, FeO ranging from about 61.4% to 68.6 %, FeT ranging from about 66.3 % to 71.1%, LOI ranging from about 0.01% to 0.05%, SiO2 ranging from about 2.0 to 6.0%, Al2O3 ranging from about 2.0 to 6.0%, P ranging from about 0.15 % to 2.0%, S ranging from about 0.08 to 0.1 %, C ranging from about 1.0 to 1.5%, CaO ranging from about 5.5% to 6.0%, MgO ranging from about 0.5 % to 0.9 % and moisture ranging from about 10% to 15%; and the BF sludge comprises Fe2O3 ranging from about 40.1 % to 43.5 %, FeO ranging from about 0.5 % to 0.8 %, FeT ranging from about 30 % to 32.5%, LOI ranging from about 0.5% to 1%, SiO2 ranging from about 7.0 % to 8.5%, Al2O3 ranging from about 3 % to 3.9 %, P ranging from about 0.08 % to 0.12 % and S ranging from about 0.3 % to 0.4 %..

11. The method as claimed in claim 1, wherein the mill scale comprises Fe2O3 ranging from about 62.5 % to 70 %, FeO ranging from about 25.0 % to 29 %, FeMet ranging from about 2.5 % to 3.8%, FeT ranging from about 66.2 % to 72.5%, LOI ranging from about 0.01% to 0.05%, SiO2 ranging from about 2.0 % to 0.5%, Al2O3 ranging from about 0.2 % to 0.06 %, P ranging from about 0.05 % to 0.08 % and S ranging from about 0.01 % to 0.06 %.

12. The method as claimed in claim 1, wherein the reducing agent is selected from a group comprising coke dry quenched (CDQ), Lean grade coking coal/fines, non-coking coal/ fines, Jhama coal ( partially oxidized coal) and a combination thereof.

13. The method as claimed in claim 12, wherein the CDQ comprises fixed carbon ranging from about 80 % to 85%, ash ranging from about 13 % to 18 %, moisture ranging from about 0.5 % to 1.5% and volatile matter ranging from about 0.4 % to 0.6%.

14. The method as claimed in claim 1, wherein the desulphurzing agent is selected from a group comprising dolomite, lime fines and a combination thereof.

15. The method as claimed in claim 14, wherein the dolomite comprises MgO ranging from about 28 % to 40 %, CaO ranging from about 45 % to 55 %, Al2O3 ranging from about 2 % to 6 %, P ranging from about 0.5 % to 1.5 % and SiO2 ranging from about 1 % to 2 %.
16. The method as claimed in claim 1, wherein the blending is carried out in absence of binding material.

17. The method as claimed in claim 1, wherein the directly reduced iron briquette has high metallization ranging from about 79%to 84%; and has low sulphur content ranging from about 0.009% to 0.018%.

18. The method as claimed in claim 1, wherein the directly reduced iron briquette has cold crushing strength ranging from about 1800 N to 5500 N.

19. A directly reduced iron briquette obtained according to the method as claimed in claim 1, wherein the directly reduced iron briquette has high metallization ranging from about 79%and 84%; and low Sulphur content ranging from about 0.009% to 0.018%.

20. The directly reduced iron briquette as claimed in claim 19, wherein the directly reduced iron briquette has cold crushing strength ranging from about 1800 N to 5500N.

21. The directly reduced iron briquette as claimed in claim 19, wherein the directly reduced iron briquette has reduced melting time ranging from about 17% to 23%.

22. A method for preparing briquette from steel plant waste, comprising:
blending the steel plant waste and water; and
optimizing moisture content of the blend to obtain the briquette;
wherein the blending is carried out in absence of binding material, and
wherein the steel plant waste is selected from a group comprising LD sludge, BF sludge, mill scale and a combination thereof.

23. The method as claimed in claim 22, wherein the blending of the steel plant waste were optimized to have moisture content ranging from about 2.5% to 5.5.

24. The method as claimed in claim 22, wherein the briquette has green strength ranging from about 18 N to 25 N per briquette.

25. The method as claimed in claim 22, wherein the LD sludge comprises Fe2O3 ranging from about 26.7 % to 34.5 %, FeO ranging from about 61.4% to 68.6 %, FeT ranging from about 66.3 % to 71.1%, LOI ranging from about 0.01% to 0.05%, SiO2 ranging from about 2.0 to 6.0%, Al2O3 ranging from about 2.0 to 6.0%, P ranging from about 0.15 % to 2.0%, S ranging from about 0.08 to 0.1 %, C ranging from about 1.0 to 1.5%, CaO ranging from about 5.5% to 6.0%; MgO ranging from about 0.5 % to 0.9 % and moisture ranging from about 10% to 15%; the mill scale comprises Fe2O3 ranging from about 62.5 % to 70 %, FeO ranging from about 25.0 % to 29 %, FeMet ranging from about 2.5 % to 3.8%, FeT ranging from about 66.2 % to 72.5%, LOI ranging from about 0.01% to 0.05%, SiO2 ranging from about 2.0 % to 0.5%, Al2O3 ranging from about 0.2 % to 0.06 %, P ranging from about 0.05 % to 0.08 % and S ranging from about 0.01 % to 0.06 %; and the BF sludge comprises Fe2O3 ranging from about 40.1 % to 43.5 %, FeO ranging from about 0.5 % to 0.8 %, FeT ranging from about 30 % to 32.5%, LOI ranging from about 0.5% to 1%, SiO2 ranging from about 7.0 % to 8.5%, Al2O3 ranging from about 3 % to 3.9 %, P ranging from about 0.08 % to 0.12 % and S ranging from about 0.3 % to 0.4 %..