SOLID AGGLOMERATED PRODUCT BASED ON IRON OXIDES AND CORRESPONDING PRODUCTION METHOD

Abstract

Solid agglomerated product, such as a briquette (B), which can be used as charge material for an electric arc furnace, comprising at least one by-product fraction (M; M1, M2, M3) deriving from a steel plant and comprising a first part containing ferrous oxide FeO and a second part containing ferric oxide Fe.sub.2O.sub.3, a solid fuel fraction (CR) containing a quantity of carbon (C_fix) and at least one inorganic binder to agglomerate a by-product fraction (M; M1, M2, M3) and the solid fuel fraction (CR) together and give the required mechanical properties to the agglomerate.

Claims

1. Solid agglomerated product, such as a briquette, usable as charge material for an electric arc furnace, said solid agglomerated product comprising: at least one by-product fraction deriving from a steel plant and comprising a first part containing ferrous oxide FeO and a second part containing ferric oxide Fe.sub.2O.sub.3; a solid fuel fraction containing a quantity of carbon; at least one inorganic binder to agglomerate said at least one by-product fraction and said solid fuel fraction together; at least one organic binder to agglomerate said at least one by-product fraction and said solid fuel fraction together; wherein said solid fuel fraction is present in a quantity by weight determined by the relation CR=K*CS/C_fix, wherein: K: is a constant comprised between 1.0 and 2.5; CS: is a quantity by weight of stoichiometric carbon defined by the relation CS=0.11*(Fe.sup.2+_tot)+0.16*(Fe.sup.3+_tot), where Fe.sup.2+_tot is a quantity by weight of iron contained in said first part, and Fe.sup.3+_tot is a quantity by weight of iron contained in said second part.

2. Product as in claim 1, wherein the at least one inorganic binder is selected from a group consisting of cement, white slag, or a combination thereof.

3. Product as in claim 2, wherein the at least one inorganic binder is present in a percentage by weight comprised between 4% and 10%, with respect to said at least one by-product fraction.

4. Product as in claim 2, wherein the at least one inorganic binder comprises cement.

5. Product as in claim 1, wherein the at least one organic binder is selected from among polysaccharides, carboxymethylcellulose, lignin or a combination of two or more of these.

6. Product as in claim 5, wherein said organic binder is present in a percentage by weight comprised between 2% and 5%, with respect to said at least one by-product fraction.

7. Product as in claim 5, wherein the at least one organic binder comprises starch.

8. Product as in claim 2, wherein the at least one inorganic binder comprises white slag and is present in a percentage by weight comprised between 2% and 10%, preferably between 5% and 9%, with respect to said at least one by-product fraction.

9. Product as in claim 1, wherein it is in the form of a briquette.

10. Method for making a solid agglomerated product comprising: making available at least one by-product fraction comprising a first part containing ferrous oxide FeO and a second part containing ferric oxide Fe.sub.2O.sub.3; making available a solid fuel fraction containing a quantity of carbon; mixing at least said by-product fraction with said solid fuel fraction and with at least one inorganic binder and with at least one organic binder, wherein, before said mixing, it comprises determining a quantity by weight of said solid fuel fraction by means of the relation CR=K*CS/C_fix, wherein: K: is a constant comprised between 1.0 and 2.5; CS: is a quantity by weight of stoichiometric carbon defined by the relation CS=0.11*(Fe.sup.2+_tot)+0.16*(Fe.sup.3+_tot), where Fe.sup.2+_tot is a quantity by weight of iron contained in said first part, and Fe.sup.3+_tot is a quantity by weight of iron contained in said second part.

11. Method as in claim 10, wherein the at least one inorganic binder is selected from a group consisting of cement, white slag, or a combination thereof.

12. Method as in claim 10, wherein the at least one organic binder is selected from among polysaccharides, carboxymethylcellulose, lignin or a combination of two or more of these.

13. Method as in claim 10, wherein during the mixing step the reactants are added in sequence according to an order based on their granulometry and/or their hygroscopicity.

14. Method as in claim 13, wherein first the solid reactants are made available, and then the reactants that react in contact with water.

15. Method as in claim 14, wherein, among the solid reactants, the by-product fractions are added first and the solid fuel and the organic binder are added subsequently.

16. Product as in claim 3, wherein the at least one inorganic binder is present in a percentage by weight comprised between 5% and 7% with respect to said at least one by-product fraction.

17. Product as in claim 5, wherein the at least one organic binder is selected from a group consisting of starch, carboxymethylcellulose, lignin or a combination of two or more of these.

18. Product as in claim 6, wherein said organic binder is present in a percentage by weight comprised between 2.5% and 4% with respect to said at least one by-product fraction.

19. Product as in claim 8, wherein the at least one inorganic binder comprises white slag and is present in a percentage by weight comprised between 5% and 9% with respect to said at least one by-product fraction.

20. Method as in claim 12, wherein the at least one organic binder is selected from a group consisting of starch, carboxymethylcellulose, lignin or a combination of two or more of these.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

[0057] FIG. 1 is a schematic representation of a method for making a solid agglomerated product based on iron oxides in accordance with the present invention;

[0058] FIG. 2 is a schematic representation of a variant of the method for making the solid agglomerated product based on iron oxides in accordance with the present invention; and

[0059] FIG. 3 is a schematic representation of a step of the method of FIG. 2.

[0060] To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can be conveniently combined or incorporated into other embodiments without further clarifications.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

[0061] We will now refer in detail to the possible embodiments of the invention, of which one or more examples are shown in the attached drawings, by way of a non-limiting illustration. The phraseology and terminology used here is also for the purposes of providing non-limiting examples.

[0062] In accordance with some embodiments of the present invention, the solid agglomerated product, in accordance with the present invention, comprises: [0063] at least one by-product fraction, which will be indicated below with the following references: M, M1, M2, M3; and which comprises a first part containing ferrous oxide FeO and a second part containing ferric oxide Fe.sub.2O.sub.3; [0064] a solid fuel fraction CR containing a quantity of carbon C_fix; [0065] at least one inorganic binder to agglomerate the at least one by-product fraction M; M1, M2, M3 and the solid fuel fraction CR together, and give the agglomerate the necessary mechanical properties; [0066] at least one organic binder to agglomerate the at least one by-product fraction M; M1, M2, M3 and the solid fuel fraction CR together, and give the agglomerate the necessary plasticity.

[0067] The at least one by-product fraction M; M1, M2, M3 can also comprise a third part containing metallic iron Fe. The by-product fraction M; M1, M2, M3 is suitably mixed and combined with the solid fuel fraction CR, in order to obtain the agglomerated product which can be used as material to feed an electric arc furnace, or possibly for other types of steel plants.

[0068] According to one possible embodiment, the solid fuel fraction can be selected from a group comprising anthracite, coke, breeze, pet coke or other fuels deriving from industrial processes, or suchlike, preferably with a suitable fineness.

[0069] In accordance with one aspect of the present invention, the quantity of carbon C_fix is the percentage of non-volatile, that is, fixed carbon present in the solid fuel fraction. This quantity of carbon C_fix can be determined as the ratio between the weight of non-volatile carbon and the total weight of the fuel which contains this quantity of carbon.

[0070] According to possible embodiments of the invention, the quantity of carbon C_fix can be measured by means of experimentation and/or known detection methods.

[0071] The quantity of carbon C_fix contained in the solid fuel fraction CR acts as a reducing agent by subtracting oxygen from the first part containing ferrous oxide FeO and from the second part containing ferric oxide Fe.sub.2O.sub.3.

[0072] In particular, the reduction reactions of the ferrous oxide FeO and ferric oxide Fe.sub.2O.sub.3 are described by the following relations:

2Fe.sub.2O.sub.3+3C=4Fe+3CO.sub.2(g)

2FeO+C=2Fe+CO.sub.2(g)

Fe.sub.2O.sub.3+3C=2Fe+3CO(g)

FeO+C=Fe+CO(g)

[0073] The products of the reduction reactions are metallic iron Fe and carbon oxides in gaseous form.

[0074] From these relations it is possible to determine the quantity by weight of stoichiometric carbon CS necessary for a correct and balanced reduction reaction:

CS=(Fe.sup.2+_tot)**(PM_C/PM_Fe)+(Fe.sup.3+_tot)**(PM_C/PM_Fe)

[0075] wherein: [0076] Fe.sup.2+_tot: is a quantity by weight of iron contained in the first part containing ferrous oxide FeO; [0077] Fe.sup.3+_tot: is a quantity by weight of iron contained in the second part containing ferric oxide Fe.sub.2O.sub.3; [0078] PM_C: is the atomic weight of carbon C, equal to 12; [0079] PM_Fe: is the atomic weight of iron Fe equal to 55.8.

[0080] Consequently, the stoichiometric reduction reaction as above can be simplified and approximated as follows:

CS=0.11*(Fe.sup.2+_tot)+0.16*(Fe.sup.3+_tot)

[0081] In accordance with one aspect of the present invention, it is provided that the solid fuel fraction CR which is provided in the agglomerated product is present in a quantity by weight determined by the relation CR=K*CS/C_fix, wherein: [0082] K: is a constant comprised between 1.0 and 2.5, preferably between 1.2 and 2.5, more preferably between 1.3 and 1.6; [0083] CS: is a quantity by weight of stoichiometric carbon CS as defined above.

[0084] The constant K represents an addition of carbon in the solid fuel fraction, to compensate for the thermal extraction corresponding to the reduction of the iron oxide. This reaction is endothermic, and therefore requires heat to occur. To prevent the heat from being absorbed in its entirety by the bath in which the reaction occurs, which would significantly increase the melting time and the corresponding absorbed electrical power, the Applicant has chosen to supply a portion of the heat useful for the reaction chemically, that is, by oxidation of the carbon. One advantage related to this choice is that the energy is released locally, that is, inside the agglomerate itself and is therefore immediately available for the reduction reaction.

[0085] The quantity of carbon to be added represented by the constant K, with respect to the stoichiometric quantity, is determined on the basis of enthalpy calculations which allow to calculate the heat absorbed by the reaction, which allows to determine an optimal quantity of carbon to be added.

[0086] It has been observed that with a K greater than 2.5, the added carbon is in excess, and this increases the costs of the process as well as the emissions, without achieving a corresponding advantage. If, on the other hand, the constant K is less than 1, there is a lack of quantity of carbon and therefore a heat deficit.

[0087] This correlation on the quantity of the solid fuel fraction CR present in each agglomerated product allows the appropriate balance between the quantity of solid fuel and the quantity of iron oxides, whether these are FeO or Fe.sub.2O.sub.3.

[0088] Furthermore, the correlation as above allows to determine the quantity of solid fuel fraction that has to be present inside the agglomerated product, necessary to supply, during melting in an electric arc furnace, an energy contribution able to favor the reduction kinetics.

[0089] The agglomerated product thus obtained can therefore be used directly as the charge product for an electric arc furnace since, thanks to its balance between reducing agent and iron oxides, it receives part of the energy necessary for its reduction from the fuel itself, for the production of liquid metal.

[0090] According to another embodiment, the quantity of solid fuel fraction CR is less than or equal to 30% by weight with respect to the at least one by-product fraction M; M1, M2, M3. This value of solid fuel CR is a good compromise between the ease of obtaining the agglomerated product and the production cost thereof.

[0091] According to another embodiment, the quantity of solid fuel fraction CR is less than or equal to 25% by weight with respect to the total weight of the solid agglomerated product.

[0092] In accordance with one possible embodiment of the present invention, the inorganic binder is selected from a group consisting of cement, white slag, or a combination thereof.

[0093] According to one possible solution, the inorganic binder comprises cement, preferably in a percentage by weight comprised between 4% and 10%, preferably between 5% and 7%, with respect to the at least one by-product fraction M; M1, M2, M3.

[0094] In other solutions, the inorganic binder is present in a percentage by weight comprised between 4% and 10%, preferably between 5% and 7%, with respect to the at least one by-product fraction M; M1, M2, M3. Preferably, the inorganic binder comprises or is cement.

[0095] In accordance with possible solutions, the cement can comprise Portland cement, preferably type III.

[0096] According to one possible solution, the organic binder is selected from among polysaccharides. Preferably, the organic binder is selected from starch, carboxymethylcellulose, lignin and a mixture of two or more of these.

[0097] More preferably, the organic binder comprises starch, even more preferably in a percentage by weight comprised between 2% and 5%, preferably between 2.5% and 4%, with respect to the at least one by-product fraction M; M1, M2, M3.

[0098] In further solutions, the organic binder is present in a percentage by weight comprised between 2% and 5%, preferably between 2.5% and 4%, with respect to the at least one by-product fraction M; M1, M2, M3. More preferably, the organic binder comprises or is starch.

[0099] In accordance with another solution of the present invention, the inorganic binder comprises, alternatively or in addition to the cement, white slag. The white slag is advantageously present in a percentage by weight comprised between 2% and 10%, preferably between 5% and 9%, with respect to the at least one by-product fraction M; M1, M2, M3.

[0100] White slag can be defined as the slag that is obtained as waste from secondary metallurgy processes, for example the steel refining processes that are usually implemented inside the ladle. The term white slag is widely used in the technical field of metallurgy, and is to be considered well known to the person of skill in the art.

[0101] The addition of white slag during the step of producing the solid agglomerated product advantageously allows to improve the mechanical properties of the agglomerate itself, creating an acicular-type structure of hydrated calcium silicate, and to increase the hygroscopicity of the agglomerate itself in order to retain the water necessary for the hydration of the main inorganic binder, for example cement.

[0102] Furthermore, the addition of white slag allows to reduce the necessary quantity of main inorganic binder, that is, cement, and to modulate the basicity of the slag in the furnace, possibly reducing the additions of slagging agents.

[0103] In accordance with possible solutions, the agglomerated product can comprise at least one additive selected from a group comprising calcium oxide CaO, also called quicklime, and calcium carbonate CaCO.sub.3.

[0104] According to one possible solution, the solid agglomerated product, in accordance with the present invention, does not contain bentonite and/or binders of the molasses type as main binders.

[0105] These materials, in fact, give the agglomerated product poor mechanical properties if it is brought to temperatures above 400 C. It is also a possible purpose of the present invention to obtain an agglomerated product which preserves its characteristics of mechanical resistance at temperatures higher than 400 C., preferably higher than 600 C. This makes it possible, for example, to add these aggregate products to the preheated direct reduction iron, usually at temperatures of about 600 C. It should be noted that bentonite and molasses do not have the correct water absorption and/or swelling properties useful for giving elasticity to the agglomerated product.

[0106] Preferably, the solid agglomerated product is in the form of a pressed product, such as for example an extrudate or with a non-circular shape. More preferably, the agglomerated product is in the form of briquettes B. The briquettes B can have sizes comprised between 20 mm and 60 mm and a weight comprised between 15 g and 1500 g.

[0107] FIG. 1 shows a method for making the solid agglomerated product, in which it is provided to use a single by-product fraction M having a granulometry smaller than 100 m.

[0108] This single by-product fraction M can be supplied by a single zone of the steel plant in which this fraction was produced, or derive from different parts of a steel plant.

[0109] Furthermore, it can be provided that the single by-product fraction M is also derived from a previous process of grinding and mixing several by-product fractions having much larger granulometries than those used for the present process.

[0110] Preferably, it is provided that at least 50% of this by-product fraction M has a granulometry smaller than 25 m.

[0111] According to one variant, it is provided that at least 80% of this by-product fraction M has a granulometry smaller than 45 m.

[0112] In accordance with this solution, it can be provided that in the event that at least part of this by-product fraction has a granulometry larger than 100 m, this part, or the entire by-product fraction, is subjected to a grinding process in order to obtain the desired granulometry sizes.

[0113] Subsequently, the method provides to determine, for example by means of laboratory tests, the quantity Fe.sup.2+_tot by weight of iron contained in the first part containing ferrous oxide FeO, and of the quantity Fe.sup.3+_tot by weight of iron contained in the second part containing ferric oxide Fe.sub.2O.sub.3.

[0114] By way of example only, it can be provided that the weight of the quantity Fe.sup.2+_tot and of the quantity Fe.sup.3+_tot are determined by the relations:

Fe.sup.2+_tot=% Fe.sup.2+.sub.M*M

Fe.sup.3+_tot=% Fe.sup.3+.sub.M*M.

[0115] Wherein M is the weight of the by-product fraction and % Fe.sup.2+.sub.M and % Fe.sup.3+.sub.M are the respective percentages of iron Fe.sup.2+, Fe.sup.3+ present in the by-product fraction.

[0116] According to some embodiments, % Fe.sup.2+.sub.M and % Fe.sup.3+.sub.M can be measured by experimentation and/or detection methods.

[0117] According to one possible solution, it can be provided that the by-product fraction M has a degree of metallization, that is, a degree of metallic iron, with respect to the total iron, comprised between 15% and 40%.

[0118] In accordance with one possible solution, it is then provided to prepare at least the solid fuel fraction CR, at least one inorganic binder and at least one organic binder. The quantity of solid fuel fraction CR is determined according to the relations described above.

[0119] In accordance with one possible solution, these binders, or part of them, and the solid fuel fraction CR, or part of it, can be subjected to a grinding process in order to reduce their granulometry, for example to a value smaller than 100 m.

[0120] Subsequently, the by-product fraction, the binders and the solid fuel fraction CR are mixed together with the addition of water in order to obtain a mixture ZB.

[0121] According to one embodiment, before the mixing, a dosing of the at least one inorganic binder, the solid fuel fraction CR and the by-product fraction M can be performed.

[0122] The production method then provides the cold agglomeration of the mixture ZB in order to obtain agglomerates SB. The cold agglomeration can be performed by pressing, for example with the aid of a mechanical compaction cycle at high pressures.

[0123] Subsequently, the method can comprise a screening step during which the agglomerates SB are screened, keeping only those that have a determinate size.

[0124] The agglomerates SB with smaller sizes than those desired are recycled, for example by introducing them into the mixer, during the mixing step or in the compactor.

[0125] Following the screening, the method can comprise a curing step. During this curing step the agglomerates SB acquire the desired mechanical characteristics thanks also to the hydration reactions that occur between the binders, for example between cement and white slag.

[0126] According to one variant, the production method schematically shown in FIG. 2 provides to supply at least two by-product fractions, in this specific case three by-product fractions M1, M2 and M3, and wherein at least a first by-product fraction M1 has a granulometry smaller than 100 m, and a second by-product fraction, in this specific case a second and a third by-product fraction M2 and M3, has a granulometry comprised between 100 m and 6 mm, preferably between 100 m and 4 mm for at least 80% of the by-product itself.

[0127] Preferably, it is provided that at least 50% of the first by-product fraction M1 has a granulometry smaller than 25 m.

[0128] According to one possible solution, it can be provided that the first by-product fraction M1 has a degree of metallization, that is, a degree of reduction of the iron oxides (FeO and/or Fe.sub.2O.sub.3) to metallic iron comprised between 15% and 40%.

[0129] According to another embodiment, it can be provided that the second by-product fraction M2 has a degree of metallization, that is, a degree of reduction of iron oxides (FeO and/or Fe.sub.2O.sub.3) to metallic iron lower than 6%.

[0130] In accordance with another embodiment, it can be provided that the third by-product fraction M3 has a degree of metallization, that is, a degree of reduction of iron oxides (FeO and/or Fe.sub.2O.sub.3) to metallic iron comprised between 70% and 100%.

[0131] In accordance with possible implementations of the method, it is then provided to determine, for all the by-product fractions M1, M2, M3, for example by means of laboratory tests, the quantity of Fe.sup.2+_tot by weight of iron contained in the first part containing ferrous oxide FeO, the quantity Fe.sup.3+_tot by weight of iron contained in the second part containing ferric oxide Fe.sub.2O.sub.3, and the quantity Fe.sup.0_tot by weight of iron contained in the third part containing metallic iron Fe.

[0132] This determination can be performed separately for each of the by-product fractions M1, M2, and M3.

[0133] By way of example only, for the example case in which there are three by-product fractions, it is provided to determine, for example by means of laboratory tests, respective percentages of iron Fe.sup.2+, Fe.sup.3+, Fe.sup.0 present in each by-product fraction, that is, the determination of % Fe.sup.2+.sub.M1, % Fe.sup.3+.sub.M1, % Fe.sup.0.sub.M1, % Fe.sup.2+.sub.M2, % Fe.sup.3+.sub.M2, % Fe.sup.0.sub.M2, % Fe.sup.2+.sub.M3, % Fe.sup.3+.sub.M3, % Fe.sup.0.sub.M3.

[0134] As a function of these percentages of iron Fe.sup.2+, Fe.sup.3+, Fe.sup.0 it is possible to determine the weights of the quantity Fe.sup.2+_tot, of the quantity Fe.sup.3+_tot and of the quantity Fe.sup.0_tot by means of the relations:

Fe.sup.2+_tot=% Fe.sup.2+.sub.M1*M1+% Fe.sup.2+.sub.M2*M2+% Fe.sup.2+.sub.M3*M3

Fe.sup.3+_tot=% Fe.sup.3+.sub.M1*M1+% Fe.sup.3+.sub.M2*M2+% Fe.sup.3+.sub.M3*M3

Fe.sup.0_tot=% Fe.sup.0.sub.M1*M1+% Fe.sup.0.sub.M2*M2+% Fe.sup.0.sub.M3*M3.

[0135] These quantities by weight are then used to determine the weight of the solid fuel fraction CR to be added in order to obtain the briquettes B.

[0136] According to some embodiments, it is also provided to screen the by-product fractions M1, M2, M3 in order to discard the components that do not satisfy a determinate size criterion. This screening is optional.

[0137] It is provided to supply the at least one inorganic binder that binds the by-product fractions M1, M2, M3 and the solid fuel fraction CR together.

[0138] It is provided to supply the at least one organic binder that binds the by-product fractions M1, M2, M3 and the solid fuel fraction CR together.

[0139] It can also be provided that the binders, or part of them, and the solid fuel fraction CR, or part of it, can be subjected to a crushing process in order to reduce their granulometry, for example to a value smaller than 4 mm.

[0140] Subsequently, the by-product fractions M1, M2 and M3, the binders and the solid fuel fraction CR are mixed together, preferably according to a suitable sequence established by the respective granulometry and/or hygroscopicity, that is, the ability to react with water, with the addition of water in order to obtain a mixture ZB (FIG. 3).

[0141] For example, it can be provided to mix, in a first step, dry products such as the by-product fractions M; M1, M2, M3, the organic binder and the solid fuel.

[0142] Subsequently, it is provided to add the hygroscopic components, that is, those that react with water, such as the inorganic binder.

[0143] More preferably, first the by-product fractions M; M1, M2, M3 and then the organic binder are made available.

[0144] According to one embodiment, before the mixing, a dosing of the at least one inorganic binder, the at least one organic binder, the solid fuel fraction CR and the by-product fractions M1, M2, M3 can be performed.

[0145] The method for making briquettes B then provides the agglomeration or cold briquetting of the mixture ZB in order to obtain agglomerates SB.

[0146] The cold agglomeration can be performed by means of pressing, for example with the aid of a mechanical compaction cycle at high pressures.

[0147] By way of example only, the mixture ZB can be fed into the space between two counter-rotating rollers. The rollers are provided with molds in their surface.

[0148] When the mixture ZB passes between the rollers, the material is compacted and the briquettes are formed with the desired shapes and sizes.

[0149] Subsequently, the method can comprise a screening step during which briquettes at exit from the cold agglomeration are screened, keeping only those that have a determinate size.

[0150] The briquettes with smaller sizes than the desired ones, typically 12 mm, are recycled, for example by introducing them into a suitable lump breaker in order to crumble them and promote their subsequent agglomeration, during the mixing step or at the briquetting machine.

[0151] After the screening, the method can comprise a curing step. During this curing step the briquettes B take on the desired mechanical properties, thanks also to the hydration reactions that are established between the binders, for example between cement and white slag. This curing period varies from a minimum of 48 hours up to 96 hours and allows adequate mechanical properties to develop.

[0152] Favorably, in the formulation of the agglomerated products in accordance with the invention, the by-product fractions M, M1, M2, M3 represent between 60% and 90%, preferably between 65% and 80% by weight, dry weight. The weight ratio between the organic binder and the inorganic binder is preferably less than 1. If the white slag is present, it represents less than 10% by weight of the agglomerated product, dry weight.

[0153] The table shows some examples of formulations of solid agglomerated products as a percentage by weight, dry weight, that is, without the addition of water.

TABLE-US-00001 Solid fuel Iron oxides % fraction % Cement % Starch % White slag % 69 17.2 5.2 4.0 8.5

[0154] In accordance with another aspect of the present invention, it is provided that after curing, the briquettes B have a compressive strength, that is, a compression weight that supports the briquette before collapsing, greater than 400 N/briquette, in particular between 400 and 600 N/briquette.

[0155] It is clear that modifications and/or additions of parts may be made to the solid agglomerated product as described heretofore, without departing from the field and scope of the present invention as defined by the claims.

[0156] In the following claims, the sole purpose of the references in brackets is to facilitate reading and they must not be considered as restrictive factors with regard to the field of protection claimed in the specific claims.