The invention relates to the field of coke and by-product process and blast-furnace production.

In the modern production of blast-furnace coke, special attention is paid to the quality of coke, especially to its parameters, which to some extent characterize the behavior of coke in blast-furnace process. These parameters include coke reactivity index (CRI) and coke strength after reaction (CSR) , determined according to the international standard ISO 18894:2006. Improvement of coke quality parameters allows blast-furnace processes to be more economic and effective. To improve such parameters as CSR (to increase) and CRI (to decrease) of coke different methods and techniques are used in coke and by-product coke plants, the main of which include preparing the charge coal for coking, selection of conditions and parameters of coking, treatment of finished coke with chemical compounds and so on. Novel cast iron technologies are directed to preserving scarce and high- cost energy (coke, gas, fuel oil, etc.) and substitution thereof by pulverized fuel (PF) . Partial substitution of coke by PF in a blast furnace advances new demands as to its quality, the demands being determined by conditions and behavior of coke in a blast furnace. Many steel mills in Europe, Asia, America achieved reducing coke consumption up to 280 - 300 kg/t of pig iron by blowing up to 200 - 240 kg/t of PF into a blast furnace. At the same time, they do not use natural gas and fuel oil. To achieve such performance metallurgical coke plant needs coke with CRI below 26.6 %, CSR in the range of 65 - 70 %.

To obtain blast furnace coke with such quality parameters it is necessary to have high-quality coking coal, which amount is insufficient for the needs of coke chemistry. Therefore, to improve quality parameters CSR and CRI of blast-furnace coke different methods and techniques based both on formulating and preparation of charge coal for coking, and on varying conditions of coking are used.

One way to improve quality parameters of coke is its post- oven treatment by inorganic substances .

It is known a method of improving the quality parameters of coke, which includes covering of hot coke lumps (t ≥ 850°C) with fine solid inorganic compounds by spraying in preheated gas flow (GB1423187, 1976-01-28, ISC SMELTING, IPC: C10L9/10; C10L9/00). As inorganic compounds for covering coke, boric acid or borates are used. This results in coke deactivation with respect to the reaction with oxygen (0 ₂ ) and carbon dioxide (C0 ₂ ) due to formation of the thin film of molten borates on the surface of coke lumps at high temperature .

The disadvantages of the known method include insufficient effectiveness of technology because of slight reducing of the CRI parameter and insignificant increase of coke strength after reaction (CSR) , uneconomic technology due to the need to reach high temperatures (t ≥ 850°C) , complexity of the process equipment, increased danger of the industrial process for environment . It is known a method of improving the quality parameters of coke (patent of Ukraine N» 23560, IPC C10L9/10, 2007, Bull. N' 7), which includes treatment of coke lumps at a temperature of 20 - 50°C by aqueous solution of tetraborate, selected from the group comprising: sodium tetraborate, potassium tetraborate, calcium tetraborate. This results in coke deactivation with respect to the reaction with oxygen (0 ₂ ) and carbon dioxide (C0 ₂ ) due to formation of a protective film of molten borates on the surface of coke lumps, while further heating (in the blast furnace) the coke treated in this way.

The disadvantage of the known method is in lack of effectiveness because of incomplete use of the possibilities of tetraborates to improve CRI and CSR quality parameters of coke, what is caused by both peculiarities of coke treatment by tetraborate solutions and the fact that the surface of coke is hydrophilic as to water droplets (tetraborate solution) . This leads to drippege of the solution down from the coke lumps, incomplete wetting thereof and accordingly non-covering the entire surface with tetraborate molecules, what does not allow protective layer creation on coke lumps surface.

A known method of improving quality parameters of blast- furnace coke (patent of Ukraine N' 31186, IPC C10L9/10, 2008, Bull. N' 6) is chosen as the closest prior art (the prototype) with respect to the essence and the results achieved by the method claimed herein, the known method including post-oven treatment of blast-furnace coke lumps at 20 - 50°C by 2 - 20 % aqueous solution of sodium, potassium or calcium tetraborate, to which 0.1 - 0.2 % of nonionic surfactant, preferably mono- and dialkyl ethers of polyethylene glycol, is added. The volume of aqueous solution of surfactant applied is in the amount in the coke corresponding to 0.0035 - 0.0070 % (mas.) of the coke mass.

This provides better coverage of the lumps surface and better penetration of tetraborate solution into the volume of coke lumps, providing a coating of coke pore surfaces by tetraborate molecules. This causes deactivation (inhibition) of coke in respect to the reaction with 0 ₂ and C0 ₂ due to formation of the protective film of molten tetraborate on the coke surface while further heating of the treated coke in a blast furnace.

The disadvantage of the method known from the prototype is that the degree of improvement of quality parameters CRI, CSR is insufficient for the needs of blast-furnace process, characterized by substitution of a significant part (200 - 220 kg/t of pig iron) of coke by PF.

The reason of the disadvantage of the method known from the prototype is too large percentage of alkali or alkali-earth metals in tetraborates of these metals, what adversely affects CRI and CSR parameters of coke, and low content of boron in tetraborate molecules (18 - 22 %) , what does not allow complete covering surface of the coke lumps by the durable protective layer.

The object of this invention is to use for post-oven treatment of coke, in a method of improving coke quality in terms of CSR and CRI, boron compounds which contain the lesser amount of alkali and alkali-earth metals, and the greater amount of boron, forming with its help a durable protective layer on coke lumps, which protects and inhibits coke with respect to the reaction of coke carbon with 0 ₂ and C0 ₂ in a blast furnace. This results in decrease of coke reactivity index (CRI) and increase of its strength (CSR) after reaction with C0 ₂ .

The object is achieved by providing a method of improving quality parameters of coke by spraying 2 - 20 % aqueous solution of borates of metals selected from the group containing: sodium, potassium, calcium, onto coke lumps at the temperature no less than 20°C, adding 0.1 - 0.2 % of nonionic surfactant to the aqueous borate solution, preferably in the form of mono- and/or dialkyl ethers of polyethylene glycol in a volume sufficient to obtain the amount of the surfactant in the coke corresponding to 0.0035 - 0.0070 % (mas . ) of coke mass,

Novelty of the method provided is in that as sodium, potassium or calcium borate pentaborate of one of these metals is used in such volume that the amount of dry pentaborate in coke corresponds to 0.09 - 0.68 % (mas.) of the coke mass.

A cause-effect relationship between the set of the invention features and the technical effect obtained at its implementation exists.

Engineering studies indicate insufficient capacity of potassium (K ₂ B ₄ 0 ₇ ) , sodium (Na ₂ B ₄ 0 ₇ ) or calcium (CaB ₄ 0 ₇ ) tetraborates applied according to the method known from the prototype to improve quality parameters CRI and CSR to the extent of meeting the blast-furnace process requirements determined by substitution of a significant part (200 - 220 kg/t of pig iron) of coke by PF. It is obviously caused by the fact that while treating coke by tetraborate solution too much amount of alkali or alkali-earth metals is introduced, what adversely affects CRI and CSR parameters of coke because of the ash basicity. Thus, based on ash basicity index (Io)

Io = (Fe ₂ 0 ₃ + CaO + gO + Na20 + K ₂ 0)/(Si0 ₂ + A1 ₂ 0 ₃ ) , Ye.T. Kovaliov with co-authors. (Ye.T. Kovaliov, I.V. Shulga, A.I. Ryshchenko A.I., I.D. Drozdnik, D.V. Miroshnichenko, Effect of charge coal quality on the reactivity, after- reaction strength of coke and technical and economic parameters of blast-furnace process// Uglehimicheskiy Journal. - 2008 . - W 3 - 4 .- p.p 41 - 48) concluded that increasing value of Io by 0.1 units worsens quality parameters of coke, namely leads to decrease of CSR by 9.5 % and increase of CRI by 7.5 %. Another possible reason for insufficient improvement of the coke quality after its treatment by the method known from the prototype is low content of boron in tetraborate molecules, which for the group of potassium, sodium and calcium tetraborates, is correspondingly 18 - 22 %, what does not allow to cover the surface of the coke lumps by a reliable protective layer and protect them from oxidation by 0 ₂ and C0 ₂ in full.

Novelty of the method provided herein is in that after oven treatment of coke pentaborates of potassium, sodium or calcium are used.

Unlike the method known from the prototype, the method claimed herein includes treatment of blast-furnace coke by an aqueous solution of not potassium, sodium or calcium tetraborate (K ₂ B ₄ 0 ₇ , Na ₂ B ₄ 0 ₇ , CaB ₄ 0 ₇ ) , but by pentaborate of one of these metals ( B ₅ 0 ₈ , NaB ₅ 0 ₈ or Ca (B ₅ 0 ₈ ) ₂ ) in such a volume that the amount of dry pentaborate in coke corresponds to 0.09 - 0.68 % (mas.) of coke mass. These inorganic compounds of boron, in which content of alkali or alkali-earth metals is half as much and boron content is 1.2 - 1.3 times as much as their content in tetraborates, makes possible to considerably improve the quality of blast-furnace coke: increase of the quality parameter CSR of coke by 9.3 - 16.1 % (relative) and a decrease of CRI by 12.3 - 21.2 % (relative) takes place (relative % - is the ratio of the absolute increase (decrease) of a parameter value to its initial value multiplied by 100 ) .

Positive effect of pentaborates in improving quality parameters CSR and CRI is based on the fact that when the pentaborate solution gets the surface of a coke lump it becomes covered by the layer of pentaborate molecules held on the surface by adhesion forces. Part of the pentaborate solution penetrates well into the cracks, pores of the coke lumps, and covers their surfaces by pentaborate molecules. The layer formed of pentaborate molecules blocks oxidizing gases 0 ₂ and C0 ₂ access to the surface of coke and is found to be able to deactivate coke with respect to the reactions with 0 ₂ and C0 ₂ , even at the temperatures below the pentaborate melting temperature. This is confirmed by adsorption-desorption isotherms of nitrogen at 77K, with which help parameters of porous structure of coke experimental samples were determined.

The following parameters were used to characterize porous structure of coke: S _BET (m ² /g) - specific surface of pores; V ₂ (cm ³ /g) - total pore volume; V _mi , V _me , V _ma (cm ³ /g) - the volume of micro- , meza- and macropores respectively. For raw coke these parameters are: S _BE T = 1.695 m ² /g, v _∑ = 0.021 cmVg, V _mi = 1.6xl0 ^~5 cmVg, V _me = 8.2xl0 ^~3 cm ³ /g, V _ma = 1.3xl0 ^~2 cm ³ /g. For coke, treated by tetraborate solution they are: S _BET = 0.743 m ² /g, V _∑ = 0.0086 cm ³ /g, V _mi = 7.1xl0 ^~6 cm ³ /g, V _me = 3.3xl0 ^"3 cm ³ /g, V _ma = 5.3xl0 ^"3 cm ³ /g. For coke, treated by pentaborate solution they are: S _BET = 0.963 m ² /g, V _s = 0.0026 cmVg, v _mi = 3xio ^"6 cmVg, v _me = ι.εχΐο ^'3 cm ³ /g, v _ma = lxio ^"3 cm ³ /g.

Considering these data, one can conclude that the treatment of coke by borates significantly reduces the volume of its pores. Surely, with such a treatment of coke borates cover not only the surface of coke by protective layer but penetrate into pores covering them, overlap them, thereby limiting the access of oxidizing gases to carbon coke, deactivating its oxidation. The results obtained show that pores volume in the coke treated by pentaborate is 8 times smaller than that in the feedstock, and 3.3 times smaller than in the coke treated by tetraborate .

At the same time, at melting temperatures borates are subject to so-called borate rearrangement. (Borates Inorganic// Chemical Encyclopedic Dictionary. - Moscow: Soviet Encyclopedia, 1983 .- p.79), what results in that the borate molecule can form corresponding metaborate and boron oxide. For example, 2KB ₅ 0 ₈ → K ₂ B ₂ 04 + 4B ₂ 0 ₃ . The metaborate is also ionized: K ₂ B ₂ 0 ₄ → 2K ⁺ + B ₂ 0 ₄ ^"2 .

Potassium cations can penetrate into the interlayer space of coke crystallite and stay there (the so-called reaction of intercalation) . Dimeric anion B ₂ 0 ₄ ^"2 forms a cycle, i.e. it has a cyclic structure:

Anion B ₂ 0 ₄ ^"2 , having got onto the plane of coke crystallite frame will be kept thereon by intermolecular forces, determined by overlapping of P-orbitals of boron with corresponding P-orbitals of coke carbon, what assists in a strong donor-acceptor interaction between boron and carbon atoms. While being on the surface of coke crystallite, anions B204-2 are firmly held thereon, forming a protective film of anions B204-2, which prevents the penetration and interaction of gaseous oxidizer with carbon coke both in the case of gasification of coke in blast furnaces and in the equipment for determination of CSR and CRI parameters of coke while transmitting carbon-dioxide gas through coke lumps at the temperature of 1100°C.

The fact that between carbon of the coke crystallite and boron compounds formed during borate rearrangement (i.e. metaborate and boron oxide) , a chemical reaction runs, is confirmed by X-ray structural analysis. Based on X-ray spectra it was shown that crystallites of coke, treated by potassium pentaborate are characterized by greater extension of polyarene layers (La) and height (Lc) of crystals and a greater number of layers in the crystallites (n) . X-ray structural parameters of the initial coke crystallites are: d ₀₀ 2 = 0-356 nm, La = 8.32 nm, Lc = 4.07 nm, n = 12.4, and those of the coke, treated by potassium pentaborate are: d ₀₀ 2 = 0.350 nm, La = 9.20 nm, Lc = 5.09 nm, n = 15.5.

Coke strength after reaction with C0 ₂ (so-called "hot strength») -CSR - obtained as a result of the proposed method using pentaborates , is increased compared with the prototype by 9.3 - 16.1 % (relative), compared with the feedstock coke - by 18.8 - 38.5 %. CRI parameter of the coke is reduced correspondingly by 12.3 - 21.2 % (relative) and 17.2 - 35.2 % (relative). This improvement of quality parameters CSR and CRI of coke, treated by pentaborate solution with the addition of surfactant according to the method suggested in comparison with the parameters of coke treated according the method known from the prototype, is determined by that only half amount of alkali metal negatively affecting CSR and CRI parameters, and 1.2 - 1.3 times greater amount of boron are introduced into coke while its treatment, what allows to create more reliable protective layer on coke lumps in comparison with the protective layer formed while treating coke by tetraborate according to the method known from the prototype. This protective layer more reliably prevents penetration and influence of oxidizing gases on coke substance by reducing reactivity index CRI and increasing "hot strength* CSR of the blast-furnace coke.

For the treatment of coke according to the method claimed the volume of pentaborate solution used is as much as it is required for the dry coke amount of 0.09 - 0.68 % (mas.) of coke mass. It was empirically proven that use of pentaborates in the amount lesser than 0.09 % (mas.), results in insufficient improvement of CSR and CRI parameters because, obviously, this amount of pentaborate is not enough for creating a reliable protective layer on the entire surface of coke lumps to be treated. Use of pentaborate in the amount greater than 0.68 % (mas.) is technologically complex and economically unreasonable.

Solving pentaborate by water up to 2 - 20 % solution and spraying at no less than 20°C are determined by properties of the solution, technological requirements of coke use in blast furnace process (coke temperature in a hopper after the heating process is 20 - 100°C) , need to completely distribute pentaborate on the entire surface of coke lumps for creating a reliable protective layer, which would cover coke lump to a greater extent .

Use of 2 - 20 % aqueous solution of pentaborate no less than 20°C is safe for the environment and staff health. It was experimentally proven that the use of nonionic surfactants in the amount of 0.1 - 0.2 % in a volume sufficient to obtain the amount of surfactant in the coke corresponding to 0.0035 - 0.0070 % (mas.) of coke mass, is optimal for achieving complete wetting of coke lumps by pentaborate aqueous solution

The claimed method of improving quality of coke can be realized as follows. After discharge from the coke ovens, extinguishing and sorting by size, fractions of coke lumps of 25 - 80 mm size, used in blast furnaces, are treated by spraying 2 - 20 % pentaborate solution, selected from the group comprising: potassium pentaborate sodium pentaborate, calcium pentaborate. The treatment of coke lumps, having temperature no less than 20°C, is carried out along the pass of the coke into the hopper after shredding and sorting by size and directly in the hopper, where coke is collected for further his loading into wagons. A volume of the solution prepared for the treatment is to be enough to obtain dry pentaborate in coke in the amount of 0.09 - 0.68 % (mas.) of the coke mass, and to wet surface of coke lumps to be treated. Calculated amount of pentaborate solution is sprayed using a pump and injectors.

Specific examples of the method embodiments.

The claimed method of improving quality parameters of blast-furnace coke was tested on samples of coke from the Makeyevka coke plant . For the treatment of coke an aqueous solution of potassium pentaborate having required concentration was prepared, 0.1 - 0.2 % of nonionic surfactant of "DB" or "OP" types having been added. The

335 calculated amount of solution was deposited onto the surface of the coke lumps by spraying through nozzles. The quality parameters of coke were determined according to the standard ISO 18894:2006. The parameters of blast-furnace coke to be treated were as follows: CSR = 50.4 %, CRI =

340 34.4 %. Table 1 shows the results of tests of the coke samples with determination of CSR and CRI parameters: raw coke (sample 1) , samples 2 - 8 (examples 2 - 8) treated under the conditions of the known method (prototype) . Samples for examples 2 - 3 - coke treated by 2.0 % solution

345 of potassium tetraborate at 45 1/t of coke, i.e. 0.09 %

(mas.) of potassium tetraborate. 0.1 % of "DB" surfactant was added to the solution for sample 2 and 0.2 % of "DB" surfactant was added to the solution for sample 3, what corresponds to 0.0035 and 0.0070 % (mas.) according to the

350 provisions of the prototype. A sample for example 4 is coke treated by 7 % solution of potassium tetraborate at 35 1/t

Influence of a treatment method on quality parameters CSR and CRI

Table 1

Exa MeComponents of aqueous solution Amount Amount Quality mpl thod for coke treatment of of parameter of es of borate, surfacta coke treat% nt, % CRI CSR ment (mas.) (mas.)

1 without treatment - - 34,4 50,4 2 proto potassium tetraborate and «DB» 0,09 0,0035 33,0 53,7

3 -type potassium tetraborate and «DB» 0,09 0,0070 32,5 54,8

4 potassium tetraborate and «DB» 0,25 0,0070 28,9 59,1

5 potassium tetraborate and «DB» 0,68 0,0070 28,3 60,1

6 sodium tetraborate and «OP» 0,25 0,0070 30,0 58,1

7 sodium tetraborate and «DB» 0,25 0,0070 28,4 59,8

8 calcium tetraborate and «DB» 0,25 0,0070 31,3 56,3

9 potassium pentaborate and «DB» 0,09 0,0035 30,3 58,0

10 potassium pentaborate and «DB» 0,09 0,0070 28,5 59,9

11 claim potassium pentaborate and «DB» 0,25 0,0070 24,9 65,7

12 ed potassium pentaborate and «DB» 0,68 0,0070 22,3 69,8

13 sodium pentaborate and «OP» 0,25 0,0070 26,0 63,8

14 sodium pentaborate and «DB» 0,25 0,0070 24,6 64,8

15 sodium pentaborate and «DB» 0,68 0,0070 24,2 65,3

16 calcium pentaborate and «DB» 0,25 0,0070 28,0 62,1

17 calcium pentaborate and «DB» 0,68 0,0070 27,0 63,4 of coke, i.e. 0.25 % (mas.) of potassium tetraborate for 1 ton of coke. 0.2 % of surfactant "DB" was also added to the solution. The sample of example 5 is coke, treated by 15 % solution of potassium tetraborate at 45 1/t of coke, i.e. 0.68 % (mas.) of potassium tetraborate for 1 ton of coke. 0.2 % of surfactant "DB" was added to the solution. Samples of the examples 6 and 7 are the samples of coke treated in accordance with the prototype as for example 4 , except that sodium tetraborate was used as tetraborate. 0.2 % of surfactant "OP" as for example 6 and 0.2 % of surfactant "DB" as for example 7 were added to the solution. A sample of example 8 is the sample of coke treated in accordance with the prototype, as for example 4, except that calcium tetraborate was used as tetraborate. Samples for examples 9 17 were treated according to the claimed method of improving quality parameters of coke. Samples 9 - 12 are samples of a coke treated under the same conditions as in examples 2 - 5, except that the solution contained potassium pentaborate. Samples for examples 13 and 14 are samples of coke treated under the same conditions as in example 6 and 7, except that sodium pentaborate was used in the solution. Sample for example 15 is coke treated under the same conditions as in example 12, except that sodium pentaborate was added to the solution. Samples for examples 16 and 17 are coke samples treated under the same conditions as in examples 11 and 12, except that the solutions contained calcium pentaborate.

Dependence of coke quality parameters CSR and CRI on the amount of potassium pentaborate used for its treatment

Table 2

Table 2 shows the results of tests of coke samples with determination of its CSR and CRI parameters dependence on the amount of potassium pentaborate used for its treatment. Untreated coke corresponds to the example 18. A sample of the example 17 is the coke sample treated under the same conditions as in the example 6. Samples for examples 19 - 25 are the coke samples treated under the same conditions as in the example 10, except that the solutions with different concentration of potassium pentaborate, respectively, 2 %, 5 %, 7 %, 10 %, 12 %, 15 %, 20 %, were used for the treatment of coke . The amount of the solution for the treatment in examples 19 - 25 was 45 1/t of coke. Each of these solutions also contained 0.2 % of surfactant of "DB".

As seen from Table 1 data, the treatment of coke by aqueous solutions of potassium, sodium and calcium pentaborates (examples 9 - 17) significantly increases the coke quality parameters CSR and CRI. The highest rate of the improvement of the coke quality parameters CSR and CRI is observed while treating coke by potassium pentaborate (examples 11 and 12). Thus, the treatment of coke with CSR = 50.4, CRI = 34.4 by potassium pentaborate in the claimed amount of 0.09 - 0.68 % (mas.) assists in improving parameters CRI and CSR with respect to those of coke treated by the method known from the prototype. Thus, CRI is decreased by 12.3 - 21.2 % (relative) (32.5 - 28.5 and 28.3 - 22.3 correspondingly) and the value of CSR is increased by 9.3 - 16.5 % (relative) (59.9 - 54.8 and 69.8 - 60.1 respectively) . Compared with the same initial values of the feedstock coke, CRI value is reduced, when treated by the method claimed, down to 17.2 - 35.2 % (relative) (34.4 - 28.5 and 34.4 - 22.3 correspondingly), and CSR value is increased by 18.8 - 38.5 % (relative) (59.9 - 50.4 and 69.8 - 50.4 correspondingly) .

As seen from the data of Table 2, coke treatment by solutions of potassium pentaborate with different concentrations, i.e. at injection of different amounts of pentaborate into coke, allows varying values of quality parameters CSR and CRI and predictably improve the coke quality (examples 19 - 25) .

Consequently, use of the method suggested, in comparison with the method known from the prototype, allows:

- to increase coke strength after its reaction with C0 ₂ (CSR) by 9.3 - 16.5 % (relative);

- to reduce the reactivity index CRI by 12.3 - 21.2 % (relative) ;

- to improve coke quality with the initial parameters CRI = 34 - 36 % or less, CSR = 50 - 55 % to the parameters values that meet the highest international standards: CRI lesser than 25 - 22 % and CSR greater than 65 - 70 %;

- to bring the use of pulverized fuel in blast furnaces to 200 - 220 kg/t of pig iron due to improvement of quality parameters of coke;

- to reduce consumption of coke in blast furnaces from 520 to 300 kg/t of pig iron due to improvement of quality parameters of coke ;

- to purposefully get coke with predetermined parameters CSR and CRI due to its processing by pentaborate solution with the concentration claimed;

to increase economic efficiency of the process of smelting.