Description:FIELD OF THE INVENTION
The present invention relates to a process for producing hot metal in blast furnace involving non-metallic fraction of Linz-Donawitz (LD) slag by injecting through tuyere. More specifically, the present invention relates to a process for producing hot metal in blast furnace by injecting non-metallic LD slag in blast furnace through selective crushing and optimized blending with coal powder. Advantageously, the present invention increases the tuyere slag basicity (B2) and final blast furnace slag basicity (B2) and further decreases the slag viscosity which ensures better slag drainage. Changes in slag basicity, viscosity and SiO generation help in suppressing the [Si] conversion in hot metal by 0.10%. Advantageously, the present invention uses the LD slag for recovery of Fe, CaO and MgO from dumped LD Slag.

BACKGROUND OF THE INVENTION
Blast furnace technology was proven to be economically and technologically advanced process for the production of hot metal in larger quantity with desired quality. Coke, coal, natural gas are mainly used as the fuel in blast furnace operation. The growing demand of quality steel with extremely low level of impurities and need for low cost of steel has set new goal for hot metal quality. Generally, Silicon, Sulphur and temperature of the hot metal decide its quality. Silicon in hot metal is an indicator for internal state of the blast furnace. Higher silicon signifies better thermal level inside the furnace. Ideally, silicon content in hot metal varies between 0.4 to 1.5 wt. %. Under abnormal situation it may go beyond 2 %. High silicon hot metal is not desired as Desiliconization consume excessive lime in steelmaking unit and consumes more heat. It may generate high slag volume during refining process causing foaming phenomena called slopping, thereby, reducing overall yield in steelmaking unit. This may also affects several other parameters like, lining life, steel quality, and cost.
Non-metallic BOF/LD slag utilization is a big concern for steel industry though it has value added minerals like CaO, MgO and Fe. It has limited application compared to BF slag.
Indian Patent Application No. IN201631009998 discloses the use of LD slag in Blast furnace. Prior art has charged LD slag from top along with iron ore and sinter. The ratio of LD Slag to iron ore and sinter was 40:60 was reported in the prior art. By utilisation of LD slag in normal blast furnace operation, higher phosphorus in pig iron (1.5 to 3.0% P), and higher fuel rate (increased by 100 to 150 kg/thm) and higher Silicon in pig iron (Si: more than 2.0 %) was experienced.
Hungary Patent No. HU9800458A3 describes a method for utilising LD slag for the production of pig iron and Ferro Chrome alloys. The objective of the prior art is to process LD slags in a complete process, in combination with a waste incineration process, so that directly usable products, such as synthetic blast furnace slags, can be obtained, which can subsequently be added to a mixed cement.
S. Chand, et al.; Metallurgist, Vol. 60, Nos. 1–2, May, 2016; demonstrates the significance of LD slag and its utilization. The paper provides various techniques like replacing lime addition with LD slag in steelmaking, road making, floor preparation, cement making etc. They emphasize on reuse and recycling of LD slag after removal of phosphorus. In order to recycle and reuse the waste, assessment of their physicochemical, mineralogical and geotechnical characterization is imperative. Prior art addresses the characterization and possible utilization of LD slag.
The present invention relates to a process for producing hot metal in blast furnace involving non-metallic fraction of Linz-Donawitz (LD) slag by injecting through tuyere. Through this method, LD slag can be injected into BF tuyeres along with pulverized coal. BOF Slag can be consumed in the blast furnace by injecting into blast furnace tuyeres along with pulverized coal. This will help in improved consistency in the quality of the Hot Metal Silicon content

OBJECT OF THE INVENTION
The basic object of the present invention is development of a process for producing hot metal in blast furnace involving injection of non-metallic fraction of Linz-Donawitz (LD) slag through tuyere.
Another object of the present invention is to use the LD slag for recovery of Fe, CaO and MgO from dumped LD Slag.
Another object of the present invention is to suppress the [Si] conversion in hot metal by 0.10%.
Yet another object of the invention is to use the LD slag in the coal blend to decrease coke rate by 1 kg/thm.
Further object of the present invention is to increase the basicity of the tuyere slag basicity (B2) from 0.01 to 0.30.
Yet another object of the present invention is to increase the final blast furnace slag basicity by 0.04.
Another object of the present invention is to decrease the slag viscosity was by 0.25 poise.
Another object of the present invention is to decrease the SiO (g) generation at tuyere level by 3.4 kg/thm.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is to provide for a process for producing hot metal in blast furnace involving LD slag in a beneficial and environment friendly manner comprising:
step of operating blast furnace for generation of molten metal wherein the LD slag alongwith pulverised coal is injected into the blast furnace through tuyeres such as to attain beneficial changes selectively in at least any one of slag basicity, viscosity and SiO generation.
Another aspect of the present invention is to provide for a process as above involving LD slag having composition (%) including:
Fe(t) CaO Fe2O3 FeO SiO2 MgO Al2O3 P2O5 MnO SO3 TiO2 Na2O K2O
18 to 23 preferably 20.83 30 to 52 preferably 43.4 5 to 10 preferably 7.23 18 to 28 preferably 20.28 6 to 20 preferably 11.96
4 to 15 preferably
8.82
2 to 7 preferably
3.86 0.8 to 2.0 preferably 1.03 1 to 2 preferably 1.61 0.4 to 0.8 preferably 0.59 0.2 to 1.0 preferably 0.57 0.01 to 0.80 preferably 0.49 0.01 to 0.20 preferably 0.04
and wherein the said step of LD slag injection alongwith pulverised coal is controlled to provide for beneficial changes in final slag basicity from 0.03 to 0.08 preferably 0.04; viscosity from 0.15 to 0.50 poise preferably 0.25 poise and SiO generation from 2.5 to 5.0 kg/thm preferably 3.4 kg/thm.
Another aspect of the present invention is to provide for a process as above which is preferably carried out involving ~20% of the LD slag having a size less than 1mm and 2.6% of LD slag having size of 0.075 mm.
Yet another aspect of the present invention is to provide for a process as above wherein said step of LD slag injection is carried out involving LD slag injection through tuyeres in blast furnace include selective crushing and optimized blending with coal powder such as to attain preferably more than 80% of the 0.075 mm sized material.
Further aspect of the present invention is to provide for a process as above wherein said step of LD slag injection is carried out involving LD slag injection through tuyeres at the rate of 5 to 25 kg/thm preferably about 15 kg/thm, such that the tuyere slag basicity (B2) increased from 0.01 to 0.30.
Yet another aspect of the present invention is to provide for a process as above wherein said step of LD slag injection is carried out involving LD slag injection through tuyeres selectively such as to control the final slag basicity (B2) got increased by 0.04 (from 1.00 to 1.04).
Another aspect of the present invention is to provide for a process as above wherein said step of LD slag injection is carried out involving LD slag injection through tuyeres at the rate of 5 to 25 kg/thm preferably about 15 kg/thm such that slag viscosity was decreased by 0.25 poise (from 5.32 to 5.07 poise at 1450 °C), which ensures better slag drainage.
Another aspect of the present invention is to provide for a process as above wherein said step of LD slag injection is carried out involving LD slag injection through tuyeres at the rate of 5 to 25 kg/thm preferably about 15 kg/thm such that SiO (g) generation at tuyere level decrease by 3.4 kg/thm (from 17.8 to 14.4 kg/thm).
Another aspect of the present invention is to provide for a process as above wherein said step of LD slag injection is carried out involving LD slag injection through tuyeres at the rate of 5 to 25 kg/thm preferably about 14.91 kg/thm the hot metal silicon content dropped by 0.10 unit (from 0.64% to 0.54%), the fuel rate was decreased by 0.9 kg/thm (from 555.1 to 554.2 kg/thm) as a result of the drop in [Si] content and hot metal [P] increased by 0.01 unit (from 0.12 to 0.13 %).
Yet another aspect of the present invention is to provide for a process as above wherein injection of LD slag along with pulverised coal through tuyeres comprises of:
(i) External mixing of non-metallic LD slag with coal for pulverised coal injection (PCI) line by forming a heap before it is fed into the grinding mill in a desired proportion;
(ii) Addition of non-metallic LD slag together with PCI Coal injection port with nitrogen/air as a carrier gas.
Further aspect of the present invention is to provide for a process as above wherein the proportion of PCI to LD slag is 93:07.

BRIEF DESCRIPTION OF THE NON-LIMITING ACCOMPANYING DRAWINGS

Figure 1 illustrates Size analysis of crushed and screened non-metallic LD slag

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
Steel plants generate many types of wastes at different stages of the processing. Recycling of waste is targeted towards optimal resource utilisation, environment friendly and cost saving measures. CaO is an important oxide present in the Basic Oxygen Furnace (BOF) slag, which can be utilized in other metallurgical processes as flux material instead of lime or lime stone. To utilise the metallic content of BOF slag, it is separated initially. Utilisation of the non-metallic part of BOF slag is a big concern for steel industry though it has value added minerals like CaO, MgO and FeO. The phosphorus of BOF or LD slag is too high to be reused in iron making and steel making. It has limited application compared to BF slag.
The present invention relates to a process for producing hot metal in blast furnace involving injection of non-metallic fraction of Linz-Donawitz (LD) slag through tuyere. The non-metallic LD slag is injected in blast furnace through selective crushing and optimized blending with coal powder. Through this method, LD slag can be injected into BF tuyeres along with pulverized coal.
Non-metallic BOF slag samples were collected from the slag yard. The chemical analysis of the BOF slags of different size fractions were evaluated using X-ray fluorescence spectrometer. The estimated average composition is shown in Table 1. It was observed that the (CaO+MgO) content is ~52% and Fe (T) of ~20%.
The as received sample was taken for size analysis and it was observed that the ~20% of the LD slag are less than 1mm as in Figure 1. Only 2.6% of non-metallic LD slag is of 0.075 mm. The present invention relates to a process for producing hot metal in blast furnace by injecting non-metallic LD slag in blast furnace through selective crushing and optimized blending with coal powder. This process results in 0.075 mm sized material more than 80 % for the final mixed material (coal and LD slag).
The external mixing of non-metallic LD slag with coal for pulverised coal injection (PCI) line was done by forming the heap before it is fed into the grinding mill in a desired proportion. LD slag injection increases the tuyere slag basicity (B2) and final BF slag basicity (B2), which results in decreased melting start and melting end temperature.
From the trial results as illustrated in Table 2, it is observed that with addition of LD slag at 14.91 kg/thm, the hot metal silicon content dropped by 0.10 unit (from 0.64% to 0.54%). The fuel rate was decreased by 0.9 kg/thm (from 555.1 to 554.2 kg/thm) because of the drop in [Si] content. During LD slag injection trial, hot metal [P] was increased by 0.01 unit (from 0.12 to 0.13 %).
The invention was further followed up based on the following non-limiting exemplary illustrations as discussed hereunder:
Example 1: Chemical and Size Analysis of LD Slag
Non-metallic BOF/LD slag samples were collected from the slag yard. The chemical analysis of the BOF slags of different size fractions were evaluated using X-ray fluorescence spectrometer. The estimated average composition is shown in Table 1. It was observed that the (CaO+MgO) content is ~52% and Fe (T) of ~20%.
Table 1: Chemical composition of LD slag (%)
Fe(t) CaO Fe2O3 FeO SiO2 MgO Al2O3 P2O5 MnO SO3 TiO2 Na2O K2O
20.83 43.4 7.23 20.28 11.96 8.82 3.86 1.03 1.61 0.59 0.57 0.49 0.04

The as received sample was taken for size analysis and it was observed that the ~20% of the LD slag are less than 1mm as in Figure 1. Only 2.6% of non-metallic LD slag is of 0.075 mm.
To inject LD slag together with PCI Coal, the 0.075 mm sized material should be at least 80 %. The present invention relates to a process for producing hot metal in blast furnace by injecting non-metallic LD slag in blast furnace through selective crushing and optimized blending with coal powder. This process results in 0.075 mm sized material more than 80 % for the final mixed material (coal and LD slag).

Example 2: Injection of LD slag along with pulverised coal through tuyeres.
The external mixing of non-metallic LD slag with coal for pulverised coal injection (PCI) line were done by forming the heap before it is fed into the grinding mill in a desired proportion. Non-metallic LD slag was added together with PCI Coal injection port with nitrogen/air as a carrier gas. The LD slag was ground with PCI coal and the mix was injected together. The proportion of PCI to LD slag is 93:07.
LD slag injection increases the tuyere slag basicity (B2) and final BF slag basicity (B2), which results in decreased melting start and melting end temperature.
Example 3: Trial results
From the trial results as shown in Table 2, it is observed that with addition of LD slag at 14.91 kg/thm, the hot metal silicon content dropped by 0.10 unit (from 0.64% to 0.54%). The fuel rate was decreased by 0.9 kg/thm (from 555.1 to 554.2 kg/thm) because of the drop in [Si] content. During LD slag injection trial, hot metal [P] was increased by 0.01 unit (from 0.12 to 0.13 %).
Table 2: Trial results of LD slag injection in Blast Furnace
LD slag injection rate, kg/thm Fuel rate,
kg/thm [Si] in Hot metal,
% [P] in Hot metal,
%
0 555.1 0.64 0.120
0.68 555.1 0.64 0.121
2.38 555.0 0.62 0.123
3.45 554.9 0.62 0.122
6.59 554.7 0.61 0.124
6.71 554.7 0.62 0.124
8.19 554.6 0.60 0.125
8.95 554.6 0.59 0.126
11.89 554.4 0.55 0.127
12.66 554.3 0.55 0.128
14.91 554.2 0.54 0.130

Thus the present advancement provides for a process for producing hot metal in blast furnace involving non-metallic fraction of Linz-Donawitz (LD) slag along with pulverized coal by injecting through tuyere which bring about changes in slag basicity, viscosity and SiO generation ultimately helping in suppressing the [Si] conversion in hot metal by 0.10%. Moreover, the present advancement uses the LD slag for recovery of Fe, CaO and MgO from dumped LD Slag.
, Claims:We Claim:
1. A process for producing hot metal in blast furnace involving LD slag in a beneficial and environment friendly manner comprising:
step of operating blast furnace for generation of molten metal wherein the LD slag alongwith pulverised coal is injected into the blast furnace through tuyeres such as to attain beneficial changes selectively in at least any one of slag basicity, viscosity and SiO generation.

2. The process as claimed in claim 1 involving LD slag having composition (%) including:
Fe(t) CaO Fe2O3 FeO SiO2 MgO Al2O3 P2O5 MnO SO3 TiO2 Na2O K2O
18 to 23 preferably 20.83 30 to 52 preferably 43.4 5 to 10 preferably 7.23 18 to 28 preferably 20.28 6 to 20 preferably 11.96
4 to 15 preferably
8.82
2 to 7 preferably
3.86 0.8 to 2.0 preferably 1.03 1 to 2 preferably 1.61 0.4 to 0.8 preferably 0.59 0.2 to 1.0 preferably 0.57 0.01 to 0.80 preferably 0.49 0.01 to 0.20 preferably 0.04

and wherein the said step of LD slag injection alongwith pulverised coal is controlled to provide for beneficial changes in slag basicity from 0.03 to 0.08 preferably 0.04; viscosity from 0.15 to 0.50 poise preferably 0.25 poise and SiO generation from 2.5 to 5.0 kg/thm preferably 3.4 kg/thm.

3. The process as claimed in anyone of claims 1 or 2 which is preferably carried out involving ~20% of the LD slag having a size less than 1mm and 2.6% of LD slag having size of 0.075 mm.

4. The process as claimed in anyone of claims 1 to 3 wherein said step of LD slag injection is carried out involving LD slag injection through tuyeres in blast furnace include selective crushing and optimized blending with coal powder such as to attain preferably more than 80% of the 0.075 mm sized material.

5. The process as claimed in anyone of claims 1 to 4 wherein said step of LD slag injection is carried out involving LD slag injection through tuyeres at the rate of 5 to 25 kg/thm preferably about 15 kg/thm, such that the tuyere slag basicity (B2) increased from 0.01 to 0.30.

6. The process as claimed in anyone of claims 1 to 5 wherein said step of LD slag injection is carried out involving LD slag injection through tuyeres selectively such as to control the final slag basicity (B2) got increased by 0.04 (from 1.00 to 1.04).

7. The process as claimed in anyone of claims 1 to 6 wherein said step of LD slag injection is carried out involving LD slag injection through tuyeres at the rate of 5 to 25 kg/thm preferably about 15 kg/thm such that slag viscosity was decreased by 0.25 poise (from 5.32 to 5.07 poise at 1450 °C), which ensures better slag drainage.

8. The process as claimed in anyone of claims 1 to 7 wherein said step of LD slag injection is carried out involving LD slag injection through tuyeres at the rate of 5 to 25 kg/thm preferably about 15 kg/thm such that SiO(g) generation at tuyere level decrease by 3.4 kg/thm (from 17.8 to 14.4 kg/thm).

9. The process as claimed in anyone of claims 1 to 8 wherein said step of LD slag injection is carried out involving LD slag injection through tuyeres at the rate of 5 to 25 kg/thm preferably about 14.91 kg/thm the hot metal silicon content dropped by 0.10 unit (from 0.64% to 0.54%), the fuel rate was decreased by 0.9 kg/thm (from 555.1 to 554.2 kg/thm) as a result of the drop in [Si] content and hot metal [P] increased by 0.01 unit (from 0.12 to 0.13 %).

10. The process as claimed in anyone of claims 1 to 9 wherein injection of LD slag along with pulverised coal through tuyeres comprises of:
(iii) External mixing of non-metallic LD slag with coal for pulverised coal injection (PCI) line by forming a heap before it is fed into the grinding mill in a desired proportion;
(iv) Addition of non-metallic LD slag together with PCI Coal injection port with nitrogen/air as a carrier gas.

11. The process as claimed in anyone of claims 1 to 10 wherein the proportion of PCI to LD slag is 93:07.

Dated this 26th Day of September, 2023. Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent & Advocate)
IN/PA-199