Melting–Dropping Property of Blast Furnace Charge on the Basis of Its Slag Formation Behavior

Round 1

Reviewer 1 Report

Comments for author File: Comments.pdf

Author Response

Note 1: You are talking about alternating layers of coke and metal-bearing charge. As I understand it with reference to Figure 2, this is a single metal-bearing layer covered with coke at the top and bottom. I recommend specifying the granulometry of the batch used and the geometry of the tested sample in figure 2.

All samples measured 8 mm to 12 mm in diameter and it is explained in the next paragraph.

Note 2: The sample designation in the figure needs to be corrected.

Corrected as crucible in figure 1.

Note 3: Please specify the design solution of the graphite crucible. How was the bottom of the crucible handled? And what about the empty spaces in the cup?

    For each test iron ore with a layer thickness of 160 mm was placed in a graphite crucible which inner diameter is 120mm, and there is a graphite gasket of the same size at the bottom on which samples can be placed, and there are 5mm holes evenly distributed on the graphite gasket, from which the drops will drop at high temperature..

Note 4: Cooling mode is missing here. Please complete the cooling phase.

Completed in figure 3.

Note 5: it would be appropriate to specify the type of equipment and the relevant standard according to which the test was performed.

The melting points of slag samples were measured by RDS-04 automatic slag melting point and melting rate tester (MPT), before MPT test the sample should machined to 3mm × 3mm cylindrical and dried for 24 hours under natural conditions, in the process of test, the heat rate should be controlled at 5-10℃/min and 3 tests for every sample.

Note 6: missing scale in image

Have remarked.

Note 7: please clarify pictures a, b, c.missing scale in image.

Have pointed in image.

Note 8&9: Image quality is poor The resolution needs to be increased.

    Picture modified.

Author Response File: Author Response.pdf

Reviewer 2 Report

I like this paper in general, but I also feel improvements can be made by addition of a few small(?) comments. I have tried to point out a few places in the manuscript where I feel such improvements can be made - see the attached file.

Comments for author File: Comments.pdf

Author Response

Note 1:Term should be defined/explained to readers not familiar with this.

In order to reveal the melting-dropping property of a charged blast furnace (BF) and the mechanism of its slag formation, such as the temperature interval of slag formation, the pressure drop during the reduction process, and the K value of each sample , the soft melt drop experiment was tested in a large-capacity melting-dropping furnace.

Note 2: Is the molten iron and slag collected continuously during the experiment? Nothing much is said later about the iron (and slag) that is "produced"; amounts, composition etc. would be of interest. Total mass balances for each experiment would also be interesting I guess.

Because the amount is not controlled, the collected is not continuously and after the  experiment it can be collected until the amount is enough to analysis.

Note 3: "Sample" is also used for the whole content of the sample holder in each experiment. I guess  you mean particle/pellet/lump or something like that here?

    Yes, in the experiment the particle of pellet/sinter/lump should be controlled between 8 to 12 mm.

Note 4: Based on the sketch with 10 mm coke layer the ore layer seems to be about 40 mm. According to the text the ore layer is 160 mm. What is the inner diameter of the sample holder?

the inner diameter of the sample holder is 120mm.

Note 5: Assuming air (79% N2 and 21% O2) in the blast 10.5 L/min N2 should give about 5.6 L/min CO. What is the linear velocity of the gas flow through the sample (diameter in comment above) compared to that in an industrial BF?

In this experiment the linear velocity of the gas flow through the sample is 1.33m3/m2, and in an industrial BF that is about (1-2)m3/m2.

Note 6: This is what I miss in note 1

Modified in the abstract.

Note 7: I assume a, b and c refer to some points on the picture, but I am not able to see those

Have remarked  in the picture.

Note 8: In physics and engineering, permeation (also called imbuing) is the penetration of a permeate (a fluid such as a liquid, gas, or vapor) through a solid. This is the only place in this manuscript where this word is used. Penetration is more or less the same as permeation.

Thanks, maybe the penetration is better for using in here, so it was modified.

Note 9: These results are all based on the melting-point tester (MPT) and this should be mentioned.

The melting points of slag samples were measured by RDS-04 automatic slag melting point and melting rate tester (MPT), before MPT test the sample should machined to 3mm × 3mm cylindrical and dried for 24 hours under natural conditions, in the process of test, the heat rate should be controlled at 5-10℃/min and 3 tests for every sample.

Note 10: Calculated liquid phase content and the percentage of the solid phase precipitated could also be shown as a fig 11 b here.

Because this is a theoretical calculation, the result is presented as point data rather than images, so there are only continuous images of point data.

Note 11: Have you considered drawing these phase diagrams with Al2O3 instead of MgO as key-variable? Diagrams, especially axis values, are not very readable, and all four diagrams look fairly identical.

OK, in my next work, i will try to draw these phase diagrams with Al2O3. In these phase diagrams, there are still differences in the high melting point area, which will directly affect the droplet characteristics. If there is a deviation greater than ten degrees, it will be very different for the blast furnace.

Note 12: Again the diagrams look fairly identical except for (d) where phase combination ① is replaced by ⑦, I am surprised that ④and ② can co-exist, I think  ① is necessary between those combinations.

Well, this is the simulation result.

Note 13: The conclusions are in line with the findings presented, but I feel it would be of interest to the readers to include some remarks relative to results presented in the cited literature.

Conclusions

This study evaluates the melting–dropping properties of single iron ores and four typical mixed BF charged with different proportions of lump ores and sinter basicity to explore the relationship between the melting–dropping property of the BF charge and its slag formation. The mechanisms underlying the change in melting–dropping property on the basis of slag formation are studied by SEM, XRD, XRF, and MPT in addition to using the FactSage thermodynamic software. The following conclusions are drawn:

A positive linear relationship exists between the melting behavior of slag and the melting–dropping property of the corresponding charge. Owing to their poor melting–dropping property, single iron ores are not suitable for BF production.

It is proposed that the effect is fundamentally dependent on the chemical , the mix charge can result in a concentration gradient of the chemical components at the contact interface, which can improve slag formation at high temperatures and enhance the melting–dropping property of the charging mix.

It is proposed that the self-softening and melting properties of the lump ores were dramatically improved by interaction between sinters and lump ores, the collocation pattern of lump ores and ratio between lump ores was optimized according to interaction. So the chemical component is the key factor causing the difference in slag formation behavior， an excessive amount of lump ore in the charging mix results in a mix charge with higher Al2O3 content, which causes SiO2 and Al2O3 in the slag to absorb O2– in order to generate (SiO4)4– and (AlO4)5–. In the CaO-SiO2-MgO-Al2O3-FeO slag system, this behavior is likely to form a high-fusion-point phase such as spinel.

Lump ores are easy to reduce at lower temperatures. The mix charge containing less lump ore retains more FeO, providing free-moving Fe2+ and O2– in the Si-O network. Al2O3 in slag absorbs O2– to generate (AlO6)5–. The main phases in the slag are feldspathic, causing variations in fluidity.

Author Response File: Author Response.pdf