Feasibility Study of Bio-Sludge Hydrochar as Blast Furnace Injectant
Round 1
Reviewer 1 Report
In the manuscript, combustion behavior of hydrochar produced from biosludge and its blend with anthracite. The research topic is quite interesting. However, the concept of the study is inadequate. The analysis of fuels were not completely done and combustion behavior was not properly investigated. The main issue is about the feedstock which contains around 98.5 % water.
-The waste has very low dry matter which simply means low hydrochar yields. HTC process is conducted large volume of reactor however the amount of product (hydrochar) is very low. Moreover, high amount of energy will be waste for heating the water during HTC. The author should indicate whether HTC of this waste which contains only 1.5% dry matter is economically feasible.
-Section 3.3. Indicate the stages in graph.
-How was explosion performance calculated?
-Why were Na and K analysis of blends not conducted?
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The topic of the paper is very important now in the context of climate changes. The problem of quantity and quality of fuels in iron making and steelmaking processes is also discussed very often. During production of pig iron, a large amount of flues (mainly coke) is needed. So, replacement of it with cheaper types of fuel brings two kinds of benefits: economic and ecological. It is impossible to replace coke in 100% because it has many functions in the process (fuel, reducer, carburizer and a component ensuring adequate gas permeability). Using alternative fuels (mainly injection of alternative fuels) in the process has positive impact on the cost of the process, but also ecological importance: in such process some kind of waste can be used. So I think the topic of the work is adequate.
The structure of the paper is correct, and its quality is adequate. However, I have a few comments which should be taken into consideration by authors:- REFERENCES: in the text there are 38 references, but I think 9 of them are self-citations (1, 2, 7, 8, 24, 26, 29, 34, 35). It is over 23% of references. For me, it is too much.
- Page 1, lines 42-42: "for the metallurgical industry, using biomass resources as the main energy source". As I wrote earlier, the main fuel in blast furnace process is coke (in some devices it is charcoal). It is impossible to replace it in 100%. As I wrote earlier, the main fuel in blast furnace process is coke (in some devices it is charcoal). It is impossible to replace it in 100%. You can write in about alternative fuels. So, it is better to say that it can be sued as alternative source of energy. It can also be used in sintering process of iron ores.
- Problem with language. In the text, you use active voice (lines 184, 314, 317, 325, 331, 334). In such text you should use passive voice (was done, was made, was investigated).
- One small problem: page 10, line 351-354 "but the content of P was 415 times that of the anthracite coal". I think something is missing here.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Authors' response is quite satisfactory and can be accepted for publication. I suggest to add the description for explosion performance.
Author Response
Thank you for pointing this out. We added the method for determining the explosiveness of fuels to Section 2.2.
The explosiveness of the samples was measured by a fuel safety performance measurement device, a schematic diagram of which was included in our previous research [24]. Inject 1 g of fuel into a pipe with a heat source of 1050 °C and observe the return flame length of the fuel to determine the explosive characteristics of the sample.
