Particle Conditioning for Improving Blockage Resistance of Denitration Catalysts in Sintering Flue Gas
, Can Zhou 1, Linghong Chen 1, Yang Yang 1, Zhengda Yang 2,*, Yifan Wang 1 and Chenghang Zheng 1,*
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Authors,
reviewing manuscript examines the morphology and size of sintered fly ash to ascertain the catalyst blockage causes. Long-term field tests under authentic flue gas conditions were then conducted to validate the effectiveness of the particle conditioning strategy in mitigating catalyst blockage, ensuring efficient and stable operation of sintering flue gas SCR systems.
The main disadvantage of the manuscript is insufficient description of the conditioner (SEM images, Particle size distribution) and conditioning process. How does gas flow move throw the powdered conditioner layer?
The behavior of mechanical mixture of the conditioner and fly ash powder may differ principally from that in gas flow.
Several remarks are listed below
1. Please, make numbering of Fig.1b and clarify it.
Line 99, Eq.(1). N2O or Na2O?
Line 186. the primary constituents of all fly ashes are alkaline oxides, including K2O, Fe2O3, Na2O, CaO, and MgO. Is Fe2O3 the alkaline oxides or basic one?
Line 217. The results show that the RF values of the 12 tested fly ash samples have a strong correlation with the alkali-acid ratio. Is RF calculated by Eq. (1)? What is the differences between RF and the alkali-acid ratio?
Line 225 . Consequently, a preliminary laboratory study was performed, examining the effects of adding an alkali-based conditioner (commercial calcium carbonate powders) to sintered fly ash.
Line 72-73. To address this, we proposed particle conditioning using calcium carbonate powders as conditioner, which significantly improved particle collection efficiency under certain conditions [18]. Please, compare the data [18] and the results of this paper, Lines 225 and so on.
Line 232. The shade intensifies when iron oxidizes to form Fe2O3 (hematite). Increasing calcium carbonate powders loading results in decolorization of the mixture due to Ca-Fe oxides interaction.
Figure 5b. Without conditioner (at a 1:0 ratio), sintered fly ash forms noticeable agglomerates. However, upon conditioner addition, fly ash particles disperse, preventing the formation of large granules and resulting in a reduced particle size. As conditioner concentration rises, particle size diminishes further, and tendencies for agglomeration and slab formation are curtailed. These findings suggest that in the mixtures of conditioner and fly ash, the conditioner crucially serves to isolate and physically modify the fly ash particles.
But, I see in the Fig.5b an opposite dependence of increasing agglomerates while conditioner concentration rises.
Best regards.
Author Response
Response to Reviewer1’s Comments
Comment 1: Please, make numbering of Fig.1b and clarify it.
Response: Thank you for pointing this out. We have corrected the numbering of Fig. 1b and ensure that it is clearly labeled in the revised manuscript.
Comment 2: Line 99, Eq.(1). N2O or Na2O?
Response: We appreciate your attention to detail. The correct notation should be Na2O. We have revised this in the manuscript.
Comment 3: Line 186. The primary constituents of all fly ashes are alkaline oxides, including K2O, Fe2O3, Na2O, CaO, and MgO. Is Fe2O3 the alkaline oxides or basic one?
Response: Thank you for your professional comments. Fe2O3 is not an alkaline oxide; it is an iron oxide and should be categorized differently. We have amended this in the manuscript to accurately reflect the nature of Fe2O3.
Comment 4: Line 217. The results show that the RF values of the 12 tested fly ash samples have a strong correlation with the alkali-acid ratio. Is RF calculated by Eq. (1)? What is the difference between RF and the alkali-acid ratio?
Response: Thank you for your comments. RF is indeed calculated using Eq. (1). We will clarify in the revised manuscript that RF is a measure derived from the alkali-acid ratio but includes additional parameters that account for specific interactions between the fly ash components and the conditioning process. We will elaborate on these differences in the section of experimental methods.
Comment 5: Line 225. Consequently, a preliminary laboratory study was performed, examining the effects of adding an alkali-based conditioner (commercial calcium carbonate powders) to sintered fly ash. Line 72-73. To address this, we proposed particle conditioning using calcium carbonate powders as conditioner, which significantly improved particle collection efficiency under certain conditions [18]. Please, compare the data [18] and the results of this paper, Lines 225 and so on.
Response: Thank you for your comment. The present work indeed employs calcium carbonate powders to enhance the blockage resistance of denitration catalysts, a method conceptually similar to previous research. However, there are notable differences between the work and the referenced study. The earlier research focused on electrostatic precipitators and evaluated the effectiveness of calcium carbonate in reducing fly ash accumulation on collection plates, using particle collection efficiency as the metric. In contrast, our study evaluates the performance through catalyst pressure drop measurements. Given these differences in experimental setup and evaluation criteria, a direct comparison between the studies is not applicable.
Comment 6: Line 232. The shade intensifies when iron oxidizes to form Fe2O3 (hematite). Increasing calcium carbonate powders loading results in decolorization of the mixture due to Ca-Fe oxides interaction.
Response: Thank you for your professional comments. Figure 5a illustrates that increasing calcium carbonate powders loading results in decolorization of the mixture due to Ca-Fe oxides interaction. We have added this to ensure the explanation of the color change and the interaction between calcium carbonate and iron oxides is clear and accurate. This includes providing a more detailed discussion on the chemical interactions responsible for the observed color changes.
Comment 7: Figure 5b. Without conditioner (at a 1:0 ratio), sintered fly ash forms noticeable agglomerates. However, upon conditioner addition, fly ash particles disperse, preventing the formation of large granules and resulting in a reduced particle size. As conditioner concentration rises, particle size diminishes further, and tendencies for agglomeration and slab formation are curtailed. These findings suggest that in the mixtures of conditioner and fly ash, the conditioner crucially serves to isolate and physically modify the fly ash particles. But, I see in the Fig.5b an opposite dependence of increasing agglomerates while conditioner concentration rises.
Response: Thank you very much for your insightful comment. After carefully reviewing Figure 5, we realized that there was an error in the arrangement of the electron microscope images in Figure 5b. This error led to the discrepancy between the observed results and our description. We have corrected this issue in the revised manuscript. We also appreciate the additional feedback from other reviewers regarding Figure 5 and have made the necessary adjustments. We are grateful for your valuable input and sincerely apologize for any confusion caused.
Reviewer 2 Report
Comments and Suggestions for AuthorsTitle: Particle Conditioning for Improving Blockage Resistance of Denitration Catalysts in Sintering Flue Gas
The potential for blockage compromises the stability and safety of selective catalytic reduction (SCR) systems within the catalyst structure due to the accumulation of fly ash. This paper proposes to improve the blockage resistance of denitration catalysts for sintered fly ash through particle conditioning.
Improvement Suggestions:
The introduction section should be expanded. Few sources have been used. The introduction should be strengthened with up-to-date references. In addition, in the introduction, it should be emphasized which gap this study fills in the literature.
The instruments and software utilized for experimental data collection and analysis should be covered in great detail.
It would be good to give brief information about the given pictures in the previous paragraph. The given graphics need to be interpreted in more detail.
In the discussion section, a more detailed discussion should be made about the compatibility of the experimental findings with the studies in the literature and how they support, contradict or extend them.
There are English errors in the text. It should be checked thoroughly.
Figure 1 and Figure 2 images should be enlarged.
Comments on the Quality of English LanguageThere are English errors in the text. It should be checked thoroughly
Author Response
Response to Reviewer2’s Comments
- The introduction section should be expanded. Few sources have been used. The introduction should be strengthened with up-to-date references. In addition, in the introduction, it should be emphasized which gap this study fills in the literature.
Response: Thank you for your valuable comment. We have expanded the introduction to include more recent references and clearly state the gaps in the literature that this study addresses. This will provide better context for our research and its contributions.
- The instruments and software utilized for experimental data collection and analysis should be covered in great detail.
Response: Thank you for your suggestion. We have provided more detailed descriptions of the instruments and software used for data collection and analysis in the methodology section to ensure transparency and reproducibility of our experimental procedures.
- It would be good to give brief information about the given pictures in the previous paragraph. The given graphics need to be interpreted in more detail.
Response: Thank you for your suggestion. We have included brief descriptions and interpretations of the images provided in the figures. This will help readers understand the significance of the graphics and how they relate to the experimental results.
- In the discussion section, a more detailed discussion should be made about the compatibility of the experimental findings with the studies in the literature and how they support, contradict, or extend them.
Response: Thank you for your suggestion. We have enhanced the discussion section by providing a more comprehensive comparison of our findings with existing literature. This will include how our results align with, differ from, or build upon previous studies.
- There are English errors in the text. It should be checked thoroughly.
Response: Thank you for your suggestion. We will conduct a thorough review of the manuscript to correct any grammatical or typographical errors. We may also consider having the manuscript professionally edited to ensure clarity and correctness.
- Figure 1 and Figure 2 images should be enlarged.
Response: Thank you for your suggestion. We have enlarged Figures 1 and 2 to improve readability and ensure that all details are clearly visible.
Thank you for your constructive comments and suggestions. We are confident that addressing these points will significantly improve the quality of our manuscript. We have revised the manuscript accordingly and resubmit it for further review.
Reviewer 3 Report
Comments and Suggestions for AuthorsCatalysts-3168352
The manuscript entitled "Particle Conditioning for Improving Blockage Resistance of Denitration Catalysts in Sintering Flue Gas" which focused on improve the blockage resistance of denitration catalysts for sintered fly ash through particle conditioning. The quality and novelty of work is appreciable and yet it requires many rectifications and modifications at several places. I recommend considering this study for publication after a major revision based on my comments and understanding. The comments and queries are listed below for your reference:
1.) Page 1, Line 17:
Why does sintered fly ash remain non-agglomerated at room temperature but form clumps at higher temperatures?
2.) Page 1, Line 19:
How does blockage in the catalyst not affect its performance in the field?
3.) Page 3, Line 105:
What is the reason of used alkali-based absorbents with sintered fly ash?
4.) Page 4:
How do particle size and surface area impact your experimental results? Please provide the specific surface area values.
5.) Page 7, Line 206:
How do the ratios of silicon to aluminium, acid to base, silicon, and iron to calcium influence the ash’s fusion and slagging properties?
6.) Figure 5a:
What impact does heating the mixture of sintered fly ash and conditioner have on the experimental results?
7.) Page 3, Line 113:
How can you confirm that the adsorbent is effectively mixed with the fly ash? Characterizations are required.
8.) Figure 5a:
Specify the y-axis label in Figure 5a and include the missing value of --: 0.5 on the y-axis. Also, ensure that the text size for "ambient temperature" in panels a and c is consistent.
9.) Figure 5b:
Include the names of the samples in the SEM morphology characterization.
10.) Figure 4:
Correct the notation of all oxide materials from Fe2O3 to Fe2O3 in fig 4
11.) Figure 2:
Please arrange the images in Figure 2 in the correct order, from fly ash 4 to 5.
12.) Page 3, Line 155:
In this study, the SEM was used to analyse the morphology of various sintered fly ashes labelled as fly ash I–IV. What does "fly ash I–IV" signify?
13.) Line 155 and Figure 2:
Ensure the notation in line 155 matches the notation in Figure 2 for consistency.
14.) Figure 4:
Mention the pore size of fly ash IV and V in Figure 4.
It is strictly recommended to spell check the manuscript as many errors have been noticed.
Comments on the Quality of English Language
Average
Author Response
Response to Reviewer3’s Comments
Comment 1: Page 1, Line 17: Why does sintered fly ash remain non-agglomerated at room temperature but form clumps at higher temperatures?
Response: At room temperature, the sintered fly ash particles have lower thermal energy, leading to less adhesion and agglomeration. At higher temperatures, increased thermal energy can cause partial melting or softening of the particles, leading to agglomeration due to enhanced particle-particle interactions. The scanning electron microscope results of the fly ash also indicate that, compared to before heating, the surface morphology of the fly ash changes after heating. The fibrous structures on the particle surfaces exhibit a partial melting or softening phenomenon.
Comment 2: Page 1, Line 19: How does blockage in the catalyst not affect its performance in the field?
Response: The deposition of fly ashes over the honeycomb walls was recognized as the major cause of performance loss [1]. However, when a blockage occurs primarily in the flow area of the catalyst's honeycomb pores, the impact on the microstructure of the catalyst's pores is minimal. As a result, gas molecules can still diffuse into the catalyst pores and undergo the necessary reactions, which is why the catalytic denitrification performance shown in Figure 6b remains largely unaffected. Catalyst poisoning and deactivation may need sufficient interaction time.
[1] A. Lanza, N. Usberti, P. Forzatti, A. Beretta, Kinetic and Mass Transfer Effects of Fly Ash Deposition on the Performance of SCR Monoliths: A Study in Microslab Reactor, Industrial & Engineering Chemistry Research, 60 (2021) 6742-6752.
Comment 3: Page 3, Line 105: What is the reason for using alkali-based absorbents with sintered fly ash?
Response: Thank you for your comment. As introduced in the introduction section, the selection of alkali-based absorbents was inspired by our previous research on enhancing the performance of electrostatic precipitators through particle conditioning. In that earlier work, we found that the adhesiveness of fly ash led to a decline in the efficiency of electrostatic precipitators. However, by using alkali-based absorbents, we were able to significantly improve dust removal performance. Motivated by this success, we decided to explore a similar approach to improve the anti-blocking performance of catalysts. However, research in this specific area remains limited.
Comment 4: Page 4: How do particle size and surface area impact your experimental results? Please provide the specific surface area values.
Response: Thank you for your comment. Particle size and surface area significantly impact the conditioning process and effectiveness. Smaller particles have a higher surface area, which can enhance the interaction with the conditioner. Based on the particle size range in Figure 3, the corresponding specific surface area is estimated to vary from about 0.05 m²/g to 10 m²/g.
Comment 5: Page 7, Line 206: How do the ratios of silicon to aluminium, acid to base, silicon, and iron to calcium influence the ash’s fusion and slagging properties?
Response: Thank you for your comment. Currently, there are certain studies on the impact of the components of coal ash, biomass ash, and coal gas fly ash on ash fusion. The ratios of these components influence the melting point and slagging behavior of the fly ash. Higher ratios of silicon to aluminum typically increase the melting point, while the acid-to-base ratio affects the slagging tendency.
Comment 6: Figure 5a: What impact does heating the mixture of sintered fly ash and conditioner have on the experimental results?
Response: Thank you for your comment. Figure 5a reveals that with rising heating temperatures, the fly ash sample's hue progressively darkens. The shade intensifies when iron oxidizes to form Fe2O3 (hematite). Increasing calcium carbonate powders loading results in decolorization of the mixture due to Ca-Fe oxides interaction as reviewer 1 suggested. Notably, fly ash samples without conditioner exhibited significant agglomeration during heating. Conversely, samples mixed with conditioner had diminished agglomeration, and the agglomeration phenomena was further suppressed as more conditioner was introduced. This variation is believed to improve the
Comment 7: Page 3, Line 113: How can you confirm that the adsorbent is effectively mixed with the fly ash? Characterizations are required.
Response: Thank you for your comment. In the laboratory, we mixed fly ash and the conditioning agent in different ratios, using both vibration and mechanical stirring methods until a uniform mixture was visually observed. To further confirm the effective mixing of the adsorbent with the fly ash, we performed morphological analysis of the mixed samples using scanning electron microscopy (SEM). The results, shown in Figure 5a, clearly demonstrate that the adsorbent was evenly distributed within the fly ash.
Comment 8: Figure 5a: Specify the y-axis label in Figure 5a and include the missing value of --: 0.5 on the y-axis. Also, ensure that the text size for "ambient temperature" in panels a and c is consistent.
Response: Thank you for your helpful suggestion. the y-axis label in Figure 5a is “ratio of fly ash to conditioner”. The missing value of --: 0.5 on the y-axis is 1, and it should be expressed as 1:0.5. The text size for "ambient temperature" in panels a and c has been revised to keep consistent. The revised Figure 5 is presented as follows. Thank you again for pointing these errors, which are valuable for improving the manuscript quality.
Comment 9: Figure 5b: Include the names of the samples in the SEM morphology characterization.
Response: Thank you for your suggestion. All fly ash samples used in the tests shown in Figure 5, including the SEM characterization, correspond to "Fly ash III" as referenced in Figures 2 and 3. Based on your recommendation, we have added a description of the fly ash sample names in the main text for clarity.
Comment 10: Figure 4: Correct the notation of all oxide materials from Fe2O3 to Fe2O3 in fig 4.
Response: Thank you for your suggestion. We have carefully reviewed the notation of all metal oxides in Figure 4 and corrected the subscripts, ensuring consistency and accuracy for materials such as Fe₂O₃.
Comment 11: Figure 2: Please arrange the images in Figure 2 in the correct order, from fly ash 4 to 5.
Response: Thank you for your suggestion. We have rearranged the images in Figure 2 as requested and ensure they are presented in the correct order.
Comment 12: Page 3, Line 155: In this study, the SEM was used to analyse the morphology of various sintered fly ashes labelled as fly ash I–IV. What does "fly ash I–IV" signify?
Response: Thank you for your comment. First, in line with your previous suggestion, we have corrected the notation from "fly ash I–IV" to "fly ash I–V" in the manuscript. Second, "fly ash I–V" refers to fly ash samples collected from different sintering machines. We have clarified this in the revised manuscript as per your suggestion.
Comment 13: Line 155 and Figure 2: Ensure the notation in line 155 matches the notation in Figure 2 for consistency.
Response: Thank you for your suggestion. We have checked the notation in the main text and Figure 2, and make necessary corrections to align both.
Comment 14: Figure 4: Mention the pore size of fly ash IV and V in Figure 4.
Response: Thank you for your valuable comment. In this study, our primary focus was on the influence of the composition and particle size distribution of the fly ash on its adhesiveness, as these factors are known to play a dominant role in adhesion behavior. By contrast, the pore size of fly ash is typically correlated to the gas diffusion and absorption characteristics. Therefore, we did not perform a detailed pore size analysis for fly ash samples IV and V.
Additional Comment: It is strictly recommended to spell check the manuscript as many errors have been noticed.
Response: Thank you for your suggestion. We have conducted a thorough spell check and proofreading of the manuscript to correct any errors and improve overall readability.
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsAccept
