Effect of the Injection Structure on Gas Velocity Distribution in a 3D Vertical Oven

Round 1

Reviewer 1 Report

1.      The model validation should be a separate subtopic after the discussion; from your section 3 go straight to the result.  Section 3.1 should be move to the last section of the manuscript and replaced it with section 3.2.

2.      Minor editing of English language is required.

Minor editing of English language is required

Author Response

y appreciate all the comments from the reviewers. The reviewers are very professional in the field of the cohesive particle flow. The comments let the authors reexamine the English grammar and figures in this paper for improving the writing and correcting the errors. The authors have taken into account of the comments and make the possible modifications, and these modifications have reflected in the revised manuscript as well as in the following reply.

 

Reviewer 1

1. The model validation should be a separate subtopic after the discussion; from your section 3 go straight to the result. Section 3.1 should be move to the last section of the manuscript and replaced it with section 3.2.

Reply:

Thanks for the suggestions. The author regulated the model validation section. The section was titled as a separate subtopic after the discussion.

2. Minor editing of English language is required.

Reply: Thanks for the suggestions. The authors revised the English language and marked in red color.

Author Response File: Author Response.pdf

Reviewer 2 Report

The article fits the journal and the only part that I would improve would be the introduction. For example, there is a need to add references from a broder point of view:

- Chen, H., Chen, Y., Hsieh, H.T. and Siegel, N., 2007. Computational fluid dynamics modeling of gas-particle flow within a solid-particle solar receiver.

- Roussel, N., Geiker, M.R., Dufour, F., Thrane, L.N. and Szabo, P., 2007. Computational modeling of concrete flow: General overview. Cement and Concrete research, 37(9), pp.1298-1307.

- Mathiesen, V., Solberg, T., Arastoopour, H. and Hjertager, B.H., 1999. Experimental and computational study of multiphase gas/particle flow in a CFB riser. AIChE journal, 45(12), pp.2503-2518.

- Baldelli, A., Esmeryan, K.D. and Popovicheva, O., 2021. Turning a negative into a positive: Trends, guidelines and challenges of developing multifunctional non-wettable coatings based on industrial soot wastes. Fuel, 301, p.121068.

- 

Good

Author Response

Reply:

Thanks for the suggestions. The author modified the introduction section and added the application of CFD technology to improve the industry design. The revised section is shown below,

“In literature, CFD provides powerful too for assisting industrial design and equipment development. Chen et al.[13] simulated gas-particle solar receiver and investigated the effect of bottom opening on heat efficiency. Mathiesen et al.[14] presented a computational fluid dynamics CFD multiphase gas solid model for a CFB Riser. Roussel [15] summarized the computed technology for modeling concrete flow. Baldelli et al. [16] think Density-functional theory (DFT) simulation method can be applied in developing non-wettable coatings. Yousefian and Pimputkar [17] used CFD techniques to determine fluid transport phenomena for design the metal organic chemical vapor deposition reactor. Guo et al. [18] applied CFD-DPM method to optimize a powder mixer. The application of CFD technology to investigate the basic gas-solid flow characteristics with the vertical oven is promising to find out a effective way to solve the industry problems.”

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper investigates the gas-solid flow characteristics in a vertical oven used for blue-coke production. Different gas injection structures are studied to improve the gas velocity distribution. A 3D physical model of a vertical oven unit is developed. The model has 3 zones - upper, conical and lower. The lower zone has rectangular gas injection orifices in 1, 2 or 3 layers. Numerical simulations using a Eulerian-Eulerian model are conducted to analyze the effect of injection layers, coal size, gas velocity and angle on the gas distribution.

Key parameters like solid fraction standard deviation, gas velocity mixing entropy and standard deviation are calculated to quantify the distribution. Using 2 injection layers gives a more uniform gas flow compared to 1 or 3 layers. The gas injection length decreases with more layers due to reduced inlet velocity.

Smaller coal particles of 6-15 mm increase the bed resistance and solid fraction deviation, making the gas distribution uneven. Increasing the inlet gas velocity increases the velocity in the vertical direction but does not affect distribution uniformity significantly. A gas injection angle of 45° is better than 90° to increase gas velocity in the upper zone and improve distribution uniformity.

In summary, the number of injection layers and coal size have a significant effect on the gas distribution in a vertical oven. The insights can help optimize the design and operation for improved performance.

I think the topic addressed in this paper is highly original and relevant in the field of coal pyrolysis and blue-coke production.

The conclusions presented in the paper are consistent with the evidence and arguments made in the results and discussion sections. The conclusions effectively address the main research question on optimizing gas injection structures to improve velocity distribution.

The references cited in the paper are appropriate and adequately support the work presented. The number of references seems reasonable - not too few or too many.

Overall, the tables and figures presented in the paper are appropriate and enhance the understanding of the work. The figures are well designed, informative, and aid the comprehension of the results.

The English usage in the paper is overall correct, clear, and readable.

This is an excellent paper investigating an important issue in vertical oven design for blue-coke production. The numerical modeling of the gas-solid flow patterns and distribution analysis provides novel insights into optimizing the gas injection structures. The work addresses a clear research gap with practical relevance.

Here are some suggestions for improving this research paper:

 Experimental validation:

The numerical model should be validated more extensively with experimental data over a wider range of operating conditions. Only limited validation is presented based on wall temperature mapping.

Pressure drop validation uses a empirical correlation. Direct measurement of pressure gradients at different heights would be better.

Particle image velocimetry (PIV) measurements could directly quantify the gas velocity distribution and validate the trends observed in simulation.

 

Modeling:

The paper assumes mono-sized coal particles for simplicity. Using a size distribution may give more realistic results.

Inter-particle cohesive forces are not considered currently. Incorporating cohesion could improve simulation accuracy.

The effect of coal moisture content on gas flow is not studied. This may be an important parameter.

Radiative heat transfer modeling can provide better temperature prediction.

 Analysis:

    The paper focuses on velocity distribution. Analyzing species concentration distribution will also provide useful insights.

    Operational parameters like coal feed rate, moisture, volatile matter and reactor temperature can be explored.

    A broader parametric study analyzing interactions between variables could better establish operating maps.

    In summary, more rigorous validation, incorporating additional physics in the model, expanding the parametric study and adding techno-economic analysis can significantly strengthen the paper.

Please, improve readability by organizing the content better, reducing repetitive statements, adding more explanatory text for figures/tables, and thoroughly proofreading the language.

     The topic addressed in this paper relevant in the field of coal pyrolysis and blue-coke production. In this connection, I suggest authors to explain and establish connection of this research topic with thematic area of the Coatings journal. Coatings publishes research on technologies related to surface coatings and films.

 The list of references should be meticulously formatted to align with the specific requirements outlined by the journal Coatings.

        I hope these recommendations are helpful for the authors.

Comments for author File: Comments.pdf

Author Response

Reply to Reviewers

First of all, the authors greatly appreciate all the comments from the reviewers. The reviewers are very professional in the field of the cohesive particle flow. The comments let the authors reexamine the English grammar and figures in this paper for improving the writing and correcting the errors. The authors have taken into account of the comments and make the possible modifications, and these modifications have reflected in the revised manuscript as well as in the following reply.

 

Reviwer 3

The paper investigates the gas-solid flow characteristics in a vertical oven used for blue-coke production. Different gas injection structures are studied to improve the gas velocity distribution. A 3D physical model of a vertical oven unit is developed. The model has 3 zones - upper, conical and lower. The lower zone has rectangular gas injection orifices in 1, 2 or 3 layers. Numerical simulations using a Eulerian-Eulerian model are conducted to analyze the effect of injection layers, coal size, gas velocity and angle on the gas distribution.

Key parameters like solid fraction standard deviation, gas velocity mixing entropy and standard deviation are calculated to quantify the distribution. Using 2 injection layers gives a more uniform gas flow compared to 1 or 3 layers. The gas injection length decreases with more layers due to reduced inlet velocity.

Smaller coal particles of 6-15 mm increase the bed resistance and solid fraction deviation, making the gas distribution uneven. Increasing the inlet gas velocity increases the velocity in the vertical direction but does not affect distribution uniformity significantly. A gas injection angle of 45° is better than 90° to increase gas velocity in the upper zone and improve distribution uniformity.

In summary, the number of injection layers and coal size have a significant effect on the gas distribution in a vertical oven. The insights can help optimize the design and operation for improved performance.

I think the topic addressed in this paper is highly original and relevant in the field of coal pyrolysis and blue-coke production.

The conclusions presented in the paper are consistent with the evidence and arguments made in the results and discussion sections. The conclusions effectively address the main research question on optimizing gas injection structures to improve velocity distribution.

The references cited in the paper are appropriate and adequately support the work presented. The number of references seems reasonable - not too few or too many.

Overall, the tables and figures presented in the paper are appropriate and enhance the understanding of the work. The figures are well designed, informative, and aid the comprehension of the results.

The English usage in the paper is overall correct, clear, and readable.

This is an excellent paper investigating an important issue in vertical oven design for blue-coke production. The numerical modeling of the gas-solid flow patterns and distribution analysis provides novel insights into optimizing the gas injection structures. The work addresses a clear research gap with practical relevance.

Here are some suggestions for improving this research paper:

 Experimental validation:

1. The numerical model should be validated more extensively with experimental data over a wider range of operating conditions. Only limited validation is presented based on wall temperature mapping.Pressure drop validation uses a empirical correlation. Direct measurement of pressure gradients at different heights would be better. Particle image velocimetry (PIV) measurements could directly quantify the gas velocity distribution and validate the trends observed in simulation.

Reply:

Thanks for the suggestions. The model validation is important for a numerical investigation work. In this work, we compared the experimentally measured pressure drop with the simulation data, as shown in Fig. 4. The data of pressure drop was measured within the gas superficial velocity range of 0.1 to 0.3 . We used three pressure differential sensors to record the bed pressure drop data along the bed height. Pitifully, the measurements is not be introduced when illustrating the experimental setup. In the revised manuscript, we introduce the pressure drop measurements, which is shown as below.

“Three pressure differential sensors were applied to measured the bed pressure drop. The location of the measurement points are shown in Fig. 3 ”

Figure 4. Comparison of pressure drops obtained by simulations, experiments, and empirical correlations for two orifice layers: (a) effect of coal diameter, (b) effect of gas velocity ( = 4 mm)

We tried to use Particle image velocity (PIV) measurements to record the gas velocity distribution. However, the PIV is not successful. The present packed bed has very large bed width of 1m, the thickness of 0.1m and height of 2.0m.The strong sheet laser cannot penetrate the bed layer, which make it hard to record the gas velocity. It works only when the particles are fluidized by feeding a large mount of gas. So we can’t obtain the PIV data.

 

Modeling:

2. The paper assumes mono-sized coal particles for simplicity. Using a size distribution may give more realistic results.Inter-particle cohesive forces are not considered currently. Incorporating cohesion could improve simulation accuracy. The effect of coal moisture content on gas flow is not studied. This may be an important parameter. Radiative heat transfer modeling can provide better temperature prediction.

Reply:

Thanks for the professional suggestions. As the reviewer pointed out, the numerical simulation model used in this study has many limitations. The factors including coal particle distribution, cohesive force, moisture content and radiation model were not considered in the present work. The coal particle distribution is not easily be considered for the Euler-Euler multi-phase flow model used in this work. We plan to develop an Euler-Lagrangian model to consider this factor. The cohesive force is ignored due to the larger particle size. The authors have developed the cohesion drag model for gas-solid flow for much smaller particle in range of 10-50. The coal moisture and radiation model are important for modeling heat transfer and reaction. The authors will develop a more comprehensive model to consider the effect of heat and reaction.

 

 Analysis:

3. The paper focuses on velocity distribution. Analyzing species concentration distribution will also provide useful insights.Operational parameters like coal feed rate, moisture, volatile matter and reactor temperature can be explored. A broader parametric study analyzing interactions between variables could better establish operating maps.

Reply:

Thanks for the suggestions. This work focus on the effect of orifice and gas flow on the gas distribution. At present, the factors of moisture, volatile matter and reactor temperature were not be considered. We plan to further investigate the effect of these factors in future. Effect of coal feeding rate on the gas distribution is limited in the given conditions in the work. The results were added in the Supplementary materials. The figures were shown as below.

 

(a) Gas velocity vectors through in-central cross-section

 

(b) Gas velocity distribution near the gas orifice inlet and umbrella outlet

 

(c) Air fraction distribution

Fig. S6 Influence of coal feeding rate on gas distribution, (a) Gas velocity vectors through in-central cross-section, (b)Gas velocity distribution near the gas orifice inlet and umbrella outlet, (c) Air fraction distribution（t = 20s）= 30 mm, = 0.24 m/s

 

 

 

 

Fig. S7 Variation of gas velocity in Y direction with increasing bed height under the effect of coal feeding rate.

 

 

(a) Coal solid fraction standard deviation (b) Gas velocity standard deviation

 

(c) Gas velocity mixing entropy

Fig. S8 Influence of coal feeding rate on gas distribution in the pyrolysis zone (a) Coal solid fraction standard deviation, (b) Gas velocity standard deviation, (c) Gas velocity mixing entropy,  = 30 mm,  = 0.24 m/s

 

4. In summary, more rigorous validation, incorporating additional physics in the model, expanding the parametric study and adding techno-economic analysis can significantly strengthen the paper.

Reply:

Thanks for the suggestions. The authors presented the preliminary economic analysis in the revised manuscript. The section is written after the end of the discussion section. The  preliminary economic analysis is shown below,

 “5. Preliminary economic analysis

Due to the fact that the scope of work in this study mainly focuses on the evaluation and optimization of the vertical furnace intake method, and the device used in this study is a cold experimental device with a small scale, it is impossible to provide detailed information and cost-benefit analysis of the entire industrial process. Therefore, this study only conducted a preliminary economic analysis on the capital cost and potential income of the improved blue-coke vertical oven process compared to the conventional blue-coke vertical oven process.

Cost breakdown. The production cost of blue charcoal usually includes:

Raw coal washing and screening

Vertical oven and auxiliary equipment

Gas purification and air system

Tar recovery equipment

Power distribution and control system

Waste gas and wastewater treatment

Compared with conventional vertical oven, the improved blue-coke vertical oven only has some cost for improving the gas intake structure, and the cost for retrofitting a 1 million ton/year blue-coke vertical oven is about 600000 yuan, with no increase in operating costs. However, it should be considered that compared to before the optimization of the intake structure, the improved structure has a more uniform gas distribution, which is beneficial for improving the quality of the blue-coke. The improvement of the production quality will balance the renovation cost.

Potential income.

By optimizing the operating parameters of the blue-coke vertical oven (optimizing gas velocity) and changing the furnace inlet mode (adjusting the number and angle of inlet layers), the gas distribution during pyrolysis can be more uniform, and the technical indicators of blue carbon products can be improved to meet the sales quality standards. According to the calculation of a 1 million ton/year coal pyrolysis plant, when the qualification rate of blue carbon products increases by 3-5%, the annual output can increase by 30000 to 50000 tons. The current price of blue-coke is about 1000 yuan/ton. The price difference between qualified and defective blue-coke is about 200 yuan/ton. It is calculated that an annual profit increase of 6-10 million yuan can be achieved.

The current analysis of cost and benefit information is relatively limited, and not all potential costs and benefits have been evaluated. However, it is clear that the improvement of the gas intake method of the blue-coke vertical oven a significant product advantage and generates net benefits. This article analyzes the parameters that are conducive to finding the optimal structure and operation, laying the foundation for further and more detailed research in future work. ”

 

5. Please, improve readability by organizing the content better, reducing repetitive statements, adding more explanatory text for figures/tables, and thoroughly proofreading the language.

 

Reply:

Thanks for the suggestions. The authors improve the text throughout the manuscript. The revised word and sentences are marked in red color.

 

6. The topic addressed in this paper relevant in the field of coal pyrolysis and blue-coke production. In this connection, I suggest authors to explain and establish connection of this research topic with thematic area of the Coatings journal. Coatings publishes research on technologies related to surface coatings and films.

 

Reply:

Thanks for the suggestions. This manuscript is submitted the special issue of “Liquid-Fluid Interfaces and Dynamics”. The present work match the topic of this issue includes “Multiphase interface behaviors and Multiphase flow and wall interactions” of this special issue.

 

7. The list of references should be meticulously formatted to align with the specific requirements outlined by the journal Coatings.

 

Reply:

Thanks for the suggestions. The references have been carefully checked and revised.

 

8. I hope these recommendations are helpful for the authors.

Reply:

Finally, the authors would like to thank the reviewers for their professional comments. The comments will help the author deepen their understanding of the paper, improve its quality, and help us better participate in international peer communication.

Author Response File: Author Response.pdf