Utilization of Palm Frond Waste as Fuel for Co-Firing Coal and Biomass in a Tangentially Pulverized Coal Boiler Using Computational Fluid Dynamic Analysis
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsI would like to reject this manuscript because the assumptions used in the CFD simulations are not convincing: (1) carbon atoms are not in mass balance in equation 20&21. (2) Assumed volatile compositions in equation 20&21 (e.g., H and O ratio) are far off from the ultimate analysis in table 2. (3) Authors use figure 5 to validate their CFD models which is not convincing at all. Particle size instead of "cell count" should be used as x-axis because "cell count" is not reflecting any meaningful property. Even though the simulated "FEGT" at a cell count of 7377426 is similar to actual FEGT, the other two data points are significantly differ from actual FEGT. If CFD model is applied to analyze flue gas compositions, CFD result must be validated with real composition measurements. (4) The reaction model including reaction parameters are gathered from multiple sources and not convincing. Authors should first clarify whether using air or pure oxygen for combustion. The air flow presented in table 3 is enough for complete combustion. So authors implication of incomplete combustion in equations 18-19 or table 1 (higher reaction rate for CO formation, lower reaction rate for CO2 formation) is not right. Even though biomass and coal has different volatile matter, the total carbon content is very similar is table 2. The reaction pathways for carbon are assumed the same for biomass or coal (i.e., either CO or CO2), so it is not convincing to see figure 13 that biomass combustion produces so much CO than coal. After all, the carbon of biomass is the same carbon as coal and the total carbon quantity is also very similar. Biomass has very diverse compositions so feedstock characterization is necessary. (5) The parameters used in mass/momentum/turbulence calculations etc. are not reported or distinguished between coal and biomass. (6) O2 is purely reactants and why the mass fraction increases in the combustion process. (7) Hydrothermal is not as common as pyrolysis or torrefaction for biomass pretreatment due to high pressure and high temperature usage and further energy is required to dry it.
Author Response
Title: Utilization of palm frond waste as fuel for co-firing coal and biomass in tangentially pulverized coal boiler using computational fluid dynamic analysis
Dear Editor,
Thanks to all the reviewers and editors for reviewing the manuscript. Also, the author especially appreciates the constructive comments, support, and contributions of the editor and reviewer that have helped improve the quality of the paper. Thank you for the opportunity to revise our paper. I have adopted most of the referees’ suggestions and believe the revised papers are substantially improved.
Reviewers’ comments on the manuscript:
Reviewer #1:
Comments (1): carbon atoms are not in mass balance in equation 20&21.
Response (1): The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower:
“The imbalance in combustion equations 20 and 21 against the material composition in Table 2 could be caused by differences in oxygen content, calorific value, and volatile matter between coal and HT-FRD” (page 7, lines 231 to 233)
Comments (2): Assumed volatile compositions in equation 20&21 (e.g., H and O ratio) are far off from the ultimate analysis in table 2.
Response (2): The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower:
“Equations 20 and 21 have been simplified to account for different chemical equation models and changes in molecule complexity. Chemical analysis typically provides a more comprehensive examination, whereas combustion equations commonly rely on average or representative values obtained from the fuel” (page 7, lines 244 to 247)
Comments (3): Authors use figure 5 to validate their CFD models which is not convincing at all. Particle size instead of "cell count" should be used as x-axis because "cell count" is not reflecting any meaningful property. Even though the simulated "FEGT" at a cell count of 7377426 is similar to actual FEGT, the other two data points are significantly differ from actual FEGT. If CFD model is applied to analyze flue gas compositions, CFD result must be validated with real composition measurements.
Response (3): The author would like to thank the reviewer for providing constructive comments. I have rewritten as follower:
“I have rewritten the validation for meshing with operational data from the original boiler with a temperature in the operational data of 1258.2 K” (page 11, lines 305 to 314), which can be seen in Figure 5 (page 11, lines 303) and table (page 11, lines 315)
Comments (4): The reaction model including reaction parameters are gathered from multiple sources and not convincing. Authors should first clarify whether using air or pure oxygen for combustion. The air flow presented in table 3 is enough for complete combustion. So authors implication of incomplete combustion in equations 18-19 or table 1 (higher reaction rate for CO formation, lower reaction rate for CO2 formation) is not right. Even though biomass and coal has different volatile matter, the total carbon content is very similar is table 2. The reaction pathways for carbon are assumed the same for biomass or coal (i.e., either CO or CO2), so it is not convincing to see figure 13 that biomass combustion produces so much CO than coal. After all, the carbon of biomass is the same carbon as coal and the total carbon quantity is also very similar. Biomass has very diverse compositions so feedstock characterization is necessary.
Response (4): The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower:
“Figure 13 shows that CO exhaust emissions increase with the addition of the HT-FRD mass ratio, this indicates that the combustion is less efficient, which is why some of the fuel is not completely burned in each zone. The different fuel characteristics of coal and oil palm fronds are one of the causes of combustion instability and incomplete combustion in co-firing. Including different residence times in the furnace to burn completely, oil palm fronds burn faster than coal. So that the combustion gas is not completely oxidized into CO2 before leaving the combustion zone, resulting in more CO” (page 16-17, lines 415 to 421)
Comments (5): The parameters used in mass/momentum/turbulence calculations etc. are not reported or distinguished between coal and biomass.
Response (5): The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower:
“In general, the computation of mass, momentum, turbulence, and radiation in coal and biomass relies on a common equation. However, the specific parameters and models employed must be tailored to the unique features of each material. Coal exhibits a greater density in comparison to biomass. Biomass exhibits greater complexity in terms of its variability and reactivity, whereas coal is comparatively more stable yet emits a higher quantity of pollutants that necessitate regulation” (page 6, lines 202 to 207)
Comments (6): O2 is purely reactants and why the mass fraction increases in the combustion process.
Response (6): The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower:
“The overall rise in the proportion of O2 during combustion is mostly attributed to the reduction in the amount of leftover fuel, resulting in a drop in combustion intensity and thus leaving a greater amount of O2 unused” (page 18, lines 440 to 443)
Comments (7): Hydrothermal is not as common as pyrolysis or torrefaction for biomass pretreatment due to high pressure and high temperature usage and further energy is required to dry it.
Response (7): The author would like to thank the reviewers for their constructive comments. I have made improvements and have rewritten as a follower:
“Nevertheless, the hydrothermal process presents various drawbacks that must be taken into account. These include substantial energy consumption, environmental repercussions stemming from energy utilization and residue management outcomes, as well as the intricate nature of the process, which involves chemical reactions that necessitate meticulous regulation of temperature, pressure, and time” (page 2, lines 74 to 79)
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper analyzed the co-firing of palm-related biomass with coal in a tangential-fired furnace. Overall, the paper structure is good. However, I recommend a major revision before publishing. Some of the comments are given below to be revised:
1. Please avoid using the abbreviation in the title (CFD).
2. The introduction part is written in a very scattered form. This needs to be deeply revised. The first paragraph is very lengthy and contains irrelevant information about the co-firing biomass with coal. The whole introduction should be rewritten in a more focused and concentrated way to the co-firing biomass with coal. There are many challenges in co-firing biomass in tangentially fired furnaces like particle size, milling, explosion risks, and so on. Literature related to these challenges should also be mentioned in the introduction.
3. The English writing required a lot of improvement. For example, lines 39, 40, and 41 are difficult to understand. Further see sentence 42 is not clear. What is meant by “fiber frequently produces electricity and steam?
4. In portion 2, the injection method is used for biomass in the furnace, however, it is not mentioned how the grinding or milling of biomass was done.
5. The information about meshing is missing. Which software (ICEM or Space Claim) is used for meshing? What is the quality of meshing? All this information should be given in Table form.
6. It is claimed that 5% is the most optimal ratio of biomass for co-firing with coal. It needs to be justified. The results from 15 and 25 are almost the same as in 5% co-firing, so why only 5% is chosen as the most optimal?
Comments on the Quality of English LanguageThe English writing required a lot of improvement. For example, lines 39, 40, and 41 are difficult to understand. Further see sentence 42 is not clear. What is meant by “fiber frequently produces electricity and steam?
Author Response
Title: Utilization of palm frond waste as fuel for co-firing coal and biomass in tangentially pulverized coal boiler using computational fluid dynamic analysis
Dear Editor,
Thanks to all the reviewers and editors for reviewing the manuscript. Also, the author especially appreciates the constructive comments, support, and contributions of the editor and reviewer that have helped improve the quality of the paper. Thank you for the opportunity to revise our paper. I have adopted most of the referees’ suggestions and believe the revised papers are substantially improved.
Reviewers’ comments on the manuscript:
Reviewer #2:
Comments 1: Please avoid using the abbreviation in the title (CFD).
Response 1: The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower:
“Utilization of palm frond waste as fuel for co-firing coal and biomass in tangentially pulverized coal boiler using computational fluid dynamic analysis” (page 1, lines 2 to 4)
Comments 2: The introduction part is written in a very scattered form. This needs to be deeply revised. The first paragraph is very lengthy and contains irrelevant information about the co-firing biomass with coal. The whole introduction should be rewritten in a more focused and concentrated way to the co-firing biomass with coal. There are many challenges in co-firing biomass in tangentially fired furnaces like particle size, milling, explosion risks, and so on. Literature related to these challenges should also be mentioned in the introduction.
Response 2: The author would like to thank the reviewer for providing constructive comments. I have rewritten as follower:
“All introductions” (pages 1-2, lines 28 to 92)
Comments 3: The English writing required a lot of improvement. For example, lines 39, 40, and 41 are difficult to understand. Further see sentence 42 is not clear. What is meant by “fiber frequently produces electricity and steam?
Response 3: The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower:
“Co-firing in boilers often involves the use of biomass fuel as a substitute fuel. Biomass co-firing is an economical approach to generating eco-friendly energy” (page 1, lines 39 to 41)
Comments 4: In portion 2, the injection method is used for biomass in the furnace, however, it is not mentioned how the grinding or milling of biomass was done.
Response 4: The author would like to thank the reviewer for providing constructive comments. I have rewritten as follower:
“In real conditions in coal-fired power plants, the process of mixing coal and biomass uses several tools, such as blending systems, pulverizers, conveyor belts, and bunkers or hoppers” (pages 2-3, lines 94 to 103)
Comments 5: The information about meshing is missing. Which software (ICEM or Space Claim) is used for meshing? What is the quality of meshing? All this information should be given in Table form.
Response 5: The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower:
“An independent research is required to establish the accuracy of the data findings. The objective is to align the grid domain with real-world conditions as closely as possible. Figure 4 displays the computational domain of the mesh for the pulverized coal boiler. Given the intricate nature of the PC boiler construction, it is imperative to streamline the model by segmenting it into multiple components. The simulation utilizes Ansys Fluent mesh software for the meshing process in pre-processing” (page 10, lines 288 to 295)
Comments 6: It is claimed that 5% is the most optimal ratio of biomass for co-firing with coal. It needs to be justified. The results from 15 and 25 are almost the same as in 5% co-firing, so why only 5% is chosen as the most optimal?
Response 6: The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower: It was corrected
"Based on the research results obtained, the HT-FRD ratio of 5% is better in terms of reducing CO2 exhaust emissions and increasing the combustion compared to the ratios of 15%, 25%, 35%, and 50%" (page 18, line 451 to 454) Please provide input and suggestions.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors1. Authors did not address comment 1. Equation 20 itself is not in mass balance. Equation 21 itself is not in mass balance either.
2. About comment 2, if composition of coal or biomass is known from table 2, what is the point of so-called simplified composition in equation 20 or 21? Does it mean the composition in equation 20 or 21 is totally wrong with totally misleading C:O ratio etc.
3. Authors did not address comment 3 that if CFD model is applied to analyze flue gas compositions, it must be validated with real composition measurements.
4. Comment 4 is not addressed completely. Authors should define “different fuel characteristics” in line 418 and clarify why HT-FRD burns faster which leads to un-oxidized CO in the presence of a lot of un-used O2. Meanwhile, authors claimed HT-FRD has higher volatile matter, thus not completely burned fuel (what fuel? CO or HT-FRD? Isn’t HT-FRD burned faster as author claimed?) thus higher concentration of CO. But line 441-444 is claiming unused O2 due to reduced amount of fuel.
Author Response
Title: Utilization of palm frond waste as fuel for co-firing coal and biomass in tangentially pulverized coal boiler using computational fluid dynamic analysis
Dear Editor,
Thanks to all the reviewers and editors for reviewing the manuscript. Also, the author especially appreciates the constructive comments, support, and contributions of the editor and reviewer that have helped improve the quality of the paper. Thank you for the opportunity to revise our paper. I have adopted most of the referees’ suggestions and believe the revised papers are substantially improved.
Reviewers’ comments on the manuscript:
Reviewer #1, Round 2:
Comments 1: Authors did not address comment 1. Equation 20 itself is not in mass balance. Equation 21 itself is not in mass balance either.
Response 1: The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower:
“The oxidation reaction of volatiles from HT-FRD and coal is considered a one-step combustion reaction mechanism, in which all the complex combustion steps and mechanisms can be simplified into one global chemical reaction” and equations 20 and 21 (page 7, lines 226 to 230)
Comments 2: About comment 2, if composition of coal or biomass is known from table 2, what is the point of so-called simplified composition in equation 20 or 21? Does it mean the composition in equation 20 or 21 is totally wrong with totally misleading C:O ratio etc.
Response 2: The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower:
“Based on the data in the table, equations 20 and 21 can be formed for the chemical reaction equation model of coal combustion and HT-FRD” (page 7, lines 248 to 249)
Comments 3: Authors did not address comment 3 that if CFD model is applied to analyze flue gas compositions, it must be validated with real composition measurements
Response 3: The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower:
“The FEGT temperature results from the simulation results and actual power plants are shown in Table 7. This shows that the overall simulation prediction results are within a range of less than 5% of the actual FEGT. Thus, its accuracy can be determined based on the FEGT validation results” (page 11, lines 320 to 323) which can be seen in table 7 (page 11, lines 324)
Comments 4: Comment 4 is not addressed completely. Authors should define “different fuel characteristics” in line 418 and clarify why HT-FRD burns faster which leads to un-oxidized CO in the presence of a lot of un-used O2. Meanwhile, authors claimed HT-FRD has higher volatile matter, thus not completely burned fuel (what fuel? CO or HT-FRD? Isn’t HT-FRD burned faster as author claimed?) thus higher concentration of CO. But line 441-444 is claiming unused O2 due to reduced amount of fuel.
Response 4: The author would like to thank the reviewer for providing constructive comments. I have made improvements as follower:
“The characteristics of coal fuel have high carbon, energy density, and combustion temperature. Meanwhile, oil palm fronds with lower carbon and energy density, as well as varying combustion quality, are one of the causes of combustion instability in co-firing, also uneven air distribution causes some of the fuel to not get enough oxygen” (page 16-17, lines 427 to 431)
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsSufficient improvement. No further comments.
Author Response
Title: Utilization of palm frond waste as fuel for co-firing coal and biomass in tangentially pulverized coal boiler using computational fluid dynamic analysis
Dear Editor,
Thanks to all the reviewers and editors for reviewing the manuscript. Also, the author especially appreciates the constructive comments, support, and contributions of the editor and reviewer that have helped improve the quality of the paper. Thank you for the opportunity to revise our paper. I have adopted most of the referees’ suggestions and believe the revised papers are substantially improved.
Reviewers’ comments on the manuscript:
Reviewer #2, Round 2:
Comments: Sufficient improvement. No further comments.
Response: The author would like to thank the reviewers for providing constructive comments and suggestions on the manuscript.
Author Response File: Author Response.pdf
