Biogas-to-Power Systems Based on Solid Oxide Fuel Cells: Thermodynamic Analysis of Stack Integration Strategies
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1. The authors need to explain the reasons for the proportions of the mixed gases in Table 1.
2. It is recommended to mark the areas where carbon deposition may occur in Figure 2.
3. There is no annotation of the Nernst Voltage for Dry Biomethane in Figure 4.
4. There are still many typos and formatting errors in the article, please carefully check and correct them
Author Response
Comment 1: The authors need to explain the reasons for the proportionsof themixed gases in Table 1.
Response 1: Thanks for this request. The reason behind the definition of the gas mixtures has now been better explained. Please address subsection 2.1 which was significantly rewritten.
Comment 2: It is recommended to mark the areas where carbon deposition may occur in Figure 2.
Response 2: Thanks for highlighting this shortcoming. The carbon deposition area was marked on the plot in Figure 2.
Comment 3: There is no annotation of theNernst Voltagefor Dry Biomethane in Figure 4.
Response 3: The paper remaks this fact: It is highlighted that the Nernst calculation is not possible for dry biomethane (m2), since the oxygen concentration at the anode is zero (no oxygen compounds available)."
Practically speaking, literature reportes Nernst voltage for methane in the thermodynamic condition assigned to be 1,11 V. (ref Journal of Cleaner Production, Volume 291, 1 April 2021, 125877). However, in Figure 4 we aim to represent only values which can be obtained by the model proposed. For this reason the Nernst voltage related to dry biomethane is absent.
Comment 4: There are still many typos and formatting errors in the article, please carefully check and correct them
Response 4: Thanks for the suggestion. A careful revision of the entire manuscript was done.
Reviewer 2 Report
Comments and Suggestions for AuthorsIn this manuscript authors investigated the impact of different gas mixtures on SOFC.
I will suggest minor revision. The authors need to extend discussions, for example they need to elaborate more technologies for CO2 separation, etc.
Author Response
Comment 1: I will suggest minor revision. The authors need to extend discussions, for example they need to elaborate more technologies for CO2 separation, etc.
Response 1: Thanks for the encouraging comment. We have gone through a detailed revision of the entire paper, addressing all Reviewers' comments, as well as a general improvement of the language and graphic items. We extended the discussion, not only elaborating on CO2 separation technology. Please go through the revised manuscript. The bibliography was enlarged in support of the specific query raised by Rev.2, see new reference items 6, 7 and 8.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe aim of reviewed paper is investigation of the theoretical operation of SOFC fueled with modified biogas , looking at stable operation comditions featured by a low risk for carbon deposition and good energetic performances. Authors showed that dry biogas or biomethane poses significant risks in terma of carbon deposition, ans CO2 enriched compositions need in significant amount of external heat. The paper can be published in "Energies", but only after some corrections in it (see below).
1. It would be better to specify in detail their affiliations, addresses etc.
2. In "Introduction" authors should explain what is Mtoe (page 1) and kWe (why not just kW?) (page 2). Also all the abbreviations should be explained at the first appearance in the text of the paper (ICE, page 2).
3. For which reasin in the Table 1 was included the column (CO)? This component is absent in all the compositions studied?
4. The formulae all the gases should be corrected: H2 instead H2 etc.
5. There are inconsistency in the dimensionalities of the parameters included in the equations (5),(6) and in the Table2: enthalpy (h) is measured in [J], but Pe in [W], Vcell is meassured in [V], but Uf (in the Table 2) in [%].
6. Note that ASR is measured in Ohm cm-2 not in W cm-2 (Table 2).
7. The diagram on the Fig.2 should be described more in detail. It is recommended to show how it aided provide the results obtained in the work. In which units scaled sides of diagram?
8. On the Fig. 4 the Nernst voltage of Dry biomethane is absent.
9. The "References" should be corrected according to the requirements of the "Energies".
Author Response
We thank Reviewer 3 for the detailed report. Our replies follow:
Comment 1. It would be better to specify in detail their affiliations, addresses etc.
Response 1. Cheked.
Comment 2 . In "Introduction" authors should explain what is Mtoe (page 1) and kWe (why not just kW?) (page 2). Also all the abbreviations should be explained at the first appearance in the text of the paper (ICE, page 2).
Response 2: Mtoe is 10^6 ton of equivalent oil. It is a standardized measurement unit for energy, yet the equivalence in term of SI units was displayed: 18 Mtoe/year (about 753 PJ/year) ICE is clarified and just “kW” is shown. All abbreviations are explained in their full forms before their first appearance in the text.
Comment 3. For which reasin in the Table 1 was included the column (CO)? This component is absent in all the compositions studied?
Response 3. The column was deleted, and CO absence and composition constitution better commented in the text.
Comment 4. The formulae all the gases should be corrected: H2 instead H2 etc.
Response 4. Checked.
Comment 5. There are inconsistency in the dimensionalities of the parameters included in the equations (5),(6) and in the Table2: enthalpy (h) is measured in [J], but Pe in [W], Vcell is meassured in [V], but Uf (in the Table 2) in [%].
Response 5. Thanks for highlighting this shortcoming. The variable definitions are corrected in the text. Also symbols used were edited to avoid ambiguous communication. The parameter K is not dimensionless, but measured in V as now detailed in Table 2
Comment 6. Note that ASR is measured in Ohm cm-2 not in W cm-2 (Table 2).
Response 6. Checked.
Comment 7. The diagram on the Fig.2 should be described more in detail. It is recommended to show how it aided provide the results obtained in the work. In which units scaled sides of diagram?
Response 7. Thanks for the comment. The CHO ternary diagram is presented with more clarity in the manuscript and the caption of the plot was extended to address the unit scale of each side. The function of this tool is also better commented.
New parts:
[1]A ternary diagram is a trinagle-shaped graphical representation used to illustrate the compositional relationships among three components. In the event of CHO, the three component are carbon (C), hydrogen (H), and oxygen (O). These diagrams are particularly useful in the fields of chemical engineering, biomass and biofuels processes to understand the stoichiometry and balance of these elements in different substances.It is a useful visualisation tool to compare several options.
Figure 2. CHO ternary diagram of the analysed (the three axis report molar fractions of each element, the composition of any point within the triangle sums to 100%)
Comment 8. On the Fig. 4 the Nernst voltage of Dry biomethane is absent.
Response 8. The paper remaks this fact: It is highlighted that the Nernst calculation is not possible for dry biomethane (m2), since the oxygen concentration at the anode is zero (no oxygen compounds available). Therefore, Figure 4 only represents results that may be obtained with the presented model. On the other hand, literature reports Nernst voltage for methane in the thermodynamic condition assigned to be 1,11 V. This is commented in the text.
Comment 9. The "References" should be corrected according to the requirements of the "Energies".
Response 9. Thanks for recalling the format rules. We have changed the style in agreement with the template instructions.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript can be considered for publication.
