Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript presents a novel low-carbon economic dispatch model for a coal mine integrated energy system (CMIES) that incorporates concentrated solar power (CSP) with thermal energy storage (TES) and an integrated flexible carbon capture system (IFCCS) utilizing abandoned mine shafts for solvent storage. The paper addresses an important and timely problem—decarbonizing energy-intensive coal mining operations—and proposes an innovative solution that repurposes existing mine infrastructure. The modeling approach is comprehensive, incorporating multiple energy carriers (electricity, heat, cooling), associated energy sources (coal mine gas, ventilation air methane, gushing water), and a tiered carbon trading mechanism. The case study with five comparative scenarios demonstrates the economic and environmental benefits of the proposed approach.

However, several issues require attention before publication.

1. Equation (1): Is GT efficiency truly time-varying in your model, or should this be a constant parameter?

2. Section II.C: How would your conclusions change if DNI uncertainty and forecast errors were included? Have you performed any sensitivity analysis on solar resource variability?

3. Equation (15): Does your tiered carbon trading mechanism account for methane slip or incomplete combustion in RTO and GT units? If VAM is oxidized to CO2 with 99% efficiency, the carbon equivalent changes dramatically. Please clarify whether your emission factors represent direct CO2 emissions or CO2-equivalent based on GWP-100 values.

4. Section II.B: Where are the heat-power ratio constraints for the CHP unit? Without these, the claimed advantage of CSP for decoupling "power determined by heat" cannot be properly evaluated.

5. Please ensure all figures (7 and 8), are properly embedded and captioned. Figure 7 is essential for understanding CSP operational strategy.

6. Section V.A: How were these specific values chosens? Are they based on current Chinese carbon market data? Please provide a justification or sensitivity analysis showing how results change with different λ values.

7. Table 5: Given typical coal mine scale annual revenues likely > 10⁸ RMB, a 0.1% cost change could be within forecast error. Have you performed any Monte Carlo or sensitivity analysis to verify that the observed improvements are robust to input parameter variations?

8. Why was CSP selected over the other renewable + storage combinations for this specific coal mine application? A brief discussion comparing levelized costs or technical suitability would strengthen the paper's practical recommendations.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

• The novelty should be sharpened and better differentiated from previous CSP–CHP–CCS/P2G studies. The introduction states that the paper integrates CSP, IFCCS, associated energy utilization, abandoned mine shaft storage, and tiered carbon trading . However, several cited studies already combine CSP, CHP, CCS, P2G, and carbon trading mechanisms.
• The physical feasibility of using abandoned mine shafts as solvent storage tanks needs deeper justification. The manuscript claims that abandoned mine shafts have favorable geometry and sealing properties for large-scale chemical solution storage. This is an important assumption, but the paper does not sufficiently discuss safety, leakage risk, corrosion, sealing requirements, MEA degradation, groundwater contamination, regulatory constraints, or retrofitting cost. Since the IFCCS concept depends heavily on this assumption, a technical feasibility subsection should be added.
• The mathematical formulation has notation inconsistencies and should be carefully revised. Several variables appear to be repeated, mislabeled, or inconsistently defined.
• Some equations are difficult to interpret because of formatting problems.
• The optimization problem type is not fully described. The manuscript says the model is solved in MATLAB. However, the paper does not clearly state whether the model is MILP, MINLP, LP, or another form. Binary variables are introduced for storage charging/discharging, but the complete optimization structure is not fully explained.
• The uncertainty of renewable energy, associated energy, and load demand is not considered. The authors acknowledge this limitation only at the end, noting that future work will use information gap theory to address uncertainties . However, because wind power, solar radiation, mine gas flow, VAM concentration, gushing water flow, and electricity/heat/cooling loads are all uncertain, the deterministic results may overestimate the system benefits. At minimum, the authors should add scenario-based uncertainty analysis or sensitivity testing for wind, solar DNI, AE availability, and load variation.
• The manuscript states that CSP power generation is influenced by TES operation and does not consider DNI uncertainty. This is a strong simplification because CSP output directly depends on solar radiation. The authors should clarify whether actual DNI data were used deterministically, whether solar prediction errors were ignored, and how this assumption affects dispatch reliability.
• The paper compares five internal cases, but there is no external benchmark, no validation against real coal mine data, and no comparison with published models. The authors should validate at least part of the model using literature data, industrial data, or a simplified benchmark case. Without validation, the numerical improvements may be model-dependent.
• The case design is useful but should include ablation logic more clearly.
• Some percentage calculations and explanations should be checked.
• Economic assumptions need more transparency. The total cost includes operation/investment cost, carbon trading cost, energy purchase cost, curtailment penalty cost, and carbon sequestration cost . However, the manuscript does not sufficiently justify all cost coefficients, investment costs, maintenance costs, sequestration costs, curtailment penalties, and carbon trading parameters. More details should be provided, preferably in a parameter table with references.
• The carbon trading model needs clearer explanation. The tiered carbon trading mechanism is central to the low-carbon claim, but the stepwise cost equation is difficult to follow and not well explained in words. The authors should add a simple illustrative example showing how carbon cost is calculated when emissions are below quota, slightly above quota, and far above quota.
• The P2G model is oversimplified. The model assumes that the volume of CO₂ consumed equals the volume of natural gas produced using Avogadro’s law . This simplification needs more explanation because methanation stoichiometry, hydrogen availability, conversion efficiency, reaction heat, electrolyzer constraints, and methane quality are important. The authors should also explain whether the produced methane is recycled internally, sold, or used to reduce external gas purchases.
• The IFCCS model should better represent carbon capture process constraints. The IFCCS model includes absorber efficiency, regeneration efficiency, split ratio, fixed energy consumption, and operating energy consumption . However, real MEA systems also involve solvent circulation rate, regeneration heat demand, compressor work, solvent degradation, lean/rich loading limits, and absorber/regenerator capacity constraints. Even if these are simplified, the assumptions should be clearly stated.
• The SST capacity sensitivity analysis is useful but incomplete. Figure 9 shows that total cost is minimized at an SST capacity of 16,000 m³ and TES capacity of 200 MW . However, the manuscript should explain the selected capacity ranges, step sizes, investment cost assumptions, and whether this optimum changes under different carbon prices, energy prices, or renewable energy profiles.
• The abstract begins with a sentence fragment: “To address issues such as high energy consumption, high emissions, resource wastage, and spatial resource constraints in coal mine production processes.” This should be rewritten as a complete sentence.
• The abstract should include quantitative results, such as the percentage reduction in total cost and carbon emissions achieved by the proposed case compared with the baseline.
• The keyword “integrated flexible carbon capture system” is appropriate, but “tiered carbon trading mechanism” may be better than “stepwise carbon trading mechanism” if used consistently.
• Section numbering uses Roman numerals and lettered subsections, but some subsection titles are inconsistent in capitalization, such as “associated energy Utilization Model”.
• “Peoples R China” should be corrected to “People’s Republic of China” or “P. R. China”.
• Some terminology should be standardized: use either “carbon capture system,” “CCS,” “CCUS,” or “IFCCS” consistently.
• Some figure captions contain grammatical errors.
• The figures are generally useful, but several plots are small and difficult to read.
• The appendix figures should be more clearly introduced in the main text.
• The conclusion is generally aligned with the results, but it should include the main numerical findings and avoid broad claims such as “invaluable guidance” unless supported by practical validation.
• The manuscript requires substantial English editing. Many sentences are understandable but grammatically awkward.
• Some paragraphs are too long and should be divided for readability.
• Several claims are repeated across the introduction, results, and conclusion.
• Equation formatting must be improved before publication.
• Tables and figures should be redesigned with clearer units and captions.
• A nomenclature table is strongly recommended because the manuscript contains many variables, devices, subscripts, and abbreviations.

Comments on the Quality of English Language

• The manuscript requires substantial English editing. Many sentences are understandable but grammatically awkward.
• Some paragraphs are too long and should be divided for readability.
• Several claims are repeated across the introduction, results, and conclusion.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

List of abbreviations and symbols needs to be provided.

Line 11, 18: Emissions of what?

References 1-7, 12, and other formatting in the text need superscript.

Line 38: The statement that 60% of energy comes from fossil fuels should be supported by a source.

Line 52: Why are the statistics incomplete, and does it matter in this case?

Line 78: The CCS technology applied on the island should be rewritten.

Line 119–120: “On the other hand” appears twice.

Line 130: What criteria are used to designate an abandoned coal mine shaft as suitable for CCS? There are many challenges, including, for example, the porosity of the rock and soil above the shaft, through which CO2 and other gases can pass.

Lines 163–167: The equation definitions need to be corrected; PGT,t appears three times. This issue persists throughout other equations in the manuscript, for example in Eq. 2.

Is the model, or the equations, based on the authors’ own work, or on existing models? This should be emphasized in the text, and proper sources should be added if applicable.

Line 208: DNI is not defined anywhere in the text.

Line 304: Which regulatory authorities?

Table 1 should be better introduced in the text. Should the conversion efficiency be under 1%? What are climb rate and operation costs? Tables 2-4 also need better explanation.

Was the day-ahead analysis validated? By this, I mean whether the authors checked whether the assumed parameters occur on a regular basis, for example by comparing whether the three random days provide similar data points.

Line 608: f[u]nding.

Stylistic choices to consider: rather than using Ref. [nn], use the surname of the first author. Use chapter and section numbering instead of Roman, Arabic, or Latin numerals, for example Line 421 V.B.1 should use Arabic numbers only: 5.2.1. Case design and result analysis

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

N/A

Comments on the Quality of English Language

N/A

Reviewer 3 Report

Comments and Suggestions for Authors

"Thank you for your response. The manuscript has been revised satisfactorily and, in my opinion, is suitable for publication, subject to the editor's final decision.