A Critical Review of CO2 Capture Technologies and Prospects for Clean Power Generation
Round 1
Reviewer 1 Report
General Comments
The manuscript present review of effective strategies for carbon capture from fossil fuel energy production, after the separation of CO2 generated. The technology and associated limitations of each of the processes is discussed. Further research is suggested based on the technological maturity, the associated cost, and knowledge needed for further improvement. The manuscript is easy to read and gather interesting literature for anyone interested in a survey of the topic. I would recommend the manuscript for publication after a revisions to address the comments below.
Major Comments
1) l. 53: Some references need to be added for the statement about using renewable resources. It is recommended to mention here the following recent papers about photocatalysis:
Zhou et al., 2014, Journal of Physical Chemistry C (2014), 118, 11649-11656, DOI: 10.1021/jp4126039.
Sharma et al., 2019, ACS Applied Energy Materials 2019, 2 (8) , 5677-5685. DOI: 10.1021/acsaem.9b00813.
2) l. 63-73: In addition to the cost analysis, there are environmental concerns that are specific to each possible technology. There should be some statement about this following the lines.
3) Figures 1 through 13 (and any figure reproduced from other paper): Also cite the previous work by indicating the authors, title, journal, and year - copyright holder following the caption.
4) The following two papers should be added to Table 3 or Table 4 or the discussion:
Thompson, J.; Combs, M.; Abad, K.; Bhatnagar, S.; Pelgen, J.; Beaudry, M.; Rochelle, G.; Hume, S.; Link, D.; Figueroa, J.; Nikolic, H.; Liu, K. “Pilot testing of a heat integrated 0.7 MWe CO2 capture system with two-stage air-stripping: Emissions.” International Journal of Greenhouse Gas Control, 2017, 64, 267-275. http://dx.doi.org/10.1016/j.ijggc.2017.08.003
Thompson, J.; Bhatnagar, S.; Combs, M.; Abad, K.; Onneweer, F.; Pelgen, J.; Link, D.; Figueroa, J.; Nikolic, H.; Liu, K. “Pilot testing of a heat integrated 0.7 MWe CO2 capture system with two-stage air-stripping: Amine degradation and metal accumulation.” International Journal of Greenhouse Gas Control, 2017, 64, 23-33. http://dx.doi.org/10.1016/j.ijggc.2017.07.004
5) l. 778-779: “demands a huge energy which”? Rewrite the confusing statement clearly.
6) Add a section before the conclusions discussing the pros and cons of each technology from the environmental viewpoint. Then summarize this also in a statement in the conclusions. This would be very important.
Minor Comments
In general, MDPI journal suggest including a list of abbreviations at the end of the paper.
13: Substitute “paper” by “work”. 61: IEA? 62: change to “… cost [4].” Use this as an example for the rest of the text to correctly insert references before punctuation marks and separated from words. 96, 97, 100, 374, 384: For equilibrium, replace the arrow by two arrows pointing in the opposite direction.
Author Response
Major Comments
1) l. 53: Some references need to be added for the statement about using renewable resources. It is recommended to mention here the following recent papers about photocatalysis:
Zhou et al., 2014, Journal of Physical Chemistry C (2014), 118, 11649-11656, DOI: 10.1021/jp4126039.
Sharma et al., 2019, ACS Applied Energy Materials 2019, 2 (8), 5677-5685. DOI: 10.1021/acsaem.9b00813.
Response: The above two papers have now been included in the manuscript and the following passage has been added on Page 2.
One of the interesting methods is the conversion of CO2 into organic compounds using photocatalytic reduction and producing fuel feedstock. Traditional fossil fuels can be used as renewable fuel following this process. Zhou et. al [3] illustrated the use of semiconductor ZnS during photoreduction of CO2 to formate (HCOO-). Sharma et. al [4] portrayed the use of sulfide based photocatalysts for production of renewable fuel in this method. They used CU3SnS4 as photocatalyst for reduction of CO2 to CH4. Excellent photocatalytic performance of the sulfide was observed along with good stability.
2) l. 63-73: In addition to the cost analysis, there are environmental concerns that are specific to each possible technology. There should be some statement about this following the lines.
Response: The following statements have been added about environmental concerns on Page 2.
In addition to the increased cost associated with CCS, the environmental impact of the methods should also be considered. A reduction in CO2 emission may lead to increasing other emissions whereby affecting the environment [7].
3) Figures 1 through 13 (and any figure reproduced from other paper): Also cite the previous work by indicating the authors, title, journal, and year - copyright holder following the caption.
Response: The source of the figures has been cited after the caption for all reproduced figure. For example for figure 1, previous work has been cited as follows:
Figure 1: Schematic diagram of pre combustion carbon capture process [10].
Theo, W. L., Lim, J. S., Hashim, H., Mustaffa, A. A., and Ho, W. S., “Review of Pre-Combustion Capture and Ionic Liquid in Carbon Capture and Storage,” Applied Energy.(2016)
4) The following two papers should be added to Table 3 or Table 4 or the discussion:
Thompson, J.; Combs, M.; Abad, K.; Bhatnagar, S.; Pelgen, J.; Beaudry, M.; Rochelle, G.; Hume, S.; Link, D.; Figueroa, J.; Nikolic, H.; Liu, K. “Pilot testing of a heat integrated 0.7 MWe CO2 capture system with two-stage air-stripping: Emissions.” International Journal of Greenhouse Gas Control, 2017, 64, 267-275. http://dx.doi.org/10.1016/j.ijggc.2017.08.003
Thompson, J.; Bhatnagar, S.; Combs, M.; Abad, K.; Onneweer, F.; Pelgen, J.; Link, D.; Figueroa, J.; Nikolic, H.; Liu, K. “Pilot testing of a heat integrated 0.7 MWe CO2 capture system with two-stage air-stripping: Amine degradation and metal accumulation.” International Journal of Greenhouse Gas Control, 2017, 64, 23-33. http://dx.doi.org/10.1016/j.ijggc.2017.07.004
Response: The suggested papers have been included in Table 3 as follows:
|
Thompson et al [42] |
2017 |
Absorption |
Two stage stripping was evaluated for amine absorber to lower the cost and increase the performance of the absorber. Secondary stripper used the heat rejected from primary stripper. Emission of different substances were compared. Overall emission level of amine, ammonia and aldehyde were comparable with other published results. |
|
Thompson et al [43] |
2017 |
Absorption |
Two stage air stripping was evaluated for amine absorber to lower the cost and increase the performance of the absorber. Secondary stripper used the heat rejected from primary stripper. Degradation of amine due to the oxygen exposure in second stripper was tested. Second stripper showed negligible impact. |
5) l. 778-779: “demands a huge energy which”? Rewrite the confusing statement clearly.
Response: The statement has been rewritten as follows:
The separation of CO2 from the gas stream in these processes requires additional energy which leads to an increase of the electricity price.
6) Add a section before the conclusions discussing the pros and cons of each technology from the environmental viewpoint. Then summarize this also in a statement in the conclusions. This would be very important.
Response: A few paragraphs has been included from environmental viewpoint as follows:
Conventional carbon capture process results in the reduction of efficiency. More fuel is burnt per unit of electricity production due to this inefficiency which leads to a more production of CO2. Also, the processes used for capturing carbon dioxide may affect the environment in different ways other than direct emission of CO2. For example, different substances used for separating and capturing CO2 may have undesired effect on human body and environment. Using a solid sorbent covered with coating were experimented to reduce the formation of dust from the substance [137]. This could also reduce the capacity of the substance to capture carbon dioxide. Also, stripping of organic solvent from membranes and sorbents is suggested to prevent undesired odor. Before employing carbon capture, it should be ensured that reducing CO2 is not being achieved at the cost of other environmental impacts.
Life cycle assessment of the plants is necessary to properly understand environmental impacts of the carbon capture methods. Schreibar et al [7] used the life cycle assessment (LCA) methodology for post combustion carbon capture using MEA whose impact on the environment and human health were investigated for five power plants. The global warming potential (GWP), human toxicity potential (HTP), acidification potential (AP), photo oxidant formation potential, eutrophication potential (EP) were considered as impact categories. As expected, GWP was found much lower with MEA compared to the power plants without capture whereas HTP was found three times greater with MEA plants. They concluded that upstream and downstream processes such as emission from fuel and material supply, waste disposal, and waste water treatment influence the environmental impact measures for power plants with carbon capture. Viebahn et al [138] work revealed about 40% increase in AP, EP, HTP when post combustion carbon capture was implemented in a power plant.
Similar result was found by Veltman et al [139]. They showed that a power plant with post combustion capture yields 10 times increase in toxic impacts on freshwater compared to a plant without capture. Impacts on other categories were found negligible. Degradation of MEA resulted in the emission of ammonia, acetaldehyde, and formaldehyde. Cuellar et al [140] compared life cycle environmental impacts of carbon capture and storage with carbon capture and utilization. GWP with utilization was found much greater than that with storage. The highest reduction of GWP was found for pulverized coal and IGCC plants employing oxyfuel capture method as well as combined cycle gas turbine plants equipped with a post combustion capture technology.
Pehnt et al [141] showed that a conventional power plant operating on coal with post combustion carbon capture would result in an increase in the environmental impact in almost all categories except GWP. Solvent degradation and energy penalty due to CO2 capture process are the main reasons for this increase. Precombustion capture showed decrease in all the environmental impact categories compared to a conventional power plant. They identified oxyfuel combustion as the most potential process to reduce all the environmental impacts categories if co-capture of other pollutants can be achieved.
Nie et al [142] investigated comparative environmental impacts of post combustion and oxy fuel combustion carbon capture. Their analysis showed that almost all environmental impact categories except GWP would increase with post combustion carbon capture. The same is true for oxyfuel combustion except GWP, AP and EP. However, the amount of increase of these impact categories was found to be less in oxyfuel combustion compared to the post combustion carbon capture. No LCA analysis was found for chemical looping combustion and newly proposed Allam cycle based on oxyfuel technology.
Further response: Two lines have been added in conclusion about environmental impact as follows:
LCA shows that oxy fuel combustion has much less effect on environment compared to other methods
LCA analysis of these new methods is also necessary to understand their impact on environment properly
Minor Comments
In general, MDPI journal suggest including a list of abbreviations at the end of the paper.
Response: List of abbreviations has been moved to the end of the paper.
1.3: Substitute “paper” by “work”. 61: IEA? 62: change to “… cost [4].” Use this as an example for the rest of the text to correctly insert references before punctuation marks and separated from words. 96, 97, 100, 374, 384: For equilibrium, replace the arrow by two arrows pointing in the opposite direction.
Response: The suggested modifications have been taken into account in the revised manuscript.
Thank you very much for the constructive comments.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript entitled “A Critical Review of CO2 Capture Technologies and Prospects for Clean Power Generation” by Sifat and Haseli provides a review highlighting various carbon capture and storage methods. This review covers a wide range of topics, including membranes, clathrates, adsorption, calcium-looping technology, water condensation, the Allam cycle, chemical looping combustion, and various other carbon capture methods.
Overall, this review is comprehensive and provides a good comparison of the different technologies near the end of the review. This topic is highly relevant, particularly given the global concerns for greenhouse gases, and should be of interest to a wide audience. The references appear to be up-to-date, with a large majority of the cited references being published within the last 10 years (2009 and later). The writing is generally clear, but could possibly benefit from some minor polishing.
Overall, I believe that this manuscript is worthy of publication pending minor revisions. I have provided some suggestions below.
Line 9: “rapid increasing the power demand” can be changed to “rapid growth in power demand” or: rapid growth in demand for energy”.
Line 18: “including largely used separation techniques” can be changed to “including widely used separation techniques”, “including commonly used separation techniques” or “including popular separation techniques”.
Line 50: “Main outcome” can be changed to “The main outcome”.
Line 60: “so it would not affect” can possibly be changed to “so that it would not affect” or “so that it does not affect”.
Line 61: Define IEA?
Line 65: “increase” can be changed to “increases”.
Line 75: The phrase “from a mixture of gas stream” is unclear.
Line 90: Define syngas?
Line 91: A reference may be needed for the statement “This process is known as steam reforming”.
Lines 93-94: references may be needed for the statements “This process is known as partial oxidation when it is applied to liquid or gaseous 93 fuels. When it is applied for solid fuels, it is known as gasification” (unless they are covered by reference [8] in the subsequent sentence on lines 94-95)
Line 106: “But the” can be changed to “However, the”.
Line 109: “staged” should possibly be changed to “stages”.
Line 120: “through water gas shift” can be changed to “through a water gas shift”.
Line 122: “Sulphur” can be written as “sulphur”.
Line 125: “is to use physical solvents” can be changed to “employ physical solvents”.
Lines 118-127: References may be needed for this paragraph, unless it is covered by the references in Table 1.
Lines 130-135: Some references may be needed for this paragraph unless the text is covered by reference 25 in Table 2.
Line 140: “is low to capture it” can possibly be changed to “is too low to capture it”.
Line 144: “They cause the separation process more costly with” can possibly be changed to “They cause the separation process to become more costly with”.
Lines 147-148: A reference may be needed for the sentence “Tim et. al has proposed a flow process to clean up the gas as shown in Fig. 3.” (This appears to be Reference 26, which is cited in Figure 3) The author name mentioned here may need to be checked as a given name instead of a surname seems to be mentioned here.
Line 149: “Sulphur” can be changed to “sulphur”.
Line 189: “from the gas mixture” can be changed to “from gas mixtures”.
Line 191: “For absorption process” can be changed to “For absorption processes” or “For the absorption process”.
Lines 204-205: A reference may be needed for the statement “If the solvent reacts with CO2 and forms chemical compounds, then the process is known as chemical absorption”.
Line 210: “by heating up to” can possibly be changed to “upon heating to”.
Line 218: “when using amine or carbonate solutions as solvent” can possibly be changed to “when amine or carbonate solutions are used as solvents”. (may need to check whether the term “solvent” is applicable here, as this is referring to solutions rather than a particular solvent.
Lines 227-228: The phrase “is their requirement of low energy for regeneration” is a little unclear.
Line 246: “Unlike absorption process” can be changed to “Unlike absorption processes
Line 246: “bond” can be changed to “bonds”.
Line 252: “gets adhered to the” can be changed to “adheres to the”.
Line 287: “less energy requirement” can be changed to “lower energy requirement”.
Line 294: “Hydrotalcites based materials” can be changed to “Hydrotalcite based materials” or “Hydrotalcite-based materials”.
Lines 297-300: May need references for the definition of description of membranes provided in these lines of text.
Line 306: “specific acid gas” can be changed to “specific acidic gas”.
Line 309: “into membrane separator” can be changed to “into a membrane separator”.
Lines 311-312: “Gas absorption system uses microporous solid membrane” can be changed to “A gas absorption system uses a microporous solid membrane”.
Line 323: “of membrane is its” can be changed to “of membranes is their” or “of membrane technology is its”.
Lines 326-331: May need references for the text appearing here.
Lines 330-331: “as wetting of membrane.” can be changed to “as wetting of a membrane.”
Lines 333-335: Need references for the sentence “Several studies have been performed with different types of membranes and absorbents to investigate the wetting effect on mass transfer through the membrane”.
Lines 344-345: “by forming hydrate crystal” can be changed to “by forming hydrate crystals” or ““by forming a hydrate crystal”.
Lines 349-351: May need references for this text.
Line 370: “method, direct reaction” can be changed to “method, a direct reaction”.
Line 376: “is called calcination reaction that” can be changed to “is called a calcination reaction, which”.
Line 376: “of carbonation” can be changed to “of a carbonation”.
Line 392: “passed to calciner” can be changed to “passed to a calciner”.
Lines 389-390: May need references for this paragraph. The reference in Figure 10 may also need to be included in the text.
Lines 412-419: References may be needed for this introductory paragraph in Section 3.
Line 425: “combustion, flame temperature becomes” can be changed to “combustion, the flame temperature becomes”.
Line 432. The reference in Figure 11 may also need to be included in the main text (maybe in lines 428-430).
Line 456: “may be improved requiring less size with” can be changed to “may be improved and require less size with” or “may be improved so that they could become smaller with” or “may be improved to enable more compact equipment with”.
Line 462: The phrase “The application of the burning fuel in pure oxygen was” is a little unclear. Maybe: “The application of the burning of fuel in pure oxygen was”.
Line 468: “as either oxy-pulverized coal process or” can be changed to “as either an oxy-pulverized coal process or an”.
Line 480: “Comparing with other” can be changed to “In comparison with other”.
Line 486: “They found no of influence of the oxy” can possibly be changed to “They found no influence of the oxy”.
Line 491: “of flame could reduce” can be changed to “of a flame could reduce”.
Lines 494-495: “of methane flame in oxy fuel environment is faster than that in air-fuel” can be changed to “of a methane flame in an oxy fuel environment is faster than that in an air-fuel”.
Line 504: “of equivalence ratio” can be changed to “of the equivalence ratio”.
Line 510: Should “combustor” be “combustion” here?
Line 518: “noticed the presence of” can be changed to “noticed that the presence of”.
Line 531: “Similar experiment was done” can be changed to “A similar experiment was performed”.
Line 547: “Allam cycle uses” can be changed to “The Allam cycle uses”.
Line 550: “produce” can be changed to “produces”.
Line 551: Units are needed for “6 to 12”.
Line 594: “if two-turbine cycle is” can possibly be changed to “if a two-turbine cycle is” or “if two turbine cycles are”.
Line 596: “on oxy fuel combustion concept” can be changed to “on the oxy fuel combustion concept”.
Line 609: “one of the cheapest technology” can be changed to “one of the cheapest technologies”.
Lines 625-632: May need references for this paragraph.
Line 650: “99.5 %” can be changed to “99.5%”.
Line 662: “found around” can possibly be changed to “found to be around”.
Line 668: “in CLC area is to” can be changed to “in the CLC area is to” or “in the CLC field is to”.
Lines 678-679: “99 percent” can be changed to “99%”.
Line 706: “become necessary” can be changed to “becomes necessary”.
Line 710: “There is also” can be changed to “There are also”.
Line 720: “demonstration plant” can be changed to “demonstration plants”.
Lines 738-766: There do not seem to be references for this text, although this text seems to describe mainly Table 6, which has references. It may be necessary to insert references into this text as well.
Line 741: “Selexol process is” can possibly be changed to “The Selexol process is”.
Line 750: “of Allam cycle” can be changed to “of the Allan cycle”.
Line 771: “will be continuing as the” can possibly be changed to “will continue to be the”.
Line 780: “in precombustion process” can be changed to “in precombustion processes”.
Line 802: “Suitable oxygen carrier” can possibly be changed to “The availability of suitable oxygen carriers”, “The availability of a suitable oxygen carrier”, or maybe “A suitable oxygen carrier”.
Note: The authors may need to obtain reprint permissions for any images in the Figures or Schemes if they were obtained from a publication such as a journal article or a book.
Lines 662, 686, 688: A space should be added between the numbers and the °C unit.
The naming format for the Figures does not seem to be consistent. For example: Figure 5 and Fig. 6. The journal guidelines may need to be checked to confirm that the correct format is used.
Author Response
Overall, I believe that this manuscript is worthy of publication pending minor revisions. I have provided some suggestions below.
Line 9: “rapid increasing the power demand” can be changed to “rapid growth in power demand” or: rapid growth in demand for energy”.
Response: The line has been changed as follows:
With rapid growth in demand for energy, the emission of CO2 is increasing due to the use of fossil fuels in power plants.
Line 18: “including largely used separation techniques” can be changed to “including widely used separation techniques”, “including commonly used separation techniques” or “including popular separation techniques”.
Response: The line has been changed as follows:
. The current state of technology and limitation of each of the processes including commonly used separation techniques for CO2 from the gas mixture is discussed in this review.
Line 50: “Main outcome” can be changed to “The main outcome”.
Response: “Main outcome” has been changed to “The main outcome”
Line 60: “so it would not affect” can possibly be changed to “so that it would not affect” or “so that it does not affect”.
Response: “so it would not affect” has been changed to “so that it would not affect”
Line 61: Define IEA?
Response: This line has been changed as follows:
International Energy Agency (IEA) has a projection to abate the CO2 emission. 17% of this abatement should be done by CCS by 2035 at the lowest cost [6].
Line 65: “increase” can be changed to “increases”.
Response: “increase” has been changed to “increases”
Line 75: The phrase “from a mixture of gas stream” is unclear.
Response: The line has been rewritten as follows:
This process requires technology to separate CO2 from a mixture of different gases.
Line 90: Define syngas?
Response: The line has been changed as follows:
At first, synthesis gas (syngas), which is a mixture of mainly H2 and CO with a trace of CO2, is produced from a fossil fuel
Line 91: A reference may be needed for the statement “This process is known as steam reforming”.
Response: Reference has been included for this line.
Lines 93-94: references may be needed for the statements “This process is known as partial oxidation when it is applied to liquid or gaseous 93 fuels. When it is applied for solid fuels, it is known as gasification” (unless they are covered by reference [8] in the subsequent sentence on lines 94-95)
Response: They are covered by the given reference.
Line 106: “But the” can be changed to “However, the”.
Response: “But the” has been changed to “However, the”
Line 109: “staged” should possibly be changed to “stages”.
Response: “staged” has been changed to “stages”
Line 120: “through water gas shift” can be changed to “through a water gas shift”.
Response: “through water gas shift” has been changed to “through a water gas shift”
Line 122: “Sulphur” can be written as “sulphur”.
Response: “Sulphur” has been changed to “sulphur”
Line 125: “is to use physical solvents” can be changed to “employ physical solvents”.
Response: “is to use physical solvents” has been changed to “employ physical solvents”. The line has been changed as follows:
Most commercially developed technologies employ physical solvents to separate CO2 from syngas.
Lines 118-127: References may be needed for this paragraph, unless it is covered by the references in Table 1.
Response: Reference has been added here for these lines.
Lines 130-135: Some references may be needed for this paragraph unless the text is covered by reference 25 in Table 2.
Response: References have been added for these lines.
Line 140: “is low to capture it” can possibly be changed to “is too low to capture it”.
Response: “is low to capture it” has been changed to “is too low to capture it”.
Line 144: “They cause the separation process more costly with” can possibly be changed to “They cause the separation process to become more costly with”.
Response: “They cause the separation process more costly with” has been changed to “They cause the separation process to become more costly with”.
Lines 147-148: A reference may be needed for the sentence “Tim et. al has proposed a flow process to clean up the gas as shown in Fig. 3.” (This appears to be Reference 26, which is cited in Figure 3) The author name mentioned here may need to be checked as a given name instead of a surname seems to be mentioned here.
Response: Reference has been added and author name has been corrected using surname.
Line 149: “Sulphur” can be changed to “sulphur”.
Response: “Sulphur” has been changed to “sulphur”
Line 189: “from the gas mixture” can be changed to “from gas mixtures”.
Response: “from the gas mixture” has been changed to “from gas mixtures”.
Line 191: “For absorption process” can be changed to “For absorption processes” or “For the absorption process”.
Response: “For absorption process” has been changed to “For the absorption process”.
Lines 204-205: A reference may be needed for the statement “If the solvent reacts with CO2 and forms chemical compounds, then the process is known as chemical absorption”.
Response: This statement is covered by reference after next line.
Line 210: “by heating up to” can possibly be changed to “upon heating to”.
Response: “by heating up to” has been changed to “upon heating to”.
Line 218: “when using amine or carbonate solutions as solvent” can possibly be changed to “when amine or carbonate solutions are used as solvents”. (may need to check whether the term “solvent” is applicable here, as this is referring to solutions rather than a particular solvent.
Response: “when using amine or carbonate solutions as solvent” has been changed to “when amine or carbonate solutions are used as solvents”.
Lines 227-228: The phrase “is their requirement of low energy for regeneration” is a little unclear.
Response: The line has been changed as follows:
Physical solvents need lower energy for regeneration which is another advantage.
Line 246: “Unlike absorption process” can be changed to “Unlike absorption processes
Response: “Unlike absorption process” has been changed to “Unlike absorption processes”
Line 246: “bond” can be changed to “bonds”.
Response: “bond” has been changed to “bonds”.
Line 252: “gets adhered to the” can be changed to “adheres to the”.
Response: “gets adhered to the” has been changed to “adheres to the”.
Line 287: “less energy requirement” can be changed to “lower energy requirement”.
Response: “less energy requirement” has been changed to “lower energy requirement”.
Line 294: “Hydrotalcites based materials” can be changed to “Hydrotalcite based materials” or “Hydrotalcite-based materials”.
Response: “Hydrotalcites based materials” has been changed to “Hydrotalcite based materials”
Lines 297-300: May need references for the definition of description of membranes provided in these lines of text.
Response: Reference has been included for these lines of texts.
Line 306: “specific acid gas” can be changed to “specific acidic gas”.
Response: “specific acid gas” has been changed to “specific acidic gas”.
Line 309: “into membrane separator” can be changed to “into a membrane separator”.
Response: “into membrane separator” has been changed to “into a membrane separator”.
Lines 311-312: “Gas absorption system uses microporous solid membrane” can be changed to “A gas absorption system uses a microporous solid membrane”.
Response: “Gas absorption system uses microporous solid membrane” has been changed to “A gas absorption system uses a microporous solid membrane”.
Line 323: “of membrane is its” can be changed to “of membranes is their” or “of membrane technology is its”.
Response: “of membrane is its” has been changed to “of membranes is their”
Lines 326-331: May need references for the text appearing here.
Response: Reference for these lines is included later in the paragraph.
Lines 330-331: “as wetting of membrane.” can be changed to “as wetting of a membrane.”
Response: “as wetting of membrane.” has been changed to “as wetting of a membrane.”
Lines 333-335: Need references for the sentence “Several studies have been performed with different types of membranes and absorbents to investigate the wetting effect on mass transfer through the membrane”.
Response: References have been included for these lines.
Lines 344-345: “by forming hydrate crystal” can be changed to “by forming hydrate crystals” or ““by forming a hydrate crystal”.
Response: “by forming hydrate crystal” has been changed to “by forming a hydrate crystal”.
Lines 349-351: May need references for this text.
Response: Reference for these lines is included later in the paragraph.
Line 370: “method, direct reaction” can be changed to “method, a direct reaction”.
Response: “method, direct reaction” has been changed to “method, a direct reaction”.
Line 376: “is called calcination reaction that” can be changed to “is called a calcination reaction, which”.
Response: “is called calcination reaction that” has been changed to “is called a calcination reaction, which”.
Line 376: “of carbonation” can be changed to “of a carbonation”.
Response: “of carbonation” has been changed to “of a carbonation”.
Line 392: “passed to calciner” can be changed to “passed to a calciner”.
Response: “passed to calciner” has been changed to “passed to a calciner”.
Lines 389-390: May need references for this paragraph. The reference in Figure 10 may also need to be included in the text.
Response: Reference for this paragraph and figure 10 has been included in the text.
Lines 412-419: References may be needed for this introductory paragraph in Section 3.
Response: references have been added for this paragraph.
Line 425: “combustion, flame temperature becomes” can be changed to “combustion, the flame temperature becomes”.
Response: “combustion, flame temperature becomes” has been changed to “combustion, the flame temperature becomes”
Line 432. The reference in Figure 11 may also need to be included in the main text (maybe in lines 428-430).
Response: Reference in Figure 11 has been added in the text.
Line 456: “may be improved requiring less size with” can be changed to “may be improved and require less size with” or “may be improved so that they could become smaller with” or “may be improved to enable more compact equipment with”.
Response: “may be improved requiring less size with” has been changed to “may be improved to enable more compact equipment with”.
Line 462: The phrase “The application of the burning fuel in pure oxygen was” is a little unclear. Maybe: “The application of the burning of fuel in pure oxygen was”.
Response: “The application of the burning fuel in pure oxygen was” has been changed to “The application of burning a fuel in pure oxygen was”.
Line 468: “as either oxy-pulverized coal process or” can be changed to “as either an oxy-pulverized coal process or an”.
Response: “as either oxy-pulverized coal process or” has been changed to “as either an oxy-pulverized coal process or an”.
Line 480: “Comparing with other” can be changed to “In comparison with other”.
Response: “Comparing with other” has been changed to “In comparison with other”.
Line 486: “They found no of influence of the oxy” can possibly be changed to “They found no influence of the oxy”.
Response: “They found no of influence of the oxy” has been changed to “They found no influence of the oxy”
Line 491: “of flame could reduce” can be changed to “of a flame could reduce”.
Response: “of flame could reduce” has been changed to “of a flame could reduce”.
Lines 494-495: “of methane flame in oxy fuel environment is faster than that in air-fuel” can be changed to “of a methane flame in an oxy fuel environment is faster than that in an air-fuel”.
Response: “of methane flame in oxy fuel environment is faster than that in air-fuel” has been changed to “of a methane flame in an oxy fuel environment is faster than that in an air-fuel”.
Line 504: “of equivalence ratio” can be changed to “of the equivalence ratio”.
Response: “of equivalence ratio” has been changed to “of the equivalence ratio”.
Line 510: Should “combustor” be “combustion” here?
Response: “combustor” has been changed to “combustion”
Line 518: “noticed the presence of” can be changed to “noticed that the presence of”.
Response: “noticed the presence of” has been changed to “noticed that the presence of”.
Line 531: “Similar experiment was done” can be changed to “A similar experiment was performed”.
Response: “Similar experiment was done” has been changed to “A similar experiment was performed”
Line 547: “Allam cycle uses” can be changed to “The Allam cycle uses”.
Response: “Allam cycle uses” has been changed to “The Allam cycle uses”.
Line 550: “produce” can be changed to “produces”.
Response: “produce” has been changed to “produces”.
Line 551: Units are needed for “6 to 12”.
Response: Since pressure ratio does not have any unit, no unit was used here.
Line 594: “if two-turbine cycle is” can possibly be changed to “if a two-turbine cycle is” or “if two turbine cycles are”.
Response: “if two-turbine cycle is” has been changed to “if a two-turbine cycle is”
Line 596: “on oxy fuel combustion concept” can be changed to “on the oxy fuel combustion concept”.
Response: “on oxy fuel combustion concept” has been changed to “on the oxy fuel combustion concept”.
Line 609: “one of the cheapest technology” can be changed to “one of the cheapest technologies”.
Response: “one of the cheapest technology” has been changed to “one of the cheapest technologies”.
Lines 625-632: May need references for this paragraph.
Response: References have been added for this paragraph.
Line 650: “99.5 %” can be changed to “99.5%”.
Response: “99.5 %” has been changed to “99.5%”.
Line 662: “found around” can possibly be changed to “found to be around”.
Response: “found around” has been changed to “found to be around”.
Line 668: “in CLC area is to” can be changed to “in the CLC area is to” or “in the CLC field is to”.
Response: “in CLC area is to” has been changed to “in the CLC field is to”.
Lines 678-679: “99 percent” can be changed to “99%”.
Response: “99 percent” has been changed to “99%”.
Line 706: “become necessary” can be changed to “becomes necessary”.
Response: “become necessary” has been changed to “becomes necessary”.
Line 710: “There is also” can be changed to “There are also”.
Response: “There is also” has been changed to “There are also”.
Line 720: “demonstration plant” can be changed to “demonstration plants”.
Response: “demonstration plant” has been changed to “demonstration plants”.
Lines 738-766: There do not seem to be references for this text, although this text seems to describe mainly Table 6, which has references. It may be necessary to insert references into this text as well.
Response: This text is basically a discussion of the values given in Table 6. References have also been included in the text.
Line 741: “Selexol process is” can possibly be changed to “The Selexol process is”.
Response: “Selexol process is” has been changed to “The Selexol process is”.
Line 750: “of Allam cycle” can be changed to “of the Allan cycle”.
Response: “of Allam cycle” has been changed to “of the Allan cycle”.
Line 771: “will be continuing as the” can possibly be changed to “will continue to be the”.
Response: “will be continuing as the” has been changed to “will continue to be the”.
Line 780: “in precombustion process” can be changed to “in precombustion processes”.
Response: “in precombustion process” has been changed to “in precombustion processes”.
Line 802: “Suitable oxygen carrier” can possibly be changed to “The availability of suitable oxygen carriers”, “The availability of a suitable oxygen carrier”, or maybe “A suitable oxygen carrier”.
Response: “Suitable oxygen carrier” has been changed to “The availability of suitable oxygen carriers”,
Note: The authors may need to obtain reprint permissions for any images in the Figures or Schemes if they were obtained from a publication such as a journal article or a book.
Response: Reprint permission has been received for all the figures and other schemes which were obtained from other publications.
Lines 662, 686, 688: A space should be added between the numbers and the °C unit.
Response: A space has been added between the numbers and the °C unit
The naming format for the Figures does not seem to be consistent. For example: Figure 5 and Fig. 6. The journal guidelines may need to be checked to confirm that the correct format is used.
Response: The naming format for the figures has been changed according to journal guidelines.
Thank you very much for the constructive comments and a comprehensive review.
Round 2
Reviewer 1 Report
Publish as is.
