Modeling and Experimental Validation of Compression and Storage of Raw Biogas
Round 1
Reviewer 1 Report
Title: Modelling and experimental validation of compression and storage of raw biogas
General comments: In this work, the authors analyze the compression of raw biogas in order to measure and estimate changes in temperature, pressure and density as they relate to the gas Z-factor. The introduction does a good job explaining/justifying the need for this research and highlighting necessary background. The experimental analysis seems to be sound and accurate; however, the materials and methods section is lacking some details that could be helpful from a reproducibility perspective. I would encourage the authors to provide as much detail as possible about the equipment used and all of the measurements taken. The results compare experimental measurements to equations of state for gas properties. While the data is thorough, the way it is presented in the figures could be improved in order to more clearly show uncertainty and/or experimental error. Please see below for some more specific comments.
Page 2, line 46: Would it be possible to provide quantitative ranges for the composition of CH4 and CO2 in biogas? Something like “40-50% CO2, 50-60% CH4” so the readers can have a rough idea without needing to check further references.
Page 2, line 76: Please also state the name of the authors in addition to providing the reference here. For example: “As it was shown by Qian et al, high amounts of CO2 in raw biomas can help to inhibit…”
Page 2, line 79: Same comment as above. For example: “It was describe in work from Jerzak et al that co-digestion of organic municipal waste…” I would recommend to use this type of convention-when referring directly to literature-throughout the paper, where ever necessary.
Page 4, line 139: Please define the variables (V1, p2, pc, m2…) at the first instance they are mentioned
Page 4, line 124: What is the material of the pressure cylinders (steel, composite…) ? Also, if possible please indicate the dimensions of the cylinder (especially the internal and external diameters). This may have an impact on the assumption that the internal gas temperature is equal to the external cylinder wall temperature.
Page 4, line 142 and Table 1: This data would be more accurately described as the “molecular composition” rather than the “elemental composition.” How was this data collected? Is the composition of the biogas a constant value throughout the experiments? Were there replicate measurements of biogas composition? Is there any variability/quantification in measurement error of biogas composition?
Page 4, line 148: Please provide more details about the thermal camera, such as brand, manufacturer/vendor, model, etc. (like the info that is given in Table 2 for the compressor)
Page 9, line 282: Define the acronyms (ARE, AARE, RMSE) at the first instance they are mentioned
Page 10, line 311: Replace “chapter” and ”subchapters” with “section” and “sections”
Section 3.1: Overlaying all of the runs in the same graph makes it difficult to see/interpret the data. For example, in Figure 4, the only really apparent run is the sixth one, because it is on the top. It would be useful to use different symbols that do not obscure the rest of the data. Another approach that may be more successful would be to plot the average of the six runs, with error bars or something similar to quantify the uncertainty and/or experimental error/variability. This information would be very useful from a reproducibility perspective. It is difficult, given the current way in which the data is presented, to estimate the experimental uncertainty/variability in the measurements.
Section 3.2: Same comment about the graphs as for section 3.1
Page 15-16, Figure 12 and 13: Should this data be 10-20 MPa? (instead of 100-200)
Page 16, Table 7: Please indicate in the title of this table that the data is for volume at 20 MPa. It is unclear looking at the table alone what is meant by “experimental results.”
Page 18, Figure 16: Please add labels to the arrows here, especially the grey, red, yellow and blue ones.
Author Response
Thank You very much for the review.
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript deal with biogas compression, a technical topic that is relevant to transportation and industrial applications of compressed biogas. I recommend it is accepted after minor revision.
Comments
- Reduce the number of figures and include in the main text only he most important ones. Same for the tables. Add the less important figures and tables to the supplementary information
- Many sentences are unclear and barely readable. The manuscript should be thoroughly revised by a technically competent native English speaker.
- The novelty of the findings should be clearly highlighted with respect to patents (e.g., https://patents.google.com/patent/US6250080B1/en), papers (Transport, 2010, 25(1): 77–80) and other previous studies.
- The conclusion section should be shortened to include only key results.
Author Response
Thank You for the review
Please see the attachment.
Author Response File: Author Response.docx
