Process Simulation and Economic Evaluation of Bio-Oil Two-Stage Hydrogenation Production
Round 1
Reviewer 1 Report
The authors have performed a techno-economical analysis on converting biomass to bio-oil using experimental studies found in literature. Performing economical analysis on research entering the start-up stages such as bio-oil, or other biofuels is of great importance to researchers in academia, start-up companies, and well established companies. One suggestion I have for the authors is to include minimum and maximum costs that reflect common fluctuations in feedstock, and material prices. This would then give a range of the minimum selling price of bio-oil. As a reference, see publications from groups such as Dr. Maravelias at University of Wisconsin-Madison.
Author Response
Response to Reviewer 1 Comments
The authors have performed a techno-economical analysis on converting biomass to bio-oil using experimental studies found in literature. Performing economical analysis on research entering the start-up stages such as bio-oil, or other biofuels is of great importance to researchers in academia, start-up companies, and well established companies.
Point 1: One suggestion I have for the authors is to include minimum and maximum costs that reflect common fluctuations in feedstock, and material prices. This would then give a range of the minimum selling price of bio-oil. As a reference, see publications from groups such as Dr. Maravelias at University of Wisconsin-Madison.
Response 1: Thanks for the recommendation of the publications from Dr. Maravelies groups. The sensitively analysis of practical and ideally scenarios about the minimum and maximum operation has been discussed. Also, the reference of Dr. Maravelias has been cited.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This was a good paper showing the modelling of hydrogenation steps to upgrade bio-oil. The methodology for building the process model and evaluating results were well-laid out. The results are enlightening, especially the quantification of the effect of catalyst degradation to yield and production cost. The paper can benefit from highlighting the novelty of the study in more attractive terms. There was also no mention if the model can be adaptable to a bio-oil from any feedstock, or if it is restricted to a particular kind of bio-oil. Some information around its applicability can further add to the repeatability of the study. The paper was written well, with only a few grammatical errors. With regards to numerical values, there is an opportunity to reduce the number of significant figures because these values, especially cost values are only estimates. Values to two decimal points might project a false sense of certainty. In line with this, the data tables 2-5 can be better presented in graphical form, to make the use of the data easier. For example, to highlight conclusion (2), it might be easier to see the effect of coking to yield if the result is presented graphically rather than in tables. Data tables can be provided as supplementary information, as applicable. Slight confusion on Table 1, where the kinetic data was presented. Some of the reactions do not have atomic balance, which can be confusing. This raises questions around the soundness of the reaction model that uses the kinetics. This could just be an oversight or a gross error and the presentation of the unbalanced reactions can raise doubts. Assumptions around these equations can help explain the use of these.
Author Response
Response to Reviewer 2 Comments
This was a good paper showing the modelling of hydrogenation steps to upgrade bio-oil. The methodology for building the process model and evaluating results were well-laid out. The results are enlightening, especially the quantification of the effect of catalyst degradation to yield and production cost. The paper can benefit from highlighting the novelty of the study in more attractive terms.
Point 1: There was also no mention if the model can be adaptable to a bio-oil from any feedstock, or if it is restricted to a particular kind of bio-oil. Some information around its applicability can further add to the repeatability of the study.
Response 1: Thanks for the comments. The organic bio-oil chemical formula used in the simulation model calculation is based on the summary of the chemical components in different bio-oils in the research (reference 10). The chemical formulas are general empirical expression for the bio-oil from different feedstock. Also, the average properties of the different bio-oils mentioned in Table 1 were changed into boarder ranges. The general applicability of the model for the bio-oil of any feedstock is mentioned in section 2.1 and the first paragraph of conclusions.
Point 2: The paper was written well, with only a few grammatical errors. With regards to numerical values, there is an opportunity to reduce the number of significant figures because these values, especially cost values are only estimates. Values to two decimal points might project a false sense of certainty.
Response 2: Thanks for the comments. The inappropriate significant figures have been changed in this manuscript.
Point 3: In line with this, the data tables 2-5 can be better presented in graphical form, to make the use of the data easier. For example, to highlight conclusion (2), it might be easier to see the effect of coking to yield if the result is presented graphically rather than in tables. Data tables can be provided as supplementary information, as applicable.
Response 3: Thanks for the comments. The figures of main streams of the mass flow and the heat duty of the main unit operations which discussed in the section 3 have been added. And the stream tables (2-5) have been moved to the Appendix.
Point 4: Slight confusion on Table 1, where the kinetic data was presented. Some of the reactions do not have atomic balance, which can be confusing. This raises questions around the soundness of the reaction model that uses the kinetics. This could just be an oversight or a gross error and the presentation of the unbalanced reactions can raise doubts. Assumptions around these equations can help explain the use of these.
Response 4: Thanks for the comments. The chemical formula of atomic composition has been replaced by global lumps in the section 2.4.
Author Response File: Author Response.pdf
Reviewer 3 Report
This manuscript is devoted to process simulation and techno-economic analysis of bio-oil hydrodeoxygenation with two-stage process. The authors investigated the effect of reaction condition and catalyst deactivation in the 1st reactor (mild hydrogenation stage) and optimized the reaction condition for the highest bio-fuel yield and the lowest coke yield, then estimated the process cost. This manuscript contains interesting results but there were some points that I could not understand well. My suggestion is that this manuscript can be accepted for publication after some appropriate revisions. Some of the problems I met during my reviewing are listed as follows.
(1) I could not understand the material balance well. For example, in the kinetic model shown in Table 1, Cs (soluble coke deposit) are produced from CH1.47O0.56, CH1.47O0.11, and CH3.02O1.09, but all of these reactions produce no by-products. I think the balance of carbon, hydrogen and oxygen cannot be satisfied in this reaction model. In addition, the material balance in the process flow is also not clear. For example, in Table 2, the input to the RCSTR is B-OIL-IN (10000 kg/h), H2-IN (345 kg/h) and H2-C (849.13 kg/h), and sum of the input is 11194.13 kg/h, whereas the output from the RCSTR is MIXTURE1 (11264.79 kg/h). Why are the values of input and output different? I want the authors to explain the material balance more.
(2) Why did the authors choose 280oC for the best reaction temperature? The authors mentioned that “the yield of the bio-fuel is the highest (45%) and the total amount of coke is the lowest with mild hydrogenation reactor temperature of 280oC”. However, as shown in Tables 3 and 4, the product yield at 280oC is 44.9% whereas that at 300oC is 45.1%. In addition, the amount of coke produced at 280oC is 37.52 kg/h whereas that produced at 300oC is 37.33 kg/h. I think the best reaction temperature should be 300oC if we consider the yields of bio-fuel and coke. On the other hand, the yields of bio-fuel and coke produced at 280oC and 300oC is very similar. Therefore, the best reaction temperature may be 280oC if we consider energy requirement and process operation cost. The authors should compare the effect of reaction temperatures considering not only the product yields but also the energy requirement and process cost.
(3) I think the authors should be careful for the number of significant figures. For example, “$15,210,059.19” is not suitable.
Author Response
Response to Reviewer 3 Comments
This manuscript is devoted to process simulation and techno-economic analysis of bio-oil hydrodeoxygenation with two-stage process. The authors investigated the effect of reaction condition and catalyst deactivation in the 1st reactor (mild hydrogenation stage) and optimized the reaction condition for the highest bio-fuel yield and the lowest coke yield, then estimated the process cost. This manuscript contains interesting results but there were some points that I could not understand well. My suggestion is that this manuscript can be accepted for publication after some appropriate revisions. Some of the problems I met during my reviewing are listed as follows.
Point 1: I could not understand the material balance well. For example, in the kinetic model shown in Table 1, Cs (soluble coke deposit) are produced from CH1.47O0.56, CH1.47O0.11, and CH3.02O1.09, but all of these reactions produce no by-products. I think the balance of carbon, hydrogen and oxygen cannot be satisfied in this reaction model. In addition, the material balance in the process flow is also not clear. For example, in Table 2, the input to the RCSTR is B-OIL-IN (10000 kg/h), H2-IN (345 kg/h) and H2-C (849.13 kg/h), and sum of the input is 11194.13 kg/h, whereas the output from the RCSTR is MIXTURE1 (11264.79 kg/h). Why are the values of input and output different? I want the authors to explain the material balance more.
Response 1: Thanks for the comments. The coke is formed by the poly-condensation reactions of radical compounds in the bio-oil and its products, therefore it contains not only carbon but also other elements, therefore the conservative of mass is not violated as the mass reduction in Bio-oil for instance is equal to the mass generation of coke, the overall mass is still conservative. In order avoid ambiguity, all the chemical formulas has been replaced by global lumps in the section 2.4. The mass-imbalance of the RCSTR reactor was caused by the inherent convergence issue of the Aspen Plus software, as the whole system combines non-linear expression of kinetic reaction rates, looping of material streams and user-specified coking subroutines, the resulting system of mathematical equations is highly non-linear. Sometimes obtaining the converged solution for such a system is difficult in spite of the solver settings. However, the discrepancy in the inflows and outflow is 0.6%, which is acceptable in the criteria of typical process engineering design and preliminary cost analysis, in which errors normally range in the order of magnitudes of 1% to 10%. Also, this has mentioned in the paragraph 3 of section 3.1.
Point 2: Why did the authors choose 280oC for the best reaction temperature? The authors mentioned that “the yield of the bio-fuel is the highest (45%) and the total amount of coke is the lowest with mild hydrogenation reactor temperature of 280oC”. However, as shown in Tables 3 and 4, the product yield at 280oC is 44.9% whereas that at 300oC is 45.1%. In addition, the amount of coke produced at 280oC is 37.52 kg/h whereas that produced at 300oC is 37.33 kg/h. I think the best reaction temperature should be 300oC if we consider the yields of bio-fuel and coke. On the other hand, the yields of bio-fuel and coke produced at 280oC and 300oC is very similar. Therefore, the best reaction temperature may be 280oC if we consider energy requirement and process operation cost. The authors should compare the effect of reaction temperatures considering not only the product yields but also the energy requirement and process cost.
Response 2: Thanks for the very helpful comments. The optimum temperature in the mild stage (280 °C and 300 °C) is obtained by comparing the bio-fuel yield and energy requirement in section 3.1 and 3.2.
Point 3: I think the authors should be careful for the number of significant figures. For example, “$15,210,059.19” is not suitable
Response 3: Thanks for the comments. The inappropriate significant figures like “$15,210,059.19” have been changed in this manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
All the points I mentioned were improved by the revision. Therefore, the revised manuscript is publishable in Applied Science.
