Thermochemical and Economic Analysis for Energy Recovery by the Gasification of WEEE Plastic Waste from the Disassembly of Large-Scale Outdoor Obsolete Luminaires by LEDs in the Alto Alentejo Region (Portugal)
Round 1
Reviewer 1 Report
This study concerns the technical-economic evaluation of some energy recovery options of a mixtures of plastic waste from dismantled urban luminaires and biomass waste from the agro-food industry through gasification and electricity generation.
The topic is of interest to this journal, but the manuscript has significant shortcomings and needs to be extensively revised and improved.
In the following some general and more specific comments.
General comments:
As regards the structure of the manuscript, this should be carefully reviewed and modified, also considering the suggestions given below.
The introduction is too lengthy, verbose, dispersive and, in certain parts, even messy. Sometimes some concepts are repeated (see, for example, in the paragraph from line 111 to 127, or in that from line 128 to 138). It is advisable to rewrite it extensively in a scrupulous way by sticking to a more linear and rigorous style (for example, phrases like "as you can see" or "we can see" are not common in scientific language) and eliminating everything that is not functional to the objectives of this study.
All results should be described in the Results section. Instead, some results are shown in the Materials and methods section. Please, rearrange accordingly.
The methodological description of the economic feasibility study (presently subsection 3.1 up to 3.3.4) should be moved to the methods Section.
The discussion section is rather sparse and should be enriched with further considerations; for example, the comparison of the results of this study with other studies in the literature is completely missing.
On the other hand, the conclusions contain some considerations that should be moved to the discussion.
In principle, there are no “clean” or “environmentally friendly” energy sources in absolute terms; there hardly exists any (energy) option which is absolutely environmentally sound. When assessed on a life-cycle basis, indeed, any kind of energy source may result to generate some kind of environmental impacts; some options may be more impacting than others, at least when given impacts are considered. Therefore, the use of terms such as “clean”, “efficient”, environmentally friendly”, etc. should be avoided as a general rule; Instead, “cleaner”, “more efficient”, “more environmentally friendly” are recommended.
Stating that the biomass used in the experiments carried out comes from the olive grove can be misleading in my opinion, as it leads readers to think that it comes from olive tree pruning residues. In reality, it is specified that these are olive pomace and stones, therefore by-products of the olive milling.
Acronyms should be introduced when they are used for the first time (e.g. , line 57: HLV)
To avoid any misunderstanding, when referring to the metric ton (1000 kg), the term “tonne” should preferably be used.
Please, carefully cross-check molecular formulas for chemical compounds and the correct use of subscripts.
In most numbers found in the manuscript, commas are used, instead of decimal points. Please, amend where needed.
Figure captions should be located below figures, not on the top of them.
Many typos and mistakes can be found in the manuscript (just some of them are reported in the specific comments hereafter); the impression one receives is that the manuscript was written hastily and roughly. Some sentences and phrases not in English are present. The manuscript should, therefore, be carefully edited for style, grammar and other mistakes.
Specific comments:
Line 46 (and elsewhere):
The term “green” has limited scientific meaning and should be avoided in a scientific paper.
Line 59:
“global heat”. Do you mean “global warming”? (check also elsewhere in the manuscript)
Line 84:
“Waste Reduced Fuels (RDF) or Waste Reduced Fuels (RDF)”
What is the difference between the two?!
Moreover, as to my knowledge, the acronym RDF stands for “refuse-derived fuel”
Lines 84-94:
Just to give an idea of how confused is the introduction, in this paragraph RDF and plastics are jointly dealt; some statements might be misunderstood (e.g., lines 89-90: “These fuels have a biogenic carbon content of around 50-60%...” seems to be referred to plastics, even though it should be referred to RDF)
Line 92:
“These operations are generally called 'energy waste'”
Are you sure? I think a more suitable term is “waste-to-energy”
Line 139:
Why “table”? This is not a table, this is a plot, indeed.
Line 275:
Why is figure 1 mentioned here?
Line 309:
“With the information provided by these sources…”
Which sources?
Line 323:
Table 3: the title of the table should be translated in English. The decimal point (instead of a comma) should be used for the values listed in the table.
Line 349:
the correct acronym for Low Heating Value is LHV
Line 363:
The right abbreviation for kilowatt is kW (only W should be capitalised)
Line 422:
Table 8: “olive sid”? What is this?
Line 451:
the energy produced per kilogram of agricultural biomass and plastics mixture should be kWh/kg, NOT kg/kWh (please, mind also correct capitalisation: kWh, kg)
Line 474:
( /F) should be (A/F)
Line 479:
LHVsyngas: “syngas” should be subscript
Line 483:
The variable Vsyngas should also be defined
For all the variable defined, the relevant units should be shown
Line 501:
“…with the energy produced by the company itself through…”
Which company?
Lines 521-522:
“…quasi-rents (net benefits, income fewer expenses)”
Not clear, cross-check terminology (e.g. “fewer”??)
Line 527:
In formula (6), it should be t=0, instead of t=1 (as this was applied in tables 12, 14 and 16).
Line 588:
Table 11: The unit for the parameter LHVbio is shown as MJ/m3; however, in formula (4), even though not explicitly stated, it seems to be expressed in terms of energy per mass unit (not per volume unit).
Line 609:
Table 13: A number of inconsistencies should be fixed (the same also applies to table 15).
e.g.:
- the term “Biomass” is referred to both olive pellets and WEEE plastics, but plastics are not biomass.
- the LHV of the input to the gasification process (line: LHVbio), expressed as MJ/m3, seems to have been calculated as the sum of the LHV (also MJ/m3) of the 2 fractions, whilst it should be a weighted mean (indeed, the LHV shown in Table 13 is the same as that reported in Table 15, i.e. 22.63 MJ/m3, whilst the composition of the input mixture is not the same)
Line 673: Table 17
It is not clear why option 2 in this comparison (a mixture of 90% olive pellets and 10% WEEE plastics scraps) is evaluated according to a power of 15 kW, whilst the other 2 options entail a power of 10 kW. This comparison does not seem to be fair, since the scale of the compared options is not the same.
Lines 711-713:
what is this claim based on? No environmental assessment was actually described in this study.
Line 782:
“Bruselas – Bélgica” should be translated into English.
Author Response
Response to Reviewer 1:
Reviewer 1
Comments and Suggestions for Authors
This study concerns the technical-economic evaluation of some energy recovery options of a mixtures of plastic waste from dismantled urban luminaires and biomass waste from the agro-food industry through gasification and electricity generation.
The topic is of interest to this journal, but the manuscript has significant shortcomings and needs to be extensively revised and improved.
In the following some general and more specific comments.
Thank you very much for your comments.
We sincerely appreciate your comments and hope that the changes made to the document will be appreciated by the reviewer.
Then we will try to answer the questions made by the reviewer one by one. In addition we will introduce in the original manuscript the changes in red the rearranged text.
We take this opportunity to thank the reviewer for his interesting comments that we have included in the text.
General comments:
As regards the structure of the manuscript, this should be carefully reviewed and modified, also considering the suggestions given below.
The introduction is too lengthy, verbose, dispersive and, in certain parts, even messy. Sometimes some concepts are repeated (see, for example, in the paragraph from line 111 to 127, or in that from line 128 to 138). It is advisable to rewrite it extensively in a scrupulous way by sticking to a more linear and rigorous style (for example, phrases like "as you can see" or "we can see" are not common in scientific language) and eliminating everything that is not functional to the objectives of this study.
Thank you very much for your comments. We have carried out an in-depth review of the Introduction section, in a less dispersive and clearer way and oriented to the objectives of the study, eliminating the expressions that you indicate to express everything in a more scientific language as you advise us.
All results should be described in the Results section. Instead, some results are shown in the Materials and methods section. Please, rearrange accordingly.
Thank you. We have carried out a reorganization of the indicated sections, incorporating all the results in their point 3.”Results" section
The methodological description of the economic feasibility study (presently subsection 3.1 up to 3.3.4) should be moved to the methods Section.
We agree with the reviewer. Indeed, these sections of the theoretical description of the economic viability analysis have been transferred to the Methodology section like 2.3 Methodological Analysis of economic viability,
The discussion section is rather sparse and should be enriched with further considerations; for example, the comparison of the results of this study with other studies in the literature is completely missing.
We agree with the reviewer. We have expanded the discussion and have contrasted it with other similar studies, referring them through the bibliographic review to similar scientific works. We have also included in the discussion a section called 3.4. Environmental Analysis, where we discuss these always interesting environmental aspects.
On the other hand, the conclusions contain some considerations that should be moved to the discussion.
We agree with the reviewer. We have moved from the Conclusions the referenced discussion part
In principle, there are no “clean” or “environmentally friendly” energy sources in absolute terms; there hardly exists any (energy) option which is absolutely environmentally sound. When assessed on a life-cycle basis, indeed, any kind of energy source may result to generate some kind of environmental impacts; some options may be more impacting than others, at least when given impacts are considered. Therefore, the use of terms such as “clean”, “efficient”, environmentally friendly”, etc. should be avoided as a general rule; Instead, “cleaner”, “more efficient”, “more environmentally friendly” are recommended.
We are again in full agreement with the reviewer's recommendation. We have proceeded to eliminate these absolutely categorical expressions by others that are softer and more comparative. ("more effcient", "cleaner", "less environmental impact", etc ...
Stating that the biomass used in the experiments carried out comes from the olive grove can be misleading in my opinion, as it leads readers to think that it comes from olive tree pruning residues. In reality, it is specified that these are olive pomace and stones, therefore by-products of the olive milling.
Thank you very much for your excellent appreciation. It can effectively create confusion for the reader. We have reviewed in the text and tables, clarifying that the biomass residues come not from pruning of the olive grove but from the by-products of the milling of the olive "Olive seed"
Acronyms should be introduced when they are used for the first time (e.g. , line 57: HLV)
Thank you. We have proceeded to review and define the acronyms the first time they appear referenced in the text.
To avoid any misunderstanding, when referring to the metric ton (1000 kg), the term “tonne” should preferably be used.
Thank you. This has been modified in the text.
Please, carefully cross-check molecular formulas for chemical compounds and the correct use of subscripts.
We have carefully reviewed and corrected in the text. Thank you very much.
In most numbers found in the manuscript, commas are used, instead of decimal points. Please, amend where needed.
We have carefully reviewed and corrected in the text. Thank you very much.
Figure captions should be located below figures, not on the top of them.
Thank you. We have reviewed and placed the legends of the figures in their correct position and place.
Many typos and mistakes can be found in the manuscript (just some of them are reported in the specific comments hereafter); the impression one receives is that the manuscript was written hastily and roughly. Some sentences and phrases not in English are present. The manuscript should, therefore, be carefully edited for style, grammar and other mistakes.
Thank you very much for your comments. We have proceeded to carry out a rigorous and detailed revision of the entire manuscript, correcting typographical errors and making a careful revision of the text. removing rough expressions and rewriting it more clearly and precisely. Thank you very much sincerely for your constructive comments.
Specific comments:
Line 46 (and elsewhere):
The term “green” has limited scientific meaning and should be avoided in a scientific paper.
We agree with you We have removed this expression and verified that it does not appear anywhere else in the manuscript. Thank you.
Line 59:
“global heat”. Do you mean “global warming”? (check also elsewhere in the manuscript)
Exactly. Thank you. We have changed to the much more scientific suggested expression. We have verified all the text but it does not appear anywhere else. Thank you.
Line 84:
“Waste Reduced Fuels (RDF) or Waste Reduced Fuels (RDF)”
What is the difference between the two?!
Moreover, as to my knowledge, the acronym RDF stands for “refuse-derived fuel”
Indeed we agree and we apologize for the repetition of this expression. We have clarified this question in the text. . The correct acronym (RDF) is refuse-derived fuel. Thank you
Lines 84-94:
Just to give an idea of how confused is the introduction, in this paragraph RDF and plastics are jointly dealt; some statements might be misunderstood (e.g., lines 89-90: “These fuels have a biogenic carbon content of around 50-60%...” seems to be referred to plastics, even though it should be referred to RDF)
We agree with your comment and have clarified in the rewritten Introduction.
Line 92:
“These operations are generally called 'energy waste'”
Are you sure? I think a more suitable term is “waste-to-energy”
Thank you. We have modified this expression according to your correct suggestion.
Line 139:
Why “table”? This is not a table, this is a plot, indeed.
We apologize. Indeed it is not a table it is a figure. We have corrected. Thank you,
Line 275:
Why is figure 1 mentioned here?
We apologize. It is a mistake that we have eliminated. Thank you,
Line 309:
“With the information provided by these sources…”
Which sources?
Specifically, we refer to the company EDP (Energias do Portugal) (Portugal) as sources within the project "Projeto Illupub- Projeto para la Melhoria energetic e Eficansa Iluminasao Publica". We have clarified this in the text. Thank you
“With the information provided by EDP (Portugal), the company in charge of promoting the "Illupub Project- Project for Melhoria energetic and Eficansa Iluminasao Publica" it has been possible to count the total number of light points of conventional luminaires (sodium, mercury and metal Halogen discharge lamps (HM) in the Alto Alentejo area (Portugal) (45,160) .The results are shown in Table 2. Of the total number of luminaires analyzed, 78% corresponded to the luminaire model, mainly installed, model Syntra, approximately (35,593).”
Line 323:
Table 3: the title of the table should be translated in English. The decimal point (instead of a comma) should be used for the values listed in the table.
We apologize for this lapsus of translation. We have corrected it in the table , now number 7in the manuscript. And corrected the decimal point (instead of comma) inside the table.Thank you so much.
Line 349:
the correct acronym for Low Heating Value is LHV
We have modified. Thank you so much.
Line 363:
The right abbreviation for kilowatt is kW (only W should be capitalised)
We have modified. Thank you so much.
“The gasification tests were performed on an AllPowerLabs PP20 Power Pallets [55]- a gasifier with a power of 15 kW (table 6 and figure 6)…..
Line 422:
Table 8: “olive sid”? What is this?
We have modified in the table 8. Thank you so much.
Line 451:
the energy produced per kilogram of agricultural biomass and plastics mixture should be kWh/kg, NOT kg/kWh (please, mind also correct capitalisation: kWh, kg)
Thank you. We have modified.
“With the values ​​of the electrical energy produced by the alternator we can determine the kWh/kg, that is, the energy produced per kilogram of agricultural biomass and plastics mixture.”
Line 474:
( /F) should be (A/F)
Thank you. We have modified.
(A/F) is the same mass ratio but under the experimental conditions that were adopted.
Line 479:
LHVsyngas: “syngas” should be subscript
We agree with the reviewer's appreciation and have proceeded to define "syngas" as a subscript. Equation (4). where we define it. Thanks
ηgas = (Vsyngás * LHVsyngas) / (mfuel * LHVfuel) (8)
ηtot = Eel * 3.6 / (LHVfuel * mfuel) (9)
ηeng = ((ηtot * ηgen) / ηgas) (10)
Where:
ηgas is the efficiency of the reactor-gasifier;
LHVsyngas is the lowest heating value of the syngas, in MJ/m3;
mfuel is the fuel mass used during the test, in kg;
ηtot is the total efficiency;
LHVfuel is the lower heating value of the fuel or inlet mixture, in MJ/kg.
- Eel [kWh] is the electrical energy generated;
- ηeng is the motor efficiency (0.3);
- ηgen is the efficiency of the generator (0,8).
Line 483:
The variable Vsyngas should also be defined
For all the variable defined, the relevant units should be shown
We agree with the reviewer's appreciation and have proceeded to define Vsyngas and display their units. Equation (2) and description of variables and units. Thank you
“For the calculation of syngas production during gasification tests, an anemometer is used that is connected to the air inlet. Also with the quality of the syngas produced, it is possible to obtain the amount of N2 present. Another important factor is related to the amount of N2 present in the air. The data are applied in formula 2 and the volume calculated.”
Line 501:
“…with the energy produced by the company itself through…”
Which company?
We wanted to say that the energy produced by the gasifier and alternator will be able to offset the cost or energy consumption of the olive oil factory or the industry that decides to install the proposed energy production equipment, as compensation for the total electric bill of the company supplying the electric power in Portugal (EDP). We have clarified this in the text.
“An economic analysis will carry out using the usual financial and economic indicators to justify the feasibility of installing the complete equipment (gasifier-engine-generator, includes installation) 1.200 € / kW of Investment in the production of electrical energy with a direct sale to the Electricity Distribution Company in Portugal (EDP).”
“It was considered that the electrical energy purchased or consumed through the national energy network, managed by (EDP,) by the company that is going to exploit the gasifier generating equipment. It will be complemented with the energy produced or sold as a result of the gasification generator process and will be sold to the same company that manages electricity in Portugal (EDP) at the legally established price”.
Lines 521-522:
“…quasi-rents (net benefits, income fewer expenses)”
Not clear, cross-check terminology (e.g. “fewer”??)
We have changed the expression to make it better understandable. Quasi-rents "Ct" is the difference between Income and expenses for each period analyzed. Thank you very much for your comment. We have left specified in the text. Thank you
Line 527:
In formula (6), it should be t=0, instead of t=1 (as this was applied in tables 12, 14 and 16).
Thank you very much for your comment. We have proceeded to unify the criteria in all the equations (7,9,10 and11). We considered the first time period, the first year of amortization, as year 1. So "t" takes values ​​between 1 and N. We consider The time period t = 0 is related to the investment during the design and construction phase of the gasifier.and we explained an clarify in the text.
Line 588:
Table 11: The unit for the parameter LHVbio is shown as MJ/m3; however, in formula (4), even though not explicitly stated, it seems to be expressed in terms of energy per mass unit (not per volume unit).
We agree with the reviewer's comment, indeed it was an error in the units that we have corrected in the tables and equations to be consistent with the indicated equation. Thank you very much
Line 609:
Table 13: A number of inconsistencies should be fixed (the same also applies to table 15).
e.g.:
- the term “Biomass” is referred to both olive pellets and WEEE plastics, but plastics are not biomass.
Thank you very much for your comment. We have changed Biomass for fuel, in both tables, as recommended and more appropriate. Thanks a lot
- the LHV of the input to the gasification process (line: LHVbio), expressed as MJ/m3, seems to have been calculated as the sum of the LHV (also MJ/m3) of the 2 fractions, whilst it should be a weighted mean (indeed, the LHV shown in Table 13 is the same as that reported in Table 15, i.e. 22.63 MJ/m3, whilst the composition of the input mixture is not the same).
Thank you very much for your appreciation. We have proceeded to clarify in the tables (11, 13 and 15) the values and units. Sure enough there was a mistake. LHVfuel is now well expressed in MJ / Kg. In fact, the mass fraction has been weighted in the case of olive biomass and plastics. We got it on an excell sheet that we could send smoothly if you wish. Thank you
22.63 MJ/m3, whilst the composition of the input mixture is not the same)
Line 673: Table 17
It is not clear why option 2 in this comparison (a mixture of 90% olive pellets and 10% WEEE plastics scraps) is evaluated according to a power of 15 kW, whilst the other 2 options entail a power of 10 kW. This comparison does not seem to be fair, since the scale of the compared options is not the same.
Thank you very much for your interesting and sharp comment. We have included this clarification in the discussion section.We try to clarify. Indeed, the power of the production equipment has been adjusted to the total power that we are going to obtain based on the energy characteristics of the synthesis gas produced. This allows the equipment to adjust to the power we expect to produce and therefore reduces the "K" investment costs, making the solution and equipment dimensions more in line with the expected production reality. As we have indicated and in clear relation to section 3.2. The syn-gas analysis produced. We have observed that gas with the highest energy quality for the reasons argued in that section results in the proportion of 10% of plastic. The consequences are that the total electrical energy that we hope to produce is also for this higher proportion of approximately 10.79 Kwh / h. approximately 38,835.08 Kwh / year, which makes us have an annual income of € 7,767.02 / year. Compared with 8.65 kWh / h, and 31,145.40 kWh / year in the case of 100% olive biomass. o 7.90 kWh / h, and 28,430.53 kWh / year 20% plastic. Despite having to make a slightly greater investment in a 15 KW gasifier, 5 Kw more in the case of 10% plastic. Then, we observe that adding the plastic fraction in a moderate proportion (10%) produces a more energetic synergistic gas with more hydrogen, capable of producing more electrical energy and producing numbers in the form of better economic indicators. In particular the VPN. However, when the plastic fraction exceeds 10% and we are at 20%, the energy quality of Syn gas decreases as we analyze in section 3.2 Analysis of Syngas produced. It is for this reason that in order to achieve a better performance of the equipment as a whole, a Gasifier with more power has been chosen in the case of 10% plastic, as we expect a higher annual energy production. However, we have also carried out the simulation for a 10 Kw Gasifier unit, observing that even the economic indicators improve even more obtaining a 4-year amortization with an NPV of 3,096 Euros and a 10-year NPV of 20,829 Euros, with an IRR 33.45% and an IBmC of 0.31. However, it would be advisable to make a design for 15 kW in anticipation of future expansions of the production plant, although the investment is higher and the indicators are slightly lower
Lines 711-713:
what is this claim based on? No environmental assessment was actually described in this study.
Thank you very much for your comment. We have introduced section 3.4. Environmental analysis. In addition, in the Discussion section, we have also incorporated the aspects of an environmental impact compared to the impact of landfill these waste in landfill or use more polluting technologies such as combustion. This, together with the indicators obtained when analyzing the gases, are quite positive, which leaves this door open to a more rigorous analysis in environmental terms for future studies. Thank you
Line 782:
“Bruselas – Bélgica” should be translated into English.
Thank you. We have proceeded to correct
We take this opportunity to thank the reviewer for his interesting comments that we have included in the text.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This paper deals with an experimental study about the convenience in terms of economic parameters of gasification of plastic materials from luminaries and olive grove pellets. A case study in Portugal was analysed in terms of economic benefits after experimental tests by a gasifier. The topic might be interesting but the presented results seems to be conflicting in some parts and not representative of the effective performances of the tested materials. Furthermore, the clarity of the paper is very poor. Thus, I suggest to reject it.
In particular:
1) The novelty of the paper has to be justified also by comparing it to a deeper analysis of the state of the art about scientific researches on gasification of plastic materials and biomass;
2) English language is poor and many typos occur (e.g. lines 58-59, lines 63-64, line 66, lines 84-85 “Waste Reduced Fuels (RDF) or Waste Reduced Fuels (RDF)”?, line 103, line 189 “the recovery or recovery”?, line 372, line 379, line 390, dots where not necessary, etc…). A deep revision by an expert in English language is needed.
3) Table 3 caption is not in English language.
4) Section 2.1 is titled “Biomass analysis”, but in lines 317-322 a not clear description of plastic materials is reported (and also in Tab.3 that is not clear).
5) In Section 2.2, the authors should describe how did they place the thermocouples to measure Tox and Tred temperatures.
6) A 15 kW gasifier was used and connected to a 3kW power generator. The adaptation between these two different power values should be discussed
7) What is the role of the heat exchanger reported in Fig.7?
8) Tab.8 is not well formatted.
9) Lines 430-432: the authors recommend that “the biomass that acts as fuel has an HLV value of no more than 18 MJ / kg”, so a low value because plastic materials has a high LHV and might damage the gasifier that is not designed for it. But the gasifier components might be designed for high HLV values; furthermore, the tested biomass has a HLV value higher than 18 (it is 20, thus it is not optimum following the hypotheses of the authors). Furthermore, in Table 8, HLV is reported in MJ/m3, while the authors discuss about values in MJ/kg (that is the right unit, I suppose).
10) Tab.9 reports the analysis of the produced syngas. When plastic material increased from 0% to 10%, LHV increased. But when plastic material increased from 10% to 20%, LHV decreased. It is very strange; I think relevant measurement errors were made (otherwise, a convincing discussion should be reported). Also, the differences of other reported values should be discussed.
11) Eq.(1) should be explained
12) In Section 3.2, what is the engine (motor)? I suppose it isn’t the generator. I don’t understand eq.(5), where ηeng is given by the authors and not calculated (it is 0.3) and also ηgen is given (it is 0.8)
13) Eq.(6): a NPV equation is reported, but the investment is not considered. Why? Thus, I suppose that in the reported results (Tables 12, 14, 16), NPV doesn’t take into account the investment value
14) Eq.(9): it would be better to report a relation where “t” is on the left side (it is the parameter to be found
15) Table 11 is not well formatte
16) In the economic analysis, the fuel with 20% plastic is the one with the worst NPV, also worse than the pure biomass. This fact should be discussed.
Author Response
Response to Reviewer 2::
Reviewer 2
Comments and Suggestions for Authors
This paper deals with an experimental study about the convenience in terms of economic parameters of gasification of plastic materials from luminaries and olive grove pellets. A case study in Portugal was analysed in terms of economic benefits after experimental tests by a gasifier. The topic might be interesting but the presented results seems to be conflicting in some parts and not representative of the effective performances of the tested materials. Furthermore, the clarity of the paper is very poor. Thus, I suggest to reject it.
Thank you for your comments.
We sincerely appreciate your comments and hope that the important changes made to the document are appreciated by the reviewer.
Then we will try to answer the questions asked by the reviewer one by one. In addition, we will present in the original manuscript the red changes to the rearranged text.
We take this opportunity to thank the reviewer for his interesting comments that we have included in the text and that we hope will contribute to improving and modifying both the substance and the form of the manuscript following his instructions.
In particular:
1) The novelty of the paper has to be justified also by comparing it to a deeper analysis of the state of the art about scientific researches on gasification of plastic materials and biomass;
We appreciate the reviewer's comment and have carried out an in-depth bibliographic review of the state of the art of the research subject, in the introductory part. So that we can justify the novelty of the experience presented in this online work with similar scientific works published in a high-impact journal and that in some way justify the line of research as well as the scientific methodology practised.
2) English language is poor and many typos occur (e.g. lines 58-59, lines 63-64, line 66, lines 84-85 “Waste Reduced Fuels (RDF) or Waste Reduced Fuels (RDF)”?, line 103, line 189 “the recovery or recovery”?, line 372, line 379, line 390, dots where not necessary, etc…). A deep revision by an expert in English language is needed.
We appreciate the critic's comment. We have carried out an in-depth review of the expressions and lines indicated, as well as the English language.
3) Table 3 caption is not in English language.
We apologize for this error, as this expression has not been translated into English and we have proceeded to correct it. Now named table 8. Thank you
4) Section 2.1 is titled “Biomass analysis”, but in lines 317-322 a not clear description of plastic materials is reported (and also in Tab.3 that is not clear).
We agree with the reviewer. We have processed to clarify this paragraph with better description of the plastic material, in point 2,1 Biomass Analysis, including it in the improved Table 7.
5) In Section 2.2, the authors should describe how did they place the thermocouples to measure Tox and Tred temperatures.
We appreciate the reviewer's comment. We have processed to better describe how and in what position the thermocouples will be placed in the gasifier to measure the oxidation and reduction temperature.
The parameters controlled during the gasification process were as follows:
- Oxidation temperature, reduction temperature, and pressure in different parts of the reactor. (Upper and lower zones respectively oxidation and reduction).
- Pressure in the biomass particle filter,
- Air inlet flow.
- Amount of biomass introduced into the reactor.
6) A 15 kW gasifier was used and connected to a 3kW power generator. The adaptation between these two different power values should be discussed
We appreciate the critic's comment. Indeed, this loss of power is associated with the gasification gas performance, the engine performance and the generator performance. Described in Equations (8) (9) and (10), the engine and alternator performances are constant and equal to 0.3 and 0.8 respectively. However, the performance of syn-gas is variable and will depend on the quality of the fuel, that is, on the biomass and plastic mixture used. This means that in the end, the electric power is approximately 1/3. So starting from a 15 kW gasifier, an alternator of 3 kW of electric power will be enought.
7) What is the role of the heat exchanger reported in Fig.7?
We have proceeded to modify Figure 7 and explained the function of the heat exchanger over the text. The heat exchanger has the function of lowering the gas temperature before passing through the particulate filter, due to the fact that it is composed of biomass compounds. Thank you
8) Tab.8 is not well formatted.
We have proceeded to modify according to format Table 8. Thank you very much
9) Lines 430-432: the authors recommend that “the biomass that acts as fuel has an HLV value of no more than 18 MJ / kg”, so a low value because plastic materials has a high LHV and might damage the gasifier that is not designed for it. But the gasifier components might be designed for high HLV values; furthermore, the tested biomass has a HLV value higher than 18 (it is 20, thus it is not optimum following the hypotheses of the authors). Furthermore, in Table 8, HLV is reported in MJ/m3, while the authors discuss about values in MJ/kg (that is the right unit, I suppose).
Thank you very much for your interesting comment. We have proceeded to review and clarify this paragraph in the text, relying on bibliographic references that make it more consistent. Furthermore, as indicated, we have proceeded to modify in Table 9, now, an error in the units detected. It should be MJ / Kg as indicated by the reviewer and then discussed. Thank you very much and we apologize for the error.
“The results from LHV of olive seed is similar to another studies [60][61], and also typical of dry pellet wood biomass [62]. The LHV obtained in the case of the polymeric fuel, 41,8 MJ/kg, was double the value of Olive seed, being results similar to those reported by other studies [63], in fact, he amount of carbon present in polymeric fuel, is responsible for the high energy value [64]. This observation, leads us to think about the interesting use of these materials as fuel with high energy power. On the other hand, it is interesting to note that plastic waste has a high energy, which can affect equipment that is not well designed for it. Due to its high LHV, to avoid damage to the equipment and following the manufacturer's instructions, the co-gasification process is used for waste with high calorific value.”
10) Tab.9 reports the analysis of the produced syngas. When plastic material increased from 0% to 10%, LHV increased. But when plastic material increased from 10% to 20%, LHV decreased. It is very strange; I think relevant measurement errors were made (otherwise, a convincing discussion should be reported). Also, the differences of other reported values should be discussed.
Thank you very much for your comment. In relation to it, we have expanded, discussed and justified the question raised with bibliographic references. Trying to justify it conveniently in the section 3.1. Analysis of the syn-gas produced.
“A first analysis of the results obtained, is possible to demonstrate that the gas produced contain a greater quantity of Hydrogen followed by Carbon Monoxide, this situation occurred in all experiments of the mixtures tested. With a less percentage in the syngas appears the Methane. The high percentage of Nitrogen is because co-gasification has been carried out with atmospheric air [65].
For the blank test, accomplish only with olive seeds, the results present an expected rich syngas in the first analysis. In water gas shift reaction, CO and H2O are consumed whereas CO2 and H2 are synthesized. The consumption rate is higher than the formation rate for CO especially at higher temperatures [66]. Because, CO is consumed to form hydrogen and methane in water–gas shift and methanation reactions:
CO + H2O < - > CO2 + H2 (water-gas shift) (1)
2CO + 2H2 < - > CH4 + CO2 (Methane reforming) (2)
The amount of H2 is highest than the other experiments with polymeric mixtures. This observation is due to the relatively high experimental temperatures during the experiments. Besides, the H2 concentration increase may also be related to the promotion of tar reforming reactions [67][68]. During the gas chromatographic analysis, small amounts light hydrocarbons, like C2H4 and C2H6 were observed. Note that in under similar experimental conditions, for un catalytic gasification of olive seed, higher temperatures increased the formation of hydrogen and light hydrocarbons like methane [69]. The cracking of tars can contribute to the increase of the CH4 and to the consumption of CO2, however, both can be consumed through the enhancement of Methane reforming, in the gasification process with the rise of temperature [70]. This behavior may be the reason for the decreasing tendency observed in the values of CO2 concentration, compared with the other experiments. Olive seeds gasification provides a gas with high energy density (5.3 MJ m-3) and similar properties than wood gas. However, our obtained values on LHV are lower than those found by Borello et al. [71], but higher than those reported by Vera et al. [72].
An interesting aspect of the presented results is that the addition of 10 % plastic to the olive seeds leads to an increase in the calorific value of the syngas regarding the experiences of 100% olive seed and 20% plastic, because of the capitalization in the production of hydrocarbons and mainly the Methane [73]. The increase of the temperature, namely the gasification temperature, is the responsibility of the greater presence of volatiles that the plastic bring fuel [74]. However, the temperature in the 10% experiment (7080C) is not so high, compared with the additional experiments, this aspect is related in the literature and indicates as the gasification temperature increases, concentration of the resulting Hydrogen and Carbon conversion efficiency increase [75]. Meanwhile, the content of CH4 increased slightly with the decrease of temperature. The main reason for the decrease of CH4 content in the product gas is the increasing proportion of gasification gas and the decreasing proportion of pyrolysis gas [76]. Another reason was attributed to the thermal decomposition of methane at the temperature superiors than 700 °C [77]. On the one hand, the produced tars were further cracked into gas at the higher temperature. The increase of temperature can activate the carbon atom and breakdown the carbon chain in the aromatic ring rapidly, reacting with the CO2 to produce gas [78]. This aspect can be observed in the 20% plastic experiment, which has a smaller amount of hydrocarbons in gas produced and also a smaller amount of tars, compared to the 10% plastic experiment.
The H2 concentration is similar in all the experiments performed, the above result indicates the concentration of H2 is not only dependent on the temperature but also on the type of feedstock and gasifying media. The main reason for the increment of H2 concentration is supposed to be the result of the chemical breakdown (thermal cracking) of heavy hydrocarbons which favors molar fraction of the permanent gases like H2 and CO at elevated temperature, what happens with the experiments with 20% plastic and agrees with the experiments conducted by Xiao et al. [79], Kim et al. [80]and Cho et al.[81].
The increase of polymeric residue favors an increase in temperature. As the reactor temperature increased, concentrations of H2 and CO increased. The reason for the increase in the concentrations of H2 and CO can be mainly explained by Le Chatelier's principle. According to this principle, the increase of temperatures favor not only the reactants in exothermic reactions, but also the products in endothermic reactions [82]. Therefore, the endothermic reactions in gasification, such as water–gas shift reaction and Boudouard reaction, will contribute to increasing concentrations of H2 and CO at higher temperatures. With increasing temperature, however, the concentration of hydrocarbons and tars content decreased in producer gas, due to active thermal cracking. These aspects lead to a decrease in LHV. The very low tar content and the high LHV (5 MJ/Nm3) of the producer gas obtained in the experiments would enable it to be used as a fuel for devices that require clean gas, such as internal combustion engines.”
11) Eq.(1) should be explained
Thank you very much for your comment. We have expanded the justification of the equation (old No. 1) and in the new text Equation No. 6. It is simply a volumetric assessment formula, which allows the volume of syn-gas produced to be calculated from the volume of gas introduced and measured with the gasifier anemometer. For the calculation of the synthesis gas production during the gasification tests, an anemometer is used, which is connected to the air inlet. Also with the quality of the synthesis gas produced, it is possible to obtain the amount of N2 present. Another important factor is related to the amount of N2 present in the air. The data is applied in formula 2 and the volume is calculated.
12) In Section 3.2, what is the engine (motor)? I suppose it isn’t the generator. I don’t understand eq.(5), where ηeng is given by the authors and not calculated (it is 0.3) and also ηgen is given (it is 0.8)
The engine used is the Otto cycle engine, as mentioned in the text. Regarding efficiencies, the values used are those provided by the respective manufacturers.
13) Eq.(6): a NPV equation is reported, but the investment is not considered. Why? Thus, I suppose that in the reported results (Tables 12, 14, 16), NPV doesn’t take into account the investment value.
We totally agree with the reviewer. In the formula of equation (7) the inversion (K) was missing, which we have included. Furthermore, the inversion K has been included in Tables 12, 14, 16 and 17. Of course, the investment K for each case has been included for the calculation of the NPV. Please excuse this lapse and apologize and sincerely appreciate the reviewer's appreciation. Thank you.
(7)
14) Eq.(9): it would be better to report a relation where “t” is on the left side (it is the parameter to be found
Thank you very much again for your comments. Indeed we had not well defined the formula of Equation 9, now Equation 10. The return period will be the moment in which the sum of the affected quasi-rents of the interest rate "i" equals the investment (K). We consider the first time period, the first year of amortization, as year1. So "t" takes values ​​between 1 and N. We consider The time period t = 0 is related to the investment during the design and construction phase of the gasifier.
(10)
15) Table 11 is not well formatte.
We have proceeded to correctly format the table and units. Thank you
16) In the economic analysis, the fuel with 20% plastic is the one with the worst NPV, also worse than the pure biomass. This fact should be discussed.
Thank you very much for your interesting and sharp comment. We have included this clarification in the discussion section. We try to clarify. Indeed, the power of the production equipment has been adjusted to the total power that we are going to obtain based on the energy characteristics of the synthesis gas produced. This allows the equipment to adjust to the power we expect to produce and therefore reduces the "K" investment costs, making the solution and equipment dimensions more in line with the expected production reality. As we have indicated and in clear relation to section 3.2. The syn-gas analysis produced. We have observed that gas with the highest energy quality for the reasons argued in that section results in the proportion of 10% of plastic. The consequences are that the total electrical energy that we hope to produce is also for this higher proportion of approximately 10.79 Kwh / h. approximately 38,835.08 Kwh / year, which makes us have an annual income of € 7,767.02 / year. Compared with 8.65 kWh / h, and 31,145.40 kWh / year in the case of 100% olive biomass. o 7.90 kWh / h, and 28,430.53 kWh / year 20% plastic. Despite having to make a slightly greater investment in a 15 KW gasifier, 5 Kw more in the case of 10% plastic. Then, we observe that adding the plastic fraction in a moderate proportion (10%) produces a more energetic synergistic gas with more hydrogen, capable of producing more electrical energy and producing numbers in the form of better economic indicators. In particular the VPN. However, when the plastic fraction exceeds 10% and we are at 20%, the energy quality of Syn gas decreases as we analyze in section 3.2 Analysis of Syngas produced. It is for this reason that in order to achieve a better performance of the equipment as a whole, a Gasifier with more power has been chosen in the case of 10% plastic, as we expect a higher annual energy production. However, we have also carried out the simulation for a 10 Kw Gasifier unit, observing that even the economic indicators improve even more obtaining a 4-year amortization with an NPV of 3,096 Euros and a 10-year NPV of 20,829 Euros, with an IRR 33.45% and an IBmC of 0.31. However, it would be advisable to make a design for 15 kW in anticipation of future expansions of the production plant, although the investment is higher and the indicators are slightly lower
We take this opportunity to thank the reviewer for his interesting comments that we have included in the text.
Author Response File: Author Response.docx
Reviewer 3 Report
Dear Authors,
The work represents an important topic of electronic wastes plastic materials processing. In a whole, the current paper extends a knowledge of plastics and electronic scrap treatment, which could be used for secondary raw products development.
Please, correct a title of paper - there are two diffrent titles in electronic submissiion system and in attached PDF file.
Author Response
Response to Reviewer 3:
Comments and Suggestions for Authors
Dear Authors,
The work represents an important topic of electronic wastes plastic materials processing. In a whole, the current paper extends a knowledge of plastics and electronic scrap treatment, which could be used for secondary raw products development.
Please, correct a title of paper - there are two diffrent titles in electronic submissiion system and in attached PDF file.
Submission Date
11 May 2020
Date of this review
19 May 2020 15:52:58
Response to Reviewer 1:
Thank you very much for your comments.
We sincerely appreciate your comments. We have proceeded to unify the two titles in the indicated files as we advise.
We take this opportunity to thank the reviewers for their work and effort. Thank you very much sincerely
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Despite the apparent effort from the authors, the manuscript does not show any significant improvements. The authors only partially considered the suggestions provided in the previous review round. Moreover, some of the suggested corrections have not been made consistently throughout the manuscript and seem to have been carried out hastily (just to give an example, the use of the term "tonne" instead of "ton", replacing the decimal point for comma as a decimal separator, the use of comma, instead of a point, as a thousand separator, the elimination of the term "olive grove", which can be misleading, etc.)
The authors claim to have carefully checked the manuscript; however, English is still poor and the manuscript is actually full of typos, grammatical and syntactic mistakes, as well as stylistic deficiencies as regards technical-scientific writing. Sometimes this even makes understanding the text difficult. There are often repetitions and, sometimes, inconsistencies. A careful and accurate style and language editing by an expert native speaker with specific technical-scientific skills is needed.
Despite the changes made, the introduction has not improved significantly and remains problematic. It is still too long, repeated concepts are present and the structure is not yet sufficiently clear and linear. It is suggested to rewrite it extensively, making it more synthetic, streamlined and improving its logical structure.
Most of the comments above do apply to other parts of the manuscript. For instance, in the results section some considerations have been added that would better fit in the discussion section.
Consistency is recommended throughout the manuscript, e.g., as regards units: MJ m-3 vs MJ/m3
Here follow some specific comments, JUST BY WAY OF EXAMPLE. However, the manuscript has to be entirely double checked with extreme attention and care.
Lines 280-282:
Why do the authors state that biomass comes from olive grove, then they specify that it does not come from olive grove pruning? If those residues are from olive milling (or from oil extraction from the pomace?), this should be clearly specified, without even mentioning olive tree growing, so as not to create confusion.
Line 325: section 2.1 - Biomass analysis
The actual contents of this section is not fully consistent with its title (the mixture gasified is not just biomass).
Line 326 (see also line 382):
why do the authors call it “forest biomass”? As I understood, this should be referred to as biomass waste (or residue) from agri-food industry.
Lines 388-409:
Some information are repeatedly reported. Please, check carefully.
Line 441:
the cost of installation here reported is not consistent with that shown at line 426.
Line 452:
Please, double check sub-section numbering (also in the following sub-sections)
Lines 453, 460, 464
Inconsistent terminology: “quasi rents” and “cash flows”
Line 470:
The acronym WACC should be defined
Line 531:
The title of table 9 mentions “biomass”; however, the data in the table also refer to PE (which is not biomass).
Line 550:
“the gas produced contain a greater quantity of Hydrogen followed by Carbon Monoxide,..”
Please, check this statement.
Lines 667-668:
Table 11 does not seem to include any results from the application of formulas (3) and (5).
Line 673:
Again, formula (4) here mentioned cannot give as a result what is stated here.
Please, double check that the cited formulas are the right ones.
Line 693:
Table 13:
In the row about LHVfuel, as I understood, the value 22,63 MJ is referred to 1 kg of mixed fuel (90% olive biomass, 10% WEEE plastics), whilst the specific LHV values for the 2 fuels shown in the same row are not referred to 1 kg of each fuel; indeed, they are referred to 900 g of biomass and 100 g of plastics, respectively (indeed, their sum is 22,63, that is the LHV of 1 kg of mixture). However, since the unit shown in that row is MJ/kg all values should be expressed in that unit (this also applies to table 15)
Line 733:
3.4. Environmental Analysis
The considerations here reported are generic and not referred to the specific case study. If an environmental analysis has to be included in this study, this should be specific and should be carried out by means of a suitable methodology (e.g.: Environmental Life Cycle Assessment).
Author Response
Comments and Suggestions for Authors
Despite the apparent effort from the authors, the manuscript does not show any significant improvements. The authors only partially considered the suggestions provided in the previous review round. Moreover, some of the suggested corrections have not been made consistently throughout the manuscript and seem to have been carried out hastily (just to give an example, the use of the term "tonne" instead of "ton", replacing the decimal point for comma as a decimal separator, the use of comma, instead of a point, as a thousand separator, the elimination of the term "olive grove", which can be misleading, etc.)
The authors claim to have carefully checked the manuscript; however, English is still poor and the manuscript is actually full of typos, grammatical and syntactic mistakes, as well as stylistic deficiencies as regards technical-scientific writing. Sometimes this even makes understanding the text difficult. There are often repetitions and, sometimes, inconsistencies. A careful and accurate style and language editing by an expert native speaker with specific technical-scientific skills is needed.
Despite the changes made, the introduction has not improved significantly and remains problematic. It is still too long, repeated concepts are present and the structure is not yet sufficiently clear and linear. It is suggested to rewrite it extensively, making it more synthetic, streamlined and improving its logical structure.
Most of the comments above do apply to other parts of the manuscript. For instance, in the results section, some considerations have been added that would better fit in the discussion section.
R: Thank you very much for your comments and recommendations. We have proceeded to a revision of the Introduction, reducing it significantly and synthesizing it trying to make it clearer for the reader. Thank you.
We respect the reviewer's assessment but we believe that in the results part we show independent results of each test and in the discussion, we compare them.
Consistency is recommended throughout the manuscript, e.g., as regards units: MJ m-3 vs MJ/m3
R: Thank you very much for your recommendation. We have modified these units in the Abstract and revised in other parts of the text
Here follow some specific comments, JUST BY WAY OF EXAMPLE. However, the manuscript has to be entirely double checked with extreme attention and care.
Lines 280-282:
Why do the authors state that biomass comes from olive grove, then they specify that it does not come from olive grove pruning? If those residues are from olive milling (or from oil extraction from the pomace?), this should be clearly specified, without even mentioning olive tree growing, so as not to create confusion.
R: This paragraph has been completely reconstructed.
Line 325: section 2.1 - Biomass analysis
The actual contents of this section is not fully consistent with its title (the mixture gasified is not just biomass).
R: We remove biomass and placed fuel analysis.
Line 326 (see also line 382):
why do the authors call it “forest biomass”? As I understood, this should be referred to as biomass waste (or residue) from agri-food industry.
R: Yes, olive kernel residues are not forest residues. We exchange for the genuine designation and the one suggested by the reviewer.
Lines 388-409:
Some information are repeatedly reported. Please, check carefully.
R: We removed the repetitions of the monitored parameters.
Line 441:
the cost of installation here reported is not consistent with that shown at line 426.
R: We corrected the values.
Line 452:
Please, double check sub-section numbering (also in the following sub-sections)
Thank you. We corrected the subsection number. 2.3.2. Internal Rate of Return (IRR).
Lines 453, 460, 464
Inconsistent terminology: “quasi rents” and “cash flows”
R. We have corrected. The correct term is cash flows.Thanks.
Line 470:
The acronym WACC should be defined
R: The acronym has been defined - weighted average cost of capital.
Line 531:
The title of table 9 mentions “biomass”; however, the data in the table also refer to PE (which is not biomass).
R: Yes, polymeric waste is not considered biomass. We changed by fuels.
Line 550:
“the gas produced contain a greater quantity of Hydrogen followed by Carbon Monoxide,..”
Please, check this statement.
R: We exchange the gases. In all gasifications carried out with air as an oxidizing agent, the concentration of Carbon Monoxide is higher than that of Hydrogen.
Lines 667-668:
Table 11 does not seem to include any results from the application of formulas (3) and (5).
R: The numbering of the formulas was incorrect. It has already been corrected, as requested.
Line 673:
Again, formula (4) here mentioned cannot give as a result what is stated here.
Please, double check that the cited formulas are the right ones.
R: We have checked and corrected the numbering of the formulas in the text.Thanks
Line 693:
Table 13:
In the row about LHVfuel, as I understood, the value 22,63 MJ is referred to 1 kg of mixed fuel (90% olive biomass, 10% WEEE plastics), whilst the specific LHV values for the 2 fuels shown in the same row are not referred to 1 kg of each fuel; indeed, they are referred to 900 g of biomass and 100 g of plastics, respectively (indeed, their sum is 22,63, that is the LHV of 1 kg of mixture). However, since the unit shown in that row is MJ/kg all values should be expressed in that unit (this also applies to table 15)
R: The units are in MJ / kg, so we have changed the values shown, according to the units mentioned.
Line 733:
3.4. Environmental Analysis
The considerations here reported are generic and not referred to the specific case study. If an environmental analysis has to be included in this study, this should be specific and should be carried out by means of a suitable methodology (e.g.: Environmental Life Cycle Assessment).
R: Right. In fact, we have no basis for carrying out environmental analysis. An analysis of all gases, namely NOx and SOx, has not been carried out, nor a comparison with the combustion of the same fuel mixtures. We decided to withdraw the environmental assessment.
Submission Date
11 May 2020
Date of this review
15 Jun 2020 12:35:27
Author Response File: Author Response.docx
Reviewer 2 Report
The authors appropriately improved the paper by solving some doubts and unclearities. I suggest only to improve English Language and correct some typos in the reviewed sentences:
E.g.
Line 90: "Another import problem…"
Line 110: "more efficiente alternatives"
Line 115: "Recent work shas found"
Author Response
Comments and Suggestions for Authors
The authors appropriately improved the paper by solving some doubts and unclearities. I suggest only to improve English Language and correct some typos in the reviewed sentences:
E.g.
Line 90: "Another import problem…"
Line 110: "more efficiente alternatives"
Line 115: "Recent work shas found"
Response:
Thank you for your comments.
We sincerely appreciate your constructive comments and your help that has helped us to improve the quality of work.
We have proceeded to revise the English language in the manuscript again, modifying the expressions to which it refers.
Thank you very much for your help and your review work.
Author Response File: Author Response.docx
