Sustainable Cooking Based on a 3 kW Air-Forced Multifuel Gasification Stove Using Alternative Fuels Obtained from Agricultural Wastes
and Paula Bastida-Molina 1,*Round 1
Reviewer 1 Report
This study presents a sustainable and optimized cooking technique based on biomass gasification principle and the utilization of alternative fuels obtained from agricultural wastes like rice husk in order to reduce the biomass and firewood consumption, to reduce CO2 emission, and thereby, to increase savings for families living in poor communities. It is well written, and provides a sustainable technique using renewable sources; and hereby, it is suitable for publication in this journal. Prior to its publication, following issues need to be carefully addressed by the authors.
(1) Introduction is well written, but needs further improvement. For example; recent publications should be included in order to better explain the current techniques, and novelty of this study.
(2) In the Introduction, page 2 - lines 59-61, the current techniques should be also discussed.
(3) The estimated total amount of solid agricultural waste in these countries (or in DRC) should be provided, if available. This data can be also provided particularly for peanut husk and rice husk used in this study.
(4) The last paragraph of the Introduction (page 2, lines 70-73) is not necessary. I recommend authors to remove it.
(5) The Materials and Method section needs to be significantly improved. In the Section 2.1, key details of the experiments are missing, such as carbonization conditions (temperature, time, atmosphere) and pressing parameters of briquettes. I highly recommend authors to include the characterization techniques of the fuels into this section. In addition, the location of the conducted study (Bandundu) and related details should be provided in this section instead of Results section.
(6) In the Section 2.2, ICS-G stove design and its all components should be discussed in detail, since this is the most important aspect of this study. Please explain its design and all components individually (page 3-4, lines 111-119).
(7) Figures 3 and 4 should be combined, and discussed in the same paragraph. Similarly, Tables 3 and 4 can be combined.
(8) Some figures are not clear enough, and there are issues with labeling (e.g. Figure 2a-b, Figure 5). Please carefully review and provide high-quality figures.
(9) The instrumentation section (2.3) is not well written. Please describe the use of each instrument specifically for each experiment.
(10) In the Results and Discussion section, the authors refer to wrong tables and/or discuss the data in the wrong tables (e.g. lines 257-261, 268-274) in multiple paragraphs. This makes this section very confusing, and authors must carefully review and revise this section (particularly 3.1 and 3.2).
(11) In the page 10, lines 273-275, this sentence is not clear, and hard to understand. Authors should clarify this point.
(12) The discussion is very limited particularly in the Sections 3.1 and 3.2. Authors should discuss their results with the recent literature, if available. This will highly improve the quality of the present paper.
(13) Authors should discuss the influence of their stove design and fuel type/composition (BSW) on their results in detail in order to clearly explain the outcome and novelty of their study compared to the TCS and charcoal.
Author Response
Response to Reviewer 1 Comments
This study presents a sustainable and optimized cooking technique based on biomass gasification principle and the utilization of alternative fuels obtained from agricultural wastes like rice husk in order to reduce the biomass and firewood consumption, to reduce CO2 emission, and thereby, to increase savings for families living in poor communities. It is well written, and provides a sustainable technique using renewable sources; and hereby, it is suitable for publication in this journal. Prior to its publication, following issues need to be carefully addressed by the authors.
Point 1: Introduction is well written, but needs further improvement. For example; recent publications should be included in order to better explain the current techniques, and novelty of this study.
Response 1: We have referenced in the introduction several recent publications dealing with our topic and commented our goals in relation to them. These publications are:
[13] Evaluation of fan-assisted rice husk fuelled gasifier cookstoves for application in sub-Sahara Africa. Ndindeng, Sali Atanga et al., Renewable Energy, 139, 924-935, 2019.
[14] Implementation and scale-up of a biomass pellet and improved cookstove enterprise in Rwanda. Jagger, Pamela and Das, Ipsita. Energy for Sustainable Development. 46, 32-41, 2018.
[15] Use of Biochar-Producing Gasifier Cookstove Improves Energy Use Efficiency and Indoor Air Quality in Rural Households. Gitau, J.K.; et al. Energies 12, 4285-4292, 2019.
[16] Feedstock Dependence of Emissions from a Reverse-Downdraft Gasifier Cookstove. Kirch, Thomas et al. Energy for Sustainable Development, 56, 42-50, 2020.
The addition to the text in the introduction is as follows:
Significant efforts are in progress to improve cooking stoves and limit the above-mentioned drawbacks. It has been found that fan-assisted cookstoves produced both lower concentrations of flue gases and particulate matter [13]. Positive experience in Rwanda promoting biomass pellets and a fan micro-gasification improved cookstove as a clean cooking alternative to charcoal has been obtained [14]. Gasifier Cookstove using biochar improves energy efficiency and air quality [15] and investigation on the gas production from a gasifier cookstove indicates the importance of primary air to reduce tars and increases combustion [16]. This paper addresses all these aspects: gasifier implementation, energy efficiency, air quality, pellets use, etc., looking for the improvement of cook stove both in the technical and economical aspects with special emphasis in the use of agriculture wastes to reduce the environmental impact of cooking in under-developed countries.
Point 2: In the Introduction, page 2 - lines 59-61, the current techniques should be also discussed.
Response 2: We have added in the introduction a reference to the standard current techniques. This addition indicates:
Most of the technologies currently in use consist of enhanced direct combustion ICS with a ceramic combustion chamber. This approach simply involves directing much of the combustion energy to the pot. In such system, it is difficult to improve the quality of combustion because the air supply is naturally ventilated, and therefore difficult to regulate, which leads to incomplete combustion with a direct negative consequence on energy efficiency and polluting emissions.
Point 3: The estimated total amount of solid agricultural waste in these countries (or in DRC) should be provided, if available. This data can be also provided particularly for peanut husk and rice husk used in this study.
Response 3: We have included in the introduction the data required by the referee:
The amount of peanut shell waste produced annually in the Democratic Republic of the Congo is estimated at 114,000 tons and that of rice husk is around 133,200 t / year. The province of Bandundu, to which the present study is applied, being a province totally dedicated to agriculture, represents almost 20% of the production of agricultural residues in the DRC
References for these data are:
[26] FAO-ONU. Perspective monde 2020.
https://perspective.usherbrooke.ca/bilan/servlet/BMTendanceStatPays?codeTheme=5&codeStat=RS.NUT.PROD.PP.MT&codePays=COD&optionsPeriodes=Aucune&codeTheme2=5&codeStat2=RSA.FAO.RicePaddy&codePays2=COD&optionsDetPeriodes=avecNomP&langue=fr.(Consulted 07 08 2020).
[27] STRATEGIE NATIONALE DE DEVELOPPEMENT DE LA RIZICULTURE (SNDR).2013.https://riceforafrica.net/images/pdf/NRDS_drc_fr-min.pdf (Consulted 07 08 2020).
Several kilograms of both types of wastes were used to prepare the different briquettes
Point 4: The last paragraph of the Introduction (page 2, lines 70-73) is not necessary. I recommend authors to remove it.
Response 4: We have removed those lines.
Point 5: The Materials and Method section needs to be significantly improved. In the Section 2.1, key details of the experiments are missing, such as carbonization conditions (temperature, time, and atmosphere) and pressing parameters of briquettes. I highly recommend authors to include the characterization techniques of the fuels into this section. In addition, the location of the conducted study (Bandundu) and related details should be provided in this section instead of Results section
Response 5: We agree to move the location of the study to section 2. In the beginning of the section appears as:
The study was conducted in the city of Bandundu located 409 km from the DRC capital Kinshasa and in an essentially agricultural region. The population size is estimated at 3,673,000 inhabitants and 90% of the population is considered dependent on biomass-firewood for cooking food. The average family size is six people and the eating habits are such that only one large meal is served daily.
Details on the briquettes fabrication have been also added. The steps in the whole `process are detailed as.
Manufacturing of briquettes follows the following steps:
1st) Carbonization: carried out in a traditional furnace composed of a cylindrical metal barrel 80cm in diameter and 120cm high. The metal barrel has about thirty vent holes. 3cm at its lower base. The removable upper base has a 10cm diameter and 100cm high chimney. Char waste is introduced from the top with a quantity of 20 kg of solid waste (rice husks or peanuts). The fire is lit from the top of this furnace. The carbonization system is endothermic in oxygen, evolving at temperatures between 250-500ºC for 2 to 3 hours. After this, holes in the lower base are covered and the lid is closed until cooled, which can last 3 to 4 hours. The carbonization yield varies between 18-20%.
2nd) Grinding: the char waste is placed in a mortar with an artisanal pestle to convert the charred waste into a fine powder with a grain size of 1 mm.
3rd) Binding: the resulting powder, combined with a binder biomass (paper pulp and cassava fibers), is mixed properly up to have a good homogenization.
4th) Densification: this mixture is manually densified to form the briquettes; and
5th) Drying: the briquettes are dried in the sun for three days before their use.
Point 6: In the Section 2.2, ICS-G stove design and its all components should be discussed in detail, since this is the most important aspect of this study. Please explain its design and all components individually (page 3-4, lines 111-119).
Response 6: The ICS-G components have been described in the new version.
ICS-G stove includes the following components:
- Reactor: it is cylindrical, 12cm internal diameter and 19cm deep, and surrounded by a 1cm layer of clay.
- Secondary Air Duct Tunnel: Another 16cm cylinder surrounds the reactor, so a 1mm gap allows secondary air to rise, sweeping through the reactor body. This allows preheating of the secondary air.
- Thermal insulation: a 4cm layer of rock wool
- Fan: A small 3W-12V DC motor provides the primary and secondary air supply.
- Power supply: a small 5W solar panel that charges a 9Ah-12V lithium battery.
- Regulation: a potentiometric circuit allows varying the supply voltage of the small motor, to control the primary and secondary airflows.
- Outer shell: it is a24cm cube made of 1mm thick sheet metal. The lower base is perforated to allow the motor to inject ambient air
Point 7: Figures 3 and 4 should be combined and discussed in the same paragraph. Similarly, Tables 3 and 4 can be combined.
Response 7: Figures have been combined in a single one. In respect to tables 3 and 4, we consider, given the amount of information to put in a single table, more adequate to keep them separated.
Point 8: Some figures are not clear enough, and there are issues with labeling (e.g. Figure 2a-b, Figure 5). Please carefully review and provide high-quality figures
Response 8: Both figures have now bigger resolution.
(they can be seen in the word document)
Point 9: The instrumentation section (2.3) is not well written. Please describe the use of each instrument specifically for each experiment
Response 9: We have rewritten the section 2.3 and indicate the use of each component.
2.3. Instrumentation
The equipment used to characterize the proposed fuel and stove includes:
-Balance OHAUS V11P6 with a 6 kg capacity and 0.1g accuracy. Used to determine the amount of fuel used in the WBT and CCT test.
-Balance OHAUS NVL 20000/2 with a 20 kg capacity and 1 g accuracy. This scale was used to measure the amount of water to boil during the WBT test and the amount of dry and cooked meal during the CCT test.
-Balance Mettler AB304-S / FACT with a 320 g capacity and 0.1 mg accuracy. It was used for the characterization of briquettes
-Select Muffle Furnace SELECT-HORN, Capacity 9 liters. Power 3000 W. Maximum temperature 1100 ºC. This muffle was used for the thermo-physical characterization of briquettes
-Combustion calorimeter CAL2K/1. Resolution 0.001 MJ/kg and 0.000001 ºC. To allow for the determination of the calorific value of the briquettes
Point 10: In the Results and Discussion section, the authors refer to wrong tables and/or discuss the data in the wrong tables (e.g. lines 257-261, 268-274) in multiple paragraphs. This makes this section very confusing, and authors must carefully review and revise this section (particularly 3.1 and 3.2).
Response 10: There were some mistakes we had not noticed. Now we have corrected them. Additionally we have compared our results with other works in recent.literature.
In a recent study done in a Kenyan village on the impact of a gasifier on improving energy efficiency and reducing polluting emissions, Gitau, J.K. et al. [15] underlines a reduction in CO and PM emissions of 57% and 79%, respectively, when compared with the traditional model. Our improved performance of the ICS-G is mainly due to the improved combustion quality due to the adjustment of the stoichiometric air quantity, which leads to an almost complete combustion of the solid biomass. Forced ventilation (ICS-G) always results in better combustion than natural ventilation (TCS), all other things being equal. In addition, the ICS-G combustion chamber is thermally insulated, this prevents heat loss on the sides of the ICS-G stove and therefore concentrates all the heat produced and directs it towards the pot with the movement of forced air. Natural ventilation does not ensure perfect combustion because its random nature and high dependence on the external atmospheric conditions, as the combustion chamber is not closed, heat losses are uncontrolled and widespread.
Obtained improvement in emissions are in agreement with the results published in [16], where at lower air supply rates, low emissions of both PM and CO are achieved.
Point 11: In the page 10, lines 273-275, this sentence is not clear, and hard to understand. Authors should clarify this point.
Response 11: Text have been changed to:
A fuel saving of 61% is observed as well as a 20% decrease in the time used for cooking when the improved ICS-G stove is used. This is an improvement on the 40% fuel economy reported in [15] for a natural air gasifier. Table 12 shows the test results using BSW3 as fuel. In this case, ICS-G has very similar fuel savings in relation to the TCS independent of the type of fuel: charcoal or BSW3 than in the previous case, 61%. Similarly, cooking time saving is almost the same for the two kind of fuel: 18% compared to the traditional system. However, BSW3 main advantage comes from the fact that this fuel is obtained from agricultural residues, so no cutting down of trees as in the use of charcoal is needed.
Point 12: The discussion is very limited particularly in the Sections 3.1 and 3.2. Authors should discuss their results with the recent literature, if available. This will highly improve the quality of the present paper
Response 12: We have included recent publications (already mentioned in the new introduction (see response 1) and compared our results with them.
A fuel saving of 61% is observed as well as a 20% decrease in the time used for cooking when the improved ICS-G stove is used. This is an improvement on the 40% fuel economy reported in [15] for a natural air gasifier.
Obtained improvement in emissions are in agreement with the results published in [16], where at lower air supply rates, low emissions of both PM and CO are achieved.
Point 13: Authors should discuss the influence of their stove design and fuel type/composition (BSW) on their results in detail in order to clearly explain the outcome and novelty of their study compared to the TCS and charcoal.
Response 13: We believe that the advantages in the different aspects: fuel economy, energy efficiency, reduction of the environmental impact by the use of agricultural wastes and improvement in the air quality, were proved along the paper and summarized in the conclusions. All these advantages come from a novel design of the cooking stove and the briquettes.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors applied two lab methods (WBT and CCT) on sustainable cooking in developing countries. It is very interesting and meaningful work. In the introduction section, more references are suggested on the lab methods and their advantages compared to other methods. In the conclusion, more details such as the value and implication of the protocols are suggested.
Author Response
Response to Reviewer 2 Comments
The authors applied two lab methods (WBT and CCT) on sustainable cooking in developing countries. It is very interesting and meaningful work. In the introduction section more references are suggested on the lab methods and their advantages compared to other methods. In the conclusion, more details such as the value and implication of the protocols are suggested.
Response: We have referenced in the introduction several recent publications dealing with our topic and commented our goals in relation to them. These publications are:
[13] Evaluation of fan-assisted rice husk fuelled gasifier cookstoves for application in sub-Sahara Africa. Ndindeng, Sali Atanga et al., Renewable Energy, 139, 924-935, 2019.
[14] Implementation and scale-up of a biomass pellet and improved cookstove enterprise in Rwanda. Jagger, Pamela and Das, Ipsita. Energy for Sustainable Development. 46, 32-41, 2018.
[15] Use of Biochar-Producing Gasifier Cookstove Improves Energy Use Efficiency and Indoor Air Quality in Rural Households. Gitau, J.K.; et al. Energies 12, 4285-4292, 2019.
[16] Feedstock Dependence of Emissions from a Reverse-Downdraft Gasifier Cookstove. Kirch, Thomas et al. Energy for Sustainable Development, 56, 42-50, 2020.
The addition to the text in the introduction is as follows:
Significant efforts are in progress to improve cooking stoves and limit the above-mentioned drawbacks. It has been found that fan-assisted cookstoves produced both lower concentrations of flue gases and particulate matter [13]. Positive experience in Rwanda promoting biomass pellets and a fan micro-gasification improved cookstove as a clean cooking alternative to charcoal has been obtained [14]. Gasifier Cookstove using biochar improves energy efficiency and air quality [15] and investigation on the gas production from a gasifier cookstove indicates the importance of primary air to reduce tars and increases combustion [16]. This paper addresses all these aspects: gasifier implementation, energy efficiency, air quality, pellets use, etc., looking for the improvement of cook stove both in the technical and economical aspects with special emphasis in the use of agriculture wastes to reduce the environmental impact of cooking in under-developed countries.
We also have added in the introduction a reference to the standard current techniques. This addition indicates:
Most of the technologies currently in use consist of enhanced direct combustion ICS with a ceramic combustion chamber. This approach simply involves directing much of the combustion energy to the pot. In such system, it is difficult to improve the quality of combustion because the air supply is naturally ventilated, and therefore difficult to regulate, which leads to incomplete combustion with a direct negative consequence on energy efficiency and polluting emissions.
Also, the amount of agriculture wastes in the DRCongo has been detailed:
The amount of peanut shell waste produced annually in the Democratic Republic of the Congo is estimated at 114,000 tons and that of rice husk is around 133,200 t / year. The province of Bandundu, to which the present study is applied, being a province totally dedicated to agriculture, represents almost 20% of the production of agricultural residues in the DRC
References for these data are:
[26] FAO-ONU. Perspective monde 2020.
https://perspective.usherbrooke.ca/bilan/servlet/BMTendanceStatPays?codeTheme=5&codeStat=RS.NUT.PROD.PP.MT&codePays=COD&optionsPeriodes=Aucune&codeTheme2=5&codeStat2=RSA.FAO.RicePaddy&codePays2=COD&optionsDetPeriodes=avecNomP&langue=fr.(Consulted 07 08 2020).
[27] STRATEGIE NATIONALE DE DEVELOPPEMENT DE LA RIZICULTURE (SNDR).2013.https://riceforafrica.net/images/pdf/NRDS_drc_fr-min.pdf (Consulted 07 08 2020).
Additionally we have compared our results with other works in recent.literature.
In a recent study done in a Kenyan village on the impact of a gasifier on improving energy efficiency and reducing polluting emissions, Gitau, J.K. et al. [15] underlines a reduction in CO and PM emissions of 57% and 79%, respectively, when compared with the traditional model. Our improved performance of the ICS-G is mainly due to the improved combustion quality due to the adjustment of the stoichiometric air quantity, which leads to an almost complete combustion of the solid biomass. Forced ventilation (ICS-G) always results in better combustion than natural ventilation (TCS), all other things being equal. In addition, the ICS-G combustion chamber is thermally insulated, this prevents heat loss on the sides of the ICS-G stove and therefore concentrates all the heat produced and directs it towards the pot with the movement of forced air. Natural ventilation does not ensure perfect combustion because its random nature and high dependence on the external atmospheric conditions, as the combustion chamber is not closed, heat losses are uncontrolled and widespread.
Obtained improvement in emissions are in agreement with the results published in [16], where at lower air supply rates, low emissions of both PM and CO are achieved.
Response 12: We have included recent publications (already mentioned in the new introduction (see response 1) and compared our results with them.
A fuel saving of 61% is observed as well as a 20% decrease in the time used for cooking when the improved ICS-G stove is used. This is an improvement on the 40% fuel economy reported in [15] for a natural air gasifier.
Obtained improvement in emissions are in agreement with the results published in [16], where at lower air supply rates, low emissions of both PM and CO are achieved.
We believe that the advantages in the different aspects: fuel economy, energy efficiency, reduction of the environmental impact by the use of agricultural wastes and improvement in the air quality, were proved along the paper and summarized in the conclusions. All these advantages come from a novel design of the cooking stove and the briquettes.
Author Response File: Author Response.docx
