Techno-Economic Analysis of BAU-STR Dryer for Rice Drying: An Approach to Accelerate Adoption

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1、The paper introduced a BAU-STR dryer and analyzed its performance and techno-economic indicators, but did not elaborate on the uniqueness of this study and lacked innovation at the technical and theoretical levels.

 

2、In response to Fig. 4(a), why is the middle grain temperature > lower grain temperature > upper grain temperature in the longitudinal distribution of grain temperature in the drying equipment?

 

3、Under the working conditions of average drying temperature of 43°C and relative humidity of 30%, we have doubts about Tab.1's mention of 4 hours to reduce the moisture content of grain from 19.5±0.5 to 13.4±0.1 (%, wet basis), and because the Average drying rate is 1.5±0.05 (%MC/h), which is prone to waist bursting, leading to quality problems. quality problems, so for the corresponding techno-economic calculations have an impact, but the study lacks this aspect of consideration and content.

 

4、How is the specific energy consumption of 2.98±0.10 (MJ/kg of moisture) in Tab.1 calculated? What is the value chosen for latent heat of vaporization?

 

5、The R_t (estimated net cash flow at a specific time) mentioned in the NPV (net present value) equation (line 200-line 202 , equation 7) is not given an exact value and calculation method in the subsequent data.

 

6、The study is intended to provide a way of drying grains for developing countries and underserved areas or populations, but the financial calculations are based on U.S.-based data/calculations (various costs and fees), and the U.S. is a developed country, with significant differences from developing countries in socio-economic dimensions such as Labor cost, Discount rate, and Investment costs. It lacks generalizability and practical application, and further improvements or additions to the calculation method and cost estimates need to be considered.

Author Response

Reviewer #1

1. The paper introduced a BAU-STR dryer and analyzed its performance and techno-economic indicators, but did not elaborate on the uniqueness of this study and lacked innovation at technical and theoretical levels.

Answer:

Thank you for your valuable feedback. This study is unique because it adapts the BAU-STR dryer, initially developed for rural communities in Bangladesh, to suit the agricultural needs of U.S. underserved communities. The innovation lies in modifying the blower and burner to improve energy efficiency and scalability in the U.S. In addition, the study offers a comprehensive techno-economic analysis that evaluates operational costs and highlights long-term benefits like reduced energy consumption and minimized post-harvest losses, positioning the technology as cost-effective and environmentally sustainable. By bridging the gap between a low-cost, accessible technology and the needs of modern agriculture, this research contributes to the advancement of sustainable farming practices in developed countries.

 

2. In response to Fig. 4(a), why is the middle grain temperature > lower grain temperature > upper grain temperature in the longitudinal distribution of grain temperature in the drying equipment?

 

Answer:

In response to Fig. 4(a), the variation in grain temperatures across the different levels of the drying equipment can be explained by the airflow dynamics (Fig. 2) and heat transfer during the drying process. Suppose you look at Figure 2(a). In that case, it will be observed that grain in the middle section of the dryer receives a higher temperature (< 0.5°C) due to the airflow dynamics of the blower, which circulates heated air more intensively in that region.

 

3. Under the working conditions of average drying temperature of 43°C and relative humidity of 30%, we have doubts about Tab.1's mention of 4 hours to reduce the moisture content of grain from 19.5±0.5 to 13.4±0.1 (%, wet basis), and because the Average drying rate is 1.5±0.05 (%MC/h), which is prone to waist bursting, leading to quality problems, so for the corresponding techno-economic calculations have an impact, but the study lacks this aspect of consideration and content.

 

Answer:

Thank you for raising these concerns. As we know, the grain drying rate depends on the drying air temperature, the temperature difference between grain and drying air, and the airflow rate. In our study, we used a blower, which created more air flow than the original version of the BAU-STR dryer.

I included a drying rate curve in the revised manuscript for better understanding. Referring to Figure 7 (revised manuscript), the moisture content curve clearly shows a reduction from approximately 19.5% to 13.4% over 4 hours under the given working conditions (43°C and 30% relative humidity), i.e., the average moisture removal rate is 1.5±0.05 (%MC/h). However, the drying rate curve illustrated that the average of 2.0%/hr was observed at the first 2 hours of drying (because more moisture is available for evaporation). Still, it gradually decreases after the second hour as less moisture becomes available for evaporation, reflecting the typical falling-rate drying period aligned with the common drying rate phenomenon of agricultural products.

 

During the drying experiment, we randomly examined the color of the dried grain and any instances of splitting kernels, but no noticeable issues were observed. However, further investigation into the relationship between the drying rate and potential grain quality issues, such as burst kernels, is necessary. Unfortunately, I cannot conduct this analysis due to resource constraints and limitations in experimental access.

 

4. How is the specific energy consumption of 2.98±0.10 (MJ/kg of moisture) in Tab.1 calculated? What is the value chosen for latent heat of vaporization?

 

Answer:

Thank you for your question. I have included an equation for calculating specific energy consumption and standard values for different parameters in the revised manuscript (Lines 168 -174). I used a value of 2398.8 kJ/kg°C as the latent heat of vaporization of water as the average drying air temperature was 43°C.

 

5. The Rt (estimated net cash flow at a specific time) mentioned in the NPV (net present value) equation (line 200-line 202, equation 7) is not given an exact value and calculation method in the subsequent data.

 

Answer:

Thank you for your valuable comment. I made a typing mistake for the NPV equation in an earlier version of the manuscript. I corrected the NPV equation in the revised manuscript (Eq. 8; Line-222).

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6. The study is intended to provide a way of drying grains for developing countries and underserved areas or populations. Still, the financial calculations are based on U.S.-based data/calculations (various costs and fees), and the U.S. is a developed country with significant differences from developing countries in socio-economic dimensions such as Labor cost, Discount rate, and Investment costs. It needs more generalizability and practical application, and further improvements or additions to the calculation method and cost estimates need to be considered.

 

Answer:

Thank you for your question. Yes, you are correct. We only considered propane gas and electricity costs to calculate the energy cost, as is typical in the USA. These factors impact drying costs and other financial factors less than hourly labor costs (Table 4). To assess the influence of varying labor costs (Table 6), discount rates (Table 7), and investment costs (Table 8) on drying cost, NPV, IRR, BCR, and the payback period, we used a wide range of values for these variables. This approach ensures that the business model remains robust.

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

 

COMMENTS:

Material and Methods:

v Comment (Line 112): During the drying experiment, the drying air temperature was kept below 43°C because higher drying temperature has significant negative effect of seed viability and germination rate.

Suggestion: This should be made clearer in the introduction and throughout the text. This suggestion is due to the fact that the objectives to be achieved in order to obtain a seed are different from those to obtain a general-purpose grain.   

Results and discussion:

v Comment (Lines 285-286): “It was also observed that the drying rate decreased 285 with the decrease in moisture content. ”

Question: Is this conclusion based only on Figure 6? The term "drying rate" should be made clearer in the text, as this term in the description of the drying process has another concept.

A general suggestion:

v Products such as rice require a specific drying technique, due to the damage caused by continuous drying. Therefore, some analysis of mechanical damage should be added to this work, in order to justify the use of this equipment for drying rice.

Author Response

Reviewer #2

 

1. Comment (Line 112): During the drying experiment, the drying air temperature was kept below 43°C because higher drying temperature has significant negative effect of seed viability and germination rate.

Suggestion: This should be made clearer in the introduction and throughout the text. This suggestion is due to the fact that the objectives to be achieved in order to obtain a seed are different from those to obtain a general-purpose grain.

 

Answer:

Thank you for your valuable suggestion. I already made it clear in the revised manuscript.

 

2. Comment (Lines 285-286): “It was also observed that the drying rate decreased 285 with the decrease in moisture content.”

Question: Is this conclusion based only on Figure 6? The term "drying rate" should be made clearer in the text, as this term in the description of the drying process has another concept.

 

Answer:

Thank you for your question. I included the drying rate curve (Figure 7) in the revised manuscript and added the necessary explanation.

 

3. Products such as rice require a specific drying technique, due to the damage caused by continuous drying. Therefore, some analysis of mechanical damage should be added to this work, in order to justify the use of this equipment for drying rice.

 

Answer:

Thank you for your valuable suggestion regarding analyzing mechanical damage associated with rice drying. While I agree that understanding the impact of drying techniques on product integrity is essential, I need help conducting this analysis due to resource constraints and limitations in experimental access. However, I acknowledge the significance of this aspect and will highlight the need for future research in this area within the manuscript. This will encourage subsequent studies to explore mechanical damage and optimize drying methods for rice, ensuring that the equipment's application is fully justified and aligned with the quality standards required for this crop.

 

 

Reviewer 3 Report

Comments and Suggestions for Authors

Introduction :

The literature review needs more references to give a deep vision of the topic.

References:

The number of it needs to increase for more concentration related to the topic.

Results:

 

It needs more curves for the drying rate because it is mentioned in the results but not in the diagrams.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Minor Revision

Author Response

Reviewer #3

 

 

1. The literature review needs more references to give a deep vision of the topic.

 

Answer:

Thank you for raising this concern. I partially revised the introduction with more literature review.

 

2. The number of it needs to increase for more concentration related to the topic.

 

Answer:

Thank you for your suggestion. I included 10 additional references in the manuscript.

 

3. It needs more curves for the drying rate because it is mentioned in the results but not in the diagrams.

 

Answer:

Thank you for your valuable feedback. I included the drying rate curve (Figure 7) in the revised manuscript and added the necessary explanation.

 

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

1. In Fig. 4(a) the authors explain the phenomenon of temperature distribution by means of a schematic diagram of airflow direction, but the explanation lacks sufficient details to support it. It is recommended that the authors further analyse the distribution of airflow and heat transfer inside the drying equipment in the paper, and combine the experimental data or simulation results to explain in detail the specific reasons why the temperature of the middle layer of grain is higher than the temperature of the lower and upper layers of grain, so as to enhance the scientificity and credibility of the explanation.

 

Overall recommendation: The article has been improved after initial revision, but there is still room for improvement in technical details. It is hoped that the authors will make further revisions according to the above suggestions to enhance the rigour and application value of the paper.

Author Response

Reviewer #1

Comments and Suggestions for Authors

In Fig. 4(a) the authors explain the phenomenon of temperature distribution by means of a schematic diagram of airflow direction, but the explanation lacks sufficient details to support it. It is recommended that the authors further analyze the distribution of airflow and heat transfer inside the drying equipment in the paper and combine the experimental data or simulation results to explain in detail the specific reasons why the temperature of the middle layer of grain is higher than the temperature of the lower and upper layers of grain, so as to enhance the scientificity and credibility of the explanation.

Overall recommendation: The article has been improved after initial revision, but there is still room for improvement in technical details. It is hoped that the authors will make further revisions according to the above suggestions to enhance the rigour and application value of the paper.

 

Answer:

Thank you for your valuable suggestions. I have provided additional explanations for Figure 4(a) in the manuscript using different font colors. While I recognize the importance of analyzing the distribution of airflow and heat transfer within the drying bin, we are currently unable to pursue a more in-depth analysis due to constraints on experimental access.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Only my observation number 2. was answered in the manuscript.

Author Response

 

 

Reviewer #2

 

Comments and Suggestions for Authors

Only my observation number 2. was answered in the manuscript.

 

Answer:

We made a mistake with my previous response. We added a sentence in the manuscript to make the statement more understandable according to your comment #1.

 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for accepting my suggestions to improve quality of the paper.

Author Response

Reviewer # 3

 

Comments and Suggestions for Authors

Thank you for accepting my suggestions to improve the quality of the paper.

 

Answer:

Thank you for your feedback and guidance in enhancing the quality of our paper. We appreciate your time and valuable suggestions.

 

Author Response File: Author Response.docx

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

After the corrections were made, I am in favor of publishing the article.