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Household biogas digesters

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Hai Anh Tran
Hai Anh Tran

This document evaluates and compares four common types of household biogas digesters in Vietnam: KT31 (brick and composite), composite, brick (KT1 and KT2), and nylon bag. The digesters are compared based on construction materials, construction method, operation and maintenance, return on investment, and sanitation. Overall, KT31 and composite digesters performed best but have higher costs, while nylon bag has the lowest cost but is less durable and difficult to maintain. KT1 and KT2 showed medium performance across criteria. The conclusions recommend different digester types based on location, budget, and long-term needs.

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Evaluation of Household Biogas Digesters
Content 1. Introduction 2. Designs 3. Constructions 4. Evaluations and Comparisons 5. Conclusions
1. Introduction
1.1 Background The mostVietnam common household biogas digesters: ï‚— Household biogas digester which is made from brick and composite (KT31) ï‚— Household biogas digester which is made from composite ï‚— Household biogas digester which is made from brick (KT1 & KT2) ï‚— Household biogas digester which is made from nylon bag
1.2. Evaluation Criteria 1. Construction material (10 scores max.) 2. Convenient of construction method (20 scores max.) 3. O&M (30 scores max.) 4. Return on Investment (30 scores max.) 5. Sanitation (10 scores max.) Total: 100 scores
2. Design
2.1 KT 31 design 1. Digester 2. Gas holder 3. Inlet 4. Outlet 5. Gas outlet 6. Compensation tank
2.2 KT1 & KT2 design KT1 KT2
2.3 Composite design 400 1000mm 1000 400 R= 2600 Inlet: 800 Outlet: 900 1300 600 80 400 200 Gas outlet Gas holder Digester
2.4 Nylon bag
2. Construction
3.1 Construction of KT31
3.2 Construction of KT1 &KT2
3.3 Construction of Composite
3.4 Construction of Nylon bag
3. Comparison and Evaluation
4.1 Comparison in terms of construction materials 8.58 6.79 5.00 10.00 7.58 4.79 5.00 9.55 - 2.00 4.00 6.00 8.00 10.00 12.00 KT31- Northern part Composite- Northern part Nylong bag- Northern part KT1 KT31- southern part Composite- Southern part Nylong bag- Southern part KT2 Total score (10 maximum) Availability (5 maximum) Strength (5 maximum)
4.2 Comparison in terms of Convenient of construction 8.01 17.03 20.00 4.00 5.53 14.06 16.17 0.50 0.00 5.00 10.00 15.00 20.00 25.00 KT31 - The north Composite- the north Nylong bag - the north KT1 KT31- the south Composite- the south Nylon bag - the south KT 2 Total score (20 maximum) Soil excavation (5 maximum) Easy to contruct (5 maximum) Manday (5 maximum) Score for construction method (5 maximum)
4.3 O&M Comparison 20.0 24.0 10.3 20.5 20.0 22.5 9.8 22.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 KT31 - the north Composite- the north Nylong bag- the north KT1 KT31-the south Composite- the south Nylong bag - the south KT 2 Total (30 maximum) Safety of the structure (6 maximum) Safety of end user (6 maximum) Gas productivity (6 maximum) Easiness for O&M (6 maximum) Easiness to dectect failure and to repair
4.3 Comparison of ROI 12.26 10.01 16.66 19.40 12.48 11.23 16.66 17.89 0.00 5.00 10.00 15.00 20.00 25.00 KT31 - the north Composite- the north Nylon bag KT1 KT31- the South Composite- the south Nylon bag - the south KT 2 Total score( 30 maximum) Total investmetn csot (10 maximum) Average Anual investmetn cost (10 maximum) Payback period (3.33 maximum) NPV (3.33 maximum) IRR ( 3.33 maximum)
4.4 Comparison of Sanitation No. Model Smell bad (5 maximum) BOD 5, COD, coliforms (5 maximum) Total (5 maximum) 1 KT31 5.00 5.00 10.00 2 Composite 5.00 5.00 10.00 3 Nylon bag 5.00 5.00 10.00 4 KT1-KT2 5.00 5.00 10.00
4.5 Overall Comparison 58.85 67.83 61.96 63.90 55.59 62.58 57.63 59.94 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 KT31 - the north Composite- the north Nylon bag- the north KT1 KT31- the south Composite- the south Nylon bag the south KT 2 Total (100 maximum) Construction material (10 maximum) Construction (20 maximum) O&M (30 maximum) Cost (30 maximum) Environment (10 maximum)
5. Conclusions
5.1 KT31 digester ï‚— Pros: ï‚— Durable and long lifetime. ï‚— Cons: ï‚— High Investment cost ï‚— More complicated to transport ï‚— Less availability. ï‚— Need trained masons.
5.2 Composite digester ï‚— Pros: ï‚— Easy to install and O&M ï‚— Higher gas productivity and longer lifetime ï‚— No need trained masons ï‚— Cons: ï‚— High investment cost ï‚— More complicated to transport. ï‚— Applicability: ï‚— Week soil foundation with high ground water level. ï‚— Places without trained masons, brick and cements.
5.3 KT1 & KT2 digesters ï‚— Pros: ï‚— Higher gas productivity and longer lifetime. ï‚— Medium initial investment cost. ï‚— Easy to operate. ï‚— Cons: ï‚— Need trained mason. ï‚— Not easy to maintain. ï‚— Need trained masons, bricks and cements.
5.2 Nylon- bag digester ï‚— Pros: ï‚— Lowest initial investment capital ï‚— Easy to install, no need trained mason. ï‚— High availability of construction material. ï‚— Cons: ï‚— Inconvenient O&M ï‚— Less durable and short lifetime ï‚— Applicability ï‚— Poor households. ï‚— No long term plan of raising animal.
Contact: Tran Hai Anh – Renewable Energy Specialist Tran_haianh@yahoo.com

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Household biogas digesters

  • 1. Evaluation of Household Biogas Digesters
  • 2. Content 1. Introduction 2. Designs 3. Constructions 4. Evaluations and Comparisons 5. Conclusions
  • 4. 1.1 Background The mostVietnam common household biogas digesters: ï‚— Household biogas digester which is made from brick and composite (KT31) ï‚— Household biogas digester which is made from composite ï‚— Household biogas digester which is made from brick (KT1 & KT2) ï‚— Household biogas digester which is made from nylon bag
  • 5. 1.2. Evaluation Criteria 1. Construction material (10 scores max.) 2. Convenient of construction method (20 scores max.) 3. O&M (30 scores max.) 4. Return on Investment (30 scores max.) 5. Sanitation (10 scores max.) Total: 100 scores
  • 7. 2.1 KT 31 design 1. Digester 2. Gas holder 3. Inlet 4. Outlet 5. Gas outlet 6. Compensation tank
  • 8. 2.2 KT1 & KT2 design KT1 KT2
  • 9. 2.3 Composite design 400 1000mm 1000 400 R= 2600 Inlet: 800 Outlet: 900 1300 600 80 400 200 Gas outlet Gas holder Digester
  • 14. 3.3 Construction of Composite
  • 15. 3.4 Construction of Nylon bag
  • 16. 3. Comparison and Evaluation
  • 17. 4.1 Comparison in terms of construction materials 8.58 6.79 5.00 10.00 7.58 4.79 5.00 9.55 - 2.00 4.00 6.00 8.00 10.00 12.00 KT31- Northern part Composite- Northern part Nylong bag- Northern part KT1 KT31- southern part Composite- Southern part Nylong bag- Southern part KT2 Total score (10 maximum) Availability (5 maximum) Strength (5 maximum)
  • 18. 4.2 Comparison in terms of Convenient of construction 8.01 17.03 20.00 4.00 5.53 14.06 16.17 0.50 0.00 5.00 10.00 15.00 20.00 25.00 KT31 - The north Composite- the north Nylong bag - the north KT1 KT31- the south Composite- the south Nylon bag - the south KT 2 Total score (20 maximum) Soil excavation (5 maximum) Easy to contruct (5 maximum) Manday (5 maximum) Score for construction method (5 maximum)
  • 19. 4.3 O&M Comparison 20.0 24.0 10.3 20.5 20.0 22.5 9.8 22.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 KT31 - the north Composite- the north Nylong bag- the north KT1 KT31-the south Composite- the south Nylong bag - the south KT 2 Total (30 maximum) Safety of the structure (6 maximum) Safety of end user (6 maximum) Gas productivity (6 maximum) Easiness for O&M (6 maximum) Easiness to dectect failure and to repair
  • 20. 4.3 Comparison of ROI 12.26 10.01 16.66 19.40 12.48 11.23 16.66 17.89 0.00 5.00 10.00 15.00 20.00 25.00 KT31 - the north Composite- the north Nylon bag KT1 KT31- the South Composite- the south Nylon bag - the south KT 2 Total score( 30 maximum) Total investmetn csot (10 maximum) Average Anual investmetn cost (10 maximum) Payback period (3.33 maximum) NPV (3.33 maximum) IRR ( 3.33 maximum)
  • 21. 4.4 Comparison of Sanitation No. Model Smell bad (5 maximum) BOD 5, COD, coliforms (5 maximum) Total (5 maximum) 1 KT31 5.00 5.00 10.00 2 Composite 5.00 5.00 10.00 3 Nylon bag 5.00 5.00 10.00 4 KT1-KT2 5.00 5.00 10.00
  • 22. 4.5 Overall Comparison 58.85 67.83 61.96 63.90 55.59 62.58 57.63 59.94 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 KT31 - the north Composite- the north Nylon bag- the north KT1 KT31- the south Composite- the south Nylon bag the south KT 2 Total (100 maximum) Construction material (10 maximum) Construction (20 maximum) O&M (30 maximum) Cost (30 maximum) Environment (10 maximum)
  • 24. 5.1 KT31 digester ï‚— Pros: ï‚— Durable and long lifetime. ï‚— Cons: ï‚— High Investment cost ï‚— More complicated to transport ï‚— Less availability. ï‚— Need trained masons.
  • 25. 5.2 Composite digester ï‚— Pros: ï‚— Easy to install and O&M ï‚— Higher gas productivity and longer lifetime ï‚— No need trained masons ï‚— Cons: ï‚— High investment cost ï‚— More complicated to transport. ï‚— Applicability: ï‚— Week soil foundation with high ground water level. ï‚— Places without trained masons, brick and cements.
  • 26. 5.3 KT1 & KT2 digesters ï‚— Pros: ï‚— Higher gas productivity and longer lifetime. ï‚— Medium initial investment cost. ï‚— Easy to operate. ï‚— Cons: ï‚— Need trained mason. ï‚— Not easy to maintain. ï‚— Need trained masons, bricks and cements.
  • 27. 5.2 Nylon- bag digester ï‚— Pros: ï‚— Lowest initial investment capital ï‚— Easy to install, no need trained mason. ï‚— High availability of construction material. ï‚— Cons: ï‚— Inconvenient O&M ï‚— Less durable and short lifetime ï‚— Applicability ï‚— Poor households. ï‚— No long term plan of raising animal.
  • 28. Contact: Tran Hai Anh – Renewable Energy Specialist Tran_haianh@yahoo.com