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Design of Scalable Biogas Digester for the Developing World

Design of Scalable Biogas Digester for the Developing World. By: Tiffany Cheng, Thomas Davis Dawn Schmidt, Kyle Schroeder, Andrew Wu BME 272 3/16/10 Advisors: Dr. Dave Owens – Owen Graduate School of Management Dr. Paul King – Vanderbilt University School of Engineering. Meet the Rezas.

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Design of Scalable Biogas Digester for the Developing World

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  1. Design of Scalable Biogas Digester for the Developing World By: Tiffany Cheng, Thomas Davis Dawn Schmidt, Kyle Schroeder, Andrew Wu BME 272 3/16/10 Advisors: Dr. Dave Owens – Owen Graduate School of Management Dr. Paul King – Vanderbilt University School of Engineering

  2. Meet the Rezas • 6 members • Two parents, four children • 1 cow (60-65% of families own at least 1 cow in rural Bangladesh) • Make $45 per month • Spend $10 on petroleum fuel per month • Spend 2 weeks per year collecting additional fuel • Interested in neighbor’s biogas digester • To improve their standard of living

  3. What is a BioGas Digester?

  4. Biological Processes

  5. Biogas Production Technology: An Indian Perspective (Nagamani, B. and K. Ramasamy, 1999) On average, a cow in India produces 3.6m3 or 3600 L of biogas per day. This yields approximately 76,280 BTU/animal/day.

  6. Neighbor’s Digester • Cost $200 • Expensive materials • Hard to install • Requires specialist

  7. Overall Design Specifications • Retail price $89 or less (present value) • Financed through Grameen Bank • 8% housing loans leading to $96 paid in equal installments over a 12 month period ($8 monthly payments) • Produces 2800 liters of biogas/day • 15,000 Kcal (59,500 BTU) • Cooks for 6 people • Lasts at least 5 years • Easy to install

  8. Biogas Digesters Worldwide • Floating Drum • Egg Shaped • http://www.water-technology.net/projects/reading_sewage/images/Island-Road-2.jpg • http://www.snisd.org.cn/images/05126b.JPG • Fixed Dome • Plastic Bag http://www.saintsfarm.org/photos/biogas_digester_2_large.jpg http://www.inforse.dk/asia/images/M_III_biogas3.jpg

  9. Brainstorming Improve C:N ratio Mixing in Digester Heating by Compost Portable Small Digester Materials

  10. Specific Design Criteria • Cost • Material availability • Efficiency of gas production • Longevity • Ingenuity • Maintenance • Ease of Use • Modular • Production

  11. Pairwise Comparison Matrix

  12. PVC Hooks 2.4m 0.15m 2.4m 1.39m Brick and Mortar 3 Proposed Designs Plastic Brick Hybrid

  13. Full-Scale Brick Design • Masonry and cement • Readily available materials • Requires sealant http://www.journeytoforever.org/biofuel_library/methane_nepal.html

  14. Full-Scale Plastic Design Plastic Easier to install Mass producible

  15. Full-Scale Hybrid Design Top View Side View Plastic Cover Brick Digester Tank

  16. Decision for Choosing Design Criteria

  17. Cost Analysis of 3 Proposed Designs

  18. Properties of Various Plastics

  19. Polyethylene Terephthalate (PET) • Lowest permeability • Highest yield strength • Tests showed that a 2L PET bottle can withstand at least 6 atm pressure • Inexpensive material

  20. Next Step: Prototype Testing • Test biogas production in large (5 gallon) PET bottles • Analyze biogas • Composition • Dr. Debelak’s gas chromatography • Quantity of production • Dr. Speece’s Wet Tip Gas Meter

  21. Further Designs and Experiments • PET 2L Bottles Testing • Determine maximum pressure • Determine fatigue limit • Quantify gas flow generated at given pressures • Accessory Design and Testing • Sealants • Water traps • PVC pipes • Estimation of per unit cost of manufacturing at various production levels

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