Post on 30-Dec-2015
description
Design of Scalable Biogas Digester for the Developing World
By: Tiffany Cheng, Thomas DavisDawn Schmidt, Kyle Schroeder, Andrew Wu
BME 2723/16/10
Advisors:Dr. Dave Owens – Owen Graduate School of Management Dr. Paul King – Vanderbilt University School of Engineering
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
What is a BioGas Digester?
Biological Processes
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.
Neighbor’s Digester
• Cost $200• Expensive materials• Hard to install• Requires specialist
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
Biogas Digesters Worldwide
http://www.snisd.org.cn/images/05126b.JPGhttp://www.water-technology.net/projects/reading_sewage/images/Island-Road-2.jpg
Floating Drum Egg Shaped
http://www.saintsfarm.org/photos/biogas_digester_2_large.jpg http://www.inforse.dk/asia/images/M_III_biogas3.jpg
Plastic Bag Fixed Dome
Brainstorming
Portable Small Digester
Mixing in Digester
Heating by Compost
Materials
Improve C:N ratio
Specific Design Criteria
• Cost• Material availability• Efficiency of gas production • Longevity• Ingenuity• Maintenance• Ease of Use• Modular• Production
Pairwise Comparison Matrix
Cost Material
Efficiency of
gas Longevity Ingenuity MaintenanceEase of
use Modular Production Total
Cost - 1 1 1 1 1 1 1 1 8
Material Availability 0 - 1 1 1 1 0 0 1 5
Efficiency of gas product 0 0 - 1 1 0 0 1 1 4
Longevity 0 0 0 - 1 0 0 1 1 3
Ingenuity 0 0 0 0 - 0 0 0 0 0
Maintenance 0 0 1 1 1 - 0 1 1 5
Ease of Use 0 1 1 1 1 1 - 1 1 7
Modular 0 1 0 0 1 0 0 - 1 3
Production 0 0 0 0 1 0 0 0 - 1
3 Proposed Designs
1.39
m 2.4m
2.4m
0.15
m
Brick and Mortar
PVC Hooks
Brick Plastic
Hybrid
Full-Scale Brick Design• Masonry and cement• Readily available materials• Requires sealant
http://www.journeytoforever.org/biofuel_library/methane_nepal.html
Full-Scale Plastic Design• Plastic• Easier to install• Mass producible
Full-Scale Hybrid DesignTop View Side View
Plastic Cover
Brick Digester Tank
Decision for Choosing Design Criteria
Criteria Brick Plastic Hybrid
Quality Weight Value Total Value Total Value Total
Cost 8 3 24 4 32 3 24
Ease of Use 7 3 21 3 21 3 21
Material Availability 5 5 25 3 15 4 20
Maintenance 5 2 10 4 20 5 25
Efficiency of Gas Product 4 3 12 3 12 3 12
Modular 3 1 3 5 15 3 9
Longevity 3 5 15 4 12 2 6
Production 1 4 4 2 2 3 3
Ingenuity 0 1 0 3 0 3 0
Total 114 129 120
Cost Analysis of 3 Proposed Designs
Brick Plastic Hybrid
Materials $40.44 $3.95 $81.66
Manufacturing $0 TBD $0
Transportation ~$0 variable ~$0
Installation $6.72 $0.96 $3.84
Sealant variable $0 $0
Total $47.16 + sealant
$4.91 + manufacturing and transportation cost $85.50
Properties of Various Plastics
High Density Polyethylene
Polyvinyl Chloride
Polypropylene UV Stabilized
Polyethylene Terephthalate
HDPE PVC PP-UV PET
Durability
Fresh water Very Good Very Good Very Good Very Good
Weak alkalis Very Good Very Good Very Good Good
UV radiation Good Very Good Good Good
Thermal properties
Max service temperature (°C) 110 50 56.2 55
Mechanical Properties
Yield Strength (MPa) 19.3 41.4 23.6 50
Relative Permeability to PVDC (Saran)
CO2 121 34.5 317 5.28
CH4 [Estimated] 148.23 42.26 388.33 6.47
Price (USD/kg) 2.16 1.52 2.14 1.61
Polyethylene Terephthalate (PET) • Lowest permeability• Highest yield strength
– Tests showed that a 2L PET bottle can withstand at least 6 atm pressure
• Inexpensive material
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
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