Design of Scalable Biogas Digester for the Developing

World

By: Tiffany Cheng, Thomas DavisDawn Schmidt, Kyle Schroeder, Andrew Wu

BME 272- Senior Design Project12/1/09

Advisors:Dr. Dave Owens – Owen Graduate School of Management Dr. Paul King – Vanderbilt University School of Engineering

Current Issue• In Bangladesh and other third-world countries:

– Poor waste management• Human health• Environment destruction

– Costly energy resources

• Potential solution: Biogas– HOWEVER, currently not

affordable for these countries

http://water1st.org/waterlog/wp-content/uploads/2009/05/hanging-latrine-480x480.jpg

Objective

• Design a scalable biogas digester that is an appropriate technology for Bangladesh in order to:– Improve human health– Protect environment– Provide affordable and accessible energy

Design Requirements

• Two primary foci– Biogas instrument design – Target population

Biogas Instrument

• Materials– Long life span

• At least 5 years

– Durability• Pressure • Temperature

– Gas permeability– Affordability and availability

Biogas Instrument

• Structure– Size

• Location • Gas capacity

– Simplistic design• Little or no training required• Simple repairs and installation

Target Population Considerations

• Cultural perspectives– Human waste– Risk averse population (needs proof)

• Socioeconomic status– Average income/family = ~$60/month

• Size of average family– 6 people (4 children)

• Degree of education– Related to ability to build and maintain digester

Goals

• Overall Goal is to provide cheap energy to the people of Bangladesh– Create a viable energy source

• One meal

– Provides economic incentive for waste management

• Pathogen free high quality fertilizer

Factors

• Economical Issues will be determining factors for the success of the product– Cost of labor, cost of materials, cost of energy

produced

• Environmental factors will affect the energy produced– Temperature, soil condition, location

Performance Metrics

• The main goal is to create a viable working product– Therefore economics will be the governing

theory in determining the success of the product

• Cost vs. benefits

Past Work

• Weekly meetings with Dr. David Owens and business students from Owen

• Met with Dr. Musaazi to learn about appropriate design for developing world

• Created survey to verify and refine current design specifications

• Researched current biogas digester solutions

Fixed-dome Plant Size: 5-200 m3

• Pro:– Potential underground construction– Low cost– No moving parts– Long life spans – Compact

• Con:– Challenging construction – Frequent gas leaks– Fluctuating gas pressure – Gas production not immediately

visible 

http://www.gtz.de/de/dokumente/en-biogas-volume2.pdf

Floating Drum Plant

Size: 5-15m3 for small to mid size farms

• Pros: – Constant pressure – Visible gas volume– Generally gas-tight

• Cons:– More expensive– High level of maintenance– Short expected lifetime

http://www.gtz.de/de/dokumente/en-biogas-volume2.pdf

Digester Shapes

• Egg-shaped vessel – Expensive

• Cylinders w/conical covers and bottom – Less favorable

surface-volume ratio

http://www.water-technology.net/projects/reading_sewage/images/Island-Road-2.jpg

http://www.gtz.de/de/dokumente/en-biogas-volume2.pdf

Digester

• Material – Steel

• Pro: Gas-tight; Con: Corrosion

– Concrete • Pro: Unlimited Useful Life, Cheap; Con: Gas-tight

– Plastic • Pro: Gas-tight; Con: Mechanical Stress, UV

radiation

– Masonry• Pro: Easy to Build; Con: Gas-tight

Gas Piping

– At least 60% of failure biogas digester is due to defect in gas piping

– Galvanized Steel Pipe• Standardized

– Plastic Tubing • Inexpensive

– No ferrous metal • biogas is 100% saturated with water vapor and

hydrogen-sulfide

Current Work

• Continuing research of current biogas solutions

• First ideation cycle of potential solutions specific to Bangladesh

Future Work

• Analyze results of survey in Bangladesh to determine true price point and product specifications

• Design sketch prototypes of digester (Dec. 10th – Jan. 14th)

• Select design and begin construction of functional prototype (Jan. 14th – Feb. 15th)

• Test and refine functional prototype (Feb. 15th – Mar. 15th)

• Finalize prototype and collect data (Mar. 15th – Apr. 1st)

Reference Human Development Index, United Nations, 2009

Project Pyramid, Information gathered during 2009 trip to Bangladesh

Van Nes, Wim J. Asia hits the gas. Renewable Energy World. 1:102-111 (2006).

http://www.gtz.de/de/dokumente/en-biogas-volume1.pdf

http://www.gtz.de/de/dokumente/en-biogas-volume2.pdf

http://www.gtz.de/de/dokumente/en-biogas-volume3.pdf

http://www.gtz.de/de/dokumente/en-biogas-volume4.pdf