Biogas Production Economics: A Minnesota Case Study

1
Comparison of Fuel Cell and a Genset Utilizing
BiogasPhilip R. Goodrich PE, David Nelson PE,
Richard Huelskamp, Dennis Haubenschild,
Matthew Drewitz, Paul Burns, David Schmidt
PE, R. Vance Morey Department of Biosystems
and Agricultural Engineering, U of Minnesota,
Haubenschild Farms, Princeton MNMinnesota
Department of Agriculture
1Other participants in this project include
Amanda Bilik, The Minnesota Project, Verlyn
Johnson, Blanca Martinez, BAE and Henry Fischer,
East Central Energy.
Background
Plug-Flow Digester - A small plug of slurry is
pumped into one end each day, causing a
comparable amount to flow out of the other end
into the storage basin in the background.
The Haubenschild Farms Digester and Energy
Recovery System
Anaerobic digestion converts volatile organic
substances in livestock wastes into methane,
carbon dioxide, gaseous contaminants and water
vapor. The remaining material is stabilized,
reducing odor during storage and land application
operations. The energy in the methane can be
converted into electrical energy in various ways.
The most popular method is an internal combustion
engine coupled to an alternating current
induction generator connected to the grid. A fuel
cell is a newer way to convert the methane into
electrical energy which is more
challenging Dennis Haubenschild is an early
adopter of anaerobic digestion using AGSTAR (US
Environmental Protection Agency) resources to
install one at Haubenschild Farms, an 800-cow,
1000-acre dairy farm an hour north of
Minneapolis/St. Paul MN. In 1999, the farm
installed a heated plug-flow digester with a
135-kilowatt engine/generator to utilize the
biogas. The successful operation of this
facility (the generator has been running over 98
of the time through July 2004) has drawn many
visitors and helped other operations to accept
the technology.
Biogas Production used in Generator
The building at the left houses the 135 kW engine
generator and the building on the right houses
the fuel cell and instrumentation. One barn is to
the right rear of the picture
SOURCE Nelson and Lamb
Objective
To demonstrate the feasibility of converting
biogas methane to electrical energy using a
commercially available fuel cell.
Comparing Electrical Generator Technologies

• Challenges to using biogas for a fuel cell
• Hydrogen sulfide removal
• Initial concentration 3000-5000 ppm
• Need concentration lt 25 ppb
• Moisture removal
• Need dry gas
• Dewpoint lt -30 degrees Celsius
• Carbon dioxide removal
• Need concentration lt 5 ppm

• Fuel Cell System
• Cost per kilowatt is very high. 10,000
  --gt20,000 per kW
• The biogas must be cleaned up to strict
  specifications. Adds cost and complexity while
  consuming energy.
• The fuel cell is an emerging technology.
• The greenhouse emissions and particulates are
  very low.
• The system is very quiet.
• There are few moving parts.
• Cost of maintenance is not yet known.
• The fuel cell technology is continuously
  improving at a rapid rate.

• Engine Generator System
• Cost per kilowatt is low. 50 --gt100 per kW
• The biogas can be used directly from the digester
  with no cleanup.
• The fuel cell is mature technology.
• The greenhouse emissions of carbon dioxide,
  sulfur dioxide carbon monoxide and particulates
  are significant.
• The noise level is very high and sound mitigation
  is necessary.
• There are many moving parts, most moving in a hot
  environment needing oil and cooling
• The technology is mature and changing slowly.

Emissions from Haubenschild Generator Compared to
Plug Power Proton Exchange Membrane (PEM) Fuel
Cell
Engine Generator Emissions 1.89 O2 0.0796
CO ( 796ppm) 0.187 NOx (1872 ppm) 0.0804
SOX (804 ppm) 1.39 CX HY Actual tests on
Haubenschild Farm Dec 2004
Fuel Cell Emissions 79 O2 and N2 15.5
H2O 4.2 Co2 lt.001 Other Other
propane,NOx,SOx,CO Per Plug Power tests

• Advancing Utilization of Manure Methane Digester
• Funding for this project was recommended by the
  Legislative Commission on Minnesota Resources
  from the Minnesota Environment and Natural
  Resources Trust Fund