Turning Onion Juice Into a Power House
Lyn Corum, Distributed Energy, March/April 2009.

"Rising energy and waste disposal costs are plaguing California’s
vibrant and valuable food processing industry. Gills Onions invested
time and research to identify technologies that will eliminate and
reduce those costs.

Looking to eliminate the hauling of onion waste to his fields, Steven
Gill began a search six years ago, for an anaerobic digester that could
turn onion waste into digester gas that could, in turn, be burned in an
onsite power generator. That search culminated in the startup of fuel
cell operations in December 2008. The state-of-the-art anaerobic
digester will start operating by summer 2009. What Gill saw as a
business opportunity, may provide the food processing industry a new set
of tools to reduce costs and join California’s drive to convert
one-third of the state’s power resources to renewable resources.

About a year ago, the plant began separating the juice from the onion
skins. Juice has higher sugar content, making it ideal for conversion to
methane. Gill’s workers now spread juice, rather than all the onion
waste, on the fields. The leftover press cake, a product of squeezing
out the juice, is shipped to Bakersfield, CA, for cattle feed.

Once the Gills decided on anaerobic digestion, the question then was
what to do with the methane gas. Gills Onions chose the Direct FuelCell
— manufactured by the Danbury, CT-based FuelCell Energy — for several
reasons. First, they wouldn’t need any air quality permits, because fuel
cells are virtually emissions-free. Second, not only are fuel cells not
noisy, they have high fuel-to-electricity conversion rates of 47% to
50%. Two 300-kW units began operating on natural gas in December 2008
and will start burning methane once the anaerobic digester is operating
and reaches a steady state production of methane gas, sometime in mid-
or late 2009. The $9-million project will have a six-year payback, says
Gill. Southern California Gas will be presenting Gills Onions a
$2.7-million check from California’s Self-Generation Incentive Program,
and the company will receive $3,000 per kilowatt in federal tax credits.

Hauling the onion waste to the fields cost the company $400,000 annually
in hard costs for diesel fuel, tractors, spreaders, and labor. These
expenses will be reduced to zero once the anaerobic digester is
operating. The company spends $120,000 to $160,000 a month on
electricity, mostly for air conditioning. These bills will be cut by
$700,000 annually, based on Southern California Edison’s current rates,
with the fuel cells contributing about 35% of the plant’s baseload
electrical needs.

Cleaning up the methane will be a particular problem because of the high
sulfur content in onions. This is the subject of a $106,000 California
Energy Commission (CEC) grant awarded to the Gas Technology Institute
(GTI) to study the biogas produced at Gills Onions. GTI is to
demonstrate high-sulfur biogas cleaning and conditioning to FuelCell
Energy’s stringent gas quality specifications, in order to displace
natural gas as a fuel source for the direct fuel cell power plant.

Gill says the goal is to run on 100% biogas, but it may need to be mixed
with natural gas, at least initially, with methane contributing 75% to
90% of the mix. Construction of the site for the anaerobic digester is
under way. A very large hole has been dug near Gills’ plant headquarters
to accommodate a 150,000-gallon tank. The digester equipment, newly
designed for onion juice, has been delivered and is in storage; it is
expected to begin operating in April or May 2009. Once both the fuel
cell and digester are operating, over 30,000 tons of carbon dioxide now
being produced by decomposing onion waste will be eliminated. The
company is already registered with the California Climate Action
Registry and will be selling greenhouse gas credits in a future
cap-and-trade program California will eventually develop."

Dr. Ann C. Wilkie                          Tel: (352)392-8699
Soil and Water Science Department          Fax: (352)392-7008
University of Florida-IFAS
P.O. Box 110960                         E-mail: [log in to unmask]
Gainesville, FL 32611-0960
Campus location: Environmental Microbiology Laboratory (Bldg. 246).
BioEnergy and Sustainable Technology Society