v>EPA
    United States
    Environmental Protectior
    Agency
             United States Environmental Protection Agency
                                                         August 2013

Renewable Energy Fact Sheet:
Fuel Cells
DESCRIPTION
This fact sheet describes the use of fuel  cells as
auxiliary and supplemental power sources (ASPSs)
for wastewater treatment plants (WWTPs). A fuel
cell  is  an  electrochemical device  similar to  a
battery. While both batteries and fuel cells generate
power through an internal chemical reaction, a fuel
cell differs from a battery in that it uses an  external
supply of reactants and oxygen that continuously
replenishes the reactants in the fuel cell. A battery,
on the other hand, has a fixed internal supply of
reactants.  The  fuel  cell  can  supply   power
continuously   as   long   as  the   reactants   are
replenished,  while  the battery can only generate
limited  power  before it must be recharged  or
replaced. Fuel  cells have been a popular choice as
an ASPS in  recent years, because they are highly
efficient and emissions-free.

Although there are many  different types of fuel
cells, each of  which  uses  its  own specific set of
chemicals  to  produce   power,   only  molten
carbonate fuel  cells (MCFC), phosphoric acid fuel
cells (PAFC)  and  solid-oxide  fuel cells  (SOFC)
can  generate enough  energy  to  power a typical
WWTP.  Each  of  these  types of fuel  cells is
appropriate for use as either a supplemental power
source or an auxiliary power source.

 A  fuel  cell  contains  hydrogen  on  its anode
(negatively charged electrode) side and oxygen on
its cathode (positively charged electrode)  side. In
contrast,  conventional batteries consume  solid
reactants, such as lead, cadmium, or  other metal.
Once these reactants  are depleted, they must be
discarded  or   recharged.    Batteries  can  be
regenerated either with electricity or by replacing
the electrodes.  In a fuel cell, reactants flow in  and
reaction products flow out. This makes continuous
long-term operation feasible as long as these flows
are maintained. An electrolyte separates the anode
and cathode sides of the fuel cell. The electrolyte
                          varies depending on the type of fuel  cell being
                          used. On the anode side, hydrogen diffuses and is
                          conducted  through  the membrane  to the cathode
                          catalyst, but the electrons are forced to travel in an
                          external  circuit  because  the   membrane  is
                          electronically insulating. This external circuit is the
                          power supplied by  the fuel cell.  On the cathode
                          side,  oxygen molecules react  with the electrons,
                          which have traveled through the  external circuit,
                          and with hydrogen ions to form water.

                          Molten carbonate  fuel  cells  (MCFCs)  use  an
                          electrolyte  composed of a molten carbonate  salt
                          mixture suspended  in a porous, chemically inert
                          ceramic lithium aluminum oxide (L1A1O2) matrix.
                          These cells have fuel-to-electricity efficiencies of
                          between 60% and 85%, meaning  60%  to 85% of
                          the energy  generated by the chemical reaction can
                          be harnessed as useable power. MCFCs operate at
                          about 1,200° F (650° C). This  high temperature is
                          needed to  achieve  sufficient conductivity of the
                          electrolyte.  Since they operate at extremely high
                          temperatures, non- precious metals can  be used as
                          catalysts at the anode and cathode, reducing costs.
                          MCFCs are available in the range of 10 kilowatts
                          (kW) to 2.8 megawatts (MW).

                          Phosphoric acid  fuel  cells (PAFCs)  use  liquid
                          phosphoric  acid  as an  electrolyte;  the acid is
                          contained  in  a  Teflon®-bonded  silicon carbide
                          matrix, and porous  carbon  electrodes containing a
                          platinum catalyst.  Operating temperatures range
                          from  300° to 400°  F  (150°-200°  C). PAFCs
                          generate electricity at more than 40% efficiency. In
                          addition, 85% of the steam by-product from the
                          chemical reaction can be  used for cogeneration
                          activities,   such  as  heating onsite buildings  and
                          keeping   WWTPs   operating    at    optimal
                          temperatures, thus reducing the use of commercial
                          electric power. Existing PAFCs have outputs up to
                          400 kW

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Solid oxide fuel  cells (SOFCs) are primarily
used in big, high-power applications, including
industrial  and  large-scale  central  electricity
generating  stations.  A  SOFC  system usually
uses a hard ceramic material of solid zirconium
oxide and a small amount of yttrium (the oxide
of the element yttrium)  instead  of a  liquid
electrolyte. Operating temperatures are around
1,800° F  (1,000° C).  This high-temperature
operation removes the need for precious-metal
catalyst,   thereby   reducing   cost.   Power
generating  efficiencies  are  around  60%.   In
addition,  85% of the  steam by-product from the
chemical reaction can be used for cogeneration
activities thus reducing  the use of commercial
electric power.  Siemens has developed a solid
oxide fuel cell system capable of producing 200
kW  of electricity.  Figure  1  shows a molten
carbonate fuel cell diagram.
MOLTEN CARBONATE FUEL CELL
Electrical Current
— fr>O,
Hydrogen In
H2















Water and
Heat Out
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3
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Anode
Electi
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Oxygen In

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Figure 1: Molten carbonate Fuel Cell Diagram
ADVANTAGES AND DISADVANTAGES
A common misconception of fuel cells is that
hydrogen is the source of energy. Hydrogen is not
the primary source of energy; it is only an energy
carrier and must be  manufactured using energy
from  other sources.  Some critics argue that the
energy needed to create the fuel in the first place
may reduce the ultimate energy efficiency of the
system to below that of the most efficient gasoline
internal combustion engines. This is especially true
if the hydrogen has  to be compressed to  high
pressures or liquefied. Most types of fuel cells can
operate on a  wide  variety of  fuels  including
hydrogen, carbon monoxide, natural gas, propane,
landfill gas, diesel, and simulated  coal gasification
products. In  some cases,  such as at  a WWTP,
methane (natural gas) from  anaerobic digesters can
be reused in the fuel cell instead of flaring off the
excess. Other advantages of fuel cells include; few
moving parts,  modular design,   and   negligible
emission of pollutants.

The high  operating temperature  serves as a  big
advantage  for the MCFC.  This  leads  to  higher
efficiency,  since breaking of carbon bonds  occurs
much  faster   at  higher   temperatures.   Other
advantages include the flexibility to use  more types
of fuels and the ability to use inexpensive catalysts.
A major  disadvantage  of MCFCs is  that  high
temperatures enhance corrosion  and the  breakdown
of cell components.

One of the main advantages of  PAFCs  is they can
use impure hydrogen as a fuel,  removing the need
of pretreatment of the fuel supply. Also the PAFC
technology is the most mature. Utilization of steam
by-products for cogeneration  can  improve  the
overall  economic  value   of   the technology.
Disadvantages  of  PAFCs  include  the need  for
expensive  platinum as  a catalyst,  relatively low
current and power generation compared to other
types of fuel  cells, and their generally larger and
heavier size.

Advantages of SOFCs are  similar to those of the
MCFCs, including higher operating temperatures.
These high operating temperatures imply  higher
efficiency and the flexibility to use more types of

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fuels.  The higher temperature also allows SOFCs
to use inexpensive catalysts.  Utilization of steam
by  products  for  cogeneration can  improve the
overall economic value of the technology.   One
disadvantage  of these higher temperatures is that
they enhance corrosion and the breakdown of the
cell components.

COST
Fuel  cell  manufacturers  currently publish  a
commercial entry price  of about  $2,400  per  kW.
Initial price does not include installation, balance
of systems costs, or other miscellaneous costs that
can  drive  the  entry price up  by 30%  to  50%.
Manufacturers believe that the entry price where
fuel  cells could compete  successfully with  other
small power generators would have to be roughly
half of the current price. This would allow for
more competition  for smaller  scale installations.
Through   improved   manufacturing  techniques,
higher efficiency and increases in production the
cost  of   manufacturing   reliable  fuel   cells  is
decreasing. As  this  technology  becomes  more
commercial available, the costs of fuel cells will
rapidly  decline.  An independent   panel  report
published for the Department of Energy, Hydrogen
Program    in   2008   estimates   the   potential
manufactured cost  for an  80  kW  system  to be  in
the range of $60 per kW to $80 per kW. This 2008
estimate  for  fuel cell systems for  transportation
was  based on  an  annual  production of  500,000
units.3

CASE STUDIES
King County Wastewater Treatment Division  in
Renton, Washington, installed a 1  MW molten
carbonate fuel cell power plant to reduce energy
costs to the treatment plant. The output is  tied to a
transformer to step-up voltage to 13,000 volts. The
fuel  cell  system was chosen because of its  high
efficiency and low  emissions. This cell is  operated
using methane from the anaerobic digesters. King
County uses  the electricity produced by  the fuel
cells to supplement its energy needs, which  also
reduces the facility's power costs by  15%.
The estimated installed cost for the MCFC system
was approximately $22.8  million,  including  the
waste  heat  recovery  system.  The  waste heat
recovery unit for the exhaust  is  sized for  1.7
million British Thermal Units  (BTUs) per hour of
waste heat. The  electrical efficiency was 43%- to
44% and the thermal efficiency was 59% to 64%.

The Palmdale Water Reclamation  Plant (WRP),
Los Angeles  County,  CA,   is  a  9.5  MOD
wastewater treatment plant. The plant's digesters
produce about 11,500 cubic feet per day of biogas
containing  55%  methane.  A  250  kW  molten
carbonate fuel cell system was  installed at a capital
cost of $1.9 million.  The cells  use 70% to 80% of
the total  gas  produced and they generate 225 kW
electricity.  The  cogeneration  system includes a
waste-heat  recovery  unit that  utilizes the waste
heat to provide  heating to the digesters. The  net
thermal and electrical efficiency was calculated to
be 73%. Based on a 90% operating capacity and a
2004 retail  electricity costs of $0.128 per kWh,  the
annual savings in energy costs was calculated to be
about $227,000.

The other  wastewater  treatment plants  that have
operational  biogas based fuel cell systems are Tulare
WWTP,  Dublin  San  Ramos  WWTP,  Riverside
WWTP, Rialto WWTP and Turlock  WWTP, all of
which are located in the state of California.
REFERENCES
1. Rastler, Dan. King County Carbonate Fuel Cell
Demonstration  Project., Electric Power Research
Institute (EPRI), February 2005.

2.  Robert  J.  Remick,  Fuel  Cells  on Bio-Gas,
Michigan   Water    Environment    Association
Biosolids and Energy Conference, 2009.

3. Fuel Cell System Cost for Transportation - 2008
Cost   Estimate,  National  Renewable  Energy
Laboratory, Golden, Colorado.

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4. Mark McDannel and Ed Wheless, The Power
of Digester Gas, Water Environment and
Technology, June 2008.

5. http://en.wikipedia.org/wiki/Fuel Cell

6. http://hydrogendoedev.nrel.gov/pdfs/45457.pdf

7. http://www.fuelcells.org/types/basic.html.

8. http ://dnr.metrokc. gov/wtd/fuelcell/.

9. http://www.eere.energy.gov/hydrogenandfuel
cells/fuelcells/fc_types.html#phosphoric.

10. http://fossil.energy.gov/programs/powe
rsystems /fuelcells/fuelcells  solidoxide.html

11.Auxiliary and Supplemental Power Fact Sheet:
Viable  Sources  (EPA  832-F-11-009),   Office  of
Wastewater Management, Revised October 2007.
Some of the information presented in
this fact sheet was provided by the
manufacturer or vendor and could not
be verified by the EPA.

The  mention of trade names, specific
vendors, or products does not
represent  an actual or presumed
endorsement, preference, or
acceptance by the EPA or federal
government.

Stated results, conclusions,  usage, or
practices do  not  necessarily
represent   the views  or policies of
the EPA.

   Environmental Protection Agency
  Office of Wastewater Management
          EPA 832-F-13-014
            August 2013

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