Fuel cells - the future of power generation by gzy18727

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									  The Ship Power Supplier


   Fuel cells – the future
   of power generation                                                                                                            by Erkko Fontell
                                                                                                                             Corporate Technology
                                                                                                                              Wärtsilä Corporation



When Sir William Grove in 1839 invented
the principle of the electrochemical                                                        Valuable Heat
reaction used in fuel cells, he hardly
thought that his invention would still be
                                                                       Air (O2, N2)
the subject of intensive R&D work
                                                                                                       ½ O2 + 2e-    O=
around the world in 2003. Development
of fuel cell technology has continued
ever since. Its first application was in                                                                    Cathode
                                                                                                                                +
the Apollo space programme where an
Alkaline fuel cell was used to produce                                                                                      Electrical
electricity and drinking water.
                                                             Electrolyte            O2-          O2-        O2-             Current

The advantages of the fuel cell – they are a
clean, efficient and reliable way of
                                                                                                              Anode
producing electricity – have been the
driving force in the development of
                                                                                                                                 -
different fuel cell technologies for                                                                   H2 + O =     H2O + 2e-
commercial applications. The working                                                                   CO + O =     CO2 + 2e-
principle of the different fuel cell types is                Fuel                   Emissions
similar, but the materials, fuels, catalyst and                                                        CH4 + 4O=      2H2O + CO2 + 8e-
                                                             Hydrocarbons           H2O, CO2
reactions vary. Figure 1 shows the working
principle of a Solid Oxide Fuel Cell                         Biofuels
(SOFC) and its primary reactions.                            H2, CO, CH4

Different fuel cell types and their
applications                                        Fig. 1 Working principle of the Solid Oxide Fuel Cell (SOFC).
Fuel cells can be divided into three main
categories: low-, intermediate- and
high-temperature fuel cells. These are used       transportation and portable applications         generation in stationary power plants and
for different applications owing to the           where fast start-up, compactness and a low       marine applications. The most potential
differences in the operating temperature          temperature level is needed. In these            technology for these applications is the
and the materials used.                           applications the waste heat is not usually       SOFC due to its high efficiency and
   Commercially the most available fuel cell      utilized. The main disadvantage of these         suitability for CHP.
technology is the Phosphoric Acid Fuel Cell       technologies is the high purity requirement         Wärtsilä intends to develop complete
(PAFC) where phosphoric acid is used as           for hydrogen and the need for noble metals       power units based on the most advanced
the electrolyte and platinum (Pt) as a            (Pt) as the catalyst.                            SOFC technology, benefiting in this work
catalyst on both the anode and cathode               The high-temperature fuel cells (SOFC         from its existing system and application
sides of the cell. Although PAFC                  and MCFC) are more suitable for                  know-how and the global Wärtsilä sales and
technology is commercially available, it has      industrial applications where their high         service network. In August 2002 Wärtsilä
not emerged as the long awaited                   efficiency and waste heat can be fully           began co-operation with the Danish
breakthrough in the fuel cell market mainly       utilized. In continuous operation the long       technology company Haldor Topsøe A/S, an
due to its high production costs and fairly       start-up time of the units is not a problem.     acknowledged developer of SOFC
low efficiency.                                   SOFC technology is currently being               technology, in order to ensure optimal
   Cheaper and more efficient fuel cell           developed intensively for APU (auxiliary         system integration. Wärtsilä will develop
technologies, such as the Solid Oxide             power unit) applications to power the            highly efficient and cost-competitive fuel cell
Fuel Cell (SOFC) and Molten Carbonate             increasing demand for electricity in cars        products based on the SOFC technology.
Fuel Cell (MCFC), have been developed             and trucks.
for industrial energy production. These                                                            Planar SOFC technology
technologies are expected to become               Wärtsilä’s role in fuel cell                     SOFC technology is divided into ‘tubular’
more competitive than PAFC within a               technology                                       and ‘planar’ technologies. Westinghouse
few years.                                        Wärtsilä’s interest in fuel cell development     started development of tubular SOFCs in
   The low-temperature fuel cells, especially     is clearly focused on development of a           the late 1950s and this development today
PEM, have been developed for                      highly efficient fuel cell system for power      is continued by Siemens-Westinghouse.


38 - Wärtsilä                                                                                                                             2-2003
                                                   FC Type             Anode          Cathode Operating   Efficiency         Application
                                                                       flow           flow    temperature (LHV)
                                                                                              (°C)

                                                   Low-temperature

                                                   PEM Proton
                                                                       H2                                                    Portable Residential
                                                   Exchange                           Air     60 - 80         30 - 40
                                                                                                                             Transportation
                                                   Membrane

                                                                       H2             O2                                     Portable Residential
                                                   AFC Alkaline                               65 - 220        30 - 40
                                                                                                                             Transportation
                                                   Intermediate-temperature

                                                   PAFC                H2                                     35 - 45
                                                                                      Air     150 - 200                      Industrial Commercial
                                                   Phosphoric Acid                                            50 - 70*
                                                   High-temperature

                                                   MCFC             H2 ,CO,           Air +                   45 - 55        Industrial CHP**
                                                                                              600 - 700
                                                   Molten Carbonate CH4, NH3          CO2                     80 - 90*       Commercial Marine

                                                   SOFC                H2, CO,                                45 - 55        Industrial CHP
                                                                                      Air     650 - 1000
                                                   Solid Oxide         CH4, NH3                               80 - 90*       Commercial Marine
                                                   * In co-generation
Fig. 2 PEM fuel cell stack.
                                                   ** CHP (Combined Heat and Power)




                                                   Table 1. Different fuel cell types and their properties.



                                                  solid oxide fuel cells because it does not         Diesel oil
                                                  require pre-reforming. However, since              For marine applications the use of diesel oil
                                                  pure hydrogen is costly and available in           would be most suitable. Diesel fuel can also
                                                  only limited quantities a number of other          be reformed after the sulphur content of the
                                                  fuels have been used with SOFCs such as            fuel is reduced prior to the reformer. In the
                                                  methanol (CH3OH), natural gas, gasoline            future the removal of sulphur will most
                                                  and even diesel oil and ethanol                    likely be done at the refineries to a level of
                                                  (CH3CH2OH).                                        5 - 10 ppm, which would allow
                                                      After removing particles from the fuel         commercially sustainable fuel cleaning in a
                                                  by filtering, the sulphur (S) compounds            marine vessel.
Fig. 3 Typical planar solid oxide fuel cells.     must be reduced to a level suitable for
                                                  the fuel reformer and fuel cell. It is             LNG
                                                  normally necessary to reduce sulphur               LNG is also an option for fuel cell ship
Planar technology is currently being              compounds to below 1 ppm (parts per                applications operating in coastal areas.
developed by a number of companies and           million), which requires efficient cleaning         However, it is not likely that LNG will be
research institutes around the world.            devices.                                            used for auxiliary power only if the main
   Wärtsilä is mainly interested in planar          The fuel can be reformed in different            engines use diesel oil. Even a small gaseous
SOFC technology due to its suitability           ways depending on the fuel used and type            fuel installation will complicate the entire
for cost-effective mass production and its       of fuel cell. Steam reforming and Auto              machinery installation. On the other hand,
potential for high power densities. Planar       Thermal Reforming (ATR) of natural gas is           it is easier to reform LNG than diesel oil.
SOFC technology can operate in the               often used for larger unit sizes. For smaller
temperature range of 650 - 800 °C,               units Partial Oxidation (POX) is a more             Hydrogen
which allows the use of conventional             compact reforming method.                           The use of hydrogen has been the subject of
materials in the balance of plant                                                                    considerable interest in several development
components. This will further improve            Natural gas                                         projects. The storage of the hydrogen is one
the competitiveness of the planar SOFC           As Wärtsilä is interested in SOFC                   of the main problem areas. For example a
technology.                                      applications larger than 200 kW for marine          high-pressure storage, metal hydride and
                                                 and stationary power production, the most           hydrogen rich chemical compounds, such
Fuels                                            potential fuels are natural gas and                 as sodium borohydride (NaBH4) have been
In an SOFC the primary reaction that             low-sulphur diesel. In stationary                   studied. After the storage issues have been
produces electricity and heat occurs when        applications natural gas is widely used and         solved and if a cost efficient hydrogen
hydrogen (H2) or carbon monoxide (CO)            reforming of natural gas is conventional            production can be established, hydrogen
atoms react with oxygen ions (O ).
                                  =
                                                 technology. For SOFCs the higher                    may become a future fuel both for fuel cells
Regardless of which fuel is used, the fuel       hydrocarbons in natural gas are converted           and for conventional combustion engines.
must be prepared in different ways and           to methane (CH4), hydrogen (H2) and
phases to provide these reactants for the cell   carbon monoxide (CO). Part of the                   Emissions
reaction.                                        methane can be internally reformed to CO            The other major benefit of fuel cell
   Hydrogen is the most suitable fuel for        and H2 in the SOFC stack.                           technology besides high electrical efficiency


2-2003                                                                                                                         Marine News - 39
  The Ship Power Supplier

                                                                                                                                      System Control
                                                               Heat recovery

is low emission levels. Generally fuel cells                                                      500 °C                                   750 - 800 °C
have no sulphur emissions since the sulphur
is removed from the fuel before use. NOX
emissions are also minimal because nitrogen                                                                             Fuel cells            Post-
(N2) is not a reactant in the fuel cell                 NG                                                                                    combustion
process. NOX emissions from SOFC                                                                                           Anode
systems are below 0.5 ppm and are mainly
formed in an afterburner where residual                 Air
gases from the fuel cell are burned. Table 2                                                                              Cathode
describes the primary fuel cell reactions for
different fuel cell types.
    As the table shows, when hydrocarbons
are used as fuel the emissions from the
reactions are water and carbon dioxide                          Sulphur removal                                    Inverter          Filter
(CO2). The table also describes how
                                                                Pre-reformer
methane can be used directly in the SOFC.

SOFC system
The main components in the SOFC system              Fig. 4 Schematic of a SOFC system.
are presented in Figure 4.
    The fuel stream is filtered, pressure           Fuel cell              Anode reaction                              Cathode reaction
controlled and preheated prior to the               PEM and PAFC           H2 ®   2H+   +   2e-                        1/2 O2 + 2H + 2e- ® H2O
sulphur removal unit. The sulphur can be
                                                    Alkaline               H2 + 2(OH)- ® 2H2O + 2e-                    1/2 O2 + H2O + 2e- ® 2(OH)-
removed either at a low or a high
temperature. After sulphur removal the fuel         Molten Carbonate       H2 + CO3= ® H2O +      CO2+    2e-          1/2 O2 + CO2 + 2e- ® CO3=
                                                                           CO + CO3= ® 2CO2       + 2e-
is led to the fuel reformer. Prior to the
reformer, part of the residual gases from the       Solid Oxide            H2 + O= ® H2O + 2e-                         1/2 O2 + 2e- ® O=
                                                                           CO + O= ® CO2 + 2e-
anode are re-circulated and mixed with the                                 CH4 + 4O= ® 2H2O + CO2 + 8e-
incoming fuel. This recirculation increases
the system’s efficiency and provides the
necessary steam for the steam reformer.             Table 2. Electrochemical reactions in fuel cells.
After the reformer the reformat is preheated
prior to the SOFC stack. After the stack the
remaining gases are burnt in a                    Of the technologies under development,                  SOFCs have been carried out for 1 kWe
post-combustion unit.                             only PAFCs, SOFCs and MCFCs are                         stack units, and tests of 5-10 kWe stacks
    The air side is simpler than the fuel side.   considered to have commercial potential in              have been started. Once the durability and
In addition to being an oxygen carrier the        stationary power production plants of 0.2 -             cost targets are achieved, the SOFC will
supplied air acts as a cooling media in the       5.0 MW size.                                            provide a very competitive alternative for
stack. For this reason the volume of air flow         Currently close to 350 PAFC units have              CHP use both in marine and stationary
varies by containing 2 - 5 times more             been sold, out of which around 200 units                applications.
oxygen than is needed in the reactions.           are in commercial operation.                               Several ongoing projects plan to
    The other main areas in a SOFC system         Siemens-Westinghouse Power Generation                   demonstrate 25 - 50 kW SOFC products in
are system control and power electronics,         have collected the widest experience of                 the next three years. Units of 250 -
which converts the low-level DC voltage to        SOFC technology with their tubular SOFC                 500 kWe size could enter the market by
a suitable AC current for connection to an        products. In the current demonstration                  2010, and plant sizes could be increased to
external grid.                                    programmes 100 kW, NG-fuelled SOFC                      several MW before 2020. Wärtsilä is among
                                                  units have been operated for over 20,000 h              the world’s front-line pioneers of this
SOFC development today                            with 46% electrical efficiency. These                   technology and plans demonstration
Development of fuel cell power generation         programmes have fulfilled the promise of                programmes on the way to developing over
applications was started in the late 1970s by     fuel cells as an efficient, emissions-free and          200 kW products based on planar SOFC
United Technologies Corp. (UTC) (PAFC)            reliable power source. However, the                     technology.
and Siemens (SOFC). The first commercial          challenge still remains to make fuel cells
unit, launched in 1991, was a 200 kW              commercially competitive.                               Fuel cells in ships
PAFC system by ONSI (a subsidiary of                  In addition to the cost, a major                    The marine industry is coming under ever
UTC).                                             development target of planar SOFC                       increasing pressure to reduce emissions and
   Other fuel cell technologies developed         technology is the lifetime and durability of            to become more environmentally friendly
for power generation are the Alkaline Fuel        the planar SOFC stack. Current                          in other respects as well. Certain segments,
Cell (AFC), the Proton Exchange                   development programmes aim to achieve a                 such as cruise vessels and coastal ferries,
Membrane Fuel Cell (PEMFC), the                   40,000 h stack lifetime with a system cost              have been a particular focus of attention
Molten Carbonate Fuel Cell (MCFC), and            target of 400 - 800 €/kW. Long-term tests               and this has created a need for more
the Direct Methanol Fuel Cell (DMFC).             (up to 15,000-20,000 hours) on planar                   environmentally friendly machinery


40 - Wärtsilä                                                                                                                                   2-2003
                                                                                                   before fuel cells are widely used as main
                                                                                                   propulsion units for larger commercial
                                                                                                   vessels where power demand is tens of
                                                                                                   megawatts.

                                                                                                   Future outlook
                                                                                                   The potential market for different fuel cell
                                                                                                   technologies is enormous given their
                                                                                                   outstanding potential advantages of clean
                                                                                                   and highly efficient power production. The
                                                                                                   applicability of fuel cell technology and the
                                                                                                   flexibility to size the units for different
                                                                                                   purposes will extend the potential market
                                                                                                   from small portable power units up to
                                                                                                   industrial applications of intermediate size.
                                                                                                       The ongoing research and product
                                                                                                   development activities around the world are
                                                                                                   making every effort to turn this potential
                                                                                                   into reality. As noted, the major challenges
                                                                                                   in the development of the commercial fuel
                                                                                                   cell are current cost levels and the lifetime
                                                                                                   of the fuel cell stacks. Therefore the first
                                                                                                   commercial applications will be seen in
                                                                                                   portable devices, in small residential
                                                                                                   applications and in Uninterrupted Power
                                                                                                   Source (UPS) solutions where their
                                                                                                   increased reliability and flexibility will
                                                                                                   justify the higher investment cost per kW.
Fig. 5 One of the potential marine fuel cell applications.                                             In large commercial and industrial
                                                                                                   power generation it is expected that MCFC
                                                                                                   and SOFC products will replace PAFC
                                                                                                   technology. Planar SOFC products have
                                                                                                   the potential to reach a competitive cost
                                                                                                   level in mass production. If, and when,
                                                                                                   low-cost manufacturing of SOFC products
                                                                                                   is achieved it will change our way of
solutions for ships. The low emission levels       applications are estimated to be private
                                                                                                   producing electricity and consuming energy
offered by fuel cells make them an                 yachts where silent and emission-free power
                                                                                                   in the power range below 2 MW. In power
interesting option as a future ship power          generation is needed during slow
                                                                                                   ranges above 5 MW the current
source.                                            manoeuvres and in harbour operation. This
                                                                                                   combustion technologies will still dominate
    In addition to increased efficiency and        niche market is also capable of bearing the
                                                                                                   for several decades to come.
environmental benefits, fuel cell                  higher investment cost.
                                                                                                       Wärtsilä is committed to providing
technologies also offer a silent and                   A more commercial application is
                                                                                                   sustainable power solutions to its customers
vibration-free method of generating                expected to be found in small passenger and
                                                                                                   and it is therefore vital that we are involved
electricity. Since a fuel cell system has very     cargo vessels that operate in coastal areas
                                                                                                   in the development of the power generation
few moving parts their service need will           where a low emission level is important and
                                                                                                   technologies of the future – such as fuel
probably be considerably lower and system          where the availability of a high-quality fuel
                                                                                                   cells. n
reliability higher when compared to                can be assured.
conventional technologies.                             Fuel cells will also be used as auxiliary
    However, there are a few drawbacks and         power units to supply power for cruise
uncertainties which need to be overcome            vessels especially during harbour operation.
before fuel cells can be introduced on the         The use of fuel cells would be motivated
marine market on a large scale. The largest        both by low emissions and by the owner’s
obstacles are the high investment cost, high       improved public image through                   References
fuel quality requirements and the relatively       environmental friendly power generation.        1- Siemens – Westinghouse Power
immature state of fuel cell technology                 In Iceland where the government is          Generation
today.                                             committed to increasing the use of              http://www.siemenswestinghouse.com/en/f
                                                   hydrogen instead of fossil fuels, fuel cells    uelcells/history/index.cfm
First marine applications                          are considered to be an alternative for         2- VTT http://www.vtt.fi/indexe.htm
Owing to the small size and high                   power generation in the Icelandic fishing       3- Forschungszentrum Jülich
investment cost of FC modules envisaged            fleet.                                          http://www.fz-juelich.de/portal/
today the use of fuel cells will initially be          These niche markets are estimated to be     4- Wärtsilä Corporation
limited to low-power installations and             the first commercial marine applications. It    5- Fuel Cell Handbook ; 5th Edition,
auxiliary applications. The first civil marine     will take several decades of development        2000, U.S. Department of Energy


2-2003                                                                                                                       Marine News - 41

								
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