Get documents about "Fuel cells - the future of power generation
Document Sample
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
Related docs
