Transcript Diapositiva 1 - Mondadori Education

ENERGY AND
ENVIRONMENT
THE ECONOMY
OF HYDROGEN
HYDROGEN
FOR A
GREENER
FUTURE
PRODUCTION
OF HYDROGEN
FUEL CELLS
WHAT FUTURE FOR
HYDROGEN?
from fossil fuels
from electrolysis of
water
Fuel cell vehicles
CLIMATE CHANGE
HYDROGEN FOR A GREENER FUTURE
• The quality of our environment is affected by many
factors, amongst which are our personal (and
government’s) choices regarding the use of fuels.
• Fuels give off numerous emissions that many say
are bringing about great climate changes, because of
the greenhouse effect, of global warming.
• All economic activity that requires energy
consumption contributes to these emissions
producing greenhouse gases.
CLIMATE CHANGE
Why are greenhouse gases dangerous for the environment?
Greenhouse gas …
… is a gas in the atmosphere that freely allows
radiation from the sun to reach the earth’s
surface, but traps the heat radiated back from the
earth’s surface towards space.
The heating effect is analogous to the manner in
which the glass of a greenhouse traps the sun’s
radiation to warm the air inside the greenhouse.
CLIMATE CHANGE
Solutions?
Hydrogen has the best potential of becoming the fuel of the future.
Hydrogen can be produced from sustainable, renewable sources
and may contribute to meeting the growth in world energy demand.
Hydrogen is a carbon-free energy carrier. When used in fuel cells,
there are no harmful emissions.
The use of energy may lead to climate changes. It is thus necessary
to make the transition to cleaner and environmentally favourable
energy carriers.
CLIMATE CHANGE
Hydrogen for a greener future
• Production of hydrogen is relatively simple compared to
processes used to make, obtain, conventional fuels.
• As a result, nobody will be able to control the supply of
hydrogen.
• Hydrogen may create freedom in the use of energy for
transportation, in a similar way that internet made mass
communication available to anyone with a PC and a
phone line.
HYDROGEN
The economy of hydrogen
At the beginning of the seventies, the world energy situation was
upset by two events: the Yom Kippur War and the petroleum crisis
that ensued and the MIT report on the limits of development.
Before
After
Abundance of energy
Run out of energy
Low prices
High prices
Low environmental awareness
Environmental movements
Consequences
Search for new sources of energy
Nuclear
Renewable
Hydrogen may be produced from different sources:
• Gas: Natural gas or bio-gas hydrogen sources with
steam reforming or partial oxidation.
• Oil: Hydrogen is produced with steam reforming or
partial oxidation from fossil or renewable oils.
• Coal: With gasification technology, hydrogen may be
produced from coal.
• Alcohols: Derived from gas or biomass are hydrogen
rich and may be reformed to hydrogen.
• Power: Water electrolysis from renewable sources.
• Wood: Pyrolysis technology for hydrogen from biomass.
• Algae: Methods of utilizing photosynthesis for hydrogen
production.
HYDROGEN
Production of H2 from fossil fuels
All fossil fuels can be converted into hydrogen with reactions of
reforming or of partial oxidation. At present the most used
reaction is the reforming with steam of natural gas:
CH4 + H2O
CO + 3 H2
The reaction is endothermic. It requires high temperatures and the
use of a catalyst. It is followed by the reaction of water shift …
CO + H2O
CO2 + H2
… and by the absorption of the carbon dioxide produced.
Reforming reactions have been used for more than a century, in
the industrial production of hydrogen (ammonia, petrochemical
industry).
How is hydrogen produced by electrolysis?
• In water electrolysis the water molecules are split into
hydrogen and oxygen gases. These gases are
produced when an electric current flows through an
electrolyte from an anode to a cathode. The electrolyte
is water mixed with a substance to optimize electrical
conductivity.
• The hydrogen and oxygen gases produced are
separated, purified, compressed and stored in gas bottle
battery banks or other storage vessels.
HYDROGEN
Production of H2: electrolysis of water
With an electrochemical system functioning in reversal to the
generator (electrolyser) the following reaction takes place:
2H2O
2H2 + O2
Because the reaction is not spontaneous, energy is provided:
water is decomposed into its elements supplying electric energy.
The electrolysis of water is used in order to produce small
amounts of very pure hydrogen, or in specific situations such as
India, Aswan and Norway.
Its possibility to be integrated with the production of electrical
energy from renewable sources is very interesting because it
could reduce the cost of storage and transport and make its use
easier.
FUEL CELLS
Fuel cells are electrochemical systems able to convert
chemical energy coming from a fuel directly into electric
energy.
A fuel cell operates like a battery as it produces electricity
(energy) through an electrochemical process.
But unlike the battery, it consumes substances from the
surrounding air and therefore is able to work continuously
without interruption until a fuel (hydrogen or methanol) and
an oxidiser (oxygen or air) have been produced.
Electricity is produced from the chemical reaction between
hydrogen and the oxygen which is pumped into the fuel
cell from the surrounding air.
FUEL CELLS
• There are several types of fuel cells with different
features and grades of development.
• Fuel cells are classified either according to type
of electrolyte:
• alkaline - AFC
• polymer electrolyte – PEFC
• molten carbonate – MCFC
• phosphoric acid – PAFC
• solid oxide - SOFC
or to the operative temperature (high and low
temperature).
FUEL CELLS
FUEL CELLS
ALKALINE CELL (AFC)
This type of FC directly converts chemical energy into electric
energy. Electrolyte: KOH 30-40 % watery; temperature: 80 – 100 C
• - Anode material: platinum
• + Cathode material: activated Ni
Cathode +
• Cells material: graphite, plastic
Anode -
• Supply: pure oxygen and hydrogen at
moderate pressure
+ Cathode H2 + 2OH- Anode
½ O2 + H2O + 2e
Total reaction
2 H2 O + 2e
2OH-
Electrolyte
H2 + ½ O2 = H2O
ALKALINE CELL (AFC)
Cathode +
Anode -
O2
O2
H2
Electrolyte
H2 + steam
FUEL CELLS
POLYMER ELECTROLYTE FUEL CELL (PEFC)
• This fuel cell consists of two thin,
porous electrodes, an anode and a
cathode, separated by a polymer
membrane electrolyte that passes only
protons.
• Catalysts coat one side of each
electrode.
• After hydrogen enters, the anode
catalyst splits it into electrons and
protons.
• The electrons travel off to power a
drive motor, while the protons migrate
through the membrane to the cathode.
• Its catalyst combines the protons
with the returning electrons and
oxygen from the air to form water.
Picture
FUEL CELLS
Areas of application of fuel cells:
Isolated application
0.5 – 10 kW
Joint generation
50kW – 2MW
Supply power
2 – 20 MW
Transport
5 – 200 kW
FUEL CELLS
Environmental impact of fuel cells
The chart below compares the production of pollutants per kWh of
energy (electricity) produced in normal power systems, with the
production of a fuel cell power system using hydrogen obtained
through reforming of natural gas.
Pollutant
Traditional System
FC
CO2 (g)
500 - 900
NOx (mg)
550 - 2400
50
SO2 (mg)
200 – 1200
50
40 – 180
20
Dusts (mg)
Noise
250
very low
FUEL CELL VEHICLES
The use of hydrogen fuel cell cars and trucks could
help ensure a future in which personal mobility – the
freedom to travel independently – could be sustained
indefinitely, without damaging or destroying the
environment or depleting Earth’s natural resources.
This new technology could help solve the increasingly
frequent environmental emergencies, created by city
traffic: if we want to continue to drive, in our own
vehicles, on the roads then we must change the way
we power them.
FUEL CELL VEHICLES
• It requires energy to extract hydrogen from
substances, which is done either by reforming
hydrocarbon molecules with catalysts or by splitting
water with electricity.
• This energy has to come from somewhere. Some
generation sources (such as natural gas, oil, coal
burning, power stations, etc.), produce carbon dioxide
and other greenhouse gases.
• Other methods of producing energy do not produce
as many or, in some cases, any greenhouse gas.
FUEL CELL VEHICLES
• When using pure hydrogen, a fuel-cell car is a zero-emission
vehicle. This solution is, therefore, ideal for urban transport in
highly polluted areas. However there is the problem of where and
how the hydrogen is produced, as this is a process which could
create pollution.
• If the hydrogen is produced on board a vehicle by reforming
fossil fuels some, but less, SO2, NOx emissions, dust and
hydrocarbons are produced than would be by an internal
combustion engine.
For carbon dioxide the values (expressed in g/km) are:
DIESEL 150
PETROL 200
FC NG 60 *
FC PETROL 90**
Considering the environmental impact the ideal solution is the
production of hydrogen from renewable sources.
*Fuel cell using natural gas;
** fuel cell using petrol
How fuel cells work in a vehicle?
• Fuel cells convert hydrogen gas into electricity cleanly,
making non polluting vehicles, powered by electric drive
motors, possible. Not only would cars become cleaner,
they could also be safer, more comfortable, more
personalised – and even perhaps less expensive to buy
and to run.
• Furthermore, these fuel-cell vehicles could be help
make a shift towards a “greener” energy economy
based on hydrogen, revolutionising the energy industry.
How fuel cells work in a vehicle?
• To understand why this technology could be so
revolutionary, consider the operation of a fuel-cell
vehicle, a vehicle with an electric traction drive. The
motor gets power from a fuel-cell unit and not from an
electrochemical battery.
• Electricity is produced when electrons are stripped from
hydrogen fuel travelling through a membrane in the cell.
The resulting current runs the electric motor, which turns
the wheels. The hydrogen protons then combine with
oxygen and electrons to form water.
How fuel cells work in a vehicle?
• Fuel cell cars are considered clean because they do not
give off harmful emission. Indeed, their only by-products
are heat and water (and if the fuel is methanol, carbon dioxide
too).
• Electricity produced by the chemical reaction in a single
fuel cell has got too little voltage to be useful, so several
fuel cells are combined to form a fuel stack, and produce a
higher voltage.
•
Then, stacks can be combined in
modules to obtain a generator with even
higher voltages.
HYDROGEN FOR A GREENER FUTURE
• Hydrogen could be the fuel of the future. But many obstacles have yet
to be overcome before it will be able to match the expectations
regarding convenience and performance, that customers have come to
expect from internal combustion cars.
• One of the biggest hurdles is to develop safe and effective onboard
hydrogen storage technology. There are various ways of storing
hydrogen, including liquid, compressed gas and solid-state methods
(metal-hydride storage). All have potential, but pose problems.
• A longer-term solution could come from nanotechnology (for example
the nanostructure of carbon), but nano materials for FC will likely take
years to be developed. They are often isolated molecules whose
properties arise from limited interactions.
HYDROGEN FOR A GREENER FUTURE
• Hydrogen will remain only a potential fuel for the future unless an
energy supply system is developed (hydrogen fuelling infrastructure).
• Large numbers of fuel cell vehicles must have adequate fuel
available to run them.
• A potentially costly hydrogen generation and distribution network
is a prerequisite to commercializing fuel cell cars and trucks, but
we won’t be able to create the required infrastructure unless there
are significant numbers of FC vehicles on the roads.
• Key solutions can be subsidy funding, incentives for developing
refuelling stations, creation of uniform standards and more general
education about this topic.
A hydrogen refueling station for cars and buses in Reykjavik, Iceland
A hydrogen refueling station for buses in Hamburg, Germany