energy
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ENERGY. Energy cannot be created or destroyed , it can only change its form of existence. Energy types. Chemical energy – stored in chemical bonds and can be released upon chemical reaction Heat energy – transferred between bodies by thermal interactions - PowerPoint PPT PresentationTRANSCRIPT
ENERGYEnergy cannot be created or destroyed, it can only change its form of existence
Energy types• Chemical energy – stored in chemical bonds and can be released
upon chemical reaction• Heat energy – transferred between bodies by thermal interactions• Mass energy – equivalence of mass and energy described as
E = m c2
• Kinetic energy – energy that object posesses due to its motionE = ½ m v2
• Potential energy – energy that object posesses due to its positionE = m g H
• Electric energy – E = q V• Magnetic energy• Nuclear energy• Etc.
Energy quality and exergy• Laws of thermodynamics:
1. The heat, Q, added to a system equals the change in the internal energy, U, of the system plus the work, W, done by the systemQ = U + W2. It is impossible to remove thermal energy from a system at a single temperature and convert it to mechanical work without changing the system surroundings in some other way
• Exergy - the useful work that can be extracted from a system which executes a loss-free process between its initial state and a dead state
• Dead state – state of equilibrium with the surroundings
Energy consumption
State of the art
Image: http://alfin2300.blogspot.com/2011/04/can-small-modular-nuclear-reactors-save.html
Image: http://ourfiniteworld.com/2012/03/12/world-energy-consumption-since-1820-in-charts/
Possible future trends
Image: http://archive.transitiontowntotnes.org/content/future-scenarios-0
Current energy consumption by various sources
Data source: British Petroleum, 2013
Scenarios for future energy sources
Image: http://www.kuuvikriver.info/the-arctic-and-you.html
Image: http://s01.static-shell.com/content/dam/shell-new/local/corporate/Scenarios/Downloads/Scenarios_newdoc.pdf
Fossil fuels as energy source
Oil• Estimated total oil reserves: • 190 km3 (1.2 trilion barrels)
without oil sands• 595 km3 (3.74 trillion barrels)
with oil sands• 1 oil barrel (bbl) = 42 US gallons
= 158.987 L
Image: http://ourfiniteworld.com/
Image: Wikipedia Image: Wikipedia
Natural gas• Major proven resources (2013):
world – 187.3 trillion m3
• Iran (33.6 trillion m3)• Russia (32.9 trillion m3)• Qatar (25.1 trillion m3)• Turkmenistan (17.5 trillion m3)• Saudi Arabia (8.2 trillion m3)• United Arab emirate (6.1 trillion
m3)• Unconventional gas, incl. shale
gas:• 900 trillions m3 • ca. 164 trillions m3 are readily
recoverable
Image: Wikipedia
Coal• Total reserve estimate:
948 billions of tonnes• Coal can undergo
cracking and gasification to produce liquid and gaseous fuels (feasibility?)
Image: http://www.eia.gov/todayinenergy/detail.cfm?id=3350
Image: Google
Oil shale• Worldwide: 7718
billions of tonnes• Green River formation
(US): 52 % of world oil shale
• Contains ca. 35 % organics (kerogen)
• Escessively studied and dealt with in Estonia
• Known Estonian reserves of 2.23 billions of tonnes
• Estonian mining: • 12 to 13 millions of
tonnes p.a.• 9 to ten tonnes p.a.
burned, rest – treated to produce shale oil and phenols
Image: Allix P. et al., Oilfield Review 22 (2010) 6
Image: adopted from Enefit
Heat engines: fuel to work
Heat engine definition• System that performs conversion of
heat or thermal energy to mechanical work
• Maximal efficiency limited by Carnot theorem:
• 3 % for proposed ocean thermal energy conversion (OTEC) power plants
• 18-20 % for petrol engines• 45 % for supercritical coal-fired power
plant• Over 80 % for heat and power co-
generation plants
Image: Wikipedia
Steam engine • First curiosities – 1st century AD (Hero of Alexandria)
• Rudimentary engines – Taqi al-Din (1551), Jerónimo de Ayanz y Beaumont (1606), Giovanni Branca (1629), Denis Papin (1679, 1690)
• Commercial steam-powered water pumps – Thomas Savery (1698), Thomas Newcomen (1712), Jacob Leupold (1720)
• 1763-75 – James Watt• 1849 – George Henry
Corliss• 1884 – sir Charles Parsons,
steam turbine
Image: http://science.howstuffworks.com/transport/engines-equipment/steam2.htm
Image: Wikipedia
Image: Wikipedia
Petrol engine • Petrol (UK), gasoline (US)• Various developments from 5th
century onwards• 1876 – Nicholaus Otto, four-stroke
engine • 1929 – Felix Wankel• Pterol engine could in theory use
hydrogen for fuel
Image: Wikipedia
Diesel engine• 1892, Rudolf Diesel• Up to 45 % efficiency, more economic• Fuel cheaper to obtain, no flammable
vapours• Turbo-pressurising limited only by
motor components mechanical strenght
• Less CO and NOx in exhaust , • Biodiesel easy to synthesize
• Greater mechanical strength, more massive and heavier motors
• Summer and winter diesel fuel
Fossil fuel-operating power plants
Overview• Fossil fuels combustion• Vapour production• Steam or gas turbine rotation
generates electricity• Excess heat removed by cooling
towers• Combined cycle plants: gas
turbine and steam turbine• 33-60 % efficiency, up to 70 % for
combined cycle• Greenhouse gas emissions
Images: Wikipedia
Example: modern coal-fired power plant
Image: Wikipedia
1 - cooling tower, 2 - cooling water pump, 3 - transmission line (3-phase), 4 - unit transformer (3-phase), 5 - electric generator (3-phase), 6 - low pressure turbine, 7 - condensate extraction pump, 8 – condenser, 9 - intermediate pressure turbine, 10 - steam governor valve, 11 - high pressure turbine, 12 – deaerator, 13 - feed heater, 14 - coal conveyor, 15 - coal hopper, 16 - pulverised fuel mill, 17 - boiler drum, 18 - ash hopper, 19 – superheater, 20 - forced draught fan, 21 – reheater, 22 - air intake, 23 – economiser, 24 - air preheater, 25 – precipitator, 26 - induced draught fan, 27 - chimney stack
Nuclear energy
Basics and overview• 1951 – Experimental Breeder
Reactor 1, USA• 1954 – Obninsk, USSR: nuclear
reactor generates electricity for power grid
• Small fuel amounts, radioactive elements often found in metallurgy slags, phosphogypsum, etc.
• Small waste amount• Operating and waste hazards
Image: http://visual.merriam-webster.com/science/chemistry/matter/nuclear-fission.php
Image: Wikipedia
Shutter UO2 tablets Zr Spring
Boiling water reactor
Image: Wikipedia
• Startup neutron source: mixture of 241Am and 9Be• Control rods: boric acid adsorbs neutrons (neutron poison)• 135I and 135Xe buildup: neutron poison that „burns off“
Pressurised water reactor
Image: Wikipedia
Breeder reactor
Image: Wikipedia
Renewable energy sources
Renewable energy use by source
63.69
1.6
7.5
18.2Hydroelectricity
Wind turbines
Solar power
Biomass, geothermal,others
Others
Total energy consumption – 8.6 %(Friday, 2013)
Electricity generation – 25.6 %(British Petroleum, 2013)
Biomass and biofuel• Biomass: when growth and harvesting are in balance, plants
are sort of „natural batteries“ storing Sun’s energy• Other processes’ residues can be used• Biofuels• Fermentation gives biogas or ethanol• Biodiesel: used vegetable oils, fats, recycled greases
• Biodiesel is produced by transeterification:
• Combustion in engines and power plants
O
O
O
O
RO
R
R
O
OH O R
O
OH
OH
OH+ 3 3 +
Hydroelectricity (1)• USA – 7 %, Norway – 99 %, Brazil –
93 %, Canada – 58 %, Sweden – 50 % of total power production
• Potential energy of falling water is transformed to electrical energy by turbine
• Pumped-storage: during low electricity demand (nighttime), most water is pumped back into reservoir
• Ecosystem damage and loss of land due to reservoirs
Images: http://ga.water.usgs.gov/edu/hyhowworks.html
Hydroelectricity (2)• Run-of-the-river
• Tidal energy
Image: Wikipedia
Image: http://www.alternative-energy-news.info/technology/hydro/tidal-power/
Wind power• Works on kinetic energy of wind• 1st century AD – Hero of Alexandria,
windwheel• From 9th century – windmills• 1887 – James Blyth made first wind
turbine for electricuty production• Over 2.5 % worldwide total power supply,
25 % in Denmark• Backing supply or power storage needed
due to the intermittency of wind• Increased bird and bat fatalities due to
collision with propeller blades – radars and microwave detectors applied in some places to prevent that
• Noise issues, officially unsupported
Images: Google
Solar power• Black dots on map – areas which
upon being covered with solar cells can serve as energy supply for the whole world
• Photovoltaics (PV): Si, thin film• Concentrated solar power (CSP)
Images: Wikipedia
Graph: http://techon.nikkeibp.co.jp/article/HONSHI/20100326/181377/
Photovoltaics: basics• n-type semiconductor – excess of
electrons• p-type semiconductor – excess of
holes (lack of electrons)• p-n junction: charge carriers diffuse
into bordering region of opposite semiconductor
• Upon photoexcitation, electron flow starts from p to n side: electrical current
• Can power standalone instruments, or be connected to electrical grid
Image: http://www.solarcell.net.in/
Image: Wikipedia
Photovoltaic power station• Solar cells linked into greater
modules• Solar trackers can be used to
maximize output• Produces direct current (DC),
inverters to get alternating current (AC)
• Energy storage is needed for power delivery at night
Image: http://www.solarserver.com/solarmagazin/solar-report_0509_e_3.html
Images: Wikipedia
Solar thermal energy• Solar energy is used for heating
up receiving liquid• Temperatures can reach from 45
C (water heaters) to 3500 C (solar furnace)
• Heat storage allows continuous energy production • steam• molten salt• graphite
Images: Wikipedia
Geothermal energy• Oldest uses – hot springs• Direct heating hot water
temperature 150 C or less (incl. geothermal heat pumps)
• Indirect: steam for turbines• Although Earth’s heat can be
considered renewable, local depletion is possible
• Emission of greenhouse gases drawn from the rocks (CO2, NH3, H2S, etc.) is considerably smaller than in case of fossil fuels
Image: http://www.way2science.com/geothermal-power-plant/
Ocean thermal energy conversion (OTEC)
• Uses temperature gradient between surface and deeper water layers
• Close circuit: circulating work fluid (low boiling temperature)
• Open circuit: produces desalinated water as well
• Carbon dioxide emissions due to temperature and pressure changes
• Bringing nutrients from the deep into shallow part
Image: http://nextbigfuture.com/2010/11/ocean-thermal-energy-conversion-otec.html
Image: Wikipedia
Fuel cells
Basics• Fuel cell – electrochemical
device that converts chemical energy of fuel directly into electrical energy („cold combustion“)
• 1838 – C. F. Schönbein, 1839 – W. Grove
• Fuels: hydrogen, alcohols, ammonia, methane, petrol, etc.
Image: Wikipedia
2 H2 – 4 e- 4 H+
O2 + 4 H+ + 4 e- 2 H2O
Types and applications
Heat pumps
Working principle• First artificial refrigeraator -1756, W. Cullen• First scientifically described by W. Thomson,
Lord Kelvin, as heat amplifier, 1852• Basics:• Heat is needed for evaporation• Heat is released upon condensation• Boiling temperature depends on pressure
• Used to operate on freons, now – ammonia, butane, propane, carbon dioxide
• Refrigerators, conditioners, heating systems• It is possible to bet up to ca. 2.5-5 kW h of
heat energy when applying 1 kW h of electric energy
Image: Wikipedia
Image: http://progressivetimes.files.wordpress.com/2012/02/geothermal_heat_pump.jpg
Energy conservation and passive buildings
Main principles• Minimize the amount of escaping heat –
superinsulation: in Sweden, min 335 mm for walls (0.1 W m-2 K-1) and 500 mm for roof (0.066 W m-2 K-1)
• Decreased primary energy consumption• Passive solar design: reduced surface
area, windows oriented towards the sun• Airtightness: air circulation provided by
mechanical ventilation with heat recovery
• Heat pumps (heat from surroundings and recuperating heat from exhaust air)
• Heat recuperation from major appliances• Excessive use of daylighting• Solar panels, where possible
Images: Wikipedia
Pinch technology: basics
Simple case: two streams, heat resuperation • A – heat supplied by steam
• B – heat taken by cooling water• Consider 20 C minimal
plausible temperature difference for heat exchanger
• X – amount of heat recuperated
Image: http://www.me.mtu.edu/~jwsuther/erdm/pinchtech.pdf
Composite curves: two hot streams
• Stream with constant heat capacity (CP) – straight line
Image: http://www.me.mtu.edu/~jwsuther/erdm/pinchtech.pdf
Combined composite curves• When minimal
temperature difference is set, composite curves can be shifted
• We get amount of recuperative heat, and minimal amounts of cooling and heating agents
• Below pinch point: heat source
• Above pinch point: heat sink
Image: http://www.me.mtu.edu/~jwsuther/erdm/pinchtech.pdf