Energy management

in fire power plant

PART 1. Fire power plant Chapter 2
PART 2. Efficiency improvement in Fire power plant
PART 3. CCS Technology
Electricity generation
Building
Transportation

Supply side Demand side

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So Much Wasted Energy

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 PART 1. Fire Power Plant
Four main components:
Steam turbine + Boiler (Steam generator) + Cooling
system (Condenser) + Electricity transmission

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Configuration of a Coal-Fired Power Plant
For a coal-fired power generator, coal as a fuel will be burned to produce heat.
The heat will be used to boil water to high-pressure steam. The steam will drive a
steam turbine to turn at high speed.
 1. Steam turbine
Steam turbines create energy by heating water in a boiler. The
water heats to a steam, which expands. The high-pressure steam
causes the turbine blades to rotate on a generator creating
electricity. The steam condenses back into water and goes back to
the boiler so it can be heated again.

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 Thermodynamics
Thermal energy is converted into mechanical energy (or kinetic energy).

Pressure, Temperature, Enthalpy

P1, T1, h1

Turbine W1-2

P2 < P1
T2 < T1
h2 < h1

 (h1 − h2 )
Power output, W1−2 = m

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 Basic theory

Nozzle converts thermal energy of steam into kinetic energy.

Pressure, P1 P2 < P1
Temperature, T1 Nozzle T2 < T1
Velocity, V1 V2 > V1
• Steam is expanded and
accelerates in nozzle.
• Higher speed implies higher
kinetic energy.

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2. Boiler (Steam generator)
• Boiler - water is heated and
turns from saturated liquid to
saturated vapor.
• Superheated steam - heat
exchanger where heat is
transferred from combustion
products to raise the
temperature of steam above
the saturation temperature;
vapor exits as superheated
steam.
• Air preheater - heat is
transferred from exhaust
gas to cold combustion air
intake; air preheating can
recover the waste heat and
increase the heating effect
of the fuel combustion.

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 Boiler efficiency
Total heat added to working fluid
boiler = 100%
Total fuel input energy

Example: In a steam power plant, 325000 kg of water per hour enters the
boiler at a pressure of 15 MPa and a temperature of 200oC. Steam leaves the
boiler at 9 MPa and 500oC. Coal is consumed at a rate of 26700 kg/hr and has
a heating value of 33250 kJ/kg. Determine the boiler efficiency ηboiler

Solution

m water (hboiler _ out − hboiler _ in )

boiler =  100%
m fuel HHV fuel
325000(3386.1 − 858.2 )
=  100%
26700  33250
= 92.5%
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 Compressed Water

Superheated Vapor Steam

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http://thermofluids.sdsu.edu/testhome/Test/solve/basics/tables/tablesPC/superH2O.html
3. Cooling tower (air cooled)

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 4. Electricity transmission
An electric coil connected to the turbine will also turn at
high speed.
A coil turning in a magnetic field will generate alternating
current (a.c.) electricity.

Left hand rule

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http://www.youtube.com/watch?v=d_aTC0iKO68&feature=related
Electricity is the main source of domestic energy. The domestic electricity supply
is centrally generated at a power plant and transmitted via a distributive network.

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 PART 2. Efficiency Improvement
in Fired Power Plant

1. Heat Recovery
2. Low-Rank Coal Drying
3. Natural Gas (Combustion)
4. Compressed Air Energy Storage (CAES)
5. Nuclear Power Plant
 1. Heat Recovery

Waste heat

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 Thermodynamic
Steam Cycle
qadd
A
2 3B
Boiler
Turbine
Pump
wturbine
wpump

Condenser
D
1 4C
qreject
Carnot Cycle

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 Example
A central power plant, rated at 800,000 Kw, generated steam at
585 K and discards heat to a river at 295 K. If the thermal
efficiency of the plant is 70% of the maximum possible value,
how much heat is discarded to the river at rated power?

ηmax = 1- (295/585) = 0.49

η = 0.49 x 0.7 = 0.343
Q= (1-0.343)/0.343 x 800,000=1,532,361 kW

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 Heat Recovery
(Cooling System Eff% 0.2% to 1%)
Recover a portion of the heat loss from the warm cooling water
exiting the steam condenser prior to its circulation thorough a
cooling tower or discharge to a water body. The identified
technologies include replacing the cooling tower fill (heat transfer
surface) and tuning the cooling tower and condenser.
 Heat Recovery
(Flue Gas Eff% 0.3% to 1.5%)
Flue gas exit temperature from the air preheater can range from 250 to 350°F
depending on the acid dew point temperature of the flue gas, which is
dependent on the concentration of vapor phase sulfuric acid and moisture. It
may be possible to recover some of this lost energy in the flue gas to preheat
boiler feedwater via use of a condensing heat exchanger.
Economiser

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 2. Low-Rank Coal Drying

Subbituminous and lignite coals contain relatively large

amounts of moisture (15% to 40%) compared to
bituminous coal (less than 10%). A significant amount
of the heat released during combustion of low rank
coals is used to evaporate this moisture, rather than
generate steam for the turbine. As a result, boiler
efficiency is typically lower for plants burning low-rank
coal. The technologies include using waste heat from
the flue gas and/or cooling water systems to dry low-
rank coal prior to combustion.
World electricity generation

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As geological processes apply pressure to peat over time, it
is transformed successively into different types of coal.
 Coal
Coal analysis for mass fractions

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SULFUR IN COAL
 3. Natural Gas
Natural gas becomes an attractive "transition" fuel, as the energy supply moves
from polluting coal toward cleaner, renewable technologies. The combustion of
natural gas produces only a fraction of the nitrogen oxide and carbon dioxide
emissions of oil and coal, and also results in essentially no particulate matter or
sulfur dioxide emissions.

1. Oil: last for 150 yrs

2. Natural gas: 300 yrs
3. Coal: several hundreds of years

Relative low efficiency → high cost

Waste storage and security

Coal fired plants:1200 kgCO2/MWh

Natural gas fired plants: 400 kgCO2/MWh
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 Fuels chemistry for combustion

• Coal – short + long-chain hydrocarbon + carbon

• Natural gas - mostly methane (CH4) and ethane (C2H6)
• Liquefied petroleum gas (LPG) - propane (C3H8) and
butane (C4H10)
• Gasoline - octane (C8H18)
• Diesel - cetane (C16H34)

C:
H:
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 Combustion of fossil fuels

Chemical reaction for complete combustion:

CH4 + 2O2 → CO2 + 2H2O

Sources: Methane Oxygen Carbon Water

(fuel) dioxide

Reactants Products

The exothermic reaction releases heat.

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Complete combustion reaction,

CH4 + 2(O2 + 3.76N2) → CO2 + 2H2O + 7.52N2

Fuel Theoretical
air
Air-fuel ratio on a mole basis,
AF = 2(1+3.76) / 1 = 9.52

If AF < 9.52 (rich mixture), incomplete combustion will occur; unburnt fuel is present
in the flue gas; C and CO (instead of CO2) will be formed; less heat will be produced.

If AF > 9.52 (lean mixture) meaning excessive air supply.

A combustion process is normally supplied with some excessive air to ensure complete
combustion as air and fuel are often not fully mixed.

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 4. Compressed Air Energy Storage (CAES)
Compressed Air Energy Storage (CAES) is a way to store energy generated
at one time for use at another time. At utility scale, energy generated
during periods of low energy demand (off-peak) can be released to meet
higher demand (peak load) periods.
CAES Adiabatic storage system
 Heat recovery in CAES
• In this storage technology, the air is compressed and stored in
reservoirs, aquifers or underground cavities.
• When air is compressed for storage, its temperature will
increase.
• The stored energy is released during periods of peak demand,
expanding the air through a turbine. Expansion requires heat. If
no extra heat is added, the air will be much colder after
expansion. Therefore, additional heat must be supplied to the
air by burning a fuel during expansion process.
• The heat generated can be retained in the compressed air or in
another heat storage medium. This way, heat can be returned
to the air before its expansion in the turbine. This method is
called adiabatic storage system and achieves a high efficiency.
 Gas turbine
Gas turbines, also combustion turbine, which employs gas flow as the
working medium by which heat energy is transformed into mechanical
energy.
 Fuel
Combustion
Chamber
Turbine

Shaft
Air Power

Internal-combustion process

340-MW gas turbine-generator

Ref.: POWER Magazine June 15, 2007

• The flow is directed through a nozzle over the turbine's blades, spinning the turbine
and powering the compressor.
• Energy is converted into the form of shaft power to drive a generator for electricity
generation. The exhaust gas can be used for propulsion.

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 The applications of gas turbine

• Industrial gas turbines that are used for CAES,

mechanical drive or used in collaboration with a
recovery steam generator.

• Airbreathing jet engines are gas turbines optimized

to produce thrust from the exhaust gases. Jet
engines that produce thrust from the direct impulse
of exhaust gases are often called turbojets.

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 5. Nuclear energy
• Nuclear energy currently provides 20% of the
electricity needs of the United States, and more than
85% of that of France.
• Nuclear electric power plants, totaling about 500
worldwide, use uranium 235, which is produced by
enriching natural uranium.
 Nuclear Fission
Nuclear fission (nuclear reaction or a radioactive decay): the
nucleus of an atom splits into smaller parts (lighter nuclei), often
producing free neutrons and photons (in the form of gamma rays),
and releasing a very large amount of energy,
 The problem of nuclear energy

Nuclear energy has grown slowly because of the concerns,

• Waste management and storage

• Weapon proliferation
• The public perception of safety
 The problem of nuclear energy
• Plutonium 239 is produced during the uranium
reactions in power reactors, and can be separated
from the spent fuel rods for use in sustained nuclear
reaction for power generation, or for nuclear
weapons.
• The limitation on fission energy, besides the waste
disposal and security concerns, is thought to be the
fuel supply.
 Nuclear Fusion
• Nuclear fusion is the process by which two or more
atomic nuclei join together, or "fuse", to form a
single heavier nucleus. This is usually accompanied
by the release or absorption of large quantities of
energy.
• Deuterium (heavy hydrogen, is one of two stable
isotopes of hydrogen) is abundant, and fusion
reactions do not produce radio active waste.

https://www.diffen.com/difference/Nuclear_Fission_vs_Nuclear_Fusion
 Nuclear Fusion (Copying the sun)
In fusion reactions, deuterium reacts with itself, with
tritium or helium to form helium.

http://www.diffen.com/difference/Nuclear_F
ission_vs_Nuclear_Fusion
 Making nuclear fusion
• In the core of the Sun, millions of tonnes of hydrogen
are turned into millions of tonnes of helium every
second (14 million oC).
• For years, scientists have tried to copy it.
• We might one day have power stations on Earth which
work like tiny suns.
 Challenges of making nuclear fusion
• It is difficult to reach the high temperatures at which the atoms
will fuse.
• It is very difficult to control. If the energy is released all at once,
there is an explosion (hydrogen bomb).
• At great heat, very hot gas called plasma is made. The walls of any
ordinary container would melt away.
 Tokamak reactor
• It uses magnetism to make powerful magnetic fields
which hold and squeeze the plasma.
• A record temperature of 200 million oC, but only
lasted for less than half a second. Even so, this was
long enough to release a large amount of energy.
 PART 3. Carbon Capture and Storage
IEA analysis in the Energy Technology Perspectives 2008 report shows that nearly 20%
of the emission reduction may be achieved by capturing CO 2 from power plants and H2-
production plants.

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What is CCS?
1. CO2 capture → 2. Transport → 3. Storage (Sequestration)

http://vimeo.com/5708590 53
1. Carbon dioxide capture

Reduction of carbon dioxide emissions from power plants burning

hydrocarbons by separating and storing CO2 has been the subject of
extensive research recently, and several schemes have been proposed.

(1) Post-combustion capture

(2) Pre-combustion capture
(3) Oxyfuel combustion
(4) Electrochemical separation

Carbon dioxide capture from power plants burning fossil fuels adds
technical complexity to the power plant, increases its capital and
operating cost and reduces its thermodynamic efficiency.

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1.1 Post-combustion capture

• In postcombustion, we're trying to remove carbon dioxide from a

power station's output after a fuel has been burned.

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• The most commonly used process for post-
combustion CO2 capture is made possible through
special chemicals called amines or chilled Ammonia.

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1.2 Oxyfuel combustion
• Fuel combustion with oxygen instead of air, to avoid nitrogen in the flue gas.
• Since the nitrogen component of air is not heated, fuel consumption is reduced.
• Fuel firing with pure oxygen would result in higher flame temperature than that can
be achieved with an air-fuel flame. So, the temperature is controlled by recycled
water (or CO2) in a complete power system.

CxHy + O2 → CO2 + H2O

CxHy + insufficient O2 → CO + H2 58
1.3 Precombustion capture
• Solid or liquid fuels such as coal, biomass or petroleum products are first gasified in a
chemical reaction at very high temperatures with a controlled amount of oxygen.
• Gasification produces two gases, hydrogen (H2) and carbon monoxide (CO).
• The hydrogen can be used as fuel to generate power in an advanced gas turbine and
steam cycle.
• Water is added to the carbon monoxide to (CO) make carbon dioxide (CO2) and
additional H2.

H2O
CO + H2O CO2 + H2 CO2 + H2

H2
CO + H2
Moisture?

To combust coal at high temperatures using insufficient Modified turbine for H2-based fuel
oxygen and steam CxHy + insufficient O2 → CO + H2 59
Economically speaking this
method costs more than a
traditional air-fired plant. The
main problem has been
separating oxygen from the air
(Air separation unit). This
process needs lots of energy,
nearly 15% of production by a
coal-fired power station can
be consumed for this process.
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1.4 Electrochemical separation

It is possible to use a high-temperature fuel cell to convert the chemical energy in fuels
directly to electricity, especially in case natural gas or coal-produced syngas are used as
fuels.

catalyst
H2 → 2H+ + 2e

4H+ + O2 + 4e → 2H2O

H2O + CO → CO2 + H2

Syngas
H2/CO

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2. Carbon dioxide transport
After capture, the CO2 would have to be transported to suitable storage sites.
This is done by pipeline, which is generally the cheapest form of transport.
There were approximately 5,800 km of CO2 pipelines in the United States, used
to transport CO2 to oil production fields.

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3. Carbon dioxide storage
CO2 can be injected into suitable coal fields where it will be adsorbed onto the
coal and locked up permanently in mineral form. According to research from
the Massachusetts Institute of Technology, the total worldwide potential for
storage in these formations could exceed 7.1 billions tonnes of CO2.

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3.1 Unmineable coal seams
CO2 can be stored in deep coal seams where it will be held in the pores
on the surface of the coal and in fractures. This has the additional benefit
of being adsorbed to displace methane (natural gas) from the coal beds
which can be used as fuel.

CH4 CO2

Coal

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3.2 Deep saline aquifers
CO2 can also be stored in deep salt water-saturated rock formations. These
exist worldwide and have the potential to store large amounts of CO2.
However the geology and effect of the CO2 on these aquifers is not yet well
understood and more research is needed.

Precipitated
Carbonate
Minerals

~800 m

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3.3 Depleted Oil and Gas Reservoirs
• CO2 is already widely used in the oil industry for Enhanced Oil Recovery (EOR)
from mature oilfields.
• When CO2 is injected into an oilfield it can mix with the crude oil causing it to
swell and thereby reducing its viscosity, helping to maintain or increase the
pressure in the reservoir.
• The CO2 is not soluble in the oil. Here, injection of CO2 raises the pressure in the
reservoir, helping to sweep the oil towards the production well.
• The combination of these processes allows more of the crude oil to flow to the
production wells.

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69
Challenge: Hole Drilling

https://www.youtube.com/watch?v=fl8L4qSqSqE
Movie: Armageddon 70
 Carbon capture & storage (CCS) technology

Main obstacles:

• Capital cost: increase overall power plant

capital costs by 20 to 25%.

• Energy Penalty Costs: The high energy requirements for

operating CO2 capture systems can reduce power generation
output by 15% to 30%.

• Total costs of electricity generated: increased by 40 to 70%

per MW.

• Current carbon reduction cost by CCS: US$ 30-90/ton CO2