Electric Power Plants Flashcards
At what point of the energy cycle is electricity often pollution free and environmentally friendly?
Electricity use.
Overall power plant efficiency (nElec) is given by what ratio?
Useful electrical energy output / total energy input.
Electrical energy is commonly expressed in what units?
Kilowatt-hours (kW-hr)
Electrical power is commonly expressed in wattages of what (2) magnitudes?
Kilowatts (kW) or megawatts (MW)
How many kW are there in a single MW?
1000 kW = 1 MW
What term is used to refer to the energy per unit mass of fuel (kJ/kg)?
The heating value.
Energy comes mainly from what two elements in fossil fuels?
Carbon and hydrogen.
What about the chemical compositions of coal, oil, and natural gas explains their different heating values?
They differ in the proportions of hydrogen and carbon.
Which bonds are broken within fossil fuels, causing the release of chemical energy?
Atomic bonds between carbon and hydrogen atoms.
The amount of environmental contaminants that are released by a plant depends on what?
The quantity of fuel burned.
The environmental concerns about fossil fuel power plants center primarily around which 4 atmospheric emissions?
Carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen oxides, and particulate matter (PM).
Which form of fossil fuel leads to highest level of sulfur impurities?
Coal - which undergoes little or no processing for sulfur removal.
Oil contains sulfur compounds when extracted from the ground.
True.
Natural gas contains sulfur compounds when extracted from the ground.
True.
Why doesn’t oil and natural gas emit much sulfur dioxide when burned?
These impurities are removed in oil refineries and by gas treatment, respectively.
When coal is burned, how much of the sulfur is retained in the solid ash particles?
2% - 5%
When coal is burned, how much of the sulfur is oxidized to gaseous SO2?
95%+
What percentage of the SO2 formed during combustion may be further oxidized to SO3?
Less than 1%.
Why is SO3 harmful?
SO3 reacts with water vapor in the combustion of gas to form gaseous sulfuric acid (H2SO4).
What 2 primary nitrogen oxides (NOx) form from fossil fuel combustion.
Nitric oxide (NO) and nitrogen dioxide (NO2).
How do nitrogen oxides form?
From high-temperature reactions between oxygen and nitrogen.
Nitrogen oxides’ environmental impacts are significant because they constitute a large fraction of total combustion products.
False - although they are significant, they constitute a small fraction of combustion products.
What solid waste arises from coal-burning plants?
Ash
What is the primary reason coal-burning plants generate water waste?
Water is often used to transport collected ash within the power plant.
What is the secondary reason coal-burning plants generate water waste?
Due to the discharge of waste heat to a body of water.
Which step in the fossil fuel life cycle remains a source of land use impacts and disturbances?
Resource extraction process (coal mining, drilling for oil and natural gas).
Name a land use disturbance associated with the transport of natural gas.
Leakage of gas from pipelines.
Name a source of environmental impact associated with the transport of electricity.
Transmission and distribution lines that carry electricity from power plants to customers.
Fission is a nuclear reaction that splits what?
The nucleus of an atom splits into two smaller nuclei - releasing a significant amount of energy in the process.
How may a fission reaction be involved in a chain reaction?
The neutrons released during fission go on to initiate further fission reactions.
What is the result of a nuclear power plant that fails to maintain a controlled chain reaction?
An uncontrolled release of energy results in a nuclear meltdown or explosion.
What two types of radioactive waste are produced by nuclear power plants?
Low-level waste & high-level waste.
Until when is LLW stored at nuclear power plants?
Until it is no longer radioactive, or there is enough to send to a LLW disposal site.
Where is HLW stored?
High-level waste must be stored in specially designed storage containers and facilities.
HLW from nuclear plants consists primarily of what?
Highly radioactive spent (used) nuclear fuel assemblies.
Name 6 sources of renewable energy.
Hydroelectric, wind, biomass, waste, geothermal, and solar energy.
List 3 basic approaches to reduce the environmental impacts of power plants.
End of pipe treatment, green design, and selecting cleaner energy sources & alternative technologies.
Describe the end of pipe treatment.
Technological measures to control or remove a pollutant before it is released to the environment.
The end of pipe treatment is more desirable than pollution prevention appraoches.
False.
When is the application of green design principles most fruitful?
When designing new facilities.
Green design also includes pollution prevention approaches, such as?
Innovations that produce useful by products rather than solid wastes.
Ash is the solid residue that results from burning what?
Solid fuels such as coal, biomass, and municipal solid waste.
Define bottom ash.
The largest particles that collect at the bottom of the combustion chamber of power plant boilers.
Define fly ash.
Smaller and lighter particulates that collect in air emission control devices.
Define ash sludge.
Ash mixed with water.
What type of fossil fuel plants store ash sludge?
Coal-fired power plants.
Where do coal-fired power plants store ash sludge?
Retention ponds.
Retention ponds pose risks to surface water.
False - ground water.
When do retention ponds cause extensive damage and pollution downstream?
When they burst.
Besides retention ponds, what two things do coal-fired power plants do with ash?
Send to landfills or sell for use in making concrete blocks or asphalt.
Which is the oldest and most noticeable form of air pollution from coal combustion?
The emission of fly-ash or soot particles.
How does an electrostatic precipitator (ESP) remove particles from a gas stream?
By using electrical energy to charge particles either positively or negatively, which are then attracted to collector plates carrying the opposite charge.
Which is the major water pollutant associated with steam electric power plants?
Thermal pollution.
Waste heat from which part of the power plant is typically transferred to cooling water drawn from a nearby stream, or river?
The power plant condenser.
Due to regulations prohibiting dumping of waste heat to bodies of water, how is waste heat disposed of by steam electric power plants?
Waste heat is transferred to the atmosphere using a cooling tower.
What categories of water pollutants originate mainly from the ash collected at coal-burning plants?
Suspended solids, acidity, and heavy metals.
How is ash transported to a disposal site in most plants?
Ash is continuously collected and mixed with water.
How does ash lead to trace metal contamination of ground water?
The leaching of metals from the bottom of an ash pond.
Ash ponds are constructed with what 3 impermeable layer of natural or synthetic materials to prevent the infiltration of contaminants into the ground?
As clay, compacted soil, or rubber linings.
List 3 techniques to improve power plant energy efficiency.
Increased operating temperatures, cogeneration, advanced cycles.
Why do power plants operate below the theoretical maximum efficiencies?
The maximum temperature of the power generation cycle is limited by material available for boilers and turbine blades.
What is cogeneration?
The practice of recovering condenser heat for some useful purpose.
Cogeneration systems typically increase the efficiency of fuel utilization by what percentage?
70% - 80%
When are cogeneration systems effective?
When there are simultaneous demands for both heat and power in the proportions delivered by the system.
Name 2 types of advanced cycles.
Integrated Gasification Combined Cycle, Integrated Gas Turbine Fuel Cell.
