lecture 6 Flashcards
True or false: Electricity pollution-free and environmentally friendly at the point of use?
True
How should one fully assess the environmental impacts of electrical power?
By asking where the electricity comes from
How is electrical energy commonly expressed (units)?
Kilowatt-hours (kW-hr)
How is electrical power commonly expressed (units)?
Kilowatts or Megawatts (1 MW = 1,000 kW)
What is the difference between power and electrical energy in a plant?
Power is the measure of plant size
Electrical energy reflect the actual usage of plant capacity
What is the heating value?
The energy per unit mass of fuel
What units are used for the heating value?
kilojoules per kilogram of fuel (kJ/kg)
True or false: Coal, oil and natural gas differ in the amounts of hydrogen and carbon they contain.
True
How do fossil fuels produce energy?
When a fossil fuel is burned, atomic bonds between carbon and hydrogen atoms are broken which release chemical energy.
The chemical energy provides heat which is converted to electrical energy in the power plant.
True or false: The quantity of fuel burned largely does not determines the amounts of environmental contaminants that are released.
False
What is the main environmental concern about fossil fuel power plants?
The atmospheric emissions of CO2, SO2, NO2 and PM
Are there any laws in place about the atmospheric emissions from fossil fuel power plants?
Federal and state regulations limit the amounts that can be released from any particular facility.
What element is one of the most important impurities in fossil fuels?
Sulfur
Does coal undergo sulfur removal?
Coal undergoes littles or no processing for sulfur removal before it is burned which leads to high levels of sulfur impurities
Do oil and natural gas also have high sulfur impurities?
Oil and natural gas also contain sulfur compounds when extracted. but most impurities are removed.
How are sulfur impurities in oil and natural gas removes?
Oil refineries and gas treatment
True or false: When coal is burned, a small amount of sulfur (~2-5%) is retained in the solid ash particles
True
What is 95% or more of sulfur oxidized to?
Gaseous sulfur dioxide
Can SO2 be futher oxidized?
Yes, to SO3
How is gaseous sulfuric acid formed (H2SO4)?
When SO3 reacts with water vapour in the combustion gas, H2SO4 is formed.
What do NOx consist of?
Nitric oxide (NO) and nitrogen dioxide (NO2) formed from high-temperature reactions before oxygen and nitrogen
How do coal-burning plants create solid wastes?
Collected ash from the plant creates a problem of solid waste disposal
How do coal-burning plants create liquid wastes?
Water pollution may be created since water is often used to transport collected ash within the power plant.
More water pollution problems may arise from the discharge of waste to rivers, lakes or streams.
How do coal mining and drilling for oil/natural gas impact the environment?
Land use impacts and disturbances are associated with any resource extraction process
What is fission?
Nuclear reaction which nucleus of an atom splits into two smaller nuclei, releasing significant amounts of energy in the process.
What is a chain reaction?
A process where the neutrons released during the fission of an atom go on to initiate further fission reactions in other atoms.
True or false: Nuclear power plants product GHG, PM, SO2, and NOx
False
What are 2 general types of radioactive wastes?
-Low-level waste
-High-level waste
How long are low-level wastes stored at nuclear power plants?
Until the radioactivity in the waste decays to a level safe for disposal as ordinary trash, or is sent to a low-level radioactive waste disposal site
How are high-level wastes stored?
Must be stored in specially designed storage containers and facilities
What are some examples of renewable energy sources?
Hydroelectric, wind, biomass, waste, geothermal and solar energy
True or false: Renewable energy offers substantial environmental benefits over conventional fossil and nuclear fuels
True
What are the 2 approaches to reduce environmental impact of power plants?
- Technological measures to control/remove pollutant before it is release to the environment
- Application of “green design” principles
- Selecting and utilizing cleaner energy sources and alternative technologies with lower environmental impacts
What is ash?
Solid residue that results from burning solid fuels (coal, biomass, municipal solid waste)
What is bottom ash?
Includes the largest particles that collect at the bottom of the combustion chamber of power plant boilers
What is fly ash?
Smaller and lighter particulates that collect in air emission control devices
How does an electrostatic precipitator work in removing particles from a gas stream?
By using electrical energy to charge particles that are them attracted to collector plates carrying the opposite charge.
What is the major water pollutant associated with steam electric power plants?
Thermal pollution
What is the waste heat from the power plant condenser typically transferred to?
It is transferred to cooling water drawn from a nearby stream or river
Due to regulations prohibiting dumping waste heat in water bodies, how is the heat transferred to the atmosphere?
Using a cooling tower
What types of water pollutants are power plants a potential source of?
Water pollutants such as suspended solids, acidity and heavy metals
How can the ash in ponds be controlled?
Ash ponds are constructed with an impermeable layer of natural or synthetic materials (clay, compacted soil, rubber linings) to prevent the infiltration of contaminants into the ground.
What are 3 improvements for efficiency of the energy conversion process?
- Increasing operating temperatures
- Cogeneration
- Advanced cycles
How would increasing operating temperatures reduce environmental impacts?
Power plants operate below the theoretical maximum efficiencies. This is mainly due to the maximum temperature of the power generation cycle limited by the construction material available for boilers and turbine blades
How does cogeneration reduce environmental impact?
The purpose is to recover the condenser heat for some useful purpose. Cogeneration systems typically increase the efficiency of fuel utilization to 70 or 80%. Such systems are effective only when there are simultaneous demands for both health and power in proportions delivered by the system
What are 2 examples of advanced cycles
- Integrated gasification combined cycle
- Integrated gas turbine fuel cell
What is a risk?
The probability of an undesired consequence (size of the loss)
What are two ways to reduce risks?
- Reduce size of the loss
- Reduce probability that the loss will occur
What does risk assessment and risk management do?
It is a way of helping to prioritize problems and identify solutions primarily on assessing and reducing risks to human health
What are the 2 categories of health risk commonly analyzed?
- Risk of contracting cancer from exposure to a chemical
- All other human illnesses and disease induced by chemical in the environment
How can the elimination of exposure to a chemical be done?
Shutting down a factory, removing all contaminated soil or containing a chemical after it is released (Note: these are all technically difficult or expensive)
What is the EPA critieria?
Provides the basis for most current risk assessments for chemical that are designated as toxic or hazardous.
What are the 4 steps in the process for risk assessment?
- Assessment of hazards
- Development of dose-response relationships
- Exposure assessment
- Risk characterization
What does hazard assessment imply?
Determining whether there is any potential problem from exposure to a given chemical.
What is the outcome of the hazard assessment step?
An evaluation and description of the nature and severity of any (carcinogenic and noncarcinogenic) effects
What quantifies the dose-response assessment?
Quantifies the relationship between the dose of a chemical (ingest or received) and the resulting response or adverse effect
Why is dose-response assessment one of the most difficult and controversial steps in a risk assessment?
There are usually insufficient data to characterize a dose-response relationship
What does exposure assessment entail?
Process of measuring the magnitude, frequency, and duration of human exposure, including future exposure to an agent in the environment
What does an exposure assessment include?
Size, nature and types of human populations expose to the agent and associated uncertainties
How can exposure be measured directly or estimated indirectly?
Consideration of measured concentrations in the environment, consideration of models of chemical transport and fate in the environment, and estimates of human intake over time.
What does a risk characterization convey the risk assessor’s judgment to?
The nature and presence or absence of risks, information about how the risk was assessed, where assumptions and uncertainties still exist and where policy choices will need to be made.
True or false: Each component of the risk assessment has an individual risk characterization
True
What does the evaluation of chemical carcinogens rely on?
Relies on animal studies in which laboratory animals (rats/mice) Are given measured doses of a particular chemical. If significantly more tumours develop in the exposed animals, the chemical is clearly a carcinogen for those animals
How is the dose of a chemical normalized on the body weight of a test animal/subject expressed as?
milligrams per day of chemical per kilogram of body weight (mg/kg-da)
What are noncarcinogenic chemicals?
Chemicals that do not induce tumours in test animals even at high dosages
What does the exposure assessment quantify?
Quantifies the dose actually received in a particular situation
What is the purpose of exposure assessment?
To measure or estimate the frequency, intensity and duration of human exposure to a chemical agent in the environment so the total exposure can be determined
What is the most significant route that people are exposed to chemical in the environment?
Inhalation
What data is required for exposure assessments?
Quantities of air, water and soil ingested by adults and children
True or false: Cancer is not treated as a stochastic response
False - It is treated as a stochastic response
What is a stochastic response (in terms of cancer)
-Any dose carries a risk
-Increasing dose of chemical doesn’t increase the severity of the response, only increase the likelihood that it will occur
What is the potency factor and what is it based on?
It is the incremental cancer risk for a chronic daily intake (CDI) of 1mg/kg-da, and is based on the dose response curve
What is the equation for chronic daily intake?
CDI = Average daily dose (mg/day) / Body weight (kg)
What level of risk is acceptable for a know or suspected carcinogen?
EPA conclude that a lifetime risk level of one chance in a million or less can generally be regarded as acceptable.
A lifetime risk of one in a thousand or greater is considered serious and is high priority for attention
What is a consequence of risk assessments involving contaminating waste disposal sites or leaking underground storage tanks?
Exposure to toxic chemical can occur via ingestion off contaminated drinking water, contaminated soil, or inhalation of vapours given off by soil or water
What is NOAEL
No Observable Adverse Effects Level is a key parameter to characterize the safe dose of a noncarcinogenic chemical
What is the last step in a risk assessment?
Comparing the actual or estimated daily intake of the chemical to the reference dose
What should be done when the dose is less than, equal or more than the reference dose?
Any dose equal to or less than the reference dose does not pose known health concerns.
Doses above the reference dose may require actions to reduce or eliminate the health risk.
What is the hazard quotient?
The metric used in risk assessments to compare an actual dose of a chemical to the reference dose
What is the equation for the hazard quotient?
HQ = average daily dose during exposure period / reference dose (or HQ = ADD (mg/kg-da)/RfD (mg/kg-da)
What is an acceptable risk for a noncarcinogen in terms of HQ?
A HQ less than or equal to 1 means there are no known adverse effects from the exposure (acceptable risk)
What are examples of sources of uncertainty?
-Measurement errors
-Modelling the relationship before contaminant sources and the amounts of chemicals that reach receptors
-Uncertainty and variability from one individual to another in the way different contaminants affect people and ecological systems
What are probabilistic risk assessments?
Present risk results as a probability distribution rather than a single value
What are 3 drivers of environmental change
- Population
- Standard of living or the level of affluence of the population (e.g. GDP)
- Technology for delivering the goods/services that people demand
How are environmental processes modelled?
Mathematical models and data are required to assess environmental impacts
What is the simplest and most common way to quantify the growth of a population?
By assuming a constant annual growth rate that is expressed as a percentage or fraction
What are important factors in the estimation of population growth?
Fertility rate, age structure and age specific birth rates and death rates per gender
What is the most common measure of economic activity at the national level?
Gross domestic product (GDP) of a country
What is GDP?
The monetary value of all final goods and services produced during a year
True or false: Any increase in economic activity does not also increase environmental emissions?
False
How are interactions between different sections and sub-sectors of an economy captured?
Through the use of an input-output model
What are the main benefits of an input-output model?
It accounts for all the indirect impacts along the supply chain as well as the direct impacts of an activity
