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Final Exam Content
Wind turbines: yaw mechanisms
controls the direction that the hub of a horizontal axis wind turbine point, can adjust based on wind direction
Wind turbines: pitch system
adjusts the angle of the wind turbine blades with respect to the wind. can be used to increase power output or produce less power or rotation
Types of hydropower?
- pumped: 2 reservoirs, not connected naturally, one is at higher elevation, water is pumped uphill or allowed to flow down into lower reservoir
- impoundment: use a dam to store river water, water is released from the reservoir to produce electricity
- diversion: "run of river", divert some water from a river, doesn't require the use of a dam
Types of hydropower turbines?
- Reaction: use pressure and kinetic energy of water to generate electricity -> Francis turbine = water is introduced above the runner all around the runner, water falls through causing blades to spin, best when mass flow rate is relatively consistent and near maximum
- Impulse: use velocity to move the runner, water is released at atmospheric pressure -> cross-flow turbine = good for large water flows, high and relatively consistent efficiency over a larger range of mass flow rates
What the efficiency improvements to Rankine cycle?
Superheat, Reheat, Supercritical, Cogeneration, Combined Cycle (Brayton + Rankine)
What are fuel sources for Rankine cycles?
Combustion (coal, waste heat, biomass), Nuclear, and Geothermal/solar thermal
Mercury & Air Toxics Standards
- EPA regulation
- Part of 1990 Clean Air Act
- Standards are set to the maximum achievable control tech
- Mercury has negative impacts on children's brain development, the primary exposure mechanism from fossil fuel combustion is inhalation of mercury emissions.
- Mercury will eventually precipitate out of air into water sources where it will bioaccumulate into the food chain
SO2
- Regulated by EPA
- Has a National Ambient Air Quality Standard NAAQS (like NOx)
- SO2 is contributor to acid rain and particulate matter emissions
- SO2 is contributor to acid rain and particulate matter emissions
- if inhaled, SO2 is harmful to human respiratory systems
Particulate Matter
- Subject to EPA NAAQS
- Regulations are based on the size of the particle (PM10 has diameter of 10 microns)
- If inhaled, particulate matter is absorbed into your lungs - smaller particles will pass into your bloodstream
Flue Gas Desulfurization (scrubbers)
- use a slurry to water and sorbent material (lime or limestone) that is sprayed into the flue gas
- concentration of water varies
- SO2 forms a salt, and the sorbent material is collected at the bottom of the scrubber
- Slurry contains high concentrations of suspended solids, metals, and nitrates
- slurry is collected in coal ash ponds
Coal Ash
- made up of: fly ash (particulate matter from combustion,) bottom ash (ash particles too heavy for exhaust gases,) flue gas desulfurization waste
- disposal methods: onsite landfills/ retention ponds or reused in concrete or drywall
- compliance with coal ash disposal regulations has lagged
What is Nuclear Fission?
- a neutron collides with a larger atom splitting into 2 atoms and releasing more neutrons and large amounts of energy
- The atoms produced are radioactive
- Uranium 235 is most common nuclear fuel
What is Nuclear Fusion?
- The reaction in the sun
- 2 atoms collide at high enough energy to form one larger atom
- the collision releases a neutron and significant amount of energy because the mass of the particle produced is less than the mass of the inputs
Pressurized Water Reactor Nuclear Power Plant
- 2 water loops: one that stays in the containment structure and captures heat from the nuclear fuel, the other that moves through the heat exchanger and then through the Rankine cycle
- Water in containment structure is always a compressed liquid
Boiling Water Reactor Nuclear Power Plant
- 2 water loops: one loop that collects heat from the nuclear fuel, flows directly into the turbine inlet, rejects heat into the condenser, and is pumped back to higher pressure before being re-exposed to the nuclear fuel.
- secondary water loop through the condenser to the cooling tower to prevent the dispersion of radioactive material
What are the three types of geothermal cycles?
Binary cycle power plant, dry steam plants, and flash steam plants
What is a Binary-cycle power plant?
- transfer heat from geothermal hot water to another liquid
- the heat causes the second liquid to turn to` steam, and the steam drives a generator turbine
What is a Dry-Steam power plant?
Use steam directly from a geothermal reservoir to turn geothermal turbines
What is a Flash Steam plant?
- take high-pressure hot water from deep inside the earth and convert it to steam that drives generator turbines.
- When the steam cools, it condenses to water and is injected back into the ground to be used again
- most geothermal power plants are flash steam plants
What is a flash tank?
- high temperature saturated or compressed liquid is naturally occurring (high pressures)
- flash tank is a vessel that rapidly reduce the pressure of heated liquid, causing some of the liquid to vaporize or "flash" into steam, while the remaining liquid condenses
What to replenish geothermal water?
1. Surface discharge: like Blue Lagoon located in permeable lava field replenishes in 2 days
2. Reinjection: pressurize the water back to near the pressure it was released at to reinject (In/Out field reinjection)
What is Infield Reinjection?
water is reinjected close to where it is extracted from, good for maintaining pressure, but can decrease the temperature of the reservoir over time
What is Outfield Reinjection?
The injection wells further away from the production wells and outside the hot part of the system
What are the types of Solar Thermal Power Collectors?
Parabolic Trough, Linear Fresnel, Parabolic Dish, Power Tower Concentrating Reactors,
What is a Parabolic Trough?
- curved solar panel with focus and absorbing surface
- Focus: light rays aligned with the axis of a parabolic surface reflect to a single focal point (or line)
- Absorbing surface: solar energy enters the aperture of the collector, solar concentration is less intense but the focus accuracy is less critical, do not need to track the sun as precisely
What is a Linear Fresnel?
Approximate a parabolic trough collector, but with flat stationary mirrors that are cheaper, typically last longer in desert environments
What is a Parabolic Dish?
- similar to parabolic troughs, but the collector is a dish and instead of tube, the focus is a point
- Can reach very high temperatures
- Must have 2 axis tracking systems
- Not commonly used for electricity generation at scale, but sometimes have a small engine
What are Power Tower Concentrating Reactors?
- Use large fields of flat mirrors (heliostats) that reflect energy to a stationary solar receiver at the top of a tower
- each mirror is a flat plate with 2-axis tracking
What materials are used for solar thermal energy harvesting?
- molten salts (potassium and sodium nitrates)
- they have low melting points, high densities
Insolation
Solar energy reaching the earth, will be lower than the amount available outside the atmosphere because of absorption and diffraction of sunlight, changing weather and nights
Zenith Angle
Angle between a line formed between a point on earth and the sun and the point on earth and a point directly overhead of that point (normal to the surface of the earth)
Solar Altitude
Angle between a point on earth and the sun and that point on earth and the horizon
Tilt angle
the angle at which a solar device is tilted from horizontal
Surface Azimuth Angle
the angle between the orientation of the surface and due south (only changes if there is some kind of tracking for the device)
Solar Azimuth Angle
the angle between the direction of the sun and due south (which will change with time)
Declination
angle between the line of the sun and the plane of the equator
Diffusion
- Light from the sun can the earth's surface directly or via diffuse transmission
- Light that is diffused by refection and aerosols in the atmosphere
- diffuse & direct light make up the total light reaching the surface - "global' insolation
Transmittance is affect by:
- the angle of the incoming sunlight relative to a point on earth and air quality
- lower during winter when solar altitude is lower
- decreases during the summer as the atmosphere becomes dustier and more humid
Direct, once-through cooling
- withdraw water from natural source
- pass it through a heat exchanger to condense the working fluid of the power cycle
- discharge higher temperature water
- total quantity of water withdrawn depends on the river temperature, regulated discharge temperature, and amount of heat to be rejected by a power cycle
- withdrawals are very high, but almost all is returned to the water source
Dry Cooling
- relies just on air flow to reject the heat from a cycle
- water is always contained in pipes, there is no water sprayed into the airflow
Cooling Tower Natural Draft
move the air through the structure without the use of fans, relies on the different densities of air at ambient temperature and higher temperature to naturally cause air to rise through the chimney, must be very tall to get adequate airflow
Cooling Tower Mechanical Draft
Force air through the structure by a fan
Cooling tower Forced Draft
Fan at bottom pushing air through of cooling tower
Cooling Tower Induced Draft
fan at top, pulling air through
Cooling Tower Draft Eliminators
Baffles that are positioned above warm water distribution, help capture water that would want to be moving out of the tower
Cooling Tower Drift
Water droplets that escape from top of cooling tower
Cooling Tower Packing
Baffles that slow the progress of warm water through the tower, ensure maximum contact between water droplets and cooling air
What is Solar PV?
- Use photovoltaic effect to generate electric current
- PV panels are made of silicon divided into 2 layers (n-type and p-type)
- an incoming photon will break loose an electron in the cell structure - the electron then travels towards the current collector on the glass surface, and the electron hole travels through the conductive backing
What are losses in PV cells?
- Quantum losses: photons with E
- Reflection losses: some fraction of the photons that hit the surface of a PV collector will be reflected
- Transmission losses: some photons will pass through the width of a cell without colliding with an atom in the structure -> sometimes add solar thermal below solar PV panels to capture this otherwise wasted energy
- Collection losses: some electrons will be reabsorbed by the structure before they leave the cell - reabsorption is very likely for very high photon energy values (E>Eg)
What factors affect PV performance?
Temperature, age, degradation, soiling, shading, snow, mismatch, wiring, connections, inverters
Utility scale solar
large-scale development of solar resources, tied into grid transmission system like other power plants would, produce MW of power, if not GW
Distributed solar
solar energy generated in small quantities in location that are collocated or in the same community as where the energy is consumed
- includes residential solar, commercial solar, and community solar projects, tied into grid distribution systems (lower voltage)
investment tax credit
federal policy, allows companies that install solar panels to deduct some of the cost of installing solar PV systems from their taxes, applies for utility scale systems
Net metering
For distributed PV systems, administered by distribution utilities, credits owners of solar PV systems for the electricity that their PV panels produce and is distributed to other customers
- Depending on the size of the credit, can help to offset the costs of distributed PV systems
Solar: Geographic Smooting
Have many solar PV plants at slightly different locations, clouds generally don't impact the same area at the exact same time, so some locations can maintain output while others are diminished.
Solar: Curtailment
The deliberate reduction of power production in order to balance energy demand and energy supply or due to transmission constraints
Rated Capacity
- in units of POWER
- the maximum rate at which a power plant can deliver electrical energy to the grid
Capacity Factor
percentage that compares the actual energy produced over a period of time relative to the maximum theoretical energy production possible over that period of time
Energy Storage: Rated Power
like the rated capacity of power plants, the maximum power output from an energy storage device
Energy Storage: Rated Energy
no natural analog to power plants that assume there's always a supply of fuel, but the maximum energy that could be stored in a device
Energy Storage: Duration
how long an energy storage device could deliver the rated power for before there is no stored energy left
Flywheel Energy Storage
- use electrical energy to power a motor that turns electrical work into rotational work
- very high efficiency, very long useful life
Batteries: electrochemical reactions
reactions that convert electrical energy into chemical energy
An electricity market where utilities can own facilities that generate, transmit, and distribute electricity to final customers is an example of a:
a) deregulated market
b) interconnect
c) wholesale market
d) regulated market
d) regulated market
A 14 stage compressor has a pressure ratio of 1.25 per stage. If the initial pressure is 95 kPa, what is the final pressure out of the last stage of the compressor?
a) 2160 kPa
b) 22.73 kPa
c) 1663 kPa
d) 4150 kPa
a) 2160 kPa
P14/P1 = (1.25)^14 → P14=95kPA*(1.25)^14
Which regulatory organization is responsible for regulating interstate transmission of natural gas, oil, and electricity?
a) EPA
b) FERC
c) NERC
d) Public Utilities Commission
b) Federal Energy Regulatory Commission (FERC)
The term of a project is:
a) one-time expenses at the beginning of a project’s lifetime
b) annual cash flow over the life of the project
c) the planning horizon of a project, usually measured in years
d) one-time positive cash flow at the end of the project planning horizon
c) the planning horizon of a project, usually measured in years
Fill in the blank: The Earth’s atmosphere __________ the temperature of the Earth’s surface:
a) increases
b) decreases
c) does not affect
a) increases
Fill in the blanks: In an axial compressor with air as the working fluid the __________ exert torque on the fluid, increasing the _________, while the ____________ convert energy to a ____________ increase
a) rotors, pressure, stators, kinetic energy
b) stators, velocity, rotors, pressure
c) stators, pressure, rotors, kinetic energy
d) rotors, velocity, stators, pressure
d) rotors, velocity, stators, pressure
Which of the following is not a challenge of using hydrogen in gas combustion turbines?
a) high flame temperature
b) high flame speed
c) heating values (energy per unit mass) are higher than other fuels
d) hydrogen is explosive over a wide range of concentrations
c) heating values (energy per unit mass) are higher than other fuels
Fill in the blank: The ______ of a subsurface CO2 storage refers to the rate at which CO2 could be inserted.
a) storage resource
b) injectivity
c) integrity
d) depth
b) injectivity
which of the following is not a common challenge in amine carbon capture and storage systems?
a) CO2 molecules are very stable
b) the pressure required to desorb amine is very high
c) amines degrade over time
d) amines can react with exhaust gases to form NOx
b) the pressure required to desorb amines is very high
Which kind of policy or regulation requires power plant operators to install and operate an amine carbon capture and storage system and limit annual emissions to 920 metric tons CO2/year?
a) a performance-based standard with a mass-based target
b) a performance based standard with a rate based target
c) a prescriptive regulation with a mass-based target
d) a prescriptive regulation with a rate -based target
c) prescriptive regulation with a mass-based target
which of the following is not true of interconnection queues?
a) all power plants that are built must go through the interconnection queue
b) queues are managed by electricity system operators or utilities
c) all projects in the interconnection queue get built
d) queues are used to study whether there is sufficient transmission line capacity for proposed power plants
c) all projects in the interconnection queue get built
Which of the following are products found at the outlet of the combustion chamber for an Allam cycle?
a) CO2
b) N2
c) H2O
d) H2
a) CO2
c) H2O
Which combination of energy source and technology would be considered green hydrogen?
a) Solar PV, Proton Exchange Membrane Electrolyzer
b) Natural Gas, Steam methane reformation and Amine CCS
c) Nuclear, Solid Oxide Electrolyzer
d) Natural Gas, Alkaline Electrolyzer
a) Solar PV, Proton Exchange Membrane Electrolyzer
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