EPS-109 Earth Resources and the Environment
Lab 1: Coal Burning Power Generation Facility
February 03, 2009
Brayton Point Station
Brayton Point Road, Somerset, MA
At A Glance
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1,599-megawatt electric generating plant
Fueled primarily by low-sulfur coal
Electricity sold into New England’s competitive power market
Historically provides eight percent of New England’s power
The Facility
Located at the confluence of the Taunton and Lee Rivers in Mount Hope Bay, at the head
of Narragansett Bay, the 1,599-megawatt Brayton Point Station is New England’s largest
fossil-fueled power plant and one of the region’s lowest-cost electricity producers.
Dominion Energy sells competitively priced power from Brayton Point into New
England’s wholesale electric market. The plant’s excellent operating record, combined
with its large output of electricity, has established the facility as an important contributor
to reliable electric service.
Goals:
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To learn how power is generated from natural earth resources.
Learn about the environmental impact of power generation from natural earth
resources.
The production of electricity basically involves heating water to make steam. The steam
spins a turbine that drives a generator to produce electricity. This cycle is the same
whether a plant gets heat from nuclear energy, or by burning gas, oil or coal.
In some parts of the region, 100 percent of electricity is generated by coal. Coal-based
electricity is a reliable and low-cost energy source.
Coal Storage and Handling
Coal is transported to the power plant by truck or
rail. It is then stockpiled or put in silos.
A coal handling system moves the coal from the
storage area into the plant.
Coal Pulverizers
The coal is taken from the conveyors
and crushed in pulverizers into a
powder.
The Boiler
Numerous burners are located inside the
boiler. The pulverized coal is blown into
the boiler where it ignites spontaneously
at temperatures of up to 3,000 degrees
Fahrenheit. The purpose of the boiler is to
turn water into steam. Air is drawn into
the plant by huge force-draft fans. As the
air enters the plant it passes through a
heat exchanger that transfers heat from
outgoing exhaust gases to the incoming
air.
Approximately half of the heated air is channeled through the coal pulverizers to dry and
blow the coal into the boiler. The other half goes directly to the boiler for combustion.
The hot gases resulting from combustion are drawn through the boiler and the heat
exchanger (where incoming air is warmed). The exhaust gases then travel to the scrubber.
The Scrubber
In the scrubber, the exhaust gases from the boiler are
sprayed with absorbents such as limestone or lime-water to
remove sulfur dioxide to comply with environmental
regulations.
BagHouse
The exhaust gases then move from the scrubber
to the fabric filter baghouse. The filter process,
which operates on the same principle as a
vacuum cleaner, removes 99.9% of the ash and
other particulates. The baghouse in this
schematic contains more than 8,000 bags that are
35 feet tall and one foot in diameter.
The Stack
Induced-draft fans, located near the stack, pull the exhaust gases through the
environmental equipment and send it up the stack. On cold days, the white plume from
the stack of this type of plant is actually just water vapor condensing. On hot days, even
though the plant is operating, stack emissions are clear.
Water Sources and Storage
The power plant needs water to create steam.
Depending on the location of the power
generating facility, water is pumped through
underground pipes to storage ponds from a
variety of sources, such as reservoirs, lakes
or rivers.
Water Treatment
The water then flows through a treatment
process to purify it for steam generation.
Water in the boiler cannot contain minerals
or particles that might collect as deposits
inside the boiler tubes or damage the
turbine blades.
Creating Steam
As water (light gray) enters the boiler, it is preheated by
hot gases leaving the boiler. The water then enters the
steam drum where it is pressurized and turns to steam (light
line). That steam is "superheated" (dark gray line) and sent
to the turbines. Water that is not converted to steam goes
down to the bottom of the boiler and is pumped through the
walls of the boiler and directed to the steam drum.
Turbines
Steam heated in the boiler first enters
the high-pressure turbine at about 2,400
pounds per square inch and 1,005
degrees Fahrenheit. As it passes through
the high-pressure turbine, the steam
cools to about 600 degrees Fahrenheit
and flows back to the boiler where it is
reheated to 1,005 degrees. The reheated
steam passes through the intermediate
and low pressure stages of the turbine
and exhausts to the condenser.
This pressurized steam causes the blades of the turbine to rotate similar to the action of
wind on a windmill. A continuous shaft connects the turbine to the generator.
Cooling the Water for Reuse
The condenser consists of several thousand
cold water pipes underneath and parallel to the
low-pressure turbines. As steam contacts these
pipes, it condenses to water, creating a
vacuum that draws steam through the turbine.
The water is pumped back into the boiler,
repeating the cycle. Cold water traveling
through the condenser picks up heat from the
steam as it condenses to water.
The steam and cooling water do not come into direct contact during the heat-exchange
process.
The hot water is pumped from the condenser to the top of the cooling tower. It cascades
to the bottom against cool air being forced up by two dozen 22-foot diameter fans at the
base of the cooling tower. Cooling takes place by evaporating thousands of gallons of
water per minute from each tower. Not all plants use cooling towers; some pump water
from a lake or river and return it.
Cooled water returns to the condenser, repeating the cycle.
Electricity is Made
The pressurized steam from the boiler causes the blades of the turbine to rotate. A
continuous shaft connects the turbine to the generator. The generator consists of a rotor
and a stator. The rotor spins inside the stator at 3,600 revolutions per minute, setting
electrons into motion and creating a flow of electricity.
As the electricity exits the generator at
approximately 22,000 volts, it passes through
the generator step-up transformer where
voltage is increased to 345,000 volts. Power
then flows through a switchyard and along a
network of high voltage transmission lines to
delivery points where the voltage is reduced
several times for use in homes, farms and
businesses.
Questions to think about:
1. Why was Brayton Point selected as the site of this power station?
2. What methods are used to minimize the release of SO2 and NOx to the atmosphere?
3. Approximately what fractions of the total S, N, As, and Hg released by the
combustion of fossil fuel are incorporated into concrete, disposed of as solid waste, and
released to the atmosphere respectively?
4. What changes in operations are made to meet large increases in the demand for
electric power? Do these changes affect the characteristics of the produced fly ash?