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National Capital Area Chapter (Washington, DC)
Overnight Field Trip Touring Energy Facilities in
Western Pennsylvania and Maryland
Laurence B. CopePresidentCope Associates, LLCBethesda, MDandJames C. McDonnellChief Operating OfficerAvalon Energy Services, LLCBethesda, MD
On October 4-5, 2013, an enthusiastic group from the National Capital Area Chapter (NCAC) of the U.S. Association for Energy Economics toured energy facilities in Western Pennsylvania and Maryland. Facilities included the Conemaugh Generating Station near Johnstown, PA; the Chestnut Flats Wind Energy Project near Altoona, PA and, a family-owned coal mine near Frostburg, MD. Twenty individuals participated including both veteran NCAC members as well as students pursuing careers in energy. It was fascinating to see the different power generation technologies in operation and gain an understanding of how they work. The tour also provided an opportunity for group members to get better acquainted with other professionals having common interests and to share quality time together.
At the Walker Brothers Mining Coal Mine near Frostburg, Maryland
Conemaugh Generating Station
The group first visited the Conemaugh Generating Station. Conemaugh is a large, supercritical coal-fired power plant. It is operated by NRG. The station is owned by the following entities:1
During lunch our NRG hosts described the electric power station. Conemaugh is a two unit power plant with a net total capacity of 1,700 megawatts (850 MW’s per unit). Unit 1 was placed into service in May 1970 and Unit 2 was placed into service in May 1971. 2 Following lunch we toured the boilers (steam generators), the turbine-generator room, the control room, the cooling towers and scrubbers.
Conemaugh was originally constructed as a minemouth power plant. Minemouth stations are built at or near the coal mine(s), in an effort to minimize the transportation costs for fuel. The electricity generated is shipped to load centers over high voltage transmission lines. In certain situations, it is simply more cost effective to ship electrons instead of fuel.
Over the years, the local coal resources near Conemaugh started to decline. Now coal is shipped in by rail and truck. On average, 700 rail cars of coal are delivered to the plant each week. The plant also maintains an inventory of coal. Coal piles function as a fuel reserve and can provide protection in the event of delivery interruptions. The station is designed to use coal with a heat content of 12,400 Btu/lb. 3
Coal is first pulverized, mixed with air and blown into the boilers at different points. The boilers are huge, rising 163 feet above the plant floor. An operator reported that the boilers expanded 14 inches vertically when taken from cold to full operating state. The boilers have 18% natural gas co-firing capability as well. The once-thru supercritical boilers generated 1,000 ⁰F steam at 3,675 psi (gauge). Total steam capacity per boiler was 6,350,000 lbs/hr. 4
Each unit has both a high pressure turbine and twin cross-compound low pressure turbines. The high pressure turbines operate at full steam temperature and pressure; and the low pressure turbines operate on 700 °F steam at 180 psi (gauge). The high pressure turbine drives a generator rated at 545,000 kVA; and, the low pressure turbine drives a generator rated at 495,000 kVA. The output voltage of the generators is 22,000 volts. 5 A portion of the electricity generated is used for station service.
The exhaust steam exiting the low pressure turbines flows into the condenser. The condenser lowers the temperature and reduces the backpressure on the exhaust side of the low pressure turbines. As a result, the steam can expand further resulting in greater cycle efficiency. The feed water from the condenser is pumped to an economizer, preheated and circulated back to the boiler tubes where the process is repeated.
The cooling water used in the condenser must also be cooled. Hyperbolic cooling towers are used. The 370 feet tall cooling towers allow naturally circulating air to cool the condenser water. Water flows between the condenser and cooling tower and then back in a closed-loop cycle. Cooling towers provide protection against thermal pollution as an alternative to discharging the hot water into a nearby body of water, in this instance, the Conemaugh River. When Cooling towers are used, there are some water losses due to evaporation.
The plant uses electrostatic precipitators to remove fly ash and limestone scrubbers to remove SOx. A wet limestone slurry is used to extract SOx. Gypsum is produced as a byproduct of scrubbing. Gypsum is the filler used to make wall board. Large investments have been made to handle new environmental systems to control for NOx and Mercury.
In the switchyard the electricity generated at 22,000 volts is stepped-up to 500 kilovolts and fed into the PJM transmission grid. The power is transmitted to Baltimore, MD and other cities along East Coast. 6
Chestnut Flats Wind Energy Project
The group next visited the Chestnut Flats Wind Energy Project. Chestnut Flats is owned and operated by EDF Renewable Energy, a subsidiary of EDF Energies Nouvelles. It features 19 Gamesa wind turbines. There are 18 – G90-2.0 MW machines and 1 – G87-2.0 MW machine. Gamesa has a contract to provide O&M work. The nameplate rating for the entire project is 38 megawatts.7
Chestnut Flats is built atop the Allegheny Front along the eastern edge of the Allegheny plateau. It can take advantage of more favorable wind conditions (greater wind velocities) that exist at its’ high elevation. The project has been in operation since December 2011.
Modern wind turbines are designed based on aerodynamic principles. The rotors function in a similar fashion to an aircraft wing. Air flowing across the rotors creates “lift.” The air pressure on the upwind side exceeds the air pressure on the downwind side. The combination of air pushing (upwind) and lift (downwind) cause the blades to rotate.
The wind turbines were impressive, towering over the autumn colored trees. The nacelles were mounted on 100 meter towers. The nacelles contain the main machine components: gearbox, generator, machine controls and a power converter. Machines had 3 rotor blades. Each blade was 44 meters in length. The rotor blades were constructed of pre-impregnated epoxy glass fiber.8
According to EDF Renewable Energy’s field manager, the machines start generating electricity when a “cut-in speed” of 3.5 meters per second (m/s) is reached. Generation continues until the “cut-out speed” of 25 m/s is reached for a consistent 5 seconds– at which point the machine shuts down. Rotation speed is controlled by varying the pitch of the turbine blades. Little or no generation is possible with low winds. Machines shut down by pitching (or feathering) the turbine blades directly into the wind. Machine controls have the capability to feather the blades if excessive wind speeds are sensed.
The gear ratio (for 60 Hz) machines is 1:120.9 So if the turbine blades are rotating at 15 R.P.M., the generator shaft rotates at 1,800 R.P.M. The power generated is at 690 volts AC. It is subsequently stepped-up to 34.5 kV.
Rotors were spinning when the group toured. The machines were amazingly quiet. Project planners spaced the machines 300 yards from each other. This was done to prevent turbulence from one machine from affecting other machines located downwind.
The field manager observed that the best winds occurred in the autumn and winter seasons. He did not observe any appreciable difference between winds occurring during day-time or evening hours.
Wind power generated at Chestnut Flats is clean. There is no air or water pollution associated with wind turbines. Further, the “fuel,” i.e., wind is free!
Electricity generated at Chestnut Flats is purchased by Delmarva Power and Light under a 20-year purchase power agreement (PPA). The electricity is wheeled to Delmarva over the PJM transmission network.
The machines can be monitored on site as well as at Gamesa’s offices in Spain.
Walker Brothers Mining Coal Mine
The next destination on the field trip was a visit to the Walker Brothers Mining coal mine near Frostburg, MD. Walker Brothers Mining is a family-owned operation. Their mine is currently operated as surface mine.
The mine is located in the George’s Creek Basin, close to the eastern edge of the Allegheny Plateau. The George’s Creek Basin is a syncline with its axis running about 20 miles northeast/southwest. In east-west cross-section, the underlying 300 million year old Pennsylvanian age strata form a very shallow five mile wide “U” shape with the upper formations exposed at surface along the eastern and western edges of the basin. The coal mine visited is along the western side of the George’s Creek Basin and also along the eastern slope of Big Savage Mountain. There are numerous coal mines, many closed and some still open, on both sides of the basin. The basin still has several hundred million tons of recoverable coal reserves.10
The coal is taken from the Pittsburgh Seam, also known as the Big Vein. In this area, the seam is about 14 feet thick which allowed miners of days gone by to stand up while they worked. The coal, which contains approximately 15,750 Btu per pound, is of bituminous rank and is of especially high quality. For example, the sulfur content is less than 1%. It is generally sold into the metallurgical coal market where it is used to make coke for use in the steel making process.
Coal was discovered in this part of Maryland in the 1700’s and mined heavily during the 1800’s and 1900’s continuing to the present day. Production in the basin peaked in 1907 and has declined since. Somewhat surprisingly, given the very long history of mining in the area, the level of coal production during 2010 was still about 1/3rd of peak production.
The mine started out as a “drift mine.” Originally, tunnels were dug into the coal beginning where it outcropped along hillsides. Over time, these tunnels were extended long distances into the seam and were connected by tunnels dug at right angles. This created a grid work of tunnels supported by the coal that remained in place (pillars). Miners would pull wagons into the mine on an upward slope, through the coal seam to the face at which they were working. When loaded, the wagons could roll, or almost drift to the exit. Thus, empty coal cars were pulled up hill into the mine and loaded coal cars were rolled down hill out of the mine. Jim McDonnell, a tour participant and geologist, stated another advantage to working the mine at an upward slope was that ground water would naturally drain downhill and out of the mine, minimizing water pumping costs.
The group was able to walk down into the mine, past large bulldozers, backhoes and shakers, to where the coal seam is exposed. The coal is pitch black and has an almost metallic luster. The owner preserved, perhaps only temporarily, an area that included two wooden rails that had been used to move coal cars into and out of the mine. Now, surface mining is exclusively performed.
Bituminous coal has a density of 55 pounds per cubic foot. A 10’ X 10’ X 10’ section of coal therefore weighs about 27.5 tons and contain 866 MMBtu. Until about the year 2004, the long term average price of metallurgical grade coal was about $50 per ton. Prices peaked during 2011 at about $200 per ton and have fallen to about $100 per ton. Today, the 10’ X 10” X10’ section of coal examined above would fetch about $2,750 or $3.17 per MMBtu.11
Many items have been found in the mine from the days it was a drift mine, including lanterns, picks and coal carts. Of particular note, excavation revealed on a coal face what appears to be a tribute to a dead miner. A miner’s initials are carved into the wall along with the letter “D” (presumably for “dead”). Affixed to the wall was the miner’s wooded tag, numbered “63.” The tags were used to associate full coal carts exiting the mine with the miner who dug the coal. Many fossils are found in the mine as well.
Jim McDonnell provided the group with extensive literature on coal. Briefly, there are two varieties of coal: thermal coal (steam coal) used in power plants, the chemical industry and brickworks; and metallurgical coal (coking coal) used in the manufacture of steel.
Coal is classified by rank and quality. Based on the amount of pressure and temperature the organic matter has been subjected to, coal grades from low rank peat to lignite to subbituminous to bituminous to high rank anthracite. Coal quality depends on a number of factors such as moisture, sulfur and ash content. Most Appalachian coal is bituminous.
Geological Site of Interest
The trip back to Washington, DC included a stop at a spectacular road cut through Sideling Hill. Sideling Hill is one of a series of tall and long northeast/southwest trending ridges that are part of the Valley and Ridge geological province that for centuries presented difficult barriers to westward travel. During the 1980’s, a notch was cut through Sideling Hill creating a travel way for a then new interstate highway I-68. 10 million tons of rock were removed, exposing the inner workings of the ridge. Viewed from the road cut, the rock strata that make up the ridge are bent downwards sharply in the center, with upward rising limbs on each side. This is the synclinal feature.
The beds exposed at the tops of the center of the syncline are hard, erosion resistant sandstones of the Mississippian age and are 330 million years old. Beds on the limbs were softer rock which have eroded away. This process is referred to as “differential erosion” and has been a dominant force in shaping the topography we see today in the Appalachians. The George’s Creek syncline to the west (where we visited the coal mine) is about 5 miles in width. This syncline is only several 100’s of yards wide, reflecting its closer proximity to the zone of deformation when large land areas converged.
Pictures from the field trip are posted to the NCAC web site. , www.ncac-usaee.org
The group praised Rodica Donaldson, Mark Lively and Jim McDonnell for arranging and orchestrating a most informative trip.
1) Conemaugh Power Plant, NRG Fact Sheet, p.1.
2) Ibid., p. 2.
3) Ibid., p. 4.
4) Ibid., pps. 2-3.
5) Ibid., p. 2.
6) Ibid., p. 2.
7) “Chestnut Flats Wind Farm Powers Up in Pennsylvania,” January 16, 2012, www.nawindpower.com
8) Gamesa 2.0-2.5MW Technical Evaluation,www.gamesacorp.com
9) Ibid., p. 18.
10) Roadside Geology of Maryland, Delaware and Washington, John Means, Mountain Press, ©2010.
11) Calculation: 10’ X 10’ X 10’ section = 1,000 ft3 X 55 lbs = 55,000 lbs / 2,000 lbs = 27.5 tons (short)
15,750 Btu/lb X 2,000 lbs = 31.5 MMBtu/ton
27.5 tons X 31.5 MMBtu = 866 MMBtu
27.5 tons X $100/ton = $2,750
$2,750/866 MMBtu = $3.17/MMBtu
The National Capital Area Chapter (NCAC) of the U.S. Association for Energy Economics (USAEE), founded in 1978, has 420 members including 80 student members and is the largest chapter of USAEE and, in turn, one of the largest members of the International Association for Energy Economics (IAEE). NCAC offers a broad range of programs and events: