Navajo Generating Station
Encyclopedia
Navajo Generating Station is a 2250 megawatt coal-fired powerplant located on the Navajo Indian Reservation, near Page
, Arizona
, USA. This plant provides electrical power
to customers in Arizona, Nevada
, and California
. It also provides the power for pumping Colorado River water for the Central Arizona Project, supplying about 1.5 million acre feet (1.85 km3) of water annually to central and southern Arizona.
A number of power projects were initially considered to fill these needs, most notably Bridge Canyon
and Marble Canyon hydroelectric dams on the Colorado River
. However, the proximity of the proposed dams to the Grand Canyon
raised opposition, initially from the National Park Service
and then more vigorously from a coalition of environmental groups which promoted construction of a thermal or nuclear power plant as an alternative. As a result, the proposed dams were abandoned in favor of the Navajo Power Project, consisting of the Navajo Generating Station
along with the Kayenta mine, BM&LP railroad, and 800 miles (1,287.5 km) of 500 KV transmission
lines.
The site selected for the new power plant was about six miles (10 km) east of Glen Canyon Dam
and three miles (5 km) south of Lake Powell
on 1786 acres (7.2 km²) of land leased from the Navajo Nation. The site was close to a source of competitively priced fuel and a reliable source of surface water for cooling. The nearby city of Page and U.S. Highway 89
provided existing infrastructure to support construction and operation of the project.
The contract for engineering and construction was awarded to Bechtel Corporation
, which began construction on the site in April, 1970.
Generating units 1, 2, and 3 were completed in 1974, 1975, and 1976 respectively at a total cost of about $650 million.
Between 1977 and 1990, following Clean Air Act amendments for assessing and protecting visibility in national parks and wilderness areas, the EPA
, Salt River Project and other entities cooperated in visibility studies to assess possible effects that NGS emissions might have on those areas.
The series of studies culminated in the Winter Haze Intensive Tracer Experiment (WHITEX) and the Navajo Generating Station Visibility Study (NGSVS). Those studies indicated that controlling SO2 emissions might improve winter visual range in the Grand Canyon by 2% to 7%, which prompted the EPA to propose a rule requiring NGS to reduce SO2 emissions by 70%.
NGS and environmental groups, however, negotiated an approach that would achieve a greater degree of improvement at lower cost. They agreed to, and recommended a requirement of a 90% reduction in SO2 emissions based on an annual average, with installation to be completed in 1999. The EPA accepted the recommendation and implemented those conditions in its final rule.
The technology selected for flue gas desulfurization was wet SO2 scrubbing with forced oxidation. Stone & Webster, the architect-engineering firm for the scrubber project, began construction in 1994 and completed the work on Units 3, 2, and 1 in 1997, 1998, and 1999 respectively. The cost of the scrubber project was about $420 million.
In 2007, a BART analysis was conducted for nitrogen oxide (NOx) emissions, prompted by Clean Air Act regional haze regulations. The analysis concluded that Low NOx burners with separated overfire air (SOFA) would provide the best available retrofit technology alternative in accordance with EPA BART guidelines.
Consequently, low NOx burners with SOFA were added to units 3, 2, and 1 during eight-week outages in February through March of 2009, 2010, and 2011 respectively.
The boilers are tangentially fired
, balanced draft, reheat type steam generators, supplied by Combustion Engineering
. Designed for supercritical
operation, they supply steam to the turbines at 3500 psi (241 bar) and 1000 °F (537 °C).
The main turbines are General Electric (GE) tandem compound reheat turbines, each directly coupled to a generator and designed to rotate at 3600 rpm.
Steam discharged from the turbines enters a condenser where water circulating through tubes cools and condenses it, producing a vacuum that maximizes the pressure drop across the turbine. The heat picked up by the circulating water is removed by evaporation in six induced-draft cross flow cooling tower
s (two per unit).
The plant uses up to 28000 acre.ft of water per year from Lake Powell, or about 1/2 gallon (1.9L) per kWh, mainly for cooling water and scrubber operation.
The plant consumes about 8 million tons of low sulfur bituminous coal each year, supplied by Peabody Energy
’s Kayenta mine near Kayenta, Arizona
. The coal is hauled 75 miles from mine silos to the plant by the Black Mesa and Lake Powell
electric railroad. Characteristics of the coal in 2010 included a sulfur content of 0.62%, an ash content of 10.4%, and higher heating value (HHV) of 10,820 Btu/lb.
The plant has three 775 ft (236 meter) tall flue gas stack
s, listed among the tallest structures in Arizona. The stacks were constructed of reinforced concrete, supporting an internal metal liner. The plant's original stacks were demolished in the late 1990's after being replaced by larger diameter stacks of the same height, resulting in the plant having six stacks visible for a time.
The new stacks were required to accommodate cooler flue gas saturated with water vapor that resulted when wet SO2 scrubbers were added.
Net capacity factor: 87%
Net heat rate: 10,112 Btu/ kWh.
The three scrubbers in total consume about 24 MW of power, and use 130,000 tons of limestone and 3000 acre.ft of water per year, producing 200,000 tons of gypsum per year.
Several lined ponds are used in conjunction with the ZLD system to capture and regulate the flow of waste water to the system.
Bottom ash and gypsum, a byproduct of the scrubber operation, are dewatered in the removal process; and, along with any fly ash not sold, are landfilled on-site as solids. No wet impoundments are used for ash or byproduct disposal.
Page, Arizona
Page is a city in Coconino County, Arizona, United States, near the Glen Canyon Dam and Lake Powell. According to 2005 Census Bureau estimates, the population of the city is 6,794.-Geography:Page is located at ....
, Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
, USA. This plant provides electrical power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
to customers in Arizona, Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...
, and California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. It also provides the power for pumping Colorado River water for the Central Arizona Project, supplying about 1.5 million acre feet (1.85 km3) of water annually to central and southern Arizona.
History
In the 1950’s and 1960’s, there was a need for new electric generation in the Southwest to supply power to growing populations in southern California, Arizona and Nevada. The US Bureau of Reclamation also needed a large source of power for running the pumps of the planned Central Arizona Project (CAP).A number of power projects were initially considered to fill these needs, most notably Bridge Canyon
Bridge Canyon Dam
Bridge Canyon Dam is a proposed dam in the lower Grand Canyon of the Colorado River, in northern Arizona in the United States. It would be located near Bridge Canyon Rapids in an extremely rugged and isolated portion of the canyon, roughly downstream of Lee's Ferry and upstream of the current...
and Marble Canyon hydroelectric dams on the Colorado River
Colorado River
The Colorado River , is a river in the Southwestern United States and northwestern Mexico, approximately long, draining a part of the arid regions on the western slope of the Rocky Mountains. The watershed of the Colorado River covers in parts of seven U.S. states and two Mexican states...
. However, the proximity of the proposed dams to the Grand Canyon
Grand Canyon
The Grand Canyon is a steep-sided canyon carved by the Colorado River in the United States in the state of Arizona. It is largely contained within the Grand Canyon National Park, the 15th national park in the United States...
raised opposition, initially from the National Park Service
National Park Service
The National Park Service is the U.S. federal agency that manages all national parks, many national monuments, and other conservation and historical properties with various title designations...
and then more vigorously from a coalition of environmental groups which promoted construction of a thermal or nuclear power plant as an alternative. As a result, the proposed dams were abandoned in favor of the Navajo Power Project, consisting of the Navajo Generating Station
Power station
A power station is an industrial facility for the generation of electric energy....
along with the Kayenta mine, BM&LP railroad, and 800 miles (1,287.5 km) of 500 KV transmission
Electric power transmission
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...
lines.
The site selected for the new power plant was about six miles (10 km) east of Glen Canyon Dam
Glen Canyon Dam
Glen Canyon Dam is a concrete arch dam on the Colorado River in northern Arizona in the United States, just north of Page. The dam was built to provide hydroelectricity and flow regulation from the upper Colorado River Basin to the lower. Its reservoir is called Lake Powell, and is the second...
and three miles (5 km) south of Lake Powell
Lake Powell
Lake Powell is a huge reservoir on the Colorado River, straddling the border between Utah and Arizona . It is the second largest man-made reservoir in the United States behind Lake Mead, storing of water when full...
on 1786 acres (7.2 km²) of land leased from the Navajo Nation. The site was close to a source of competitively priced fuel and a reliable source of surface water for cooling. The nearby city of Page and U.S. Highway 89
U.S. Route 89
U.S. Route 89 is a north–south United States Highway with two sections, and one former section. The southern section runs for 848 miles from Flagstaff, Arizona, to the southern entrance of Yellowstone National Park...
provided existing infrastructure to support construction and operation of the project.
The contract for engineering and construction was awarded to Bechtel Corporation
Bechtel
Bechtel Corporation is the largest engineering company in the United States, ranking as the 5th-largest privately owned company in the U.S...
, which began construction on the site in April, 1970.
Generating units 1, 2, and 3 were completed in 1974, 1975, and 1976 respectively at a total cost of about $650 million.
Between 1977 and 1990, following Clean Air Act amendments for assessing and protecting visibility in national parks and wilderness areas, the EPA
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
, Salt River Project and other entities cooperated in visibility studies to assess possible effects that NGS emissions might have on those areas.
The series of studies culminated in the Winter Haze Intensive Tracer Experiment (WHITEX) and the Navajo Generating Station Visibility Study (NGSVS). Those studies indicated that controlling SO2 emissions might improve winter visual range in the Grand Canyon by 2% to 7%, which prompted the EPA to propose a rule requiring NGS to reduce SO2 emissions by 70%.
NGS and environmental groups, however, negotiated an approach that would achieve a greater degree of improvement at lower cost. They agreed to, and recommended a requirement of a 90% reduction in SO2 emissions based on an annual average, with installation to be completed in 1999. The EPA accepted the recommendation and implemented those conditions in its final rule.
The technology selected for flue gas desulfurization was wet SO2 scrubbing with forced oxidation. Stone & Webster, the architect-engineering firm for the scrubber project, began construction in 1994 and completed the work on Units 3, 2, and 1 in 1997, 1998, and 1999 respectively. The cost of the scrubber project was about $420 million.
In 2007, a BART analysis was conducted for nitrogen oxide (NOx) emissions, prompted by Clean Air Act regional haze regulations. The analysis concluded that Low NOx burners with separated overfire air (SOFA) would provide the best available retrofit technology alternative in accordance with EPA BART guidelines.
Consequently, low NOx burners with SOFA were added to units 3, 2, and 1 during eight-week outages in February through March of 2009, 2010, and 2011 respectively.
Design and Specifications
The plant has three identical 750 MW steam electric generating units. Major components of each unit include a boiler, turbine, generator, closed-cycle cooling system, and environmental control equipment.The boilers are tangentially fired
Tangential firing
Tangential firing is a method of firing a fuel to heat air in thermal power stations. The flame envelope rotates ensuring thorough mixing within the furnace, providing complete combustion and uniform heat distribution....
, balanced draft, reheat type steam generators, supplied by Combustion Engineering
Combustion Engineering
Combustion Engineering was an American engineering firm and leading firm in the development of power systems in the United States with approximately 30,000 employees in about a dozen states at its peak. Headquartered in Stamford, Connecticut, C-E owned over two dozen other companies including...
. Designed for supercritical
Supercritical steam generator
Supercritical steam generators are frequently used for the production of electric power. They operate at supercritical pressure. In contrast to a "subcritical boiler", a supercritical steam generator operates at such a high pressure that actual boiling ceases to occur, the boiler has no liquid...
operation, they supply steam to the turbines at 3500 psi (241 bar) and 1000 °F (537 °C).
The main turbines are General Electric (GE) tandem compound reheat turbines, each directly coupled to a generator and designed to rotate at 3600 rpm.
Steam discharged from the turbines enters a condenser where water circulating through tubes cools and condenses it, producing a vacuum that maximizes the pressure drop across the turbine. The heat picked up by the circulating water is removed by evaporation in six induced-draft cross flow cooling tower
Cooling tower
Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely...
s (two per unit).
The plant uses up to 28000 acre.ft of water per year from Lake Powell, or about 1/2 gallon (1.9L) per kWh, mainly for cooling water and scrubber operation.
The plant consumes about 8 million tons of low sulfur bituminous coal each year, supplied by Peabody Energy
Peabody Energy
Peabody Energy Corporation , previously Peabody Coal Company, is the largest private-sector coal company in the world. The company is headquartered in Downtown St. Louis, Missouri....
’s Kayenta mine near Kayenta, Arizona
Kayenta, Arizona
Kayenta is a census-designated place which is part of the Navajo Nation and is in Navajo County, Arizona, United States. The population was 5,189 at the 2010 census. Kayenta is located south of Monument Valley and contains a number of hotels and motels which service visitors to Monument...
. The coal is hauled 75 miles from mine silos to the plant by the Black Mesa and Lake Powell
Black Mesa and Lake Powell
The Black Mesa and Lake Powell Railroad is a electrified private railroad operating in Northern Arizona, USA within the Navajo Nation which transports coal from the Peabody Energy's Kayenta Mine near Kayenta, Arizona to the Navajo Generating Station power plant at Page, Arizona...
electric railroad. Characteristics of the coal in 2010 included a sulfur content of 0.62%, an ash content of 10.4%, and higher heating value (HHV) of 10,820 Btu/lb.
The plant has three 775 ft (236 meter) tall flue gas stack
Flue gas stack
A flue-gas stack is a type of chimney, a vertical pipe, channel or similar structure through which combustion product gases called flue gases are exhausted to the outside air. Flue gases are produced when coal, oil, natural gas, wood or any other fuel is combusted in an industrial furnace, a power...
s, listed among the tallest structures in Arizona. The stacks were constructed of reinforced concrete, supporting an internal metal liner. The plant's original stacks were demolished in the late 1990's after being replaced by larger diameter stacks of the same height, resulting in the plant having six stacks visible for a time.
The new stacks were required to accommodate cooler flue gas saturated with water vapor that resulted when wet SO2 scrubbers were added.
Performance
Annual net generation: 17,136,152 Megawatt-hoursNet capacity factor: 87%
Net heat rate: 10,112 Btu/ kWh.
Particulate
Hot side electrostatic precipitators (ESP’s), constructed as part of the original plant, remove 99% of particulate from the flue gas. The SO2 scrubbers remove an additional 50% of particulate remaining in the flue gas after passing through the ESP’s.Flue-gas desulfurization
Each unit has a forced oxidation wet scrubber for flue-gas desulfurization, using limestone slurry in two countercurrent–flow absorber vessels to remove 92% of SO2 from the flue gas.The three scrubbers in total consume about 24 MW of power, and use 130,000 tons of limestone and 3000 acre.ft of water per year, producing 200,000 tons of gypsum per year.
Nitrogen oxide
Low NOx burners with separated overfire air used to control nitrogen oxide emissions.Emissions summary
| Component | Rate (lb/mmBtu) | Rate (lb/MWh) | Annual plant total (tons/year) |
|---|---|---|---|
| SO2 | 0.471 | 4,076 | |
| NOx | 0.21 | 2.385 | 20,633 |
| CO2 | 2,295 | 19,859,041 |
Wastewater handling
NGS was built with one of the first zero liquid discharge (ZLD) systems in a power plant, recovering all cooling tower blow-down and runoff from developed areas of the site. The waste water is processed through three brine concentrators and a crystallizer, which remove the solids and produce distilled water for re-use within the plant.Several lined ponds are used in conjunction with the ZLD system to capture and regulate the flow of waste water to the system.
Byproducts handling
The plant sells about 500,000 tons of fly ash per year for use in the manufacture of concrete and Flexcrete insulating block building product.Bottom ash and gypsum, a byproduct of the scrubber operation, are dewatered in the removal process; and, along with any fly ash not sold, are landfilled on-site as solids. No wet impoundments are used for ash or byproduct disposal.
External links