Waste to Energy
Municipal Solid Waste is Burned in Fairfax County
All municipal solid waste in Fairfax County that is not recycled through curbside or drop off programs ends up at the Covanta waste-to-energy facility located at the I-95 Landfill in Lorton. In the waste-to-energy conversion, the volume of trash is reduced by 90%.
Every day about 150 to 200 trucks, each carrying as much as 20 tons of trash, arrive at the facility. The trucks enter a huge garage-type structure and dump the trash on the tipping floor.
A bulldozer pushes the trash into a pit that has a maximum capacity of 16,000 tons but typically holds 8,000 tons. Big cranes pick up the trash and feed it into the hopper, which goes to the boiler. This is where combustion happens.
The trash is burned on a grate at 2,400 degrees Fahrenheit, 24 hours a day, seven days a week. The heat from the combustion heats water in tubes, which creates steam. The steam turns the turbine, which combined with a generator, generates electricity. The steam leaves the turbine and goes to cooling tanks. The steam is then returned to a liquid state with cooling water. During the process the cooling water can be seen evaporating as water vapor clouds above the cooling tower.
The ash from the incinerated trash is sifted for ferrous and nonferrous
metals, which are recycled. About 25,000 tons of ferrous metals and 600
tons of nonferrous metals are removed per year. The remaining ash is land
filled, which represents only about 25% of the original weight of the
The combustion air goes through several forms of air pollution control equipment to remove nitrogen oxides, sulfur dioxide, hydrogen chlorides, mercury, and dioxins.
Ammonia is sprayed into the furnace to remove nitrogen oxides which, when released into the atmosphere, can contribute to a “ground level” ozone or smog. From the furnace, the combusted air goes to a scrubber that neutralizes acid gases—sulfur dioxide and hydrogen chloride—which contribute to acid rain. Carbon is sprayed into the combusted air to help remove mercury and dioxins. Finally, the combusted air goes through fabric filters in the “bag house.” The bag house works like a big vacuum cleaner in reverse. There are 2,520 bags which are each 14 feet long. As the dirty gas goes through the bags, more than 99 percent of particulate matter is removed. Clean gas rises and goes out through one of four stacks.
The plant generates 79 megawatts of electricity, enough to power about 75,000 homes. Covanta sells the electricity to Virginia Dominion Power, and Fairfax County receives a portion of the revenue.
The county has a contract with Covanta to process trash until 2011 with the option to extend the contract to 2021.
Fairfax County guarantees the delivery of 930,750 tons of waste to the facility. Until 2003, about three-fourths of the waste came from Fairfax County and the rest from Washington, D.C. Today, the county’s population exceeds one million and generates enough trash to fill the facility. A small amount of waste from D.C., Prince William and Loudoun Counties is currently being taken at the facility; however, these amounts are less than in previous years. Most DC waste is taken to landfills south of here.
History of Waste to Energy
Kent Burton, Senior Vice President of National Environmental Strategies and a consultant to Covanta, is eager to talk about the solid waste industry. “Solid waste management, from the standpoint of protecting public health, is relatively new,” said Burton.
“A hundred years ago, we disposed of our garbage with little regard for ground water contamination or air emissions. The evolution in waste management started when people realized that how we disposed of our waste had environmental consequences. It was the Europeans who got creative with trash disposal because there was less land available for burying it. They devised technologies to improve and control combustion of trash. The Germans discovered that if you burn trash hot enough, the energy can turn a turbine. The Martin grate, which is the type used at Fairfax, is the most used technology for burning municipal solid waste in the world. It was introduced to the U.S. in the 1970’s.”
Derek Porter, a chemical engineer, is the business manager for Covanta Fairfax. “In the 1970’s and 80’s, interest in the waste-to-energy process increased because landfills were running out of space. However, in the 1990’s landfills increased capacity so interest in WTE slowed. In the last few years, as capacity for landfills is again going down, interest in WTE is up. This is particularly true in New York where land is too expensive to use for landfills and in Florida where the water table is so high that municipalities cannot dig deep enough to bury trash.
“WTE has grown,” added Burton. “It is absolutely the most environmentally sound way to deal with garbage. In the northeast and other populated areas, it is economically comparable to other disposal methods. If you look at the environmental benefits, there is no comparison.”
“In 1989, when the Clean Air Act passed, there was a separate title specifically addressing WTE” said Burton. “Many environmental activists were pushing for strict recycling—all waste material should be converted to its original use. However, it would be astronomically expensive and impractical to recycle everything. The Clean Air Act required WTE facilities to be at the leading edge with respect to air emissions. New facilities had to meet stringent emissions criteria and older facilities had to be retrofitted. (Covanta Fairfax was built after 1989.) In 2003 the EPA completed a facility by facility inspection of WTE facilities. It was an amazing report. The EPA said that taken together, these retrofits make for an industry that has less environmental impact than almost any other source of electricity in the country. For example, these retrofits reduced dioxins by 99% and mercury by 90%.”
WTE accounts for 15-16% of waste management in the U.S. Recycling falls in the high teens. According to Burton, more recycling occurs in communities with WTE than in communities without it. He credits communities like Fairfax County for taking the lead in municipal solid waste management.