Draft Notes from Site Visit at Covanta Fairfax’s I-95 Energy/Resource Recovery Facility on July

21, 2009

EPA conducted a site visit at Covanta Energy’s Covanta Fairfax plant (Covanta Fairfax) located in 

Lorton, VA on July 12, 2009 to learn about the operations at the municipal solid waste (MSW) 

electricity generation plant. These notes describe the information collected during the site visit, as well 

as information provided by the plant prior to the visit. The water balance diagram for the plant is 

included as Attachment 1 to these notes. 

Covanta Energy operates over 40 MSW electric generating facilities in the U.S. According to plant 

personnel, there are approximately 93 MSW electric generating facilities in the U.S.; therefore, 

Covanta Energy operates between 40 and 45 percent of all MSW electric generating facilities. 

According to plant personnel, all of the Covanta MSW facilities are similar in operation, although not 

identical.

Plant Overview

• Covanta Fairfax is located on an approximately 23-acre site within the boundaries of the I-95 

Landfill. The area is approximately 1.75 miles from US Highway 1 on Furnace Road in the 

vicinity of Lorton, Virginia and approximately 25 miles southwest of Washington D.C.

• Covanta Fairfax owns and operates the I-95 Energy/Resource Recovery Facility (I-95 E/RRF) 

under an agreement with Fairfax County. The I-95 E/RRF is a 3,000-ton per day (TPD) refusefired electric generating facility. The I-95 E/RRF has operated continuously since it began 

commercial operation in June 1990. The facility consists of four nominal 750 TPD refuse-fired 

boilers and two 63.8-megawatt (MW) turbine generators, along with ancillary equipment. 

• The facility processes 3,000 TPD MSW for a population of more than 900,000 in the 

Washington, D.C. suburbs of Fairfax County. Air pollution control equipment consists of spray 

dryer absorbers for acid gas reduction, fabric filter baghouses for particulate removal, activated 

carbon injection system for mercury control, and selective non-catalytic reduction (SNCR)

system for reduction of nitrogen oxides. The heat energy produced during the combustion of 

municipal solid waste is converted into electricity that is sold to Virginia Dominion Power 

Company.

• Waste is delivered to the facility via refuse trucks. The refuse trucks enter the facility through a 

controlled access gate and proceed to a weigh station. The weigh station determines the total 

tonnage of waste delivered and, when applicable, the total amount of unacceptable waste 

rejected. Once through the weigh station, the trucks proceed to the tipping bays located within 

the enclosed tipping hall to deposit the waste in the refuse pit, or temporarily onto the tipping 

floor. Several loads a day are dumped onto the tipping floor, in order to allow the loads to be 

inspected for unacceptable waste. Unacceptable waste is deposited into a large drop box inside 

the tipping hall. The rejected waste is subsequently transported to an appropriate disposal site. 

All acceptable waste is pushed into the refuse pit using a front-end loader. Waste from the 

refuse pit is mixed, stockpiled, and deposited into the furnace feed hoppers by overhead cranes. 

The refuse pit and tipping hall are maintained at a slightly negative pressure by the combustion 
air fans (forced draft fans) that draw air from the building. This design feature provides 

effective odor control. Waste accepted at the facility is primarily MSW, which includes 

household, commercial and institutional waste.

• Waste is continuously fed into the combustion units from the feed hoppers through refractorylined feed chutes. The combustion units are integrated reciprocating grate stokers and top 

supported, single pass, membrane waterwall boilers equipped with superheaters and 

economizers. The design steaming rate for each combustor is 205,625 lbs/hr. Natural gas, 

which is used as auxiliary fuel in the boilers during start-up and shutdown, is received by 

pipeline.

• The combustion air is divided into underfire and overfire air. The underfire air is heated in a 

steam coil then evenly distributed below the stoker grate before entering the combustion zone. 

Underfire air cools the grates, aids in the suspension of the waste for combustion, and provides 

combustion air. Overfire air, which is added above the stoker grate at the front and rear walls of 

the combustor, assures complete combustion of volatile off-gases.

• The combined high-pressure superheated steam generated by the four combustion units is piped 

to either of two turbine generators. Total energy generation capacity at rated combustion rates 

is 80 MW. Plant load is approximately 10 MW. The balance of the electricity generated is sold 

to Virginia Dominion Power Company.

• The air pollution control equipment includes four spray dryer absorbers, four baghouses, 

associated screw conveyers which convey collected fly ash back into the boiler building to the 

Martin Ash Discharger (described below), a carbon storage silo, two pebble lime storage silos, 

lime slurry tanks, quench reactors, and associated equipment. 

• The facility injects a 19% aqueous solution of ammonia into the upper portion of the boiler to 

help reduce NOx emissions. This injection is associated with the SNCR system.

• The flue gas exiting the boiler is transferred to the spray dryer absorbers. Prior to entering the 

spray dryer absorbers, the facility injects activated carbon into the flue gas for mercury control.

• The facility has lime slakers on site to create the lime slurry used in the spray dryer absorbers. 

The facility uses cooling tower blowdown to slake the lime to a 21% solids slurry. The spray 

dryer absorber removes over 90 percent of the SO2 in the flue gas.

• The flue gas then passes through the baghouse to remove the fly ash, scrubber solids, and 

activated carbon. The clean flue gas is transferred to the stack and emitted from the facility. 

The fly ash and other solids are collected in the baghouse hoppers and the facility uses screw 

conveyors to convey the collected solids back into the boiler to combine with the bottom ash. 

The combined bottom ash, fly ash, and other solids are conveyed away from the waste 

combustors by a series of different conveyors. All conveyors are either located within 

buildings or are otherwise enclosed. The ash is combined in the proprietary Martin Ash 

Discharger and is conditioned with cooling tower blowdown as both a cooling agent and as a 

dust suppression agent. The facility also adds dolomite lime to the ash discharger to stabilize 
the ash. Dewatering of the ash is accomplished by gravity, by the squeezing action of an ash 

extractor ram, and by a vibrating pan. [QUESTION FOR COVANTA: What components make 

up the Martin Ash Discharger and what does the ash discharger do?]

Martin Ash Discharger.

The basic design is the same for all dischargers. The discharger is filled with water and a 

constant amount of bottom ash up to the level of the front air sealing wall. This creates an air 

seal against the furnace, thus preventing flue gas and thermal pollution in the basement on the 

one hand and false air ingress into the boiler on the other. 

The hot, burnt-out bottom ash is transported from the grate end to the 

discharger's water bath where complete quenching occurs. The water consumption depends 

exclusively on the temperature of the bottom ash and its capacity to absorb water. Only 

sufficient water to quench the bottom ash is fed to the discharger. Neither a water overflow nor 

recirculation is required nor does the area around the discharger remain clean. 

The discharging ram pushes the bottom ash under the air sealing wall towards the drop-off 

edge. As a result, the bottom ash is discharged in a dust-free and odorless manner. There is a 

drain-off section before the drop-off edge where excess water is extracted by the compressing 

action of the discharging ram. The bottom ash is therefore moist rather than wet when 

discharged.
• Oversize material (>10 inches in diameter) is removed from the ash stream by a grizzly scalper 

in a separate outbuilding. The remaining ash is sent through a series of sizing screens in the 

residual ash building. Appropriately sized ash is further processed through a non-ferrous metal 

processing unit (the non-ferrous system, which was not operational for a period, is currently 

being brought back into service) to remove valuable non-ferrous metals for recycling. Ferrous 

metal is separated from the ash stream, as well. Recovered ferrous and non-ferrous material is 

removed from the site by truck. The ash residue is loaded into covered trucks for removal to the 

I-95 Landfill operated by Fairfax County.

• Exhaust steam from the turbine is condensed to water. The water used to condense the steam is 

pumped to the facility’s cooling towers. The facility uses sulfuric acid and other biocides to 

treat the cooling water. The plant also uses a chlorine generator to generate chlorine for 

treating the cooling water. 

• Excess water and ash from cleaning and maintenance activities drains into floor trenches 

located in the boiler building and in the air pollution control area. These floor trenches drain 

into sumps and subsequently to two settling basins. Solids settle to the bottom of the settling 

basins. Water is pumped from the settling basins to the ash dischargers to provide quench water 

for the ash residue. Ash and sediment from the trenches and the settling basin is disposed either 

with the combined ash residue or with the refuse in the main storage pit.

• Process wastewater from the facility consists of boiler blowdown, cooling tower blowdown, 

neutralization tank batch discharges, and sanitary sewage from facility buildings. These 

wastewaters, along with effluent from the Fairfax County Landfill, are pumped from a lift 

station to the Noman M. Cole Jr. Pollution Control Plant, which is a publicly owned treatment 

works (POTW) operated by Fairfax County.
Attachment 1

Covanta Fairfax Water Balance Diagram