Final Notes from Site Visit at Covanta Fairfax ’s I

- 95 Energy/Resource Recovery Facility on July 21 , 20 09

EPA conducted a site visit at Covanta Energy’s Covanta Fairfax plant (Covanta Fairfax) located in Lorton, VA on July 12 , 20 09 to learn about the opera tions 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 inclu ded 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 operat es 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

- a cre 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 mil es 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) refuse

fired electric generating facility. The I

- 95 E/RRF has operated continuously since it began commercial operatio n 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 Washingt on, 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

- catalyti c 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 refus e 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 al low 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 ref use 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 combustionPage 2

air fans (fo rced 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 combu stion units from the feed hoppers through refractory

lined feed chutes. The combustion units are integrated reciprocating grate stokers and top supported, single pass, membrane waterwall boilers equipped with superheaters and economizers. The d esign stea ming 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 sto ker 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 gene ration 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.

**•** T he air pollution control equipment includes four spray dryer absorbers, four bagh ouses, 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 equipmen t.

**•** 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. P rior 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 tow er blowdown to slake the lime to a 21 % solids slurry. The spray dryer absorber removes over 90 % of the SO 2 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 tra nsferred 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 Discharg er and is conditioned with cooling tower blowdown as both a cooling agent and as aPage 3

dust suppression agent. The facility also adds d olomite lime to the ash discharger to stabilize the ash

.

**•** The hot bottom ash, and dolomite lime, is transported to the Marti n Ash Discharger where it is mixed with only enough cooling tower blowdown to achieve complete quenching. The amount of water fed to the discharger depends on the temperate of the ash and its capacity to absorb water; the system does not have a water over flow or recirculation line. The discharger is filled with water and a constant amount of bottom ash up to the level of the front air sealing wall as shown in Figure 1. This creates an air seal against the furnace, thus preventing flue gas and thermal pol lution in the basement and false air ingress into the boiler. The discharging rams push the bottom ash under the air sealing wall towards the drop

- off edge , r esulting in a dust

free and odorless bottom ash discharge. Dewatering of the ash is accomplished by gravity, by the compressing action of the discharging ram, and by a vibrating pan.

Figure 1. Martin Ash Discharger Diagram

**•** 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 b eing 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 isPage 4

removed from the site by truck. The ash residue is loaded into cove red 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 biocid es to treat the cooling water. The plant also uses a chlorine generator to generate chlorine for
treat ing 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 discharge r s to provide quench water for t he 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 public ly owned treatment works ( POTW ) operated by Fairfax County

.Attachment 1

Covanta Fairfax Water Balance Diagram