Waste-to-energy-plant's Maintenance Problem Solved

By Kevin Stimpfl

Engineers at OEG faced a predicament during a planned "cold-iron" outage for preventive-maintenance of their ejector-equipped waste-to-energy facility. They would need to perform vacuum leak testing on turbine-exhaust valves to the air-cooled condenser. In its cold-iron condition, however, the facility has no steam to power the vacuum-producing ejectors.

OEG (Ogden Energy Group, Inc.) engineers turned to Croll-Reynolds, providers of the facility's three steam-jet ejectors. Croll-Reynolds set parameters for operating the facility's single "hogging" ejector with motive air. Although air is less efficient than steam as a motive force, the engineers considered it adequate for short-term need. Croll-Reynolds's engineers supplied complete data for the volume and pressure of compressed air required for satisfactory operation of the ejector, and the vacuum leak test was successfully completed.

OEG designs, builds, and operates waste-to-energy facilities in the U.S. and abroad. Its waste-to-energy process combusts municipal solid waste to produce saleable steam or electricity. The company operates 27 waste-to-energy facilities across the U.S.

The waste that enters an Ogden facility is reduced to an inert ash, constituting 10% of its original volume-conserving valuable landfill space.

The OEG subsidiary, Ogden Martin Systems of Huntington, L.P., (on Long Island, NY) processes approximately 900 tons per day of municipal solid waste. The plant outputs approximately 25 MW of electricity. Most of it is sold to the Long Island Lighting Co.; 3 MW is used to run the facility itself.

Haulers, after collecting waste from such towns as Huntington and Babylon tip their loads into a refuse pit from which the waste is transferred by crane to one of three stoker/boiler feed chutes. Each chute accepts the waste fuel into its respective stoker/boiler unit from hydraulic ram feeders. With its three boilers, the facility keeps operating continuously while one is serviced. The facility, however, shuts down every two years for preventive maintenance.

The Huntington facility incorporates steam-jet air ejectors from Croll Reynolds (Westfield, NJ). * A twin-engine, two-stage ejector removes air and non-condensable gases from the exhaust of the turbine and air-cooled condenser.

Housed on the same skid is a single-stage hogging air ejector. It evacuates large quantities of non-condensable gases from the system at start-up. The higher-vacuum, lower-capacity two-stage ejector takes over after startup. The ejectors use 90-psig steam from the plant's steam supply. (Ogden-to prevent plume emission--uses an air, rather than a water-cooled condenser, at the Huntington facility.)

Engineers customarily select ejectors rather than vacuum pumps for power plants for vacuum needs because ejectors have no moving parts. In more than six years of operation, the Croll-Reynolds ejectors at the Huntington facility have required little or no maintenance.

*The Croll-Reynolds's two-stage ejector consists of two 6×5-ft "Y" stages and a 3×3-ft "Z" stage, constructed of carbon steel with 303 stainless-steel steam nozzles. A 12-in.-dia inter-condenser and an 8-in.-dia after-condenser have carbon-steel shells and 304 stainless-steel tubes, tube sheets, and channels. The unit is rated for 55 lb/hr of air and 121 lb/hr of water vapor at 1 in. Hg (abs), discharging to 14.7 psig. The single-stage hogging ejector is made of carbon steel with stainless-steel nozzle and carbon-steel silencer. Its design allows evacuating 14,250 cu ft of air from atmosphere to 10 in. Hg (abs), in 30 minutes.

Kevin Stimpfl is chief engineer, Ogden Energy Group, Inc., Huntington, NY.

Croll-Reynolds Clean Air Technologies/Croll-Reynolds Company, Inc., 751 Central Avenue, Westfield, NJ, 07091-0668.