A typical Covanta Energy-from-Waste facility

After refuse collection trucks are weighed at the scalehouse and monitored for safety, they enter the tipping building and dump their waste into the storage pit. An overhead crane mixes the waste in the pit and lifts it up into a feed chute leading to the furnace. From the feed chute, waste is pushed by hydraulic ram feeders onto a stoker grate.

The MARTIN Reverse-Reciprocating Stoker Grate slopes downward and is composed of alternating rows of fixed and moving grate bars. The grate bars push upward against the natural downward movement of the waste. This ensures that the burning waste is continually agitated and pushed back, to serve as underfire for freshly-fed waste. A forced-draft fan supplies primary combustion air underneath the grate, and overfire air is injected through the front and rear walls of the furnace.

Heat from the combustion process converts water inside the steel tubes that form the furnace walls and boilers, to steam. The superheater further heats the steam before it is sent to a turbine generator to produce electricity. After passing through the boiler sections, the hot combustion gases are used to preheat boiler feedwater in the economizer.

While the combustion gases move through the boiler, bottom ash slowly makes its way to the end of the grate where it falls into the water quench trough of the MARTIN Ash Discharger. From the boiler, the cooled gases enter the advanced air pollution control system. Using lime slurry, the dry scrubber neutralizes any acid-forming gases, such as sulfur oxides and hydrogen chloride.

Particulates are captured by a high-efficiency baghouse. As the gas stream travels through these filters, more than 99 percent of particulate matter is removed. Captured fly ash particles fall into hoppers and are transported by an enclosed conveyor system to the MARTIN Ash Discharger where they are wetted to prevent dust, and mixed with the bottom ash from the grate. The ash residue is then conveyed to an enclosed building where it is loaded into covered, leak-proof trucks and taken to a landfill designed to protect against groundwater contamination. Ash residue from the furnace can be processed for removal of recyclable scrap iron.

All aspects of the plant's operation are monitored from a central control room 24 hours a day, seven days a week, 365 days a year.

Covanta operates ten different types of Energy-from-Waste technologies, representing virtually every proven system in the world including the Martin Gmbh inclined and horizntal grates technologies.