Emissions from Energy-from-Waste (Waste to Energy) Facilities
Controlling Air Emissions
Covanta’s Energy-from-Waste facilities meet or exceed the strictest standards set by regulatory bodies and employ sophisticated technologies to achieve superior environmental performance which is fully protective of human health and the environment. In the United States for example, the emissions from our facilities are dramatically below the established limits, usually operating at 60-90% or more below the required limit and Covanta is committed to doing even better.
Our sustainability program has been an important driver of our success to reduce emissions and is an example of our commitment to achieving strong environmental performance. Since launching our sustainability program in 2007, we have reduced emissions by up to 53 percent.
State-of-the-art emissions control technologies
Our boilers are specifically designed to recover as much energy as we can out of the waste resource, minimize formation of dioxins and ensure complete combustion, including volatile organic compounds (VOCs) and other organic compounds.
Nitrogen Oxides (NOx) Control:
Our facilities are equipped with selective non-catalytic reduction (SNCR) systems, which inject ammonia or urea into the furnace to chemically convert NOx into gaseous nitrogen, a harmless gas that makes up the majority of our atmosphere. In addition, we have installed Covanta’s proprietary low nitrous oxide system (Low NOx™) in more than 20 units, which helps us control NOx emissions and reduce reagent consumption.
After leaving the boiler, combustion gases travel through an extensive air pollution control system. At many of our plants, activated carbon is added to the flue gas stream as it exits the boiler. Gaseous phase contaminates such as mercury and dioxins adsorb to the surface of the carbon so it can be removed downstream in the baghouse.
A scrubber neutralizes acid gases, including sulfur dioxide and hydrochloric acid, by spraying a lime slurry into the exhaust stream. This process removes more than 95 percent of sulfur dioxide and hydrochloric acid.
Operating like a very efficient vacuum cleaner, the baghouse removes 99.5 percent of the particulate matter from the combustion gases. As air is drawn through the baghouse, particulate matter and fly ash are caught on the surface of the bags. Periodically, the bags are cleaned by temporarily reversing the airflow or, in other designs, pulsing the bags with a strong jet of air. The particulate and fly ash are removed from the bottom.
All of our facilities operate under strict air emissions control limits. To demonstrate compliance, we use a combination of continuous emission monitoring systems that monitor emissions 24 hours a day, seven days a week and stack tests performed at least annually.