Waste-to-Energy and Government Regulations
The waste-to-energy industry is one of the most stringently regulated industries in the United States. Wheelabrator’s waste-to-energy plants use the most advanced emissions control and monitoring technology yet developed to meet federal, state, and local requirements.
Waste-to-energy plants use the most advanced emissions control and monitoring technology yet developed to meet federal, state and local requirements.
The Emission-Control Process
The technology employed by Wheelabrator’s waste-to-energy plants is highly sophisticated and environmentally sound. The emissions-control process begins in the furnace where the trash is combusted at temperatures exceeding 2000°F to ensure complete combustion.
The first step is to inject an ammonia compound called urea into the boiler in order to reduce smog-forming nitrogen oxide (NOx) emissions. This system process is called Selective Non-Catalytic Reduction (SNCR).
Next the flue gas enters a Spray Dryer Absorber (SDA) where a slurry of lime and water is sprayed to significantly reduce acid gases. Then, a dry-powered, activated carbon is sprayed into the flue gas to remove mercury and trace organic compounds such as dioxins and furans.
The final step is the fabric filter baghouse. The baghouse functions as a giant vacuum cleaner with hundreds of fiberglass bags designed to filter particulates from the flue gas. The baghouse process removes 99.9 percent of the particulates from the gases before they are finally released from the stack.
Emissions Monitoring
Wheelabrator also uses Continuous Emission Monitors (CEMs) to automatically gather and analyze samples of gas from the ducts leading to the stack. Once samples are analyzed, the results are sent to the plant control room where the data can be tracked in real-time to ensure proper operation of the pollution control systems.
This constant flow of data allows operators to maintain the efficiency of the facility by catching problems well before a permit limit is reached. This data is also used to generate a performance report which is sent to the state and federal agencies regulating waste-to-energy facilities.
According to the U.S Environmental Protection
Agency, modern waste-to-energy plants produce electricity cleaner
than almost any other source of electricity, and do so using a renewable
source of fuel: trash
(U.S.
EPA, 2003).
Every facility has extensive quality control and reporting requirements that include verification and calibration of CEM recording instruments, third-party quarterly and yearly audits of calibration practices and data accuracy, and third-party stack testing to verify emission compliance.
Proper calibration is critical to ensure the accuracy of the CEM data. We take this very seriously and perform calibration of the CEM equipment daily.
Ash Testing
Waste-to-energy facilities use combustion to convert trash into clean, renewable electricity. The combustion process produces an ash residue disposed of in a conventional landfill.
In accordance with federal law, waste-to-energy ash is tested to ensure it is non-hazardous. The U.S. Environmental Protection Agency (EPA) developed an aggressive test called the Toxicity Characteristic Leaching Procedure to determine if metals will leach from the material. If metals leach in amounts greater than a fraction of a percent, the ash is considered hazardous. Years of testing ash from every waste-to-energy facility in the country have proven that ash is safe for disposal and even reuse. Waste-to-energy ash consistently passes the EPA test, despite the fact that the test greatly exaggerates the potential for metals to leach from ash.
While landfill wastewater is regulated as an industrial discharge, test results and measurements taken from operating ash landfills show the levels of metals present in the actual ash leachate are most often below the significantly more restrictive drinking water standards and far lower than the EPA toxicity criteria.
When trash is combusted in a waste-to-energy facility, the resulting ash represents about 10 percent of the volume of the original trash. Metals, such as iron, steel, copper and zinc are recovered from the ash at the facility and sent to be recycled into new metal products, leaving a residue that looks a lot like wet cement. This reside actually has physical properties similar to construction mixtures such as concrete. After a short time, the ash “cures” and resembles concrete.
But disposal is not the only option. Nearly three million tons of ash, or more than one-third of all residues, are being reused annually as landfill roadbed materials, daily and final landfill cover, road aggregate, asphalt-mixture, and even cement blocks.