Waste-to-Energy Facility Meets Changing Needs with McGill AirClean Equipment

Because emissions control regulations can change, requiring greater reductions in particulate and acid gas emissions, even the most efficient air pollution control equipment may need to be upgraded periodically. McGill AirClean (formerly United McGill) has the technology and experience to help its customers solve their changing air pollution control problems. McGill AirClean supplied electrostatic precipitator (EP) systems that are practical to upgrade, as well as fabric filter and spray-dry scrubber systems that can meet the latest performance standards. McGill AirClean's continuing commitment to its customers' changing needs keeps customers coming back when additional equipment is necessary.

McGill AirClean has installed three complete air pollution control systems at the New Hanover County Refuse-Fired Steam Generation Facility in Wilmington, North Carolina. This facility was the first waste-to-energy plant in North Carolina and has been recognized both nationally and by the state.

The purpose of this facility is to provide a safe mechanism to handle the county's solid waste," says New Hanover County's director of environmental management Ray Church. "We want to provide the best facility for solid waste management."

The plant earns money for its operations by selling steam to a nearby industrial plant. The steam not needed by the industrial plant is directed through a condensing turbine system to generate electricity, which is sold to the electric utility. Tipping fees are another source of revenue for the county.

The three boilers at the plant burn approximately 140,000 tons of solid waste per year, reducing the volume of solid waste that must be hauled to the county's synthetically-lined landfill by 85 percent. This dramatically reduces the amount of landfill space needed and greatly extends the life of the county landfill. When municipal solid waste is incinerated, however, hydrochloric acid (HCl) and sulfur dioxide (SO2 ) are produced.

Air pollution control equipment was installed at the New Hanover County Refuse-Fired Steam Generation Facility in two stages. The first phase began when the waste-to-energy plant was built in 1984. At that time, the facility had two boilers, each burning 100 tons of waste per day. A McGill AirClean two-field EP system was installed on each boiler to control particulate. McGill AirClean had previous experience designing air pollution control equipment for municipal solid waste incinerators and was able to supply a system that would meet performance standards. Because increasingly stringent regulations were probable, the support steel for a third field was installed on each EP to make a future upgrade easier.

The second phase of the New Hanover County project began in 1987 when a significant increase in the county's solid waste made expanding the plant's incineration capacity necessary. The county decided to add a third boiler, which would require its own air pollution control system. To meet tougher regulations requiring acid gas reduction, spray-dry scrubbers and upgrades to the EP systems would also be necessary.

The county contacted Stanton Peters, founder of SMP Engineers of Chattanooga, Tennessee. Peters had worked with the county on the first phase of the project in 1984 and was familiar with the performance of McGill AirClean's equipment. SMP engineers was contracted to provide the design, procurement, and construction management for the additional equipment based on the latest regulations. McGill AirClean submitted the best cost proposal for the upgrade, and because the county was pleased with the performance of the two EPs, McGill AirClean was selected to supply the additional air pollution control equipment and a computerized control system.

"We selected McGill AirClean equipment because we had experience with it, and it worked," said New Hanover County plant manager Troy Flanagan.

McGill AirClean's ability to supply all of the equipment for the EP upgrade and for the new air pollution control system provided New Hanover County with a single-source supplier for its emissions control needs.

One factor that Peters and McGill AirClean engineers had to consider was the variance of the materials in the waste stream. Because the incinerators are mass-burn (meaning no sorting takes place with the exception of large, bulky items) the garbage varies widely, particularly when the seasons change.

Church explains that from March through October, the volume of solid waste increases by 2,000 to 3,000 tons per month. He adds that this increase is mainly a result of the tourist season garbage, construction debris, and yard wastes.

"The equipment has to be of such a size and capacity that it can treat the wide variance of emissions. But the electrical control system is also important," Peters said. "McGill AirClean's automated control system makes the equipment capable of handling the variance in the waste stream," he added.

In 1990, a McGill AirClean four-module fabric filter was installed to handle emissions from the facility's new 250-ton-per-day boiler. To reduce the acid gas emissions, a lime-based spray-dry scrubber was installed on each of the three air pollution control systems.

Flue gas from their incinerators enters the spray-dry scrubbers, where the flue gas mixes with a finely atomized spray of water and lime. The lime slurry is distributed into the gas stream with dual-fluid air-atomizing nozzles. The lime reacts with the acid gases to neutralize them and form salts, which are then collected by the EPs or fabric filter. A single lime slurry preparation system feeds lime slurry to all three spray-dry scrubbers.

Because of the configuration of the boilers, the flue gas enters the spray-dry scrubbers from the bottom. It is typically more difficult to achieve sufficient distribution of lime slurry through the flue gas in bottom-entry spray-dry scrubbers. To ensure sufficient mixing of the lime slurry and acid gas, McGill AirClean performed laboratory tests on a model of the spray-dry scrubber systems. McGill AirClean's ability to design efficient bottom-entry systems minimized the amount of ductwork required and enabled the spray-dry scrubbers to be installed on the two older systems without having to move the EPs.

Because scrubbing equipment increases the amount of particulate, a third field was added to each of the EPs. McGill AirClean's modular design made adding the new fields easy.

A single computerized control system combines a programmable logic controller and a personal computer to control the operations of the equipment in all three systems.

The EPs easily controlled particulate to less than 0.02 grains per dry standard cubic foot and reduced SO2 acid gas emissions by more than 70 percent and HCl emissions by more than 90 percent, as was required. The fabric filter controlled particulate to less than 0.01 grains per dry standard cubic foot and reduced the acid gas emissions to far below the requirements.

McGill AirClean was able to supply the necessary air pollution control equipment to meet New Hanover County's changing needs. This equipment has helped the county handle its solid waste disposal problem in a manner that is both economical and safe for the environment.

"The systems were able to meet the performance standards," Church said. "New Hanover County is a leader in solid waste disposal," he added.

McGill AirClean Corporation, 1779 Refugee Rd., Columbus, OH 43207-2119. Tel: 614/443-0192; Fax: 614/445-8759; Email: mcgillairclean@compuserve.com; Website: http://www.mcgillairclean.com.