McGill AirClean Equipment Qualifies Waste-to-Energy Facility
A case study in point is the New Hanover County Refuse-Fired Steam Generation Facility in Wilmington, NC.
McGill AirClean (formerly United McGill) has staged the installation of three complete air-pollution control systems at what is the first waste-to-energy plant in the state. The facility provides for the disposition of Hanover County's MSW.
The plant sells steam to a nearby industrial plant. Excess steam goes through a condensing turbine to generate electricity that is sold to the electric utility.
The three boilers at the plant burn approximately 140,000 tpy of solid waste, reducing the volume of MSW to the county's landfill by 85%.
Incinerating the MSW, however, generates hydrochloric acid (HCl) and sulfur dioxide (SO2), requiring pollution-control equipment.
That equipment was installed in two stages.
The first stage included two boilers and occurred in 1984 when the waste-to-energy plant was built. Each, comprising a McGill AirClean two-field EP system to control particulates, burns 100 tpd.
Because more stringent regulations were likely, the support steel for a third field—the plan-ahead aspect—was installed on each EP to facilitate a future upgrade.
The second stage began in 1987 when a significant increase in the county's solid-waste load required an increase in the plant's capacity. The county decided to add a third boiler with a separate air-pollution control system.
To meet tougher regulations requiring acid-gas reduction, spray-dry scrubbers and upgrades to the EP systems also would be needed.
The county contacted Stanton Peters, founder of SMP Engineers of Chattanooga, TN. Peters had worked with the county on the first phase of the project in 1984. SMP's engineers then provided the design, procurement, and construction management for the additional equipment.
SMP decided on awarding the contract to supply the additional equipment and a computerized control system to McGill. The award was based on the benefit of having a single source of pollution-control equipment—especially considering the good past performance of the McGill equipment—as well as the merits of McGill's proposal.
In 1990, McGill AirClean installed a four-module fabric filter to handle emissions from the facility's new 250-tpd boiler.
A lime-based spray-dry scrubber installed on each of the three air-pollution-control systems neutralizes the acid-gas emissions,
Flue gases enter the spray-dry scrubbers from each of the incinerators, where they mix 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 form salts that are collected by the EPs or fabric filter. A single preparation system feeds lime slurry to all three spray-dry scrubbers.
The boiler configuration mandates that the flue gas enters the spray-dry scrubbers from the bottom, increasing the difficulty of achieving sufficient distribution of lime. To ensure sufficient mixing of the lime slurry and acid gas, McGill AirClean performed model tests. Based on the tests, the company designed systems with minimal ductwork, which enabled installation of the spray-dry scrubbers on the two older systems without having to move the EPs.
Because the scrubbing equipment increases the amount of particulates, a third field was added to each of the EPs.
McGill AirClean's automated control system enables the pollution equipment capable to handle the load and composition variability of the waste stream. 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 control particulates to less than 0.02 grains/dry scf. Also it reduces SO2 acid-gas emissions by more than 70% and HCl emissions by more than 90%, as required. The fabric filter controls particulates to less than 0.01 grains/dry scf and reduces the acid-gas emissions to well below requirements.
McGill AirClean Corporation, 1779 Refugee Road, Columbus, OH 43207-2119. Tel: 614-443-0192; Fax: 614-445-8759; E-mail: mcgillairclean@compuserve.com.
Edited by Paul Hersch