Over 29 million tonnes of solid non-hazardous waste was generated in Canada and managed offsite in 1998, according to the most recent data available from Environment Canada. One third came from residential sources and the remainder from industrial, commercial and institutional generators as well as construction and demolition projects.
Landfill is still the main destination of Canadian solid waste sent for disposal, containing approximately 90 to 95 per cent of the total amount. In 1998 nearly 21 million tonnes of waste was disposed of in 767 public and privately owned and/or operated landfills, and in 45 incinerators around the country.
In light of NAFTA and other close ties with the U.S., Canadian waste management regulators aim to harmonize practices with those found south of the border. These include harmonization of the provincial and federal waste definitions, a pre-treatment standard for hazardous waste, a phase-out of hospital incinerators and certain waste management activities.
A municipality in the U.S. serves as a good example of how to upgrade pollution control equipment to meet harmonized waste management regulations.
Wasatech Energy Systems (WES) owns and operates the Davis County Energy Recovery Facility, a mass burn municipal solid waste incinerator, and the Davis County Landfill, both located in Davis County, Utah. WES is a “special service” district that provides integrated solid waste disposal services to more than 200,000 residents in 15 cities and two counties.
In October 1999 WES solicited proposals from qualified contractors for new air pollution control equipment as required to meet proposed federal regulations. In June 2000 WES awarded AirPol Inc. of Parsippany, New Jersey a turnkey contract to supply, install and start up a dedicated gas suspension absorber (GSA) provided by FLS Inc. upstream of each existing electrostatic precipitator (ESP). Under the contract AirPol also supplied a common lime slurry storage and preparation system, carbon storage and delivery system, ash conveying system, MCC, and control system.
The energy recovery facility consists of two mass burn refractory lined furnaces. The units each produce approximately 52,000 pph of steam at 550 psi and 515F (or 268C).
Originally, each incinerator was equipped with an Environmental Element Corporation (EEC) three-field ESP for control of particulate emissions. Acid gases were controlled by dry sorbent injection at the economizer inlet. Performance of the dry sorbent injection system was marginal due to short retention times and poorly controlled temperatures. The dry sorbent injection also aggravated fouling of the economizer section and increased particulate loading to the ESP.
WES selected the semi-dry scrubber system and awarded a contract for a turnkey installation. The existing dry sorbent injection system was removed from operation and one GSA was added upstream of each existing ESP. The semi-dry system uses pebbled lime for acid gas removal and powder-activated carbon (PAC) injection as an adsorbent for mercury and dioxin/furan control.
In addition, the existing ESP structure was reinforced and larger induced draft fans were installed to meet the increased pressure drop across the GSA. A common lime slurry storage and preparation system, carbon storage and delivery system, ash conveying system, MCC, and control system were also included in the contract.
To suit the general arrangement of the facility, each GSA is located upstream of the existing precipitators (see Figure 1). To maintain access to the existing precipitator, a length of ductwork was provided to direct the flue gas from the economizer outlet to the GSA reactor and back to the ESP inlet.
The startup in September 2001 went without any substantial problems. Purchasing records from the first six months of operation indicate an overall pebble lime consumption rate of approximately 6 kg per tonne of waste combusted. Results of testing indicate that performance objectives can be met with no carbon injection. However, the facility is currently injecting carbon at a rate of approximately 0.14 kg per tonne of waste combusted.
Engineering stack testing was conducted during October 2001 after minor operational issues were resolved. The engineering testing was conducted to assess system performance prior to the performance testing required by the Utah Division of Air Quality. (Six 120-minute samples were collected.)
Compliance stack testing was also conducted in November 2001. Testing results demonstrate that particulate, metals, acid gas and dioxin/furan emissions from the retrofit facility are substantially lower than required under the now final 40 CFR, Part 60, Subpart BBBB Emission Guidelines for Existing Small Municipal Waste Combustors. The new GSA system has demonstrated more then 98 per cent efficiency since system startup.
Robert Levy is president of Levy & Associates based in New York, New York.