A municipal waste incinerator meets federal regulations with a semi-dry sorbent injection system

In this installment of What Works, a company searches for new air pollution control equipment to meet federal regulations.

Wasatch Energy Systems 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.

The energy recovery facility consists of two mass-burn refractory-lined furnaces. The units each produce approximately 52,000 pounds of steam per hour at 550 psi and 515° F. Each incinerator was originally equipped with an Environmental Element Corp. three-field electrostatic precipitator (ESP) for controlling particulate emissions. Acid gases were controlled by dry sorbent injection at the economizer inlet. Performance of the dry sorbent injection system was marginal because of its short retention times and poorly controlled temperatures. The dry sorbent injection also aggravated economizer section fouling and increased particulate loading to the ESP.

In October 1999, the company solicited proposals from qualified contractors for new air pollution control equipment as required to meet proposed federal regulation 40 CFR, Part 60, Subpart BBBB, Emission Guidelines for Existing Small Municipal Waste Combustors.

In June 2000, it awarded AirPol Inc., Parsippany, N.J., a turnkey contract for supply, installation and startup of a dedicated FLS milj, Inc. gas suspension absorber (GSA) upstream of each existing ESP.

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 powdered activated carbon (PAC) injection as an adsorbent for controlling mercury, dioxin and furan.

In addition, the existing ESP structure had to be reinforced and larger induced draft fans installed to meet the increased pressure drop across the GSA. To suit the general arrangement of the facility, each GSA was located upstream of the existing precipitators. To maintain access to the existing precipitator, a length of ductwork was provided which directs the flue gas from the economizer outlet to the GSA reactor and back to the ESP inlet.

The new APC system was commissioned and put into service during September 2001. The startup on both systems went smoothly without encountering any substantial problems. Engineers checked each piece of equipment and subsystem thoroughly during the construction and pre-startup.

Engineering stack testing was conducted during October 2001 after minor operations issues had been 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. Results demonstrate that particulates, metals, acid gas and dioxin/ furan emissions from the retrofit facility are substantially lower than mandated under, now final, Subpart BBBB.

Operation of the GSA system is relatively simple and has demonstrated more then 98 percent availability since system startup.