SELECTION AND DESIGN OF EMISSION CONTROL TECHNOLOGY FOR INDUSTRIAL LANDFILL GAS

The presence of chlorinated volatile organic compounds and methane in industrial landfill gas presents challenges in the selection and design of emission control technology. This paper summarizes engineering work during the selection and design of control technology for a capped industrial landfill in the eastern U.S. Gas extracted from the landfill contains up to 7,700 ppm (by volume) vinyl chloride, and up to 4,300 ppm of 1,2-dichloroethene. Methane concentrations range from 7 to 70 percent by volume. Several control technologies were initially considered for gas emissions, including granular activated carbon adsorption, proprietary adsorbents, flaring, thermal oxidation, catalytic oxidation, ultraviolet light oxidation, and electron beam destruction. Based upon comparisons of effectiveness and life-cycle cost, thermal oxidation was selected for this application. The paper also describes basic system sizing, key instrumentation and safety interlocks, atmospheric dispersion modeling of the oxidizer combustion products, and permitting activities.A combined landfill and soil vapor extraction system was installed in the landfill area and two adjacent soil areas known as the “toe” and the “crest” areas. The total system consists of a vapor extraction system, vapor collection header system, vapor treatment system (thermal oxidizer), monitoring components, and controls. The treatment equipment is located outdoors. The vapor extraction/treatment portion of the system includes a thermal oxidizer, blower(s), demister, condensate removal tank, condensate water pump, controls, and instrumentation.The design and implementation of vapor extraction within a landfill environment required consideration of factors not typically associated with soil vapor extraction. The initial methane concentrations in the vapor from the landfill were as high as 70 percent. This required consideration of explosion hazards. Also, the presence of biodegradable materials, as evidenced by methane concentrations at elevated levels, results in the potential for a landfill fire when vapor extraction is implemented.Oxygen is introduced into the subsurface as a result of vapor extraction. Vapor extraction typically utilizes a higher applied vacuum and increased rate of vapor movement as compared to landfill gas recovery systems. The vapor extraction was therefore carefully monitored and controlled to avoid introducing excess oxygen, which might result in aerobic conditions conducive to a landfill fire. Temperatures within the landfill and extracted vapor were measured; oxygen levels and opacity were also monitored initially and methane levels are monitored. Although no problems have been encountered, contingency measures were developed. These include system shutdown, pulsed operation, and injection of a fire suppressant.The extraction system includes three vapor extraction wells located in the landfill, six vapor extraction wells located in the crest area, and a buried horizontal extraction pipe located in the toe area. Each extraction well and horizontal extraction pipe has a vacuum gauge and valve for monitoring and balancing the system. Temperature probes have been installed at each extraction well in the landfill and in the header pipe to monitor extracted vapor temperature.Temperature probes and vacuum gauges have also been installed in 12 wells constructed in the landfill to monitor the temperature and vacuum within the landfill. The thermal oxidizer treats the VOCs through combustion. The system has removed a significant mass of VOCs and continues to reduce the VOC source remaining in the landfill and surrounding soils.The system operates automatically with only occasional on-site inspections and operations. The system is monitored and controlled using a personal computer. Remote monitoring, control, and recovery of data are performed. An alarm system has also been provided to alert the operator of unfavorable operating conditions via an automatic dialing system, and will shut down the system in the case of a malfunction. The system has been operating as designed and is being maintained in accordance with the approved operation and maintenance manual.