Liner System. In the modern landfill, gas management begins with liner system design. This tool prevents liquid waste or leachate from contaminating the soil and groundwater beneath the landfill, but it also is a highly effective for containing and assisting in the capture of landfill gas (LFG).
A clay or membrane liner system seals the bottom and sides of the landfill to minimize the potential for LFG escaping through migration. With the sides and bottom sealed, the easiest escape route for the gas is through the top. A good clay or membrane cap should stop the gas from escaping through the surface. However, if a site is sealed on the bottom, sides and top, a LFG system to prevent pressure from building up within the landfill cell is necessary.
Gas Wells. Placed horizontally or vertically in the landfill cell, gas wells provide the conduit through which gas can be collected. Vertical wells are the most common and are highly effective when properly designed and installed. While gas well design components may vary based on a site's parameters, the basic criteria that must be considered are: location; spacing; depth; diameter; well screen material; perforation or slotting detail; filter pack specifications; well seals; and wellheads. Each component affects price, efficiency, aesthetics, longevity and maintenance costs, so choose carefully.
Header System. Once gas collection wells are in place, a pipe network to connect the wells must be installed at a central location. Typically, the header system consists of a primary header that is connected to the blower system and extends out into the field to a series of sub-headers, or laterals, that connect each well in the field. The critical design criteria are:
* Size - Selecting the appropriate size header, subheader, laterals, wellheads and valves for the estimated vacuum requirements and the estimated amount of gas to be extracted and the estimated vacuum requirements.
* Material - Selecting of the appropriate material types for each component of the header system, including the pipe, flexible connectors, wellheads, valves, flanges and hardware.
* Placement - Selecting the header system location, then choosing an above or below ground system.
* Condensate Recovery Methodology - Determining the approach, then selecting of size, placement and materials.
Blower/Flare. Considered the heart of the landfill gas system, the blower pumps the gas out and sends it to its final destination. A gas incineration system (flare station) normally is an integral component to the blower system. Even when LFG is used to produce energy, a backup blower/flare system must be in place to prevent gas pressure build-up when the gas utilization equipment isn't operating. When equipment isn't running, this normally would be the flare station.
Today, blower/flare stations typically are self-contained, automated gas recovery and destruction devices. Blowers are used to recover or vacuum the gas, then they discharge the gas under pressure into an incineration unit. A typical system consists of blowers; demister and particulate removal system; automatic safety shut-off valve; flame arrester; utility or enclosed flare; temperature and flame control instrumentation; ignition system; power control and distribution system; and other instrumentation, control and monitoring systems. The complete blower/flare system typically is the single most expensive and critical component of the LFG management system.