What is Landfill Gas Extraction?
Municipal solid waste (MSW) landfill management includes layering and compounding the waste in a specific construct to create a successful environment for anaerobic breakdown. During anaerobic digestion, microbes produce landfill gases (LFG), mainly Methane (CH4) and carbon dioxide (CO2) with other trace gases. In order to prevent explosions and reduce greenhouse gas emissions, LFG extraction is conducted at the MSW site.
Land fill gases are extracted throughout the life of the landfill and even after the landfill closes, LFG can be collected for 20+ years depending on size and other environmental factors.
LFG beneficial-use facilities extract and process the Methane into renewable natural gas or biomethane. The gas can be combined with pipeline gas or be used to generate electricity. The schematic below from the EPA website illustrates the process.
How are LFG vacuum systems designed?
Active LFG collection uses vacuum extraction methods with vacuum blowers connected to underground vent pipes often called “gas extraction wells” or “gas collection wells.”
Vacuum systems for landfill gas extraction are controlled very precisely in inches of water column (inWC). For maxiumum efficiency, the vacuum system is designed to have constant vacuum level at each gas extraction well. Large fluctuations could cause condensate build-up or blockages in the system. The goal is to pull enough vacuum to collect maximum gas from the wells without so much vacuum that O2 is introduced into the extraction system. It takes a very narrow window of vacuum control, making it a complex process setup.
Some systems are designed with variable frequency drives on the vacuum pump connected to a feedback loop with vacuum pressure control. This type of system takes a long time to tune and if there is a large variation in vacuum system pressure, the well vacuum pressure can suffer.
An Equilibar vacuum regulator (EVR) can be used to improve vacuum control in this application. The EVR can be installed upstream of the vacuum pump to maintain a constant vacuum on the gas collection well regardless of the vacuum source or system pressure. See schematic below.
As conditions change in the collection wells, vacuum pressure in the system will change but the EVR adjusts instantaneously to keep the pressure setpoint.
The EVR is a non-relieving vacuum regulator that throttles flow between the vacuum supply pump and the well system to precisely control the system vacuum at a specific setpoint. It is a dome-loaded, pilot operated regulator, so the setpoint is determined by a vacuum pilot regulator on the dome of the EVR. The EVR will maintain vacuum level on a 1:1 ratio with the vacuum setting of the vacuum pilot regulator.
Learn more about how the EVR works.