A recent case study demonstrated that measuring and monitoring landfill gas using thermal mass flow meters solves many of the issues commonly associated with the use of traditional flow measurement devices, resulting in more accurate measurement and field labor savings.

Municipal solid waste landfills are one of the largest human-generated methane emission sources In the U.S. At the same time, methane emission that’s not collected represents a significant loss of energy, never mind the negative impact to our carbon emissions. Did you know that a typical municipal landfill has the resources to generate enough landfill gas (LFG), a renewable energy, to power as many as 4000 homes for twenty years?

According to the EPA, “As of July 2011, there are 558 operational LFG energy projects in the United States and approximately 510 landfills that are good candidates for projects.” If my math is correct, if all these candidates adopted LFG projects, over 4 million homes would have power for twenty years . . . that’s putting waste to work, while simultaneously improving carbon emissions.

When municipal solid waste is broken down through biological agents, landfill gas is produced. This blend of methane and carbon dioxide can be harnessed and used as a source of renewable energy. In fact, landfill gas is currently being used to heat buildings, kilns and boilers, fuel generators to make electricity, and produce liquefied natural gas (LNG) to fuel vehicles.

Harnessing landfill gas requires the gas to be collected under vacuum. Shallow wells are drilled into landfill and connected to a header system and using a blower, the gas is collected in a central point. At various points, from wells to the collection area, gas flow measurements are needed; however, traditional flow measurement equipment doesn’t work properly in a landfill environment and the measurements are often off by 10-20%.

Within the wells, measurements are needed to assure that liquid has not accumulated which would reduce gas collection. Because landfill gas can be warm, fully saturated, and humid, there are performance issues using pilot tube flow meters because the pilot tube openings can clog. Saturated LFG can also accumulate on orifice plates then freeze, making it difficult to obtain accurate measurements with an orifice flow meter. Additionally, because of flow changes, extensive field labor is required to assure the orifice plates are changed to correspond with the change in gas flow. The weakness of the venturi flow meter in this application is the device can restrict gas flow at higher pressure rates.

Recently, Sage Metering teamed with QED Environmental Systems, a leading supplier of LFG pumping and flow control products to address some of the issues of measuring LFG. In the case study, the Sage Prism, a portable thermal mass flow meter with datalogging capability was evaluated measuring landfill gas. The gas mass meter effectively overcame the issues linked to traditional flow measurement equipment. The Prism is accurate as it provides direct mass flow, not a calculated value which has been corrected for temperature and humidity. A technician inserts the probe of the meter into an access port of the pipe. After simply selecting pipe size and gas mixture calibration channel, a flow rate is displayed and recorded in the instrument’s memory. The probe can then be removed easily and has limited exposure to the corrosive, humid environment typical of landfill gas. The data can later be exported into an Excel spreadsheet.

As more and more landfills move into LFG energy projects, I’m sure we’ll be hearing more about the use of the Sage Prism portable thermal mass flowmeter to monitor landfill gas, since it’s more accurate, saves time and money in the field and is the one thermal mass meter with an on-site (in-situ) calibration check.

Sources:
http://epa.gov/lmop/
http://www.sagemetering.com/pdf/QEDCaseStudy.pdf