Reducing Greenhouse Gas Emissions through Landfill Gas Conversion

Renewable natural gas is indistinguishable from natural gas

The market for RNG is similar to that of conventionally sourced natural gas. The final product is considered pipeline-quality and, true to its name, the RNG is transported via existing natural gas pipelines. Traditional natural gas and RNG are indistinguishable from one another. To generate RNG, clients are able to collect LFG. This offsets greenhouse gas emissions, provides a clean energy source, and replaces some of the demand for conventionally sourced natural gas.

Converting landfill gas to renewable natural gas

EDL Energy’s Indy High BTU plant in Indianapolis, Indiana, receives LFG from a nearby landfill and converts it to RNG. LFG is a by-product of material breakdown and decomposition of organic waste. As the waste degrades, it releases carbon dioxide, methane, and other gases. These emissions are captured within the landfill before they are released into the atmosphere using a gas collection and control system (GCCS). The GCCS, upgraded as part of the RNG plant project, consists of a series of drill holes and pipelines installed within the landfill, compressors, and gas filtration and drying equipment to collect and pre-process the LFG. The LFG is then treated by the RNG plant to purify the gas stream into pipeline-quality methane (RNG).

Environmental impacts of the plant upgrade

Implementation of the GCCS upgrades and RNG plant project avoids methane emissions and maintains compliance with environmental regulations requiring the collection and control of LFG. If not captured, the LFG, which consists of about 50 percent methane, would be released into the atmosphere. According to the U.S. Environmental Protection Agency (EPA), methane is 28 times stronger than CO₂ as a greenhouse gas. The project also provides an alternative to conventionally sourced natural gas, which in turn offsets carbon emissions. It also reduces landfill odor associated with the conventional flaring of LFG.

Tetra Tech’s services and project contributions

Tetra Tech provided project management and process, mechanical, and structural engineering services to evaluate the condition and sizing of existing equipment and specify new equipment for the GCCS upgrades. The upgrade included piping modifications, a new compressed air system, valves, vane separators, a three-phase separator, pressure safety valves, coalescing filters, and a waste heat recovery system. Tetra Tech also designed and fabricated a custom-engineered refrigerated gas drying system, including a heat exchanger skid, glycol system, and packaged air-cooled chiller. The use of state-of-the-art engineering tools and process industry design standards resulted in increased reliability and uptime of the GCCS, consistent suction applied to the landfill wellfield, and consistent delivery of dry (34°F dew point) conditioned LFG to the RNG plant.

Tetra Tech provided owner’s engineering services during the design, construction, and commissioning of the RNG plant, keeping the owner informed of the details included in the project design, the progress of construction, and potential issues needing resolution with the contractors. As a result, communication between the owner and contractors was more streamlined, and the end product was more aligned with the owner’s expectations. The owner provided the following positive feedback to Tetra Tech: