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In the next episode of the Pittsburgh Region Clean Cities' webinar series, Professor and the Director of Penn State's Institutes for Energy and the Environment, Tom Richard, will be discussing the renewable natural gas (RNG) and its potential as an alternative and sustainable fuel.
Over the last four years, the natural gas grid has begun to carry methane from a vast new energy source. Different than every other natural gas source, it occurs at the surface, literally from farm fields, along with residues from the crops grown on those fields in the forms of livestock manure, food waste, landfill gas and sewage sludge. The crops grown in farm fields absorb CO2 from the atmosphere to grow plant biomass (about 50% carbon). These crops, crop residues, and various organic wastes can be decomposed in an anaerobic digester to produce biogas (a mixture of CH4 and CO2) from which the CH4 can be separated and marketed as renewable natural gas (RNG, aka biomethane).
Some farms and wastewater treatment plants have been operating anaerobic digesters for decades, but only recently have been upgrading their biogas to pipeline quality RNG. RNG is a renewable energy resource that is dispatchable (use it when you want it) instead of intermittent like wind and solar. With a month of natural gas storage already built into the US gas grid, RNG can provide low cost energy storage at the scale of weeks, far longer than grid scale batteries whose capacity is measured in minutes and hours. Right now most RNG is used as a transportation fuel that can deliver zero carbon emissions at the tailpipe, but it can also serve as a feedstock for chemicals and materials. And when the biogas is separated to produce RNG there is a pure CO2 "waste stream" that can either be injected into geologic storage reservoirs or upgraded into long-lived chemicals and materials, in either case going beyond zero emissions to negative carbon emissions.