Vermont Gas Systems leads the way
H. Clattenberg
A November 14th press release from Vermont Gas Systems (VGS) trumpeted a bold new initiative: “VGS Targets Elimination of Greenhouse Gas Emis-sions by 2050.”¹ It sounds revolutionary and wonderful. The poser, though, is how can VGS eliminate greenhouse gas emissions from its product, which is essentially pure methane (CH4)? Methane in itself is a greenhouse gas, and when burned, carbon dioxide (CO2) – another greenhouse gas – is produced. According to the laws of chemistry, CH4 + 2(O2) = CO2 + 2(H2O).² No artful business plan can alter the equation. Production, storage, shipment and burning of methane emits greenhouse gasses, whether through “fugitive” methane that escapes into the atmo-sphere prior to combustion, or through the generation of carbon dioxide at the gas jet. So how exactly is VGS going to eliminate greenhouse gas emis-sions? (This appears to be the premise, although the word “targets“ in the press release headline suggests a measure of non-commitment). The answer features a novel trademarked commodity called “RENEWABLE NATURAL GAS.”³
What is Renewable Natural Gas? Renewable Natural Gas (RNG) is captured from waste in landfills, waste-water treatment plants, farms, food processing by-products and the like. The source material (“feedstock”) is col-lected into the tank of an anaerobic bio-digester, where it gets broken down by methods that favor the production of methane. The bio-digester yields “biogas,” a mixture containing roughly 2/3 meth-ane and 1/3 carbon dioxide and traces of gaseous sulfur and nitrogen compounds. The fermentation within a biodigester will also produce a low-odor solid or semi-sol-id residue that can be used as animal bed-ding or fiberboard or fertilizer, depending on the design of the installation. It is important to understand that the biogas generated directly from fermentation of bio-waste is not considered “Renewable Natural Gas,” until and unless it has been enriched to consist of nearly pure (90%) methane. This isn’t a necessary extra step, small farm biodigester set-ups in develop-ing countries, for example, use the mixed biogas, as is, to produce heat and electricity. The souped-up product, “Renewable Natural Gas” simply contains more methane. The methane in RNG is still methane, chemically indistinguishable from the methane that was in the original biogas, and chemically indistinguishable from the methane in fossil-derived natural gas. The difference between RNG and biogas is that Renewable Natural Gas meets purity standards that allow it to be offered for sale to natural gas markets worldwide.
Let’s count the beans: To appreciate the hollow promise Re-newable Natural Gas offers for mitigating the climate crisis, it is useful to consider the environmental consequences of us-ing biogas without the extra purification needed to produce RNG. Responsibly-generated, locally consumed biogas can have benefits as a fuel source, as for example, in situations where farm waste would otherwise be allowed to decom-pose in a heap and contaminate air and water. However, even when farm waste is used to generate biogas without further processing, greenhouse gas reduction is not a guaranteed result. What puts biogas in the plus column relative to regular natural gas is the fact that methane gas generated from waste contains carbon molecules that are already at large in the biosphere, cycling between the soil, trees, atmosphere, crops, chicken poop, etc. Fossil-derived natural gas, in contrast, is mined from carbon that was put into deep storage around the Mesozoic era. When fossil carbon sources burn, essen-tially new atmospheric greenhouse gas is introduced. A close and comprehensive calculation is required to establish that the use of biogas will successfully curtail atmospheric greenhouse gasses, because the combustion of the already-circulating carbon in biogas as opposed to previ-ously-unavailable carbon in fossil fuels is the only gain that can be realized in the substitution. And, while the environmen-tal costs of storage, shipping and burning methane have not changed, there are fur-ther considerations as well. An anaerobic biodigester must be tight so that it does not leak gas, and never over-charged with bio waste, or methane will have to be vented to relieve excess pressure. To minimize the fuel consumed in the course of generating biogas, feedstock for the biodigester must be from a nearby source and likewise the product biogas should be transported only a short distance to the end-user. Other inputs to the calcu-lation can further erode environmental advantages. If feedstock is sourced from dedicated crops instead of from true waste, or if the biodegradable waste was diverted from a preferable fate as compost (which tends to sequester carbon in the soil, rather than releasing it into the atmosphere) the scale again tips the wrong way.
Perhaps the most effective way to un-dermine potential gains from the use of biogas is go the next step and process biogas into Renewable Natural Gas. This is because industrial methods for sepa-rating and purifying RNG from biogas all consume energy. More energy still is required to compress RNG and trans-port it to distant markets. This quickly becomes a zero-sum game: the energy in biogas is useable, but the gratuitous energy input required to bump biogas to a higher grade of fuel eradicates the already marginal payback and serves only to make money. Perhaps the most insidious impact of Renewable Natural Gas is that it provides a spe-cious justification for yet more pipeline infrastructure (as VGS readily mentions in its current report to the Public Utility Commission⁴). VGS urges us to believe that Renewable Natural Gas can help lower greenhouse gas emissions. Not true. Whereas there is some possibility that an anaerobic biodigester coupled with equipment that burns the biogas directly to co-generate heat and elec-tricity for a farm and some neighbors might not make matters worse, Renewable Natural Gas merely paves the way for “building out” an obsolete infrastructure that will keep us burning fossil fuels for decades to come.
Magical, Mythical Attributes? VGS aims, by 2030, to provide 20% of the gas consumed by its customers as RNG. As of mid 2019, VGS had enrolled all of 54 custom-ers in its RNG plan. These residential and commercial customers volun-tarily pay a premium for Renewable Natural Gas. The customers do not actually receive Renewable Natural Gas from VGS, what the company provides is “attributes.” The physical Renewable Natural Gas associated with the attributes is introduced into the pipeline at the Canadian border. Sourced from Quebec and Idaho (yup, Idaho, via Canada) the gas goes out equally to all VGS consumers. And how much RNG is coursing through VGS pipelines at present? According to VGS’ latest report to the Public Utilities Commission of Vermont, Renew-able Natural Gas constitutes one twentieth of 1%.⁴ of the total gas supplied to its customers. The idea that there is such a program on the road to reducing greenhouse gas emissions is questionable. Where will VGS get RNG for a 400-fold increase in ten years? Should Vermonters anticipate a future of permanent dependence on foreign cow patties? Some final food for thought: Vermont’s only gas company is 100% owned by private Canadian corporations. Among these, Enbridge, with its notorious environmental track record, has heaped 40% of the VGS pie on its own plate. Is this a reasonable state of affairs as we navigate a climate crisis?
Footnotes:
1. VGS Press release; https://www.vermontgas.com/vgs-targets-elimination-of-greenhouse-gas-emissions-by-2050/
2. https://www.middleschoolchemistry.com/multimedia/chapter6/lesson1
3. VGS Renewable Natural Gas Program Manual August 2019 update Version 1.02 http://www.vermontgas.com/wp-content/uploads/2018/09/VGS-RNG-Manual-Final-V-1.01.pdf
4. Vermont Gas Systems Supply Overview June 28, 2019 (obtained from the Public Utilities Commission)
General references:
Florio, C., Fiorentino, G., Corcelli, F., Ulgiati, S., Dumontet, S., Güsewell, J., and Eltrop, L. (2019). A Life Cycle Assessment of Biomethane Production from Waste Feedstock Through Different Upgrading Technologies. Energies12, 718.
Rotz, C.A. (2017). Modeling greenhouse gas emissions from dairy farms. Journal of Dairy Science 101.
Vu, V., Vu, Q., Jensen, L., Sommer, S.G., and Bruun, S. (2015). Life Cycle Assessment of Biogas Production in Small-scale Household Digesters in Vietnam. Asian-Australasian Journal of Animal Sciences 28.
This article was submitted to Green Energy Times as an op-ed.
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