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Renewable Natural Gas Helps Reduce Emissions, Policy Support Needed

Ed Dodge's picture
  • Member since 2013
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  • Dec 8, 2014

Corn Harvest For Generation Of Electricity

Natural gas use is growing throughout the world as new drilling techniques open up vast shale and other tight resources. The result is low-cost gas flooding the market. The environmental advantages of natural gas over other fossil fuels have put it in a favored position as emissions regulations continue to tighten around the world. But conventional natural gas is still a fossil fuel with significant carbon emissions that need to be contained.

So how do we avoid damaging carbon emissions while embracing the engineering and emissions advantages offered by natural gas? By blending renewable natural gas (RNG) into the natural gas supply.

Read additional Breaking Energy coverage of renewable biomethane here.

Natural gas is primarily methane, the simplest of all hydrocarbons (CH4), and methane is renewable. Methane can be produced in substantial quantities from food waste, farms, sewage and landfills. Renewable methane can be blended in unlimited ratios with fossil natural gas and is undetectable to end-users. There are a wide variety of technologies and feedstocks that can be used to produced renewable natural gas at competitive costs.

Recently, the Bioenergy Association of California issued a report titled Decarbonizing the Gas Sector: Why California Needs a Renewable Gas Standard. The BAC argues that the use of RNG will help eliminate millions of tons of greenhouse gas emissions and provide the lowest carbon-emitting transportation fuels among other benefits.

A Renewable Gas Standard (RGS) would be modeled on California’s successful Renewable Portfolio Standard that has contributed to a doubling a renewable electricity in a decade. BAC proposes a very modest proportion of 1% RNG blended into the fossil natural gas supply in 2020 and increasing up to 10% by 2030.

The RGS should apply to all retail sellers of natural gas, beginning with sales that fall under the jurisdiction of the California Public Utilities Commission, which covers 82% of the state’s gas sales and expanding ultimately to all utilities and gas providers.

Price impacts to rate payers are expected to be negligible under the proposal as presented because the volume requirements are so modest and the phase-in time gradual. Nonetheless it is important that protections are built to insulate rate payers as well as allow utilities to bank and borrow on their compliance measures.

According to figures used by the BAC, organic waste converted into biogas could meet more than 10% of California’s natural gas demand. Total organic waste in CA could be used to produce 284 billion cubic feet (bcf) of renewable natural gas. This RNG is equal to 2.5 billion gge (gasoline gallon equivalents) of transportation fuel, enough to replace ¾ of all the diesel fuel used in the state. Alternatively, the RNG could produce 5,000 – 6,000 MW of flexible electric power generation capacity.

dodge RNG

California, like much of the world, has abundant resources to produce RNG. More than 16 million tons of organic waste are landfilled every year in the state. Additionally, there are over 500 wastewater treatment plants, 278 landfills, 1,600 dairies, and extensive forests. It is estimated that food waste could provide 82 bcf of gas, landfill gas could provide 53 bcf, livestock manure could provide 43.4 bcf, sewage treatment could provide 23 bcf, and forest waste could provide 82.4 bcf every year.

Renewable natural gas can be produced in a variety of ways. The most common is through the process of anaerobic digestion (AD) where microbes in an oxygen-starved container decompose organic materials. AD is commonly deployed at wastewater treatment plants to break down sewage and on farms to help dispose of animal manure.

Landfills produce methane naturally through the decomposition of organic materials and in many areas this methane effluent is regulated. So the landfill industry has been collecting methane in many landfills for years and this is the leading commercial source for renewable natural gas today. The waste disposal industry have been leaders in converting their garbage trucks to run on landfill gas which is typically cleaned up and upgraded to road quality CNG.

In addition to digestion processes, RNG can be produced through gasification of woody biomass and related thermochemical processes. Power-to-Gas offers the ability to convert electric power from renewables and nuclear plants into RNG to help meet energy storage needs. In a related process, CO2 methanation is a technique for recycling captured carbon dioxide back into methane using Power-to-Gas methods.

In addition to providing many jobs and economic opportunities, there are numerous environmental benefits to producing RNG. Aside from reduced carbon emissions resulting from replacing fossil natural gas, use of RNG also reduces fugitive methane emissions by putting the methane to work and also reduces black carbon. RNG production reduces the amount of waste going into landfills and helps reduce wildfires by using by fuel from the forest floor. RNG helps improve energy security and offers flexible and reliable power generation opportunities.

RNG needs policy to support the growth of the industry because currently RNG is more expensive to produce than fossil natural gas. But since RNG offers additional environmental and social benefits not accompanied by fossil natural gas, it should be worthy of public support.

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James Thurer's picture
James Thurer on Dec 9, 2014

Edward, I’m all for this in concept, but two numbers that I rarely see presented with what seem to be great ideas for a low carbon or carbon neutral energy source are unit cost and eroei.  Do you know of any estimates for these?

Bob Meinetz's picture
Bob Meinetz on Dec 9, 2014

Ed, in your last two articles you’ve been claiming methane is “renewable”. Except that in contemporary parlance, and in reference to energy,  “renewable” is defined as

(of a natural resource or source of energy) not depleted when used

Natural methane, the kind that comes from deep underground, is clearly depleted when used, and synthesized methane isn’t a source of energy. So labeling any methane “renewable” is disingenuous greenwashing.

Second, almost a third of BAC’s feedstock comes from “Forestry and Forest Product Residue”.  I would guess “Forestry”, aka pelletizing old-growth timber, would make up in excess of 99% of the mass of the towering CA pines targeted for destruction, with <1% coming from the resulting sawdust and that from CA paper mills. There’s considerable debate whether old-growth timber is renewable in a time frame consistent with addressing the exigencies of global warming.

Third, IPCC admits in its Fifth Assessment Report (AR5) that natural gas can help lower carbon emissions in the short term if it replaces coal, but .5% of CA generation comes from coal.

Finally, AR5 found that in the majority of low-carbon stabilization scenarios fossil fuels without CCS are reduced by two-thirds by 2050 and completely absent by 2100. A very optimistic 10% by 2030 is too little, too late.

Ed Dodge's picture
Ed Dodge on Dec 9, 2014

Bob, I suggest you review a basic chemistry textbook. Methane is produced all day every day by the Earth’s natural biological processes. Methane that is produced biologically today is most certainly a renewable fuel and has been validated repeatedly by leading authorities.

LNG and CNG produced from biogas are considered to be the lowest carbon transportation fuel, more detail can be found in my upcoming article that compares RNG to cellulosic ethanol.

You make a completely disingenous and intellectually dishonest argument when you claim I am suggesting we cut old growth forest to make biogas. No one is suggesting any such activity, though there are very good forest management reasons for clearing out dead trees and limbs to prevent forest fires, and that collected timber is excellent biofuel.

You go on to say that CA only gets .5% of their electricity from coal, but neglect to say that over 50% is from fossil natural gas. It is pretty obvious that substituting RNG for fossil gas will help reduce GHG emissions, especially since most of the RNG is methane that is already being produced naturally and is bound to go into the atmosphere anyway as a more potent GHG. Do you have a better suggestion for managing the methane from landfills, sewage and farms?

The cherry on top is your promotion of methanol in another post today, “carbon-neutral fuels, especially methanol synthesized from hydrogen and captured carbon using nuclear energy, would be capable of powering clean cookstoves in the developing world with no net addition of carbon to the biosphere.” You promote methanol using the same logic I have been using and then turn around and bash methane. Methanol is CH4O and methane is CH4, only one oxygen atom separates them, but methanol is extremely toxic and nasty while methane is completely non-toxic. Do you even understand the science behind the arguments you are making?

My arguments may run afoul of the green political narrative, but they do not run afoul of science.

Ed Dodge's picture
Ed Dodge on Dec 9, 2014

James, I don’t have hard numbers for unit cost or EROI. Generally speaking, RNG is more expensive to produce than fossil gas, but not dramatically so. As for EROI, most of the processes to make RNG involve waste conversion where you are diverting resources from going into a landfill. Actual EROI figures would have to be calculated on a case by case basis, but the real benefit arrives from keeping material out of landfills where it is a long term liability and converting it into an asset. Of all the biofuel options, methane is likely the simplest and easiest to produce.

James Thurer's picture
James Thurer on Dec 9, 2014


Bob Meinetz's picture
Bob Meinetz on Dec 10, 2014

Ed, now you’re grasping at straws. Call “natural” and “nasty” whatever you like, because both are scientifically meaningless terms only useful in marketing. But apparently “renewable” is now a feelgood generic too, because according to your definition, another product of “the Earth’s natural biological processes” – fossil fuels – are renewable. Aren’t they?

In 2003, the methane used to heat our homes, cook our food, and power our city buses  was .6% biogas. If that percentage has not changed significantly, what’s the justification for assigning the other 99.4% a “renewable” label? At least in the dictionary definition of the word that part is anything but, and is responsible for 25% of all fossil fuel GHG emissions in the U.S.

That LNG and CNG produced from biogas are cleaner than natural gas is great, but there’s not enough of them – and never will be – to make a dent in consumption. Unlike carbon-neutral nuclear synfuels, with which we could potentially replace all fossil fuels. That’s the difference.

The principal purpose of RNGs is to greenwash the continued extraction of fossil fuels indefinitely.

Ed Dodge's picture
Ed Dodge on Dec 10, 2014

Bob, what is the difference between nuclear synfuels and nuclear produced methane which I made the case for in my power to gas article? The difference is that methane is more efficient to produce and non toxic and has an existing infrastructure. Not that I have anything against synfuels.

You are clearly misrepresenting my work to say that I am giving all of natural gas a renewable label. There is clearly a distinction between fossil natural gas and renewable natural gas. I have never suggested otherwise.

It is simply ironic that methane happens to be the most renewable of all renewable fuels. Funny what you discover when you follow the science. 

Bob Meinetz's picture
Bob Meinetz on Dec 10, 2014

Ed, using non-nuclear means at best we can “renew” a tiny percentage of the methane we use, so categorically calling it “the most renewable of all renewable fuels” is just silly. We’d be equally justified in claiming uranium is renewable because we can transmute lead into it with a cyclotron, atom by atom.

I’m done arguing this point, but curious: you say this definition of renewable has been “validated repeatedly by leading authorities”. Who are they?

Ed Dodge's picture
Ed Dodge on Dec 10, 2014

Bob, we can synthesize methane more readily than we can synthesize methanol or any other synfuel. Methane is easy to produce. investigate the chemistry for yourself. 

As far as leading authorities go, EPA for one.  My computer is crashed right now and I am writing this on my phone so I don’t have access to my data but my new article presents some of it. I will be writing a lot on this subject going forward so there will be plenty of opportunity to debate. 

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