Why We Need Renewable Natural Gas

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Joseph Sullivan, Concord Engineering’s vice president of energy policy and development, explores the importance of renewable natural gas in today’s energy markets, as well as potential sources and recent RNG legislation and regulation moves. 

renewable natural gas

Joe Sullivan, vice president energy policy and development, Concord Engineering

The organized environmental community has abandoned their previous position that natural gas is better than imported oil as it emits vastly less carbon dioxide (CO2) than gasoline in automobiles and light trucks and vastly less CO2 than coal or oil in electric power generation. This seems eerily like George Orwell’s dystopian fictional “new speak” where facts, enemies and everything else can be abruptly changed. The new villain is any fossil fuel, and the new target for opposition is natural gas pipelines. I often wonder how may of the strident anti’s refuse to drive in cars, do not travel by rail, forego airplanes, do not heat or air-condition their homes and don’t use electric lights or computers.

The United States mostly due to the shift from coal to natural gas leads the world in carbon reduction. The newest combined cycle natural gas power plants are 64% efficient, whereas the old boiler steam turbine plants rarely got above 32% efficient.  Natural gas also on a BTU basis has vastly less carbon. We have not come near exhausting this path to carbon reduction. Despite the noise around this issue economics, not politics, has enabled this trend. Natural gas combined cycle power plants have service life of around 30 years, so if they represent a viable part of the energy system over that time frame we should understand and optimize this. Unfortunately, there is a conundrum or inconvenient truth which is that there is a limit that this technology can reach, and it still uses a finite extracted resource, natural gas.

We need to understand that natural gas is not a boogey man — it is a naturally occurring organic chemical. Natural gas no matter what its source is simply methane; good old CH4. Theoretically, the ideal component for thermal fuel is hydrogen the major constituent of methane. Hydrogen plus oxygen equals water; how elegant. It is worth pointing out though that there are issues associated with using pure hydrogen as a fuel, the most common is hydrogen embrittlement of steel. It is straight forward chemistry to reform CH4 to make H2 and not that difficult to do the opposite and produce a synthetic methane from hydrogen. Methane sources are not limited to fracking and extraction. There are multiple ways we can manufacture methane which does not involve extraction. For example, in Denmark as of 2019, more than 10% of the gas in the Danish gas grid is green throughout the year. In the summertime the decarbonized share is 25%. The major source for this is anaerobic digesters. An assessment from Aarhus University and Green Gas Denmark has estimated that 100% of the expected gas consumption could be green by 2035.

In the United States a common source of methane is from landfills. Waste decomposes producing methane, and in a capped landfill that methane is captured and either used onsite, typically for electric generation, or cleaned up to pipeline standards and injected into the natural gas pipeline system. There are several flaws in this pathway. First it involves large land resources which makes these sites unusable for potentially generations. Secondly the landfills, even if lined, often pollute groundwater. And thirdly only a portion of the biodegradable waste converts to methane and of that only a portion is captured for beneficial use. In California initially landfill natural gas (LFG) was recognized as a renewable fuel and delivery of RNG comingled in the natural gas pipelines was recognized. More recently California RNG incentives have been restricted to exclude LFG. In New Jersey if you use LFG for electric generation on-site it is considered a Class 1 Renewable Energy source. If you gasified the same municipal solid waste, it would be considered a low value Class 2 Renewable Energy source.  There is no provision for pipeline delivery of any RNG in New Jersey or adjacent states.

Another source for RNG is food waste. In the United States, food waste is estimated at between 30-40% of the food supply. This is based on estimates from USDA’s Economic Research Service which includes 31% food loss at the retail and consumer levels that corresponds to approximately 133 billion pounds and $161 billion worth of food in 2010. This amount of waste has far-reaching impacts on society. Food accounts for 21% of the solid waste in American landfills alone.

As we look at the development of a robust electric grid and expansion of renewable energy resources renewable natural gas  can play a significant role.

A recent piece of legislation was passed by both houses of the New Jersey Legislature which will mandate food waste separation and recycling.  This is Senate Bill No. S865 and its companion bill in the Assembly No. A2371. Ironically one of the concerns was the exclusion from landfills of methane producing food waste. A large percentage of food waste will decompose before the landfill is capped and the methane collection system becomes active. The pending Food Waste recycling bill in NJ will require large food waste generators to separate and recycle food waste and amends definition of “Class I renewable energy.” Senate bill No. 865 will require large food waste generator that are located within 25 road miles of an authorized food waste recycling facility to:

  1. source separate its food waste from other solid waste; and
  2. send the source separated food waste to an authorized food waste recycling facility that has available capacity and will accept 15 it.

The bill currently is before the governor, and there is hope that it will become law.

Even before this legislation there are two very interesting projects that have been developed to convert food waste to energy in N.J.

Trenton Biogas is an anaerobic biodigester facility located in Trenton, N.J. with the capacity to divert 110,000 tons of organic material from being sent to landfills each year while generating 27,000 MWh of renewable energy and 23,000 tons of premium fertilizer for local farms. Unlike the residuals from public Sewer Wastewater Treatment Facilities which cannot completely control their input a dedicated Food Waste Anaerobic Digester can assures a higher value residual.

A similar project has been undertaken as a partnership between Waste Management and Rahway Valley Sewerage Authority (RVSA). This project separates the collection and preparation of the food waste from the anaerobic digestion and power production. The collection and processing of the food waste stream is done by Waste Management at their CORe Organics Recycling Facility in Elizabeth, which opened in March of 2018. The proprietary CORe process transforms industrial food waste, from coffee grounds to green beans, into an engineered bio-slurry. As part of a public-private partnership, the slurry is then transported to the Rahway Valley Sewerage Authority (RVSA) wastewater-treatment facility. There, it is added to their existing waste digester tanks. The bio-slurry provides a natural supplement to the wastewater anaerobic digesters, enhancing the breakdown of solids and dramatically increasing biomethane production. The biomethane is further processed and used onsite for production of electric power. The power generation is a Combined Heat and Power (CHP) system which also supplies heat as needed to the anaerobic digesters.

There is also a potential to produce RNG from electricity when it is produced from renewable resources is not concurrently needed by the electric power supply grid. This currently happens in both Vermont and Texas as well as several other states with significant wind energy resources. There is also a surplus of low-cost electric power during the peak solar output in California. This would enable utilization of the gas grid for electricity storage (whereby electricity is converted to hydrogen and the hydrogen is reacted with CO2 to produce methane). This could be a behind-the-meter energy storage option or a grid supply option. We currently have very significant natural gas storage resources on the gas transmission and distribution system.

As we look at the development of a robust electric grid and expansion of renewable energy resources, RNG can play a significant role. It would be foolish to assume that the current solar PV, terrestrial wind and offshore wind are the whole picture. In many cases where there is a need to provide hospitals, healthcare, industrial and commercial buildings and process loads with heat and power, these renewable generation resources alone will not get us there — or will fail to get us there in the most economical and environmentally responsible manner.

Joseph Sullivan is VP of energy policy and development at  Concord Engineering.

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Comments

  1. Herman Gnuechtel says:

    Do you believe that CO2 conversion to gasoline and jet fuel has a future ?????

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