Can Renewable Natural Gas Save the Gas Industry from an Existential Threat?

Dec 20, 2018
Power-to-gas (P2G) and other renewable natural gas (RNG) sources are emerging viable alternatives to fossil natural gas that, unlike hydrogen, would utilize the appreciable existing infrastructure.
As society transitions to renewable energy, natural gas is a bridge to get us there.  Natural gas is a fossil fuel with a lower carbon footprint.  That is, when it burns, its carbon dioxide emissions are lower than gasoline's, and much lower than coal’s.  But along the value chain, before natural gas gets to our stoves and our power plants, as it passes from the ground through processing, compressors, and pipelines, natural gas leaks methane into the atmosphere.  Methane is a far more potent greenhouse gas than carbon dioxide is.  Some environmental advocates, notably in California and New York, argue to dispense with natural gas altogether.  Replace it with hydrogen, they say. 
Hydrogen is a non-greenhouse gas that can technically substitute for other fuels.  But that substitution would entail building a new infrastructure at a cost of trillions of dollars.  A better bet is to use renewable power to produce hydrogen and then react that hydrogen with concentrated CO2 from the stacks of plants whose owners are anxious to abate their carbon emissions anyway.  The result is renewable natural gas (RNG) that can be injected right into existing pipelines to substitute directly for fossil gas.  Or RNG can be used to power engines or fuel cells.  And it gets rid of carbon without the need to spend precious resources on expensive capture and storage systems.
An earlier Nexant blogpost, Fugitive Methane and Fracking – Unintended Consequences, discusses fugitive anthropogenic methane and remediation options along the natural gas supply chain.  Other ways to avoid greenhouse gas emissions are detailed in Bury or Use Captured Carbon, or Just Avoid It?   Carbon capture and storage technology is getting a lot of attention, as a way to remove CO2 from dilute sources from the air.  We say start with plants that produce concentrated carbon dioxide and then send it up their smokestacks.  Think fermentation and steam methane reforming, for instance, or ammonia synthesis and hydrogen production.  There is financial incentive for these businesses to convert carbon dioxide to high value chemicals and fuels.  

Further Considerations

There is a growing need in the United States, Europe, and emerging countries for optimal capacity utilization of existing natural gas transportation and distribution infrastructure serving the wholesale and retail end-customer base.  This includes integration of liquefied natural gas (LNG) supplies, which are being traded globally to meet demand of regions with limited indigenous supplies.  Meanwhile, there are many proponents advocating a “hydrogen economy” by displacing or even adapting the existing natural gas infrastructure (e.g., with hydrogen as an energy carrier).  Such initiatives would incur potential investments estimated in trillions of dollars.  Also, the actual implementation will most likely take decades, and may entail several inherent technical and commercial risks which need to be assessed, qualified, and quantified along with a viable mitigation strategy.  As a primary energy source, natural gas can be best utilized in the existing infrastructure much more conveniently, economically, and more in the near-term than hydrogen for stationary end-use applications.  The end-uses include heat engines such as gas turbines, low speed internal combustion engines (ICEs), and commercial grid-scale fuel cell systems such as solid oxide or molten carbonate fuel cells (SOFCs or MCFCs, respectively).  
Additionally, many stakeholders in both developed and emerging countries are concerned over the viable integration of intermittent and non-dispatchable renewable energy sources (e.g., solar photovoltaics and wind energy) into the overall energy system.  Accordingly, major legislation is being enacted and substantial investments are being made in the research, design and development (RD&D), demonstration, and commercialization of a wide array of energy storage technologies.

Leveraging Viable Alternative Options

In some jurisdictions, there is pressure to block expansion of gas supply, or even eliminate it, creating an existential threat to the gas industry.  Power-to-gas (P2G) and renewable natural gas (RNG) are viable alternative options that can provide stakeholders with definitive leverage in effectively utilizing the existing natural gas infrastructure.  Currently, there is considerable focus and activity among stakeholders (e.g., local distribution companies [LDCs] of natural gas) related to P2G, RNG, biogas, CO2, and hydrogen.  Beyond just a concept, P2G is already commercially utilizing renewable power sources to produce hydrogen for synthesizing renewable natural gas (RNG).  The RNG can either supplement existing pipeline natural gas supplies, or be utilized for gas-fueled engine of fuel cell power generation.  The synthesis process consists of the renewable hydrogen produced reacting with captured CO2.  Depending on the P2G pathway, it in clearly preferable to utilize stack CO2 that is already concentrated, rather than capturing and separating it from various dilute streams, such as combustion stacks, or even worse, from the atmosphere.
Another viable primary energy source is biogas, which can be derived from anaerobic digestion (AD) or landfill gas (LFG).  AD is basically a process that ferments food scraps, manure, and other waste biomass to generate biogas.  Typically, biogas is a combination of various mixtures (i.e., 50:50 of methane and CO2).  Biogas can be treated to remove typical minor contaminants, and the methane and CO2 can be separated, or can be processed together in so-called “dry-reforming” process.  LFG is practically the same as biogas, except it may potentially be more contaminated.  Available commercial treatment and cleaning systems are typically modular.  Nexant’s report, Biorenewable Insights: Biogas and LFG, provides technical details and economics for these supply sources and their effective utilization.  Another report, Biorenewable Insights: Electrochemicals and Electrofuels, provides technical and economic details of technologies that use renewable electricity to convert CO2 into fuels, including methane. 

Recent Developments

One of the leading commercial systems that have emerged is from Germany, where there are over 8,000 AD systems, mainly converting agricultural wastes such as manure, but also food wastes, to biogas.  ETOGAS, in cooperation with Audi, developed a system to utilize biogas by cleaning, and separating the bio-methane (RNG) from CO2 on a 24/7 basis and injecting the RNG into the natural gas pipeline grid.  Normally, the biomass-generated CO2 is vented, but with a near-zero net atmospheric carbon impact.  As and when excess renewable electricity is available from the grid (e.g., wind energy), it can be utilized to produce renewable hydrogen via electrolysis.  The hydrogen is reacted with the captured CO2 to generate additional RNG for supply into the pipeline.  This RNG can be considered to have a negative carbon footprint because it captures and utilizes otherwise vented low-carbon CO2.  The base-load and additional volumes of RNG supplied into the pipeline are accounted for by Audi, which makes its RNG available at no cost for refueling at natural gas vehicle (NGV) stations to customers who buy a certain NGV bi-fuel model car.  The RNG technology, as shown in this image, was acquired by Hitachi Zosen INOVA, is a fully commercialized turnkey modular plant system, which is licensed to project sponsors. 


Similar to the German example cited, a Danish company is deploying RNG to fuel 10,000 similar automobiles in Denmark.
Nexant has extensive experience with planning and conducting feasibility studies for NGVs (CNG, LNG, and LCNG) systems, globally.  In 2003 and 2004 with United States Trade Development Agency (USTDA) sponsorship, Nexant supported and assisted a Thai energy company to convert all taxis and buses, and many trucks in Bangkok to CNG fuel.  Other similar work was carried out in Chile and Egypt.  There are many other project sponsors at various stages of commercialization, with different economic feasibilities, technical risks and other competitive aspects.

Meetings Stakeholders' Needs

Nexant provides assessments of specific technologies, including process descriptions, operating experience, economics, and development status of specific projects or process routes to potential investors, adaptors, licensors, or partners.
Nexant has developed a diverse range of specialized offerings and value-added resources with regards to the various technical and economic issues that are important for supporting and assisting stakeholders.  The scope broadly covers identifying and analyzing the overall P2G and RNG process options.  Nexant can provide insights into key pathways and technology segments for P2G and RNG, including their operating principles, general advantages and disadvantages associated with their operation, and technical readiness.  Accordingly, evaluations and assessments can be organized to reflect the different categories of pathways and technologies and provide a landscape of the value chain and important supply chain segments, which would include primary energy sources, methane production and conversion technologies, production options, and end-use applications:
  • Primary energy sources are fuels, and feedstocks, including conventional hydrocarbons, grid electricity, and renewable energy resources such as solar PV, solar thermal, wind, and bio-based, as well as electricity generated in fuel cells with renewable fuels
  • Methane production and conversion technologies include such as, steam methane reforming (SMR), the most conventional, or partial oxidation (PO), gasification, electrolysis, and other renewable methods such as fermentation and electrofuels bio-methanation, etc.
  • Production options are for centralized production, distributed production, and on-site modular production (including compression, storage, transportation, and distribution)
  • End-use applications are primarily power generation, non-power applications, and transport vehicles (CNG and LNG)
Nexant also undertakes the screening process related to the status of technologies:
  • Preparation of a set of criteria and weightings to screen and rank the pathways and technologies from Nexant’s database.  The criteria and weightings are typically agreed with the stakeholders.  The focus is on specific pathways that have technologies with Technology Readiness Level (TRLs, a ranking index of 1-10) greater than 5 (pilot, demonstration, and deployment) and with increased emphasis on technologies that are most likely to achieve TRL 9 (commercialization).  This utilizes a well-defined process that allows the stakeholders to qualitatively rank the different technologies and determine their attractiveness.  From the screening process, typically, the two or three (maximum) most promising technologies are identified and subsequently considered for detailed analysis
  • Patents are generally a critical aspect of these technology developments, especially if investments, partnering, or licensing are to be involved.  Patent landscape assessments are conducted for selected technology pathways.  Assessments typically consist of a patent search, focused on specific key geographic/regional jurisdictions, and performing a high-level patent review of both patents granted and patent applications
Nexant frequently carries out such engagements for a wide array of stakeholders that are a combination of the above, customized to meet specific needs.