Renewable Natural Gas (RNG) or biomethane

By | 2016-10-14

Worldwide climate change driven policies are forcing the displacement of fossil fuels with renewable alternatives. Since biogas is generated from renewable biomass, the methane it contains is carbon neutral and renewable, which confers it the term biomethane, or renewable natural gas.  Therefore, biomethane is the solution to reducing carbon emissions originating from conventional natural gas combustion.

By cleaning biogas from its water vapor, carbon dioxide, and impurities we obtain a gas with over 97% of methane which makes it completely interchangeable with conventional natural gas.

Thus, this gas is called either upgraded biogas, renewable natural gas (or RNG), or biomethane (Europe). It is interchangeable because it presents the same properties as natural gas and it can be transported, distributed and consumed within the existing natural gas grids and equipment without any modification.

Biogas upgrading technologies for biomethane

There exist several technologies that allow for cleaning or upgrading the biogas into a renewable natural gas of quality suitable for injection into the gas grid.

These technologies are:

  • Water wash
  • Membranes
  • Adsorption or PSA (pressure swing adsorption)
  • Absorption or Organic solvent dilution
  • Others

These technologies allow for removal of carbon dioxide (CO2) and other impurities (H2O, N2, H2S,  Siloxane, etc.) so that that the biomethane becomes interchangeable with conventional natural gas and can be injected safely into gas pipelines.

Typically these technologies will capture approximately over 90% of the methane in the biogas (loss of 10% of less) and will bring biomethane or renewable natural gas to a quality of over 97% methane (CH4).

If the biogas contains air (N2 and O2), such as biogas generated from landfills or garage style dry digesters, certain technologies will not be able to remove these inert gas components. Typically, N2 and O2 are removed with PSA technologies. A combination of technologies may be used to achieve the gas quality required for grid injection.

Partial biogas upgrading

There exist applications where biogas does not need to be upgraded all the way to natural gas quality. It can be upgraded to a lower grade “natural gas” to save on upgrading cost.

For example, biogas can be quite easily upgraded to 85% methane (remaining 15% CO2, no water vapor) and be used directly in compressed natural gas vehicles (CNG).  The vehicle will need to be calibrated for this fuel mix and will get less autonomy (DGEs, or combustible fuel in the tank) but it may be suitable for certain applications requiring inexpensive fuel.

The same approach can be used for biogas pipelines, combined heat & power (CHP) and/or boiler applications.

Renewable Natural Gas Markets

Once the biogas has been upgraded to RNG, it can be used in the same applications as conventional natural gas.

RNG can be generated and consumed without any connection to the natural gas grid. However, connecting the RNG production facility to the natural gas grid opens up to a very wide market of potential RNG users.

European and North American gas grids are all interconnected, and thus allow the travel of this source of combustible energy from about any point to any point on the continent.

Connecting to the grid and moving the RNG from one location to the other come with grid related fees such as injection fees, transportation fees, distributions fees, balancing fees, brokering fees, etc. Nevertheless, the opportunity to move the RNG anywhere it may be needed enables fantastic opportunities to RNG producers.

In markets where there is a renewable portfolio standard (RPS), a carbon tax, or a cap & trade system for the reduction of greenhouse gas (GHG) emissions, there is a significant demand for RNG to achieve goals of emission reduction.

Moreover, recently the US EPA Renewable Fuel Standard (RFS) regulation recognized that burning RNG in transportation applications will generate Renewable Identification Numbers (RINs). RINs are credits used by conventional fuel distributors to not comply with the RFS mandatory blend of ethanol and biodiesel. RINs are a valuable commodity.

For example, today a landfill in Montreal, Canada is selling its RNG to a Californian CNG station operator for three (3) times the price of natural gas in Montreal.

All the environmental policies and regulations are pushing for an ever-expending demand for RNG and, by association, a constantly growing demand for biogas obtained through anaerobic digestion.