Volume 25, number 1, June 2011

Renewable natural gas: Another reason to build “blue”!

Among the many renewable energies that are emerging in response to the climate change challenge and the depletion of conventional energy sources, reclaimed biogas is at the
top of the list.

Glossary
Biogas Raw gas composed essentially of methane (CH4) and carbon dioxide (CO2) produced by the anaerobic fermentation (oxygen starvation) of organic matter.
Residual materials

Any obsolete material or object discarded by households, industries, businesses and institutions (synonym: waste).

Organic matter

Matter from living organisms that contain large quantities of carbon (e.g. domestic waste, agricultural and agri-food wastes).

Biomethanation (or methanization or anaerobic digestion)

Biological process involving the decomposition of oxygen-starved organic matter, which produces biogas.

Biomethane

Biogas processed and scrubbed. It has characteristics similar to natural gas (composition and calorific value).

Gasification Thermochemical reaction at high temperatures (about 7050C) that converts biomass into a synthetic gas: carbon monoxide (CO) and hydrogen (H2).
Methanation Catalytic conversion of synthetic gas into methane (CH4).

Biogas and biomethane

Energy reclamation from organic matter is a process whereby energy is recovered in the form of methane. The methane can be injected into the gas distribution system, helping to heat buildings or supply vehicle fleets that run on natural gas.

Another source of methane that has even greater potential is on the horizon: the conversion of wood residues by gasification and methanation.

The gas industry and biomethane

The similarities between biomethane and natural gas have led the gas industry to invest in projects to develop this promising alternative. The natural gas system offers the following advantages:

  • Biogas production is rarely close to the end consumer.
  • The natural gas distribution system serves as a reservoir, so supplies can be managed and the biomethane used to advantage, resulting in higher revenues for the producer.
  • No modification of combustion equipment that operates on natural gas is needed for it to burn biomethane.


Evolution of biomethane injection in Europe

Technological development, government policies, and the involvement of gas companies have led to a remarkable growth in the biomethane industry in the last decade. The six steps in the production and distribution of biomethane are illustrated in Figure 1.

Figure 1 – Steps in the production and distribution of biomethane

Technological development

As well as methane, unrefined biogas contains other substances that are removed during the scrubbing and refining processes. A typical composition of biogas that may be refined is presented in the following table:

Typical composition
Methane (CH4)

50-75%

Carbon dioxide(CO2)

25-50%

Nitrogen (N2)

0-10%

Water (H2O)

0-5%

Oxygen (O2)

0-2%

Hydrogen sulphide (H2S)

0-0.1%

Other (PAH, siloxanes, dust, etc.)

< 0.1%

A quite concentrated methane product can currently be obtained after the impurities have been removed. Its typical composition is shown in the following table:

Typical composition
Methane (CH4)

>96%

Carbon dioxide(CO2)

<2%

Nitrogen (N2)

<3%

Water (H2O)

Dew point below –10°C

Hydrogen sulphide (H2S)

<5 ppm

All other contaminants reduced to a trace or are not detectable

In order to choose the most appropriate refining technology (PSA adsorption, washing, membranes or cryogenics, energy consumption, rate of methane recovery and ease of operation first need to be considered.

Potential and prospects

Québec’s energy context is characterized by the following factors:

  • The desire for independence from petroleum;
  • The desire to introduce a renewable content into fuels;
  • The desire to reduce GHG emissions in the transportation sector;
  • The desire to diversify the forestry industry.

Renewable natural gas (i.e. gas produced by methanation or methanization) appears to be an appropriate alternative to meet the challenge.

There is potentially about 1 billion m3 of biomethane to be recovered annually in Québec: five times more if the methanation alternative progresses as expected.

Several Québec municipalities, in collaboration with Gaz Métro, now have projects. One tonne of residual waste can generate 50 m3 of methane. For example, a medium-sized municipality can produce up to 5 million m3, a level well above the break-even point, given the range of technologies available today.

It is also evident that the standards and codes that currently apply to natural gas must also apply to renewable natural gas: CSA B149.1 (combustion), CSA Z662 (integrity of pipelines), as well as CSA B149.6 (to come) for methanation facilities.

Key factors

  • Learn from the lessons of the past and the progress made: these are no longer the techniques of 30 years ago.
  • This a renewable energy whose production (and often consumption) is local. It therefore offers several opportunities for development that can benefit the community.
  • Quality control needs to be introduced along the entire supply chain.
  • Potential for diversified reclamation and thus demand from several sectors, including the transportation sector.
  • Potential for development in regulations and standards.

Abdelhaq El Ouardi, Eng.
DATECH Group