It is in this context that many countries have made global commitments to reduce their greenhouse gas emissions. Some countries, such as France, have set ambitious targets, such as achieving carbon neutrality within 30 years.
To reduce our emissions, we must change our energetic model :
- reduce our energy needs, because the best energy is the one we do not consume;
- produce the necessary energy from renewable sources.
The energy transition corresponds to the transition from a system based on the production of energy from fossil and fissile sources (coal, oil, gas, nuclear) to renewable sources.
The term ofrenewable energy is used to refer to energies that, at least on a human scale, are inexhaustible and available in large quantities. Thus there are five main types of renewable energy: solar energy, wind energy, hydropower, biomass and geothermal energy. Their common characteristic is that they do not produce, during the operating phase, polluting emissions (or few), and thus help to fight against the greenhouse effect and global warming.
Renewable gases, an alternative in full development
What is a renewable gas?
We consider as renewable gasany gas produced from renewable energy resources. "Renewable energy sources are wind, solar, geothermal, aerothermal, hydrothermal, marine and hydropower, as well as energy from biomass, landfill gas, sewage treatment plant gas and biogas.
Biomass is the biodegradable fraction of products, waste and residues from agriculture, including plant and animal substances from land and sea, forestry and related industries, as well as the biodegradable fraction of industrial and household waste."
Renewable gases come from three main sectors:
-• MethanizationBiological pathway: a biological pathway based on the use of microorganisms to break down organic matter and produce biogas mainly composed of methane and carbon dioxide. This biogas can then be purified to obtain a gas with thermodynamic properties equivalent to natural gas.
-The pyrogasification or gasificationThermochemical process in the broad sense, allowing solid, liquid or gaseous fuels to be produced from organic matter. Depending on pressure and temperature conditions, the process can be oriented towards the production of synthesis gas called syngas and composed mainly of methane, hydrogen, carbon monoxide and carbon dioxide. It is possible to complete the process to obtain a gas with thermodynamic properties equivalent to natural gas.
-• The power-to-gas (PtG)Process for the conversion of electricity into synthesis gas. Electricity must be of renewable origin to consider the gas produced as renewable energy. The first step is an electrolyzer producing hydrogen. A second step can be added to convert hydrogen to methane through a methanation reaction. This last reaction requires a CO2 source.
Usually, the methanization is about rapidly biodegradable materials. Bio-methane production units use by-products from agriculture (livestock manure, crop residues, intermediate crops, grass), industry (agri-food by-products and effluents), sludge from urban wastewater treatment plants, and bio-waste (households, catering, distribution). It is also possible to methanize agricultural crops or algae produced for this purpose.
Gasification is mainly aimed at ligno-cellulosic materialsWood and wood products, straw, and various wood by-products of agriculture. In addition to these main resources, there are other minor resources, such as waste gasification (some of which is of biomass origin and some of which is derived from petrochemicals), or the recovery of fatal hydrogen in certain industries. This is more a question of recuperative energies than of renewable energies strictly speaking, we generally speak of ENRR to include "new renewable and recuperative energies".
Finally, the gas production from electricitysaid again power-to-gas(PtG)is used in scenarios with a high proportion of solar or wind power, in order to control the supply-demand balance of the electricity system. Power-to-gas makes it possible to transform excess electricity into injectable gas that can be stored on the natural gas network.