Biomethane is a mix of gases and can be produced from both biological and thermochemical processes.
The biological processes are based on upgrading biogas produced by anaerobic digestion of municipal waste streams, process residues, agriculture waste streams and energy crops such as various types of grasses as well as landfill gas, by removing the carbon dioxide and other contaminants from the biogas.
In thermochemical processes, biomethane is produced by the catalytic treatment of synthesis gas downstream of biomass gasification processes (see Mandate to CEN n. M/475 EN).Biogas has a low thermal efficiency and a chemical composition not in compliance with fuel gases of transmission and distribution infrastructures, so it has a restricted range of uses: it’s generally used by the producer to produce heat and electricity for its own purpose and it cannot be added to the network and put on the market.
Biomethane, on the contrary, due to its upgrading process from biogas, has compatible characteristics (and same benefits) with natural gas. According to the new regulation framework, biomethane can now be added to the natural gas pipeline networks. In addition, most countries have established incentives to increase the presence of biomethane in the grid.
The reason why biomethane is gaining so much consideration lately is due to the growing attention to the environment (see e.g. European Climate and Energy Policy). All the countries are encouraged to reduce their emissions and increase their efforts to use renewable energies.
Biomethane is a renewable gas, and its injection into the grid contributes to meet the European Union renewable energy targets. For this reason, it’s showing the highest level of growth of any gas market in the world. The implementation of biomethane can decisively contribute to the de-carbonization of the economy, helping the transition to an energy system based on sustainable resources.
Europe has a potential of biomethane production between 151 and 246 billion cubic meters per year by 2025. New biogas plants will be built to produce around 2.600 MW. Europe is the most important contributor to this growth and is expected to continue to be the leader.
Germany has been the leading country so far, even if a decrease in growth is foreseen; this growth expected in other markets such as France, UK, Italy and Poland. Combined, this growth will be able to compensate for Germany’s decrease.
In order to convert biogas into biomethane, it’s necessary to go through 2 processes: purification and upgrading. The purification process eliminates water, H2S and traces of undesired contaminants (ashes, ammonia, siloxanes, etc.) The upgrading process removes the CO2 to reach the quality standards required by the gas network and the uses as biofuel.
There are several methods used for the upgrading, each one with pros and cons:
- Absorption, also defined ‘Washing’ or ‘Scrubbing’
- Washing systems with water and amines
After those treatments, the biomethane reaches a quality with characteristics compatible with natural gas with at least 95% of methane, and can be added into the network, after the necessary stages of compression and odorization.
After the conversion of biogas into biomethane, this has to be injected into the grid. Here we can see an example of schematic showing the process:
After the production area, where biomethane is manufactured from biogas, the quality (chemical composition) of the gas has to be carefully checked and monitored by using a gas chromatograph or gas analyzer. Only if the gas characteristics meet the standards requirement, it can be added into the grid. A 3-way valve installed downstream the production process will receive a signal of the gas composition and, depending on its quality, will send the gas back to processing or send it to the pressure reducing and metering station. This is very similar to a standard station for natural gas: the gas will be filtered and then measured with a custody transfer meter and a flow computer. Pressure regulators will reduce and stabilize the injection pressure to the final destination value.
Another important component of the plant is the odorant injection system; exactly like natural gas, biomethane cannot be added to the distribution grid without the appropriate odorization. Since biomethane, like natural gas is odorless and combustible, these odorants are added as a safety measure so that leaks can be detected by smell.
In addition to these components, the plants require PLCs, SCADA systems and uninterruptable power supplies (UPS) to handle all the equipment, instrumentation and signals.
Producers dealing with biomethane face different challenges. In some countries, like Italy, this is a fairly new topic and the relevant authorities and bodies are in the process to complete the whole framework of commercial rules and technical standards. It’s important to work with suppliers that can help you understand all this emerging legislation, keep you updated and save you time and money.
It can also be difficult to deal with many different suppliers, so it’s important to select a supplier that can provide the necessary instrumentation and automation equipment and support at every step. This reduces project complexity and ensures your process compliance with safety legislation and regulations. This choice of equipment can also reduce maintenance in the long term decrease the ownership costs, and provide a lifecycle support for the life of your plant.
Emerson can help you manage the challenges related to biomethane production and distribution with the equipment, instrumentation and expertise necessary to safely inject biomethane in the grid. Contact us for more on how we can help solve these challenges.
From Jim: You can also connect and interact with other oil & gas experts in the Oil & Gas group of the Emerson Exchange 365 community.