Biogas is the raw gas naturally produced by the decomposition of residues and organic effluents. Organic matter, called substrate in a biogas plant, is decomposed by different microorganisms in an anaerobic environment, capable of a mixture of gases, primarily methane (CH4) and carbon dioxide (CO2).
Anaerobic digestion, or biodigestion, consists in a complex and continuous process in which complex organic structures are reduced to simple mineral compounds by different microorganisms. This conversion process takes place in four main steps: hydrolysis, fermentation (acidogenesis), acetogenesis and methanogenesis.
Biomethane, also knows as renewable natural gas, is the biofuel resulting from biogas purification with a minimum composition of 90% methane. Biomethane is an interchangeable fuel with natural gas and its specification is established by ANP Resolutions No. 08/2015 and No. 685/2017.
The outturn directly depends on the type of substrate being treated. Methane concentration varies between 50% and 75% in biogas.
The amount of biogas effectively obtained per ton of residue depends on several factors, especially the composition of the substrate and the type of reactor used. The most common residues can yield 25 to 800 Nm3 of biogas per ton. The Brazilian biogas potential study conducted by ABiogás takes into account the amount of biogas produced by dry matter from each residue in real plants operating in Brazil.
The main component of a biogas plant is the biodigestor, which is a reactor that will provide the anaerobic condition for biodigestion. Other very common components in biogas plants are reception, pre-treatment and/or homogenization tanks prior to the biodigester and post-treatment and/or digestate tank. Depending on the final biogas application, the plant must have biogas cleaning and/or purification systems.
For the production of biomethane, a purification process (upgrading) is required, which aims to remove CO² and other gases that make up the biogas. The most applied technologies include chemical and physical absorption, adsorption, cryogenics and membrane technologies. To find purification technology suppliers, click here.
Biodigestion is a complex process that involves different groups of microorganisms. This process can be inhibited by the composition of the substrate itself, such as insufficient micronutrients, inadequate ratio between carbon and nitrogen, excessive presence of toxic compounds – such as free ammonia – and low pH. Also, the operation of a biogas plant must be rigorous, for stresses such as high organic loading and temperature shocks can be fatal for the maintenance of the microorganisms responsible for the process.
Current equipment varies between 30% and 42% of electrical efficiency for converting biogas energy into electric energy. ABiogás has specific recommendations for different sizes and levels of investment in biogas, with a minimum efficiency of 35% being recommended.
In Brazil, there are several capable and specialized suppliers in the development, implementation and operation of biogas plants from the most diverse substrates. Here you will find a list of members who are waiting for your contact!
It is possible to biodigest several substrates without prior preparation or pre-treatment. However, some substrates require homogenization, mechanical treatment (such as grinding) or mixing between two or more substrates to improve the composition. Furthermore, it is possible to apply thermal, chemical or biological pre-treatment to facilitate the digestion process and increase the efficiency of biogas production.
It is highly recommended that biogas production and composition be monitored online. Real-time monitoring, especially for the production of biomethane, in which it is vital to guarantee the composition within the applicable standards. Specifically in the case of composition measurement, the most applied technology today is NDIR (non-dispersive infrared).
The environmental licensing process for a biogas plant follows the same basic protocols as other licenses. As this process is under the responsibility of state agencies, the specific criteria for each state must be consulted. Some States already have regulatory instruments to facilitate and accelerate the licensing process for these projects.
The legislation is divided into instruments applied at National, State or Municipal level. Brazil has developed many laws in all these areas, especially in the last 5 years. The main decrees, laws and norms that regulate the production and use of biogas in Brazil can be found in the tool developed by Sebrae in conjunction with several institutions.
Yes, there are four ABNT standards applied to biogas and biomethane. They are:
– ABNT NBR 16560:2017 – Biogas and biomethane – Determination of siloxanes by gas chromatography and sampling with impingers
– ABNT NBR 16561:2017 – Biomethane – Determination of siloxanes by gas chromatography and sampling with thermal desorption tube
– ABNT NBR 16562:2017 – Biogas and biomethane – Determination of volatile organic compounds by gas chromatography and sampling with thermal desorption tube
– ABNT NBR 16837-1:2020 – Biomethane injection in piped gas distribution networks
The prices of oil and its derivatives have a proportional impact on investment and in the development of biofuels. When prices are low, the market is naturally less interested in developing alternatives to conventional fuel. On the other hand, when prices are high, the market tends to invest in the development and application of new options.
After the conception and approval of the basic and executive projects, from implementation to start-up of the plant can take from one to two years.
The energy component of biogas is methane, therefore, the amount of energy that each cubic meter of biogas can generate depends on the concentration of methane, which can vary between 50 and 70%. If considered an average of 60% methane, biogas contains the equivalent of 6 kWh of energy.
Each liter of diesel is equivalent to 1.08 m3 of biomethane. To calculate the amount of biomethane needed to replace diesel consumption, simply multiply diesel consumption by 1.08.
Biogas quality monitoring can be carried out both online or offline. It is possible, in smaller plants, to carry out periodic collections for biogas analysis in a gas chromatograph or portable meter. For online measurement, there are infrared gas analyzers that can be installed in-line. It is important to emphasize that the equipment used must be specifically for the analysis of biogas, since the components of this gas can be highly corrosive to inappropriate technologies.
The cost of a plant varies by the type of substrate, the location, the type of technology and the level of automation of the plant. In general, the cost of a plant with minimum efficiency standards costs around R$ 9 million per installed MW.
For biomethane distribution through gas pipelines in the national grid, it is necessary to comply with the quality requirements indicated by Normative Resolutions 008/2015 and 685/2017. For distribution through dedicated gas pipelines, the applicable state regulations must be observed.
The pricing of biomethane must take into account the CAPEX and OPEX of the installation and operation of the plant. Still, the pricing proposed by ABiogás considers the costs with capital and specific characteristics found in the financing. Need help pricing your product? Count on ABiogás to help you with your economic model!
Biomethane can be sold directly to the end customer or it can rely on intermediaries. For the transportation of biomethane into existing gas pipelines, the existing state regulations must be respected.
Biogas can be sold, but the most common is the sale of final products: electricity, biomethane and biofertilizer.
The digestate can be subjected to a separation process in order to obtain a liquid and a solid fertilizer. In Brazil, there are still few experiences in the commercialization of this by-product, as the specifications for registration, packaging and labeling of organic fertilizers were only recently established, through Normative Instruction MAPA n°61/2020. However, in the world, several examples of commercialization of biofertilizers from biodigestion in retail can already be found.
