Bio-CNG (Compressed Natural Gas) is refined biogas made from agricultural waste, animal manure, food waste, and sewage water. Its composition and energy potential are comparable to that of fossil-based natural gas. Anaerobic decomposition creates biogas from waste or biomass sources, including agricultural residue, bovine dung, sugarcane press mud, municipal solid waste, sewage treatment plant waste, etc.
Compressed biogas, which contains more than 90% methane, is created after purification. Compressed biogas, which can be utilized as an alternative, sustainable car fuel, possesses characteristics comparable to those of commercially available natural gas.
Did You Know? Bio-CNG (Compressed natural gas) contains more than 90% methane owing to which it has carbon emissions.
What is Bio-CNG?
Agricultural waste, manure, municipal garbage, plant matter, sewage, green waste, and food waste can all be broken down into biogas without oxygen. This mixture becomes bio-compressed natural gas after additional purification and processing. It is a cleaner alternative to fuels like gasoline and diesel and is similar to natural gas in terms of composition and quality.
In India, bio-CNG has enormous potential, particularly as a substitute for the more popular CNG and liquefied petroleum gas (LPG or Liquefied Petroleum Gas). Bio-CNG can be a better substitute for CNG and LPG in hotels, households, automobiles, etc.
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How Bio-CNG is Produced?
Bio-CNG is created from biogas through the simple and easy process of desulfurization, upgrading, and compression. Biogas is first desulphurized if the hydrogen sulphide content is greater than 1,500 ppm. The improved desulfurized biogas is then compressed and packaged in a cylinder to produce bio-CNG, a composition similar to CNG's.
Biogas has a methane content of 55–65% and a carbon dioxide content of 35–45%, compared to 92–98% for Bio-CNG and just 2–8% for biogas. Bio-CNG is the most ideal fuel for cars and power plants due to its high methane concentration, calorific value, low moisture, hydrogen sulfide, and impurity content. Additionally, Bio-CNG is a more environmentally friendly fuel than biogas due to its low emission levels.
In general, Bio-CNG is produced in four steps:
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Extraction
Natural anaerobic decomposition of waste or biomass sources, such as agricultural residue, cow dung, sugarcane press mud, municipal solid waste, sewage treatment plant waste, etc., produces biogas. Methane (CH4), carbon dioxide (CO2), and hydrogen sulfide are all components of biogas (H2S).
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Purification
The process then moves on to filter the biogas created by the anaerobic breakdown of straw to produce highly purified biomethane.
Due to its acidic composition, H2S can cause equipment to corrode when it is present in biogas, and it is also harmful to both human and animal health. Since CO2 in biogas is also corrosive, it should be considered an impurity. This necessitates the purification process to qualify biogas as natural gas, which is both healthy and environmentally friendly.
Popular methods of purification are
- Scrubbing
- Chemical absorption
- Membrane purification
- Cryogenic separation
- Biological processes
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Compression
Once the biogas is purified, the gas occupies a larger space for storage and transportation to the point of use. Therefore, the gas is compressed under extreme pressure. The cylinders could then be transported or stored.
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Dispersion
Bio-CNG has now been collected and is ready for distribution in two-wheelers, vehicles, trucks, and tractors. The economics of bio-CNG are examined. Since the cost of producing Bio-CNG is 20 to 50% lower than that of other fuels like CNG and other petroleum products, it is significantly less expensive than CNG and other fuels. The most effective alternative to the gaseous and petroleum fuels that are currently available is bio-CNG.
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Bio-CNG Production Technology
The following are the most common production technologies for the Bio-CNG economy -
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Pressure Swing Adoption
In India, most biogas plants use this technology. This method uses high-pressure absorption on a surface to remove carbon dioxide from biogas. The technique's name comes from how the adsorbing material (typically activated carbon or zeolites) is renewed before the column is once more loaded. Before the PSA column, hydrogen sulphide and water need to be eliminated. Methane is lost significantly in this process (20–30%).
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Water Scrubbing
Methane is less soluble in water than carbon dioxide. Therefore, carbon dioxide dissolves more completely than methane, especially at lower temperatures. While methane concentration in the gas phase rises, carbon dioxide is dissolved in water in the scrubber column. Methane is, therefore, more concentrated in the scrubber's gas. There are methods available that can produce methane with a purity of 97% and only 5% methane loss.
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Membrane Separation
Carbon dioxide, water, and ammonia are all permeable to the materials used to make dry membranes for biogas upgrading. While oxygen and hydrogen sulphide can partially flow through the barrier, methane and nitrogen can only do very little. Typically, membranes have the shape of bundles of hollow fibres.
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Chemical Scrubbing
This is one of the finest systems for purifying biogas, achieving 99.9% purity with barely any methane loss. In Germany, the systems are widely utilized for biogas purification. Along with being absorbed by the liquid, carbon dioxide also undergoes a chemical reaction with the amine. The methane loss could be as low as 0.1% because of the extremely selective chemical reaction. In addition to those above, emerging technologies include cryogenic upgrading.
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Conclusion
Fossil fuels are a limited, exhaustible source of energy. Despite their ease of extraction, they emit a ton of carbon dioxide into the atmosphere to the point that the environment can no longer regenerate.
Bio-CNG, on the other hand, can be produced economically. There is already a market for CNG, and it has a low carbon footprint. This makes it the most viable commercial opportunity in India. While government-backed departments have installed successful plants in Pune and other parts of Maharashtra, private initiative is still lacking in producing bio-CNG commercially.
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