Compressed Bio Gas (CBG)

Biogas is a renewable energy source produced from the anaerobic decomposition of organic waste materials such as agricultural residues, cattle dung, sugarcane press mud, municipal solid waste (MSW), and sewage treatment plant waste.

The other waste streams viz. rotten potatoes from cold storage, rotten vegetables, dairy plants, chicken/ poultry litter, food waste, horticulture waste, forestry residues and industrial Effluent Treatment Plants (ETPs) treating organic waste can be used in the generation of biogas.

In the absence of oxygen, microorganisms break down these organic materials, producing a mixture of gases, primarily methane (CH₄), carbon dioxide (CO₂), hydrogen sulfide (H₂S), and trace gases.

The biogas produced contains approximately 55% to 60% methane, 40% to 45%carbon dioxide and trace amounts of hydrogen sulphide.

To obtain purified biogas suitable for use as a fuel, a series of purification processes are employed to remove the impurities:

1-Hydrogen Sulfide (H₂S): This compound is removed because it is corrosive and can damage equipment. It is typically eliminated using adsorption methods or chemical scrubbing.

2-Carbon Dioxide (CO₂): As carbon dioxide reduces the calorific value of biogas, it must be separated. Techniques like pressure swing adsorption (PSA), water scrubbing, or membrane filtration are used to remove CO₂.

3-Water Vapor: The biogas is typically saturated with water vapor, which needs to be removed to prevent condensation during compression. This is done using cooling or drying systems.

Once these impurities are removed, the resulting biogas is called Compressed Bio Gas (CBG), which typically has a methane content of more than 90%. CBG can be used in the same way as natural gas for various applications, including cooking, as a green renewable automotive fuel, and power generation.

The conversion of agricultural residue, cattle dung, and municipal solid waste (MSW) into Compressed Bio Gas (CBG) on a commercial scale is expected to offer several key benefits :

• Import reduction of natural gas and crude.

• Utilizing agricultural residue, cattle dung, and MSW for CBG production helps reduce emissions and pollution

• Providing a buffer against energy security concerns and crude/gas price fluctuations.

• Providing an additional source of revenue for farmers, creating rural employment, and boosting the rural economy

The biogas produced contains approximately 55% to 60% methane, 40% to 45%carbon dioxide and trace amounts of hydrogen sulphide. Biogas is purified to remove carbon dioxide and hydrogen sulphide gases to prepare CBG. The CBG can be transported through cylinder cascades or pipelines to retail outlets.

Compressed Bio Gas (CBG) to be supplied shall meet IS 16087:2016 specifications :

1- Methane percentage (CH4), minimum- 90%

2- Only Carbon Dioxide percentage (CO2), maximum- 4%

3- Carbon Dioxide (CO2)+ Nitrogen (N2)+ Oxygen (O2) percentage maximum – 10%

4- Oxygen (O2) percentage maximum-0.5%

5-Total sulphur (including H2S) mg/m3, maximum- 20mg/m3

6- Moisture mg/m3, maximum- 5mg/m3

Also as per the IS 16087:2016 specifications, the following shall also be met :

• CBG must be free from liquids across the entire range of temperatures and pressures experienced in its storage and dispensing systems.

• The CBG shall be from particulate matter like dirt, dust, and other solid impurities.

• CBG delivered shall be odorized to a level similar to that found in local distribution systems aligns with standard practices for ensuring safety and usability.

• The CBG is to be compressed at 250 Bar and supplied through Cascades to the Oil Company Retail Outlets

CBG Production Technology

Biogas is produced through the anaerobic digestion of organic matter by microorganisms. This process occurs in four sequential chemical and biochemical stages: Hydrolysis, Acidogenesis, Acetogenesis, and Methanogenesis. Each stage is essential for breaking down complex organic materials into methane (CH₄) and carbon dioxide (CO₂), which form the main components of biogas.

Hydrolysis reaction decomposes organic molecule such as carbohydrates, proteins and fats into glucose, amino acids and fatty acids, respectively.

Acidogenesis converts those generated small organic molecules to volatile organic acids with help from bacteria.

During Acetogenesis process, bacteria in the acetic group digests volatile organic acids and releases acetic acid.

Lastly, anaerobic bacteria in the methanogenic producing bacteria group will complete the Methanogenesis process by converting acetic acid to methane gas and other gases like carbon dioxide and hydrogen sulfide.

Estimated Basic Price Range for CBG

Given the costs outlined above and assuming IS 16087:2016 standards are followed, the basic price for CBG can be estimated as follows:

1-Base Price for Production: The cost of producing CBG, including feedstock procurement, biogas plant setup, and operating costs (such as labor and maintenance), typically falls within the range of ₹35 to ₹45 per kg.

2-Compression and Storage Costs: The cost to compress the biogas to 250 bar for transportation and storage, as well as the use of cascades, adds an additional ₹5 to ₹10 per kg.

3-Logistics and Distribution Costs: Transporting the CBG to retail outlets, particularly using cascade systems, and maintaining distribution infrastructure typically adds ₹5 to ₹10 per kg.

Final Estimated Basic Price Range: Considering all factors, the basic price range for CBG can be estimated at ₹50 to ₹60 per kg