CNG & CBG – The Future of Clean Energy

Explore complete production technology, standards, government policies, global initiatives and business models for Compressed Bio Gas.

CBG Production Technology

Complete biogas-to-CBG conversion system using anaerobic digestion, purification and high-pressure compression.

CBG (Compressed Bio Gas) is produced through the anaerobic digestion of agricultural residue, cattle dung, sugarcane press mud, MSW, sewage waste and industrial organic residue. The resulting biogas is purified to remove CO₂, H₂S and moisture, achieving **methane content above 90%**, then compressed up to **250 bar** for bottling.

Anaerobic Digestion Stages

Four-step biological process that converts organic material into methane-rich biogas.

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1. Hydrolysis

Organic materials like carbohydrates, proteins and fats break down into glucose, amino acids and fatty acids. This is the **first step of biogas formation** and sets the foundation for microbial conversion.

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2. Acidogenesis

Acidogenic bacteria convert the broken-down molecules into **volatile fatty acids**, alcohols, hydrogen and carbon dioxide. This increases acidity and prepares the feed for acetogenic bacteria.

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3. Acetogenesis

Volatile organic acids are converted into **acetic acid**, CO₂ and hydrogen. This step directly feeds the final methane-producing stage.

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4. Methanogenesis

Methanogenic bacteria convert **acetic acid into methane**, and produce CO₂ and small amounts of H₂S. This creates raw biogas: ~55–60% methane and ~40–45% CO₂.

Acidogenic bacteria convert the broken-down molecules into **volatile fatty acids**, alcohols, hydrogen and carbon dioxide. This increases acidity and prepares the feed for acetogenic bacteria.

Volatile organic acids are converted into **acetic acid**, CO₂ and hydrogen. This step directly feeds the final methane-producing stage.

Methanogenic bacteria convert **acetic acid into methane**, and produce CO₂ and small amounts of H₂S. This creates raw biogas: ~55–60% methane and ~40–45% CO₂.

Hydrogen Sulfide Removal

H₂S is corrosive and reduces calorific value — hence removal is essential.

Specialized microorganisms convert hydrogen sulfide into sulfur or sulfate under controlled conditions.

Iron chloride reacts chemically with H₂S to produce iron sulfide, reducing corrosive gases effectively.

H₂S dissolves more readily in water. Passing biogas through a water column reduces sulfur content significantly.

Biogas flows through activated carbon beds where H₂S binds chemically, ensuring deep purification.

Iron media oxidizes H₂S forming stable compounds. Effective for medium-sized plants.

Alkaline scrubbing neutralizes acidic impurities in the biogas stream.

Process Flow Diagram

Anaerobic Digestion Technologies

Different types of digesters used to convert organic biomass into biogas efficiently.

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Continuously Stirred Tank Reactor (CSTR)

A CSTR digester is continuously fed with organic material and provides uniform mixing, ensuring **steady and predictable biogas output**. Ideal for **large-scale commercial CBG plants** where consistent production is crucial.

Advantages

Efficient digestion
Handles different dry matter levels
Can digest energy crops
Good solids degradation due to mixing

Disadvantages

Complex digestion process
High capital cost
Requires skilled operators

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Horizontal Plug-Flow Reactor

Organic feedstock flows horizontally through a long rectangular chamber with progressive gas injection. Suitable for **medium-scale plants with semi-solid feed**.

Advantages

Inexpensive construction
Easily adapted to hydraulic flushing
Simple management

Disadvantages

Hard top makes solid removal difficult
Membrane covers are sensitive to weather

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Batch-Type Digesters

The digester is filled once, sealed, and left for the full retention period. Most common in **low-cost rural systems**.

Advantages

Cheapest & simplest to build
Ideal where raw material supply is uncertain

Disadvantages

Biogas production is uneven
Requires multiple digesters to maintain continuous gas flow
Occupies more land area

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Covered Lagoon Digesters

Essentially a lined pond with a flexible cover that captures biogas. Best suited for **large livestock farms, dairy waste, and agricultural sludge**.

Advantages

Very low cost
Large volume capacity
Simple construction
Ideal for farms & large waste streams

Disadvantages

Poor mixing
Lower energy yield
Cover maintenance can affect lifespan

Detailed Digester Comparison

Advantages

Efficient digestion
Handles different dry matter levels
Can digest energy crops
Good solids degradation due to mixing

Disadvantages

Complex digestion process
High capital cost
Requires skilled operators

Organic feedstock flows horizontally through a long rectangular chamber with progressive gas injection. Suitable for **medium-scale plants with semi-solid feed**.

Advantages

Inexpensive construction
Easily adapted to hydraulic flushing
Simple management

Disadvantages

Hard top makes solid removal difficult
Membrane covers are sensitive to weather

The digester is filled once, sealed, and left for the full retention period. Most common in **low-cost rural systems**.

Advantages

Cheapest & simplest to build
Ideal where raw material supply is uncertain

Disadvantages

Biogas production is uneven
Requires multiple digesters to maintain continuous gas flow
Occupies more land area

Essentially a lined pond with a flexible cover that captures biogas. Best suited for **large livestock farms, dairy waste, and agricultural sludge**.

Advantages

Very low cost
Large volume capacity
Simple construction
Ideal for farms & large waste streams

Disadvantages

Poor mixing
Lower energy yield
Cover maintenance can affect lifespan

Biogas Purification Technologies

Technologies used to upgrade raw biogas into high-purity CBG with >90% methane content.

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Pressure Swing Adsorption (PSA)

PSA is one of the most widely used technologies in India for large-scale biogas upgrading. It separates **carbon dioxide (CO₂) from methane** by adsorbing CO₂ at high pressure on materials like activated carbon or zeolites. When pressure is reduced, the adsorbent regenerates and becomes ready for the next cycle.

Advantages

High methane recovery
Low operating cost after installation
Reliable and suitable for large plants

Disadvantages

Requires pre-removal of H₂S and moisture
High capital cost
Requires stable biogas flow

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Vacuum Swing Adsorption (VSA)

VSA is a non-cryogenic gas separation technology that uses **molecular sieves** to selectively adsorb CO₂ at near-ambient pressure. A vacuum is applied to regenerate the adsorbent. Effective for medium-scale CBG plants.

Advantages

Lower power consumption than PSA
Efficient CO₂ separation
Good for medium-sized installations

Disadvantages

Vacuum pumps require maintenance
Less methane purity compared to PSA

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Water Scrubbing

CO₂ is more soluble in water than methane. Biogas is passed through a **high-pressure water column**, dissolving CO₂ and H₂S, and producing methane-rich gas. Works best when water can be recirculated.

Advantages

Simple and robust technology
Removes both CO₂ and H₂S
Low chemical usage

Disadvantages

High water consumption
Requires cooling for efficiency

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Membrane Separation

Gas passes through **semi-permeable membranes**. CO₂, water vapor and ammonia permeate faster than methane, enriching methane concentration. Typically used in 2 or 3-stage membrane systems. Ideal for modular installations.

Advantages

Compact, modular and scalable
Low maintenance
High purity levels achievable

Disadvantages

Sensitive to impurities
Requires pre-filtration

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Chemical Scrubbing (MEA System)

Monoethylamine (MEA) solution **chemically reacts with CO₂**, forming a stable compound. The solution is regenerated by heating, releasing CO₂ and allowing MEA reuse. It delivers extremely high methane purities.

Advantages

Very high CO₂ removal efficiency
High methane purity (> 98%)

Disadvantages

Energy-intensive regeneration
Chemical handling required

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Cryogenic Upgrading

CO₂ is liquefied at very low temperatures while methane remains gaseous. This allows high purity methane separation. Used in large industrial-scale bio-LNG or CBG production.

Advantages

Extremely high methane purity
CO₂ byproduct can be reused

Disadvantages

Very high energy requirement
High CAPEX equipment

Detailed Technology Explanation

Advantages

High methane recovery
Low operating cost after installation
Reliable and suitable for large plants

Disadvantages

Requires pre-removal of H₂S and moisture
High capital cost
Requires stable biogas flow

Advantages

Lower power consumption than PSA
Efficient CO₂ separation
Good for medium-sized installations

Disadvantages

Vacuum pumps require maintenance
Less methane purity compared to PSA

Advantages

Simple and robust technology
Removes both CO₂ and H₂S
Low chemical usage

Disadvantages

High water consumption
Requires cooling for efficiency

Advantages

Compact, modular and scalable
Low maintenance
High purity levels achievable

Disadvantages

Sensitive to impurities
Requires pre-filtration

Advantages

Very high CO₂ removal efficiency
High methane purity (> 98%)

Disadvantages

Energy-intensive regeneration
Chemical handling required

CO₂ is liquefied at very low temperatures while methane remains gaseous. This allows high purity methane separation. Used in large industrial-scale bio-LNG or CBG production.

Advantages

Extremely high methane purity
CO₂ byproduct can be reused

Disadvantages

Very high energy requirement
High CAPEX equipment

Moisture & H₂S Management

Moisture is typically removed using **dryers, silica gel, or refrigeration systems**. Removing water vapor prevents corrosion and freezing during CBG compression up to 250 bar.

Hydrogen sulfide is corrosive, toxic and reduces calorific value. Removal methods include:

Biological fixation
Iron chloride dosing
Water scrubbing
Activated carbon filters
Iron oxide/hydroxide media
Sodium hydroxide scrubbing

Effective H₂S removal extends plant life and protects compressors.

Purification System Flow Diagram

CBG Bottling & High-Pressure Storage

Purified biogas is compressed and stored safely in steel or composite cascades according to national standards.

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High Pressure Compression (250 Bar)

Purified biogas with 90% methane is compressed using a **high-pressure compressor** to approximately **250 bar**. This compression makes CBG suitable for storage, transport, and vehicle fueling. The system includes multistage compression, cooling, moisture traps and safety valves.

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Cascade Storage (3000 L / Higher Capacity)

The compressed gas is filled into several cylindrical vessels arranged as a **cascade**. Cascades enable controlled filling and delivery to CBG dispensers. Standard sizes include **3000-liter cascades** and larger composite variants.

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Steel Cylinder Cascades (IS 7285)

Steel cascades are manufactured according to **IS 7285 standards**. They consist of Type-1 or Type-2 cylinders designed specifically for high-pressure gas storage at 250 bar. These are widely used in transport vehicles delivering CBG to fuel retail outlets.

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Composite Cylinder Cascades (IS 15935)

Type-3 and Type-4 composite cylinders offer **lighter weight**, higher corrosion resistance, and better storage efficiency. Manufactured according to **IS 15935** and related BIS standards, they reduce transport cost and vehicle payload.

Cylinder Types & Standards

Type	Material	Notes
Type 1	All-steel cylinder	Highest weight, most economical
Type 2	Steel with hoop-wrapped fiberglass	Moderate weight reduction
Type 3	Aluminum liner with full composite wrap	Much lighter, improved durability
Type 4	Plastic liner + full composite wrap	Lightest & most efficient

IS 7285 — Specifications for steel gas cylinders.
IS 15935 — Specifications for composite pressure vessels.
Transport guidelines must follow Petroleum & Explosives Safety Organization (PESO) norms.
CBG delivered to fuel retail outlets must meetIS 16087:2016 quality standards.

CBG cascades are mounted on trucks or trailers and transported to retail dispensing units located within a **25 km radius** of the CBG plant (as per SATAT guidelines).

Only approved cascades with valid test certificates permitted
Safety valves and burst discs mandatory
Pressure testing required periodically

Compression & Cascade Diagram

CBG Quality Standards — IS 16087:2016

Specifications defined by the Bureau of Indian Standards for Compressed Bio Gas used as automotive fuel.

Characteristic	Requirement
Methane (CH₄), Minimum	90.0%
Carbon Dioxide (CO₂), Maximum	4%
CO₂ + Nitrogen (N₂) + Oxygen (O₂), Maximum	10%
Oxygen (O₂), Maximum	0.5%
Total Sulphur (Including H₂S), Maximum	20 mg/m³
Moisture, Maximum	5 mg/m³

Additional BIS Requirements

CBG must be free from liquids across all operating temperatures & pressures.
CBG must be free from dust, dirt, and any particulate matter.
Gas must be odorized similar to local distribution gas (as per IS 15319).
Compressed and stored at ~250 Bar for transportation to OMC retail outlets.

CBG Specification Chart

Global Initiatives in Biogas & CBG

Countries worldwide are rapidly adopting biogas for transportation, grid injection and renewable energy generation.

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Germany

Germany is the world leader in biogas adoption with nearly 9,000 biogas plants, up from 4,136 in 2010. These plants generate about 8.98 BCM of biogas. Most plants are operated by farmer cooperatives using energy crops like maize.

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Italy

Italy aggressively supports biomethane production and grid injection. Strong incentives have accelerated upgrading of biogas into CBG/Bio-CNG.

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United Kingdom

The UK promotes renewable gas for residential heating, electricity generation, and transportation. Biogas is widely injected into natural gas grids.

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France

France supports biomethane through regulated tariffs and long-term purchase agreements, resulting in rapid biogas grid expansion.

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Switzerland

Switzerland uses biogas mainly for **vehicle fuel** and **grid injection**, ensuring high purity through strict national standards.

European Biogas Strategy

Across Europe, biogas is used for **grid injection**, **electricity generation**, **district heating**, and **transportation fuel**. Countries provide strong policy frameworks, education programs, and technology support to accelerate renewable gas adoption.

Global Biogas Growth Map

Government Policy Support

Strong national policies drive the adoption of Compressed Bio Gas across India.

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National Biofuel Policy (2018)

Promotes advanced biofuels such as **CBG**, enabling reduction of crude oil imports and boosting renewable fuel adoption. Supports waste-to-energy technologies and encourages private investment.

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GOBAR-DHAN Scheme

A national initiative to convert cattle dung and rural solid waste into Bio-CNG (CBG) and organic fertilizer. Planned rollout includes **700 projects across India**.

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MNRE Central Financial Assistance (CFA)

MNRE provides subsidies to promote Bio-CNG production, making CBG plants more financially viable for rural and industrial deployment.

India's Energy and Sustainability Vision

India is one of the fastest-growing economies with rapidly increasing energy demand. The government has outlined major reforms to strengthen energy access, security and sustainability:

Increase natural gas contribution in India's energy mix from 6.5% → 15%
Reduce crude oil imports by 10%
Double farmers’ income through biomass supply and residue monetisation
Promote circular economy & decentralized rural energy

India’s Renewable Energy Roadmap

Business Model for CBG Production Under SATAT

The SATAT initiative establishes a structured and profitable ecosystem connecting farmers, CBG plant owners, and Oil Marketing Companies.

The SATAT (Sustainable Alternative Towards Affordable Transportation) scheme outlines a business model where **CBG producers supply compressed bio-gas to Oil Marketing Companies (OMCs)** for use as a renewable automotive fuel. The model creates value across the chain — from farmers supplying biomass to OMCs retailing green fuel.

Benefits of the SATAT Business Model

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Reduces natural gas & crude oil imports

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Promotes rural economy & employment generation

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Utilizes agricultural waste & MSW responsibly

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Supports Swachh Bharat Mission

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Reduces pollution & carbon emissions

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Generates bio-manure as a valuable by-product

CBG Production & Distribution Flow

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1. Biomass / Waste Collection

Agricultural residue, cattle dung, press mud, MSW, and sewage waste are collected locally.

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2. Transportation to Plant

Biomass delivered to CBG plants located close to farming or waste generation hubs.

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3. Biogas Production

Anaerobic digestion technology converts biomass into raw biogas (~55–60% methane).

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4. Purification & Upgrading

Biogas is purified (H₂S, CO₂, moisture removal) to increase methane concentration above 90%.

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5. Compression to 250 Bar

Purified biogas is compressed into CBG using high-pressure compressors.

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6. Cascade Filling

Compressed gas stored in steel or composite cascades (3000 L and above).

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7. Delivery to OMC Retail Outlets

Cascades transported to fuel stations within a radius of 25 km as per SATAT guidelines.

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8. CBG Dispensing

CBG dispensed as a green automotive fuel similar to CNG, meeting IS 16087:2016 standards.

Revenue Streams for CBG Plant Owners

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CBG Sale to OMCs

OMCs (HPCL, BPCL, IOCL) purchase CBG under long-term assured offtake agreements.

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Sale of Fermented Organic Manure (FOM)

Bio-manure generated during digestion sold to farmers, improving soil fertility.

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Tipping Fees (MSW-based Plants)

Municipal bodies may pay processing fees for waste disposal services.

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Carbon Credits

CBG plants may earn carbon credit income due to methane capture & emission reduction.

Applications of CNG / CBG

Clean, renewable and versatile — CBG unlocks value for transport, industry and power sectors.

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Transportation

Used in cars, auto rickshaws, buses, and commercial vehicles as a clean and economical alternative to petrol and diesel.

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Industrial Applications

Industries use CBG as a reliable and efficient fuel for heating, boilers, furnaces, and thermal applications.

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Power Generation

CBG is used to produce electricity through gas engines and turbines, reducing emissions dramatically.

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Commercial Cooking

Hotels, restaurants, and institutions use CBG for clean and efficient cooking solutions.

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Agricultural Applications

Bio-manure from CBG plants improves soil health, replacing chemical fertilizers.

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Grid Injection (Future Roadmap)

Upgraded biomethane can be injected into natural gas pipelines, widely practiced in Europe.

Usage Scenarios Diagram

CNG vs Petrol

A cleaner and more economical choice for modern transportation.

Feature	CNG	Petrol
Emissions	Significantly lower emissions	Releases harmful pollutants
Cost	40–50% cheaper fuel cost	High running cost
Environmental Impact	Eco-friendly, minimal pollution	High carbon & particulate emissions
Maintenance	Cleaner combustion → lower maintenance	Higher engine deposits
Safety	Lighter than air — dissipates quickly	Highly flammable, pools on ground
Fuel Availability	Rapidly expanding in India	Widely available, but costly

Why CNG Is the Better Choice

✓ Cuts emissions by up to 90%
✓ Reduces operating costs drastically
✓ Improves engine life due to clean combustion
✓ Safer handling & lower fire risk

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