How do you convert biogas or gobar gas to vehicle-grade Bio-CNG?

To convert biogas or agricultural gobar gas to CNG, raw gas must pass through four sequential engineering stages: pre-cooling to knock out liquid water, upstream H₂S removal down to sub-3 ppm using high-capacity adsorbents (SULAFER®) or chemical-free thermocatalytic units (Sulaway), membrane CO₂ separation elevating methane content above 97%, and multi-stage high-pressure compression for storage in cylinder cascades, tube trailers, or vehicle fuel tanks.

Why is raw biogas unsafe to fill directly into high-pressure gas cylinders?

Compressing raw biogas into steel cylinders is a severe hazard. Raw biogas contains water vapor, CO₂, and H₂S. Compressing H₂S under high pressure amplifies its partial pressure, triggering rapid sulfide stress corrosion (SSC) and hydrogen embrittlement in cylinder walls and valves, risking catastrophic rupture. Additionally, uncleaned CO₂ wastes nearly 40% of the cylinder’s storage volume on non-combustible gas.

What technical factors dictate the CAPEX and OPEX of a 500 Nm³/h Bio-CNG plant?

For a 500 Nm³/h biogas plant (producing ~300 Nm³/h of biomethane / ~7,000 liters diesel equivalent per day), CAPEX is driven by the choice of high-pressure compression stages, material grades (RVS316/Duplex), and membrane efficiency. OPEX is dictated by H₂S media replacement frequency and methane slip. Gazpack’s SULAFER® media provides a 1:1 H₂S reaction capacity, keeping maintenance OPEX under 2% of CAPEX, while our <0.5% methane slip guarantee prevents gas revenue loss.

How does upstream H₂S removal down to sub-3 ppm protect high-pressure CNG compressors and cylinder valves?

Under high compression pressures, even trace H₂S (above 5 ppm) reacts with residual water vapor to form sulfurous acid, causing pitting corrosion on compressor valves, piston rings, and cylinder seals. Gazpack removes H₂S down to <3 ppm upstream using SULAFER® media (Sulago) or thermocatalytic conversion (Sulaway) before gas enters high-pressure stages, extending compressor overhaul intervals and ensuring compliance with ISO 15403 fuel standards.

How does Gazpack’s automated PLC recirculation loop prevent gas flaring during Bio-CNG production?

During feedstock swings or system startups, gas purity may briefly stray off-spec. Traditional converters vent or flare this gas, wasting methane and degrading Carbon Intensity (CI) scores under RED III. Gazpack’s PLC architecture monitors gas purity in real time. If gas quality strays from the filling setpoint, automated valves instantaneously route the gas back to the inlet process loop for re-purification. Zero methane is flared, zero gas is lost, and non-compliant gas never enters filling cylinders.

Industry related topics

Bio-CNG from biogas

Bio-CNG from biogas: engineering high-pressure conversion and cylinder filling systems

Converting raw biogas into Compressed Natural Gas (Bio-CNG) offers one of the highest financial returns in the renewable energy sector. However, Bio-CNG production is vastly different from basic pipeline grid injection. To use biomethane as a vehicular fuel or transport it via virtual pipeline cascades, the gas must be upgraded to >97% methane (CH₄) purity, stripped of moisture and H₂S, and compressed for high-pressure storage and dispensing.

Gazpack

At Gazpack, we engineer integrated Bio-CNG conversion packages. Rather than selling standalone, unintegrated compressors, we design complete process skids that combine pre-cooling, H₂S removal (SULAGO® or SULAWAY®), membrane CO₂ separation, and high-pressure compression into a single, automated, ATEX-compliant system.

Can raw biogas be filled directly into cylinders?

A common question among farm operators and project developers is whether raw biogas can be compressed and filled directly into gas cylinders. Compressing raw biogas into steel cylinders without upgrading creates severe safety, mechanical, and economic hazards:

High-pressure corrosion: Raw biogas contains moisture, CO₂, and H₂S. When compressed for cylinder storage, H₂S partial pressure is amplified, forming acidic condensation that triggers rapid sulfide stress corrosion (SSC) and hydrogen embrittlement in high-pressure cylinders, valves, and fittings.

Wasted storage volume: Raw biogas contains 35% to 45% CO₂. Compressing uncleaned gas means spending energy to compress an inert gas, reducing your cylinder storage capacity by nearly half.

Vehicle engine damage: Raw biogas fails to meet vehicle fuel specifications (such as ISO 15403). Uncleaned H₂S rapidly degrades engine oil and destroys fuel injectors.

To safely fill gas cylinders or supply Bio-CNG vehicle fleets, raw biogas must first pass through a multi-stage upgrading and drying process.

How to convert biogas to Bio-CNG: the 4-stage process

Converting raw biogas (or agricultural gobar gas) into vehicle-grade Bio-CNG requires a controlled process chain to ensure safety and continuous operation.

Stage 1: upstream H₂S removal (SULAGO® or SULAWAY®)

Gazpack

Before gas reaches high-pressure compression stages, H₂S must be reduced to sub-3 ppm levels. In our Sulago systems, patented SULAFER® media chemically binds H₂S down to <3 ppm without clumping or "bricking". For high-volume or high-H₂S facilities, our chemical-free Sulaway system converts H₂S into 40% commercial-grade sulfuric acid (H₂SO₄).

Stage 2: deep pre-cooling and dew point control

To prevent liquid water from condensing inside storage cylinders, gas is cooled to knock out moisture. Gazpack pre-treatment modules lower the pressure dew point to <-40°C, protecting compressor valves and downstream storage cascades.

Stage 3: high-efficiency membrane CO₂ separation

Using multi-stage membrane separation, CO₂ is removed to elevate methane concentration to >97%. Gazpack’s system architecture guarantees methane slip remains under 0.5%, ensuring maximum gas recovery and protecting your carbon intensity (CI) score under RED III.

Stage 4: high-pressure compression and cascade filling

Purified biomethane is compressed to 200–250 bar using multi-stage, oil-free or specialized lubricated compressors. Integrated PLC controls manage cylinder cascade filling, priority panels, and automated recirculation.

Understanding the cost of a 500 Nm³/h Bio-CNG plant

When evaluating a Bio-CNG converter project, CAPEX and OPEX are heavily dictated by plant scale, raw gas flow rate, and inlet H₂S concentration. A typical 500 Nm³/h biogas plant produces approximately 300 Nm³/h of pure Bio-CNG, equivalent to over 7,000 liters of diesel equivalent per day.

Key cost drivers in Bio-CNG converter economics include:

H₂S media and chemical OPEX: Traditional activated carbon filters require frequent, expensive media replacements at high H₂S loads. Gazpack’s SULAFER® media offers a 1:1 reaction capacity, keeping annual maintenance costs below 2% of CAPEX.

Methane slip losses: A system with 2% methane slip loses tens of thousands of euros in gas value annually at 500 Nm³/h scale. Gazpack’s <0.5% slip guarantee preserves maximum product volume.

Compressor valve wear and downtime: Corrosive gas ruins standard compressor components. Gazpack utilizes RVS316 stainless steel and Duplex alloys in all critical gas-wetted zones, preventing premature component failure.

Off-spec gas management: During startup or feedstock swings, off-spec gas must not enter storage cylinders. Gazpack’s automated PLC recirculation loop routes non-compliant gas back to the inlet automatically, preventing flaring and gas waste.

Industry applications for Bio-CNG conversion systems

Agricultural digesters and farm co-ops: Convert cow dung, pig slurry, or poultry litter biogas into Bio-CNG to fuel farm tractors, supply local logistics fleets, or transport gas via virtual pipeline tube trailers to off-grid injection points.

Renewable gas plants and transport fleets: Establish dedicated Bio-CNG refueling hubs for heavy-duty trucking and public bus fleets, securing long-term off-take contracts with guaranteed ISO 15403 gas purity.

Engineering firms (EPCM): Incorporate fully integrated, factory-tested (FAT) Bio-CNG conversion skids into turn-key project designs. Gazpack units arrive pre-cabled and pre-programmed, cutting on-site installation time from weeks to hours.

Municipal water treatment and landfills: Valorize sewage sludge digester gas or landfill gas into clean Bio-CNG fuel for municipal utility vehicles and waste collection trucks.

Strategic comparison: standard conversion vs. Gazpack Bio-CNG system

Process feature	Basic / DIY conversion methods	Standard commercial converter	Gazpack integrated Bio-CNG plant
High-pressure safety	Extremely high risk (SSC corrosion)	Moderate	Maximum (RVS316 / Duplex alloys)
H₂S output	Uncontrolled	< 5 - 10 ppm	< 3 ppm (SULAFER®) or < 1 ppm (Sulaway)
Pressure dew point	Poor (liquid water in cylinders)	-20°C	<-40°C deep drying standard
Methane slip	> 3%	1% - 2%	< 0.5% (guaranteed)
Off-spec gas handling	Venting or manual shut-off	Flaring	Automated PLC recirculation loop
Cylinder filling	Slow, unmonitored	Basic filling panel	Integrated cascade priority management

Frequently asked questions about Bio-CNG conversion

Evaluate your Bio-CNG project feasibility

Do not risk high-pressure compressor failure or wasted methane. Contact Gazpack’s engineering team to design an integrated Bio-CNG conversion and cylinder filling system tailored to your gas composition.

Request a Bio-CNG feasibility check: Send us your raw gas flow (Nm³/h), H₂S load, and target compression pressure.

Calculate 500 Nm³/h plant ROI: Compare the 10-year TCO of Gazpack systems against standard market converters.

Consult a gas engineer: Book a direct technical review with our process integration team.

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