The main difference between a natural gas generator and a biogas generator is the fuel supplied to the engine and the treatment required before combustion. Natural gas generally has a higher and more consistent methane content, while raw biogas contains varying amounts of carbon dioxide, moisture, hydrogen sulfide, and potentially other contaminants. These differences affect fuel flow, engine compatibility, gas conditioning, maintenance, and operating costs.
Both generator types can produce electricity using gas engines, but they are not automatically interchangeable. Natural gas equipment is typically designed around a specified fuel quality, while biogas installations must match the engine and gas-treatment system to the actual composition of the gas produced on site.
1. How Do Natural Gas and Biogas Differ as Fuels?
Natural gas is a fossil fuel extracted from underground reservoirs, while biogas is produced when microorganisms break down organic material under anaerobic conditions. Common biogas sources include agricultural waste, food waste, wastewater treatment, and landfills.
Raw biogas commonly contains approximately 45–65% methane, with much of the remaining gas consisting of carbon dioxide. Its composition depends on the feedstock, digestion process, and treatment system. The U.S. Energy Information Administration's biogas overview explains how source material affects gas composition and why upgrading is necessary for some applications.
| Property | Natural gas | Raw biogas |
|---|---|---|
| Primary source | Underground gas reservoirs or processed gas supplies | Anaerobic digestion or decomposition of organic waste |
| Methane content | Depends on supply specification; generally high | Often around 45–65%, depending on the source |
| Carbon dioxide | Usually controlled by the applicable gas specification | Often a substantial component |
| Moisture | Controlled according to supply and equipment requirements | Often requires dehumidification |
| Potential contaminants | Depends on source and gas processing | May include hydrogen sulfide, siloxanes, and other contaminants |
| Fuel preparation | Typically pressure regulation and filtration as specified | May require dewatering, filtration, sulfur removal, and additional treatment |
Raw biogas should not be confused with renewable natural gas (RNG), also called biomethane. RNG has been upgraded to remove much of the carbon dioxide, moisture, and other contaminants, making it suitable for applications that require pipeline-quality gas when the relevant specification is met.
2. Why Does Biogas Require Different Engine and Fuel-System Considerations?
Gas engines require fuel with suitable heating value, pressure, combustion characteristics, and contaminant levels. Raw biogas often has a lower energy content per unit volume than natural gas, so the engine may need a greater volumetric fuel flow to deliver comparable electrical output.
Three fuel properties are particularly important:
- Methane content and heating value: These determine how much usable energy is available in each unit of gas.
- Gas pressure and flow: The fuel system must supply the required volume at the engine's specified inlet pressure, including during load changes.
- Contaminant concentration: Moisture, sulfur compounds, siloxanes, and particulates can affect combustion, corrosion, deposits, and component life.
Carbon dioxide dilutes the combustible portion of raw biogas and lowers its heating value per unit volume. The engine and control system must therefore be compatible with the actual fuel specification rather than assuming the same gas consumption and output as a natural gas installation.
Some engines can be configured for different gaseous fuels, but that does not establish universal compatibility. The manufacturer must confirm acceptable fuel composition, pressure, heating value, and maximum contaminant levels for the specific engine model.
3. What Biogas Treatment Is Needed Before Power Generation?
Biogas treatment removes contaminants that could damage the engine or prevent stable operation. The required treatment train depends on the gas source, measured composition, engine specifications, and local environmental requirements.
| Contaminant or condition | Potential problem | Common control approach |
|---|---|---|
| Excess moisture | Condensation, corrosion, and operating problems | Cooling, condensate separation, and dehumidification |
| Hydrogen sulfide (H₂S) | Corrosion and sulfur-related emissions | Suitable biological, chemical, or adsorption-based removal |
| Siloxanes | Hard silica deposits on combustion and exhaust surfaces | Adsorption or other treatment selected for the gas composition |
| Particulates | Abrasion, blockage, and equipment wear | Appropriate filtration |
| Excess carbon dioxide | Lower fuel heating value and increased volumetric demand | Fuel-compatible engine selection or gas upgrading where justified |
Hydrogen sulfide is especially important because sulfur compounds can contribute to corrosion and damage exhaust aftertreatment systems. Siloxanes, which may occur in landfill and wastewater-treatment gas, can form hard deposits when combusted.
The U.S. EPA describes moisture removal and contaminant reduction as key steps in preparing biogas for specific energy applications. Its anaerobic system design guidance discusses biogas handling, treatment, and electricity generation.
Gas treatment should be designed using laboratory analysis of the actual gas. Assuming that every digester or landfill produces the same fuel can result in unsuitable filters, inadequate sulfur removal, or unnecessary treatment equipment.
4. Which Generator Is Better for Industrial Applications?
The better option depends on fuel availability, required output, operating hours, gas quality, and the cost of preparing and delivering the fuel. Natural gas is often practical where a reliable pipeline supply already exists, while biogas can be attractive when an industrial facility or waste-treatment operation produces a usable gas stream.
| Application condition | Potentially suitable option | Important consideration |
|---|---|---|
| Factory with reliable pipeline gas | Natural gas generator | Gas tariff, pressure, and required electrical output |
| Farm with anaerobic digestion | Biogas-compatible generator | Seasonal gas production and contaminant control |
| Wastewater treatment plant | Biogas generator or suitable upgraded-gas system | H₂S, moisture, siloxanes, and gas-production variability |
| Landfill energy project | Generator designed for landfill gas | Gas composition, contaminants, and changing methane levels |
| Facility with upgraded biomethane | Potentially a compatible natural gas generator | Confirm that the upgraded gas meets the engine's fuel specification |
Biogas can reduce reliance on purchased fossil fuel when a dependable on-site supply exists. However, the project must account for digesters or gas collection, gas treatment, compression where needed, storage or buffering, and additional maintenance.
Natural gas systems may have simpler fuel handling where pipeline infrastructure is available, but they remain exposed to utility tariffs and supply interruptions. Neither fuel is automatically cheaper: the comparison must include the complete fuel system and the expected net electricity generated.
5. How to Evaluate Engine Compatibility and Long-Term Maintenance
Before selecting equipment, compare the measured gas specification with the engine manufacturer's documented fuel limits. The evaluation should cover methane content, heating value, gas pressure, moisture, hydrogen sulfide, siloxanes, and other relevant contaminants.
Use this checklist when assessing a proposed installation:
- Obtain a representative gas analysis, including expected variation over time.
- Confirm the engine's permitted fuel composition and heating-value range.
- Verify the required gas flow and inlet pressure at full output.
- Specify treatment equipment for measured contaminants, not assumed averages.
- Check whether the engine requires a dedicated biogas configuration or approved modification.
- Review oil analysis, filter replacement, inspection, and overhaul requirements.
- Confirm emissions compliance, installation safety, and local permitting requirements.
Biogas installations may need more frequent inspections or additional treatment maintenance when contaminants are present. Actual service intervals depend on fuel quality, engine design, operating hours, and manufacturer requirements.
For projects considering natural gas generator sets, request confirmation of the approved fuel specification before assuming a model can operate on raw biogas. If biogas use is intended, the engine, controls, gas train, and treatment system should be evaluated as one integrated installation.
Conclusion
Natural gas and biogas generators can both produce electricity, but their fuel characteristics and preparation requirements differ. Natural gas generally offers a more standardized supply, while raw biogas requires careful analysis and may need substantial conditioning before it can be used reliably in an engine.
The most important selection step is to match the generator to the actual fuel specification and operating profile. With suitable treatment and a compatible engine, biogas can support useful on-site energy recovery; without those controls, contaminants and unstable fuel quality can increase maintenance and reduce reliability.
Frequently Asked Questions
Can a natural gas generator run on biogas?
Not automatically. The engine manufacturer must approve the fuel composition, heating value, pressure, and contaminant levels. Raw biogas may require treatment or a generator specifically configured for biogas.
Why does a biogas generator need gas cleaning?
Raw biogas may contain moisture, hydrogen sulfide, siloxanes, and particulates. These contaminants can cause corrosion, hard deposits, abrasion, or equipment damage unless controlled to the engine's specified limits.
Is biogas less energy-dense than natural gas?
Raw biogas generally has a lower heating value per unit volume because it contains substantial carbon dioxide and often less methane. The actual value depends on its composition and must be measured or specified.
Is biogas electricity cheaper than natural gas electricity?
It can be when the biogas is available at low cost and treatment requirements are manageable. The comparison must include gas collection, treatment, compression, maintenance, generator efficiency, and the net electricity produced.
What is the difference between biogas and renewable natural gas?
Biogas is the gas produced from organic material and commonly contains methane, carbon dioxide, and impurities. Renewable natural gas is upgraded biogas processed to meet a defined fuel specification for applications such as pipeline injection or compatible gas equipment.
Reference Sources
- U.S. Energy Information Administration — Landfill Gas and Biogas. Explains biogas composition, methane content, and the role of gas upgrading.
- U.S. EPA — Anaerobic System Design and Technology. Covers biogas handling, moisture and contaminant control, and energy applications.
- U.S. EPA — Renewable Natural Gas. Describes raw biogas treatment and upgrading for use as a natural-gas substitute.
Technical note: Fuel limits, treatment requirements, emissions performance, and maintenance intervals vary by engine and gas source. Confirm the actual gas analysis and obtain written compatibility data from the generator manufacturer before finalizing the system design.
