Natural Gas

Overview

Natural gas is a fossil fuel composed primarily of methane (CH₄) with smaller amounts of heavier hydrocarbons, carbon dioxide, nitrogen, and trace sulfur compounds. It is widely used for heating, power generation, and industrial processes due to its high energy density per unit mass and relatively clean combustion compared to coal or oil.

Pipeline-quality natural gas typically contains 85–98 % methane by volume and has a specific gravity of 0.58–0.72 relative to dry air. Its Lower Heating Value (LHV) ranges roughly from 34–40 MJ/m³ depending on composition and measurement conditions.

Original Glossary Scope

The source page is titled Natural Gas Glossary and describes natural gas as a fuel used extensively in residential, commercial, and industrial applications. It functions primarily as a glossary/search entry page and points readers to an external natural gas glossary from the American Gas Association. The engineering reference sections below preserve that source scope while adding the calculation context needed for design and combustion work.

Original source text preserved: "Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!" Original glossary paragraph preserved: "A natural gas glossary with search terms." External glossary link preserved: American Gas Association Natural Gas Glossary.

Key Formulas

Heat Release Rate

$Q = \dot{m} \cdot LHV$

Where $\dot{m}$ is the fuel mass flow rate and LHV is the lower heating value on a mass basis.

Volumetric Heat Release

$Q_v = \dot{V} \cdot HI_v$

Where $\dot{V}$ is the volumetric flow rate and $HI_v$ is the heating intensity per unit volume at standard conditions.

Stoichiometric Air-Fuel Ratio

$AF_{stoich} = \frac{m_{air}}{m_{fuel}}$

For pure methane the stoichiometric air-fuel ratio by mass is approximately 17.2:1.

Excess Air from Flue Gas Oxygen

$EA = \frac{O_{2,\,flue}}{21 - O_{2,\,flue}} \times 100\%$

A common field method for estimating excess air from a dry flue gas oxygen measurement.

Wobbe Index

$WI = \frac{HI_v}{\sqrt{SG}}$

Gases with equal Wobbe indices can be interchanged in a burner without changing the heat input rate.

Variables

Typical Composition

Combustion Properties of Key Components

Heat Release Calculator

Unit Converter

Restored Original Source Tables

The following tables are restored from the original source page to preserve the complete reference data.

The cached original page contained a search/navigation table because the source is primarily a glossary/search entry. The engineering content from that table is the external American Gas Association glossary link and the "A natural gas glossary with search terms" description, both preserved in the Original Glossary Scope section above. Non-engineering search controls are recorded below.

Engineering Notes

• Heating value basis matters. HHV includes the latent heat of water vapour in combustion products; LHV excludes it. Boiler efficiency calculations in North America often use HHV, while European practice commonly uses LHV. Mixing conventions leads to efficiency figures above 100 % for condensing boilers.
• Moisture and altitude. Reported heating values are for dry gas at standard conditions (typically 15 °C or 20 °C, 1 atm). Real supply varies with water vapour content, barometric pressure, and ambient temperature.
• Specific gravity and metering. Orifice and turbine meters are sensitive to gas density. Uncorrected readings can drift 5–10 % if actual specific gravity differs from the assumed value.
• Excess air control. Natural gas burners are typically tuned to 3–15 % excess air (1–3 % O₂ in flue gas). Too little excess air risks incomplete combustion and CO formation; too much penalizes efficiency and increases NOₓ.
• Wobbe Index tolerance. Many burner specifications accept a Wobbe Index variation of ±5 % without retuning. Pipeline operators monitor this parameter to ensure appliance compatibility across supply sources.
• Hydrogen blending. Blending up to 10–20 % hydrogen by volume into natural gas pipelines is under active study. The lower volumetric heating value and wider flammability range of hydrogen require careful burner and safety assessment.
• Supercompressibility (Z-factor). At pressures above roughly 10 bar the ideal gas law introduces errors of several percent. The Z-factor corrects for intermolecular forces; it is computed from equations of state such as AGA 8 or GERG-2008.

References

• Engineering ToolBox — Natural Gas
• NFPA 54 / ANSI Z223.1, National Fuel Gas Code
• ISO 6976, Calorific values, density, relative density and Wobbe index