天然气

概述

天然气是一种主要由甲烷 (CH₄) 组成的化石燃料，含有少量较重的烃类、二氧化碳、氮气和微量硫化合物。由于单位质量能量密度高，且与煤或油相比燃烧相对清洁，它广泛用于供暖、发电和工业过程。

管道品质的天然气通常按体积含有 85–98% 的甲烷，相对于干空气的比重为 0.58–0.72。其低热值 (LHV) 大致范围为 34–40 MJ/m³，取决于成分和测量条件。

原始词汇表范围

来源页面标题为天然气词汇表，将天然气描述为广泛用于住宅、商业和工业应用的燃料。它主要作为词汇表/搜索入口页面，并引导读者查阅美国天然气协会的外部天然气词汇表。下方的工程参考部分保留了该来源范围，同时添加了设计和燃烧工作所需的计算上下文。

保留原始来源文本："Engineering ToolBox — 工程技术应用的设计与工程资源、工具和基础信息！"保留原始词汇表段落："带搜索词条的天然气词汇表。"保留外部词汇表链接：美国天然气协会天然气词汇表。

关键公式

热释放速率

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

其中 $\dot{m}$ 为燃料质量流量，LHV 为按质量计算的低热值。

体积热释放

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

其中 $\dot{V}$ 为体积流量，$HI_v$ 为标准条件下每单位体积的热强度。

化学计量空燃比

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

对于纯甲烷，按质量计的化学计量空燃比约为 17.2:1。

由烟气氧含量计算过量空气

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

从干烟气氧含量测量估算过量空气的常用现场方法。

沃泊指数

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

具有相同沃泊指数的气体可以在燃烧器中互换，而不改变热输入速率。

变量

典型成分

Combustion Properties of Key Components

Heat Release Calculator

单位换算器

还原的原始源表

以下表格还原自原始来源页面，以保留完整的参考数据。

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.

工程要点

• 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.

参考资料

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