Gas Detector Knowledge Gas Awareness: General Combustible Gases

[Gas]
Gas refers to a range of gaseous fuels that are used for heating and energy production. These include natural gas, artificial gas, liquefied petroleum gas (LPG), and biogas. Each type has distinct properties and applications, depending on its source and composition.
[Types of Gas]
Gas: A mixture of various gases such as methane, ethane, propane, butane, hydrogen, and carbon monoxide, along with impurities like sulfur compounds, water vapor, and tar. The exact composition varies based on the production method. Oil Gas: Produced from heavy oil or naphtha through cracking processes in industrial furnaces. By-products may include crude benzene and alkali slag. Gasification Gas: Generated by burning coal or coke in a furnace while introducing air and steam. The main components are carbon monoxide and hydrogen. Retorted Gas: Created by heating coal in an oven without oxygen, leading to dry distillation. This process yields flammable gases, as well as chemical products like tar and ammonia. Biogas: Formed through anaerobic digestion of organic materials. It mainly contains methane and carbon dioxide, with a calorific value of approximately 22 MJ/Nm³. Liquefied Petroleum Gas (LPG): Derived from refining crude oil or processing natural gas. Its main components are propane and butane, with a high calorific value—around 93 MJ/Nm³ when gaseous and 46 MJ/Nm³ when liquid. Pure Natural Gas: Found underground and extracted directly, typically consisting mostly of methane. LNG (Liquefied Natural Gas): Natural gas cooled to -160°C, turning it into a liquid form for easier transport via specialized ships and vehicles. Compressed Natural Gas (CNG): Natural gas compressed to 200 kg/cm², reducing its volume significantly for use in vehicles. It is clean, efficient, and suitable for short-distance transportation. Condensate Gas: Contains light hydrocarbons and is often processed for easier transport. CBM (Coal Bed Methane): Methane extracted from coal seams, serving as an alternative energy source. Mine Gas: Collected during coal mining operations, often containing methane. Petroleum Associated Gas: Released alongside oil during extraction, this gas can be used as fuel or processed further. [Basic Characteristics of Gas]
Density: Measured as weight per unit volume. For example, LPG has a density of 2.0–2.5 kg/Nm³. Calorific Value: Refers to the heat released during combustion. It is divided into high calorific value (includes heat from condensing water vapor) and low calorific value (does not). Theoretical Air Volume: The minimum amount of air required for complete combustion. LPG requires three times more air than natural gas, and six times more than artificial gas. Expansion and Compression: Liquid LPG expands rapidly when heated, increasing pressure inside containers. Its expansion coefficient is about 16 times that of water. Saturated Vapor Pressure: The pressure exerted by a liquid's vapor in equilibrium at a given temperature. It depends on the gas composition and temperature. Latent Heat of Vaporization: The heat required to turn a liquid into vapor. LPG absorbs heat during evaporation, which can affect its performance in cold conditions. Pressure Classification: Includes gauge pressure (relative), absolute pressure (actual), and vacuum (negative pressure). Fire Temperature: The minimum temperature at which a gas will ignite. LPG ignites between 365–460°C, lower than other fuels, making it highly flammable. Explosion Limit: The concentration range of gas in air that can explode when exposed to fire. It includes both lower and upper limits. Combustion: Requires three elements: fuel, oxygen, and an ignition source. The heat released from combustion is called the calorific value, measured in KJ/m³ or kcal/m³. [Common Gas Introduction]
Natural Gas: Colorless, odorless, non-toxic, and primarily composed of methane. It can be found in gas fields, associated with oil, or extracted from coal seams. Liquefied Natural Gas (LNG): Natural gas cooled to -162°C, making it easier to transport. It occupies about 1/600th the volume of its gaseous form. Compressed Natural Gas (CNG): Stored under high pressure, it is widely used in vehicles due to its environmental benefits and cost-effectiveness. Liquefied Petroleum Gas (LPG): A byproduct of petroleum refining, mainly composed of propane and butane. Used in cooking, heating, and vehicle fuel. [City Gas]
City gas includes natural gas, artificial gas, and LPG. Natural gas is often compressed or liquefied for transport. Artificial gas is produced from coal or oil, while LPG is derived from refining processes. All are used for residential and industrial purposes. Artificial Gas: Made from coal or heavy oil through processes like dry distillation, gasification, and cracking. It provides an alternative to natural gas in certain regions. Liquefied Petroleum Gas (LPG): Widely used in homes and industries. It can also be blended with air to mimic natural gas properties for easier integration into existing systems. Alternative Natural Gas: LPG can be modified to function similarly to natural gas, allowing it to be used in existing infrastructure without requiring major upgrades.