Industrial Engineer Gas key terms

The exact quantity of air that supplies just enough oxygen to burn all the fuel completely, with no oxygen left over and no unburned fuel remaining. It is the reference point for calculating excess air.

Air supplied beyond the stoichiometric amount to ensure complete combustion and compensate for imperfect mixing. It is measured as a percentage above the theoretical requirement and directly affects flue losses and efficiency.

The heat released by burning a fuel when the water vapour formed stays in the vapour state, so its latent heat is not recovered. It is the basis for most gas appliance efficiency and rating calculations.

The total heat released by combustion when the water vapour produced is condensed and its latent heat is recovered. It is numerically larger than the lower heating value and is used for condensing appliance ratings.

A measure of the heat input delivered through a fixed orifice at constant pressure, calculated from the heating value divided by the square root of relative density. It lets appliances be grouped by gas interchangeability.

A condition where flame detaches from the burner port and rises, often caused by excessive gas velocity or too little primary aeration. It risks flame extinction, unstable ignition, and release of unburned gas.

A condition where flame travels back into the burner or mixing tube because the burning velocity exceeds the gas-air mixture velocity. It can damage the burner and create unsafe combustion inside the appliance.

The air mixed with gas before it reaches the burner ports, forming the combustible mixture at the flame base. Correct primary air produces a stable blue cone and limits carbon monoxide formation.

Air drawn from the appliance surroundings into the flame after the gas leaves the burner, completing combustion. Inadequate secondary air causes incomplete burning, soot, and carbon monoxide.

Measurement of oxygen, carbon dioxide, carbon monoxide, and temperature in combustion products to assess air-fuel ratio and combustion quality. Results guide burner adjustment and confirm safe, efficient operation.

A rating of a gaseous fuel's resistance to knock in spark-ignition engines, analogous to octane number for liquid fuels. It is relevant for gas-fuelled compressors and engine-driven equipment.

The ability of an appliance to operate safely and satisfactorily on a gas different from the one it was adjusted for. It depends mainly on Wobbe index, flame speed, and combustion characteristics.

An installation that reduces incoming gas pressure to a controlled downstream level and holds it within limits despite flow changes. It includes filters, regulators, safety devices, and monitoring instrumentation.

A pressure regulator installed on a distribution main or service to reduce transmission pressure to distribution pressure. It may be direct- or pilot-operated and is normally protected against overpressure.

An emergency shut-off device that closes rapidly when downstream pressure exceeds or falls below set limits. It protects the distribution system from overpressure and loss of supply.

The deliberate addition of a warning odorant, typically a sulfur compound, to gas so leaks can be detected by smell. Odorant injection is monitored and tested at points throughout the system.

The use of a device called a pig that travels through a pipeline to clean it, separate products, or inspect its internal condition. Intelligent pigs carry sensors for wall-thickness and defect measurement.

A technique that applies a small electrical current or sacrificial anodes to buried steel pipe so it becomes the cathode and does not corrode. It is verified through potential surveys and test stations.

The condition of a pipeline being fit for safe service, maintained through inspection, defect assessment, pressure testing, and corrosion control. It is documented in an integrity management programme.

A controlled pressurization of pipework or equipment, usually with air, nitrogen, or water, to prove strength and leak-tightness before commissioning. Test pressure, duration, and acceptance criteria follow the applicable code.

Displacing air or gas from pipework with an inert gas or the fuel gas itself before commissioning or maintenance. Correct purging prevents explosive mixtures and ensures the appliance receives the right gas.

Use of fixed or portable instruments to sense flammable or toxic gas concentrations and trigger alarms or shutdown. Detectors are calibrated and placed according to the properties of the gas handled.

The minimum concentration of gas in air that will support combustion when ignited. Below this limit the mixture is too lean to burn, and instruments commonly alarm at a fraction of it.

The maximum concentration of gas in air that will support combustion when ignited. Above this limit the mixture is too rich to burn, but dilution can bring it back into the flammable range.

A permanently open passage that supplies outdoor air to an appliance room or enclosure for burning fuel. Its size depends on appliance input, grille free area, and whether air is taken from inside or outside.

A room or enclosure with limited volume and restricted ventilation where gas appliances are installed. Codes require specific combustion and ventilation air provisions for such spaces.

Air admitted to an appliance draft hood or flue system to mix with combustion products and reduce their temperature. It affects draft stability and the required flue size.

A device fitted at the flue outlet of an appliance that admits dilution air and breaks the effect of stack pressure on combustion. It helps maintain stable draft and prevents backdrafting into the space.

Escape of combustion products from the appliance draft hood or flue into the room instead of up the chimney. It indicates inadequate draft and is a serious carbon monoxide hazard.

A colourless, odourless, toxic gas formed by incomplete combustion. It binds to haemoglobin and can cause illness or death, so appliances must be adjusted and vented to keep levels low.

A boiler designed to cool flue products enough to condense water vapour and recover latent heat. It achieves higher efficiency than non-condensing designs and needs a suitable condensate drain.

The proportion of fuel heat released that is usefully transferred to the load, after subtracting flue and casing losses. It is estimated from flue temperature and oxygen or carbon dioxide readings.

The ratio of average load over a period to the peak load in that period. It guides sizing of mains, storage, and equipment because it shows how fully capacity is used.

The ratio of the sum of individual maximum demands to the maximum demand of the whole system. It recognises that not all connected appliances operate at full load at the same time.

The highest gas flow rate required by a system or customer over a defined period. It determines pipe size, meter capacity, and regulator sizing and is used in network planning.

A procedure that isolates energy sources, applies locks and tags, and verifies zero energy before work begins. It prevents accidental start-up or release of gas during maintenance and repair.

A formal written authorisation that defines the task, hazards, controls, and validity period before hazardous work starts. It coordinates isolation, gas testing, and fire watch for hot work or confined-space entry.

The structured process of proving that installed gas equipment is safe, correctly adjusted, and performing to design before handover. It includes pressure testing, purging, combustion checks, and documentation.