Industrial Engineer Gas flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Stoichiometric air for methane

About 9.52 m³ of air per m³ of methane at standard conditions, because 1 m³ CH4 needs 2 m³ O2 and air is 21 % oxygen.

Wobbe index

The calorific value divided by the square root of relative density. It characterises the heat input delivered through a fixed orifice at fixed pressure.

Methane flammability limits

Roughly 5 % to 15 % methane by volume in air. Below the lower limit the mixture is too lean to ignite; above the upper limit it is too rich.

HHV versus LHV

HHV includes the latent heat recovered from condensing water vapour in the products; LHV excludes it. Natural gas HHV is about 11 % higher than LHV.

CO/CO2 ratio

A combustion quality indicator. For natural gas a ratio below 0.004 indicates clean combustion; higher values suggest incomplete combustion and carbon monoxide formation.

Relative density of natural gas

About 0.6 compared with air, so natural gas rises and collects at high points, unlike LPG vapour which is heavier than air and settles low.

MOP and MAOP

Maximum operating pressure is the pressure at which a system may normally operate; maximum allowable operating pressure is the design limit set by the weakest component rating.

Monitor regulator function

A second regulator in series that takes over if the active regulator fails, limiting downstream pressure to a safe value and protecting connected equipment and pipework.

Purge volume rule

Displacing air from gas pipework typically requires two to five pipe volumes of gas, confirmed by measuring gas concentration at the purge outlet.

Odorisation target

Gas must be odorised so it is detectable at about one fifth of the lower explosive limit, commonly achieved with tetrahydrothiophene at 10–20 mg/m³.

Type C appliance

A room-sealed appliance that takes combustion air from outside and discharges products outside through a balanced flue, so it is independent of room air.

Flame rectification sensing

A flame ionises gas and conducts a small current between electrode and burner. Loss of flame breaks the circuit and the control shuts the gas valve.

Gas valve class A

A multiblock valve class with the tightest closing requirement, used where downstream leakage is critical or appliance input exceeds about 120 kW.

Appliance turndown ratio

Maximum rated input divided by minimum stable input. Higher turndown improves part-load efficiency but can destabilise the flame and raise carbon monoxide.

Combustion air free area

Open-flue appliances typically need about 5 cm² of permanent free ventilation per kW of input, measured as free area rather than grille dimensions.

Draught diverter spillage

Smoke or products escaping at the diverter indicates blocked flue, inadequate combustion air, or adverse pressure, and the appliance must be shut down.

Balanced flue terminal clearance

Terminals must be kept clear of openings, boundaries, and mechanical extractor terminals, typically at least 300 mm from an extractor, to prevent recirculation of products.

Condensing flue materials

When flue gas falls below its dew point, the flue must resist acidic condensate; stainless steel or polypropylene is used instead of conventional mild steel.

Gas family definition

IEC/EN 437 groups gases into families and test gases. Approval applies only to the family and pressure declared on the appliance data plate.

EN 1775 scope

The European standard for gas pipework installations in buildings, covering design, materials, installation, testing, and commissioning up to specified pressure limits.

ATEX zoning

Hazardous areas are classified into zones by the frequency and duration of explosive gas atmospheres, which determines the permitted electrical equipment category.

Manufacturer instructions status

They form part of the compliance basis for installation and maintenance; any deviation needs an engineering assessment and a written record.

Tightness test procedure

Pressurise with air or inert gas, allow temperature stabilisation, then measure pressure drop over a defined period against the permitted allowance for the pipe volume.

Gas detection alarm settings

Typical settings are 10 % of the lower explosive limit for warning and 20 % for action or automatic shutdown, with calibration checked periodically.

Hot work permit controls

Requires gas-free certification, continuous gas monitoring, fire watch during work and a defined period after, and isolation of the gas system.

Strength versus tightness test

The strength test runs at a higher pressure, typically 1.5 times design, to prove integrity; the tightness test follows at operating pressure to prove no leakage.

Excess air from oxygen

For natural gas, about 5 % oxygen in flue gas corresponds to roughly 30 % excess air; the relationship is used to set burner air during commissioning.

Gas rate check

Timing a known volume on the meter confirms rated input. A deviation beyond about 5 % from the data plate points to pressure, orifice, or calorific value issues.

Regulator lock-up pressure

The downstream pressure reached at zero flow when the regulator seat closes. A rising lock-up pressure indicates seat leakage and requires servicing.

MTBF and availability

MTBF is operating time divided by failure count. Availability is MTBF divided by MTBF plus mean time to repair, used to prioritise maintenance and spares.

Simple payback

Capital cost divided by annual savings. It ignores the time value of money, so it is used with net present value for project decisions.

Degree-day load analysis

In heating-dominated buildings, gas consumption is proportional to heating degree days; deviations from the trend reveal control faults or envelope problems.