Testing - gases

Natural gas is a gaseous fuel obtained from underground sources, consisting of a mixture of hydrocarbons, mainly methane. The mixture also contains ethane, propane and other higher hydrocarbons, but in significantly lower amounts. 

Natural gas can be liquefied (LNG – liquified natural gas) for storage or transport, or compressed (CNG – compressed natural gas) as a fuel for motor vehicles. Natural gas can also be produced or blended, and in such a case is called substitute natural gas (or synthetic natural gas) and must have characteristics that allow it to replace natural gas. Gases produced from biomass through thermal treatment are also considered substitute natural gas.

It is possible to check various parameters of natural gas based on purpose or use. The natural gas parameters that can be checked are the following:

Gas composition

• The content of the main components (methane, ethane, propane, butanes, pentanes, hexanes and above, nitrogen and carbon dioxide)
• The content of secondary components (hydrogen, oxygen, carbon monoxide, helium)
• The content of trace components (sulphate, mercaptan sulphur, dialkyl-(di)-sulphide, carbonyl sulphide, total sulphur content, mercury)

Gas physical properties

• The energy content on a molar, mass or volume basis*
• Density, relative density
• Wobbe number**
• Compressibility factor
• Methane number
• Water dew point
• Water content
• Hydrocarbon dew point

*The energy content is split into two types: heat of combustion and calorific value.

Heat of combustion is the quantity of heat released through the complete combustion of 1 m³ of natural gas at a pressure of 101 325 Pa under adiabatic conditions provided that the combustion products are cooled to the temperature of the initial substances and the water vapour contained in the combustion products condenses to a liquid state.

The calorific value differs from the heat of combustion in that the water vapour remains in a gaseous state after combustion.

**The Wobbe number is the basic criterion for the interchangeability of types of natural gas and expresses the condition of maintaining the thermal input of an appliance when the combustion properties of natural gas are changed.

Other properties

• The content of water and hydrocarbons in the liquid state
• Solid particles
• Other gases

These substances are not usually contained in natural gas in quantities that would negatively influence the transport, distribution or use of the natural gas.

LPG (Liquified Petroleum Gas) is a mixture of hydrocarbon gases (propane, butane and others) used as a fuel in combustion appliances and vehicles.

The quality requirements for LPG use in motor vehicles are determined by the ČSN EN 589 + A1 standard.

Controlled parameters:

• Motor octane number (MON)
• Total diene content (including 1,3-butadiene)
• Hydrogen sulphide
• Total sulphur content (after odorization)
• Copper strip corrosion (1 h at 40°C)
• Residue after evaporation
• Vapour pressure, manometric, at 40°C
• Vapour pressure, manometric, min. 150 kPa, at a temperature according to classes A to E
• Water content
• Odour
• Density

The quality requirements for liquefied petroleum gases (propane, butane and their mixtures primarily intended for heating) are determined by the ČSN 65 6481 Opr.1. standard.

Quality requirements for propane:

• Hydrocarbon composition
  • C2 hydrocarbons and inerts
  • C3 hydrocarbons
  • C4 hydrocarbons
  • C5 and higher hydrocarbons
  • unsaturated hydrocarbons
• Total sulphur content
• Ammonia content
• Oily residue
• Hydrogen sulphide content

Quality requirements for propane-butane:

• Hydrocarbon composition
  • C2 hydrocarbons and inerts
  • C3 hydrocarbons
  • C4 hydrocarbons
  • C5 and higher hydrocarbons
  • unsaturated hydrocarbons
• Total sulphur content
• Ammonia content
• Oily residue
• Hydrogen sulphide content
• Water content

Quality requirements for butane:

• Hydrocarbon composition
  • C2 hydrocarbons and inerts
  • C3 hydrocarbons
  • C4 hydrocarbons
  • C5 and higher hydrocarbons
  • unsaturated hydrocarbons
• Total sulphur content
• Ammonia content
• Oily residue
• Hydrogen sulphide content

Quality requirements for industrial heating mixtures:

• Hydrocarbon composition
  • C2 hydrocarbons and inerts
  • C3 hydrocarbons
  • C4 hydrocarbons
  • C5 and higher hydrocarbons
  • unsaturated hydrocarbons
• Total sulphur content

Analysis of biomethane according to Decree No. 108/2011 Coll., Annex No. 5, paragraph 3; Composition of gaseous fuels - requirements for the qualitative parameters of biomethane