Quality of gas

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The quality specifications of the gas introduced into the Gas System are set out in the Detailed Protocol 01 "Measurement, Quality and  Odorization of gas" according to the Resolution of 22nd September 2011 which modifies the detailed protocol mentioneda above.

Capacities are expressed under the reference conditions [ GCV at 0ºC; V (0ºC, 1.01325 bar)]. According to Annex J of ISO 6976 the factor applied for converting GCV from 0ºC to 25ºC shall be 1 / 1.0026.

The following table lists the quality specifications established in the detailed protocol that are to be met by any gas introduced in the gas system's entry points must meet are set out in the following table.


Property Unit Minimum Maximum
Wobbe index KWh/m3 13.403 16.058
GCV kWh/m3 10.26 13.26
Relative Density m3/m3 0.555 0.700
S Total mg/m3 - 50
H2S + COS (as S) mg/m3 - 15
RSH (as S) mg/m3 - 17
O2 mol% - 0.01
CO2 mol% - 2.5
H2O (dew point) ºC at 70 bar (a) - +2
HC (dew point) ºC at 1-70 bar (a) - +5
Dust/ particles - Technically pure Technically pure

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In addition to the features shown above, the gas from unconventional sources, such as biogas, gas from biomass or other types of gas produced by microbial digestion processes must comply with the quality specifications in the following table.


Property Unit Minimum Maximum
Methane (CH4) mol % 95 -
CO mol % - 2
H2 mol % - 5
Halogenated compounds: Fluoride/ Chlorine mg/m3 - 10/1
Ammonia mg/m3 - 3
Mercury mg/m3 - 1
Siloxanes mg/m3 - 10
Benzene, Toluene, Xylene (BTX) mg/m3 - 500
Micro-organisms - Technically pure  
Dust/ particles - Technically pure  

In the case of biogas, biogas injection will be accepted in the network with a content of O2 of up to 0.3 mol % provided that the following conditions are met simultaneously at the injection site:

  • 1. The CO2 content must not exceed 2% mol at any time.
  • 2. The dew point of water should not exceed minus eight degrees Celsius (- 8 ° C) at any time.
  • 3. The injection volume of biogas in the trunk transport network must never exceed 5,000 m3/h (in reference conditions). For greater volumes and in any case for other entry points to the gas system, the maximum injection volume of biogas will be determined by the network owner in each specific case depending on the quality and volume of gas transported from the network to which it is connected, and shall be communicated to the Directorate General for Energy Policy and Mines, to the Technical System Manager and the National Commission of Markets and Competition.