Gazociągi Morza Północnego

European position

European Commission Directives 98/30/EC and 2003/55/EC aim to create a fully operational internal natural gas market with common rules for transmission, distribution, supply, and storage of natural gas. The differences in gas-quality specifications across EU member states have been a barrier to cross-border trade.

The European Union Gas Regulatory Forum (Madrid Forum) consists of representatives of member states, national regulatory authorities, gas industry operators and suppliers, large industrial gas consumers, traders, and producers. In 2002, the forum established EASEE-gas (European Association for the Streamlining of Energy Exchange), with a group objective of giving all participants in the gas chain a forum voluntarily to agree on a set of common business practices. One part of this has been to establish such a practice for harmonization of natural gas quality. The EASEE-gas specification for gas quality includes a proposed Wobbe range of 13.60 kw-hr/std, cu m to15.81 kw-hr/std. cu m (47.0 MJ/cu m to 54 MJ/cu m).

Different parameters in EC
Many parameters are in use worldwide to represent gas interchangeability. In many cases, including Europe, more than one factor may be used to set maximum and minimum thresholds that form an envelope of acceptable operation for downstream plant and equipment. A selection of the following factors is typically used:

-Heating value or calorific value.
-Wobbe Number or Wobbe Index.
-Relative density or specific gravity.
-Weaver indices.
-AGA indices.
-Incomplete combustion factor.
-Lift index.
-Soot index.
UK position
The UK gas specification is set by Gas Safety (Management) Regulations, which use the Wobbe Index as the main parameter of interchangeability. The GSMR set the limits of Wobbe at between 47.20 MJ/cu m and 51.41 MJ/cu m. This is a narrower band of acceptable Wobbe, however, than many other countries specify, including those in mainland Europe.

QUALITY CERTIFICATE

1. Natural gas in delivery point shall correspond to the following
specification
Chemical mixture of natural gas
Methane (C,)
Ethane (C2)
Propane (C3), Butane (C4) and
Heavier hydrocarbons
Nitrogen (N2)
Carbon Dioxide (CO2)
Content of Sulphur
Hydrogen Sulfide (H2S)
Mercaptan
Total Sulfur
(m mol percent)
92min
4max
2max
2max
1max
2.0mg Nm3 max
5.6 mg/NmJ max
no more than 20 mg Nmj
2. Natural gas shall not contain mechanical additives, gum, gum formers
3. Due-point on water at P 40 kg/cm2 in winter, not more than -8 C° in
summer not more than 0 C°
4. Net heating value at T 20 C at abs pressure 1.033227 kg/cm2: 8000
kcal/Nm3 +/- 100 kcal/Nm3.
5. Pressure at delivery point: 48.0 +/- 1 bar