Natural gas quality
The Energy Act (the Official Gazette 68/01, 177/04, 76/07, 152/08, 127/10) and General conditions for the natural gas supply – Appendix 1 (the Official Gazette 43/2009) proposes the standard natural gas quality..
Based on the natural gas samples taken from the measuring-reduction stations (MRS) by the authorized laboratory, the distribution system operator delivers twice a month the reports on the gas quality analysis to the natural gas suppliers.
Natural or terrestrial gas is a fossil fuel consisting of methane (CH4) (volume fraction 85% - 95%), complex hydrocarbons of ethane (C2H6) and propane (C3H8), as well as nitrogen (N2) and carbon dioxide, with the volume fraction from 5% to 15%. Gas is without odour and taste; it is very flammable and explosive.
Standard natural gas quality is regulated by the General conditions for the natural gas supply (the Official Gazette 43/09), as well as with the article Contractual conditions for the natural gas supply and delivery. All values apply for the gas volume of 1 m3 in standard state where the absolute gas pressure amounts 101.325 Pa (1.01325 bar) and gas temperature is 288.15 K (15°C).
Natural gas delivered to the Buyer is the mixture of the natural gas produced in the Republic of Croatia and imported gas. Its quality and heating value are defined in the table below.
|
NATURAL GAS |
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|
|
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A. Chemical structure (volume fraction, %): |
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|
|
Methane (CH4) |
minimal |
85 |
% |
|
Ethane (C2H6) |
maximal |
7 |
% |
|
Propane (C3H8) and other hydrocarbons |
maximal |
6 |
% |
|
Nitrogen (N2), carbon dioxide (CO2) and other inert gases |
maximal |
7 |
% |
|
B. Sulphur content: |
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|
|
|
Hydrogen sulphide (H2S)) |
maximal |
7,0 |
mg/m3 |
|
Sulphur total (S2) |
maximal |
100,0 |
mg/m3 |
|
C. Upper calorific value Hg |
|
|
|
|
minimal |
36.400 |
kJ/m3 |
|
|
maximal |
44.300 |
kJ/m3 |
|
|
D. Bottom calorific value Hd |
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|
|
|
minimal |
33.100 |
kJ/m3 |
|
|
maximal |
40.200 |
kJ/m3 |
|
|
E. Upper Wobbe – index Wg |
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|
|
|
minimal |
45.100 |
kJ/m3 |
|
|
maximal |
55.000 |
kJ/m3 |
|
|
E. Bottom Wobbe – index Wd |
|
|
|
|
minimal |
41.000 |
kJ/m3 |
|
|
maximal |
49.900 |
kJ/m3 |
|
|
F. Dew point (at the 50 bar pressure) (pri tlaku od 50 bar) |
|
|
|
|
water |
-10 |
°C |
|
|
hydrocarbons |
0 |
°C |
|
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G. Unodourised gas, without mechanical additives, rosins or compounds that form rosin |
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Table 1 – Standard natural gas quality