Natural gas quality_old

Natural gas quality is determined by the analysis of chemical composition and physical features of natural gas. There are two main reasons for regular gas quality control and determining natural gas calorific value in the transmission system:

• Safety
  • of the transmission system: defects of gas pipelines and equipment by corrosion, functioning of technical equipment of the transmission system depending on the gas composition and impurity content.
  • of final customers: technical compliance with devices of final customers (industrial facilities, home appliances).
• Energy calculation

Valid by-laws prescribe the use of metering energy units [kWh] in all business transactions on the natural gas market.
The basic metering unit is volume of gas that has flown through an accounting point in a time unit [m3/h]. For the calculation of gas energy [kWh/h], gas volume that has flown through the accounting point in an hour [m3/h] is multiplied by the amount of the net calorific value [kWh/m3, at 15°C/15°C] determined for a particular gas day. Daily gas quantity is expressed in the metering unit kWh/d, and it is calculated as a sum of hourly quantities [kWh/h].

Determining natural gas quality
In compliance with the General conditions of gas supply  the Transmission System Operator is obliged to provide gas quality monitoring.
Standard gas quality defines minimum and maximum values of gas quality parameters, prescribed in General conditions of gas supply, Enclosure 2, Table 3.
For the purpose of calculation of gas transported in metering unit of energy, transmission system is divided into specific areas consisting of physically connected parts of the transmission within which gas of similar quality and calorific value is transported. Specific points are locations at the transmission system within a specific area at which gas quality is determined, while the measured values represent reference value for all exits from the transmission system associated to this specific area. The Transmission System Operator announces the valid list of specific points and associated connections: Specific points and associated connections

The Transmission System Operator determines specific areas and specific points based on its knowledge of technical-operative features of gas flow, structure of the gas transmission system and the information received by gas composition analysis.
The determining of the quality and calorific value of delivered gas is carried out by periodic sampling, twice a month at specific points.

At the authorised and licensed laboratory a chromatographic gas analysis is carried out. It determines:

• gas composition (accredited in accord. with HRN ISO 6974-5:2014),
• gross calorific value, net calorific value, Wobbe feature, molar mass, density, relative density, specific gas constant (accredited in accord. with HRN ISO 6976:2016)

The information received in an authorised laboratory by a chromatographic gas samples analysis, sampled in specific points, is used to calculate the delivered gas quantities expressed in the metering unit of energy. The Transmission system operator publishes reports on the gas quality pursuant to Network Code for the transmission system:

•  Laboratory reports on the gas quality for particular specific points
• Annual report on the gas quality -table

The Transmission system operator publishes also average annual values of gas quality parameters for all specific points:

• Report on the gas quality, 2018
• More details can be found here.