Quality of natural gas supplied to consumers

In Ukraine, the quality of natural gas (more precisely, its physical and chemical parameters) supplied to consumers, including the public, must comply with the applicable standard GOST 5542-87 “Combustible natural gases for industrial and domestic use. Specifications”. This standard establishes a minimum permissible value for the lower heating value of natural gas of 7,600 kcal/m³ (31.8 MJ/m³).

The permissible range of the higher Wobbe number is from 9,840 kcal/m³ (41.2 MJ/m³) to 13,020 kcal/m³ (54.5 MJ/m³), with a permissible maximum deviation from the nominal value of ±5%. This standard does not regulate the content of methane, nitrogen, hydrogen or heavy hydrocarbons in natural gas. The basic requirements of the standard regarding the physical and chemical parameters of natural gas correspond to the norms of European Union countries.

The Wobbe number is the quotient of dividing the volumetric (lower or higher, respectively) heat of combustion under given standard conditions by the square root of the relative density under the same standard measurement conditions. It is the Wobbe number that directly affects the burner power of a stove. With an increase in the heat of combustion accompanied by an increase in the gas density (in proportion to the square root of the relative density), the burner power will not change. Conversely, with a constant heat of combustion, a decrease in the gas density will lead to an increase in the burner power.

The Gas Transmission System Code, approved by NEURC Resolution No. 2493 of 30 September 2015, sets the quality norms, physical and chemical parameters and other characteristics of natural gas admitted for transmission through the gas transmission system. However, it does not regulate the permissible Wobbe number value. In practice, over the past ten years the lower heating value of natural gas in Ukraine has been 8,300 ± 300 kcal/m³ (the maximum deviation is ±3.6%).

Natural gas pressure

The range of permissible values of the gauge pressure of natural gas supplied to the public is determined by regulations.

According to clause 3 (Table 1) of DBN V.2.5-20-2001 “Engineering equipment of buildings and structures. External networks and structures. Gas supply”, approved by Order No. 101 of the State Construction Committee of Ukraine of 23 April 2001 and effective from 1 August 2001, the maximum pressure difference inside and outside the pipe (gauge pressure) supplied to gas-consuming equipment in residential buildings is 306 mm of water column (3 kPa).

According to clause 2.5 of the Gas Supply System Safety Rules, approved by Order No. 285 of the Ministry of Energy and Coal Industry of 15 May 2015, for low-pressure gas supply systems up to 306 mm w.c. (300 daPa), the lower limit is set by the gas distribution company so that, in front of the consumer’s gas-consuming equipment connected to the gas pipeline at the most distant point from the gas regulating station (GRS), the gauge pressure is no less than 71 mm w.c. (70 daPa).

Standards for gas-consuming equipment

The Ukrainian national standards in force for gaseous-fuel appliances or water heaters set the requirements for the permissible ranges of (gauge) pressure and concentrations of natural gas components within which the safe and efficient combustion of fuel must be ensured.

In particular, gas stoves manufactured under DSTU 2204-93 (GOST 10798-93) “Domestic gas stoves. General specifications” must ensure complete and safe combustion of natural gas (without flame separation, without yellow flame tongues, and without flame penetration into the burner) when operating at two nominal (gauge) pressure values: 130 mm w.c. (1.274 kPa) or 200 mm w.c. (1.960 kPa). According to DSTU 2204-93, the efficiency of stove burners with a nominal heat output of more than 1.05 kW must be at least 59% at the time of release from manufacture.

Note that for heating equipment, maximum fuel-utilisation efficiency is achieved at the nominal pressure. When pressure deviates from the nominal value, the efficiency of gas-consuming equipment significantly decreases. This in turn leads to an increase in the volume of natural gas required, which is reflected in the gas meter readings.

Pressure variations in distribution networks

During a single day, due to uneven consumption of natural gas by users, significant pressure variation occurs in distribution networks in Ukraine. Gauge pressure in the pipeline decreases with increased gas flow, especially in front of gas-consuming equipment connected to the pipeline at the most distant point from the GRS. Such an increase in flow occurs in particular as the ambient temperature drops in winter, when gas begins to be intensively used for heating.

Gauge pressure depends on the elevation of the pipeline and increases as the gas-offtake point rises in altitude. Thus, if a low-pressure pipeline runs from a GRS located at a low elevation, then at an elevation of 100 m the gauge pressure in the pipe additionally increases by approximately 40 mm w.c.

Gas-consuming appliances are first tested at nominal pressure to determine their thermal output, which is verified using reference gas G20 (corresponding to natural gas containing only methane). The appliances are then tested under the Ukrainian national standard DSTU GOST EN 437:2014 “Test gases. Test pressures. Categories of appliances”, identical to the corresponding European standard.

Quality control and response to non-compliance

If a malfunction of gas-consuming equipment is detected (in accordance with the Gas Distribution Systems Code, approved by NEURC Resolution No. 2494 of 30 September 2015), the consumer of gas must submit a written application to the relevant gas distribution company concerning the control of pressure and the heat of combustion of natural gas in the distribution networks.

The gas distribution company (as the gas distribution system operator) within five working days from the date of receipt of such application provides the consumer with copies of the natural gas physical-chemical parameters passport for the last calendar month, agreed with the Gas Transmission System Operator.

Upon receipt of the relevant application, the GDS operator is obliged to send its representative to verify the gas pressure and/or the physical and chemical parameters of the gas supplied to the consumer at the call location within two working days in cities and five calendar days in rural areas, at a time agreed with the consumer.

If, based on the results of the inspection, the GDS operator confirms non-compliance with the requirements of the Code, the operator recalculates the volumes of distributed/consumed natural gas at the consumer’s facility in accordance with the Code, and the consumer receives compensation from the operator calculated under Chapter 3 of Section 2 of the Code. Otherwise, the consumer must compensate the GDS operator for the costs incurred in checking the quality and pressure of the gas.

Gas quality vs. quality of distribution service

It is important to distinguish between the quality of natural gas and the quality of natural gas distribution services:

• Quality of natural gas — compliance of physical and chemical parameters with regulatory requirements, which depend on the sources of gas supply and over which gas distribution companies have no actual influence.
• Quality of natural gas distribution services — compliance with regulatory requirements regarding pressure values, water content and solid particle content in the natural gas reaching the consumer. It is determined by the quality of operation of gas distribution networks and the quality of equipment-maintenance services, the correctness of operating mode (regime maps) of GRSs (especially during the autumn-winter period), and the condition of pressure regulators, filters, water and heavy hydrocarbon condensate collectors, etc.

No less important for the high-quality use of natural gas is the user’s correct operation of household gas equipment. In addition, efficiency and safety of gas use is ensured by high-quality, qualified and timely maintenance of gas-consuming appliances (correct installation, adjustment, leak testing, and periodic cleaning of contamination during operation) by employees of specialised service centres.