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Componental content, heat of combustion, relative density and the Wobbe number determination method for natural gas.

1. Designation and application field.

1.1. Thist document establishes method for measurement of componental content, heat of combustion, relative density and the Wobbe number of natural gas using gas and gas-liquid chromatography technique.

1.2. Natural gas componets covered by this method:

  • methane,
  • ethane,
  • propane,
  • i-butane,
  • n-butane,
  • i-pentane,
  • n-pentane,
  • neopentane,
  • oxygen,
  • nitrogen,
  • carbon dioxide.

1.3. Natural gas characteristics determined by this method:

  • qualitative and quantitative componental content of natural gas sample,
  • each component content in natural gas sample (quantitative analysis),
  • heat of combustion of natural gas,
  • relative density of natural gas,
  • the Wobbe number ant its deviation from nominal value.

1.4. Range of concentration being measured is determined by known literature sources and experimental date about typical natural gas content.

2. Norms and measurement precision

2.1. Method makes available determination of qualitative and quantitative componental content of natural gas, and also heat of combustion, relative density and the Wobbe number with precision which is not exceed values shown in Table 2.2.

2.2. Norms of measurement precision while determinating of quantitative content of natural gas.

Table 1. Measurement precision norms

Name of measured parameter

Range of main abs. errors at confidence probability of 0.95
no more

Heat of combustion at 20 ° C, kkal/m3

14

Relative density at 20 ° C

0.0012

The Wobbe number at 20 ° С, MJ/m3 (kkal/m3 )

25


Natural gas
component name

Concentration range,
% mol

Range of main abs. errors at confidence probability of 0.95
no more

Ethane

0.7—1

± 0.027

Propane

0.2—0.4

± 0.020

Isobutane

0.02—0.05

± 0.004

n-Butane

0.02—0.1

± 0.007

Neopentane

0—0.002

± 0.003

Isopentane

0—0.015

± 0.007

n-Pentane

0—0.015

± 0.011

Carbon dioxide

0.01—0.05

± 0.006

Nitrogen

0.8—2.5

± 0.050

Oxygen

0—0.6

± 0.042

Methane

95—99

± 0.100

3. Measuring means, additional devices, materilas, solvents.

3.1. During measurement it is used the following measuring installations, measuring systems, measuring means, devices, meaterials and substances:

3.2. Measuring installations, measuring systems, measuring means

Gas chromatograph of type “Tswett-500”,

“Tswett-500M”,

“Agath”,

double column, equipped with thermal conductivty detector and dosage valve which allows inject gase probe from 0.25 to 5.0 cm3

 

on TU 5E1.550.168-01

on ТU 5E1.550.150

on ТU 25-7473.024-91

Stopwatch

 

on TU 25-1894.003-90

Data system for acquisition, processing and storage of spectromentric information UniChrom 97

 

on ТU RB 14597800.001-98

3.3. Devices

Chromatographic packed column filled with mole sieves NaX or CaA, length 3 m, diameter 3 mm. Fractions 0.15-0.25 mm.

 

on GOST 23781-87

Chromatographic packed column filled with inert solid phase (Silipor 600), length 1 m, diameter 3 mm. Grain diameter 0.15-0.25 mm.

 

on GOST 23781-87

Drying chamber, capable of heating to 150° C ± 5 ° C

   

Sampling devices

 

on GOST 14921-78

Electrical muffle oven, provides heating to 1100 ° C ± 20 ° C

   

Porcelain mortar

 

on GOST 9147-80

Desiccator

   

Set of sieves “Physpribor” or of analog type with diameter 0.15 - 0.25mm.

   

3.4. Materials

Helium gas (compressed)

On TU 51-940-80

3.5. Reagents and standard reference materials

Ethyl ether technical

On GOST 6265-74

Rectified ethanol technical

On GOST 18300-87

Zeolites of type NaX or CaA

 

Work natural gas reference sample of known content, certified on quantitative content in sample by SP “D.I Mendeleev Research Institute”, see Appendix 2.

 

3.6. It is allowed to use other measuring means and devices which is not worst on precision class than given in 3.2 and 3.3.

3.7. It is allowed to use another certified data acquisition and processing system for quantitative calculation with the following minimal requirements:

  • Limit of allowed main relative errors range for peak area measurement for componets taken i account is not more 0.1%
  • Chromatogram registration time is not less 35 minutes;
  • Max number of peaks per analysis not less 15;
  • Componental identification using retention times;
  • Quantitative calculation using absolute calibration method.

4. Measurement method.

4.1. Concentration measurement method is based on using gas-chromatography technique with thermal conductivity detector. Hydrocarbon components are separated using gas-liquid chromatography with packed "hydrocarbon" column. Non hydrocarbon components are separated using mole sieve packed column. Analysis is carried out in isothermal mode on two clumns simultaneously. Results from "hydrocarbon" column are joined with mole sieve column results. Componental content calculated using method of absolute calibration.