Test of the Yamatake HGC303 gas chromatograph

Project Report April 2003

Test of the Yamatake HGC303 gas chromatograph

Leo van Gruijthuijsen

Danish Gas Technology Centre Hørsholm 2003

Title : Test of the Yamatake HGC303 gas chromatograph

Report Category : Project Report

Author : Leo van Gruijthuijsen

Date of issue : 30-04-03

Copyright : Danish Gas Technology Centre

File Number : 722.66; H:\722\66\report 722-66 HGC303 rev2.doc

Project Name : Afprøvning af udstyr til gaskvalitetsbestemmelse

ISBN : 87-7795-239-1

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• DGC shall be liable in accordance with "Almindelige Bestemmelser for Teknisk Rådgivning og Bistand, ABR 89" ("General Conditions for Consulting Services (ABR 89)"), which are considered adopted for the assign-ment, unless otherwise agreed upon in writing.

• DGC's liability per error and negligence and damages suffered by the Client or any third party is limited to a maximum of 100% of the fee received by DGC for the respective assignment. The Client shall indemnify and hold DGC harmless against all losses, expenses and claims which may exceed the liability of DGC.

• DGC shall - without limitation - re-perform its own services in connection with errors and negligences con-tained in the material delivered to the Client by DGC. This is valid until five years after completion of the as-signment.

• The Client shall be held responsible that the existing legislation concerning health and safety at work can be complied with by DGC when carrying out the assignment. In the event that DGC will have to stop, interrupt and/or postpone an assignment because this legislation cannot be complied with, the Client shall pay any addi-tional expenses incurred by DGC in this connection.

• Reports are protected by copyright, and must not be reproduced in whole or in part without the prior written consent of DGC.

This English translation is provided for convenience only and in case of discrepancy the Danish wording shall be applicable.

March 2000

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Table of Contents Page

Preface............................................................................................................................................. 2

Summary and conclusions............................................................................................................... 3

1 Introduction........................................................................................................................... 4 1.1 Description of the Yamatake HGC303 gas chromatograph............................................ 4 1.2 Goal and scope of this study ........................................................................................... 5

2 Experimental ......................................................................................................................... 6 2.1 Instruments ...................................................................................................................... 6

2.1.1 HGC303 .................................................................................................................. 6 2.1.2 DGC gas chromatograph......................................................................................... 8

2.2 Test duration.................................................................................................................... 9 2.3 Reference conditions ..................................................................................................... 10

3 Results................................................................................................................................. 11 3.1 Initial test with factory calibration ................................................................................ 11 3.2 Stability test................................................................................................................... 12 3.3 Tests at different temperatures ...................................................................................... 16 3.4 Measurement on gas with high CV............................................................................... 17 3.5 Repeatability.................................................................................................................. 19 3.6 Consumption of carrier gas and instrument air ............................................................. 19

Annex 1 Results of stability test .............................................................................................. 20

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Preface As the variations in gas quality of Danish natural gas have increased during recent years, there is an increasing demand for information about the actual gas properties (calorific value, methane number) at different locations in the natural gas grid. In order to supply the desired information, it may be neces-sary to install a number of field instruments at measurement and regulation stations or customer sites, in addition to the gas chromatographs that already are installed at central locations.

The aim of the test described in this report is to determine if the Yamatake HGC303 Heat Value Gas Chromatograph can be used for these purposes.

The test of the HGC303 was performed by the Danish Gas Technology Cen-tre (DGC) as part of a project that was supported by the Danish gas compa-nies and the Swedish Gas Technology Centre (SGC).

The instrument tested was kindly provided by Flonidan. DGC thanks Mr. Lars Fagerlind (Flonidan) and Mr. Deddy Yudha (Yamatake Europe) for their assistance.

Hørsholm, April 2003

Leo van Gruijthuijsen Lars Jacobsen Project Manager Head of Laboratory

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Summary and conclusions The Yamatake HGC303 gas chromatograph was tested on Danish natural gas and synthetic natural gas mixtures.

The test shows that:

1. There is no significant difference between the calorific value, density and compressibility factor determined with the HGC303 and values de-termined with a laboratory gas chromatograph that is optimised for the analysis of natural gas.

2. The instrument is stable for a period of 6 months, provided that it is used at constant temperature.

3. Temperature variations have an influence on (in particular) the measured methane and ethane concentrations and on the calculated calorific value. The error on the calorific value is approximately 0.2 % for a 30 °C tem-perature change.

4. The instruments gives satisfactory results for gas with a lower calorific value of 42.65 MJ/m3, corresponding to the upper limit of the calorific value that is to be expected in the Danish natural gas grid.

Based on these tests it may be concluded that the HGC303 gas chromato-graph is suited for measurements on Danish natural gas. When used at con-stant temperature, it is sufficient to calibrate the instrument two times per year. It is recommended that the gas chromatograph is re-calibrated after a significant change in ambient temperature.

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1 Introduction As the variations in gas quality of Danish natural gas have increased during recent years, there is an increasing demand for information about the actual gas properties (calorific value, methane number) at different locations in the natural gas grid. It is expected that this demand will increase in the future as a result of the work on gas metering by OIML (International Organization of Legal Metrology).

In order to supply the desired information, it may be necessary to install a number of field instruments at measurement and regulation stations or cus-tomer sites, in addition to the gas chromatographs that already are installed at central locations. The most important requirements to these instruments are that they should be reliable, cheaper than traditional gas chromato-graphs, and only require a minimum of supervision and maintenance.

The Yamatake HGC303 Heat Value Gas Chromatograph is one of the in-struments that are potentially suited for these purposes. This instrument was tested as part of a project that was supported by the Danish gas companies and the Swedish Gas Technology Centre.

1.1 Description of the Yamatake HGC303 gas chromatograph

The HGC303 Heat Value Gas Chromatograph is a dedicated instrument for the analysis of natural gas. It analyses up to 11 components in a natural gas flow using a micro thermal conductivity detector (TCD), and calculates the calorific value, density, Wobbe index and compressibility factor of the gas in accordance with ISO 6976. The cycle time is 5 minutes. The instrument uses helium as a carrier gas and air (or other gas) for actuating valves.

summarises the specifications of the instrument. Table

1

Figure 1 Yamatake HGC303

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Table 1 HGC303 specifications

Component Range [mol-%] Minimum detection [mol-%]

CH4 50-100 5 C2H6 0-10 0.05 C3H8 0-5 0.05 i-C4H10 0-1 0.01 n-C4H10 0-1 0.01 i-C5H12 0-1 0.01 n-C5H12 0-1 0.01 neo-C5H12 # 0-1 0.01 C6+ 0-0.5 0.01 N2 0-15 (0-8) ## 0.3 (0.05) ## CO2 0-10 0.05

Repeatability +/- 0.1% calorific value

Carrier gas Helium, >99.99% purity Pressure 400 ± 50 kPa Consumption 25 ml/min

Instrument air Pressure > 400 kPa

Natural gas Temperature –10 - 50 °C Pressure 50 - 490 kPa Flow rate 30 - 70 ml/min Moisture <23°C saturation

Ambient temperature -10 – 50 °C # Concentration in Danish natural gas less than minimum detection limit. ## The lower limit for detection of nitrogen should be less than 0.2 for measurements on Danish natural gas. 1.2 Goal and scope of this study

The aim of this study is to determine if the Yamatake HGC303 is suited for measurements on Danish natural gas at measurement and regulation stations or customer sites.

This study focuses on the accuracy and stability of the instrument.

Communication with flow computers, which also will be an important factor for practical applications, is not investigated.

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2 Experimental

2.1 Instruments

2.1.1 HGC303

The test was performed with the instrument that is described in Table 2. The instrument was connected to a computer using a National Instruments PCMCIA-FBUS interface. Data collection was done with the HGC software Version 2.07.

Table 2 HGC303 product identification

The gas chromatograph was used with factory calibration for approximately one week, after which the instrument was calibrated with a natural gas cali-bration mixture manufactured by Praxair (Belgium), number BD62699F. Details about the gas mixture are given in Table 3.

During the first calibration the nitrogen lower detection limit was 0.3 % (default setting), which meant that calibration of this component with a gas mixture containing 0.29 % nitrogen was not possible. Therefore, another gas mixture was used for this component (Praxair, number BD58642F; see

). This calibration was used for the stability test that is described in section 3.2. Later calibrations were done with only gas BD62699F, as the minimum nitrogen concentration was reduced to 0.1 %.

Table 3

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The calibration was done with the total content of hexane, 2-methylpentane, methylcyclopentane and benzene (700.6 ppm) as “C6+”.

Table 3 Composition of calibration mixtures

Component Concentration Uncertainty [%]

Calibration gas BD62699F

Methane 86.75 mol-% ± 0.02 abs Ethane 7.05 mol-% ± 0.5 rel Propane 3.450 mol-% ± 1 rel i-Butane 3502 molppm ± 1 rel n-Butane 5801 molppm ± 1 rel i-Pentane 1202 molppm ± 1 rel n-Pentane 900 molppm ± 1 rel Hexane 380.9 molppm ± 1 rel 2-Methylpentane 50.0 molppm ± 1 rel Methylcyclopentane 249.6 molppm ± 1 rel Benzene 20.15 molppm ± 1 rel Nitrogen 2898 molppm ± 1 rel Carbon dioxide 1.250 mol-% ± 0.5 rel

Calibration gas BD58642F

Methane 54.50 mol-% ± 0.02 abs Carbon dioxide 44.99 mol-% ± 0.02 abs Nitrogen 5054 molppm ± 1 rel

During the stability test the gas chromatograph was placed on a table in the laboratory at a temperature of approximately 22 °C. During subsequent tests the instrument was mounted in a plastic box inside a small freezer that was kept at a temperature of –10 °C (see Figure 2, left). Due to the heat output from the gas chromatograph, the temperature in front of the instrument was approximately –9 °C and the temperature near the door of the freezer –3 °C. When the plastic box was closed ( , right), the temperature around the instrument increased to 11 °C. With the plastic box placed at the labora-tory at room temperature, the temperature around the instrument increased to approximately 35°C.

Figure 2

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-9 °C 11 / 35 °C

Figure 2 Test at different temperatures.

2.1.2 DGC gas chromatograph

A Chrompack Natural Gas Analyzer was used as a reference for the test of the HGC303. This is a laboratory instrument with 2 packed columns (Hayesep Q/Molsieve 13X) and a capillary column (CP-SIL 5 CB). Meth-ane, ethane, nitrogen and carbon dioxide are analysed on the packed col-umns with a thermal conductivity detector. Higher hydrocarbons (up to C8) are analysed on the capillary column with a flame ionisation detector. The duration of an analysis cycle is approximately 45 minutes.

The gas chromatograph was calibrated weekly with three calibration gases (Praxair natural gas calibration mixtures, number BD62699F, BD61281F and BD63905F) with a total of 13 components in a concentration range that covers the normal composition of Danish natural gas.

Table 4

Table 4

shows the uncertainty of the measured concentrations and the calcu-lated gas properties. The uncertainty of the measured concentrations in-cludes the uncertainty of the calibration mixtures, the repeatability of the calibration and the repeatability of the analysis. The uncertainty of the cal-culated gas properties is based on the uncertainty of the measured concen-trations and the uncertainty of the calculation method, which according to ISO 6976 is 0.1 %. The values given are for the standard range of composi-tions ( ), i.e. the concentrations that are covered by the calibration mixtures with the requirements in Table 5. The uncertainty will be slightly higher for measurements outside the standard range of concentrations.

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Table 4 Uncertainty of measured and calculated values

Table 4

Component Standard range [mol-%] Uncertainty [%]

Methane 82.6-100 ± 0.1 abs Ethane 5.0-8.4 ± 1.5 rel Propane 2.1-4.1 ± 2 rel i-Butane 0.18-0.90 ± 2 rel n-Butane 0.29-1.36 ± 2 rel i-Pentane 0.05-0.24 ± 2.5 rel n-Pentane 0.04-0.18 ± 2.5 rel C6+ 0.003-0.075 ± 5 rel Nitrogen 0.15-0.76 ± 2.5 rel Carbon dioxide 0.89-1.75 ± 1.5 rel

Calorific value -- ± 0.25 rel Density -- ± 0.23 rel Wobbe index -- ± 0.34 rel

DGC is accredited by DANAK (Danish Accreditation) for the analysis of natural gas samples within the standard range of concentrations shown in

.

Table 5 Values used for the calculation of standard concentration ranges.

Concentration [mol-%] Allowed difference between concentration in calibration mixture and gas sample

50-100 5 10-50 10 1-10 20 <1 50

2.2 Test duration

The HGC303 was installed at DGC on 21 September 2001. The instrument was used with factory calibration until 1 October. A stability test with DGC calibration was performed from 1 October 2001 until 8 April 2002. During this period the gas chromatograph was installed at the laboratory at room temperature. Tests at other temperatures were done in the period July-October 2002.

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2.3 Reference conditions

All gas properties mentioned in this report are calculated for the following reference conditions:

• Combustion: 25 °C

• Volume: 0 °C, 101.325 kPa

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3 Results

3.1 Initial test with factory calibration

During the first week of the test period the HGC303 was used with factory calibration. This was done to get a first impression of the stability of the instrument. The factory calibration was done more than a month before the start of the test, and between calibration and use the instrument was trans-ported from Japan to Europe.

The initial test was done in the same way as most other tests that will be discussed in this report, by comparing measurement on line gas with both HGC303 and DGC gas chromatograph. shows the results of meas-urements done with the HGC303 in blue and DGC gas chromatograph in red. Data from the DGC gas chromatograph is missing in some cases, as the instrument is also used for measurements on other gas samples.

Figure 3

Figure 3

Figure 3 Calorific value measured during the initial test with factory calibration

shows that the agreement between the measurements with the two gas chromatographs is good. It also shows that the HGC303 in some cases measures rapid changes in gas quality that are not detected by the DGC gas chromatograph due to the longer analysis time.

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3.2 Stability test

Figure 4 Concentration before normalisation during measurements

over a 6-month period (for technical reasons, data is missing in some periods).

After the first test with factory calibration, the HGC303 was calibrated as described in section 2.1.1 and a new test was started. The aim of this test was to test the stability and accuracy of the HGC303:

• The stability was determined by measuring over a 6-month period with-out re-calibrating the instrument.

• The accuracy was determined by measuring a wide range of gas compo-sitions with the DGC gas chromatograph as a reference.

The test was started with the nitrogen lower detection limit at 0.3 % (factory setting). With this setting nitrogen was not measured in all cases, as the ni-trogen content of Danish natural gas is between approximately 0.25 and 0.45 mol-%. When nitrogen is not measured, the inaccuracy of all measured parameters is increased by 0.25-0.3 %.

After approximately 2 weeks the nitrogen lower detection limit was changed to 0.1 %. All graphs shown in this section and Annex 1 are from this date. However, it should be noted that the calibration was done 2 weeks before.

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The concentration before normalisation depends on the atmospheric pres-sure, but in addition to this, it is also a good measure for the stability of the instrument. ISO 6974 requires that the concentration before normalisation should be between 98 and 102 %. shows that this is the case over the whole 6-month period.

Figure 4

During the 6-month period, a total of 2350 gas compositions within the normal range of Danish natural gas were measured with both HGC303 and DGC gas chromatograph. The results of these measurements are shown in Annex 1. The most important results are also shown in Figures 5-7.

Figure 5 Comparison of calorific value calculated from data measured

with DGC gas chromatograph and HGC303

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In Annex 1, the upper graphs shows a parameter measured with the HGC303 (black dots + lines), the difference between the measurements with HGC303 and DGC gas chromatograph (red dots) and the accuracy of the measurement with DGC gas chromatograph (blue lines). The latter corre-spond to the values in Table 4.

The lower graph shows a direct comparison between the values measured with DGC gas chromatograph and HGC303. The blue lines again give the

Figure 6 Comparison of compressibility factor (SGERG, 20 bar(a),

6 °C), calculated from data measured with DGC gas chro-matograph and HGC303

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accuracy of the DGC measurement, and the black line is a trend line through the measured data points. The equation for the trend line is given in the up-per left corner of the graph.

From the graphs in Annex 1 it follows that there generally is a good agree-ment between the analyses done with the HGC303 and DGC gas chromato-graph. As a result, there is also a good agreement for the parameters that are calculated from the gas analyses. As is seen in Figures 5-7, there is no sig-nificant difference between the calorific value, density and compressibility factor determined with HGC303 and DGC gas chromatograph.

Figure 7 Comparison of density calculated from data measured with

DGC gas chromatograph and HGC303

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3.3 Tests at different temperatures

The HGC303 was calibrated at room temperature and at –9 °C (temperature in front of HGC303, see section 2.1.1) and tested by measuring on calibra-tion gas (number BD62699F, see section 2.1.1) at different temperatures. For practical reasons it was not possible to cover the whole temperature range that is allowed according to the product specifications (-10 to 50 °C), but only the range between –9 and 35 °C. The results are given in Tables 6 and 7.

The results show that the temperature mainly has an influence on the meas-ured methane and ethane concentrations. The methane concentration de-creases at higher temperature, while ethane increases with increasing tem-perature.

As a result of the error on the measured gas composition, there is also an error on the calculated gas parameters such as the calorific value. As is shown in Figure 8, a 30 °C temperature change causes an error up to 0.2 %

Table 6 Measurement at different temperatures after calibration at room temperature

Temperature Component 23 °C -9 °C 11 °C 35 °C

Methane 86.75 87.09 86.85 86.64 Ethane 7.03 6.71 6.92 7.17 Propane 3.47 3.50 3.47 3.45 i-Butane 0.35 0.35 0.36 0.35 n-Butane 0.58 0.59 0.58 0.59 i-Pentane 0.12 0.11 0.12 0.12 n-Pentane 0.09 0.09 0.09 0.08 n-Hexane 0.07 0.07 0.07 0.07 Nitrogen 0.29 0.31 0.31 0.25 Carbon dioxide 1.24 1.19 1.22 1.27

Concentration before normalisation

99.84 97.09 98.81 101.66

Lower calorific value 40.39 40.31 40.35 40.41 Density 0.848 0.846 0.847 0.849 z(SGERG, 20 bar, 6 °C) 0.9470 0.9474 0.9472 0.9469

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on the lower calorific value. The compressibility factor is less sensitive to-wards temperature changes: here the maximum error is 0.05 %.

Based on these results it is recommended that the HGC303 is used a rela-tively stable temperature, e.g. within ± 10°C depending on accuracy re-quirements. Alternatively the instrument should be re-calibrated after a sig-nificant change in ambient temperature.

Table 7 Measurement at different temperatures after calibration at -9 °C

Temperature Component -9 °C 11 °C 23 °C 35 °C

Methane 86.73 86.56 86.40 86.28 Ethane 7.05 7.20 7.38 7.50 Propane 3.46 3.45 3.42 3.41 i-Butane 0.35 0.35 0.35 0.35 n-Butane 0.58 0.58 0.58 0.58 i-Pentane 0.12 0.13 0.13 0.13 n-Pentane 0.09 0.09 0.08 0.08 n-Hexane 0.07 0.07 0.08 0.08 Nitrogen 0.29 0.28 0.27 0.27 Carbon dioxide 1.25 1.27 1.30 1.32

Concentration before normalisation

99.99 101.41 102.89 103.82

Lower calorific value 40.38 40.42 40.45 40.47 Density 0.848 0.850 0.851 0.851 z(SGERG, 20 bar, 6 °C) 0.9470 0.9468 0.9467 0.9466

3.4 Measurement on gas with high CV

The lower calorific value of Danish natural gas is normally within the range 39-41 MJ/m3, but under special circumstances the calorific value may be up to 42.6 MJ/m3.

The HGC303 was tested with a calibration gas mixture (Praxair BD58419F) with a calorific value of 42.65 MJ/m3. It should be noted that the propane and i-butane content of the high-CV gas mixture is outside the specified measuring range of the HGC303.

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Figure 8 Error on the calculated calorific value and compressibility factor due to temperature change

The results show that the HGC303 measures slightly too low on C2 and higher hydrocarbons ( ), but this does not lead to an unacceptable error on the calorific value or density. It may therefore be concluded that the HGC303 is also suited for measurements on high-CV gas.

Table 8

Table 8 Measurement on high-CV gas

Component Praxair Certificate of analysis

DGC [mol-%]

HGC303 [mol-%]

Difference HGC-DGC [% rel.]

Methane 81.12 mol-% 81.10 81.30 +0.2 Ethane 9.87 mol-% 9.87 9.75 -1.2 Propane 5.57 mol-% 5.59 5.48 -1.9 i-Butane 1.121 mol-% 1.123 1.11 -1.5 n-Butane 4003 molppm 0.398 0.392 -1.6 i-Pentane 701 molppm 0.069 0.074 +7.0 n-Pentane 901 molppm 0.085 0.079 -7.5 n-Hexane 199 molppm 0.016 0.015 -8.4 Nitrogen 2314 molppm 0.24 0.28 +17 Carbon dioxide 1.510 mol-% 1.51 1.52 +0.8

Calculated values based on above concentrations

Lower calorific value 42.65 MJ/m3 42.65 42.51 -0.3 Density 0.904 kg/m3 0.904 0.902 -0.3 z(SGERG, 20 bar, 6 °C) 0.9381 0.9381 0.9386 +0.1

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3.5 Repeatability

The repeatability of the instrument was tested by measuring 100 times on calibration gas mixture BD62699F. The results are shown in Table 9.

Table 9 Repeatability test

Component average standard deviation

minimum maximum

Methane 86.69 mol-% 0.01 % rel. 86.66 86.72 Ethane 7.10 0.07 7.08 7.11 Propane 3.45 0.23 3.43 3.48 i-Butane 0.352 0.39 0.348 0.355 n-Butane 0.582 0.32 0.577 0.585 i-Pentane 0.121 1.17 0.117 0.124 n-Pentane 0.088 0.71 86.66 1.25 n-Hexane 0.069 0.84 0.067 0.07 Nitrogen 0.309 0.71 0.304 0.313 Carbon dioxide 1.25 0.22 1.24 1.25

Concentration before normalisation

100.44 0.07 100.26 100.62

Lower calorific value 40.38 MJ/m3 0.02 % rel. 40.35 40.4 Density 0.848 kg/m3 0.02 0.848 0.849 Wobbe index 55.07 MJ/m3 0.01 55.06 55.09

3.6 Consumption of carrier gas and instrument air

The HGC303 gas chromatograph uses helium as carrier gas and air (or other gas) for actuating valves.

During the test the gas supply was done with 50-litre bottles (200 bar initial pressure). Over a period of 13 months the helium pressure decreased from 200 to 40 bar, corresponding to a gas flow of approximately 14 ml/min (Yamatake specification: 25 ml/min). The instrument air pressure decreased from 200 to 170 bar.

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Annex 1 Results of stability test

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