On-line gas chromatography Gerard Nieuwenkamp Research and Development Money in the Pipeline Delft, 2 November 2010
Natural gas metering 2" 2" 65 m3/h usm 6" 400 m3/h M etering runs 2500 m3/h Gas Oil Piston Prover NMi TraSys Cross over line 6500 m3/h usm 16" 16" 30" Metering runs 16" 24" 30" 6500 m3/h Flow finetuning 30" 2" 8" 30" Heat Exchanger Blower and variable speed drive GC
Why Gas chromatography? Energy (MJ) = Quantity (m 3 ) x Quality (MJ/m 3 ) quantity = flow measurement quality = calorific value composition gas chromatography Error / uncertainty in both parts have the same impact!!
What is gas chromatography?
Gas Chromatography : calibration Gaschromatogramof of calibration gas (with Elster Encal 3000) Peak area is proportional to concentration
Result of GC analysis Gas composition is used to calculate the Calorific Value (inferior and superior), Wobbe index, compressibility, density, viscosity (Reynolds number), V.O.S. (ultrasonic flow meter), etc. Validation is required by contracts
Objectives for validation Need for reliable measurement results - Confidence and trust between buyer / seller - Comply pyto contractual issues - Comply to legislation In practice: Comply to EN1776: Gas supply Natural gas measuring stations Functional requirements For on-line GC: comply to ISO 10723: Natural gas Performance evaluation for on-line analytical systems P 7
Some quotes from EN1776 4.8 National regulations may require that the inspection and testing have to be witnessed and accepted by independent d experts 6.3.1 Gas chromatograph operating conditions determined from a performance evaluation complying with ISO10723 6.3.2 The quality of the calibration gas is the key issue for the quality of the results of the measuring system 6.4.2 These calibration gases shall be prepared according to ISO6142 or ISO6143 or certified according to ISO6141. The traceability of the calibration gas shall be established. 7.1.4.1 The measurement instruments shall be calibrated with traceability to national standards and shall be done by accredited d laboratories P 8
(VSL) implementation of EN1776/ISO10723 (+additional issues) - Factory Acceptance Test (FAT) - At VSL or at the manufacturer s site - Site Acceptance Test (SAT) P 9
Factory Acceptance Test - GC performance (peak separation) - Use of 7 traceable Primary Standard Gas mixtures to test: - Repeatability - Reproducibility (calibration interval) - Detector linearity P 10
Detector linearity check with 7 PSM - during field operation: single point calibration! 80000 70000 assumed response WRM response curve 60000 50000 res sponse 40000 30000 unknown response true response curve 20000 10000 unknown mole fraction bias WRM WRM mole mole fraction 0 0 3 6 9 12 15 mole fraction Advise on calibration gas composition Take non linearity effect as additional uncertainty in calculation
Site Acceptance Test - Performance - Repeatability - Test with two independent traceable VSL gas mixtures (matched to the line gas composition) - Analytical result should match to the VSL certificate within uncertainty criteria of ISO10723 Validation of the complete system! P 12
Example: Example of impact of error in GC analysis Mixture of 94% CH 4 (mol/mol) 3% C 2 H 6 (mol/mol) 3% N 2 (mol/mol) What is (are) the most critical component(s) for the analysis? P 13
P 14 Initial GC measurement result : raw data Component x (kg/kg) H (MJ/kg) x H (MJ/kg) Methane 0.900 55.52 49.97 Ethane 0.050 51.90 2.60 Nitrogen 0.050050 0 0 Total 1.000 52.56 In case of error in measurement/calibration: Raw data! Component x (kg/kg) H (MJ/kg) x H (MJ/kg) Methane 0.895 55.52 49.69 Ethane 0.050 51.90 2.60 Nitrogen 0.050 0 0 Ttl Total 0.995 52.2929 0.50% 0 Component x (kg/kg) H (MJ/kg) x H (MJ/kg) Methane 0.9000 55.52 49.97 Ethane 0.0450 51.90 2.34 Nitrogen 0.0500 0 0 Total 0.9950 52.30 0.50% Component x (kg/kg) H (MJ/kg) x H (MJ/kg) Methane 0.900 55.52 49.97 Ethane 0.050 51.90 2.60 Nitrogen 0.045 0 0 Total 0.995 52.56 no effect
GC measurement results in practice Component x (kg/kg) H (MJ/kg) x H (MJ/kg) Methane 0.900 55.52 49.97 Ethane 0.050 51.90 2.60 Nitrogen 0.050 0 0 Total 1.000 52.56 after normalization: Component x (kg/kg) x' (kg/kg) H (MJ/kg) x' H (MJ/kg) Methane 0.895 0.899 55.5252 49.9494 Ethane 0.050 0.050 51.90 2.61 Nitrogen 0.050 0.050 0 0.00 Total 0.995 1.000 52.55 no effect Component x (kg/kg) H (MJ/kg) x' H (MJ/kg) Methane 0.9000 0.9045 55.52 50.22 Ethane 0.0450 0.0452 51.90 2.35 Nitrogen 0.05000500 0.05030503 0 000 0.00 Total 0.9950 1.000 52.57 no effect Component x (kg/kg) H (MJ/kg) x' H (MJ/kg) Methane 0.900 0.9045 55.5252 50.22 Ethane 0.050 0.0503 51.90 2.61 Nitrogen 0.045 0.0452 0 0.00 Total 0.995 1.000 52.83 +0.5% Nitrogen (and CO 2 ) very critical nitrogen most vulnerable to air leakage (also in cal line!) peak separation between N 2 and CH 4 is very important
VSL offers - Factory Acceptance Test - Site Acceptance Test - Including metrological l and analytical l issues - Uncertainty calculation for energy (including flow, temperature, pressure and composition) - Certification of calibration gas mixtures - Training course on gas flow metrology g g gy - In Delft, but also on location
Any Questions? VSL PO Box 654 2600 AR Delft The Netherlands T +31 15 269 15 00 F +31 15 261 29 71 E info@vsl.nl I www.vsl.nl