Improved Reliability in Natural Gas Energy Measurement with the Revised ISO 10723 Standard Gerard Nieuwenkamp - VSL
Improved reliability in natural gas energy measurement with the revised ISO 10723 standard Gerard Nieuwenkamp VSL Research and Development VSL/CEESI: 3 rd European USM workshop Noordwijk, 17 March 2015
Natural gas measurement VSL - Beyond all doubt 2
Natural gas energy measurement - Why measuring flow and composition Energy (MJ) = Quantity (m 3 ) x Quality (MJ/m 3 ) quantity = flow measurement quality = calorific value (H) composition gas chromatography Error / uncertainty in both parts have the same impact!! VSL - Beyond all doubt 3
Contribution of uncertainty sources With: U flow = 0.2% rel. U H = 0.5% rel. With: U flow = 0.1% rel. U H = 0.5% rel. With: U flow = 0.2% rel. U H = 0.2% rel. } U energy = 0.54% rel. } U energy = 0.51% rel. } U energy = 0.28% rel. To reduce U flow from 0.2% to 0.1% can be big investment To reduce U H from 0.5% to 0.2% can be a much smaller investment VSL - Beyond all doubt 4
Natural gas metering 2" 10" 2" 65 m3/h 10" usm 6" 10" 10" 400 m3/h Metering runs 10" 2500 m3/h 10" Gas Oil Piston Prover NMi TraSys 10" Cross over line 10" 6500 m3/h usm 10" 16" 16" 30" Metering runs 16" 10" 24" 30" 6500 m3/h Flow finetuning 30" 2" 8" 30" Heat Exchanger 10" Blower and variable speed drive GC
Gas Chromatograph: is it a Black Box and is that bad? Bad: if output is simply taken for granted Not bad: if black box model is validated and output can be taken for granted VSL - Beyond all doubt 6
What is gas chromatography? t 0 t 1 t r
Gas Chromatography : calibration Gas chromatogram 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.
Calculation of the unknown composition In case of single point calibration (common practise in many gas metering stations): Concentration X of component Y unknown sample X Y, unknown = Peak area Y, unknown * X Y, cal gas Peak area Y, cal gas X CH4 X CH4 X C2H6 X C3H8 Normalisation X C2H6 X C3H8 e.g., ISO 6976 H Z AGA8 W X CO2 X CO2 AGA10 n s X N2 X N2 VSL - Beyond all doubt 10
Measuring / integration peak area X unknown = Peak area unknown * X cal gas Peak area cal gas Requires: reliable peak area (system efficiency and repeatability) equal detector sensitivity for both peaks! (detector linearity) VSL - Beyond all doubt 11
Reliable peak area: system efficiency Channel 1: N 2, CH 4, CO 2 and ethane Very critical! 0.1% error (abs) in N 2 0.1% (rel) error in H Channel 2: propane and higher Poor integration, but less critical for H (normalization) Critical for T dew 12
response Detector linearity check with 7 PSMs 80000 70000 60000 WRM response assumed response curve 50000 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 -during field operation: single point calibration! -How the quantify the bias and the associated uncertainty? VSL - Beyond all doubt 13
Calibration gas quality X unknown = Peak area unknown * X cal gas Peak area cal gas Requires reliable values for all individual components: prepared in accordance with ISO 6142 or certified in accordance with ISO 6143 (ISO 6974) issued under ISO 17025 / ISO Guide 34 accreditation (with uncertainty that is fit for purpose!) VSL - Beyond all doubt 14
Objectives for validation Need for reliable measurement results - Confidence in analytical results - Confidence and trust between buyer / seller - Comply to contractual issues - Comply to legislation In practice: Comply to e.g. EN 1776: 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 VSL - Beyond all doubt 15
Validation with ISO 10723 Use of (at least) 7 high quality, traceable, natural gas reference gas mixtures: - to demonstrate proper peak seperation (for many combinations) - to calculate repeatability (U peak area) - to demonstrate reproducebility (calibration interval) - to determine true response function (linearity) - Calculate total uncertainty on gas properties Reference gas ranges expressed in amount-of-substance fractions Component Unit Min Max Methane cmol/mol 64.19 98.30 Nitrogen cmol/mol 0.200 11.66 Carbon dioxide cmol/mol 0.050 8.06 Ethane cmol/mol 0.114 13.933 Propane cmol/mol 0.051 7.990 i-butane cmol/mol 0.01171 1.1856 n-butane cmol/mol 0.01553 1.1943 neo-pentane cmol/mol 0.01007 0.300 i-pentane cmol/mol 0.0059 0.2973 n-pentane cmol/mol 0.01149 0.351 n-hexane cmol/mol 0.005254 0.3499 VSL - Beyond all doubt 16
The revised ISO 10723 What has changed? Maturity! -Improved uncertainty calculation (GUM compliant) -Benchmark evaluation -Monte Carlo simulation (a.o. implementation of nonlinearity and uncertainty sources) Dedicated calculations for different measurement ranges Dedicated calculations based on the selected calibration gas VSL - Beyond all doubt 17
Results of linearity tests Calibration curve Ethane 1 st order Goodness of Fit 5.9 (>2) Absolute X and Y residuals >2 Calibration curve Ethane 3 rd order Goodness of Fit 0.9 (<2) Absolute X and Y residuals <2 Not linear: advise on composition of calibration gas 18
Monte Carlo simulation Simulate 10.000 compositions within range of interest (dedicated to the location/source)! - random, but with some restrictions - increasing concentrations for decreasing carbon number - rectangular distribution on the ranges -iso- and normal- isomers with the same carbon number concentrations within 10% relative Calculate the peak area based on the true respons functions Calculate the composition based on single point calibration Compare calculated composition (single point) to generated composition Expres the results in terms of %error VSL - Beyond all doubt 19
Error gross calorific value (MJ/m 3 ) Result of Monte Carlo simulation 0.150 0.100 0.050 0.000-0.050-0.100-0.150 60 65 70 75 80 85 90 95 100 105 amount-of-substance fraction methane (cmol/mol) VSL - Beyond all doubt 20
Error gross calorific value (MJ/m3) Error gross calorific value (MJ/m 3 ) 0.150 0.100 0.050 0.000-0.050-0.100-0.150-0.200 Monte Carlo simulation, using different calibration gas composition Cal gas contains78 % CH 4-0.250 0.150 0.100 60 65 70 75 80 85 90 95 100 105 amount-of-substance fraction methane (cmol/mol) Cal gas contains 91 % CH 4 0.050 0.000-0.050-0.100-0.150-0.200-0.250 VSL - Beyond all doubt 21 60 65 70 75 amount-of-substance 80 fraction methane 85 (cmol/mol) 90 95 100 105
Result of ISO 10723 evaluation summary of the performance of the GC: Satisfactory / Acceptable Not satisfactory / Not acceptable Mean error in superior calorific value Uncertainty in superior calorific value Uncertainty in superior calorific value Uncertainty in carbon dioxide emission factor Chromatography (peak separation) Traceability of the calibration gas(es) Values from the GC can be taken for granted ( H, W, z, T dew, ρ, ϑ s ± U H, W, z, Tdew, ρ, ϑs ) Dedicated performance for the on-line analyzer within the used application Demonstrated effect of the calibration gas composition and uncertainty VSL - Beyond all doubt 22
VSL implementation of EN 1776 / ISO 10723 (+additional issues) - Factory Acceptance Test (FAT) based on ISO 10723 - At VSL or at the manufacturer s site - Site Acceptance Test (SAT) based on ISO 10723 - demonstrate performance on-site (NG, LNG, green gas) and help to solve non-conformities on-site! perform re-calibration under ISO 17025 accreditation - Supply of traceable Certified Reference Materials (ISO 6142 / ISO 6143) ISO 10723, ISO 6142 and ISO 6143 activities performed within the scope of VSL s ISO 17025 accreditation - Train operators to perform ISO10723 validation - Perform type approval for new GC s - Organization of Proficiency Testing schemes (PT, round robin) under ISO 17043 accreditation 23
Proficiency Testing (ISO 17043): to prove good performance Individual cylinders with natural gas mixture, certified by VSL, send to 15 participants: CH 4 Reported data (10-2 mol/mol) Lab ID Value std.dev U (k=2) n flag z raw z E n Y ref U ref L001 83.12 0.00 0.18 5-0.90-0.42-0.22 83.17 0.16 L002 83.32 0.03 1.17 5 2.56 1.45 0.15 83.14 0.16 L003 83.18 0.00 0.83 5 0.22 0.27 0.04 83.15 0.16 L004 82.72 0.11 0.03 5 * -7.68-3.43-2.63 83.15 0.16 L005 83.17 0.00 0.02 3-0.03 0.23 0.18 83.14 0.16 L006 83.15 0.00 0.13 3-0.35 0.08 0.05 83.14 0.16 L007 83.14 0.00 0.21 2-0.53-0.16-0.08 83.16 0.16 L008 83.17 0.02 0.08 5 0.00 0.00 0.00 83.17 0.16 L009 83.21 0.02 0.93 5 0.76 0.44 0.06 83.16 0.16 L010 83.20 0.01 0.22 5 0.57 0.43 0.20 83.15 0.16 L011 82.86 0.00 0.66 5 * -5.29-2.23-0.41 83.14 0.16 L012 83.20 0.01 2.64 5 0.48 0.39 0.02 83.15 0.16 L013 83.02 0.01 0.22 5-2.63-1.07-0.49 83.15 0.16 L014 83.21 0.00 0.18 2 0.72 0.50 0.26 83.15 0.16 L015 83.21 0.01 0.26 4 0.67 0.48 0.20 83.15 0.16 VSL - Beyond all doubt 24
L001 L002 L003 L004 L005 L006 L007 L008 L009 L010 L011 L012 L013 L014 L015 E n -number L001 L002 L003 L004 L005 L006 L007 L008 L009 L010 L011 L012 L013 L014 L015 (10-2 mol/mol) Proficiency Testing results Results for CH 4 85.56 84.56 83.56 82.56 81.56 80.56 Laboratory ID 2.00 1.50 1.00 0.50 0.00-0.50-1.00-1.50-2.00 E n -numbers for CH 4 Laboratory ID VSL - Beyond all doubt 25
VSL: related activities Leading role in world-wide metrology for preparation of energy-gas Primary Reference materials - organizer of all CCQM Key comparisons for natural gas - organizer of first CCQM Key comparison on biogas - co-ordinator of EMRP LNG I and II - co-ordinator of EMRP biogas - participant (WP-leader) in EMRP energy gases - active in ISO TC 158 gas analyses - active in ISO TC 193 natural gas (ISO 6976, ISO 10723) Accredited laboratory for organization of Proficiency Testing schemes (PT s, PT on demand) VSL - Beyond all doubt 26
Conclusion: ISO 10723 describes a good method to obtain reliable results from an on-line natural gas analyzer The revision of the standard has improved the quality of the results and gives the possibility to match the results with the actual on-site situation (implementation of the standard may have become more complicated / more specialized) VSL - Beyond all doubt 27
VSL PO Box 654 2600 AR Delft The Netherlands T F E I +31 15 269 15 00 +31 15 261 29 71 info@vsl.nl www.vsl.nl Any Questions? - ISO 10723 - VSL - gas chromatography - EMRP/EMPIR - PT-schemes - etc.