Improved Reliability in Natural Gas Energy Measurement with the Revised ISO Standard. Gerard Nieuwenkamp - VSL

Transcription

1 Improved Reliability in Natural Gas Energy Measurement with the Revised ISO Standard Gerard Nieuwenkamp - VSL

2 Improved reliability in natural gas energy measurement with the revised ISO standard Gerard Nieuwenkamp VSL Research and Development VSL/CEESI: 3 rd European USM workshop Noordwijk, 17 March 2015

3 Natural gas measurement VSL - Beyond all doubt 2

4 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

5 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

6 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

7 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

8 What is gas chromatography? t 0 t 1 t r

9 Gas Chromatography : calibration Gas chromatogram of calibration gas (with Elster Encal 3000) Peak area is proportional to concentration

10 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.

11 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

12 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

13 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

14 response Detector linearity check with 7 PSMs WRM response assumed response curve unknown response true response curve unknown mole fraction bias WRM WRM mole mole fraction mole fraction -during field operation: single point calibration! -How the quantify the bias and the associated uncertainty? VSL - Beyond all doubt 13

15 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 / ISO Guide 34 accreditation (with uncertainty that is fit for purpose!) VSL - Beyond all doubt 14

16 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

17 Validation with ISO 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 Nitrogen cmol/mol Carbon dioxide cmol/mol Ethane cmol/mol Propane cmol/mol i-butane cmol/mol n-butane cmol/mol neo-pentane cmol/mol i-pentane cmol/mol n-pentane cmol/mol n-hexane cmol/mol VSL - Beyond all doubt 16

18 The revised ISO 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

19 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

20 Monte Carlo simulation Simulate 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

21 Error gross calorific value (MJ/m 3 ) Result of Monte Carlo simulation amount-of-substance fraction methane (cmol/mol) VSL - Beyond all doubt 20

22 Error gross calorific value (MJ/m3) Error gross calorific value (MJ/m 3 ) Monte Carlo simulation, using different calibration gas composition Cal gas contains78 % CH amount-of-substance fraction methane (cmol/mol) Cal gas contains 91 % CH VSL - Beyond all doubt amount-of-substance 80 fraction methane 85 (cmol/mol)

23 Result of ISO 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

24 VSL implementation of EN 1776 / ISO (+additional issues) - Factory Acceptance Test (FAT) based on ISO At VSL or at the manufacturer s site - Site Acceptance Test (SAT) based on ISO demonstrate performance on-site (NG, LNG, green gas) and help to solve non-conformities on-site! perform re-calibration under ISO 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 accreditation - Train operators to perform ISO10723 validation - Perform type approval for new GC s - Organization of Proficiency Testing schemes (PT, round robin) under ISO accreditation 23

25 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 L L L L * L L L L L L L * L L L L VSL - Beyond all doubt 24

26 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 Laboratory ID E n -numbers for CH 4 Laboratory ID VSL - Beyond all doubt 25

27 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

28 Conclusion: ISO 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

29 VSL PO Box AR Delft The Netherlands T F E I info@vsl.nl Any Questions? - ISO VSL - gas chromatography - EMRP/EMPIR - PT-schemes - etc.