The New ISO Advances and new concepts in the performance evaluation and benchmarking of on line natural gas analysers.

Transcription

1 The New ISO Advances and new concepts in the performance evaluation and benchmarking of on line natural gas analysers. Dr Paul Holland BD Director, EffecTech Group

2 Natural gas quality measurement composition (content) of natural gas inert gases nitrogen, carbon dioxide, helium, (argon & hydrogen) hydrocarbons methane, ethane, propane, iso butane, n butane, pentanes, hexanes +... properties (characteristics) of natural gas calorific value, Wobbe number, standard density (ISO 6976) compression factor, line density (ISO 12213) hydrocarbon dew point (ISO 23874) emission factors

3 Energy determination

4 Risks in energy metering Annual Value / 4,500,000 4,000,000 Typical gas fired power station Power output : 500 MW Energy Price : 60 / MWh 3,500,000 3,000,000 2,500,000 2,000,000 1,500,000 1,000,000 Typical 500, U(Energy) / %

5 Gas quality measurement instruments

6 Legal / commercial requirements legislation customer protection (example in UK law) Public Gas Transporters (PGTs) shall carry out performance evaluations of gas quality metering instruments in accordance with ISO following installation or maintenance. Provided that the results of the procedure show that the error on the calculated calorific value of transmission gas will not exceed 0.10 MJ.m 3 for gas compositions allowed in the system, the PGT may then use that instrument for the determination of calorific values for the purposes of section 12 of the Gas Act control of GHG emissions (example in EU directive) commercial gas contracts sales gas agreements / contracts (end users) allocation agreements (upstream)

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8 Revision of ISO : 1995 revision to existing standard required for inclusion of measurement uncertainties instrument precision, instrumental errors working calibration gas compliance with GUM more rigorous assessment of errors and uncertainties of measurement of revision by composition (gas content amount fraction) gas properties (calculated from composition) ISO/TC193/WG15 (with liaison from ISO/TC158) Drafting by G Squire (EffecTech, UK) and D Lander (NGG, UK)

9 ISO/DIS : 2011 Scope Determine E(x), E(P) and U(x), U(P) over a pre defined range of compositions for each specified component Determine a range of compositions for each specified component which satisfy predefined maximums in E(x), E(P) and U(x), U(P) using a specified calibration gas composition and uncertainty calibration gas redesign composition and uncertainty

10 Instrument errors response / (peak area) y=f ass (x) x cal content / (% mol/mol)

11 Instrument errors response / (peak area) y=f ass (x) y=f true (x) x cal content / (% mol/mol)

12 Instrument errors response / (peak area) y=f ass (x) y=f true (x) x cal content / (% mol/mol)

13 Instrument errors response / (peak area) y=f ass (x) y=f true (x) x cal content / (% mol/mol)

14 Challenge measurement of TRUE (actual) response functions for the instrument for all components (i=1..q) calibration functions y = F i,true (x) analysis functions x = G i,true (y) function types for F & G polynomials of order 1, 2 or 3 y i = F i,true (x i ) = a 0 + a 1 x i + a 1 x i2 + a 3 x i 3 x i = G i,true (y i ) = b 0 + b 1 y i + b 2 y i2 + b 3 y i 3

15 Design of reference gases a series of reference gases is measured by the instrument being calibrated components included in reference gases depends on application range of composition equal or greater than that expected to be measured by the instrument (no extrapolation) number of mixtures dependent upon expected order of F and G 3 (1 st order), 5 (2 nd order), 7 (3 rd order) approximately equally spaced within the range

16 ISO Performance evaluations of on line analytical systems ISO accredited calibration gases well established reference values & uncertainties 7 10 cylinders each containing 10,11 or 12 components wide range natural gas compositions

17 Experimental design replicate measurements reference gases Batch wise calibration simplest / manual / most practical (p gas changes) temporal drift has more significance

18 Experimental design replicate measurements reference gases Drift compensation calibration compensates for temporal drift (due to sample size effects) automation required

19 Drift correction Samples are injected at (or with reference to) ambient pressure. response effective sample size ambient pressure Batch wise calibration Drift compensation calibration measure ambient pressure at time of sample injection (P ijk ) y ijk = y ijk. P ref / P ijk

20 Gas fired power station

21 Gas fired power station

22 Witnessed factory evaluation

23 LNG receiving terminal

24 Custody transfer border station

25 Drift compensation calibration (automated)

26 Offshore allocation / sales gas

27 Regression analysis parameters F and G are calculated using GLS maximum liklihood functions relationships (MLFR) uncertainties in both variables (amount and response) procedure identical to that prescribed in ISO 6143 response functions validated for each component and in each domain F and G using ISO 6143

28 Calibration results

29 Errors content / amount fraction & properties assumed true x G i y F i ( y i, ass i ( x i, true i measured amount following calibration (where functions coincide) ) ) x * i, meas x i, cal Gi. G, ass i, ass ( F ( F i, true i, true ( x ( x i, true i, cal )) )) normalise x i, meas x * i, meas * xi, meas errors x i, meas xi, meas xi, true P meas P meas P true

30 Uncertainties in errors contributions from calibration gas instrument precision properties any property / characteristic calculated from composition ) (,cal x i u ) ( & ) (,, meas i cal i y u y u ),...,,,,...,, ( m n w w w x x x P f ) ( ) ( ) ( i m i i i n i i c w u w f x u x f P u

31 Off line model produce a off line model of instrument errors as a function of amount fraction repeatability as a function of amount fraction uncertainties as a function of amount fraction use Monte Carlo simulation generate 10,000 different gas compositions for each composition calculate errors in physical properties uncertainties in physical properties

32 Errors and uncertainties on errors E(CV SUP ) / MJ.m methane content / (% mol/mol)

33 Error distribution E(CV SUP ) / MJ.m methane content / (% mol/mol)

34 Mean error (bias) E(CV SUP ) / MJ.m methane content / (%mol/mol) mean error = bias B(P) Maximum Permissible Bias (MPB) P MPB

35 Uncertainty on mean error E(CV SUP ) / MJ.m methane content / (%mol/mol) uncertainty on the mean error uncertainty on bias U(B(P)) Maximum Permissible Error (MPE) P MPE P Uc

36 Errors and uncertainties summary

37 Example design of calibration gas

38 Example design of calibration gas x C1,cal = 0.88 mean E(CV) = ± MJ.m 3

39 Example design of calibration gas x C1,cal = 0.88 mean E(CV) = ± MJ.m 3 x C1,cal = 0.81 mean E(CV) = ± MJ.m 3

40 Analysis function correction superior CV

41 Instrument errors response / (peak area) y=f ass (x) y=f true (x) x cal content / (% mol/mol)

42 Dove House Dove Fields Uttoxeter Staffordshire ST14 8HU United Kingdom tel : +44 (0) e mail : paul.holland@effectech.co.uk web site : ISO9001:2008 FS