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A new mass & time primary standard for natural gas in China and the uncertainty evaluation
Accepted Manuscript A New Mass & Time Primary Standard for Natural Gas in China and the Uncertainty Evaluation Jia Ren, Jiqin Duan, Min Huang, Min He PII:
S0955-5986(18)30257-7
DOI:
https://doi.org/10.1016/j.flowmeasinst.2019.05.001
Reference:
JFMI 1567
To appear in:
Flow Measurement and Instrumentation
Received Date: 22 August 2018 Revised Date:
4 April 2019
Accepted Date: 6 May 2019
Please cite this article as: J. Ren, J. Duan, M. Huang, M. He, A New Mass & Time Primary Standard for Natural Gas in China and the Uncertainty Evaluation, Flow Measurement and Instrumentation, https:// doi.org/10.1016/j.flowmeasinst.2019.05.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
A New Mass & Time Primary Standard for Natural Gas in China and the Uncertainty Evaluation Ren Jia1, Duan Jiqin1, Huang Min1,He Min2 Chengdu Verification Branch of National Oil & Gas Large Flow rate Measurement Station, Huayang Town,Chengdu 610213, China 2 Southwest Oil & Gas Field Company, Chengdu 610000, China E-mail: [email protected]
RI PT
1
put into operation on March 2017 and approved by AQSIQ on Oct.15 2017. The technical details of the new balance weighting system and diverting system are presented in the paper as well as uncertainty evaluation and preliminary comparison of CFV calibration between CVB and CEESI(Colorado Engineering Experiment Station Inc.) .
1. Introduction
2. The new primary standard system
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The new primary system consists of a weighting system, two diverter valves and relevant auxiliary devices as shown in figure 1.
Mass Time
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Keywords: Primary standard Principle Uncertainty
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Abstract: A new mass-time primary standard for high pressure natural gas, which is based on electromagnetic balance and hydraulic fast-acting valves, was set up at the beginning of 2017 in Chengdu, China. The full load of the electromagnetic balance is 3 tons and the measurement uncertainty of mass is better than 1.0g(k=2).The opening and closing time of the hydraulic fast-acting valves can achieve 33ms±3ms.The operation pressure and flowrate range of the facility is (4-60)bar.a and (5-410)m3/h respectively. In accordance with the preliminary tests, the estimate uncertainty of sonic nozzles calibration is between 0.10%-0.12%(k=2).The operation principle, testing results and the uncertainty evaluation are presented in the paper as well as some improving ideas.
In many gas flow calibration institutes, mass-time standards have been used as high level gas primary standards worldwide since 1990’s.As a natural gas flow calibration institute authorized by the General Administration of Quality Supervision, Inspection and Gurantine of China in 1998, CVB(Chengdu Verification Branch of National Oil & Gas Large Flow rate Measurement Station) used to maintain a mass-time primary standard to calibrate CFVs(critical sonic nozzles). This masstime primary standard was based on a 3-ton scale and pneumatic diverting system.The mass flow measurement uncertainty was 0.1% (k=2) and the calibration uncertainty of CFVs was 0.22%(k=2).The flowrate and pressure range were (5-320)m3/h and (4-38)bar respectively.
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Fig. 1- Flowchart of CVB Primary Facility
AC C
The test rig(see figure 2) is practically based on the findings of a static weighing system,which is located in a closed room with temperature and humidity controlling system, and a fast-acting diverting system.
With the development of natural gas industry in China, lower traceability uncertainty and higher capability are required. In order to increase the metrological performance and capability, CVB started to build up a new mass-time primary standard in 2014. This new primary facility was
Fig. 2- Sketch of the Test Rig
The weighing system mainly has a 3-ton electromagnetic balance, two tanks with thermal isolation, two platforms and two big weights which are used for special test(see figure.3) . In 1
ACCEPTED MANUSCRIPT addition, there are three dowels in the platforms that relatively match up to the grooves in the “feet” of tanks to keep the proper position during execution.Then tanks and platforms can be move together steadily on the roller guide rail to be connected to pipeline system or to be weighted by the balance which also reduces the pipeline length between tanks and pipeline system.
Computer
RS485
RS485 Calibration Control module (including a timer)
Controlling signal Pulses for position
Pluses for position Optical gateings
bypass valve
Control module
driving
controlling signal
Hydraulic station1
Generally one tank is used for collecting natural gas and another one is used for balancing. For some special tests, two tanks could be used to collect gas simultaneously and two big weights are used to balance the weight of the tanks respectively. Both two tanks are moved to be weighted or connected to the pipeline and the reference weights are loaded or unloaded automatically by PLC. The results indicates there is lack of existence of access or exit by operators. The substitute weighing method is used for high accurate weighting and the whole system is located in a thermal isolated room with temperature and humidity controlling.
Control module
RS485
controlling signal
driving
PLC2
Hydraulic station2
PLC1
Optical gateings
tank valve
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Fig. 5- Diagram of Diverter controlling principle
SC
acuating time of opening tank valve(ms)
These two valves were tested to get the exact actuating time, opening time and closing time (shown in fig.6 to fig.11) in the factory over one year. Because of good repeatability these data can be used to calculate the delay time of tank valve.
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53 52 51 50 49 48 47 46 45 44 43
0
1
2
3
4
n
5
6
7
8
9
10
11
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actuating time of closing bypass valve(ms)
Fig.6- actuating time of opening tank valve
53 52 51 50 49 48 47 46 45 44 43
0
1
2
3
4
5
n
6
7
8
9
10
11
9
10
11
9
10
11
Fig.7- actuating time of closing bypass valve
open time of tank valve (ms)
Fig. 3- Overview of Weighting System
EP
The whole diverter system(shown in figure 4) consist of two hydraulic systems, two hydraulically actuated valves equipped with 13 optical gratings. The controlling principle of the fast-diverting valves is shown in figure 5.
35 34 33 32 31 30 29 28 27 26 25
AC C
0
1
2
3
4
5
n
6
7
8
close time of tank valve (ms)
Fig. 8- opening time of tank valve
Fig. 4- Overview of Diverter System
35 34 33 32 31 30 29 28 27 26 25 0
1
2
3
4
5
n
6
7
8
Fig. 9- closing time of tank valve
2
open time of bypass valve(ms)
ACCEPTED MANUSCRIPT state for the gas and to obtain an initial mass in the inventory volume (mi) [3].
35 34 33 32 31 30 29 28 27 26 25 0
1
2
3
4
5
n
6
7
8
9
10
11
9
10
11
6) In accordance to pre-set calibration time interval which is calculated referring to choke ratio of 0.85 and size of different sonic nozzles, the calibration control module sends a signal to close the tank valve.When the optical gatings show that the tank valve is completely closed, the control module of tank valve sends a signal to calibration control module to trigger timer to obtain the stop time (tf) and open bypass valve. Then the pressure and temperature in the inventory volume ( Pf and Tf ) are acquired several seconds before tf which are used to calculate (mf) [3].
35 34 33 32 31 30 29 28 27 26 25 0
1
2
3
4
5
n
6
7
8
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close time of bypass valve(ms)
Fig.10- opening time of bypass valve
Then the following equation for the average mass flow during the collection time can be derived[2]:
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Fig. 11- closing time of bypass valve
In figure 6 to 11, n means how many times the valves are opened or closed.In addition an online GC is used to get the real-time gas composition for molar mass calculation(see 3.2 equation 2 ). An offline GC is used for checking periodically.
∆m ∆mT + ∆ma + ∆mb = t t (1) f i f mT − mT + ma − mai + mbf − mbi = t Where qms is the mass flow rate,
M AN U
qm =
3. Operation principle
(
The process of making a mass flow measurement normally entails the following steps:
) (
) (
)
2) Close the tank valve, disconnect tank 1 from the test pipe and move it to the balance side.
4. Calibration performance of sonic nozzles and uncertainty evaluation
3) Use the weighting system to get the initial mass of gas in tank 1 while tank 2 is used to balance. Then move tank 1 and connect it to the test pipe.
4.1 calibration performance
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1) Evacuate the collecting tank volume through the vent pipeline and inventory volume Va while the tank is connected to the test pipe.
∆mT , ∆ma , ∆mb are the mass difference in collecting tank, inventory volume Va and Vb respectively between ti and t f , t is the collecting time.
EP
To test the calibration performance of the primary standard over (4-60) bar, a sonic nozzle with throat diameter of 14.836mm was used. The tests included repeatability and stability of sonic nozzle calibration over 6 months from March to August 2017 according to the national metrology regulation. Test results(see fig.12 to fig.13) show that the repeatability and stability are better than 0.02% and 0.06% respectively.
AC C
4) Open the bypass valve, and establish a stable flow through the CFV.Then start the acquisition for stagnation and inventory pressure, temperature. 5) Referring to figure 5, the computer sends a signal to the tank valve control module which is configured to be delayed for several milliseconds as the calibration start. The delayed time is calculated by pre-test data and time interval which maintains the sonic choking condition when two valves are both closed and achieves “zero overlap”[1][2]. When the optical gatings show the tank valve is just open, tank valve control module sends a signal to calibration control module to trigger the timer to obtain the calibration start time (ti) and acquire Pi and Ti of Va and Vb(see Fig.1) over several seconds respectively. These values will be used along with the equation of
Repeatability test result of 14.836mm SN 0.019%
Repeatability（%）
0.020% 0.016%
0.015%
0.016% 0.012%
0.012%
0.012% 0.008% 0.008% 0.004% 0.000% 5.8MPa
3.5MPa
2.0MPa
0.9MPa
0.67MPa
Fig. 12- Repeatability Test Results
3
0.4MPa
ACCEPTED MANUSCRIPT Where qms is mass flow given by primary standard,
Stabilty test result of 14.836mm SN
0.07% 0.06%
0.06%
0.06%
C* is the critical flow function, P0 and T0 are the
Stability（%）
0.06% 0.05% 0.04%
0.04%
stagnation pressure and temperature respectively, M is molar mass, d is diameter of Veturi nozzle
0.04% 0.03% 0.03% 0.02% 0.01%
throat and R is universal gas contant。
0.00% 5.8MPa
3.5MPa
2.0MPa
0.9MPa
0.67MPa
0.4MPa
Fig. 13- Short-term Stability Test Results
Then according to ISO/IEC Guide 98-3:2008[4], estimation of the measurement uncertainty budget of the primary facility can summarized as follow:
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To check the long term stability, the above sonic nozzle was calibrated against the primary standard under 35bar and 20bar on May 2018. The calibration results showed the repeatability was 0.015% and the difference from the average of last 6 month tests are 0.03% which shown a very good metrological performance of the primary standard(see Fig.14 and 16).
1 u r2 (cd ) = ur2 (qms ) + u r2 + u r2 (C* ) + 4ur2 (d ) + u r2 ( P0 ) + (u r2 (T0 ) + ur2 (M )) 4
SC
u r2 (qms ) = ur2 (t ) + ur2 ( ∆m) + ur2 (QT )
0.99477 0.99475
0.99473 0.99470
0.99457 0.99455
0.99453 0.99450
0.99450
0.99450
0.99505 0.99500 0.99498 0.99495 0.99490 0.99487 0.99485 0.99480 0.99480 2017.3-2017.8 35bar 0.99475 2018.5 35bar 0.99470 0.99465 0.99460 0.99460 0.99457 0.99455 0.99450 0.99450 0.99447 0.99445 Rent 0.99440 7.900E+06 8.000E+06 8.100E+06 8.200E+06 8.300E+06 8.400E+06 8.500E+06 8.600E+06
TE D
Cd
Fig. 14- Reproducibility test results under 20bar
Fig. 15- Reproducibility test results under 35bar
EP
0.99630 0.99623
0.99610 0.99600
Cd
0.99590
0.99607
0.99587
0.99580
0.99560 0.99550 0.99540
2017.3-2017.8 4bar 2018.5 4bar
AC C
0.99570
0.99557 0.99553 0.99550
0.99544
Rent
9.10E+05 9.20E+05 9.30E+05 9.40E+05 9.50E+05 9.60E+05 9.70E+05 9.80E+05 9.90E+05 1.00E+06 1.01E+06 1.02E+06
Fig. 16- Reproducibility test results under 4bar
4.2 uncertainty evaluation
Referring to the operation principle of the primary standard, the overview of quantities that exert an influence on measurement uncertainty in sonic nozzle calibration is summarized by the following equation: Cd =
π
qms
u (∆mVa / b ) = ∆mVa / b × ur2 ( Pa / b ) + ur2 (Ta / b ) + u r2 (Va / b )
(6)
Where u ( ∆m T ) is uncertainty component of balance[5] [6], u (F ) is the uncertainty component of buoyancy which can be calculated according to test results. u r ( Pa / b ) , u r (Ta / b ) and u r (Va / b ) are the relative uncertainty component of pressure, temperature and volume of inventory volume a or b. u r2 (QT ) is the uncertainty component of internal leakage of diverter valves which can be less than 0.02%. (2) ur is the uncertainty component of repeatability which can be calculated as the standard deviation of the test results of Cd. (3) ur (C* ) is the relative uncertainty component of [7] C* . According to ISO 9300 , a relative uncertainty on C* of 0.05% at 95% confidence level can be ensured when AGA 8 is used as the state equation. (4) ur (d ) is the relative uncertainty component of throat diameter of sonic nozzle. It is a combination of diameter measurement resolution and temperature difference between calibration and operation condition of sonic nozzle. (5) ur ( P0 ) , ur (T0 ) are the uncertainty components of stagnation pressure and temperature upstream of sonic nozzle (6) ur (M ) is the uncertainty component of molar weights of natural gas mixture which related to reference gas and GC performance. According to engineering practice[3][5], 0.05% can be achieved.
Re nt 0.99445 4.550E+0 4.600E+0 4.650E+0 4.700E+0 4.750E+0 4.800E+0 4.850E+0 4.900E+0 4.950E+0 5.000E+0 6 6 6 6 6 6 6 6 6 6
0.99620
(5)
M AN U
Cd 0.99460
u 2 (∆mT ) + u 2 (∆mVa ) + u 2 (∆mVb ) + u 2 ( F ) ∆m
u r2 (∆m) =
0.99467 2017.3-2017.8 20bar 2018.5 20bar
(4)
Referring to equation (1), ur2 (∆m) can be calculated as following:
0.99480
0.99465
(3)
（2）
P0 d ⋅ C* ⋅ 4 ( R / M )T0 2
4
ACCEPTED MANUSCRIPT Fig. 17- Inter-lab Comparison Test Data for S.N.38241#
(7) ur (t ) is the uncertainty component of collecting time which is calculated through repeatability by on-line calibration of timing system against frequency standard and nanosecond counter. From above, the uncertainty evaluation results are obviously closely related to the process conditions. A typical uncertainty evaluation result for a 20.948mm nozzle calibration under 4 bar is shown in Table 1.
1.0000
2
CVB polynomial: y = -3.5444E-05x + 6.7427E-04x + 9.9157E-01 0.9990 0.9980
2
R = 9.8698E-01
Cd
0.9970 0.9960 0.9950 0.9940 0.9930 0.9920
CVB natural gas CEESI air
0.9910 0.9900
5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5
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Re/10^6
Fig. 18- Inter-lab Comparison Test Data for S.N.38242#
Table 1 Cd calibration uncertainty results of 1.0000
20.984mm sonic nozzle Sensitive coefficient
quantities
2
CVB polynomial: y = -3.9158E-05x + 6.8006E-04x + 9.9164E-01
Standard uncertainty component
0.9980
2
R = 4.5278E-01
0.9970 0.9960
Cd
name
0.9990
0.9950 0.9940
0.5g
1
0.5g
SC
0.9930
u (mc)
0.9920 0.9910
0.023g
1
0.023g
u (mVa)
0.046g
1
0.046g
u (F )
0.4g
1
0.4g
/
2575g
u r(m)
/
0.025%
0.01%
1 1
0.02%
ur
0.02%
1
0.02%
u r (d )
0.0085%
2
0.017%
u r ( P0 )
0.025%
1
0.025%
0.034%
u r (M )
0.05%
0.017%
0.5
0.025%
U r(Cd)=2* u r(Cd)
0.12%
EP
U r(Cd)
0.5
1.0000 0.9990
0.9930 0.9920
5.5
6.5
7.5
8.5
9.5
10.5 11.5 12.5 13.5 14.5 15.5 16.5 17.5 18.5 19.5 20.5
Re/10^6
Fig. 21- Inter-lab Comparison Test Data for S.N.38245#
Cd
AC C
1.0000 0.9990 0.9980 0.9970 0.9960 0.9950 0.9940 0.9930 0.9920 0.9910 0.9900
2
CVB polynomial: y = -2.7557E-05x + 5.4184E-04x + 9.9195E-01 R2 = 5.9867E-01
CVB natural gas CEESI air 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 Re/10^6
Fig. 22- Inter-lab Comparison Test Data for S.N.38246#
Cd
9.0 9.5
CEESI air 4.5
CEESI air 8.0 8.5
CVB natural gas
0.9910 0.9900
CVB natural gas
7.5
2
0.9960 0.9950 0.9940
0.9950
6.5 7.0
3
2
R = 9.0891E-01
0.9970
2
5.5 6.0
CVB polynomial: 4
y = -8.6441E-07x + 4.3534E-05x - 7.7376E-04x + 5.7439E-03x + 9.8001E-01
0.9980
2
5.0
Re/10^6
Fig. 20- Inter-lab Comparison Test Data for S.N.38244#
R = 8.6817E-01
0.9910 0.9900
CEESI air
5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5
CVB polynomial:y = -6.7941E-05x + 1.2607E-03x + 9.8880E-01
0.9940 0.9930 0.9920
CVB natural gas
0.9910 0.9900
To identify the claimed uncertainty of CVB new primary standard, an inter-lab comparison was carried out between CEESI which has maintained a PVTt primary standard with compressed air in Colorado[8] since 1970’ and CVB using 8 sonic nozzles. The Cd calibration uncertainty of CEESI and CVB is from 0.124%-0.168%(k=2) and 0.10%-0.12%(k=2) respectively.The data is shown in Fig.17-24. 0.9980 0.9970 0.9960
2
R = 4.4598E-01
0.9920
5. Preliminary Inter-lab comparison
1.0000 0.9990
2
CVB polynomial: y = -2.9425E-05x + 5.7764E-04x + 9.9169E-01
0.9970 0.9960 0.9950 0.9940 0.9930
Cd
u r (T0 )
1.0000 0.9990 0.9980
TE D
0.02%
Re/10^6
Fig. 19- Inter-lab Comparison Test Data for S.N.38243#
0.01%
u r (QT )
CEESI air
5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5
Cd
u (m)
ur(t)
0.9900
M AN U
u (mVb)
CVB natural gas
10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5
Re/10^6
5
ACCEPTED MANUSCRIPT CVB would keep doing further research to improve the calibration uncertainty related to ambient temperature, buoyancy and high frequency monitoring of pressure and temperature while diverting, etc.In near future, CVB would be a participant of national high pressure primary standard comparison organized by NMi.
CVB polynomial: 4
3
2
y = 1.6068E-07x - 9.1790E-06x + 1.9136E-04x - 1.6174E-03x + 9.9942E-01 2
R = 9.9943E-01
0.9960 0.9950 0.9940 0.9930 0.9920
CVB natural gas CEESI air
0.9910 0.9900 4.5
5.5
6.5
7.5
8.5
9.5
10.5 11.5 12.5 13.5 14.5 15.5 16.5 17.5 18.5 19.5 20.5
Re/10^6
Fig. 23- Inter-lab Comparison Test Data for S.N.38247#
Acknowledgments The authors gratefully acknowledge Dr. Li Chunhui from NMi for her essential technical and theoretical contributions and CVB staffs who were involved in the construction, commissioning and testing of the new primary standard.
1.0000 2
0.9990
CVB polynomial:y = -3.9665E-05x + 7.4302E-04x + 9.9134E-01
0.9980
R = 9.9516E-01
2
Cd
0.9970 0.9960 0.9950 0.9940 0.9930
CVB natural gas
0.9920
CEESI air
0.9910 0.9900
References
4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5
SC
Re/10^6
Fig. 24- Inter-lab Comparison Test Data for S.N.38248#
[1]R E Harris ,J.E. Johnson, “Primary Calibration of Gas Flows with A Weight/t Method”, 5th ISFFM， 1990. [2]John D. Wright ， Aaron N. Johnson, “Uncertainty in Gas Flow Primary Standards Due to Flow Work Phenomena”, 6th FLOMEKO,2000. [3]John D Wright，et al. “Design and Uncertainty Analysis for a PVTt Gas Flow Standard”, Journal of Research of NIST, Volume 108, Number 1,JanuaryFebruary 2003. [4]ISO/IEC Guide 98-3:2008, “the Guide to the Expression of Uncertainty in Measurement”. [5]Joel T. Park, et al, “Uncertainty Estimates for the Gravimetric Primary Flow Standards of the MRF”, 3rd ISFFM,1995. [6]Ren Jia, Duan Jiqin,et al, “Uncertainty Estimates of a New Gravimetric primary Standard”, Measurement Technique,August,2015. [7]ISO 9300:2005,“Measurement of gas flow by means of critical flow Venturi nozzle”. [8]Thomas Kegel, “Primary System for calibrating Compressible Fluid Flowmeters ”, ISA/94 International Conference and Exhibit, Oct.24-27, 1994. [9]ISO/IEC 17043:2010,“Conformity assessment-General requirements for proficiency testing”.
M AN U
Referring to ISO/IEC 17043[9] ， EN ,which is calculated as following equation, is used to determined whether the comparison results could be accepted or not. If En≤1, the claimed
uncertainty of each lab would be validated. EN =
x1 − x 2
(7)
U ( x1 ) + U 2 ( x 2 ) 2
In accordance to Fig.10-17, EN of inter-lab comparison between CVB and CEESI is shown in Fig.25. 1.2
TE D
38241# 38242# 38243# 38244# 38245# 38246# 38247# 38248#
1
EN
0.8
0.6
0.4
0 4
5
6
7
8
9
EP
0.2
10
11
12
13
14
15
16
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Cd
1.0000 0.9990 0.9980 0.9970
17
18
19
20
21
Re/10^6
AC C
Fig. 25- Inter-lab Comparison Results between CVB and CEESI
From Fig.25, EN is less than 1 for all calibration results which identify the claimed uncertainty of sonic nozzle calibration against CVB new primary standard with natural gas achieved 0.10%0.12%(k=2). 6. Conclusions Because of the application of new weighting and timing technology , the metrology performance of mass-time primary facility has been improved a lot.The uncertainty analysis, short-term stability test and inter-lab comparison results shows that the sonic nozzle calibration uncertainty of new primary standard for natural gas in CVB could achieve 0.10%-0.12%(k=2). 6
ACCEPTED MANUSCRIPT Highlights 1.A new mass-time primary standard for natural gas based on 3t electromagnetic balance and hydraulic fast-acting valves 2.Two tanks , one is for gas collecting and another is for balancing, and weights are operated
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automatically by PLC without air turbulence 3.Two hydraulically actuated valves equipped with 13 optical gratings operated in about 33ms achieve “zero overlap” and sonic choking condition during single calibration
4. Uncertainty evaluation and one year time stability test results show that the CMC is about
AC C
EP
TE D
M AN U
SC
0.10%-0.12%(k=2) and inter-lab comparisons with NMi and CEESI also verify the CMC
S0955-5986(18)30257-7
DOI:
https://doi.org/10.1016/j.flowmeasinst.2019.05.001
Reference:
JFMI 1567
To appear in:
Flow Measurement and Instrumentation
Received Date: 22 August 2018 Revised Date:
4 April 2019
Accepted Date: 6 May 2019
Please cite this article as: J. Ren, J. Duan, M. Huang, M. He, A New Mass & Time Primary Standard for Natural Gas in China and the Uncertainty Evaluation, Flow Measurement and Instrumentation, https:// doi.org/10.1016/j.flowmeasinst.2019.05.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
A New Mass & Time Primary Standard for Natural Gas in China and the Uncertainty Evaluation Ren Jia1, Duan Jiqin1, Huang Min1,He Min2 Chengdu Verification Branch of National Oil & Gas Large Flow rate Measurement Station, Huayang Town,Chengdu 610213, China 2 Southwest Oil & Gas Field Company, Chengdu 610000, China E-mail: [email protected]
RI PT
1
put into operation on March 2017 and approved by AQSIQ on Oct.15 2017. The technical details of the new balance weighting system and diverting system are presented in the paper as well as uncertainty evaluation and preliminary comparison of CFV calibration between CVB and CEESI(Colorado Engineering Experiment Station Inc.) .
1. Introduction
2. The new primary standard system
M AN U
The new primary system consists of a weighting system, two diverter valves and relevant auxiliary devices as shown in figure 1.
Mass Time
TE D
Keywords: Primary standard Principle Uncertainty
SC
Abstract: A new mass-time primary standard for high pressure natural gas, which is based on electromagnetic balance and hydraulic fast-acting valves, was set up at the beginning of 2017 in Chengdu, China. The full load of the electromagnetic balance is 3 tons and the measurement uncertainty of mass is better than 1.0g(k=2).The opening and closing time of the hydraulic fast-acting valves can achieve 33ms±3ms.The operation pressure and flowrate range of the facility is (4-60)bar.a and (5-410)m3/h respectively. In accordance with the preliminary tests, the estimate uncertainty of sonic nozzles calibration is between 0.10%-0.12%(k=2).The operation principle, testing results and the uncertainty evaluation are presented in the paper as well as some improving ideas.
In many gas flow calibration institutes, mass-time standards have been used as high level gas primary standards worldwide since 1990’s.As a natural gas flow calibration institute authorized by the General Administration of Quality Supervision, Inspection and Gurantine of China in 1998, CVB(Chengdu Verification Branch of National Oil & Gas Large Flow rate Measurement Station) used to maintain a mass-time primary standard to calibrate CFVs(critical sonic nozzles). This masstime primary standard was based on a 3-ton scale and pneumatic diverting system.The mass flow measurement uncertainty was 0.1% (k=2) and the calibration uncertainty of CFVs was 0.22%(k=2).The flowrate and pressure range were (5-320)m3/h and (4-38)bar respectively.
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Fig. 1- Flowchart of CVB Primary Facility
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The test rig(see figure 2) is practically based on the findings of a static weighing system,which is located in a closed room with temperature and humidity controlling system, and a fast-acting diverting system.
With the development of natural gas industry in China, lower traceability uncertainty and higher capability are required. In order to increase the metrological performance and capability, CVB started to build up a new mass-time primary standard in 2014. This new primary facility was
Fig. 2- Sketch of the Test Rig
The weighing system mainly has a 3-ton electromagnetic balance, two tanks with thermal isolation, two platforms and two big weights which are used for special test(see figure.3) . In 1
ACCEPTED MANUSCRIPT addition, there are three dowels in the platforms that relatively match up to the grooves in the “feet” of tanks to keep the proper position during execution.Then tanks and platforms can be move together steadily on the roller guide rail to be connected to pipeline system or to be weighted by the balance which also reduces the pipeline length between tanks and pipeline system.
Computer
RS485
RS485 Calibration Control module (including a timer)
Controlling signal Pulses for position
Pluses for position Optical gateings
bypass valve
Control module
driving
controlling signal
Hydraulic station1
Generally one tank is used for collecting natural gas and another one is used for balancing. For some special tests, two tanks could be used to collect gas simultaneously and two big weights are used to balance the weight of the tanks respectively. Both two tanks are moved to be weighted or connected to the pipeline and the reference weights are loaded or unloaded automatically by PLC. The results indicates there is lack of existence of access or exit by operators. The substitute weighing method is used for high accurate weighting and the whole system is located in a thermal isolated room with temperature and humidity controlling.
Control module
RS485
controlling signal
driving
PLC2
Hydraulic station2
PLC1
Optical gateings
tank valve
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Fig. 5- Diagram of Diverter controlling principle
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acuating time of opening tank valve(ms)
These two valves were tested to get the exact actuating time, opening time and closing time (shown in fig.6 to fig.11) in the factory over one year. Because of good repeatability these data can be used to calculate the delay time of tank valve.
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5
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actuating time of closing bypass valve(ms)
Fig.6- actuating time of opening tank valve
53 52 51 50 49 48 47 46 45 44 43
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n
6
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9
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Fig.7- actuating time of closing bypass valve
open time of tank valve (ms)
Fig. 3- Overview of Weighting System
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The whole diverter system(shown in figure 4) consist of two hydraulic systems, two hydraulically actuated valves equipped with 13 optical gratings. The controlling principle of the fast-diverting valves is shown in figure 5.
35 34 33 32 31 30 29 28 27 26 25
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0
1
2
3
4
5
n
6
7
8
close time of tank valve (ms)
Fig. 8- opening time of tank valve
Fig. 4- Overview of Diverter System
35 34 33 32 31 30 29 28 27 26 25 0
1
2
3
4
5
n
6
7
8
Fig. 9- closing time of tank valve
2
open time of bypass valve(ms)
ACCEPTED MANUSCRIPT state for the gas and to obtain an initial mass in the inventory volume (mi) [3].
35 34 33 32 31 30 29 28 27 26 25 0
1
2
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n
6
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6) In accordance to pre-set calibration time interval which is calculated referring to choke ratio of 0.85 and size of different sonic nozzles, the calibration control module sends a signal to close the tank valve.When the optical gatings show that the tank valve is completely closed, the control module of tank valve sends a signal to calibration control module to trigger timer to obtain the stop time (tf) and open bypass valve. Then the pressure and temperature in the inventory volume ( Pf and Tf ) are acquired several seconds before tf which are used to calculate (mf) [3].
35 34 33 32 31 30 29 28 27 26 25 0
1
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n
6
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close time of bypass valve(ms)
Fig.10- opening time of bypass valve
Then the following equation for the average mass flow during the collection time can be derived[2]:
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Fig. 11- closing time of bypass valve
In figure 6 to 11, n means how many times the valves are opened or closed.In addition an online GC is used to get the real-time gas composition for molar mass calculation(see 3.2 equation 2 ). An offline GC is used for checking periodically.
∆m ∆mT + ∆ma + ∆mb = t t (1) f i f mT − mT + ma − mai + mbf − mbi = t Where qms is the mass flow rate,
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qm =
3. Operation principle
(
The process of making a mass flow measurement normally entails the following steps:
) (
) (
)
2) Close the tank valve, disconnect tank 1 from the test pipe and move it to the balance side.
4. Calibration performance of sonic nozzles and uncertainty evaluation
3) Use the weighting system to get the initial mass of gas in tank 1 while tank 2 is used to balance. Then move tank 1 and connect it to the test pipe.
4.1 calibration performance
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1) Evacuate the collecting tank volume through the vent pipeline and inventory volume Va while the tank is connected to the test pipe.
∆mT , ∆ma , ∆mb are the mass difference in collecting tank, inventory volume Va and Vb respectively between ti and t f , t is the collecting time.
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To test the calibration performance of the primary standard over (4-60) bar, a sonic nozzle with throat diameter of 14.836mm was used. The tests included repeatability and stability of sonic nozzle calibration over 6 months from March to August 2017 according to the national metrology regulation. Test results(see fig.12 to fig.13) show that the repeatability and stability are better than 0.02% and 0.06% respectively.
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4) Open the bypass valve, and establish a stable flow through the CFV.Then start the acquisition for stagnation and inventory pressure, temperature. 5) Referring to figure 5, the computer sends a signal to the tank valve control module which is configured to be delayed for several milliseconds as the calibration start. The delayed time is calculated by pre-test data and time interval which maintains the sonic choking condition when two valves are both closed and achieves “zero overlap”[1][2]. When the optical gatings show the tank valve is just open, tank valve control module sends a signal to calibration control module to trigger the timer to obtain the calibration start time (ti) and acquire Pi and Ti of Va and Vb(see Fig.1) over several seconds respectively. These values will be used along with the equation of
Repeatability test result of 14.836mm SN 0.019%
Repeatability（%）
0.020% 0.016%
0.015%
0.016% 0.012%
0.012%
0.012% 0.008% 0.008% 0.004% 0.000% 5.8MPa
3.5MPa
2.0MPa
0.9MPa
0.67MPa
Fig. 12- Repeatability Test Results
3
0.4MPa
ACCEPTED MANUSCRIPT Where qms is mass flow given by primary standard,
Stabilty test result of 14.836mm SN
0.07% 0.06%
0.06%
0.06%
C* is the critical flow function, P0 and T0 are the
Stability（%）
0.06% 0.05% 0.04%
0.04%
stagnation pressure and temperature respectively, M is molar mass, d is diameter of Veturi nozzle
0.04% 0.03% 0.03% 0.02% 0.01%
throat and R is universal gas contant。
0.00% 5.8MPa
3.5MPa
2.0MPa
0.9MPa
0.67MPa
0.4MPa
Fig. 13- Short-term Stability Test Results
Then according to ISO/IEC Guide 98-3:2008[4], estimation of the measurement uncertainty budget of the primary facility can summarized as follow:
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To check the long term stability, the above sonic nozzle was calibrated against the primary standard under 35bar and 20bar on May 2018. The calibration results showed the repeatability was 0.015% and the difference from the average of last 6 month tests are 0.03% which shown a very good metrological performance of the primary standard(see Fig.14 and 16).
1 u r2 (cd ) = ur2 (qms ) + u r2 + u r2 (C* ) + 4ur2 (d ) + u r2 ( P0 ) + (u r2 (T0 ) + ur2 (M )) 4
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u r2 (qms ) = ur2 (t ) + ur2 ( ∆m) + ur2 (QT )
0.99477 0.99475
0.99473 0.99470
0.99457 0.99455
0.99453 0.99450
0.99450
0.99450
0.99505 0.99500 0.99498 0.99495 0.99490 0.99487 0.99485 0.99480 0.99480 2017.3-2017.8 35bar 0.99475 2018.5 35bar 0.99470 0.99465 0.99460 0.99460 0.99457 0.99455 0.99450 0.99450 0.99447 0.99445 Rent 0.99440 7.900E+06 8.000E+06 8.100E+06 8.200E+06 8.300E+06 8.400E+06 8.500E+06 8.600E+06
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Cd
Fig. 14- Reproducibility test results under 20bar
Fig. 15- Reproducibility test results under 35bar
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0.99630 0.99623
0.99610 0.99600
Cd
0.99590
0.99607
0.99587
0.99580
0.99560 0.99550 0.99540
2017.3-2017.8 4bar 2018.5 4bar
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0.99570
0.99557 0.99553 0.99550
0.99544
Rent
9.10E+05 9.20E+05 9.30E+05 9.40E+05 9.50E+05 9.60E+05 9.70E+05 9.80E+05 9.90E+05 1.00E+06 1.01E+06 1.02E+06
Fig. 16- Reproducibility test results under 4bar
4.2 uncertainty evaluation
Referring to the operation principle of the primary standard, the overview of quantities that exert an influence on measurement uncertainty in sonic nozzle calibration is summarized by the following equation: Cd =
π
qms
u (∆mVa / b ) = ∆mVa / b × ur2 ( Pa / b ) + ur2 (Ta / b ) + u r2 (Va / b )
(6)
Where u ( ∆m T ) is uncertainty component of balance[5] [6], u (F ) is the uncertainty component of buoyancy which can be calculated according to test results. u r ( Pa / b ) , u r (Ta / b ) and u r (Va / b ) are the relative uncertainty component of pressure, temperature and volume of inventory volume a or b. u r2 (QT ) is the uncertainty component of internal leakage of diverter valves which can be less than 0.02%. (2) ur is the uncertainty component of repeatability which can be calculated as the standard deviation of the test results of Cd. (3) ur (C* ) is the relative uncertainty component of [7] C* . According to ISO 9300 , a relative uncertainty on C* of 0.05% at 95% confidence level can be ensured when AGA 8 is used as the state equation. (4) ur (d ) is the relative uncertainty component of throat diameter of sonic nozzle. It is a combination of diameter measurement resolution and temperature difference between calibration and operation condition of sonic nozzle. (5) ur ( P0 ) , ur (T0 ) are the uncertainty components of stagnation pressure and temperature upstream of sonic nozzle (6) ur (M ) is the uncertainty component of molar weights of natural gas mixture which related to reference gas and GC performance. According to engineering practice[3][5], 0.05% can be achieved.
Re nt 0.99445 4.550E+0 4.600E+0 4.650E+0 4.700E+0 4.750E+0 4.800E+0 4.850E+0 4.900E+0 4.950E+0 5.000E+0 6 6 6 6 6 6 6 6 6 6
0.99620
(5)
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Cd 0.99460
u 2 (∆mT ) + u 2 (∆mVa ) + u 2 (∆mVb ) + u 2 ( F ) ∆m
u r2 (∆m) =
0.99467 2017.3-2017.8 20bar 2018.5 20bar
(4)
Referring to equation (1), ur2 (∆m) can be calculated as following:
0.99480
0.99465
(3)
（2）
P0 d ⋅ C* ⋅ 4 ( R / M )T0 2
4
ACCEPTED MANUSCRIPT Fig. 17- Inter-lab Comparison Test Data for S.N.38241#
(7) ur (t ) is the uncertainty component of collecting time which is calculated through repeatability by on-line calibration of timing system against frequency standard and nanosecond counter. From above, the uncertainty evaluation results are obviously closely related to the process conditions. A typical uncertainty evaluation result for a 20.948mm nozzle calibration under 4 bar is shown in Table 1.
1.0000
2
CVB polynomial: y = -3.5444E-05x + 6.7427E-04x + 9.9157E-01 0.9990 0.9980
2
R = 9.8698E-01
Cd
0.9970 0.9960 0.9950 0.9940 0.9930 0.9920
CVB natural gas CEESI air
0.9910 0.9900
5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5
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Re/10^6
Fig. 18- Inter-lab Comparison Test Data for S.N.38242#
Table 1 Cd calibration uncertainty results of 1.0000
20.984mm sonic nozzle Sensitive coefficient
quantities
2
CVB polynomial: y = -3.9158E-05x + 6.8006E-04x + 9.9164E-01
Standard uncertainty component
0.9980
2
R = 4.5278E-01
0.9970 0.9960
Cd
name
0.9990
0.9950 0.9940
0.5g
1
0.5g
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0.9930
u (mc)
0.9920 0.9910
0.023g
1
0.023g
u (mVa)
0.046g
1
0.046g
u (F )
0.4g
1
0.4g
/
2575g
u r(m)
/
0.025%
0.01%
1 1
0.02%
ur
0.02%
1
0.02%
u r (d )
0.0085%
2
0.017%
u r ( P0 )
0.025%
1
0.025%
0.034%
u r (M )
0.05%
0.017%
0.5
0.025%
U r(Cd)=2* u r(Cd)
0.12%
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U r(Cd)
0.5
1.0000 0.9990
0.9930 0.9920
5.5
6.5
7.5
8.5
9.5
10.5 11.5 12.5 13.5 14.5 15.5 16.5 17.5 18.5 19.5 20.5
Re/10^6
Fig. 21- Inter-lab Comparison Test Data for S.N.38245#
Cd
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1.0000 0.9990 0.9980 0.9970 0.9960 0.9950 0.9940 0.9930 0.9920 0.9910 0.9900
2
CVB polynomial: y = -2.7557E-05x + 5.4184E-04x + 9.9195E-01 R2 = 5.9867E-01
CVB natural gas CEESI air 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 Re/10^6
Fig. 22- Inter-lab Comparison Test Data for S.N.38246#
Cd
9.0 9.5
CEESI air 4.5
CEESI air 8.0 8.5
CVB natural gas
0.9910 0.9900
CVB natural gas
7.5
2
0.9960 0.9950 0.9940
0.9950
6.5 7.0
3
2
R = 9.0891E-01
0.9970
2
5.5 6.0
CVB polynomial: 4
y = -8.6441E-07x + 4.3534E-05x - 7.7376E-04x + 5.7439E-03x + 9.8001E-01
0.9980
2
5.0
Re/10^6
Fig. 20- Inter-lab Comparison Test Data for S.N.38244#
R = 8.6817E-01
0.9910 0.9900
CEESI air
5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5
CVB polynomial:y = -6.7941E-05x + 1.2607E-03x + 9.8880E-01
0.9940 0.9930 0.9920
CVB natural gas
0.9910 0.9900
To identify the claimed uncertainty of CVB new primary standard, an inter-lab comparison was carried out between CEESI which has maintained a PVTt primary standard with compressed air in Colorado[8] since 1970’ and CVB using 8 sonic nozzles. The Cd calibration uncertainty of CEESI and CVB is from 0.124%-0.168%(k=2) and 0.10%-0.12%(k=2) respectively.The data is shown in Fig.17-24. 0.9980 0.9970 0.9960
2
R = 4.4598E-01
0.9920
5. Preliminary Inter-lab comparison
1.0000 0.9990
2
CVB polynomial: y = -2.9425E-05x + 5.7764E-04x + 9.9169E-01
0.9970 0.9960 0.9950 0.9940 0.9930
Cd
u r (T0 )
1.0000 0.9990 0.9980
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0.02%
Re/10^6
Fig. 19- Inter-lab Comparison Test Data for S.N.38243#
0.01%
u r (QT )
CEESI air
5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5
Cd
u (m)
ur(t)
0.9900
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u (mVb)
CVB natural gas
10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5
Re/10^6
5
ACCEPTED MANUSCRIPT CVB would keep doing further research to improve the calibration uncertainty related to ambient temperature, buoyancy and high frequency monitoring of pressure and temperature while diverting, etc.In near future, CVB would be a participant of national high pressure primary standard comparison organized by NMi.
CVB polynomial: 4
3
2
y = 1.6068E-07x - 9.1790E-06x + 1.9136E-04x - 1.6174E-03x + 9.9942E-01 2
R = 9.9943E-01
0.9960 0.9950 0.9940 0.9930 0.9920
CVB natural gas CEESI air
0.9910 0.9900 4.5
5.5
6.5
7.5
8.5
9.5
10.5 11.5 12.5 13.5 14.5 15.5 16.5 17.5 18.5 19.5 20.5
Re/10^6
Fig. 23- Inter-lab Comparison Test Data for S.N.38247#
Acknowledgments The authors gratefully acknowledge Dr. Li Chunhui from NMi for her essential technical and theoretical contributions and CVB staffs who were involved in the construction, commissioning and testing of the new primary standard.
1.0000 2
0.9990
CVB polynomial:y = -3.9665E-05x + 7.4302E-04x + 9.9134E-01
0.9980
R = 9.9516E-01
2
Cd
0.9970 0.9960 0.9950 0.9940 0.9930
CVB natural gas
0.9920
CEESI air
0.9910 0.9900
References
4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5
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Re/10^6
Fig. 24- Inter-lab Comparison Test Data for S.N.38248#
[1]R E Harris ,J.E. Johnson, “Primary Calibration of Gas Flows with A Weight/t Method”, 5th ISFFM， 1990. [2]John D. Wright ， Aaron N. Johnson, “Uncertainty in Gas Flow Primary Standards Due to Flow Work Phenomena”, 6th FLOMEKO,2000. [3]John D Wright，et al. “Design and Uncertainty Analysis for a PVTt Gas Flow Standard”, Journal of Research of NIST, Volume 108, Number 1,JanuaryFebruary 2003. [4]ISO/IEC Guide 98-3:2008, “the Guide to the Expression of Uncertainty in Measurement”. [5]Joel T. Park, et al, “Uncertainty Estimates for the Gravimetric Primary Flow Standards of the MRF”, 3rd ISFFM,1995. [6]Ren Jia, Duan Jiqin,et al, “Uncertainty Estimates of a New Gravimetric primary Standard”, Measurement Technique,August,2015. [7]ISO 9300:2005,“Measurement of gas flow by means of critical flow Venturi nozzle”. [8]Thomas Kegel, “Primary System for calibrating Compressible Fluid Flowmeters ”, ISA/94 International Conference and Exhibit, Oct.24-27, 1994. [9]ISO/IEC 17043:2010,“Conformity assessment-General requirements for proficiency testing”.
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Referring to ISO/IEC 17043[9] ， EN ,which is calculated as following equation, is used to determined whether the comparison results could be accepted or not. If En≤1, the claimed
uncertainty of each lab would be validated. EN =
x1 − x 2
(7)
U ( x1 ) + U 2 ( x 2 ) 2
In accordance to Fig.10-17, EN of inter-lab comparison between CVB and CEESI is shown in Fig.25. 1.2
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38241# 38242# 38243# 38244# 38245# 38246# 38247# 38248#
1
EN
0.8
0.6
0.4
0 4
5
6
7
8
9
EP
0.2
10
11
12
13
14
15
16
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Cd
1.0000 0.9990 0.9980 0.9970
17
18
19
20
21
Re/10^6
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Fig. 25- Inter-lab Comparison Results between CVB and CEESI
From Fig.25, EN is less than 1 for all calibration results which identify the claimed uncertainty of sonic nozzle calibration against CVB new primary standard with natural gas achieved 0.10%0.12%(k=2). 6. Conclusions Because of the application of new weighting and timing technology , the metrology performance of mass-time primary facility has been improved a lot.The uncertainty analysis, short-term stability test and inter-lab comparison results shows that the sonic nozzle calibration uncertainty of new primary standard for natural gas in CVB could achieve 0.10%-0.12%(k=2). 6
ACCEPTED MANUSCRIPT Highlights 1.A new mass-time primary standard for natural gas based on 3t electromagnetic balance and hydraulic fast-acting valves 2.Two tanks , one is for gas collecting and another is for balancing, and weights are operated
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automatically by PLC without air turbulence 3.Two hydraulically actuated valves equipped with 13 optical gratings operated in about 33ms achieve “zero overlap” and sonic choking condition during single calibration
4. Uncertainty evaluation and one year time stability test results show that the CMC is about
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0.10%-0.12%(k=2) and inter-lab comparisons with NMi and CEESI also verify the CMC