COMMISSIONING OF A MAGNETIC SUSPENSION DENSITOMETER FOR HIGH-ACCURACY ...

347 Pages·2005·3.46 MB·English

COMMISSIONING OF A
MAGNETIC SUSPENSION DENSITOMETER
FOR HIGH-ACCURACY DENSITY MEASUREMENTS
OF NATURAL GAS MIXTURES

A Dissertation
by
PRASHANT VITHAL PATIL

Submitted to the Office of Graduate Studies of
Texas A&M University
in partial fulfillment of the requirements for the degree of
DOCTOR OF PHILOSOPHY

May 2005

Major Subject: Chemical Engineering
COMMISSIONING OF A
MAGNETIC SUSPENSION DENSITOMETER
FOR HIGH-ACCURACY DENSITY MEASUREMENTS
OF NATURAL GAS MIXTURES

A Dissertation
by
PRASHANT VITHAL PATIL

Submitted to Texas A&M University
in partial fulfillment of the requirements
for the degree of
DOCTOR OF PHILOSOPHY
Approved as to style and content by:
______________________________ ______________________________
Kenneth R. Hall James C. Holste
(Co-Chair of Committee) (Co-Chair of Committee)
______________________________ ______________________________
Maria A. Barrufet David M. Ford
(Member) (Member)
______________________________
Kenneth R. Hall
(Head of Department)
May 2005

Major Subject: Chemical Engineering
iii
ABSTRACT

Commissioning of a Magnetic Suspension Densitometer for High-accuracy Density
Measurements of Natural Gas Mixtures. (May 2005)
Prashant Vithal Patil, B. Chem. Engg., University of Bombay, Bombay, India;
M.S., Chemical Engineering, The University of Tulsa
Co-Chairs of Advisory Committee: Dr. Kenneth R. Hall
Dr. James C. Holste

High-accuracy density measurement data are required to validate
equations of state (EOS) for use in custody transfer of natural gas through pipelines. The
AGA8-DC92 EOS, which is the current industry standard has already been validated
against a databank of natural gas mixtures with compositions containing up to 0.2 mole
percent of the heavier C fraction and is expected to predict densities of natural gas
6+
mixtures containing higher mole percentages of the C fraction with the same accuracy.
6+
With the advances in exploration, drilling and production, natural gas streams containing
higher percentages of the C fraction have become available from the deepwater and
6+
ultra-deepwater Gulf of Mexico in recent years. High-accuracy, density data for such
natural gas mixtures are required to check if the AGA8-DC92 EOS covers the entire
range of pressure, temperature and compositions encountered in custody transfer.
A state-of-the-art, high pressure, high temperature, compact single-sinker
magnetic suspension densitometer has been used to measure densities of two simulated
natural gas mixtures named M91C1 and M94C1 after validating its operation by
measuring densities of pure argon, nitrogen and methane in the range (270 to 340) K
[(26.33 to152.33) oF, (-3.15 to 66.85) oC] and (3.447 to 34.474) MPa [(500 to 5,000)
psia]. Measured densities of M91C1, not containing the C fraction show larger than
6+
expected relative deviations from the AGA8-DC92 EOS predictions in regions 1 and 2
but agree well with predictions from the recently developed REFPROP EOS, implying
iv
that the AGA8-DC92 EOS may be unreliable in its present state even for natural gas
mixtures not containing the C fraction. Measured densities of M94C1 containing more
6+
than 0.2 mole percent of the C fraction deviate from the AGA8-DC92 EOS predictions
6+
by more than the expected values in region 1 which is not surprising but the agreement
with AGA8-DC92 EOS predictions in region 2 is misleading which becomes evident
when the measured densities are compared to the REFPROP EOS predictions. The
measured data can be used to recalibrate the parameters of the AGA8-DC92 EOS or to
validate an entirely new EOS.
v
ACKNOWLEDGMENTS

I wish to thank Dr. Kenneth R. Hall and Dr. James C. Holste for giving
me the opportunity of working on the present research project, for their guidance and
support and most importantly for their understanding and patience during difficult
periods of this work. I also want to thank Dr. David M. Ford and Dr. Maria A. Barrufet
for serving on my research advisory committee.
I wish to express my sincere appreciation of the funding provided by the
National Institute of Standards and Technology over the earlier part and by Mardi Gras
Transportation Systems, LLC over the latter part of this research work. I owe Dr.
Kenneth R. Hall a special sense of gratitude for providing financial support for my
graduate studies beyond the anticipated period of completion.
I also thank Mr. Ronald E. Beaty of Premier Measurement Services and
Mr. James E. Gallagher of Savant Measurement Corporation for not only making the
funding for this research work possible but also for investing their time and effort giving
suggestions and feedback on technical matters, for their encouragement and for sharing
their invaluable experiences in the oil and gas industry.
Dr. Hans Wilhelm Lösch and Mrs. Cornelia Lösch of Rubotherm
Präzisionsmesstechnik GmbH, Bochum, Germany helped troubleshoot the operation of
the unique magnetic suspension densitometer used in this research work at several
stages. Their long-distance customer support interactions through e-mail and telephonic
conversations are greatly appreciated.
I consider myself fortunate to have enjoyed the opportunity of visiting
The University of Valladolid over the summer of 2001 for a fortnight. The visit helped
me get my first close look at the operation of a magnetic suspension densitometer similar
to the one used in the present work and gave me a head start for the present work. I
appreciate the sponsorship of this visit by Dr. Miguel Angel Villamanan Olfos and the
hospitality and friendship of Dr. Cesar R. Chamorro Camazon.
vi
Although, I did not interact with them directly, I appreciate the provision
of the NIST-12 and NIST-23 (REFPROP) software programs by Dr. Eric W. Lemmon
and the technical feedback from Dr. Mark O. McLinden. Contributions from both
working at the National Institute of Standards and Technology helped make important
research related decisions.
Several individuals within the chemical engineering department helped
the research work in various ways, which I would like to acknowledge. Mr. Randy
Marek helped with several of the ancillary equipment, Dr. Philip T. Eubank graciously
allowed the use of the differential pressure indicator from his laboratory, Dr. William
Rogers offered advice based on his experience and the undergraduate student workers
Mr. Mark Standlee, Mr. Noel Wilcoxon, Ms. Amber Smades and Ms. Aundria Harrell all
offered valuable support in trying to meet research goals in a timely manner. Ms. Valerie
Green, Ms. Towanna Hubacek and Ms. Ninette Portales helped me stay focused on my
research by handling administrative procedures and paperwork. My fellow graduate
students Ms. Widya Syamsul, Mr. Jingjun Zhou, Mr. Saquib Ejaz and Mr. Mert Atilhan
who also worked on the present research project made work enjoyable by having
discussions and offering their friendship, which I shall always cherish.
Finally, I would like to thank my friends Dr. Shyamkumar Surthi, Dr.
Srinivas Vuddagiri and Dr. Vijay Mhetar who offered me encouragement and support
whenever the going got tough in my career endeavors.
vii
TABLE OF CONTENTS

Page
ABSTRACT.............................................................................................................. iii
ACKNOWLEDGMENTS......................................................................................... v
TABLE OF CONTENTS.......................................................................................... vii
LIST OF FIGURES................................................................................................... ix
LIST OF TABLES.................................................................................................... xiii
CHAPTER
I INTRODUCTION................................................................................... 1
1.1 Energy Review and Outlook.......................................................... 1
1.2 Deepwater Gulf of Mexico as the New Energy Frontier............... 9
1.3 Necessity of Thermodynamic (P – ρ – T) and Phase Equilibrium
Data................................................................................................ 11
1.4 Organization of Dissertation Chapters........................................... 15
II EQUATIONS OF STATE AND PHILOSOPHY OF
MEASUREMENTS................................................................................ 17
2.1 Equations of State for Fluids and Fluid Mixtures.......................... 17
2.2 Prelude to Density Measurements.................................................. 29
2.3 Philosophy of Measurements......................................................... 50
III THE MAGNETIC SUSPENSION DENSITOMETER SETUP............. 57
3.1 Density Measurement Methods...................................................... 57
3.2 Description of the Compact Single-sinker Magnetic Suspension
Densitometer.................................................................................. 61
3.3 Description of Ancillary Equipment.............................................. 88
3.4 Specific Tests and Observations with the Magnetic Suspension
Densitometer Operation................................................................. 121
viii

CHAPTER Page
IV INSTRUMENT CALIBRATION AND TRACEABILITY................... 144
4.1 Pressure Transducer Calibration and Traceability......................... 144
4.2 Platinum Resistance Thermometer Calibration and Traceability... 155
4.3 Weighing Balance Calibration and Traceability............................ 159
4.4 Sinker Volume Calibration and Traceability................................. 159
4.5 Natural Gas Mixture Composition Traceability............................. 160
V PURE COMPONENT AND NATURAL GAS MIXTURE DENSITY
MEASUREMENTS................................................................................ 162
5.1 Pure Component Density Measurements....................................... 162
5.2 Natural Gas Mixture Density Measurements................................. 197
5.3 Density Measurement Uncertainty Analysis.................................. 240
VI CONCLUSIONS AND RECOMMENDATIONS.................................. 244
6.1 Conclusions.................................................................................... 244
6.2 Recommendations.......................................................................... 245
NOTATION.............................................................................................................. 248
LITERATURE CITED............................................................................................. 254
APPENDIX A........................................................................................................... 271
APPENDIX B........................................................................................................... 302
APPENDIX C........................................................................................................... 307
APPENDIX D........................................................................................................... 313
APPENDIX E............................................................................................................ 316
APPENDIX F............................................................................................................ 320
APPENDIX G........................................................................................................... 322
VITA......................................................................................................................... 332
ix
LIST OF FIGURES

FIGURE Page
1.1 History and Outlook for Annual Domestic Fossil Fuel Energy
Production and Consumption for the US................................................ 2
2.1 Predicted Phase Envelopes for RR-NIST2 Mixture Using PR, SRK
and PT EOS............................................................................................. 32
2.2 Predicted Phase Envelopes for RR-NIST2, M91C1, M94C1, M88C1
and M78C1 Mixtures Using PR EOS..................................................... 33
2.3 Comparison of HY, AGA8-DC92 and REFPROP EOS Density
Predictions for RR-NIST2 Mixture......................................................... 43
2.4 Comparison of HY, AGA8-DC92 and REFPROP EOS Density
Predictions for M91C1 Mixture.............................................................. 44
2.5 Comparison of HY, AGA8-DC92 and REFPROP EOS Density
Predictions for M94C1 Mixture.............................................................. 45
2.6 Comparison of HY, AGA8-DC92 and REFPROP EOS Density
Predictions for M88C1 Mixture.............................................................. 46
2.7 Comparison of HY, AGA8-DC92 and REFPROP EOS Density
Predictions for M78C1 Mixture.............................................................. 47
2.8 Philosophy of (P – ρ – T) Measurements Used in RR Project................ 51
2.9 Points for Density Measurement of M91C1 Mixture Using MSD,
Relative to Its Phase Envelope................................................................ 55
2.10 Points for Density Measurement of M94C1 Mixture Using MSD,
Relative to Its Phase Envelope................................................................ 56
3.1 Schematic Diagram of the Compact Single-sinker MSD........................ 62
3.2 Details of the MSA Parts inside the Pressure Cell.................................. 65
3.3 Relative Engagement of Permanent Magnet Piece with Bearing Cone
Piece........................................................................................................ 66
3.4 Horizontal Clearances along the Radius among the MSA Parts,
the Sinker and the Cell Inner Walls........................................................ 67
3.5 Vertical Clearances among the MSA Parts, the Sinker and the
Cell Inner Walls along the Axis.............................................................. 68
3.6 Attachment of the High Pressure Cell to the Weighing Balance Base
Plate through the Thermostating Tube.................................................... 70
x
FIGURE Page
3.7 Attachment of the Weighing Balance to the Balance Base Plate
through the Balance Frame ..................................................................... 71
3.8 Magnetic Suspension Densitometer Support Structure........................... 73
3.9 The Entire MSD Apparatus to be Supported on the Support Structure.. 74
3.10 Operation of the MSA in Vacuum.......................................................... 79
3.11 Operation of the MSA in Presence of Fluid under Pressure................... 81
3.12 Ideal and Real Calibration Curves for the Weighing Balance and
Need for the Weight Changing Device................................................... 83
3.13 Operation of the MSA in Vacuum Using Weight Changing Device...... 85
3.14 Operation of the MSA under Pressure Using Weight Changing
Device...................................................................................................... 86
3.15 Old and New Locations of the MSD and Relative Positions of the
Old and New Feed Manifolds................................................................. 90
3.16 Schematic Flow Diagram of the Old Manifold with the MSD in the
Old Location............................................................................................ 93
3.17 Schematic Flow Diagram of the Old and New Manifolds with the
MSD in the New Location, with PT06K Moved to the New Manifold.. 95
3.18 Schematic Flow Diagram of the Old and New Manifolds with the
MSD in the New Location, with PT06K Moved to the New Manifold
and Thermostated with an Aluminum Block Heater............................... 97
3.19 Schematic Flow Diagram of the Old and New Manifolds with the
MSD in the New Location with PT02K and PT06K Thermostated
with Aluminum Block Heaters................................................................ 99
3.20 Thermostating Scheme for Pressure Transducers................................... 106
3.21 MSD Cell Thermostating Scheme........................................................... 109
3.22 Isolation Tube between PRT and Cell Bath Liquid................................ 113
3.23 Four-lead Resistance Measurement........................................................ 115
3.24 Current Reversal for Thermoelectric EMF Elimination......................... 115
3.25 Temperature Measurement Scheme with Four-lead PRT and
Current Reversal...................................................................................... 118
3.26 Effect of Stray Magnetic Sources on Magnetic Field of
Electromagnet in the Old Location of the MSD..................................... 127