A Study on the Analysis of Measurement Errors of Specific Gravity Meter

HWAHAK KONGHAK Vol. 40, No. 6, December, 2002, pp. 676-680 (2001 7 2, 2002 8 5 ) A Study on the Analysis of Measurement Errors of Specific Gravity Meter Kang-Jin Lee, Jae-Young Her, Young-Cheol Ha, Seung-Hee An, Seung-Jun Lee and Cheol-Gu Lee Fluid Measurement Research Division, R & D Training Center, KOGAS, Ansan 425-790, Korea (Received 2 July 2001; accepted 5 August 2002),!. " # $ % &' ( )*+,-./ 0 1 23/456 78 9 :- ;< =!. 9: >?, @ AB? CD E AB? F @G 9:>? HI JK LM 5, 1G - NO %P @Q R;%QS, TG UN VW XY 0, UN Z [\] JK ^ _ 1P`a!. Abstract The specific gravity meter is the instrument used to measure the density of fluids under the reference conditions and it can be widely used in industrial areas, especially in massive flow rate natural gas industry. This study has been carried out in an attempt to improve measurement accuracy of natural gas flow rate calculation, providing the adequate installation and proper operation conditions of specific gravity meter. The test results are 1) the density measurement errors in case of using methane and standard gas as calibration gases are smaller than using methane and nitrogen gas, 2) the periodical calibration to maintain accurate density measurements is essential, and 3) the specific gravity meter is sensitive to changes of environmental conditions, especially environmental temperature surrounding the specific gravity meter. Key words: Natural Gas, Base Density, Specific Gravity Meter, Gas Chromatograph, Calibration 1. 5b $ cd 1G - NO C - U Q e Qf RgG _Q h Qi $ $ Q!. >I jg 1 0k S, lmn$ mog ^p qr $ nqs cd >$ t1g JK uv wx yg *2- z'{ ;' # K 1} _Q ~g!. cd > 2! / Q![1-3]. ƒ 9( X%\ ˆ 0 $ p #Š NO 9 G!) 0 Œ h +ŽQ5[4, 5], $ P-V-T Q _Q!. b? Z P b p Z `5, $ T Q 0 #G - Q 0 %\ h #G!. Np I 2 / c To whom correspondence should be addressed. E-mail: kjlee@kogas.re.kr d 9 $G Œ %P +ŽQ š œ` ˆ 9 ž VWG Q5 @ K Ÿ O )*/ ž U$ 0kˆ 1 - ; c d Q c![6, 7]. K%\ cd 9! $G > + - % 5 e Ug Q "%\ $G >/ ` JK ªd«a5[8, 9], 9$ ž d f Q!. " # &'`d )*~P KOGAS(G l )$ G lm D &' 0, p $G ±- 78 9:- ²O ³@ S, ) *3 LM ; c. ( @ +,- µ 0 % )* 1} 56 G!. 2. $ ( @ +,- µ 56 # 9:8'$ Fig. 1?!. 9: KOGAS ` ¹º(Solartron NT 3096)? h G _\ 1»5 ¼0.1% of readingq![10]. 676

78$ 9. lm` )* +Ž ( - ½¾ NO KOGAS$ G lm D 9:- ;< =5 ³@ 3\ I (HP 5890 series II)$ &'N' 5 0 lm P À c 9, &' =\S, Á` Âà ÄÅt &'`d )*`5 c $ Âà ÄÅtp jg h tn Å =!. " 9: Æ )* &³ *2-, z'ç +Å\ ` È - Á` Âà P? >`Ç =5, b 0 Áb - =!. b p > Âà P- ²O lmè Å Âà 9, &' Á!. TG PÁ É ÊK b - NO b &'`d c\s, %\ ËÌ ( - 1P NO ÃÍ ÎÁ &' =!. $ ÏtN i] % Eœ Å G Âà PÅ P- ²O 9 Ð\ > + Å P? >!. É À$ PI 316L ÑÒ Ó ÔÕ- =\S Ö ØqG ÙÚÛ Üt Ý&Q Þ.ß- =!. Fig. 2 8³$ ²Q!. tà Å ` Eœ RS-232 áqâ- Q 0, 789:9 &' Eœ ãä(signal converter) >`S eqà 586 åæà Á!. 78 I X 9:9! Z ( Üt Q ç¾g 3èQ{!, %\ 9:- ;< NO X PC éê,%p åæ à ëì =!. Eœ ãä ŒÛ É lmtà É - lm í5 RS-232 áqâ- Q 0 controllerp 586 åæà. d í!. TG $ UNZ ãî $G ½¾- N O 2 $ ïðz(rtd) &' =!. tà Å ` $ 1 ^ NO ³ @ 3\ I _I lm D uv\ ` QS, 1/ U - 5 ñ ±- Å G!. Q \tà tò` PóñÒQ à(ôi õö 5 q) `d S t GPA(Gas Processors Association) 2172 õñøq 8`d c![11, 12]. Fig. 3I " 9:- ;</ eqà$ ï8? 9:$ ùú - [Q NO H õñø- 9</û î]q!. 24/ 9/ \ eqà ï8 NO 1 o\ üý ï8`ç =5 Eœ ãä Å, ³~? U ±I ¹þ à h/ F/`Ç =!. TG ³@ 3\ I 78$ tà Å ( ³~ iî a\s, Q ±? $ ±?$ JK h/ iîiç 0 9:- ;< Fig. 1. Schematic diagram of test equipment. 677 Fig. 2. Schematic diagram of measurement equipment system. Fig. 3. Example of density calculation program. h, JK ãî 1P ; cç =!. ñ 5 UNZ \ &' ïð Z$ Z /`Ç =!. 3. 3-1. 3-1-1. @ AB? F f $ XY $ 1 U ÿ(reference chamber) b $ ì, N, @ 6 $ 1 ž!. @ 1 *2- z'e QG @ 1 % G @ ì 5 O K @- Okˆ 1 - ; c!. 0 % G @ 56 ÂÃ$ - FOk G!. 78 9:/ 5 AB? F Q 0 @- 9/ =!. F G F?#.G KF, 9:Q ;< f 78 lm` $ ( p G Q!. Fig. 4 AB? F @/ 20 h, Å ` U ±- G _Q!. Q U ±I $ ÿ, 9. lm 0.6 MPa ë) 3è, Q 5 c AB ( F Q 0 0.64 MPa$ b \ / Å ` ±- $G!. d U ± HWAHAK KONGHAK Vol. 40, No. 6, December, 2002

678 Fig. 4. Periodic time of calibration gases. Q, 20 $ Å U±- G _\ XI / ( ) Q5 YI tà Å ` U ±(µs)q!. @Q $O @ 3; #G Q ;' Eœãä(signal converter) Á G!. Q @Q ÿ, G lm ë 3 è, lmtà Âà / $ - µo =!. QG 9:$ %I ;/ ñ Q ã lm$, i 1, TG @ Û $ ( 1 é 56 qq!. Q. lmè $ Âà ÄÅt &' b b - 0.68 MPa 5/û, ÉÀ$ b Q 0 ÿ,$ b! [I 0.64 MPa ÂÃ$ lmb - Ç G!. Fig. 5(a) tà Å ` p, ³@ 3\ I 78$ uv tà Å ³@ G _Q!. XI 9:/ \ 12/ h, Å ` eqà 1 o \ G _Q!. Q $ JK iî _Q Fig. 5(b)Q!. YI JK iî _\( / 1)100\ _Q!. ñ Q 9:/ h, ¼0.1 % JK ã _- ; c!. TG ñ $ JK ; ce, ³@ 3\ I 78$ "%\ 1/ o\ - f, ~ ãî/ W À Q c!. 22:22tà 23:22!, 4:22tà 5:22! eqà ] lm$ ãî " W ˆ, tà Å #$ / \tà ; 'Q5 Q ;' h 1/ h, $ %Q ` f ÉX %\! /! KQ š i _- ; c!. QG J K $ U jg % ] ªd«; c.q!. 40 6 2002 12 Fig. 5. Density errors due to changes of calibration gases. 3-1-2. @ AB? CD f $ XY!& @ 5 AB? CD '- (žq!. AB? CD ìg Q.H )3 */ _+, l P ; AB? F% -. @ ] Q3%Q ˆ, 9. lp -. d 5 // -., 0Q 10 { E2 ; Þ CQ `{ ñ,\ ; AB? ; CD - 5 c f Q!. 3 $ +, G lm ÿ, 0.6 MPa ë) 3 è Q 5 c AB ( CD Q 0 / Å ` U ±- G!. d U ±Q, 20 $ Å U±- G $ O @ 3; #G Q ;' Eœãä(signal converter) Á G!. Q @Q ÿ, G lm ë 3 è lmtà Âà / $ - µo 4!. Fig. 6I Q AB? CD @ É5 $ JK G _\ @ É 2%$ JK Q! @ $ JK ] 0.6% ªdü _- ; c!. @É$ JK 2%! ^G Q Ê@ 6 6 @ tà 4 7Q Q8d _Q PQ 5 M#!. %\ @- OUdk % @U i JK ^G _\ M#!. Fig. 7I AB? CD @- 9/G lm / $ JK G _\ 18/ 9: eqà Q!. ÉX%\ 0.6% JK ÆÊ _- ; c\s t / JK mo WD ui ^G _I 3 &*'Q $ U f Q!. ñ Q AB? F @ 0 9:G >?p ³@/ ÉX%\ JK ^ _- ; ca!. QG 9:>? QÉ$ JKp ³@/ 7o G KQ Qe @$ Û AB? F AB? C

679 Fig. 6. Density errors due to recalibration. Fig. 8. Density errors due to environmental temperature variations. Fig. 7. Density errors due to changes of calibration gases. D @ G _ Ü! ¹; Q h G _\ 4- f @ Û $ ãî M#!. Np I 9:>?.O f $ @ AB? CD!, AB? lmp G F % G _\ QS, @ 56 hp jg h Q Ç <5.H$./? 'G!. 3-2. h=g Z ( b ÿ, c p!qéõø(diaphragm)- Q 5 3œH $ O T ³~- Å Q!. UN VW XY e, Fig. 8I QG UN, UNZ ãî d> XY 9:G >?Q!. Fig. 8(a) ë? 1, ë? 2 UN &' ïð Z(RTD) iî S, ë? 1I $ Z@(thermal insulating cover), &' ZQS ë? 2 UN$ Z, 9$ Z G ZQ!. 9:/ h, ë? 1$ Z 23.21-23.28 o C!, ë? 2$ Z 21.13-21.92 o C! ã 0 ZK 1.4-2.1 o CQ=\S QG ZK Fig. 8(b) Q A2%\ ^ ui WD B5 U ^p WD XŸ _- ; c!. QG Z ãî O JK CD XY- Q B _- ; c\s À 13:22 14:22! JK 0.7%! /%\ ^G _- ; ce, Q_I $ ³3P ;'P _\!. 9 9: E F $ GHQ 0.8059 kg/m 3 Pe XO, 13:22 eqà ˆQ 0.8118 kg/m 3 GH- IJ 6? ;'=!. K / VWG Üt D& ( *2 $O / LM ; c\s Q L \ `d PO JK LMG _\ P!. Fig. 9 K/ UN Z - iî _\ QÉ$ 9:>?p M UNZ *2- z' _ - ; c!. ë? 1? ë? 2$ Z ## 27-29 o C, 27-36 o C! ã S ZK 0.1-7 o C! ãî Q _- ; c!. Q É$ 9:>?p M, UN Z [é Q, 9,$ Z [én f Q!. v 9, O+ 8' P dq cd Z `Ç =e 9 : É h, O+8'$ h- ~À 0 9,$ Z ^G _Q!. TG QÉ$ 9:>?p M UNZ $ Z @,$ Z! [I _- ; c\s QG [I UNZ P 0 JK ^G _\ P!. HWAHAK KONGHAK Vol. 40, No. 6, December, 2002

680 _- ; ca!. TG @U i] JK % N Q3 \ ^ 0 %\ @Q RgG _ 1P =\S, UN VW XY 0, UNZ [\] JK ^ _ ; cd, 2 9. &³ )* (ž, 9 &' U\ 5, UNZ Z `Ç Ok G!. Fig. 9. Density errors due to environmental temperature variations. 4. " # KOGAS$ G lm D &' 0 ±? $G ±- 78 9:- ²O ³@ G _\ 9:>? G >RI!&?!. @ AB? CD E AB? F @ G 9:>? HI JK LM _- ; ca\s QG 9:>?, @ 56 p jg h Q Ç <5.H$./? 'G!. TG ÿ, c p h G $ ], ñ S úq ui!d!tš 1 ñ 1. Alan T., Hayward J.: Flowmeters, A Basic Guide and Source- Book for Users, 111(1979). 2. Wilson. C. W.: Gas Density and Specific Gravity, 47(1987). 3. The Basic Principles and Practice of Flow Measurements, National Engineering Laboratory, 23(1988). 4. Jaeschke. M., Hinze. H. M.: Using Densitometers in Gas Metering, Hydrocarbon Processing, June, 37(1987). 5. John, H. Day.: Application of Densitometer to Orifice Meters, A.G.A Operating Section Transmission Conference, 67(1968). 6. IGU Sub-Committee C2 Report, International Gas Union(1993). 7. Lee, K. J. and Her, J. Y.: A Study and Analyzing Error Sources and Establishing Normal Operational Schemes of Gas Densitometer, KOGAS Report(1996). 8. ISO 6976: Natural Gas-Calculation of Calorific Values, Density, Relative Density and Wobbe index from Composition, International Organization for Standardization(1995). 9. AGA Report No. 8, Compressibility Factors of Natural Gas and Other Related Hydrocarbon Gases, American Gas Association(1992). 10. 3096 Specific Gravity Transducer-Technical Manual, Schlumberger(1992). 11. GPA Standards 2145, Table of Physical Constants of Paraffin Hydrocarbon and Other Components of Natural Gas, Gas Processors Association(1993). 12. GPA Standards 2172, Calculation of Gross Heating Value, Relative Density and Compressibility Factor for Natural Gas Mixtures from Compositional Analysis, Gas Processors Association(1986). 40 6 2002 12