compressor vibration problems due to changed gas composition - a

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Purdue University

Purdue e-Pubs

International Compressor Engineering Conference School of Mechanical Engineering

1986

Compressor Vibration Problems Due to ChangedGas Composition - A Case StudyS. N. Dwivedi

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Dwivedi, S. N., "Compressor Vibration Problems Due to Changed Gas Composition - A Case Study" (1986). International Compressorf
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The final build-up of amplitudes of individual pulsation components i s controlled by the effects of the manifold and thepiping system attached to the compressor. These pulsationssometirres get coupled to the mechanical system a t points such asclosed ends of vessels or pipes, bends, orif ices, reducers, etc .to produce acoustic shaking forces. These acoustical shakingforces excite vibrations, the magnitude of which depends uponthe location of mechanical natural frequencies relative to thefrequencies of acoustical shaking forces and the amount ofdamping in the mechanical system.

The level of pulsations generated by a compressor, i s relatedto a number of parameters which include compressor operatingpressures, compression ra t io , cylinder clearance volumes, phasingbetween cylinders, thermodynamic gas properties and COJ!llressorcylinder and valve design. These pulsations are further anplified by the attached piping systems. The consequant vibrationsdepends upon the acoustical and mechanical characteristics ofthe vessels and piping systems.

Gas composition i s one of the most important parameters thatmust be exactly specified by the cOQpress-or user. Severeproblems may arise in case the actual gas composition i s widelydifferent from that specified. The present paper discusses acase s"b.I dy of viliration prdJ lems faced on a r : ~ u l t i - s t a g e Reciprocating compressor handling a complex mixture of hydrocarbons.THE COMPfi.ESSOR

The compressor involved was a three-stage Il.eciprocatingCompressor cO!ilpressing associated gas having composition as perTable 1 (as indicated by cl ient in their order) from a suctionpressure of 1.068 Kg/em'" absolute to a discharge pressure of51.533 Kg./cml'. abs. The scteroo of compression i s shown in Fig 1.Tm compressor was designed to handle specified gas and thedesign was also checked by Analog study as per design approach3 of API 618 - 1974, and modifications as required during studywere incorporated in the f inal design. I t was expected that


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analytical stlldy.In view of above i t was decided to adopt a qualitative solution, thatwas well proven by manufac tur : ' !r 's experience andas such acre dcdgned and int roduce:J in suction and discharge vassals of 2nd stage and also suction vessel of 3rdstage, for force balancing of these vessels over a w ide rangeof gas composit ion as specified by the client. This solutioninvolves shifting pulsation origination ~ o i n t insiJ:! a d


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.lliJT IAL GA5 CWPCSITIOHThe conpre3s-ors shall haQlle Gas 1 from 1st to 3rd stg andGas 2 from 2nd to 3rd stage. Tho gas composit ions (f.lol ;;)ofGas 1 and 3as 2 are as follow s:

Case I casa II---Coq:> o_':= nt Gas l Gas 2 Gas 1 Gas 2C02 2.71 3.01 2.81 3.01C1 14.74 54 .20 15 .11 54.20C2 21.52 20 .74 22.10 20 .74 C3 31.76 13 .79 31.19 13.79IC4 6.30 2.14 6.50 2.14NC4 10.90 3.16 10.46 3.16IC5 2.99 o.7s 2.91 o.1sNC5 o.7o o.19 0.70 0.19C6 + 7.89 1.99 8.22 1.90


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TABLE 2VIBRATIC l' l lviE.ASUHEMENTS BY B&K INSTRUMENIS (mcnms PEAK TO PEAK)

LCCA- 1ST STG CYL 1ST STG CYL I I ZIG CYL IISTG CYL I I I STG C'llTIO!l {PUt.iP SIDE) (MOTOR SIDE) (PUMP SID E) (MOTOR SIDE)Overall Major Peaks Overall Major Peaks Olrerall Major PeaksCbserved Cbserved Ci>servedAA 100 100 220 70 at1xRPM 180 70 atlxRP M 230 160 at lxRPM.110 atlx RPM 80 at6x!FM 40 a t 6xRPMBJ


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TABLe 3_SHAKING HRCES m C O . : P ~ S S C R DA.'.1PEN!!f!S( BASED ON It!ITIA L GAS CO!.IPCBITION )

I STG. SUCTION DAMPHER {D l) II STI;. DISCHAaJE DAMPNER (02)I I I STG. SUCTICl-l DAMPNER {03)I I STG DISCHARGE DAUPNER (D 4)III STG SUCTION DAMPNER (05)III STG DISCHARGE DAMPNl:!R {06)

; 510 lit: . 300 ~I . 56Dfi.I . 520liI . 595 \1 .Negligible.

TABLE 4FINAL RAi'K;E CF GAS CCl:lPCSITIOH (MOLE PERCENT)

COMPO- FIRST SUCTI Olt SEGCND SUCTim THIRD sucrrrnNENT (Press. 1.068 (Press. 4.013 (Press. 15,Y crn iabs .) J/cm '-a) lfj/cm2- a)C02 2.51 - 3.71 2.81 - 3.63 3 .21 - 4.03Cl 20.04 - 44.11 34.06 - 48 .62 38.83 - 50.10C2 - 23 .00 15.45 - 21.59 16.87 - 23.70C3 18.70 - 28.2 0 17.20 - 22.6 0 17.20 - 22.65IC 4 3 .70 - 4.47 2.62 - 3.57 2.54 - 3.01 NC4 3.24 - 5.04 2.30 - 4.:3 1 2.6 3 - 3.33IQ) 0.39 - 0.74 o .33 - 0.54 0 .27 - 0.33NQ) 0 .30 - o .63 0 .26 - 0.49 0 .19 - o.24NC6 0.12 - Q.2 8 0.10 - 0.17 o.b4 - o.o7NC7 o .o1 - o .o3 o.o1 - o.o1 o.oo - o .oo2CB + 6.33 - 18 .98 5.72 - 12.58 3 .85 4.97


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(M !C:lCNS PeAK TO PEAK)I STG CYL. I STG CYL. I I STG CYL. I I STG CYL.

( P U ~ ' 3IDS) (hlOTCR SIDE) {PUI.JP SIDE) (/J!OTOR SIDE)X 110 lC) 180 150y 180 185 300 330z 45 40 360 340" 140 110 110 100 ,y 220 200 220 200z 60 60 80 100

X axis is along crank-shaft axis.Y axis is along cylinder axis.z axis is along vertical axis.

II I STI3 CYL.

230

340220100340130

compressor vibration problems due to changed gas composition - a

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