Research Papers: Gas Turbines: Structures and Dynamics

Design and Development of a Specially Modified Positive Displacement Rotary Screw Pump and Relevant Hydraulic Circuit to Enhance “Entrained Air Handling” Capability in a Closed Loop Lube Oil System

[+] Author and Article Information
Simone Berti

General Electric Oil and Gas,
Via Mattoucci, 2,
Florence 50127, Italy
e-mail: simone.berti1@ge.com

Pietro Fracassi

Leistritz SpA,
Via dei Fontanili, 26,
Milan 20141, Italy
e-mail: pfracassi@leistritz.com

Alessandra Mattioli

General Electric Oil and Gas,
Via Matteucci, 2,
Florence 50127, Italy
e-mail: alessandra.mattioli@ge.com

Varuna Reddy Potula

Petrofac Int. Ltd.,
1 Al-Khan Road,
Sarjah 23467, UAE
e-mail: Varuna.Reddy@petrofac.com

Cristiano Lotti

General Electric Oil and Gas,
Via Matteucci, 2,
Florence 50127, Italy
e-mail: cristiano.lotti@ge.com

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received January 9, 2014; final manuscript received January 21, 2014; published online February 18, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(7), 072502 (Feb 18, 2014) (12 pages) Paper No: GTP-14-1009; doi: 10.1115/1.4026543 History: Received January 09, 2014; Revised January 21, 2014

Rotary screw type positive displacement (RSPD) pumps are commonly used in oil and gas industry for pumping of mineral lube oil in services where they can be mechanically driven by gears coupled to a train driver. Installation of these pumps is critical and should be designed jointly by vendors and users according to project specific restrictions (i.e., the arrangement of the entire oil circulation system). This paper describes a real case in which restrictions due to lube oil system arrangement have produced low pump suction head and have amplified the influence of air bubbles that remained entrained in oil despite lube oil tank degassing. The investigations have been directed toward the mathematical modeling of the aeration phenomenon coupled with experimental measurements of critical parameters taken on the shop plant. Among corrective actions identified and considered there are reduction of quantity of air entering the lube oil system and revamping of the entire lube oil system with changes in piping, tank and also in pump model together with special modifications of internal path to enhance air handling capabilities. In order to validate pump behavior with reference to resistance to aeration (monitoring noise and vibration) a special simulation setup was jointly developed by end user and manufacturer on a pilot test bench to carry out the various performance tests. The numerical data collected during shop aeration test have confirmed that the pump was able to handle the expected amount of entrained air with noise and vibrations within industrial limits. The pumps tested in the pilot bench were installed at user's site and the effectiveness of the synergic corrective actions listed above was successfully verified. The study concludes that an early estimation of entrained air in the lube oil system is critical for design and development of either the RSPD pump or the entire lube oil circuit of a motor compressor train. When a critical quantity of entrained air is likely to be reached at pump suction (near 10% in volume), pump manufacturers and end users should apply some basic rules related to “design for aeration” of the pump and agree on a nonroutine test to be performed at manufacturer's shop before pump installation at site. This will serve as a reliable prediction of pump air handling capabilities, without which effective operation, reliability and durability of the pump could be jeopardized.

Copyright © 2014 by ASME
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Fig. 3

Main parameters of lube oil circuit arrangement

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Fig. 2

Shop arrangement during complete unit (string) test

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Fig. 1

Mechanism of air bubble collapse on solid surfaces

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Fig. 4

Graphical representation of causes of noncorrect NPSHR estimation

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Fig. 6

Increase in air volume due to reduction in pressure

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Fig. 7

RSPD pump with 2 spindles

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Fig. 8

How the constant flow is achieved in a RSPD pump

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Fig. 5

Discharge pressure and flow rate trend of test run with chamfered pump

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Fig. 9

Effect of slip on a 2-spindles RSPD pump

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Fig. 10

Suction and delivery flows when pumping compressible emulsions

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Fig. 12

Simplified P&I of the aeration test

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Fig. 16

3D Model of the original lube oil console

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Fig. 13

Validation of the aeration rule for modified RSPD pump

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Fig. 11

Effect of entrained gas on liquid rate of flow of rotary pumps (metric) [5]

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Fig. 18

Position of main parameters used for site verification of pump operation

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Fig. 15

Lubrication circuit schematic

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Fig. 19

Inlet piping circuit characteristic curve

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Fig. 20

Graphical calculation of air volume fraction content

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Fig. 17

3D Model of the revamped lube oil console



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