Jay M. Koch

Investigation of the Circumferential Static Pressure Non-Uniformity Caused by a Centrifugal Compressor Discharge Volute

The paper describes experimental and computational fluid dynamics analyses of the non-uniform static pressure distortion caused by the discharge volute in a high pressure, centrifugal compressor. The experiments described in this paper were done using a heavily instrumented gas re-injection compressor operating at over 6000 psia discharge. Instrumentation was installed to measure static, total, and dynamic pressure as well as impeller strain and mechanical vibrations. A brief description of the compressor and instrumentation are provided. Concurrent with the experimental work, CFD runs were completed to study the reasons for the pressure nonuniformity. The CFD pressure profile trends agreed well with the experimental results and provided analytical corroboration for the conclusions drawn from the test data. Conclusions are drawn regarding: a) the response of the non-uniformity to changing flow rates; b) the extent to which the non-uniformity can be detected upstream of the impeller; and c) the mechanical influences of the nonuniformity on the impellers.

Performance Evaluation Of A Centrifugal Compressor Operating Under Wet Gas Conditions.

This paper presents the results of performance testing of a single-stage centrifugal compressor operating under wet gas conditions. The test was performed at an oil and gas operator’s test facility and was executed at full-load and full-pressure conditions using a mixture of hydrocarbon gas and hydrocarbon condensate. The effect of liquid was investigated by changing the gas-volume fraction between 1.0 and 0.97, which covers the range encountered by the operator during regular gas/condensate field production in the North Sea. Other parameters that were evaluated include the 111 PERFORMANCE EVALUATION OF A CENTRIFUGAL COMPRESSOR OPERATING UNDER WET GAS CONDITIONS by Lars Brenne Staff Engineer Tor Bjorge Staff Engineer Statoil ASA Trondheim, Norway Jose L. Gilarranz Senior Aero/Thermodynamics Engineer Jay M. Koch Staff Engineer, Aero/Thermodynamics and Harry Miller Product Manager, Marketing Dresser-Rand Company Olean, New York compressor test speed, the suction pressure, and two different liquid injection patterns. During the tests, the machine flowrate was varied from near surge to choke conditions; hence, the evaluation covered the entire operating range of the machine. Although the test was primarily intended to evaluate the effects of the wet gas on the thermodynamic performance of the machine, the mechanical performance was also investigated by measuring the machine vibration levels and noise signature during the baseline dry gas tests as well as during the tests with liquid injection. INTRODUCTION Centrifugal compressor packages utilized for upstream gas processing often must operate under wet gas conditions in which the fluid handled by the compression package contains a mixture of liquid and gaseous phases. Typically, the liquid components of the mixture are separated from the gas stream before they enter the compressor by the use of scrubbers and separators located upstream of the compressor inlet. These devices are very large and heavy, requiring a large “footprint” (amount of floor space) as compared to the gas compression package. A compressor with the ability to directly handle wet gas without the need for separation equipment is very attractive from an economic standpoint, as it would drastically reduce the size, weight, and cost of the gas compression package. For the case of future subsea compression systems, this capability is even more attractive because of the high costs of deploying a compressor train and all of its associated equipment under water. Wet gas compression (WGC) technology represents new opportunities for enhanced, cost-effective production from existing and future gas/condensate fields. Many oil and gas operators face future challenges in tail-end production, unmanned operation, and improved recovery from topside and subsea wells. This emphasizes the need to develop more robust compression systems, which can be designed for remote operation in unmanned topside installations, or could be designed for subsea operation for reinjection and/or transport boosting. The use of this technology for subsea boosting represents a new and exciting application for rotating equipment, which will allow new gas/condensate field production opportunities as well as enhanced recovery of existing gas/condensate fields and cost-effective production from marginal gas fields. As mentioned above, these wet gas compression systems could be based on the use of a liquid tolerant dry gas compressor, which could boost a coarsely separated (via a scrubber) well-stream, however, an even more attractive solution would be the development of compression systems that can boost the well-stream directly. Many research projects and product qualification programs are currently underway to develop such a system either by modifying existing multiphase pump technology or by the adaptation of currently available gas compression technologies (Scott, 2004). Regardless of the choice of concept, the compressor solution should be able to tolerate liquid ingestion for an extended time without failure. For the case of subsea applications, the high cost associated with the retrieval of the compressor from the sea floor accentuates the importance of a reliable design. The work presented herein served as an initial test to verify the multiphase boosting capabilities of a centrifugal compressor as well as to provide an oil and gas operator with data to compare the performance of this technology with other available wet gas compression concepts. It is important to state that the test compressor used for this investigation was not originally designed for wet gas boosting, nonetheless it provided an economically viable test bed for centrifugal compressor technology. DESCRIPTION OF TEST VEHICLE The test vehicle used for this work was a barrel-type, singlestage compressor, manufactured by the coauthors’ company. Said compressor was equipped with a high-head impeller, with a diameter of 0.384 m (1.26 ft), and a design flow coefficient of 0.02380. The compressor was originally designed to handle an inlet flow of 4332 Kg/min [2167 Am3/hr (76,526.88 ft3/hr)] of dry hydrocarbon gas (molecular weight of 18.49), with an inlet pressure of 130.2 bar (1888.4 psi)and a discharge pressure of 161.8 bar (2346.7 psi). Figure 1 shows a cross-section of the test compressor; the inlet and discharge nozzles are located at a 45 degree angle with respect to the top dead center of the machine. The original design of this machine, which dates to 1986, was not intended for wet gas service, and hence the internal geometry was not optimal. Nevertheless, in order to increase the reliability of the machine, the original rotor design was modified to accommodate an electron-beam welded and vacuum furnace brazed impeller with a shrink fit to the shaft. The rest of the machine remained the same (i.e., casing and stationary components). This compressor was equipped with a vaneless diffuser configuration. Figure 1. Cross-Section of the Test Compressor. The compressor was driven by a 2.8 MW synchronous electric motor, through a speed increasing gearbox, with a gear ratio of 6.607. A variable speed drive permitted the operation of the compressor within its speed range of 6000 to 13,000 rpm. The test compressor is utilized in the coauthor’s closed loop test facility, and was equipped to simulate the conditions expected for a centrifugal compressor operating under wet gas conditions. Figure 2 shows a schematic diagram of the test loop that was used for the evaluations. The major components of the test loop included a scrubber, the test compressor, a pump, a cooler, and a liquid injection module (mixer). The scrubber, here called guard separator, was used to separate the dry gas (saturated hydrocarbon mixture) from the liquid (hydrocarbon condensate) in order to permit accurate measurement of the massflow of each stream (liquid and gas). The liquid stream was measured with a Coriolis flowmeter while the gas stream was measured with a calibrated orifice plate. Figure 2. Schematic Diagram of the Wet Gas Test Loop. PROCEEDINGS OF THE THIRTY-FOURTH TURBOMACHINERY SYMPOSIUM • 2005 112 Variable Speed Electric Motor (MW) Gas Flow 2 Phase Flow Condensate

Full-Scale Aerodynamic And Rotordynamic Testing For Large Centrifugal Compressors.

This paper describes a full-scale, flexible test vehicle designed and built by the original equipment manufacturer (OEM) to validate the aerodynamic and mechanical performance of large compressors for a variety of applications. This paper provides a description of the test vehicle as well as mechanical and aerodynamic performance data gathered during testing of the vehicle.

The Influence of Low Solidity Vaned Diffusers on the Static Pressure Non-Uniformity Caused by a Centrifugal Compressor Discharge Volute

The paper is a sequel to an earlier work by Sorokes et al. 1998, “Investigation of the Circumferential Static Pressure Non-Uniformity Caused by a Centrifugal Compressor Discharge Volute.” The earlier work described experimental and computational fluid dynamics analyses of the non-uniform static pressure distortion caused by the discharge volute in a high pressure, centrifugal compressor with vaneless diffusers. This paper describes additional testing and analytical work done using low solidity vaned diffusers (LSD’s) in place of select vaneless diffusers to determine the alternate diffuser’s effectiveness in eliminating or reducing the magnitude of the non-uniform pressure field. As in the earlier studies, the experiments described in this paper were done using a heavily instrumented gas re-injection compressor operating at over 6000 psia discharge pressure. Instrumentation was installed to measure static, total, and dynamic pressure as well as impeller strain and mechanical vibrations. A brief description of the compressor and instrumentation are provided.Concurrent with the experimental work, CFD runs were completed to study the effect of the alternate vaned diffusers. The CFD pressure profile trends agreed well with the experimental results and provided analytical corroboration for the conclusions drawn from the test data.Conclusions are drawn regarding: a) the effectiveness of the LSD’s on the pressure non-uniformity; b) the associated effects on the measured dynamic strains in the impellers; and c) the usefulness of computational fluid dynamics (CFD) in assessing the aerodynamic forces associated with the non-uniformity.© 2000 ASME

Modeling And Prediction Of Sidestream Inlet Pressure For Multistage Centrifugal Compressors

It is common for some compressors in certain applications to have one or more incoming sidestreams that introduce flow other than at the main inlet to mix with the core flow. In most cases, the pressure levels at these sidestreams must be accurately predicted to meet contractual performance guarantees. The focus of this paper is the prediction of sidestream flange pressure when the return channel outlet conditions are provided. A model to predict the impact of local curvature in the mixing section is presented and compared with both Computational Fluid Dynamics work and measured test data.

Design and Numerical Investigation of Advanced Radial Inlet for a Centrifugal Compressor Stage

The performance of a centrifugal compressor stage can be seriously affected by inlet flow distortions due to an unsatisfactory inlet configuration and the resulting flow structure. In this study, two radial inlets were designed for a centrifugal compressor stage and investigated numerically using a commercially available 3D viscous Navier-Stokes code. The intent of the design was to minimize the total pressure loss across the inlet while distributing the flow as equally and uniformly as possible to the impeller inlet. For each inlet model, the aerodynamic performance was calculated from the simulation results and then the results from both models were evaluated and compared. The second radial inlet design outperformed the initial design in terms of total pressure loss, flow distortion and uniformity at the impeller inlet. Furthermore, the aerodynamic performance of the second radial inlet was insensitive to wide range of mass flow rates compared to the initial design due to the distinctive geometric features implemented for the second inlet

The Consequences Of Compressor Operation In Overload.

This work describes the potential consequences associated with operating a centrifugal compressor in overload. Nomenclature is offered to explain what is meant by overload operation, and methods that are used by original equipment manufacturers (OEMs) and end users to define overload limits are presented. The paper also describes the conditions that can lead to overload operation. Computational fluid dynamics (CFD) results are used to illustrate the forces acting on an impeller when it operates at very high flow. Finally, this paper suggests considerations that should be addressed when designing (or selecting) an impeller that could be subjected to extended overload operation.

Modeling and Evaluation of Centrifugal Compressor Performance Variations Using Probabilistic Analysis

This paper presents a methodology for analyzing the variation in compressor stage performance due to component dimensional variations for a range of flows, speeds, gas compositions and scale factors. Due to the large number of input parameters involved, a Design of Experiments (DOE) approach was used to develop key variables, and to develop response surface models of head coefficient and efficiency in terms of these key variables. These response surface-based performance models then are used for a probabilistic analysis of head coefficient and efficiency as functions of dimensional variations, for a range of compressor sizes. The variations in dimensions are expressed as probability distributions and evaluated using a Monte-Carlo integration technique. The techniques for developing the response surfaces and performing the probabilistic analysis are described, as are methods for evaluating both the effects of dimensional variation on performance and for evaluating how much dimensional variation can be tolerated before the variation exceeds established limits.© 2005 ASME

Investigation of Advanced CFD Methods and Their Application to Centrifugal Compressors

The past decade has seen considerable growth in the application of CFD to centrifugal compressors. As computational methods applicable to compressors have improved, and computing power has increased dramatically, so has the scope of application. Impellers, diffusers, return channels, inlets, volutes and other components are now routinely analyzed, sometimes simultaneously. With the expansion of CFD, the user is now faced with many choices in establishing the most effective and efficient way to perform a given analysis. Advice, guidance and reports as to the experiences of other practitioners are of considerable value. This paper aims to investigate and compare relevant computational factors such as mesh type and density, and CFD solver discretization scheme as applied to the impeller, vaneless diffuser and volute of a centrifugal compressor.Copyright

Actuation and Control of a Moveable Geometry System for a Full-Scale, Multi-Stage Centrifugal Compressor Test Vehicle

In recent years, several papers have been written regarding the use of moveable geometry systems to enable the rotation of otherwise stationary vanes used in centrifugal compressor research test vehicles. These systems typically are installed in single stage rigs or are placed at the inlet of the first stage of multi-stage centrifugal compressor test vehicles. This paper describes the capabilities of a state-of-the-art test vehicle that was developed by the Original Equipment Manufacturer (OEM) as a result of the OEM’s ongoing Research and Development Program aimed towards the implementation of novel and advanced technologies during the development of high-performance centrifugal compressors. The test vehicle is equipped with a variety of internal instrumentation that allow the collection of detailed aero/thermodynamic inter-stage performance data that is used to evaluate the behavior of the machine. The design of the unit also incorporates moveable vanes at the inlet guides upstream of each impeller, at each diffuser inlet and at the inlet of each return channel. The moveable geometry components allow infinite tuning of these components in a multistage environment, which allows the optimization of the aerodynamic performance of the stages based on design and/or off-design operating requirements of the process. The variable geometry system also allows the vanes to be positioned in such a way as to maximize the operating range of the compressor. The incorporation of adjustable vanes into the test vehicle allowed the OEM to significantly reduce the test cycle time, while maximizing the test data that was obtained from a single build. The positioning of the moveable vanes is controlled by a PC-based system that has been integrated into the OEM’s data acquisition system. This paper presents the work executed during the specification, design and implementation of the moveable geometry control system that was developed for the test vehicle. It covers topics such as the selection of the actuators and control hardware, as well as the integration of the actuators with the moveable vanes and other test unit components. Also discussed are the specification and development of the control software and the techniques, hardware and procedures used for the calibration of the moveable geometry system. The calibration was required to accurately determine the transfer function between the actuator movement and the actual rotation of the vanes. The paper also discusses the use of 5-hole pressure probes during the actual test to measure the flow direction upstream of the moveable vanes and how this information was used to achieve the test objectives. Finally, sample test data is presented to illustrate the impact that the moveable geometry system had over the performance of the compressor stages.Copyright