A Revised Compressor Polytropic Performance Analysis

2006 ◽  
Author(s):  
O̸yvind Hundseid ◽  
Lars E. Bakken ◽  
Tor Helde
Keyword(s):  
Equation Of State ◽  
Gas Production ◽  
Phase Changes ◽  
Direct Integration ◽  
Compression Process ◽  
Liquid Phases ◽  
Wet Gas ◽  
Direct Integration Method ◽  
Compressor Performance ◽  
Gas Properties

The compressor polytropic head and efficiency analysis are based on the assumption that the compression process follows the path of a constant polytropic exponent n. Both the ASME PTC10-97 and the ISO 5389 refer to the polytropic analysis by John M. Schultz. The procedure utilizes a head correction factor and two compressibility functions to obtain a solution of the integral Δhp = ∫vdp. Present computer technology renders possible a direct integration of the compression path where the variation in actual gas properties along the path is included. This method eliminates the averaging of gas properties which the Schultz procedure includes. This paper reports deviation in compressor performance using the Schultz procedure with different average gas properties. The implementation of a direct integration procedure, employing actual gas properties from the new GERG-2004 equation of state, is given. The GERG-2004 equation of state has proven to give accurate density values both in the vapour and liquid phases. Depending on how the polytropic compression analysis is implemented, the work has revealed up to 4% deviation in polytropic head and efficiency for some specific compressors. This adds an extra uncertainty in compressor performance verification. Even though the API 617 allows up to 4% deviation, some compressors have to meet a more stringent demand, for instance 2% at the Sno̸hvit LNG plant. Future challenges within oil and natural gas production are related to wet gas compressors. The present paper points out the advantages in using a direct integration method for wet gas performance predictions as this takes phase changes along the compression path into account.

Wet Gas Performance Analysis

2006 ◽  
Author(s):  
O̸yvind Hundseid ◽  
Lars E. Bakken
Keyword(s):  
Performance Analysis ◽  
Performance Prediction ◽  
Volumetric Flow Rate ◽  
Phase Changes ◽  
Direct Integration ◽  
Compression Performance ◽  
Wet Gas ◽  
Gas Compression ◽  
Performance Predictions ◽  
Fluid Properties

The growing interest in wet gas compressors calls for accurate methods for performance prediction. Present evaluation methods for compressor and pump performance fail when evaluating the compression of gases containing liquid. Gas compression performance predictions given in ASME PTC-10-97 and ISO 5318 are based on the method John M. Schultz proposed in 1962. This method assumes a polytropic compression path and is based on averaged gas properties of inlet and outlet condition. The polytropic compression path is defined by keeping pvn constant, where n is constant along the compression path. When employing the Schultz method there is a challenge in defining the polytropic constant. This is seen in cases where dry gas compressors are exposed to wet components and compressor efficiency estimates exceed 100%. Today’s computer technology makes a direct integration of the polytropic head (∫vdp) possible where actual fluid properties along the compression path are included. Phase changes along the compression path are included with this method. This enables a detailed prediction to be made of the actual volumetric flow rate for the various compressor stages. This paper reports the implementation of the direct integration procedure for wet gas performance prediction. The procedure enables generic wet gas compression to be studied which forms the foundation for performance analysis with variations in operation at conditions and fluid components and properties.

Wet Gas Compression: Characterizing Two-Phase Flow Inside a Compressor With Flow Visualization

2017 ◽  
Author(s):  
Melissa Poerner ◽  
Ryan Cater ◽  
Craig Nolen ◽  
Grant Musgrove ◽  
David Ransom
Keyword(s):  
Flow Visualization ◽  
Flow Structure ◽  
Two Phase Flow ◽  
Gas Production ◽  
Liquid Volume ◽  
Phase Flow ◽  
Two Phase ◽  
Wet Gas ◽  
Gas Compression ◽  
Compressor Performance

Wet Gas Compression (WGC) continues to be an important topic as oil and gas production is driven further out into the ocean and moves critical equipment to the ocean floor. In the last year, significant milestones have been reached for WGC by the installation of the first wet gas compressor off the coast of Norway. Even with this achievement, there is a lack of understanding of the physics behind WGC and there are deficiencies in the ability to predict the compressor performance. Understanding the two phase flow structure inside the compressor is important for validating WGC simulations and being able to predict compressor performance. This paper reviews the results from a test program focused on characterizing the flow inside the compressor by using flow visualization. An open impeller centrifugal compressor was outfitted with windows to view the flow inside the compressor at the inlet, inside the impeller and in the diffuser section. Testing was conducted with an ambient suction pressure at various compressor speeds, flow rates, and liquid volume fractions. Images and videos were captured at the different conditions in order to observe the two phase flow structure. The general patterns and trends that characterize wet gas flow are discussed in this paper.

Volute Flow Influence on Wet Gas Compressor Performance

2017 ◽  
Author(s):  
Martin Bakken ◽  
Tor Bjørge
Keyword(s):  
Energy Demand ◽  
Oil And Gas ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Gas Production ◽  
Test Facility ◽  
Centrifugal Impeller ◽  
Stable Operation ◽  
Wet Gas ◽  
Compressor Performance

The world’s energy demand is increasing, asking for new and cost-efficient ways to extract oil and gas. With traditional technologies, oil and gas production relies on a sufficiently high well head pressure for transportation to nearby process facilities. Utilization of subsea wet gas compression systems enables production at significantly lower pressures and is a favourable solution concerning production in remote regions. Wet gas compressors are particularly useful when handling multiphase mixtures consisting of 95%–100% gas, on a volumetric basis. The remaining content is water and liquid condensate, which introduces flow mechanisms such as droplet deposition, liquid film formation and momentum transfer, which influence the fundamental flow behavior through the compressor. Previous tests have documented the occurrence of compressor hysteresis at low compressor flow rates. Recent findings have revealed the flow interaction between the diffuser and the volute is a governing factor concerning the documented hysteresis. This kind of behaviour induces challenges with regard to compressor performance prediction and securing stable operation. An experimental test campaign has been performed at the Norwegian University of Science and Technology (NTNU). The test facility is an open loop configuration consisting of a shrouded centrifugal impeller, a vaneless diffuser and a circular volute. The test was performed by establishing the compressor characteristics while monitoring the diffuser/volute flow regime. Emphasis was put on the volute flow characteristics and the correlation with the compressor performance. The investigation reveals that the volute flow characteristics and the interaction with the diffuser has a distinct impact on the compressor performance, particularly at lower gas mass fractions. Furthermore, the test reveals that the diffuser design is a key factor concerning the performance impact.

An Experimental Investigation on Hysteresis in a Wet Gas Compressor

2017 ◽  
Author(s):  
Martin Bakken ◽  
Tor Bjørge
Keyword(s):  
Liquid Phase ◽  
Multiphase Flow ◽  
Open Loop ◽  
Operating Conditions ◽  
Test Facility ◽  
Centrifugal Impeller ◽  
Compression Process ◽  
Wet Gas ◽  
Liquid Load ◽  
Compressor Performance

Performance monitoring of wet gas compressors is challenging due to the liquid phase impact on performance. Introduction of a liquid phase alters both the thermodynamics as well as the fluid dynamics of the compression process. Hence, understanding the flow interaction between the impeller, diffuser and volute is pivotal. Previous investigations have detected occurrence of compressor hysteresis at certain wet gas operating conditions, resulting in temporary deviations from the steady state compressor characteristics. This kind of behavior influences both the compressor stability and performance. Thus, being able to understand the onset of hysteresis and its impact on the compressor is paramount. An experimental test campaign has been performed at the Norwegian University of Science and Technology (NTNU). The test facility is an open loop configuration consisting of a shrouded centrifugal impeller, a vaneless diffuser and a circular volute. The current investigation document the compressor performance shift and the occurrence of compressor hysteresis when gradually increasing the liquid load on a centrifugal compressor. Emphasis was put on the compressor performance and its correlation to the diffuser multiphase flow regime. The investigation revealed that there is a clear dependence between the diffuser multiphase flow characteristics and the compressor performance.

Bright and dark optical solitons for the generalized variable coefficients nonlinear Schrödinger equation

2020 ◽  
Vol 21 (7-8) ◽  
pp. 675-681
Author(s):  
Rehab M. El-Shiekh ◽  
Mahmoud Gaballah
Keyword(s):  
Schrödinger Equation ◽  
Nonlinear Schrödinger Equation ◽  
Schrodinger Equation ◽  
Integration Method ◽  
Variable Coefficients ◽  
Nonlinear Schrodinger Equation ◽  
Equation Method ◽  
Direct Integration ◽  
Wave Solutions ◽  
Direct Integration Method

AbstractIn this paper, the generalized nonlinear Schrödinger equation with variable coefficients (gvcNLSE) arising in optical fiber is solved by using two different techniques the trail equation method and direct integration method. Many different new types of wave solutions like Jacobi, periodic and soliton wave solutions are obtained. From this study we have concluded that the direct integration method is more easy and straightforward than the trail equation method. As an application in optic fibers the propagation of the frequency modulated optical soliton is discussed and we have deduced that it's propagation shape is affected with the different values of both the amplification increment and the group velocity (GVD).

scholarly journals Instantaneous longwave radiative impact of ozone: an application on IASI/MetOp observations

2015 ◽  
Vol 15 (15) ◽  
pp. 21177-21218
Author(s):  
S. Doniki ◽  
D. Hurtmans ◽  
L. Clarisse ◽  
C. Clerbaux ◽  
H. M. Worden ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Longwave Radiation ◽  
Polar Regions ◽  
Direct Integration ◽  
Direct Integration Method ◽  
Radiative Impact ◽  
Ozone Variation ◽  
Atmospheric Sounding ◽  
Stratospheric Intrusions

Abstract. Ozone is an important greenhouse gas in terms of anthropogenic radiative forcing (RF). RF calculations for ozone were until recently entirely model based and significant discrepancies were reported due to different model characteristics. However, new instantaneous radiative kernels (IRKs) calculated from hyperspectral thermal IR satellites have been able to help adjudicate between different climate model RF calculations. IRKs are defined as the sensitivity of the outgoing longwave radiation (OLR) flux with respect to the ozone vertical distribution in the full 9.6 μm band. Previous methods applied to measurements from the Tropospheric Emission Spectrometer (TES) on Aura, rely on an anisotropy approximation for the angular integration. In this paper, we present a more accurate but more computationally expensive method to calculate these kernels. The method of direct integration is based on similar principles with the anisotropy approximation, but deals more precisely with the integration of the Jacobians. We describe both methods and highlight their differences with respect to the IRKs and the ozone longwave radiative effect (LWRE), i.e. the radiative impact in OLR due to absorption by ozone, for both tropospheric and total columns, from measurements of the Infrared Atmospheric Sounding Interferometer (IASI) onboard MetOp-A. Biases between the two methods vary from −25 to +20 % for the LWRE, depending on the viewing angle. These biases point to the inadequacy of the anisotropy method, especially at nadir, suggesting that the TES derived LWRE are biased low by around 25 % and that chemistry-climate model OLR biases with respect to TES are underestimated. In this paper we also exploit the sampling performance of IASI to obtain first daily global distributions of the LWRE, for 12 days (the 15th of each month) in 2011, calculated with the direct integration method. We show that the temporal variation of global and latitudinal averages of the LWRE shows patterns which are controlled by changes in the surface temperature and ozone variation due to specific processes, such as the ozone hole in the Polar regions and stratospheric intrusions into the troposphere.

scholarly journals Piecewise Polynomial Fitting with Trend Item Removal and Its Application in a Cab Vibration Test

2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
Wu Ren ◽  
Qiongqiong Ren ◽  
Lin Han ◽  
Ying Liu ◽  
Bo Peng
Keyword(s):  
Integration Method ◽  
Vibration Signal ◽  
Vibration Test ◽  
Measured Signal ◽  
Direct Integration ◽  
Piecewise Polynomial ◽  
Modal Parameter ◽  
Polynomial Fitting ◽  
Special Equipment ◽  
Direct Integration Method

The trend item of a long-term vibration signal is difficult to remove. This paper proposes a piecewise integration method to remove trend items. Examples of direct integration without trend item removal, global integration after piecewise polynomial fitting with trend item removal, and direct integration after piecewise polynomial fitting with trend item removal were simulated. The results showed that direct integration of the fitted piecewise polynomial provided greater acceleration and displacement precision than the other two integration methods. A vibration test was then performed on a special equipment cab. The results indicated that direct integration by piecewise polynomial fitting with trend item removal was highly consistent with the measured signal data. However, the direct integration method without trend item removal resulted in signal distortion. The proposed method can help with frequency domain analysis of vibration signals and modal parameter identification for such equipment.

The Phase Changes in CH4 + C2H6 Hydrates, and Their Impact on Oil and Gas Production

2001 ◽  
pp. 195-203
Author(s):  
Sivakumar Subramanian ◽  
Adam Ballard ◽  
Ramesh A. Kini ◽  
Steven F. Dec ◽  
E. Dendy Sloan
Keyword(s):  
Oil And Gas ◽  
Gas Production ◽  
Phase Changes ◽  
Oil And Gas Production
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