Overview of Important Considerations in Wet Gas Compression Testing and Analysis
During upstream production of natural gas fields, it is common that a gas-liquid mixture of product is brought to the surface. The mixture, termed wet gas, is generally made up of mostly gas with a small amount of liquid, typically up to 5% by volume of the mixture. Because of the difficulties of compressing wet gas, the practical approach has been to separate the liquid and gas phases before compression. However, large separation equipment is unfavorable for subsea installations because of the cost to place machinery on the sea floor. Instead, a compressor designed for wet gas operation is preferred because it eliminates the need for large separation equipment leading to plant simplification and cost reduction. To address this design need, researchers have been active in addressing the challenges with wet gas compression. As result, experimental work has been conducted to study the effects of wet gas on compressor aerodynamic and mechanical performance. This experimental research has presented many challenges in recreating wet gas conditions and quantifying the effect of the liquid on the compressor performance. The results from this testing have helped to characterize the performance effects. But so far each work has focused on a range of test variables without identifying those that have the largest effect on compressor performance. This paper aims to provide the reader with an overview of the completed wet gas research, the challenges associated with doing the experimental work, and a discussion of the resulting trends observed in most of the wet gas research. This will include an in-depth review of relevant literature on wet gas compression testing and performance, a discussion of the important
Wet Gas Performance Analysis
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.Copyright © 2006 by ASME
Fatigue effects on the coordinative pattern during cycling: kinetics and kinematics evaluation.
The aim of the present study was to analyze the net joint moment distribution, joint forces and kinematics during cycling to exhaustion. Right pedal forces and lower limb kinematics of ten cyclists were measured throughout a fatigue cycling test at 100% of PO(MAX). The absolute net joint moments, resultant force and kinematics were calculated for the hip, knee and ankle joint through inverse dynamics. The contribution of each joint to the total net joint moments was computed. Decreased pedaling cadence was observed followed by a decreased ankle moment contribution to the total joint moments in the end of the test. The total absolute joint moment, and the hip and knee moments has also increased with fatigue. Resultant force was increased, while kinematics has changed in the end of the test for hip, knee and ankle joints. Reduced ankle contribution to the total absolute joint moment combined with higher ankle force and changes in kinematics has indicated a different mechanical function for this joint. Kinetics and kinematics changes observed at hip and knee joint was expected due to their function as power sources. Kinematics changes would be explained as an attempt to overcome decreased contractile properties of muscles during fatigue.