In the first part, the author highlighted how VFD technology has become a common feature in compressors. In this article, he explains why the VFD can be advantageous despite being an expensive addition to the compressor system.
This article applies to centrifugal and axial compressors. Reciprocating, screw, and scroll compressors and ejectors have different considerations. For “dynamic” radial or axial gas compressors the predominant noise source is rotating blade passing frequency. There is also noise due to flow turbulence and vortex shedding from stationary vanes and rotating blades. The blade passing frequency is due to interaction of non-uniform flow. Noise levels increase as power increases, but especially as equivalent tip speed goes higher.
Monitor control valve position in all oil systems to determine component wear (rotary pumps, bearings and seals) to ensure corrective action is taken during a turnaround.
Marking the position of control valves (marking the stem and valve yoke with a straight edge) at the beginning of a run will give an instant indication of component wear for the following items:
Ending a manned mission to Mars would represent an engineering feat for the ages. But not far behind in terms of technological innovation is the subject of subsea compression. As the quest for raw materials drives oil and gas companies farther offshore into deeper and deeper waters, at some point it becomes nearly impossible to push hydrocarbons to the surface with the existing degree of natural pressure.
Siemens AG and Dresser-Rand Group Inc. (Dresser-Rand) have entered into a definitive merger agreement under which Siemens will acquire all of the outstanding shares of Dresser-Rand common stock for $83.00 per share in cash.
Axial compressors are modern and compact turbo-compressors for applications with very large flows. They are used in air applications (in air compression units or as an air compressor in a gas turbine), natural gas services and mixed refrigerant applications (in some large LNG plants).
When a fluid, either liquid or gas, is constrained within the space between two concentric cylinders, one rotating and one stationary, the fluid in the clearance between the two cylinders will be set into circumferential motion.
The root cause analysis of vibration problems related to critical turbomachinery is an engineering science based on what is often referred to as the "First Law of Machinery Diagnostics". The 1st Law states that displacement (vibration) is equal to the summation of the dynamic forces acting on the rotor divided by the complex dynamic support stiffness of the rotor bearing system.
A paper by Klaus Brun and Terence Grimley of SWRI, Rainer Kurz of Solar Turbines, and William Folles at ASME/IGTI, 2014 dealt with ‘Experimental evaluation of the effectiveness of online water washing in gas turbine compressors.’ Below are excerpts from the paper.
A friction bound control valve (right and/or oil sludge in packing) can cause a unit trip during a main oil pump trip if sufficient system oil (because the valve does not immediately close) is not available during the transient event to prevent a low oil pressure unit trip. A fail
LVDTs (Linear Variable Differential Transformers) are very commonly used as position sensors in power plants throughout the world. Working from AC voltages and frequencies not available from power lines, LVDTs require a signal conditioner to provide the necessary operating power. Alliance Sensors Group's model S1A module is a single channel LVDT signal conditioner on the market today. It can operate practically any inductive or LVDT-type position sensor currently in use.
Case of probable structural resonance
During a mechanical run test of an axially split centrifugal compressor, polar plots from the rotor’s Y-direction probe showed an unusual pattern for a healthy machine at steady state running condition.
Who would have thought that the Winsurance field could provide insight into the operations and maintenance of turbomachinery? Yet that is exactly what occurred at the 39th annual Combustion Turbine Operations Technical Forum (CTOTF) Spring 2014 meeting in Palm Beach Gardens, Florida.
To prevent a unit shutdown on low oil pressure, continuously vent the non-operating cooler and filter by installing orificed return lines, and keep the transfer valve bypass fill line opened to ensure warm-up of the cooler and filter prior to transfer, in cold climates. In cold climates (ambient temperatures below 15oC at any time of the year), cool, static oil in the non-operating cooler and filter will cause a transient pressure drop when it is charged on-line.