Internal hysteresis experienced on a high pressure syn gas compressor

A vibration instability phenomenon experienced in operating high pressure syn gas centrifugal compressors in two ammonia plants is described. The compressors were monitored by orbit and spectrum analysis for changes from baseline readings. It is found that internal hysteresis was the major destabilizing force; however, the problem was further complicated by seal lockup at the suction end of the compressor. A coupling lockup problem and a coupling fit problem, which frettage of the shaft, are also considered as contributors to the self excited vibrations

Cavitation effects on the pressure distribution of a squeeze film damper bearing

High speed motion pictures have revealed several operating regimes in a squeeze film damper. Pressure measurements corresponding to these distinct regimes were made to examine their effect on the performance of such dampers. Visual observation also revealed the means by which the pressure in the feed groove showed higher amplitudes than the theory predicts. Comparison between vapor and gaseous cavitation are made based on their characteristic pressure wave, and the effect this has on the total force and its phase

Fluid Film Bearing Fundamentals And Failure Analysis.

Tutorialpg. 161-186Fluid film bearing technology is presented in this tutorial as it applies to turbomachinery equipment. The focus here is on the practical aspects of fluid film journal bearings, as opposed to theoretical analysis. Failure modes and the mechanisms leading to these failures will be discussed, along with techniques used to identify and cure them. The influence of different bearing configurations on the dynamics of rotor bearing systems will also be discussed

Vibration And Eccentricity Measurements Combined With Rotordynamic Analyses On A Six Bearing Turbine Generator.

LecturePg. 85-92This lecture discusses how the vibration characteristics and eccentricity measurements were combined with rotordynamic analyses to help improve the reliability of a turbine generator unit. It also explains certain vibration characteristics at partial load conditions that resulted in changes of the bearing load magnitude and direction. The measurements of a stable backward whirl orbit at certain load conditions will be shown and discussed. The rotordynamic analyses also simulated field balancing measurements that compared well with the synchronous response calculations. These analyses were also used to examine the benefits of retrofitting a steady bearing at the unsupported shaft pump extension

Application Of High Speed And High Performance Fluid Film Bearings In Rotating Machinery.

Tutorialpg. 209-234Some of the critical parameters in the design and application of high performance fluid film bearings are emphasized. The limitations and problems associated with high speed and highly loaded bearings will be discussed. Examples of bearing failures, the symptoms associated with these failures, and their impact on the machine performance will be shown. Some of the common failure mechanisms will also be described with suggestions on how to eliminate the failures or reduce their consequences by changes to some of the bearing design features. New developments in bearing technology and testing specifically designed to address some of these limitations will be demonstrated. Case studies and analysis will be used in many common and newly developed turbomachinery equipment to help illustrate some of the key attributes in the design and application of high performance fluid film bearings and squeeze film dampers

Design, Analysis, And Testing Of High Performance Bearings In A High Speed Integrally Geared Compressor.

LecturePg. 31-42Analysis, design, and optimization of high performance journal and thrust bearings in a high speed integrally geared compressor are described. The high speed and relatively small bearing size stretches the applicable limits of conventional style tilt pad bearings. The variation in the load magnitude, as is the case with most gear loaded bearings, requires careful analysis of the stability and unbalance response characteristics. An optimized new flexible pivot bearing was used in this application to provide stable operation throughout the wide ranges of load and inlet temperature. The bearing incorporated a directed lubrication feature to reduce the hot oil carry over which is known to be a major contributor to high bearing temperatures in high speed applications. The precision inherent in the manufacturing process used to produce this style of bearing allowed further optimization of the preload and pivot offset. The use of an offset pivot configuration demonstrated lower sensitivity to bearing clearance variation. The necessity for high rotational speeds in integrally geared compressors increases the frictional power losses in the journal and thrust bearings. The parasitic losses constitute a significant percentage of the overall bearing power losses. Bearing designs that were utilized to reduce both the frictional and parasitic losses in the thrust bearings are discussed. The new thrust bearings were designed to provide an optimum crown-to-film thickness ratio allowing the bearing to carry the design thrust load with fewer pads. The analytical results for the conventional and deflection journal and thrust bearings are presented and compared to the test data. The new bearing resulted in lower steady state vibrations. At surge conditions, the synchronous and subsynchronous vibrations were about 25 percent of the conventional tilt pad bearing. The frictional and parasitic power losses with the new thrust bearing were about 20 percent lower than those of the conventional bearings. The temperature rise was also lower which indicated that the inlet temperature can be further increased with the new bearing allowing a wider operating temperature range and lower frictional losses

Use Of Honeycomb Seals In Stabilizing Two Centrifugal Compressors

LecturePg. 3-16The stabilizing effects achieved by replacing labyrinth seals with honeycomb seals are described. Although honeycomb seals have been used for some time in high pressure compressors and other turbomachinery applications, their stabilizing influence has only recently been recognized. The pioneering work of Childs et al. [1,2,3], in the theoretical analyses and accompanying experimental investigations have had a significant influence on advancing the use of honeycomb seal technology. A major beneficiary of the application of honeycomb seals has been the space shuttle turbo pumps. There are other major applications for honeycomb seals but, for the most part, they have remained in a narrow area encompassing the aerospace industry and the higher performance turbomachinery applications. The authors address how honeycomb seals were used to stabilize two process-type compressors. Two stability problems experienced on two different compressor configurations were solved using a common approach. These two cases should serve to enlighten users who might experience similar problems. It also sheds light on other sources of instability in turbo machinery, and some of the means available to counter their destabilizing effects. In both cases, the application of honeycomb seals was instrumental in enhancing the stability of each of the compressors

Electric Shaft Currents In Turbomachinery.

LecturePg. 51-64Electrical damage to turbomachinery parts has caused a number of machinery failures and many hours of costly downtime. The problem of electrical voltages and currents being generated in non-electrical machines has puzzled both users and manufacturers of these equipment, and has prompted ongoing research at Texas A&M to help identify and better classify the different sources of these voltages and the mechanisms by which they cause damage to bearings, seals, and other critical machinery parts. Electrostatic and electromagnetic type voltages are often misidentified, a situation that might lead to a wrong or costly remedy. The distinctions between these two major sources of shaft voltages and currents are clearly drawn herein. Lubricating oil characteristics and their influence on the buildup of shaft voltage potential have also been carefully scrutinized. Breakdown voltages were generated and measured at different operating conditions to help highlight the influence of the different variables such as bearing clearance and dielectric strength of the oil

Design And Application Of Squeeze Film Dampers In Rotating Machinery.

Tutorialpg. 169-188There are common misconceptions and occasional misapplications associated with squeeze film dampers. The authors have worked for more than 25 years researching, experimenting, and applying this subject matter to all types of turbomachinery. Major strides have been made in advancing the state-of-the-art by accounting for the fluid inertia effects in the analysis of squeeze film dampers. These effects are very important at high speeds and high temperatures (high squeeze film Reynolds numbers) due to the dominance of the inertial effects in comparison to the viscous effects. A comprehensive discussion is provided of squeeze film dampers, outlining their major advantages and the proper use of these components. Since squeeze film dampers are more complex to design and analyze than other machinery elements, they have often been used in the process industry as a last resort to reduce vibration or improve the rotordynamic characteristics of a machine. This stigma has often tainted their use as a "band aid" solution and resulted in rejection even when properly applied, with the exception of the aircraft gas turbine industry where their use is widespread. The influence of cavitation in squeeze film damper bearings that is distinctly different than cavitation in journal bearings has only been recently understood. Cavitation, however, is still not amenable to a rigorous quantitative analysis, thus making it essential to rely on experience and knowledge of the applications at hand. It is, therefore, of importance to review the historical events leading to the invention of this device and discuss the major developments in squeeze film dampers to gain a better understanding of the subject matter and an appreciation for the benefits it provides