The 7EA User Group conference this year featured a rotor lifecycle roundtable where vendors and consultants answered questions regarding a TIL by GE indicating that 200,000 hours or 5000 starts were the end-of-life limits for the 7EA.
A steam turbine diaphragm is also a very difficult component to manufacture due to the following conflicting requirements:
- it consists of three major parts made from different materials;
- it must have exceptional mechanical strength;
A turbine diaphragm, due to its complex structure and harsh operating conditions, is a very difficult subject for mechanical strength calculations. Structural complexity of the diaphragm is characterized by the following features:
- It is a complicated 360 degree plate, composed of three major components (an outer ring, a set of vanes with complex geometry, and an inner ring) made from different materials;
- A diaphragm is always split in two halves;
- The outer ring is supported by its outer diameter;
- The inner ring is supported only by vanes.
Long term operation and extensive R&D of steam turbines have shown that steam leakages from the main steam flow beyond the rotating blade shrouds and their roots as well as between the shaft and diaphragm ID is the main source (75-81%) of turbine performance deterioration due to:
EEC is the axial distance between the vane exit edge and rotating blade inlet edge in each stage (Figure 1). EEC is an important factor that affects stage performance (both efficiency and reliability). The required EEC for optimal performance is dependent on whether or not the stage has effective tip and root seals.
This innovative design feature is applicable to several first stages operating with high steam conditions. High steam pressure and temperature results in high density steam. Small volumetric steam flow requires partial arc steam admission, short vanes and rotating blades.
A smooth and unimpeded steam flow entrance into the rotating blades, with proper distribution of steam along the heights of these blades, is one of the most substantial factors related to stage efficiency. Such a steam entrance is defined by the compound (axial and tangential) angle of the steam flow. The axial angle is achieved by the optimal va
Figure shows the comparison between the original and current airfoil designs. The old airfoils form a channel in which steam flow accelerates and turns to exit with maximum steam velocity resulting in high secondary losses.
Seal system issues are a common reason for alarms and shutdowns in turbocompressors. Upgrades to dry gas seal systems typically consist of two options:
• Seal gas filter system — the original filters are typically small in capacity and large in the mesh size. In most cases, new filters should be used which are 4-to-6 times bigger while having a mesh that is 5-to-8 times smaller
• Operation range of seal system instruments — seal panels are complex systems with various kinds of instrumentation.
The 42nd Annual Turbomachinery Symposium and 29th International Pump Users Symposium took place in early October in Houston, Texas. Almost six thousand attendees enjoyed aprogram consisting of short courses, tutorials, technical sessions, discussion groups and 325 exhibits.
Wood Group and Siemens AG have entered into an agreement to form a joint venture ("JV") consisting of the Maintenance and Power Solutions businesses of Wood Group GTS (excluding its Rolls Wood Group, TransCanada Turbines and Sulzer Wood joint ventures) and Siemens TurboCare business unit ("TurboCare") which provides aftermarket gas turbine, steam turbine and generator design, repair and manufacturing services.
As the quest for raw materials drives oil and gas companies further offshore, both risk and potential gains increase. At some point in offshore operations, it becomes nearly impossible to push oil and gas to the surface with the existing degree of natural pressure. Some hydrocarbons become non-recoverable due to the loss of pressure during production.
There is always concern about the transient behavior of a lubrication oil system for any turbomachinery. Two of the most critical issues are the oil pump changeover and the oil accumulator. Cutting off the oil flow to turbomachinery could result in catastrophic failure of lubricated bearings in a few seconds.
A cartridge seal design should be used whenever possible to ensure proper seal assembly and optimum mechanical seal MTBFs. The use of cartridge mechanical seals significantly minimizes installation errors. While cartridge seals are more expensive than component seals, the additional cost can be justified in many cases based on the material costs and revenue losses of component seals.
When would certain flush systems be better than others? It is necessary that one has to pre-select mechanical seal and flush system design during the pre-FEED project phase, based on plant, company and/or industry experience, to optimize mechanical seal MTBF. Use plant, company and industry lessons learned to properly select a flush system that will result in optimum seal life – in your plant!
Experience shows that pump MTBFs (mean time between failures) are directly related to mechanical seal reliability. Pump mechanical seal MTBF is the lowest of all machinery components. Of all machinery components, mechanical seals are the most affected by the process conditions.
Accurate definition of the following parameters on the pump and seal data sheet will go a long way towards assuring optimum pump mechanical seal MTBFs:
Fluid vapor pressure
Fluid specific gravity and viscosity
Fluid pumping temperature (PT)
Gas turbines were initially used in the early 1940s for military purposes. In the 1950s, gas turbines first entered mechanical service applications. Since gas turbines are production type equipment and not custom designed, we usually refer to generations of gas turbines. The first generation of gas turbines began in the 1950s, and progressed through the 1970s (second generation) and 1980s (third generation) to present day efficiency improvements.
Aeroderivative gas turbines (initially designed for flight and using anti-friction bearings) have been thought to have lower MTBFs than industrial types. End user fleet experience has shown anti-friction bearing life to exceed 100 months. One should always consider aeroderivative gas generator/industrial power turbine (hybrid type) gas turbine units.
The use of an aeroderivative gas generator while using an industrial type power turbine (with hydrodynamic bearings) has the following advantages:
The last decade has seen monumental advances in computer power. The average laptop, these days, would put a supercomputer of the nineties to shame. This has propelled the field of data analytics into the stratosphere. Calculations which used to take months can be accomplished in minutes.
Now factor in gains in sensor and wireless technology, which make it possible to gather an ocean of information from plants and turbomachinery. This combination of compute power, analytics and the assembly of huge quantities of data is known under the collective title of ‘Big Data.’
In 2006 I was asked to give a presentation at the ASME Turbo Expo about the impact of U.S. LNG imports on gas turbine operation and infrastructure. At the time, the U.S. had five operating LNG import terminals, three on the east coast and two in the Gulf of Mexico, with a total capacity of 5.3 BCF per day. There were also an additional 17 new LNG import terminals in the advanced stages of development which should have added another 25 BCF per day of LNG import capacity. The resulting LNG imports would have accounted for almost 10 percent of total gas consumption in the U.S.
In this day and age with daily revenues for power and oil & gas producers exceeding $1 million (and in many cases over $5 million), it has become imperative to tackle machinery problems before an unplanned shutdown. Yet, in the author’s experience, this is rarely the case. However, through the increased accuracy and quality of instrumentation and data collection, it is much easier to diagnose potential issues (via proactive maintenance) before a failure.