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.
A centrifugal compressor, packaged by Cooper Industries (now part of Rolls-Royce), was used in an offshore facility to compress natural gas. It was a three-stage assembly: from 6 kg/cm3 to 90 kg/cm3 with two stages combined in the low pressure (LP) bundle and a third stage separately operating in the high pressure (HP) bundle assembly.
During load operations, a gas turbine is characterized by cyclic transients and long dwell times. As a result, variation in clearance occurs. Tight clearances in both the compressor and the turbine section are the key to high efficiency. However, some clearance must be maintained in order to avoid contact between rotating and stationary parts.
For rolling element bearings that are not lubricated by a forced lubrication system, there are a few methods available to the user. Oil mist has been presented as the best method of lubricating bearings. It is the best and has some advantages.
The US Department of Energy (DOE) is providing $4,998,319 in funding for ten university research projects on making gas turbines more durable and fuel-flexible, covering the lion's share of the total project costs of $6,314,361.
The funds are granted as part of the Office of Fossil Energy's University Turbine Systems Research (UTSR) Program. DOE is the main financer of the projects, while the remaining costs will be provided by the universities.
In the third part of this series, the author pointed out that natural gas proved to be a good fuel in larger locomotive units and they ran well for long periods of time between overhauls. In this article, he talks about the prospects of the GT-EL locomotives in this era.
Complete predictive maintenance monitoring of gas turbines requires trends of compressor, gas generator and power turbine performance to optimize run times between maintenance cycles.
The end users of ‘best of the best’ turbines optimize their gas turbine performance monitoring methodology to extend their run times significantly beyond vendor’s recommendations (by as much as 60,000 hours). This requires review of vendor’s performance monitoring capabilities during the bid stage of the project and complete performance monitoring capabilities.
Tilting pad radial bearings provide stability at any load angle. Lemon bore (elliptical) or offset sleeve (to achieve an elliptical arrangement) bearings do not eliminate vibration instabilities if the load angle lies in the major axis of the ellipse, since the oil film stiffness in this region may not be sufficient to prevent vibration instabilities.
In the first part of this series, we saw that the present conditions are most favorable for the GT-EL, a clean burning train hauling machine, to make a comeback and become a winner. In this article, the author discusses how UPRR, GE and ALCO came together on the first locomotive and tested it.
There is an old saying that goes like this: "What goes around comes around". This adage could very well apply to the reintroduction of the gas turbine-electric locomotive (GT-EL) in the USA driven by and fueled by the new abundant supply of shale natural gas brought about by fracking.
An $18 million program to install a state-wide microgrid, powered by distributed gas-fired turbines, has recently been launched in the US coastal state of Connecticut, to keep the lights on in public buildings during grid outages in severe weather. The scheme comes after hurricane Sandy last year caused 5 deaths in the state, and $68 billion in damages nationwide.