Aeroderivative gas turbines are rotating thermal engines whose main use is in cogeneration, in other words, the simultaneous generation of electrical and heat energy. Smaller than combined cycle turbines, they are used in industrial processes that require the generation of both energy sources - electricity and heat - and their operating strategy is continuous. Therefore, start-ups and shutdowns severely impact the whole system. Furthermore, they necessitate stopping the associated industrial process, with the financial losses that entails. That is why it is essential to minimize unwanted start-ups and shutdowns. In this article we give you 4 tips which may help to prevent wear on Gas turbines.
Keep lubricant clean, cold, and dry
Turbine oils are designed to lubricate bearings, the gear reducer, and the generator, as well as regulating the temperature of all parts. Good lubricating oil should have specific characteristics such as appropriate viscosity, rust resistance, anti-corrosive properties, and the ability to expel both air and water quickly. Turbine lubricant should be kept clean, cold, and dry. These three variables should be monitored to avoid faults that may lead to unscheduled shutdowns.
Aeroderivative gas turbines are highly compact machines with especially small clearance of one micrometer. If the oil is dirty, particles will likely scratch contact surfaces. Therefore, cleanliness codes are very low and should be monitored closely as daily operation significantly affects the generation of particles. All filtering procedures must be very well defined, including the inspection and changing of filters as necessary and the monitoring of the condition of the lubricant. It is also important to emphasize that new oil should be filtered before being added to the turbine for the first time in order to ensure that it is sufficiently clean before being used.
One of the functions of lubricant is the cooling of parts. For that reason, oil temperature during operation must be monitored. Furthermore, if it is hotter than normal, the oil will degrade more quickly: a 10 degree increase in oil temperature may decrease its service life by up to 20%. Lastly, the presence of water is a serious problem, given that it causes rust and corrosion in the machinery. Therefore, it is essential that the oil is kept dry. These machines are often placed outdoors so it is essential to protect the lubrication systems from external agents and inspect the ventilation systems to ensure that water and dust cannot enter.
Using the lubricant to monitor the start-up system
One of the most critical parts is the turbine start-up system. In an ideal world, we would only make sparing use of the start-up system. However, it has to be available when required. This is why it should be regularly inspected to ascertain its condition and, in this regard, the lubricant can provide us with valuable information. By analyzing the particles present in the oil we can gather data on the condition of the machine, and we can detect contamination problems without having to disassemble or run it.
Monitoring the lubricant can also prevent unscheduled shutdowns resulting from false alarms. These machines have automatic shut-down systems for wear. However, the sensors scan for large metallic particles and they often give false positives when they detect other types of non-metallic particles. Using more accurate sensors would delete these errors and increase the availability of the turbine.
Continuous online analysis
Aeroderivative gas turbines are very sensitive to weather conditions and for that reason oil contamination values may vary greatly depending on what time of day the sample is taken. This must be taken into consideration when taking samples and we should be aware that the best solution lies in continuously monitoring the oil using dynamic condition analysis. There are currently enough technical means to carry out predictive maintenance online which help us to ascertain the condition and prevent unwanted wear on gas turbine machinery.
Foaming prevention tools
One of the most critical events that can happen is the presence of bubbles in lubrication systems. These appear when the oil is unable to expel air. Foaming may occur for a number of reasons: a fault in the additives, an error when refilling oils, contamination, or mechanical problems causing aeration. If this happens, foam will be generated which will cause serious problems when it reaches lubrication areas. To prevent this from happening, there are various analytical techniques for monitoring how the oil expels air and detecting the presence of bubbles in the lubricant before the turbines sustain serious damage.
Aeroderivative turbines have operating characteristics, such as the high cost of non-availability and stable operating conditions, which mean that the lubrication of the machinery and its condition are critically important. Appropriate monitoring of the condition of the lubricant in the different parts that make up these systems, alongside the removal of possible contaminants, improves availability and prevents possible unwanted start-ups and unscheduled shutdowns.