A gas turbine is a rotary thermal internal combustion engine which uses the energy provided by fuel to produce mechanical energy and generate a large amount of heat in the form of hot gases. The combustion process of the raw material is in turn used to produce electrical energy. This simultaneous generation of two energy sources, electrical and heat, is called cogeneration, a high energy efficient system with a great number of applications.
There are various types of gas turbines, which are generally categorized in two models: combined cycle gas turbines which are large scale and used for mass energy generation, and aero-derivative gas turbines, which this article will focus on
These turbines, which are smaller, have adapted their original aeronautical design to make use of exhaust gas to supply electricity to industrial plants, as well as provide production processes with heat. As they support industrial processes whilst providing energy, they must be fully available as often as possible.
However, although they are mechanically simple, they are not free from possible failures that may lead to significant costs, both in repairs and as a result of being unavailable. Furthermore, unlike other industrial components, their scheduled shutdowns also pose numerous challenges in carrying them out optimally and with the least possible damage to the machinery.
Atten2 optical sensors, through monitoring the behavior of these engines’ most critical parts, are an excellent means of minimizing the risk of damage and taking informed maintenance decisions.
1. Turbine and electric generator bearings
The mechanics of turbines is optimized. Bearings are set very accurately, with almost no clearance. Therefore, the lubrication of these systems is a delicate operation. A lubrication fault can be critical, whether it is a result of thin oil film or extreme demands on the lubrication. It is with good reason, therefore, that the most advanced oils are used for this purpose, oils that can withstand the highest operating temperatures.
In such a sensitive point as this, where any problem with the lubrication can lead to the risk of a fault, the full potential of Atten2 optical sensors can be put to use. These advanced monitoring systems provide valuable real-time information on the presence of a potential problem and also identify its source.
The electric generator bearings are also of critical importance: As supporting components of an electric generator linked to a functioning turbine, they have a function in which any unforeseen shut-down could damage their condition. Certain electrical circumstances deform the axis mechanism, which has a clear impact on the condition of the bearing.
Atten2 sensors count the particles present in lubricating oil as indicators of potential anomalies. The presence of a high number of particles in suspension is symptomatic of increased wear and identifying their form, another functionality of Atten2 sensors, makes it easier to ascertain the source of the wear. This information signals the presence and source of a possible fault in its earliest stages and, therefore, action can be taken before a breakdown occurs.
For turbine bearings, Atten2 sensors provide another added value: determining their condition without having to open the system. Bearings in these systems are not visible; rather, given their dangerous nature, they are enclosed in a CO2-sealed system. Atten2 technology provides continuous accurate information on their condition without depending on scheduled maintenance shutdowns and, consequently, minimizes the risk of breakdowns in these critical parts.
Atten2 systems are also able to detect air bubbles, which are potentially harmful to bearings as their presence indicates that the oil film is not intact.
2. Hydraulic start-up system
As mentioned previously, the operating rate of aero-derivative gas turbines is very high, and these systems are designed to be in constant operation. Precisely because of their prolonged operation, shutdowns of these systems can be particularly damaging. It is for good reason that the start-ups and shutdowns of these machines are measured in work hours. Therefore, a maintenance shut-down may guarantee operating hours, but the time involved in the shut-down process must be subtracted from this figure. In other words, the time until the turbine returns to stable operating conditions.
Shutdowns and start-ups severely affect the device, particularly its bearings. Traditionally, the machine manufacturer provides an estimate of the effects of this process in terms of maintenance. In contrast, Atten2 technology measures particles to offer detailed information on the real level of wear the process has had on the bearings and, therefore, what condition they are in.
In turbines under 50 MW, the rotational speed of the axis is usually higher than needed to drive the alternator or compressor. This is why gearboxes are necessary to lower turbine revolutions to the number necessary for generating electrical energy. Gearboxes are another critical component of these systems, because although they could continue to produce heat, a fault in this part means losing the entire electrical generation potential.
In gearboxes, the Atten2 online monitoring systems offer high added value data that highlight potential faults that other maintenance technologies simply cannot see.
By counting particles and with its ability to identify their nature and shape, the system is able to detect the onset of wear in gear tooth, the source of advanced deterioration, and the presence of contaminants. All these factors have a negative impact on gearboxes performance and may lead to considerable damage.