Gases are an essential component of many industrial processes and are used in a variety of quantities and defined states. Compressors are used when gases are required to be at a certain pressure and the exact pressure required will determine the type of compressor that is needed. In many situations it is only turbocompressors that are capable of continuously providing large quantities of gas at the highest pressure. Examples of turbocompressors are found in industrial plants such as petro-chemical refineries and metallurgical smelting works and are used to provide oxygen for sewage plants. Exhaust gas turbochargers are now commonplace in the automotive industry as are turbo jet engines in turbine technology and process turbocompressors in the chemical industry.
Turbocompressors are being studied as part of the SAKE project. They are typically aerodynamic and fluid machines designed to compress gases to a pressure ratio greater than 1.3. They are characterized by a rotating mechanism and the ability to continuously deliver the compressed gas.
As turbocompressors are required to provide a specified quantity of gas at a specified pressure their operation can be illustrated as characteristic lines or a characteristic map of the two process factors. What must be considered is the fact that dangerous situations can arise during operation, such as if the turbocompressor is run too close to or above the stability limits. The most important operating limit is described as the surge limit which restricts operation to quantities of gas greater than a pre-determined minimum.
Foto and Graphics
© AviComp Control GmbH
|Performance map of a turbocompressor. The red line shows the surge limit, which may not be exceeded during operation.||Surging is an intensive oscillation of pressure and flow. The dashed line indicates a large rate of change.|
If the compressor is operated with less than the minimum flow, the surging – an aerodynamically unstable compressor state – will kick in. This occurs when the normally continuous flow of gas is heavily disturbed and the discharge pressure and flow begin to cyclically oscillate and continue to the point when the direction of the gas flow is inverted leading to serious disturbances in the compression process. In addition to the highly negative technological impact of this process it also causes the compressor's components to be subjected to enormous strain which can lead to their complete destruction. The surging is self-perpetuating and continues until a counter-measure is initiated.
Vibration monitoring systems have often been used to avoid undesirable operating modes in compressor plants and AviComp Controls is currently in the process of finalizing the prototype phase of a new hardware development. With the help of the CCM-221 vibration monitoring system the compressors' storage status can be continually monitored as can the condition of potentially dangerous mechanical parts. Owing to the complexity of the task, however, it is still difficult to forecast impending maintenance issues and undesirable operating modes. Because of the sensors' high sampling rate combined with the number of sensors installed per machine and the quantity of machines themselves, the volume of data generated is vast. Data volumes of this size require IT-based evaluation and processing as well as specially developed algorithms.
For this reason, the aim of SAKE is to develop systems which will guarantee the optimized and safe operation of compressor plants. The target results are as follows:
- Casing vibration analysis and early detection of aerodynamic instabilities within compressor plants.
- The early detection of impending maintenance issues based on vibration analysis, such as in relation to potential storage damage.
- Long-term measurements and analysis based on database evaluation such as the recording of processing values, the creation and analysis of pV diagrams and the monitoring of the long-term drift of frequency response locus.
- The remote connection of the CCM-221 vibration monitoring system to a dedicated machine state analysis or failure prognosis.
- The integration and adaptation of the CCM-221 vibration monitoring system in the SAKE platform.