Instrumentation and Control Department, Government Polytechnic College, Ahmedabad, India
Received Date: January 27, 2017; Accepted Date: March 06, 2017; Published Date: March 10, 2017
Citation: Joshi DM (2017) Performance Analysis of a Helium Turbo-expander for Cryogenic Applications with a Process Modeling Tool: Aspen HYSYS. J Appl Mech Eng 6:259. doi: 10.4172/2168-9873.1000259
Copyright: © 2017 Joshi DM. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Cryogenic system refers to interacting group of components involving low temperature. Cryogenic engineering deals with the development and improvement of low temperature techniques, processes, and equipment. They are applicable to helium refrigerators and various liquefiers. Nowadays, the energy crisis has forced the need to recover the energy which is normally wasted in other industrial processes. Reduction of gas pressure is one of such process in which there is a high loss of energy. To prevent such high wastage of energy, Turbo-expander which is the heart for the production of low temperature by reducing the pressure to a low value, has been introduced in the industries. Turbo-expanders are used in almost every segments of the oil and gas industry to produce Cryogenic refrigeration. Before implementation of such a critical component in the plant, it is necessary to carry out the performance analysis of turbo-expander.
In this paper, a process simulator called Aspen HYSYS is used for the analysis of Helium turbo-expander (Helium gas is taken as a process sample gas) and detailed observation is carried out for checking the performance of helium turbo-expander at various adiabatic efficiencies. The results provide useful indications on the selection of turboexpander to obtain required output at various efficiencies with variation in temperature. Keeping the constraints of the plant in mind, this analysis can thus result in the design of an efficient productive plant
Aspen HYSYS; Cryogenic; Helium; Performance analysis; Turbo-expander
Aspen HYSYS is a powerful and innovative engineering tool especially designed for the chemical and gas industries. Cryogenics is an important area for the gas industries, where you have to deal with extremely low temperature. This process modeling tool helps in avoiding production delays by giving an analysis of the performance of various equipment that are to be placed in the processing plant.
Performance analysis of various equipment like compressor, expander, control valves, distillation column, that plays a keen role in a Cryogenic plant can all be analyzed for its performance by this process modeling tool. Such analysis gives a clear idea about the selection of equipment and thus production costs can be reduced which leads to the profitability of the organization [1-4].
The expansion turbine or the turbo-expander is one of the important component of most cryogenic system. Since the turbo-expander plays the role of the main cold generator, its properties – reliability and working efficiency, to a great extent, affect the cost effectiveness parameters of the entire cryogenic plant.
Turbo-expander is a machine, which continuously converts kinetic energy into mechanical energy. This is done by expanding the high pressure gas from upstream to a lower pressure downstream through the expander. The high pressure gas causes the radial expander to rotate. Rotation is transmitted to the shaft, which is supported by a set of bearings. The energy transmitted to the shaft can be used to drive a compressor (i.e., wastage of energy can be prevented). Figure 1 show a helium turbo-expander, that is, helium gas is used as a process sample gas [5-8].
Analysis of helium turbo-expander is carried out with the process modeling tool called Aspen HYSYS. This tool helps in analyzing the important parameters of turbo-expander like temperature, pressure, heat flow, work done and mainly the optimum efficiency of turboexpander can be analyzed. Hence, we can wisely choose the efficiency of turbo-expander for getting the optimum productivity.
Figure 2 shows the model of turbo-expander, where the sample gas is taken as helium and the work output is used to drive a compressor.
Table 1 shows the values of various parameters used and obtained from modeling of helium turbo-expander.
|Liquid volume flow||m3/h||3.482||3.482||3.482||3.482|
Table 1: Material streams of turbo-expander in Aspen HYSYS.
Table 2 shows the energy obtained from the helium expander. This energy which was else wasted can be used to drive a compressor. This is carried out in Aspen HYSYS, which can be observed in Figure 2.
Table 2: Energy/work output stream of turbo-expander in Aspen HYSYS.
The efficiency of turbo-expander plays the major role while selecting or purchasing procedure. Efficiency of an expander is the maximum expansion it can provide by reducing the temperature in the most efficient way. Aspen HYSYS is a platform where you can easily choose the parameter on which you are supposed to do expansion and can observe its behaviour.
Figure 3 shows the graph for adiabatic efficiency vs. outlet temperature. It is observed that with increased efficiency of expander, we can get more reduction in the temperature which is a very important point while dealing with cryogenics.
It is observed from the graph the we can get approximately 23K of temperature at the outlet of expander with the 100% efficiency ideally. So, practically we can choose the optimum efficiency required for the plant.
Thus, it is seen that the helium gas is expanded from a temperature of 35K to 23K approximately, which is quite a good expansion ideally. Similarly, we can analyze the expander and can get the optimum required efficiency of expander which can help us in the costing of the device and hence the overall plant.
Now, at last we can have the overall details of the modeling we have carried out in Aspen HYSYS. Figure 4 below shows the overall details of the plant.
The analysis of the turbo-expander plant is carried out with the simulation tool Aspen HYSYS. The result obtained plays an important role in performing experiments with the actual hardware before its actual implementation in the plant. The optimum adiabatic efficiency can be obtained with variation in the outlet temperature of expander. Thus, Aspen HYSYS as a process modeling simulation tool, proves to be very useful in deciding the productivity and thus the profitability of the plant efficiently.