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To investigate the model and control for the boiler- and steam-heated coil systems

Osman, Nur Mazliyana (2018) To investigate the model and control for the boiler- and steam-heated coil systems. Honours thesis, Murdoch University.

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The boiler is part of an essential system in process control and instrumentation that requires precise control to maintain its efficiency. Based on previous works, the boiler system in Instrumentation Control Engineering (ICE) laboratory was reported as being unable to fully support the steam demand for the heating purpose in the steam-heated coil system. The causes of this problem were not explained. In this thesis project, further investigation was conducted to find the causes. The report will start with a brief introduction about project background, chronology of previous works and project objectives. The project background will address the steam demand problem and why it can affect the heating process in the steam-heated coil system. There are three objectives highlighted in this thesis. One of the objective to control the temperature of the outlet water from steam-heated coil system. The following section provides a more in-depth about the control strategies and instrument used in boiler- and steam-heated coil systems. Two control strategies will be presented within this thesis, which is Proportional Integral (PI) and cascade control to control the temperature of the outlet water from steam-heated coil system. Following this, calibration was undertaken on instruments to establish their reliability for data collection. Open loop testing on the steam-heated coil system is carried to find the best model for better controllability. This test also proves the steam supply from boiler unable to support the heating process for steam-heated coil system. It concluded that the pressure of the steam supply is the disturbance variable in steam-heated coil system. A detailed analysis on the pressure behaviour of steam supply form the boiler system is conducted to find the causes of the steam demand problem. The boiler system produces an ON and OFF pattern due to inbuilt ON-OFF control for controlling water level inside the drum boiler in the system. Furthermore, this pattern shows that the boiler system has a nonlinear behavior that requires an extreme understanding in the modeling phase. Then, a simplified model and dynamics model were created for the boiler- and steam-heated coil systems by using two methods, which are an experimental and theoretical method. These models are used to aid in the controller tunning process. Only the steam-heated coil system was allowed to have a controller implementation. Two different tuning methods were used for finding PI controller parameter, which were relay and Ziegler - Nichols stability margin tunings. Then, both models are tested out for accuracy before used for tuning phase. A few recommendations for improvement in boiler system were listed in future works section.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Engineering and Information Technology
Supervisor(s): Cole, Graeme
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