Transient model of a driven compressor

University essay from Lunds universitet/Institutionen för energivetenskaper

Abstract: Industrial gas turbines are widely used in different applications. These can be divided into two main categories; power generation (PG) and mechanical drive (MD). To be able to predict the performance of the system, Siemens has during the years developed simulation models for both steady state and transient operation. These models are mainly designed for PG, so there is a need for new MD models. An MD model includes a gas turbine, a driven component, in this case a compressor, and auxiliary systems which ensures stable operation and avoid rotating stall and surge in the compressor. The purpose of this thesis is to develop a transient model of a driven compressor based on characteristics and connect it with the existing dynamic gas turbine model of the Siemens Gas Turbine 750 (SGT-750) in Dymola. Auxiliary systems are developed for both the compressor system and for the compressor train in order to reflect the reality and get reliable simulation results. An analysis is performed to study the behaviour of the compressor train when controller and physical parameters are changed. The developed compressor model is based on the existing basic compressor model developed by Siemens. Compressor maps from the reference project El-Encino were implemented in the model and were verified against data sheets and the model was then connected to the existing SGT-750 model in Dymola. New controllers were developed to ensure reliable operation of the compressor train and the complete model was then tuned in and verified towards measured data from two different sites with the SGT-700 as the driving component. Different cases were simulated to assure stable operation for varying starting conditions and to study the behaviour of the compressor train. The verification shows that the developed model corresponds to reality with deviations within the approved area, with regard of the limitations of the project. The model now makes it possible to study the gas turbine behaviour in an MD application with the SGT-750 as the driving component. The configuration of the gas turbine control system makes it possible to use it in different applications with different gas turbines, both for PG and MD. The behaviour analysis shows that a lower fuel ramp during start-up increases the stability of the compressor train. It also indicates that the power turbine acceleration controller could be redundant for certain cases but further analysis is needed in the matter. Due to the focus of the project and limitations in Dymola, more work is needed to ensure accuracy of all parameter values. There are improvement opportunities in the program's basic thermodynamic functions, which is a part of the future work.

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