Simulation and analysis of a combined cycle gas turbine heat and power plant process

Abstract

The regulations of process efficiency and stricter environmental policies form a new operating environment for utility power plants. The new environment requires analysis and energy audits of large-scale thermal energy systems to produce cost effective, highly efficient and low environmental impact energy. For analysis, it is beneficial to simulate an energy system.

The objective of this thesis work is to develop simulation models for the analysis of 'Rya combined cycle heat and power plant' process located in Göteborg, Sweden. The procedure utilizes data acquisition, simulation, analysis and practical troubleshooting. The plant's thermodynamic behaviour is simulated by means of a process simulator 'PROSIM'. With the help of simulation models, characteristics between district heating water temperature and key parameters such as overall district heat duty, electrical power and electrical efficiency has been developed. The characteristics are useful to estimate the key parameters during varying DH water temperature.

An advanced sensitivity analysis on the district heating water temperature provides optimum values for key parameters to achieve better operational efficiency. One of the result suggest that at 100% fuel load, maximum district heat duty of 304 MW is delivered at 91°C district heating water temperature with an electrical efficiency of 43.5% for the selected power plant. A detailed analysis of the heat recovery steam generator and gas turbine process indicates the sources of losses that drop the performance in the plant.

According to a comparison between the full-load simulation models of 2006 and 2013, a loss of 2 MW is noticed for gas turbine and a loss of 2.18 MW of heat flow occurs for HRSG in the year 2013. Combined heat and power plants are often operated at part load conditions, which make the knowledge of their part load behaviour very important. Moreover, by analysing the operational data of Rya combined heat and power plant, it is found that the most expensive operation takes place during part-load condition.

So, the parametric information provided by the part-load simulation models will investigate the losses during such operation. A feasibility study for modifying the connection between district heating economizer and main district heating line is also performed as a part of this work. For winter scenario, one of the modified connections provides good performance indicators.

In general, the process improvement suggestions, identification of losses, simulation models and optimum operational methods presented here can be useful to plan and improve the performance of existing large-scale utility power plants.