Combinedcyclepowerplant
Description
This is a detailed system model example of a gas-combined cycle power plant with a 3-pressure level heat recovery steam generator and an optional carbon-capture plant.
This model is a simplified representation of the Mainz-Wiesbaden power plant in Germany, based on publicly available process parameters and engineering guess values.
Summary of the reference power plant data according to [1]:
- Rated heat inputs gas turbine: 682 MW
- Nominal GT power: 285 MW
- Nominal ST power: 140 MW
- Flue gas flow: 650kg/s
- Nominal HP steam pressure: 110bar
Simulation Scenarios:
Study load changes, ramp rates, thermal and mechanical stresses:
In the block "controlSystem", the setpoints for the power plant can be specified. The main purpose is to deliver power to the grid. The "loadChangeTable" allows to specify the plant load in percent over time. With the default settings, the plant starts at 100% load, and will perform a load change to 75% starting at the time 10000s and finalizing the ramp at 23000s. The user can adapt this schedule, e.g. specifying a quicker or a larger load change and analyze the transient behavior of thermodynamic properties such as temperature, pressures, flows etc. The turbine system includes a thick-walled header component, that can be used to study mechanical and thermal stresses during these transient load changes. It is verified that the system will work well in the range of 58% -110% when the CCU is inactive and 60% - 110% when the CCU is active.
Plant size adaption with scaling
The experiments top-level parameter ���scalingFactor��� can be used to adapt the plant model size to the desired plant while keeping the structure and the specific state points the same. For the reference value, the size will be matching a 400MW combined cycle plant. It is assumed that for reasonable plant sizes with the same layout, boundary conditions such as ambient temperature and pressure, as well as technical boundaries like maximum allowable pressures and temperature, will define intensive thermodynamic (pressures, temperature), while extensive properties, such as mass flows and volumes are scaled linear with plant size. The scaling will involve all relevant size-defining parameters, for both steady-state and transient e.g. heat transfer areas, nominal flows, volumes, metal masses. For example, if the scaling factor will be set from 1 to 0.5, the plant component sizes will be adapted to represent a 200MW combined cycle unit. The scaling range is verified to work between 0.3 to 2 .
Carbon capture unit: efficiency effects and dynamic behavior:
The carbon capture unit can be activated from the top-level parameter ���use_CarbonCaptureUnit���. This will include the absorption plant for capturing CO2 from the flue gas. As this model adds complexity, it will result in a longer simulation time. It is therefore recommended to only use this option when needed. The absorption unit allows nearly carbon-neutral operation, however, it needs to continuously regenerate the absorbent medium (MAE) using steam. This steam is extracted from the combined-cycle plant���s turbine, therefore reducing its efficiency.
Hydrogen blending in the gas turbine
Another option to reduce carbon emissions is using hydrogen as a fuel for the gas turbine instead of natural gas. The share of Hydrogen can be set in the ���openBraytonCycle���. E.g. setting hydrogenShare=0.2 will result in replacing 20mass% of Methane with Hydrogen.
Study ambient temperature effects, summer / winter operation:
Environmental conditions are very important for the performance of gas turbines and therefore the combined cycle power plants. Temperature or pressure differences (e.g. due to high altitude installation regions) lead to significant differences on air compression and affecting all downstream components such as the heat recovery steam generator. The block ���system_TPL��� allows the user to specify ambient temperature and pressure, which will be applied to underlying components such as the gas turbine system automatically.
[1] Meinke, Sebastian,