More flexibility for low-emission coal-fired power plants
Steam power plants are known for providing stable and reliable electricity generation from coal. They can run for longer periods to meet the base and medium loads. However, in the future the grid will demand more flexibility when onshore and offshore wind power yields change with the weather. If wind turbines, for example, have to be switched off because of high winds, this loss of energy will need to be dynamically compensated for within a very short period of time. That is why it needs to be known whether future power plants that capture CO2 can also be flexible enough to contribute to a balanced electricity supply. Are they capable of balancing out supply gaps caused by fluctuating electricity generation (wind and solar energy)? Does CO2 capturing and the subsequent CO2 compression enable the flexibility to be increased in terms of providing balancing energy in comparison with conventional power plants or does it at least keep it the same?
- Assessment of the technical feasibility of providing balancing energy from steam power plant processes with and without CO2 capturing
- Simulation of ramping up and down processes and load changes with steam power plants and steam power plants with post combustion capture and oxyfuel
- Identifying possibilities for optimising the interaction between the various components of coal-fired power plants and CCS technologies (oxyfuel process and CO2 flue gas scrubbing)
- Developing and applying a comprehensive model library in Modelica (Programming language for physical models)
- Analysing the economic potential of steam power plant processes with CO2 capturing
The investigations are focussing on the dynamic transitional behaviour of future plants and the extent to which power plants with CCS technology can participate in the provision of balancing energy. In addition to balancing out load fluctuations, the provision of balancing energy is also important for ensuring a secure grid operation with increasing fluctuations in the electricity fed into the grid by renewable energies.
As part of the project, the “ClaRaCCS” Modelica library is being created. ClaRaCCS stands for Clausius-Rankine with Carbon Capture and Storage. The Clausius-Rankine cyclical process provides a comparison process for steam power plants.
By means of open source code, robust initialisation and variable detailing, the model library is intended to describe all relevant components. ClaRaCCS will have the following scope:
- Basic components for heat exchangers (various work media, typical geometries of the power plant technology)
- Models of pumps, turbines and compressors (including the transport of condensed exhaust gases)
- Models of absorber and desorber columns
- Models of air separation systems
- Material models of flue gases and solvents
- Validation scenarios for the conventional cyclical process and the gas separation process
The freely available model library shall be both an outcome of the project as well as a tool for answering the described questions. The individual models will be physically interpretable and transparently implemented under Modelica. This will enable a more long-term and sustained use of the library that extends far beyond the end of the DYNCAP project.
The electrical devices used by consumers require stable, alternating current to flow out of the sockets with 230 volts and 50 hertz. To ensure that these values always remain the same, the grid operators have to balance out fluctuations in the grid with considerable effort. This requires balancing energy in order to ensure that the electricity customers always receive precisely the required amount of electrical power, even when unforeseen events occur in the mains grid.
The costs of balancing energy can be considerable. This is partly because they have to be covered by peak load power plants whose production costs are comparatively high because they are often ramped up in less than a minute. Depending on the state of provision in the mains grid, energy suppliers charge up to 1.5 euros for a kilowatt-hour – six times as much as the end consumers pay. The increased balancing capacity required by the expansion of renewable energies costs several hundred million euros each year.
The other source of balancing energy is equally expensive. Operating power plants at a few percentage points less than full load also creates reserves for balancing purposes. However, these reserves lower the yields from these power plants in regular operation, which is compensated for through the electricity price.
The power plant management system tries to balance out the output generated by the power plants with the removed output, including transport losses. This is based on the physical requirement that mains grids are unable to store electricity, which means that at any point in time the power fed into the grid has to correspond to the sum of the power removed and the power lost through transport. If the electricity fed into the AC mains grid deviates from the electricity consumed, this changes the grid frequency, which is uniform throughout the entire AC mains grid (synchronous): if there is oversupply, this causes the grid frequency to exceed the rated frequency and if there is an undersupply, this causes a so-called under frequency.
Joint project with four partners
DYNCAP – Dynamic Capture of CO2 – Dynamic investigation of steam power processes with CO2 capturing for providing balancing energy