• Energy Research
• 7. Clean energy close
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In this work, a semi-empirical column model is developed to represent post-combustion CO2capture processes with chemical solvents in coal-fired steam power plants. The solvents are represented by empirical correlations on the basis of fundamental measurement data (CO2 solubility, heat capacity, density). The model of a CO2 capture process including the column model is coupled to detailed models of a hard-coal-fired steam power plant and of a CO2 compressor to evaluate and compare the impact of CO2 capture on the overall power plant process using six different solvents.

In this work, the closed-cycle and open-cycle process design for the conditioning of a CO₂-stream for ship transport are compared in terms of the minimum specific energy demand. In contrast to other works, a high-pressure pipeline CO₂-stream is assumed as an input stream rather than a low pressure CO₂-stream from a capture plant. An output temperature of -50 °C is selected, which corresponds to an output pressure of 6.75 bar for pure CO₂ and output pressures of less than 25 bar for typical Post-Combustion and Oxyfuel CO₂-streams. It is shown that the minimum specific energy demand for closed-cycle refrigeration processes can be significantly reduced by a 2-stage or 3-stage temperature cascade. With approximately 46 kJ/kgCO₂, the minimum energy demand of the 3-stage open-cycle process is almost the same as for the 3-stage closed-cycle process. It is shown that the open-cycle process design cannot be used for CO₂-streams with impurities, unless the stream is purified in the refrigeration process. The results for typical Post-Combustion and Oxyfuel CO₂-streams show that the minimum specific energy demand slightly increases with an increasing impurity concentration. For the 1-stage closed-cycle process, it rises from 82.1 kJ/kgCO₂ for pure CO₂ to 83.4 kJ/kgCO₂ for an Oxyfuel stream with 98% CO₂ purity. That increase is smaller for the 2-stage closed-cycle and even smaller for the 3-stage process.

The flexible and part load operation of fossil-fuelled power plants will increase due to the higher share of fluctuating renewable energies, like wind and solar power. In this work the part load behaviour of the post-combustion CO₂ capture (PCC) process is evaluated. The net efficiency of the conventional hard-coal-fired power plant decreases from 45.6% at full load to 41.5% at 40% load. The net efficiency with PCC using 7 m MEA (monoethanolamine) as solvent decreases to 34.8% at full load and to 30.1% at 40% load. The pressure of the intermediate pressure/low pressure crossover section has major influence on the efficiency. In part load higher pressures are in advantage due to lower throttling losses. The shutdown of the PCC is a possibility to generate balancing power. A reduced capture rate of 75% leads to a generation of 5% additional power.