Thermodynamic indices assessing the integration of coal-fired CHP plants with post-combustion CO2 processing units (CPU)

• Although, CHP plants are pro-ecological, they also need CO2 capture units.
• CHP integrated with CO2 capture needs a modification of thermodynamic indices.
• Indices of the relative internal load of heat and electricity have been elaborated.
• Formulae of the net Energy Utilization Factor have been calculated.
• Partial energy efficiencies of heat and electricity production have been determined.

Although cogeneration is an effective way of reducing the CO2 emission in CHP plants, installations permitting the removal of CO2 ought to be applied. Installations based on chemical absorption using amine solvents is justified in the case of power plants and CHP plants. The CO2 processing unit (CPU) is characterized by a large amount of stream for solvent regeneration and the consumption of electricity mainly in compressors of CO2 product. Additional internal consumption of heat and electricity produces waste heat due to the condensation of H2O in the mixture of CO2 and H2O resulting from the desorption of CO2 and interstage cooling of the CO2 compressors. The waste heat recovery system can be connected with the preheating of network water in the district heating systems cooperating with CHP plants. In this way the integration of the CHP plants with the post-combustion CO2 processing unit is realized. This integration requires some supplements in algorithms describing the thermodynamic indices in comparison with traditional cogeneration systems. Firstly, the indices of the internal load of heat and electricity was changed. This influences the net Energy Utilization Factor, secondly the analyzed thermodynamic index, and thirdly the partial energy efficiencies of the production of heat and electricity in a CHP unit. In this last case the principle of avoided fuel expenditure and the exergy method in coupled processes have been applied. The new algorithms for calculations mentioned above thermodynamic indices and the results of their analysis have been presented for two variants of integrated CHP-CPU systems: with and without waste heat recovery. The parameter in these analyses was unit heat for regeneration of the solvent. For comparison, the results of the analysis of reference CHP plant have been presented, too.