(698g) Study of Efficiency Improvements of Pre-Combustion CO2 Removal Units By Means of Validated Steady-State Simulations

Pre-combustion CO₂ capture in combination with the integrated gasification combined cycle (IGCC) process is an advanced technical solution for the implementation of carbon capture and storage (CCS) in the power sector aiming at high efficiency and effective emission reduction. The removal of CO₂ from the synthetic gas leads to a large efficiency penalty for the thermal power plant.  Solutions to reduce the energy consumption in the pre-combustion capture unit must therefore be investigated. In order to study the optimal design and operation of the capture unit, a unique and fully instrumented CO₂-capture pilot plant has been designed and realized at the Buggenum IGCC power station in the Netherlands by the utility company Vattenfall. The pilot plant comprises a three-stage, sweet, high-temperature water-gas shift process with inter-stage cooling and a physical absorption/desorption process utilizing a mixtures of homologues, polyethylene glycol dimethyl ethers for the removal of CO₂ which is further compressed by a multi-stage compressor.

Steady-state models of the pilot plant process have been developed and implemented in a commercial software tool. The thermophysical properties of the highly non-ideal mixtures involved in the capture process are calculated with the implementation of the PC-SAFT Equation of State (EoS) provided by an in-house software tool. The binary interaction parameters for the solvent-gas and gas-gas interaction are fitted against data from literature and experimental data. The pilot plant system model is validated against experimental data obtained from the CO₂ capture pilot plant. Finally, the validated models are modified for the simulation of a large-scale pre-combustion capture unit. The system model is extended in order to encompass an H₂S removal process, which is integrated with the CO₂ absorption process and hence utilizes the same solvent. One of the main design variables of the absorption/desorption section is the solvent temperature. Operation at refrigerated solvent temperature leads to an increase in absorption efficiency and therefore to a reduction in solvent flow rate and solvent pumping power, thus maintaining a constant capture efficiency. However, this comes at the cost of energy required for solvent chilling. For operation at medium solvent temperature higher solvent flow rates and solvent pumping power are required to compensate for the less efficient absorption, though no energy for chilling is required.      

The two capture unit configurations (with and without solvent chilling) are compared in terms of energy consumption and maintaining a CO₂-capture efficiency of 85%. Other variables considered in the optimization problem are the H₂O:CO ratio, the CO conversion efficiency of the water-gas shift section, and the CO₂ removal efficiency and flash pressures of the absorption section.