Modelling, Simulation and Performance Evaluation of Post-Combustion Carbon Capture based on Chemical Absorption

Carbon dioxide is a greenhouse gas and its emissions contribute to climate change. Fossil-fuel-fired power plants are the largest emitter of CO2. The solvent-based post-combustion carbon capture (PCC) is the most developed technology to cut down CO2 emissions from power plants. The downsides of the PCC process are the high costs (capital and operating costs) and the high energy needed for solvent regeneration. These have prevented the large-scale deployments of the PCC process. Through accurate scale-up, modified process configurations, use of solvent such as piperazine (PZ) in place of monoethanolamine (MEA) and the use of rotating packed bed (RPB) in place of packed (PB), the energy consumption and the cost of the solvent-based PCC process can be reduced significantly.
A steady-state rate-based model of the PCC process in PB using MEA solvent was developed and validated with pilot-scale experimental data in Aspen Plus®. The model predictions agreed with experimental data. A new scale-up method based on the flooding gas velocity was proposed and validated by using it to scale up between two existing pilot plants of different sizes. The scale-up method accurately predicted the diameter of the absorber and stripper with a deviation of 2.6% and 1.54% respectively. This method was also used to develop a PCC plant for a 250 MWe CCGT power plant. It was found that the proposed scale-up method gives a lower column size compared to the generalized pressure drop correlation (GPDC) method.
The use of new solvents and modified process configurations are some of the options being pursued to reduce the cost and energy consumption of the solvent-based PCC process. A steady-state rate-based model of the PCC process in PB using PZ as a solvent was developed in Aspen Plus®. The accuracy of the model was verified by validating with pilot-scale experimental data. The model predictions were within ±10% of experimental data. The model was used to assess the technical and economic performances of a large-scale PCC process using PZ solvent for a 250 MWe CCGT power plant. The technical and economic assessments were performed in Aspen Plus® and Aspen Process Economic Analyzer® (APEA) respectively. Three configurations of the process including the standard, absorber intercooling (IC) and absorber intercooling with advanced flash stripper (AIAFS) were evaluated. Results obtained from the process evaluations of the three configurations of the PCC process using PZ were compared to those of the benchmark process using 30 wt% MEA solvent. The technical assessment results revealed that the total energy needed to capture and compress a tonne of CO2 by the PCC process was 3.56 GJ/tCO2 with the standard process configuration using 30 wt% PZ as against 4.57 GJ/tCO2 with the standard process configuration using 30 wt% MEA. The lowest total energy attained was 2.41 GJ/tCO2 with the AIAFS process configurations using 40 wt% PZ. Economic assessments results indicated that the least total annual cost (TAC) and the least cost of CO2 capture were M$26.58/year and $34.65/tCO2 respectively. These were attained with the AIAFS process configuration using 40 wt% PZ solvent. Thus, the PCC process using 40 wt% PZ offers both technical and economic benefits over the current 30 wt% MEA PCC process.
RPB has the potential to significantly reduce the size of the absorber and stripper when used in place of PB for CO2 capture. A steady-state rate-based model of the RPB absorber was developed and validated at a pilot scale using Aspen Custom Modeller® (ACM). A new methodology for RPB scale-up was proposed. The RPB model was scaled up using an iterative procedure for a 250 MWe CCGT power plant. Technical and economic assessment of the large-scale PCC process using RPB shows that a 5-13 times volume reduction factor was achieved with the RPB absorber (using 75 wt% MEA) compared to the PB absorbers (using 30 wt% MEA and 40 wt% PZ). The CAPEX also reduced by 39-69% with RPB absorbers compared to PB absorbers. This shows that the size, cost and footprint of the entire PCC process can be reduced with RPB as an absorber.