Large-scale Biomass-fired Power Plant integrated with solvent-based Post-combustion Carbon Capture: Simulation, Techno-economic Analysis, Optimisation and Life cycle Assessment

Bioenergy with carbon capture and storage (BECCS) is a key negative emission technology (NET) for reducing atmospheric CO2 levels. Solvent-based post-combustion carbon capture (PCC) is the widely used method of capturing CO2 emissions from power plants, but its high energy and cost demands limit commercial application.
This PhD study aims to investigate a cost-effective, energy-efficient and environmentally sustainable supercritical biomass-fired power plant (BFPP) integrated with a solvent-based PCC process. The models of the large-scale BFPP and the pilot-scale PCC process using monoethanolamine (MEA) and piperazine (PZ) solvents were developed and validated in Aspen PlusⓇ V11. The validated pilot-scale models of both the MEA-based and PZ-based PCC processes were scaled up to process flue gas from a 550 MWe BFPP. Different configurations of the solvent-based PCC process were simulated, including the standard PCC, PCC with absorber intercooling (AIC) and advanced flash stripper (AFS), additionally, the combination of AIC and AFS with side stream extraction (SSE). Furthermore, a model for CO2 compression utilising a heat pump (HP) and a supercritical CO2 cycle (sCO2) was developed.
The energy analysis revealed that the PCC process, which uses 40wt% PZ and process configuration consisting of AIC-AFS-SSE-sCO2, achieved the lowest energy consumption of 2.78 GJ/tCO2. This configuration reduced the specific heat duty by 1.01 GJ/tCO2 compared to the standard PCC process using 30wt% MEA which serves as the benchmark in this study. The economic performance of the various PCC processes was evaluated using the Aspen Process Economic AnalyzerⓇ (APEA). The results indicated that the AIC-AFS-SSE-sCO2 configuration with 40wt% PZ as solvent achieved the lowest CO2 capture costs (CCC) of 57.5$/tCO2. This represents a 17% cost reduction compared to the standard 40wt% PZ process, which has a cost of 69.2 $/tCO2.
Furthermore, the optimisation of the PZ-based PCC process was conducted to determine the solvent concentration and stripper pressure that would minimise the CCC. The recommended PZ concentrations were found to be 37.5wt% for the standard configuration and 32.5wt%, for the AIC-AFS configuration. Additionally, a stripper pressure of 7 bar was recommended for AIC-AFS configuration, which demonstrated a reduction in specific heat duty and CCC by 41.6% and 32.4% respectively, compared to the standard PCC process (with 40wt% PZ) without optimisation.
The exergy analysis of three cases was carried out, including Case 1: 550 MWe BFPP integrated with standard PCC process using 30wt% MEA, Case 2: 550 MWe BFPP integrated with standard PCC process using 40wt% PZ, and Case 3: 550 MWe BFPP integrated with optimised PCC process using AIC-AFS configuration and 32.5wt% PZ. The results showed that Case 3 can decrease the exergy destruction of the PCC subsystem by 71.8 MW corresponding to a 37.8% reduction, performing the best thermodynamic performance. Furthermore, the Life Cycle Assessment (LCA) of the three integration cases were conducted. On a basis of generating 1MWh net electricity, Case 1 with standard PCC process using 30wt% MEA achieved the highest CO2 sequestration of -1724 kgCO2/MWh and net-negative emissions of -1330 kgCO2/MWh, although it has the highest energy demand for carbon capture. This is because it has the lowest power output and thus has the highest CO2 sequestration per unit of electricity generated. On the basis of consuming one-tonne biomass, Case 3 with the optimised PCC process achieved the highest net-negative CO2 emissions of -1493 kgCO2/t, the lowest biomass requirement of 0.72 t/MWh, and the minimum supply chain emissions of 458 kgCO2/t. The results indicate that using BFPP integrated with the optimised PCC showed the highest net-negative CO₂ emissions both per MWh of net electricity generated and per tonne of biomass consumed.