A thermal power plant employing amine-based post-combustion CO2 capture (PCC) stands as a key technology for low-carbon, stable power sources aiming to economically achieve net zero CO2 emissions in the electric power sector. However, the high cost associated with amine-based PCC has prevented its swift implementation. This study proposes a novel power-to-heat amine-based PCC system featuring solvent storage tanks. This system provides CO2 absorption during the operation of the thermal power plant and facilitates CO2 desorption through a heat pump driven by exceptionally inexpensive electricity procured during peak power generation periods from the grid. To demonstrate this concept, we evaluated the profitability of the proposed system using mathematical modelling and the calculation of the capital expenditure (CAPEX) and fixed operating expenses. The mathematical model optimizes the operational modes of the system facilities based on actual annual electricity prices. The results demonstrated that the novel PCC system decreased the average cost for energy consumption during the CO2 stripping and compression process per tonne of CO2 by approximately 30% compared with the conventional, flexible PCC system with venting. Consequently, it increased the net present value by approximately 15%. This showcases the feasibility of the power-to-heat amine-based PCC system in electricity markets prone to extreme fluctuations in electricity prices, where prices plummet during periods of surplus and escalate during peak demand. Notably, results also revealed that despite the low-capacity factor of the power plant (<30%) in such markets, retrofitting an amine-based PCC system into fully depreciated existing natural gas combined cycles yielded positive net present values even without economic incentives like credits for captured and stored CO2 or grant funding for CAPEX. This suggests potential economic sustainability of the system, even in the imminent rise of inexpensive variable renewable energy. However, the results also indicated that such a low-capacity factor and high PCC CAPEX require high CO2 price (350–400 USD/t-CO2) to incentivize carbon capture and storage (CCS) adoption in a power plant in the market. Therefore, reduction in PCC CAPEX should be emphasized as a future challenge in the scenario of swiftly employing thermal power plants equipped with CCS as a dispatchable firm power source. Finally, implementing the power-to-heat amine-based PCC system will bolster power supply reliability and alleviate the curtailment of power generation caused by variable renewable energy sources.

Integrating post-combustion CO2 capture (PCC) into thermal power plants can reduce CO2 emissions but results in a significant decrease in net thermal efficiency. Optimizing PCC operating conditions, such as the ratio of the liquid flow rate to the gas flow rate (L/G) and stripper bottom temperature, reduces the net efficiency penalty. However, previous studies partially neglected the propagation effects of altered operating conditions on process performance, such as the effect of altered L/G and resultant change in fluid velocity on the heat transfer and pressure drop in the rich and lean solution heat exchanger. This study simulated amine-based PCC integrated into a natural gas combined cycle and explored optimal operating conditions comprehensively considering the propagation effects. The net efficiency penalty was minimized to 6.02%-pts. at a stripper bottom temperature of 130 °C and L/G of 0.82 for PCC operation with CO2 compression. Meanwhile, neglecting propagation effects of altered L/G led to underestimation of the efficiency penalty and erroneous determination of optimal operating conditions. The system evaluation methods suggested in this paper contribute to correctly optimizing PCC operating conditions and can be broadly applied to amine-based PCC studies employing novel amine solutions or process modifications.

Degradation of amine is often regarded as a major problem for amine-based post-combustion CO2 capture. However, the observed regeneration energy in long-term pilot plant operations does not necessarily increase, regardless of the accumulation of degradation compounds. This paper provides a mechanistic explanation for this seemingly paradoxical behavior by focusing on the influence of heat stable salts and the CO2 loading range on solution properties. Post-combustion CO2 capture using degraded amine solution was simulated in Aspen Plus®, and the influence of heat stable salts on CO2 loading, solution properties, and regeneration energy were analyzed. Results indicate that the alteration of the operational CO2 loading range and the physical properties of heat stable salts themselves cause changes in solution properties that dictate overall energy consumption, such as viscosity, vapor liquid equilibrium, and specific heat capacity. These effects often offset each other to some extent, thereby obscuring the influence of individual factors on regeneration energy. These counteracting effects can largely explain the seemingly paradoxical behavior of post-combustion capture maintaining relatively low energy consumption even when amine degradation proceeds.

Carbon capture and storage (CCS) is an important technical option to reduce CO2 emissions and chemical absorption by amine solutions is the most mature post-combustion carbon capture technology. Reducing costs is critical to accelerate large-scale deployment of CCS. Cost estimates of CCS vary markedly depending on the CO2 capture performance, CO2 transport method, characteristics of CO2 storage site, and the like. This study estimated the cost of CCS by amine-based CO2 capture integration into thermal power plants in Japan. The thermal power plant system with CO2 capture process was modeled on a process simulator, and CO2 capture cost was calculated based on the modelling results. The CCS chain feasible in Japan at this time is transportation by ship and injection onshore into subseafloor storage sites. Transport cost was estimated via bottom-up analysis of each transportation sub-process. Injection cost was based on the values reported by the Tomakomai demonstration project. In total, transport and storage costs were roughly equivalent to capture costs. Full chain CCS implementation is likely necessary to markedly reduce costs through learning-by-doing.

Chemical absorption using amine solutions is a promising technology for post combustion CO2 Capture (PCC) from flue gas. Monoethanolamine (MEA) aqueous solution has been used in many projects as a benchmark solution and the experimental and analytical results are available in the literature for diverse operating conditions. Aspen Plus® is a widely used computational simulation software for design of PCC systems including operating conditions. Two example files of rate-based MEA models using electrolyte non-random two liquid (e-NRTL) methods are included in Aspen Plus. Basically, e-NRTL models can provide relatively accurate results by fitting parameters to experimental data within a limited temperature and concentration range. However, there are a non-negligible difference between experimental and calculation results, especially in regard to the vapor-liquid equilibrium (VLE) at high temperatures and high MEA concentrations. This paper updates the e-NRTL model for the solutions with 30 wt% and higher MEA by data regression of the specific heat capacity, the heat of CO2 absorption, and VLE experimental data obtained at high temperatures. Since these thermodynamic properties are mutually dependent and affected by internal model parameters such as activity coefficients, standard enthalpy change of formation of principal ions, all properties in the MEA-H2O-CO2 ternary system that are consistent with the MEA-H2O binary system were fitted by using a combination of the built-in data regression functionality and external spread-sheet software. The updated model more accurately simulates thermodynamic properties of high concentration MEA solutions at high temperatures.