Mathematical modelling of CO2 capture from industrial flue gas by absorption into amine solutions such as monoethanolamine (MEA) has been undertaken for decades and steady state, rate-based and dynamic models have been constructed to predict the changes in the process. Recently, dynamic models have been used to predict the effect that physical operational changes have on the absorption process. As more is learnt about the chemistry of MEA and CO2 it becomes evident that the absorption system is losing available MEA, by degradation and by vaporization into the gaseous phase. This paper describes a dynamic model of the absorber column that can be used to predict the reduction of available MEA, the loss of MEA to the atmosphere, and the build-up of heat stable salts. The proposed mathematical model consists of a system of partial differential equations to represent the change of each component with height of the column and with time. It has been validated with data from a pilot capture plant located at the brown coal fired Loy Yang power station in Australia.
Coal is the dominant and most reliable source of energy in Australia. However, the increasing global temperatures and its impact on the climate raises concerns on the use of coal worldwide. Due to availability of abundant, cheap quality coals, Australia is researching how it and its international customers can continue to use its abundant coal resources whilst limiting greenhouse emissions. Hence, low CO2 emitting energy technologies like carbon capture and storage (CCS) have an important role to play not only in power but also the cement and steel industries Post-combustion CO2 capture (PCC), the most developed technology in CCS using aqueous amines to capture CO2, still face challenges for its large-scale commercialisation. The cost of electricity with PCC rises to almost double that produced without integrating PCC technology in new power stations. The retrofit of PCC technology into existing power stations is very site specific and costs can be around half of the cost of building a new power plant. Apart from this, the implementation of PCC poses an energy penalty to the power station as the efficiency of the plant can drop almost by 10-11% due to the increased solvent heating and CO2 compression loads. Particularly with the nations like Australia, the cost of PCC installation is even higher as there are no flue gas desulfurisation (FGD) units in Australian power stations. The presence of harmful gases like SO2 in coal-fired power plant flue gases affect CO2 capture performance during PCC due to the higher affinity of amines to absorb stronger acidic gases against CO2 which is a weaker acid gas than SO2. These stronger acidic gases tend to form heat stable salts with the absorbent amines used to capture CO2 . Heat stable salts refer to the thermally non-regenerable protonated amines which are usually produced when the amine solution is contaminated by organic acids (Weiland et al., 2004). Hence, the bonded amine is not available for CO2 capture, increasing the requirement for makeup amine resulting in higher operating cost. Therefore, FGD units are an essential requirement before the installation of PCC facilities in a coal-fired power station. This results in a levelised cost of electricity in Australian power plants that is high compared to nations which have FGD installed in their power stations. CSIRO has developed a combined capture process to simultaneously capture CO2 and SO2 from Australian power plant flue gases using a single amine absorbent in order to lower the cost of PCC installation in Australia. The process generates a unique sulfur rich amine absorbent which needs regeneration. This thesis investigates various amine regeneration processes, using MEA as a reference, and their commercial viability to the CS-Cap process. Due to the unique nature of the sulfur rich absorbent generated in the CS-Cap process, its amine is recoverable through many other regeneration processes besides standard thermal reclamation. My thesis investigates the effectiveness of regeneration techniques like Ion exchange, Electro-dialysis, Crystallisation, Nano-filtration in regenerating the sulfur rich amine. Initially the theoretical investigation was carried as a part of literature review and further a brief exploratory laboratory scale evaluation of the most suited technologies was carried out. The results obtained from laboratory scale experimentation were fed to an Aspen Plus simulation model in order to understand the behaviour of the system under various operating conditions. Further a cost estimation was carried out in order to produce a high level cost for the selected regeneration technologies in the CS-Cap process. The cost of the regeneration technologies were further integrated into the overall CO2 capture process in order to compare the cost of standard FGD + PCC process against the CS-Cap process which answers the broader research question whether the CS-Cap process will be economical for Australian coal power plants. Overall this thesis reveals the effectiveness of various technologies in regenerating sulfur rich amines. It suggests CSIRO’s patented CS-Cap process is a cost-effective approach for capturing CO2 from Australian coal fired power plants despite its sensitivity to regeneration cost.