• Energy Research

Abstract The energy penalty associated with solvent regeneration accounts for the largest part of overall energy consumption in aqueous ammonia (NH3)-based post-combustion capture (PCC) processes. While extensive research focus on the process improvements to reduce the energy burden of solvent regeneration, little attention has been paid to techno-economic assessments that analyse the related energy savings and capital costs. In the present study, we assessed the technical and economic benefits of stripping modifications in an NH3-based PCC process integrated into a coal-fired power station. The stripping configurations included a rich-split process, cold-rich bypass, inter-heating, and combinations of these processes. We used a rigorous, rate-based model in the Aspen Plus® RateSep simulator to determine the technical performance of these new process modifications, while capital investment was estimated with a cost model based on the Aspen Capital Cost Estimator (AACE). All the proposed stripper modifications have technical and economic advantages compared to the reference case. The best configuration was inter-heating integrated with the rich-split process, which reduced reboiler duty by 40.7% and saved 29.2% of annual costs. The sensitivity study suggests that the modified stripping processes can maintain the economic benefits over the wide variations of the important parameters.

AbstractThe energy penalty associated with solvent absorption based Post Combustion CO2 Capture is one of the main stumbling blocks for the implementation of this technology into new and existing fossil-fired power stations. Modifying the flow sheet of the standard chemical absorption process can allow for reductions in the energy and resource usage of such plants. A review of the open and patented literature highlighted modifications, predominantly related to applications in the gas processing industry. These modifications were modelled using commercially available rate based simulation software. This allowed the expected energy consumption of a CO2 capture pilot plant, based in Australia, to be estimated. The modelling results pointed towards the optimal conditions for each modification. Selected modifications were then added together to determine whether any synergistic effects could be observed. The split flow process was found to have one of the highest energy savings (reduction in reboiler duty) over the reference plant. Adding inter-cooling on the absorber column with splitting of the rich solvent stream entering the stripping column showed a reduction in reboiler duty slightly greater than anticipated based on the results of the individual modifications.

AbstractThe energy penalty of post-combustion capture of CO2 (PCC) presents a major hurdle in the application of this technology for CO2-emission reduction and CO2 utilisation in China. Huaneng CERI and CSIRO have been collaborating since 2008 with the aim of developing low-cost, energy-efficient and environmentally benign amine- based PCC processes. This paper provides an update on recent advancements in this area which has focused on:–Development of new liquid absorbent formulations–Assessment of PCC process modifications–Pilot plant evaluation in two facilities; one in Australia and one in China.The intermediate results indicate excellent progress towards a halving of the energy penalty of amine based PCC processes.

Using a rate-based model, we assessed the technical feasibility and energy performance of an advanced aqueous-ammonia-based postcombustion capture process integrated with a coal-fired power station. The capture process consists of three identical process trains in parallel, each containing a CO2 capture unit, an NH3 recycling unit, a water separation unit, and a CO2 compressor. A sensitivity study of important parameters, such as NH3 concentration, lean CO2 loading, and stripper pressure, was performed to minimize the energy consumption involved in the CO2 capture process. Process modifications of the rich-split process and the interheating process were investigated to further reduce the solvent regeneration energy. The integrated capture system was then evaluated in terms of the mass balance and the energy consumption of each unit. The results show that our advanced ammonia process is technically feasible and energy-competitive, with a low net power-plant efficiency penalty of 7.7%.

A rigorous rate-based model for CO2 absorption using aqueous ammonia in a packed column has been developed and used to simulate results from a recent pilot plant trial of an aqueous ammonia-based post-combustion capture process at the Munmorah Power Station, New South Wales, Australia. The model is based on the RateSep module, a rate-based absorption and stripping unit operation model in Aspen Plus, and uses the available thermodynamic, kinetic and transport property models for the NH3–CO2–H2O system to predict the performance of CO2 capture. The thermodynamic and transport property models satisfactorily predict experimental results from the published literature. The modelling results from the rate-based model also agree reasonably well with pilot plant results, including CO2 absorption rate, NH3 loss rate, temperature profiles and mass transfer coefficients in the absorber. To gain insights into absorption performance, we used the rate-based model to analyse the species concentration profile, temperature profile, mass transfer rate and coefficient in the gas and liquid bulk phase along the packing height.

The energy penalty associated with solvent based capture of CO2 from power station flue gases can be reduced by incorporating flow sheet modifications to the standard process. Fifteen process flow sheet modifications for chemical based CO2 absorption processes are reviewed, with a particular focus on the patent literature. The proposed flow sheet modifications identify potentially moderate to large improvements in the energy performance of the chemical absorption process. Most process modifications suggested in the patent literature report very little if any supporting experimental evidence. Where supporting data does exist it tends to be based on process modelling results. Moreover, earlier patents tend to focus on the gas processing industry and it is not immediately clear whether the same benefits can be extended to CO2 capture from near atmospheric pressure flue gases. It is clear from the survey that there is considerable scope for achieving improved process performance through process flow sheet modifications. However further process modelling and, in particular, experimental work focused on post-combustion CO2 capture is needed to map the technical potential for improvements.

Abstract Although recent studies on the application of enzyme-catalyzed reactive absorption of carbon dioxide (CO2) with thermodynamically favorable solvents such as tertiary amine N-methyldiethanolamine (MDEA) have demonstrated competitiveness with kinetically favorable solvents such as primary amine monoethanolamine (MEA), experimental data on the desorption of CO2 in MDEA are scarce. However, these data are necessary to validate the energetic benefit expected from an enzyme-catalyzed reactive absorption process with an aqueous MDEA solvent. To bridge this gap, the current work presents the experimental results of aqueous MDEA solvent regeneration at the pilot scale with consideration of different solvent flow rates, CO2 loadings and applied reboiler duties. Furthermore, a process model that accurately describes the experimental data was developed to evaluate the energy requirements in a closed-loop absorption-desorption process. For this purpose, the desorption process model was extended using a previously validated enzymatic reactive absorption model to determine the energy efficiency of the overall enzymatic reactive absorption-desorption process. Although the MEA benchmark process requires a specific reboiler duty of approximately 3.8 MJ · kg CO 2 - 1 , it was found that this value could be reduced by more than 40% to 2.13 MJ · kg CO 2 - 1 with use of the enzymatic reactive absorption process based on aqueous MDEA solvent.

Abstract A rigorous, rate-based model was developed to simulate the regeneration of CO 2 in aqueous ammonia-based CO 2 capture process. The model was based on the Aspen RateSep module, which adopts the kinetic, thermodynamic and transport properties of the NH 3 –CO 2 –H 2 O system available in Aspen Plus V7.3. We compared the modelling results with those obtained from pilot-plant trials at the Munmorah Power Station, New South Wales, Australia. The results agreed reasonably well for all 30 cases considered, including the energy requirement for regeneration, stripping temperature, and ammonia concentration in the product. Using the validated model, we then further analysed the pilot plant results to gain insights into the CO 2 regeneration process.