In this paper, we present improvements to postcombustion capture (PCC) processes based on aqueous monoethanolamine (MEA). First, a rigorous, rate-based model of the carbon dioxide (CO 2 ) capture process from flue gas by aqueous MEA was developed using Aspen Plus, and validated against results from the PCC pilot plant trials located at the coal-fired Tarong power station in Queensland, Australia. The model satisfactorily predicted the comprehensive experimental results from CO 2 absorption and CO 2 stripping process. The model was then employed to guide the systematic study of the MEA-based CO 2 capture process for the reduction in regeneration energy penalty through parameter optimization and process modification. Important process parameters such as MEA concentration, lean CO 2 loading, lean temperature, and stripper pressure were optimized. The process modifications were investigated, which included the absorber intercooling, rich-split, and stripper interheating processes. The minimum regeneration energy obtained from the combined parameter optimization and process modification was 3.1 MJ/kg CO 2 . This study suggests that the combination of a validated rate-based model and process simulation can be used as an effective tool to guide sophisticated process plant, equipment design and process improvement. 24

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The CSIRO is involved in three CO2 capture pilot plants operating at different coal‐fired power stations throughout Australia. The most recently completed of these is the Tarong CO2 capture pilot plant located at Tarong power station, Nanango, Queensland. The first phase of the experimental program with this pilot plant included operation with monoethanolamine (MEA). This involved parametric studies, process modifications, and finally implementation of 24 h operation. Operation of the pilot plant has shown MEA to be effective in capturing CO2 from the flue gas from Tarong Power Station. CO2 capture efficiencies of up to 94%, and regeneration energies as low as 3.6 MJ/kgCO2 have been achieved. The design of the pilot plant was completed using a commercially available process modeling software tool. Results obtained from the pilot plant were then compared to the model predictions including temperature, solvent CO2 loading, and CO2 gas concentration profiles through the absorber column. A good match has been obtained between the modeling and pilot plant data, verifying the software can be used to predict the performance of the pilot plant when operating on MEA. During this project, the rich‐split process modification was also evaluated. The results suggest that the rich‐split modification can achieve some reduction in reboiler duty and a considerable reduction in the condenser duty. The amount of reduction is dependent on plant design, particularly the efficiency of the lean/rich heat exchanger. © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd

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Coal-derived chars formed during air-blown gasification processes may rapidly lose reactivity, and this can limit the extent of their conversion. To study this effect, a laboratory-scale fluidized bed reactor has been modified to enable char samples to be prepared under strictly controlled conditions of temperature, pressure, particle size, gaseous environment, and residence time. This has been used to gain an insight into the deactivation of the chars as they form and during their subsequent residence time in the bed of the gasifier. The work shows that the char reactivity declines rapidly during its formation as part of the pyrolysis of the coal. This is thought to result from the rapid deposition of secondary, unreactive char within the pores of the material. In this work, it has been shown to occur within the initial 10 s in the reactor, but in reality, this effect probably occurred within 1 s. Temperature, pressure, and particle size have an impact on this process. Subsequently, and over a longer time scale, structural reorganization occurs in the solid char, and this anneals the structure by graphitization. This has been indicated by the identification of graphite, by X-ray diffraction in longresidence-time chars. The presence of steam in the fluidizing gas seemed to reduce the reactivity of small char particles, which could be due to the gasification of the more reactive parts. This effect does not seem to be present in data obtained with larger particles, and this is thought to be due to the greater influence of secondary char deposition in the larger particles. The reactivities of the largest particles formed over the longest time in this work are getting close to the reactivity values seen in char particles formed in a pilot-scale gasifier.

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