Paul Feron

CO2 capture from power plants. Part I: A parametric study of the technical performance based on monoethanolamine

Capture and storage of CO2 from fossil fuel fired power plants is drawing increasing interest as a potential method for the control of greenhouse gas emissions. An optimization and technical parameter study for a CO2 capture process from flue gas of a 600 MWe bituminous coal fired power plant, based on absorption/desorption process with MEA solutions, using ASPEN Plus with the RADFRAC subroutine, was performed. This optimization aimed to reduce the energy requirement for solvent regeneration, by investigating the effects of CO2 removal percentage, MEA concentration, lean solvent loading, stripper operating pressure and lean solvent temperature. Major energy savings can be realized by optimizing the lean solvent loading, the amine solvent concentration as well as the stripper operating pressure. A minimum thermal energy requirement was found at a lean MEA loading of 0.3, using a 40 wt.% MEA solution and a stripper operating pressure of 210 kPa, resulting in a thermal energy requirement of 3.0 GJ/ton CO2, which is 23% lower than the base case of 3.9 GJ/ton CO2. Although the solvent process conditions might not be realisable for MEA due to constraints imposed by corrosion and solvent degradation, the results show that a parametric study will point towards possibilities for process optimisation.

New absorption liquids for the removal of CO2 from dilute gas streams using membrane contactors

A new absorption liquid based on amino acid salts has been studied for CO2 removal in membrane gas–liquid contactors. Unlike conventional gas treating solvents like aqueous alkanolamines solutions, the new absorption liquid does not wet polyolefin microporous membranes. The wetting characteristics of aqueous alkanolamines and amino acid salt solutions for a hydrophobic membrane was studied by measuring the surface tension of the liquid and the breakthrough pressure of the liquid into the pores of the membrane. The dependence of the breakthrough pressure on surface tension follows the Laplace–Young equation. The performance of the new absorption liquid in the removal of CO2 was studied in a single fiber membrane contactor over a wide range of partial pressures of CO2 in the gas phase and amino acid salt concentrations in the liquid. A numerical model to describe the mass transfer accompanied by multiple chemical reactions occurring during the absorption of CO2 in the liquid flowing through the hollow fiber was developed. The numerical model gives a good prediction of the CO2 absorption flux across the membrane for the absorption of CO2 in the aqueous amino acid salt solutions flowing through the hollow fiber.

CO2 separation with polyolefin membrane contactors and dedicated absorption liquids: performances and prospects

Evidence continues to mount that the enhanced greenhouse effect is caused by increased emissions of infrared light absorbing components. Carbon dioxide is the largest contributor as a result of the large amounts emitted in power generation processes. This has brought about a sizeable academic and industrial interest in ways to remove carbon dioxide from various feed gas streams. Membrane gas absorption (MGA) using dedicated absorption liquids (CORAL) in conjunction with porous polypropylene hollow fibre membranes for carbon dioxide removal is discussed in this paper. Mass transfer results achieved in a pilot plant, including regeneration of the absorption liquids, are presented. The impact of carbon dioxide partial pressure, liquid loading and liquid temperature on the carbon dioxide membrane flux is discussed and compared with literature data for other systems. The novel absorption liquids show an excellent performance in terms of system stability and mass transfer, when used in combination with commercially available, inexpensive polyolefin membranes. The largest application under development is the production of carbon dioxide for the horticultural industry. Amongst the spin-off activities the life support applications are prevalent.

Towards Commercial Scale Postcombustion Capture of CO2 with Monoethanolamine Solvent: Key Considerations for Solvent Management and Environmental Impacts

Chemical absorption with aqueous amine solvents is the most advanced technology for postcombustion capture (PCC) of CO(2) from coal-fired power stations and a number of pilot scale programs are evaluating novel solvents, optimizing energy efficiency, and validating engineering models. This review demonstrates that the development of commercial scale PCC also requires effective solvent management guidelines to ensure minimization of potential technical and environmental risks. Furthermore, the review reveals that while solvent degradation has been identified as a key source of solvent consumption in laboratory scale studies, it has not been validated at pilot scale. Yet this is crucial as solvent degradation products, such as organic acids, can increase corrosivity and reduce the CO(2) absorption capacity of the solvent. It also highlights the need for the development of corrosion and solvent reclamation technologies, as well as strategies to minimize emissions of solvent and degradation products, such as ammonia, aldehydes, nitrosamines and nitramines, to the atmosphere from commercial scale PCC. Inevitably, responsible management of aqueous and solid waste will require more serious consideration. This will ultimately require effective waste management practices validated at pilot scale to minimize the likelihood of adverse human and environmental impacts from commercial scale PCC.

Dynamic modelling and optimisation of flexible operation in post-combustion CO2 capture plants—A review

Abstract The drive for efficiency improvements in post-combustion CO2 capture (PCC) technologies continues to grow, with recent attention being directed towards flexible operation of PCC plants. However, there is a lack of research into the effect of process disturbances when operating flexibly, justifying a need for validated dynamic models of the PCC process. This review critically examines the dynamic PCC process models developed to date and analyses the different approaches used, as well as the model complexity and their limitations. Dynamic process models coupled with economic analysis will play a crucial role in process control and optimisation. Also discussed are key areas that need to be addressed in future dynamic models, including the lack of reliable dynamic experimental data for their validation, development of feasible flexible operation and process control strategies, as well as process optimisation by integrating accurate process models with established economic analysis tools.

Approximate solution to predict the enhancement factor for the reactive absorption of a gas in a liquid flowing through a microporous membrane hollow fiber

Approximate solutions for the enhancement factor (based on the traditional mass transfer theories) for gas–liquid systems with a liquid bulk have been adapted to situations where a liquid bulk may be absent and a velocity gradient is present in the mass transfer zone. Such a situation is encountered during the absorption a gas in a liquid flowing through a hollow fiber. The explicit solution of DeCoursey [Chem. Eng. Sci. 29 (1974) 1867] for a second-order irreversible reaction has been used as a representative sample of the approximate solutions available in literature. It was chosen because of the accuracy of its predictions and the simplicity in use. The solution of DeCoursey was adapted, but still has limitations at long gas–liquid contact times. Under these conditions, the actual driving force for mass transfer of the gas phase species may not be identical for physical and reactive absorption. Also for these situations, there may be a significant depletion of the liquid phase reactant at the axis of the fiber (which is considered to be analogous to the liquid bulk in traditional mass transfer models). A criterion has been proposed for the applicability of the adapted DeCoursey’s approximate solution for a second-order irreversible reaction. Within the range of applicability, the approximate solution has been found to be accurate with respect to the exact numerical solution of the mass transfer model as well as the experimentally determined values of enhancement factor in a single hollow fiber membrane gas–liquid contactor. The single hollow fiber membrane contactor that has been used in this study has potential for use as a model gas–liquid contactor. This contactor can thus be used, along with the present approximate solution of the enhancement factor, to obtain the physicochemical properties of a reactive gas–liquid system from the experimental absorption flux measurements or vice versa, as described in the present work.

Membrane Gas Absorption Processes in Environmental Applications

Membrane gas absorption processes are absorption processes utilising hollow fiber membranes as contacting media for gas and liquid flows. The principle of operation is discussed, followed by a number of environmental applications. Benefits are shown to exist for a variety of environmental problems, as a result of the equipment compactness and flexibility. The use of a crossflow, modular membrane unit enhances the opportunities for the application of membrane gas absorption. Finally, other areas of application of this new membrane based contacting equipment are discussed.

Process Modeling of an Advanced NH3 Abatement and Recycling Technology in the Ammonia-Based CO2 Capture Process

An advanced NH3 abatement and recycling process that makes great use of the waste heat in flue gas was proposed to solve the problems of ammonia slip, NH3 makeup, and flue gas cooling in the ammonia-based CO2 capture process. The rigorous rate-based model, RateFrac in Aspen Plus, was thermodynamically and kinetically validated by experimental data from open literature and CSIRO pilot trials at Munmorah Power Station, Australia, respectively. After a thorough sensitivity analysis and process improvement, the NH3 recycling efficiency reached as high as 99.87%, and the NH3 exhaust concentration was only 15.4 ppmv. Most importantly, the energy consumption of the NH3 abatement and recycling system was only 59.34 kJ/kg CO2 of electricity. The evaluation of mass balance and temperature steady shows that this NH3 recovery process was technically effective and feasible. This process therefore is a promising prospect toward industrial application.

Technical and Energy Performance of an Advanced, Aqueous Ammonia-Based CO2 Capture Technology for a 500 MW Coal-Fired Power Station.

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%.

Innovative Use of Membrane Contactor as Condenser for Heat Recovery in Carbon Capture

The gas-liquid membrane contactor generally used as a nonselective gas absorption enhancement device is innovatively proposed as a condenser for heat recovery in liquid-absorbent-based carbon capture. The membrane condenser is used as a heat exchanger to recover the latent heat of the exiting vapor from the desorber, and it can help achieve significant energy savings when proper membranes with high heat-transfer coefficients are used. Theoretical thermodynamic analysis of mass and heat transfer in the membrane condensation system shows that heat recovery increases dramatically as inlet gas temperature rises and outlet gas temperature falls. The optimal split mass flow rate is determined by the inlet gas temperature and the overall heat-transfer coefficient in the condensation system. The required membrane area is also strongly dependent on the overall heat-transfer coefficient, particularly at higher inlet gas temperatures. Mass transfer across the membrane has an insignificant effect on heat transfer and heat recovery, suggesting that membrane wetting may not be an issue when a membrane condenser is used for heat recovery. Our analysis provides important insights into the energy recovery performance of the membrane condensation system as well as selection of operational parameters, such as split mass flow rate and membrane area, thickness, and thermal conductivity.