N. Mac Dowell

Modelling the fluid phase behaviour of aqueous mixtures of multifunctional alkanolamines and carbon dioxide using transferable parameters with the SAFT-VR approach

Among the many applications that alkanolamines find in industry, carbon dioxide (CO2) capture from large stationary sources is becoming the most relevant. Aqueous mixtures of amines and CO2 exhibit complex behaviour, characterized by extensive hydrogen bonding and other types of chemical reactions. An implicit treatment of the key reactions via appropriate association schemes has been shown to provide a promising physical basis for the modelling of these systems. Here, we introduce association models for use with SAFT-VR for some of the more promising multifunctional alkanolamines in the context of CO2 capture: monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), diethanolamine (DEA) and methyldiethanolamine (MDEA), and their mixtures with H2O and CO2. A revised model of the MEA + H2O + CO2 mixture is presented with an extension to high temperature. Excellent predictive capabilities are demonstrated for pure components and binary aqueous mixtures. A good overall description is also obtained for the ternary aqueous mixtures of alkanolamines and CO2, particulary for DEA and MDEA. Furthermore, the degree of speciation is successfully predicted for the MEA + H2O + CO2 mixture. Since only a limited number of parameters need to be estimated from vapour–liquid equilibrium data, the ternary SAFT-VR reaction-implicit models developed in this work offer a useful initial assessment of the different solvents and blends.

The multi-period optimisation of an amine-based CO2 capture process integrated with a super-critical coal-fired power station for flexible operation

Abstract In this work, we present a model of a super-critical coal-fired power plant integrated with an amine-based CO 2 capture process. We use this model to solve a multi-period dynamic optimisation problem aimed at decoupling the operation of the power plant from the efficiency penalty imposed by the CO 2 capture plant, thus providing the power plant sufficient flexibility to exploit price variation within an electricity market. We evaluate four distinct scenarios: load following, solvent storage, exhaust gas by-pass and time-varying solvent regeneration. The objective is to maximise the decarbonised power plants short run marginal cost profitability. It is found that while the solvent storage option provides a marginal improvement of 4% in comparison to the load following scenario, the exhaust gas bypass scenario results in a profit reduction of 17% whereas the time-varying solvent regeneration option increases the profitability of the power plant by 16% in comparison to the reference scenario.

Integrated solvent and process design for the reactive separation of CO2 from flue gas

Abstract A model-based platform for assessing alternative designs and solvent blends for reactive separation processes is presented and applied to the problem of chemisorption of CO 2 from flue gas with amine solvents. We combine state-of-the-art thermodynamics with rigorous process simulation techniques for this purpose. A rate-based model of chemisorption units for CO 2 capture is implemented in the gPROMS modelling environment, using the statistical associating fluid theory for potentials of variable range (SAFT-VR) 1 to represent mixture thermodynamics. Important features of our model are that both the reaction and phase equilibria are incorporated in the thermodynamic model, and as a result, enhancement factors are not required in the process model. As reaction products are accounted for at the level of the thermodynamic model (from a physical perspective), the generation of reaction products or heat is considered implicitly in the mass and energy balances, further simplifying the model. We validate our model using published pilot plant data, and subsequently apply this approach to the treatment of a typical industrial scale flue gas stream and demonstrate how it can be used to optimise simultaneously solvent composition and process operating conditions.

Time for global action: an optimised cooperative approach towards effective climate change mitigation

The difficulties in climate change negotiations together with the recent withdrawal of the U.S. from the Paris Agreement call for new cooperative mechanisms to enable a resilient international response. In this study we propose an approach to aid such negotiations based on quantifying the benefits of interregional cooperation and distributing them among the participants in a fair manner. Our approach is underpinned by advanced optimisation techniques that automate the screening of millions of alternatives for differing levels of cooperation, ultimately identifying the most cost-effective solutions for meeting emission targets. We apply this approach to the Clean Power Plan, a related act in the U.S. aiming at curbing carbon emissions from electricity generation, but also being withdrawn. We find that, with only half of the states cooperating, the cost of electricity generation could be reduced by US

Closing the carbon cycle to maximise climate change mitigation: power-to-methanol vs. power-to-direct air capture

41 billion per year, while simultaneously cutting carbon emissions by 68% below 2012 levels. These win–win scenarios are attained by sharing the emission targets and trading electricity among the states, which allows exploiting regional advantages. Fair sharing of dividends may be used as a key driver to spur cooperation since the global action to mitigate climate change becomes beneficial for all participants. Even if global cooperation remains elusive, it is worth trying since the mere cooperation of a few states leads to significant benefits for both the U.S. economy and the climate. These findings call on the U.S. to reconsider its withdrawal but also boost individual states to take initiative even in the absence of federal action.

Modeling the Fluid Phase Behavior of Carbon Dioxide in Aqueous Solutions of Monoethanolamine Using Transferable Parameters with the SAFT-VR Approach

It is broadly recognised that CO2 capture and storage (CCS) and associated negative emissions technologies (NETs) are vital to meeting the Paris agreement target. The hitherto failure to deploy CCS on the required scale has led to the search for options to improve its economic return. CO2 capture and utilisation (CCU) has been proposed as an opportunity to generate value from waste CO2 emissions and improve the economic viability of CCS, with the suggestion of using curtailed renewable energy as a core component of this strategy. This study sets out to quantify (a) the amount of curtailed renewable energy that is likely to be available in the coming decades, (b) the amount of fossil CO2 emissions which can be avoided by using this curtailed energy to convert CO2 to methanol for use as a transport fuel – power-to-fuel, with the counterfactual of using that curtailed energy to directly remove CO2 from the atmosphere via direct air capture (DAC) and subsequent underground storage, power-to-DAC. In 2015, the UK curtailed 1277 GWh of renewable power, or 1.5% of total renewable power generated. Our analysis shows that the level of curtailed energy is unlikely to increase beyond 2.5% until renewable power accounts for more than 50% of total installed capacity. This is unlikely to be the case in the UK before 2035. It was found that: (1) power-to-DAC could achieve 0.23–0.67 tCO2 avoided MWh−1 of curtailed power, and (2) power-to-Fuel could achieve 0.13 tCO2 avoided MWh−1. The power-to-fuel concept was estimated to cost

Dynamic modelling and analysis of an amine-based post-combustion CO2 capture absorption column

209 tCO2 avoided−1 in addition to requiring an additional

Identification of the cost-optimal degree of CO2 capture: An optimisation study using dynamic process models

430–660 tCO2 avoided−1 to finally close the carbon cycle by air capture. The power-to-DAC concept was found to cost only the

Flexible operation of solvent regeneration systems for CO2 capture processes using advanced control techniques: Towards operational cost minimisation

430–660 tCO2 avoided−1 for air capture. For power-to-fuel to become profitable, hydrogen prices would need to be less than or equal to

The role of flexible CCS in the UK's future energy system

1635 tH2−1 or methanol prices must increase to