Kathryn H. Smith

Review of solvent based carbon-dioxide capture technologies

Currently, a large proportion of global fossil fuel emissions originate from large point sources such as power generation or industrial processes. This trend is expected to continue until the year 2030 and beyond. Carbon capture and storage (CCS), a straightforward and effective carbon reduction approach, will play a significant role in reducing emissions from these sources into the future if atmospheric carbon dioxide (CO2) emissions are to be stabilized and global warming limited below a threshold of 2 °C. This review provides an update on the status of large scale integrated CCS technologies using solvent absorption for CO2 capture and provides an insight into the development of new solvents, including advanced amine solvents, amino acid salts, carbonate systems, aqueous ammonia, immiscible liquids and ionic liquids. These proposed new solvents aim to reduce the overall cost CO2 capture by improving the CO2 absorption rate, CO2 capture capacity, thereby reducing equipment size and decreasing the energy required for solvent regeneration.

Performance of an Industrial Pulsed Disc-and-Doughnut Extraction Column

ABSTRACT Axial-dispersion and plug-flow models have been used to describe the solvent extraction performance of a 18 m high and 4 m diameter industrial pulsed disc-and-doughnut column. Uranium extraction phase-equilibrium data were fitted with the Langmuir model. Using the industrial column dimensions, operational parameters, physical properties, and the Langmuir parameters, the axial-dispersion model was shown to predict the organic-phase outlet concentration and the aqueous-phase outlet concentration, respectively, while the plug-flow model exhibited a poorer predictive ability.,

Extraction of Phenol by Toluene in the Presence of Sodium Hydroxide

Phenol is a good model compound to study extraction of alkaloids as its acidity constant is close to that of many alkaloids, for example, morphine. In addition, extraction of phenol is important environmentally as it is a water pollutant. In this study the distribution ratio of neutral phenol and total phenol between water and toluene with varying pH and varying concentration of sodium hydroxide is determined and discussed. The phase equilibrium is modelled by the symmetric electrolyte nonrandom two-liquid model and the calculated values agree well with the experimental results.

Energy and Exergy Analyses of an Integrated Gasification Combined Cycle Power Plant with CO2 Capture Using Hot Potassium Carbonate Solvent

Energy and exergy analyses were studied for an integrated gasification combined cycle (IGCC) power plant with CO2 capture using hot potassium carbonate solvent. The study focused on the combined impact of the CO conversion ratio in the water gas shift (WGS) unit and CO2 recovery rate on component exergy destruction, plant efficiency, and energy penalty for CO2 capture. A theoretical limit for the minimal efficiency penalty for CO2 capture was also provided. It was found that total plant exergy destruction increased almost linearly with CO2 recovery rate and CO conversion ratio at low CO conversion ratios, but the exergy destruction from the WGS unit and the whole plant increased sharply when the CO conversion ratio was higher than 98.5% at the design WGS conditions, leading to a significant decrease in plant efficiency and increase in efficiency penalty for CO2 capture. When carbon capture rate was over around 70%, via a combination of around 100% CO2 recovery rate and lower CO conversion ratios, the efficiency penalty for CO2 capture was reduced. The minimal efficiency penalty for CO2 capture was estimated to be around 5.0 percentage points at design conditions in an IGCC plant with 90% carbon capture. Unlike the traditional aim of 100% CO conversion, it was recommended that extremely high CO conversion ratios should not be considered in order to decrease the energy penalty for CO2 capture and increase plant efficiency.

Comparison of the Hydrodynamic Performance of Pulsed Solvent Extraction Columns with Tenova Pulsed Column Kinetics Internals and Standard Disc and Doughnut Internals for Copper Extraction Using the LIX 84 System

ABSTRACT The dispersed phase holdup and droplet size are important parameters for understanding the hydrodynamic performance of pulsed solvent extraction columns. This study provides a comparison of the hydrodynamic performance between a Tenova Pulsed Column with Kinetics Internals (TPC-KI) and a pulsed column with standard disc and doughnut internals. The TPC-KIs are designed to improve the performance of systems with slow reaction kinetics, such as copper extraction with LIX 84, which was the focus of the current study. Holdup and drop size have been measured as a function of pulsation intensity and phase velocities for both types of column internals. Lower holdup and larger drop sizes were obtained with the TPC-KI, which indicates a higher flood point and a higher throughput. Correlations have been developed to predict the performance of these internals over a range of operating conditions.

CFD Simulation of Liquid–Liquid Two-Phase Hydrodynamics and Axial Dispersion Analysis for a Non-Pulsed Disc and Doughnut Solvent Extraction Column

ABSTRACT A two-phase computational fluid dynamics (CFD) simulation for a non-pulsed disc and doughnut solvent extraction column has been developed with commercial CFD software FLUENT. Simulated hydrodynamic results including phase distribution, velocity fields, and holdup are given, which enables predicted holdup to be compared with experimental data. Average absolute relative deviation (AARD) of experimental data and CFD prediction in this study is found to be 10.8%, which is comparable to the estimated error in the experimental data and the predictions from traditional correlations in the literature. To estimate the extent of axial dispersion, a species transport model is used for the continuous phase with a small amount of tracer introduced in the continuous phase, when Sauter mean diameter of the dispersed phase is set to be 3.5 mm. A two-point monitoring method is used to estimate a Peclet number. The tracer concentration distribution in the two-dimensional distance–time space is interpreted with MATLAB along with the experimental measurement. The simulated Peclet numbers are compared with column experiments, and in general the simulation underestimates the experimental data by 60%. Introducing a modified drag law improves the predictions. This work shows that CFD can successfully model the performance of a non-pulsed disc and doughnut solvent extraction column.

IGCC Precombustion CO2 Capture Using K2CO3 Solvent and Utilizing the Intercooling Heat Recovered From CO2 Compressors for CO2 Regeneration

CO2 capture (CC) using hot K2CO3 solvent in integrated gasification combined cycle (IGCC) plant is a promising technology for CO2 emission reduction. Based on pilot scale trials, an innovative IGCC system with CC using hot K2CO3 solvent is proposed, in which the intercooling heat between CO2 compressors is recovered for CO2 regeneration (IGCC + CC + HR). Thermodynamic performance and exergy and energy utilization diagram (EUD) analysis are presented. Results show that recovery of the intercooling heat between CO2 compressors reduces the steam extraction requirement from turbines for CO2 regeneration by around 18% and enhances the efficiency of IGCC with CO2 capture (IGCC + CC) plant by 0.3–0.7 percentage points. With 90% CC, the efficiency of the IGCC + CC + HR plant is around 35.4% which is higher than IGCC + CC plant using Selexol technology. Compared to IGCC, the energy penalty for CC in IGCC + CC + HR plant is mainly caused by the exergy losses in CO2 separation (45.2%), water gas shift (WGS) (28.5%), combined cycle (20.7%) and CO2 compression units (5.6%). EUD analysis shows that the IGCC + CC + HR plant realizes good match of the energy levels between the intercooling heat and the recovered steam for CO2 regeneration, thereby obviously reducing the exergy losses in CO2 compression and separation units and improving the plant efficiency. The results presented in this paper confirm the sources causing the energy penalty for CC in IGCC power plant and the new IGCC + CC + HR system helps to reduce the energy penalty for CC in IGCC power plant based on solvent technologies.

Effect of Plate Wettability on Dispersed-Phase Holdup in a Pulsed Disc-and-Doughnut Solvent Extraction Column

ABSTRACT The effect of plate wettability on the dispersed-phase holdup in a pulsed disc-and-doughnut solvent extraction column is presented. Teflon, nylon, and stainless steel plates have been used to simulate a change in the wetting characteristics of the plate material that can occur in an operating column due to ageing or deposits accumulating on the plate. Experimental holdup data have been measured over a range of operating conditions using a 1.0 m long glass column with an internal diameter of 72.5 mm containing alternating discs and doughnuts. The liquid-liquid system studied was tri-n-octylamine (TOA)-kerosene-water with sulphuric acid as the solute. Results show that there are noticeable changes in the characteristic velocity (determined from measured holdup) and operational regimes for the different plate materials, particularly at low pulsation intensities, when operating under dispersed aqueous conditions. Experimental holdup data from this study have also been compared to correlations from literature for predicting holdup. As none of these correlations for holdup incorporate plate wettability, a new correlation for predicting holdup has been proposed that incorporates the contact angle of the plate material to allow for changes in the wettability of the plate surface. This correlation is able to predict the holdup data from this study to within 10.5% for aqueous dispersed conditions.

Comparison of the Axial Dispersion Performance of Pulsed Solvent Extraction Columns with Tenova Pulsed Column–Kinetics Internals and Standard Disc and Doughnut Internals

ABSTRACT Axial dispersion performance of a 2-m high 76-mm diameter pilot-scale pulsed solvent extraction column has been studied using two liquid–liquid systems, Alamine 336/isodecanol/Shellsol 2046 (continuous)–tap water (dispersed) and LIX 84/Shellsol 2046 (continuous)–tap water (dispersed). The pulsed column was operated with standard disc and doughnut internals and Tenova pulsed column–kinetics internals using pulsation intensities from 0.005 m/s to 0.025 m/s with polyvinylidene fluoride internal plates of 22.4% open area. The effect of pulsation intensity, dispersed phase velocity, and continuous phase velocity on axial dispersion coefficient have been investigated and compared with the two different column internals, and the experimental data has been correlated with empirical relationships.

Bio-Based Molecular Solvents

Bio-based molecular solvents can provide environmentally sustainable alternatives to traditional petrochemical solvents. Increasingly strict regulatory pressures, as well as economic, environmental and health concerns are driving the separations field toward more green practices. In light of this, solvent selection guides and principles are able to aid in identification of replacements, with additional discussion of how these address issues with defining sustainability. Key parameters to aid in predicting solvent performance and replacement are described, such as Hansen solubility parameters. Promising bio-based solvents are provided alongside physical characteristics, and key solvents are presented in the context of current solvent extraction research. Industries looking to replace petrochemical solvents should consider bio-based solvent alternatives for separations applications.