Analysis of the energy consumption of supercritical water desalination (SCWD)

An experimental and modelling study was done to investigate supercritical water desalination (SCWD) with respect to energy consumption as a function of the NaCl concentration (0 to 20 wt%). Pilot plant experiments were performed for different flow rates and feed concentrations, and used for the validation of the thermodynamic models (eNRTL and Anderko & Pitzer) employed for phase equilibria and enthalpy calculations. Experimental and modelling results showed that the lowered heat capacity of the feed streams, while increasing the concentration from 0 to 7 wt%, leads to improved performance of the feed - supercritical water (SCW) heat exchanger (HEX), evident from a higher feed outlet temperature. For concentrations of ≥14 wt%, pre-heating of the feed, prior to the HEX, is recommended due to the decrease in the SCW recovery in the SCW-brine separator. The calculated duty, of the heater bringing the heat-exchanged feed to the separation temperature, decreases with NaCl concentration due to the decrease in the feed heat capacity. The calculated overall energy consumption of SCWD was between 0.71 and 0.90 MJth/kgfeed. For higher concentration feeds, the energy input is divided between low – and high quality (temperature) heat

Supercritical water desalination (SCWD) of multi-component brines

The phase behaviour of two model multi-component salt-water mixtures (NaCl-KCl-H2O and NaCl-Na2SO4-H2O) was investigated for the application of supercritical water desalination (SCWD). The experimental investigation was a two-step procedure starting with qualitative analysis followed by quantitative measurements. The qualitative experiments served as a screening step to visually inspect phase behaviour. The quantitative results for NaCl-KCl-H2O, showed similarities in phase behaviour between the salts, which led to the assumption that the ternary mixture behaved as an ideal mixture between two binary solutions. The ternary equilibrium concentrations in the SCW phase could therefore be predicted using the binary salt-water models of the respective salts and accounting for the feed concentrations. Based on the quantitative results for NaCl-Na2SO4-H2O, the phase behaviour of the mixture was divided into three regions. The third region was the suitable region for SCWD, as the precipitated salts (Na2SO4) dissolved in the hydrothermal brine (NaCl), forming a vapour-liquid equilibrium

A novel method for determining the optimal operating points of reactive distillation processes

Reactive distillation (RD) allows reaction and separation to take place simultaneously in the same unit, thus giving major benefits especially to equilibrium limited reactions. Although the application of RD in chemical industries is attractive, it is considerably challenging. Unlike classic distillation, the optimal configuration of RD from an economical perspective is hardly identified quickly. Usually, any specific reaction system may need extensive studies and rigorous simulations to develop a RD model. This study aims to determine the optimal operating points of a RD application in a quick and reliable way. A novel method is employed for a clear visualization of the RD applicability area (i.e. a plot of reflux ratio vs number of stages). Using this method, an economic analysis can be performed resulting in essential insights into the optimal configurations. The production of amyl acetate by esterification of amyl alcohol and acetic acid is selected as case study, since this reaction sufficiently represents non-ideal behaviours in real systems. The outcome of the analysis reveals that the boundary line of its RD applicability graph consists of the optimal points of RD configurations which generate the lowest total annual cost in the RD operation. Furthermore, it is observed that the additional cost for the reactive section (relative to a separation section) is marginal, which means that the rules of thumb for the optimal configurations in classic distillation could also be applied

Beyond Haber-Bosch: The renaissance of the Claude process

Ammonia may be one of the energy carriers in the hydrogen economy. Although research has mostly focused on electrochemical ammonia synthesis, this however remains a scientific challenge. In the current article, we discuss the feasibility of single-pass thermochemical ammonia synthesis as an alternative to the high-temperature, high-pressure Haber-Bosch synthesis loop. We provide an overview of recently developed low temperature ammonia synthesis catalysts, as well as an overview of solid ammonia sorbents. We show that the low temperature, low pressure single-pass ammonia synthesis process can produce ammonia at a lower cost than the Haber-Bosch synthesis loop for small-scale ammonia synthesis (<40 t-NH3 d−1)

Procedure to determine the phase region of high-pressure, high-temperature binary salt-water mixtures

A decision tree to determine the phase region of high-pressure, high-temperature binary salt-water mixtures was developed. Based on the temperature, pressure and feed concentration of binary salt-water mixtures, the phase regions of either a type I or II salt were identified for a selected condition range. The Anderko and Pitzer equation of state (AP EoS) was used to calculate the equilibrium concentrations of the respective salt-water mixtures under high-pressure (P > 220 bar) and high-temperature (T > 300 ºC) conditions. The EoS was adapted to calculate the thermodynamic properties of KCl-H2O and Na2SO4-H2O mixtures, in addition to the properties of NaCl-H2O. The developed decision tree was able to accurately identify the phase regions and indicate the transition from one phase to another for different feed concentrations. The developed decision tree can be useful in determining operating conditions and preventing solid deposition for processes operating under the supercritical conditions of water

Potential of supercritical water desalination (SCWD) as zero liquid discharge (ZLD) technology

A modelling and economic study was done to evaluate the suitability of supercritical water desalination (SCWD) as zero liquid discharge (ZLD) technology. ZLD was achieved with a two stage brine treatment process. The hydrothermal brine, remaining after separation of supercritical water (SCW), under supercritical conditions, was expanded in the first stage (flash-step), and the remaining brine was then expanded and dried in the second stage (flash-evaporation step) using the produced steam of the first stage expansion. A window of operation for the first and second stage pressures was determined. For the process, the optimum point of operation was at the maximum second stage pressure, where the exergy of the second stage produced steam was also at a maximum. The economic evaluation showed that the SCWD brine treatment price, for an ideal case where all the products were sold, decreased from $ 9.61 to 1.16/m3brine when increasing feed concentration from 3.5 to 20 wt% NaCl. The decrease was due to the income from the sale of salts, which increases with feed concentration. The brine treatment price was highly dependent on the brine source and it was recommended that SCWD be used for the treatment of concentrated waste streams

Kinetic analysis of an ionic liquid-based metal extraction process using a single droplet extraction column

In this study a liquid-liquid extraction (LLX) process has been investigated based on experimental analysis and kinetic modelling. The purpose of this investigation is (1) to understand the mass transfer behaviour, (2) to determine the rate limiting step via evaluating different mass transfer models, and (3) to estimate the mass transfer and kinetic parameters. This has been discussed in the context of the extraction of Co by the ionic liquid (IL) [P8888][Oleate] as an example of LLX with chemical reaction. Mass transfer models, with and without a chemical reaction, are evaluated based on a statistical cross-validation method. The following operational parameters are included in the analysis: column lengths, droplet diameter, droplet rising velocity and continuous and dispersed phase concentrations on Co uptake. This method reveals that a single parameter representing the external mass transfer resistance can describe the forward extraction of Co (i.e., into the IL) for the whole data set sufficiently accurate (error ±30%) regardless of the studied operational conditions. Back-extraction of Co from pre-loaded IL droplets shows a different transfer mechanism. Now the mass transfer in the dispersed IL phase dominates the process which is attributed to a change of the physical properties of the pre-loaded IL

Recovery of metals from spent lithium-ion batteries using ionic liquid [P8888][Oleate]

A separation method to selectively recover valuable metals (Co, Ni, Mn and Li) from synthetic spent lithium-ion battery cathodes leachate using a fatty-acid-based ionic liquid, tetraoctylphosphonium oleate [P₈₈₈₈][oleate] is demonstrated. The investigated parameters for this selective separation and recovery process include extraction pH, contact time and composition of the regeneration solution. The benefit of using this ionic liquid is that >99% of Co and >99% of the Mn can be separated from the Ni and the Li by a two-stage extraction process. A subsequent single regeneration process separates the Co from the Mn. Finally, Ni and Li are completely separated in an additional regeneration process. An economic potential analysis concludes the paper, revealing that given the current cobalt price, the process outlined here shows a positive zero-order Economic Potential (bases on product sales and raw material cost) when using a 4 M HCl leaching solution and for leachates containing at least 4.5 g Co per liter

Islanded ammonia power systems: Technology review & conceptual process design

Recent advances in technologies for the decentralized, islanded ammonia economy are reviewed, with an emphasis on feasibility for long-term practical implementation. The emphasis in this review is on storage systems in the size range of 1–10 MW. Alternatives for hydrogen production, nitrogen production, ammonia synthesis, ammonia separation, ammonia storage, and ammonia combustion are compared and evaluated. A conceptual process design, based on the optimization of temperature and pressure levels of existing and recently proposed technologies, is presented for an islanded ammonia energy system. This process design consists of wind turbines and solar panels for electricity generation, a battery for short-term energy storage, an electrolyzer for hydrogen production, a pressure swing adsorption unit for nitrogen production, a novel ruthenium-based catalyst for ammonia synthesis, a supported metal halide for ammonia separation and storage, and an ammonia fueled, proton-conducting solid oxide fuel cell for electricity generation. In a generic location in northern Europe, it is possible to operate the islanded energy system at a round-trip efficiency of 61% and at a cost of about 0.30–0.35 € kWh−1

Novel method for mapping the applicability of reactive distillation

Reactive distillation (RD) is a great process intensification concept applicable to equilibrium limited reaction systems, but how can anyone decide quickly if RD is indeed worth applying? To answer this question, this study proposes a mapping method for checking the applicability of reactive distillation (RD). The initial development is for one of the most relevant subset of quaternary reversible reactions (A + B ⇄ C + D, with boiling points Tb,C < Tb,A < Tb,B < Tb,D), by using only basic chemical (equilibrium and kinetics) and physical (relative volatilities) parameters. Generic cases, assuming ideal thermodynamics and constant parameters, are used to obtain a set of RD applicability graphs that provide broad insights into the RD operation. In addition, the new mapping method provides reasonable estimates of the RD applicability to real (non-ideal) chemical systems based on the available pre-defined maps (which are actually applicability graphs of the generic ideal cases). This new approach leads to a straightforward estimation of the applicability of RD to real systems, prior to performing any rigorous process simulations and without any clear-cut decision making (as used in previous studies)