• Energy Research

CO2 capture by CaO in molten salts is a variant of calcium looping in which the active substances (CaO/CaCO3) are dissolved or in a slurry with inorganic molten salts. One of the main advantages is the nonexistence of degradation in the reactivity between the active material and CO2. Previous research has revealed good absorption and desorption characteristics with CaO contents up to 20 wt% in eutectic CaF2-CaCl2. The hypothesis is that the formed CaCO3 continuously dissolves in the melt, leaving highly reactive CaO readily available for the incoming CO2. In the present study, the CaO content is increased to 40 wt%, and the absorption characteristics is investigated with focus on the sorption capacity and CO2 removal rate. The chemical system is also evaluated experimentally with regards to viscosity and solubility of the formed CaCO3 during CO2 absorption, with the aim of determining chemical upscaling limitations. The results show that the practical CaO content limit is 30 wt%, in which a sorption capacity of 20 g CO2/100 g sorbent is observed, without any deterioration of the reaction kinetics. For 40 wt% CaO, the sorption capacity is higher, but on the expense of the CO2 removal rate and CaO conversion. This is attributed to a significant increase in viscosity and the solubility limit of CaCO3 being exceeded.

The decarbonization of the power sector involves electrification and a massive deployment of variable renewable energy sources, leading to an increase of local transmission congestion and ramping challenges. A possible solution to secure grid stability is local flexibility markets, in which prosumers can offer demand-side flexibility to the distribution system operator or other flexibility buyers through an aggregator. The purpose of this study was to develop a framework for estimating and offering short-term demand-side flexibility to a flexibility marketplace, with the main focus being baseline estimation and bid generation. The baseline is estimated based on forecasts that have been corrected for effects from earlier flexibility activations and potential planned use of internal flexibility. Available flexibility volumes are then estimated based on the baseline, physical properties of the flexibility asset and agreed constraints for baseline deviation. The estimated available flexibility is further formatted into a bid that may be offered to a flexibility marketplace, where buyers can buy and activate the offered flexibility, in whole or by parts. To illustrate and verify the proposed methodology, it was applied to a grocery warehouse. Based on real flexibility constraints, historic meter values, and forecasts for this use-case, we simulated a process where the flexibility is offered to a hypothetic flexibility marketplace through an aggregator.

Calcium halide based molten salts have recently attracted interest for a number of applications such as direct reduction of oxides for metal production and as liquefying agent in cyclic sorption processes for CO2 by CaO from dilute flue gases (Ca-looping). A fundamental aspect of these melts is the possible hydrolysis reaction upon exposure to gaseous H2O forming corrosive and poisonous hydrogen halides. In this work experiments have been performed investigating the formation of HCl and HF from a molten salt consisting of a 13.8 wt% CaF2 in CaCl2 eutectic exposed to a flowing gas consisting of 10 vol% H2O in N2. Hydrolysis has been investigated as function of content of CaO and temperature. HCl and HF are shown to be formed at elevated temperatures; HCl forms to a substantially larger extent than HF. Addition of CaO has a marked, limiting effect on the hydrolysis. Thermodynamic modeling of the reaction indicates activity coefficients for CaO above unity in the system. For cyclic CO2-capture based on thermal swing, it is advisable to keep the temperature in the carbonation (absorption) reactor well below 850 ℃ while maintaining a high CaO content if molten CaCl2 is employed. Similar conclusions can be drawn with regards to CaF2.

AbstractThe thermal behavior of wood particles in molten salt pyrolysis was investigated. Cylindrical beech wood particles (L = 30mm, d = 3.5mm) were pyrolyzed using different mixtures of molten salts (FLiNaK, (LiNaK)2CO3, ZnCl2–KCl, KNO3–NaNO3) over a temperature range of 400–600°C. The temperature at the particle center was measured during the process, and used to evaluate heating rates, reaction temperatures and devolatilization times. A general observation was that beech wood is heated faster in fluoride and carbonate melts, but the differences diminish with increasing reactor temperatures. The highest heating rates at the particle center were observed in FLiNaK (46 – 56°C/s). The effective pyrolysis temperature at which the main decomposition of cellulose and hemicellulose takes place showed a weak dependence on reactor temperature, but no significant difference between the heating media was discovered. The devolatilization time corresponding to conversion of 95% may be empirically correlated with the power law expression . Arrhenius plots were constructed to show the exponential dependence of temperature on the parameter A. The correspondingly low activation energies (13.3 – 27.4kJ/mol) indicate heat transfer control during the decomposition process.

A tubular electrostatic precipitator (ESP) was designed and tested for collection of pyrolysis oil in molten salt pyrolysis of milled beech wood (0.5-2 mm). The voltage-current (V-I) characteristics were studied, showing most stable performance of the ESP when N2 was utilized as inert gas. The pyrolysis experiments were carried out in FLiNaK and (LiNaK)2CO3 over the temperature range of 450-600 ℃. The highest yields of pyrolysis oil were achieved in FLiNaK, with a maximum of 34.2 wt% at 500 ℃, followed by a decrease with increasing reactor temperature. The temperature had nearly no effect on the oil yield for pyrolysis in (LiNaK)2CO3 (19.0-22.5 wt%). Possible hydration reactions and formation of HF gas during FLiNaK pyrolysis were investigated by simulations (HSC Chemistry software) and measurements of the outlet gas (FTIR), but no significant amounts of HF were detected.

The dataset contains raw data and experimental results of thermodynamic properties of different compositions of KCl-CuCl molten salt. Thermal stability, melting point and hydrolysis rate of compositions are studied experimentally.

With the higher penetration of intermittent renewable energy sources in the electric power grid, more flexibility is needed to cope with challenges related to stability and reliability. Consumers can be part of the solution through demand response, for example, by investing in residential batteries that can charge and discharge based on price signals (implicit flexibility) or externally controlled based on grid-related needs (explicit flexibility). In this study, we investigate the feasibility of deploying residential batteries through a case study consisting of 20 households located in south-eastern Norway. The potential annual savings from implicit flexibility are optimized based on the retail electricity price, a power-based tariff, and potential revenues by selling electricity to the grid. Real historical price and consumption data with hourly resolutions from the entire year of 2022 are used as input for the optimization, yielding a theoretical profit potential. Based on this, profitability analyses are performed. The results show that the battery investments will not reach an economic break-even point during their lifetime under today’s electricity price conditions. However, future developments in profit increase from implicit flexibility, substantial investment support, or additional revenues from emerging flexibility markets could make the investment economically attractive for a regular consumer.

Abstract Carbon Capture in Molten Salts (CCMS) is a high temperature method for extracting CO 2 from a variety of flue gases related to power generation and carbon-intensive industries. The chemical principles are similar to those in calcium looping in the solid state; a carbonation reaction of CaO with CO 2 to form CaCO 3 followed by regeneration of CO 2 through the reverse reaction. In CCMS, the active substances (CaO/CaCO 3 ) are dissolved or partly dissolved in molten salts, allowing fast reaction kinetics, high CO 2 sorption capacities, and avoiding solids attrition issues. In our previous studies, the focus has been on the total CO 2 sorption capacity and demonstration of cyclic absorption and desorption. Experiments have been performed with up to 20 wt% CaO in molten CaCl 2 and eutectic CaF 2 /CaCl 2 . It has been demonstrated that up to 85% of the CaO reacts during absorption, and ∼100% of the CaCO 3 is decomposed during desorption. No degradation of the sorbent has been observed after 12 cycles. In the present study, the focus is turned to the reaction kinetics between CO 2 and CaO. The raw data from previous experiments are analyzed to obtain the sorption capacity (g CO 2 / 100 g sorbent) as a function of time, and the linear region of the capacity is further used to evaluate the reaction kinetics. The effect of absorption temperature, molten salt composition, CaO content and cyclic CO 2 capture is studied. The results show that CaF 2 /CaCl 2 is more favorable for CCMS than pure CaCl 2 ; the kinetically controlled regime lasts longer and the total sorption capacity is higher. For both of the salt mixtures, the sorption capacities are stable during cyclic CO 2 capture, without any deterioration of the reaction kinetics.