24 research outputs found
Predicting the power grid frequency of European islands
Modelling, forecasting and overall understanding of the dynamics of the power
grid and its frequency is essential for the safe operation of existing and
future power grids. Much previous research was focused on large continental
areas, while small systems, such as islands are less well-studied. These
natural island systems are ideal testing environments for microgrid proposals
and artificially islanded grid operation. In the present paper, we utilize
measurements of the power grid frequency obtained in European islands: the
Faroe Islands, Ireland, the Balearic Islands and Iceland and investigate how
their frequency can be predicted, compared to the Nordic power system, acting
as a reference. The Balearic islands are found to be particularly deterministic
and easy to predict in contrast to hard-to-predict Iceland. Furthermore, we
show that typically 2-4 weeks of data are needed to improve prediction
performance beyond simple benchmarks.Comment: 16 page
DNA Methylation and Gene Expression Changes in Monozygotic Twins Discordant for Psoriasis: Identification of Epigenetically Dysregulated Genes
Monozygotic (MZ) twins do not show complete concordance for many complex diseases; for example, discordance rates for autoimmune diseases are 20%–80%. MZ discordance indicates a role for epigenetic or environmental factors in disease. We used MZ twins discordant for psoriasis to search for genome-wide differences in DNA methylation and gene expression in CD4+ and CD8+ cells using Illumina's HumanMethylation27 and HT-12 expression assays, respectively. Analysis of these data revealed no differentially methylated or expressed genes between co-twins when analyzed separately, although we observed a substantial amount of small differences. However, combined analysis of DNA methylation and gene expression identified genes where differences in DNA methylation between unaffected and affected twins were correlated with differences in gene expression. Several of the top-ranked genes according to significance of the correlation in CD4+ cells are known to be associated with psoriasis. Further, gene ontology (GO) analysis revealed enrichment of biological processes associated with the immune response and clustering of genes in a biological pathway comprising cytokines and chemokines. These data suggest that DNA methylation is involved in an epigenetic dysregulation of biological pathways involved in the pathogenesis of psoriasis. This is the first study based on data from MZ twins discordant for psoriasis to detect epigenetic alterations that potentially contribute to development of the disease
Molten salt pyrolysis of milled beech wood using an electrostatic precipitator for oil collection
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
Carbon Capture with Metal Oxides in Molten Salts: MgO, SrO and CaO AS Sorbents
Carbon Capture in Molten Salts (CCMS) is an absorption-based method of separating CO2 from a flue gas or industrial gas through a thermal swing technique, where the sorbent is dissolved or partially dissolved in molten salts. The method takes advantage of the reversible carbonation reaction of alkaline earth metal oxides and has previously been studied with CaO as sorbent, showing excellent absorption capacity, regeneration and cyclability compared to similar methods. If the molten salt contains certain alkaline metal halides, these may react with the formed metal carbonates in an exchange reaction, shifting the equilibrium towards further carbonation. The CCMS process is however energy intensive and the regeneration of the sorbent has been identified as a main cost driver due to high operating temperatures and high reaction enthalpy. In this study, a screening of alternative chemical systems with MgO, SrO and CaO as sorbents has been performed. The aim is to find chemical systems with lower operating temperatures and reaction enthalpies that work as efficiently as in previous studies, as this could reduce energy demand and thus operational costs. Promisingly high reaction stability and conversion ratio was found with MgO-FLiNaK, but more experiments are needed to see if the absorption efficiency may be sufficiently improved. SrO-NaCl-CaCl2 showed an even higher conversion ratio, but lower reaction stability which may be improved in a different salt mixture. Furthermore, it was found that the chemical system CaO-LiF-CaF2, which has been very efficient in previous studies, seemed to have no active exchange reaction when the CaF2 was replaced by CaCl2. Another new finding is that even though studies have shown that CCMS may operate well above the solubility limit of the sorbent, the sorbent does need to have a certain solubility in the melt in order to absorb any CO2.publishedVersio
A Framework for Offering Short-Term Demand-Side Flexibility to a Flexibility Marketplace
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 aggregato
Experimental evaluation of chemical systems for CO2 capture by CaO in eutectic CaF2-CaCl2
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
Techno-Economic Study of the CCMS Technology for CO2 Capture From Ferro-Silicon Production
Carbon Capture in Molten Salts (CCMS) is a method for capturing CO2 from a variety of flue gases related to power generation and energy intensive industry processes. The chemical principles are similar to those of the calcium looping process in solid state (using CaO-based solid sorbents), where CO2 is captured in a carbonation reaction to form CaCO3, and then released through the reverse calcination reaction in a second step. In the CCMS concept, the novelty is to operate the process in the liquid state in CaO-rich molten salts. The formed CaCO3 dissolves continuously in the melt, thus leaving highly reactive CaO readily available for the incoming CO2. In the present study, the technical and economic feasibility of the CCMS process has been investigated for capturing CO2 from metallurgical ferro-silicon (FeSi) production using relevant industrial parameters. We have evaluated a generic plant based on one of the existing 40 MW FeSi furnaces the company Elkem owns and operates, but with theoretical considerations regarding recycling of the flue gas with the purpose of recovering energy. The input parameters for the capture process are based on experimental data. With the assumption of 85 % CO2 capture and CO2 compression to 70 bar (at 20 oC), the capture cost is estimated to be 60 EUR/ton, indicating that CCMS is a promising competitive alternative technology for fullscale CO2 capture for FeSi production. The main cost driver for the process has been identified as the cost of desorption. The desorber has a high investment cost, and also requires high temperature heat transfer for operation. However, the evaluations show that the introduction of an integrated system with combustion and heat pipes is a viable technical option