Sosial kapital blant marginaliserte

Begrepet sosial kapital i moderne samfunnsvitenskap er knyttet til en sentral idé i sosialt arbeid – at sosiale relasjoner og nettverk representerer ressurser som kan hjelpe folk videre i livet. I forskningen er denne forestillingen så sterk at kontakt med familie, venner og naboer ofte brukes som indikator på ressurser. I denne artikkelen skilles det mellom nettverk og ressurser og belyses hvilke ressurser som finnes i det sosiale nettverket til brukerne av Frelsesarmeen og Kirkens Bymisjons tjenester. Undersøkelsen viser at brukerne har mye kontakt med venner, men lite med familien. Deres nettverk gir tilgang til ressurser som kan hindre ytterligere marginalisering, mens de har færre sosiale relasjoner som gir tilgang til ressurser som kan bidra til at de bedrer sin situasjon

Thermochemically Stable Novel Oxygen Carriers Based on CaMn1–x–yTixFeyO3−δ for Chemical Looping

The understanding and development of stable redox materials based on cheap and abundant elements, forming Ca–Mn–Ti–Fe–O-based perovskites, have been in focus for applications in renewable technologies such as chemical looping combustion and thermal energy storage. The present research focuses on developing stable materials to be utilized up to 1050 °C in a CLC process and has shown that the structure stability and oxygen transfer capacity can be achieved by tuning the content of different elements on B-sites of the perovskites. Various experiments, such as redox cycling under various fuels, temperatures, and pO2, were carried out to evaluate the oxygen transfer capacity, reaction rates under various fuels, etc. The redox stability at high temperatures was evaluated by redox cycles at 1050 °C followed by post SEM analyses on surface and depth profiling. The three developed materials can avoid phase change during redox due to the moderate oxygen transfer capacity of up to 5.6 wt % O2 for CaMn0.5Ti0.375Fe0.125O3−δ at 1050 °C, which is important for having stable particles. Cation diffusion was also investigated during redox cycling in the development of stable redox materials, and only a minor diffusion of Mn to the grain boundaries is seen in the least stable material. The findings show that perovskites with high stability can be obtained with more Ti on B-sites, termed as CaMn0.375Ti0.5Fe0.125O3−δ. The developed stable oxides, to some extent, have a reduced activity compared to the less stable composition with less Ti and more Mn, termed as CaMn0.5Ti0.375Fe0.125O3−δ, which possesses a higher oxygen release to inert ca. 1.1 wt % O2 compared to more stable CaMn0.375Ti0.5Fe0.125O3−δ that can release up to 0.8 wt % O2. Two of the materials have faster kinetics than ilmenite by a factor of 2 in H2.publishedVersio

Evaluation of two CaMn1−x−yTixFeyO3−δ-based granules oxygen carriers for chemical looping applications

Upscaling of the laboratory oxygen carriers while keeping comparable performance as laboratory powders remains a challenge in the field of chemical looping combustion (CLC). In this work, two perovskite compositions of CaMn0.375Ti0.5Fe0.125O3 (termed CMTF8341) and CaMn0.5Ti0.375Fe0.125O3 (CMTF8431) have been fabricated by means of spray granulation. The fabricated granules were evaluated by redox cycles under CLC conditions and showed comparable performance with laboratory-prepared powders, i.e. high oxygen transfer capacity and fast redox kinetics. Under chemical looping oxygen uncoupling (CLOU) conditions, it has been found that steam leads to a slower kinetics and lower oxygen transfer capacity for these two compositions. When it comes to sulphur effect on the oxygen carriers, redox cycles with deep reduction showed no influence with H2S since the CaSO4 formed in air decompose but it affected the materials under mild CLOU due to calcium sulphate formed under such condition. Nonetheless, redox performance can be recovered by deep reduction with an enhanced oxygen capacity. These two oxygen carriers showed no degradation as compared to other tested minerals in the field of CLC. Microstructure analyses from SEM showed high degree of structure integrity after redox cycles at temperatures up to 1050 °C for the CMTF8341. Good mechanical strength was evidenced from cold attrition test, and the lifetime of the two granules was also predicted based on a standard reference.publishedVersio

Materials challenges in hydrogen-fuelled gas turbines

With the increased pressure to decarbonise the power generation sector several gas turbine manufacturers are working towards increasing the hydrogen-firing capabilities of their engines towards 100%. In this review, we discuss the potential materials challenges of gas turbines fuelled with hydrogen, provide an updated overview of the most promising alloys and coatings for this application, and highlight topics requiring further research and development. Particular focus is given to the high-temperature oxidation of gas turbine materials exposed to hydrogen and steam at elevated temperatures and to the corrosion challenges of parts fabricated by additive manufacturing. Other degradation mechanisms such as hot corrosion, the dual atmosphere effect and hydrogen diffusion in the base alloys are also discussed.acceptedVersio

Perovskite oxygen carrier with chemical memory under reversible chemical looping conditions with and without SO2 during reduction

Oxygen carrier materials (OCM) are usually exposed to sulfur-contained gases in the fuel reactor for chemical looping combustion. This work provides both experimental and model work to understand the SO2 effect on the heterogeneous redox kinetics of a CaMn0.375Ti0.5Fe0.125O3-δ-based perovskite oxygen carrier. The cycle reactivity and redox kinetics under reducing conditions were conducted with and without SO2 in a micro-fluidized bed thermogravimetric analysis technology (MFB-TGA). The redox kinetic behaviors were simulated by a bubbling fluidized bed reactor model coupled with a two-stage kinetic model. The SO2 can react with the perovskite to increase the oxygen transfer capacity from 4 wt% to 5 wt%. When the temperature is higher than 1173 K, SO2 has almost no effect on the H2 reduction reactivity, while the oxidation reactivity decreases by 50%, but the oxidation is still fast enough to achieve 4 wt% capacity within 8 s. When the temperature is lower than 1173 K, there is a significant sulfur-poisoning effect during oxidation and reduction. The analyses of XRD, SEM-EDS, and in-situ DRIFTS indicated that most of the absorbed sulfur mainly existed in the sulfate/sulfide shell on the particle surface. The chemical kinetics and physical structure of CaMn0.375Ti0.5Fe0.125O3-δ perovskite can be completely recovered in the absence of SO2, and this perovskite oxygen carrier is chemically memorable and reversible in its solid structure. The fundamental understanding of the sulfur effect on the redox kinetics and solid structure of the perovskite oxygen carrier provides a new insight to the material development and corresponding reaction mechanisms.acceptedVersio

Sosial kapital blant marginaliserte

Begrepet sosial kapital i moderne samfunnsvitenskap er knyttet til en sentral idé i sosialt arbeid – at sosiale relasjoner og nettverk representerer ressurser som kan hjelpe folk videre i livet. I forskningen er denne forestillingen så sterk at kontakt med familie, venner og naboer ofte brukes som indikator på ressurser. I denne artikkelen skilles det mellom nettverk og ressurser og belyses hvilke ressurser som finnes i det sosiale nettverket til brukerne av Frelsesarmeen og Kirkens Bymisjons tjenester. Undersøkelsen viser at brukerne har mye kontakt med venner, men lite med familien. Deres nettverk gir tilgang til ressurser som kan hindre ytterligere marginalisering, mens de har færre sosiale relasjoner som gir tilgang til ressurser som kan bidra til at de bedrer sin situasjon

Integration of chemical looping oxygen production and chemical looping combustion in integrated gasification combined cycles

Abstract Energy penalty is the primary economic challenge facing CO2 capture technology. This work aims to address this challenge through a novel power plant configuration, capable of achieving 45.4% electric efficiency from coal with a 95% CO2 capture efficiency. The COMPOSITE concept integrates chemical looping oxygen production (CLOP) and packed bed chemical looping combustion (PBCLC) reactors into an integrated gasification combined cycle (IGCC) power plant. Hot gas clean-up technology is implemented to boost plant efficiency. When commercially available cold gas clean-up technology is used, the plant efficiency reduces by 2%-points, but remains 2.3%-points higher than a comparative PBCLC-IGCC power plant and 8.1%-points higher than an IGCC power plant with pre-combustion CO2 capture. It was also shown that the COMPOSITE power plant performance was not sensitive to changes in the performance of the CLOP reactors, implying that uncertainties related to this novel process component do not reduce the potential of the COMPOSITE concept. The outstanding efficiency obtained for this concept is made possible by a complex and highly integrated plant configuration, whose operability and techno-economic feasibility must be demonstrated

Industry-scale production of a perovskite oxide as oxygen carrier material in chemical looping

How to upscale the production of oxygen carrier particles from laboratory level to industrial level is still challenging in the field of chemical looping. The upscaled oxygen carrier must maintain its physical and chemical properties. In the present contribution, a spray drying granulation protocol was developed to produce a perovskite oxygen carrier (CaMn0.5Ti0.375Fe0.125O3-δ) at an industrial scale. The micro-fluidized bed thermogravimetric (MFB-TGA) experiments were performed to measure the oxygen uncoupling and redox reaction kinetics under the fluidization state with enhanced heat and mass transfer, and the obtained experimental data at different temperatures were fitted by a fluidized-bed reactor coupled with a semi-empirical kinetic model. The physical and chemical properties of granulates were compared with those of the same perovskite composition prepared at the laboratory level. The results show the volume fraction of particle size at 75–500 μm is greater than 90% for the upscaled granulats, and the particles show no degradation in reactivity and no agglomeration for more than 20 redox cycles at high temperatures. The heterogeneous reaction rates are high, especially for the oxidation, e.g. it only spent ∼ 5 s to achieve full oxidation. Low attrition index of 3.74 wt% was found after the five-hour attrition test. The industrial-scale particles possess similar chemical and physical properties as the laboratory-scale particles with regards to the reaction kinetics, attrition index, crystalline phase, etc. The required bed inventories and fan energy consumption were finally estimated and found to be lower than other oxygen carriers reported in the literature.acceptedVersio

Oxygen production at intermediate temperatures using Ca2AlMnO5+δ double perovskite-type oxides

Double-perovskite Ca2AlMnO5+δ exhibits promising oxygen uptake and release capacity at intermediate temperatures (400–700 °C), which makes it an interesting candidate for in situ oxygen production in an integrated gasification combined cycle (IGCC) process. Experiments were conducted at 10 bars by alternating gas feeds of air and various sweep gases to a packed bed filled with 300 g of granular oxygen carrier materials. These realistic operating conditions demonstrated that 15–20% oxygen can be introduced to the sweep gas, which is sufficient for autothermal gasification of solid fuels in IGCC. Argon performed slightly better than CO2 as a sweep gas, presumably because of some CO2 absorption or the higher O2 partial pressure of CO2 that inhibited O2 release. Further O2 concentration increases can be expected from increasing the temperature under reduction by feeding a fuel gas to combust with the released O2, but experiments with H2 did not produce the desired effect because the combustion reaction was too slow at the optimal reactor temperature (~ 600 °C). In general, the reduction stage was more prone to kinetic limitations, as illustrated by a significant decrease in O2 concentration when the sweep flowrate was increased. A longer oxidation stage to fully charge the oxygen carrier also increased O2 concentrations in the sweep, but this requires a process integration such as IGCC where the large quantity of warm depleted air can be effectively utilized. Furthermore, the enthalpy of oxidation of Ca2AlMnO5+δ was obtained from density functional theory modeling, equilibrium conditions in thermogravimetric analysis, packed bed experiments and directly from differential scanning calorimetry. The enthalpy of oxidation obtained by these techniques range from − 166 to − 196 kJ mol−1 O2.publishedVersio