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- Baina, Fabiola, et al.
(författare)
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Analysis of a high-temperature heat exchanger for an externally-fired micro gas turbine
- 2015
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 75, s. 410-420
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Tidskriftsartikel (refereegranskat)abstract
- The externally-fired gas turbine (EFGT) can convert fuels such as coal, biomass, biomass gasification gas and solar energy into electricity and heat. The combination of this technology with biomass gasification gas represents an interesting option for gasification, for which it has been difficult to find a conversion technology. In this system, the heat exchanger deals with the contaminants of biomass derived gas instead of the turbine itself. However, these contaminants can build a deposit layer in the heat exchanger that can affect its performance. The heat exchanger is important in externally fired gas turbines since the turbine inlet temperature is directly dependent on its performance. Several studies on heat exchangers for externally fired gas turbines have been carried out. However, very few detailed studies were found comparing the performance of heat exchangers for externally fired gas turbines considering the effect of deposit materials on the surfaces. In this regard, this work compares the performance of a corrugated plate heat exchanger and a two-tube-passes shell and tube heat exchanger considering the effect of thickness of deposit material with different thermal conductivities on pressure drop and effectiveness. The results show that the effectiveness of the corrugated plate heat exchanger is more influenced at larger thicknesses of deposit materials than the two-tube-passes shell and tube heat exchanger. There is an exponential increase in the pressure drop of the plate heat exchanger while a monotonic increase of pressure drop is seen for the shell and tube heat exchanger. The increase in the thickness of the deposit material has two effects. On one hand, it increases the resistance to heat transfer and on the other hand, it reduces the through flow area increasing the velocity and hence the heat transfer coefficient. Additionally, the effectiveness of the heat exchangers had a stronger influence on the power output than the pressure drop.
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| 2. |
- Baina, Fabiola, et al.
(författare)
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Effect of the fuel type on the performance of an externally fired micro gas turbine cycle
- 2015
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 87, s. 150-160
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Tidskriftsartikel (refereegranskat)abstract
- Externally fired gas turbines open the possibility of using fuels of lower quality than conventional gas turbines and internal combustion engines. This is because in externally fired gas turbines, the flue gases heat the compressed air in a high temperature heat exchanger. This heat exchanger can more easily deal with contaminants present in the flue gases. In this regard, the configuration of externally fired gas turbines represents an interesting option for biomass gasification gas. The contaminants and low heating value (LHV) of this fuel have made it difficult to find a conversion technology for heat and power generation. For this reason, it is important to study the influence of biomass derived gas as fuel on the performance of this system and consider the effects of the contaminants in the high temperature heat exchanger. This is studied in this work through simulations using Aspen Plus and Matlab. The test data of an externally fired micro gas turbine prototype was used to validate the simulation. The fuel considered was biomass gasification gas with varying concentrations of benzene 100, 10 and 1 g/Nm3 (hereafter named m100, m10, and m1 respectively). Additionally, mixtures of biomass derived gas and methane were studied for 10 and 50% of the thermal power of the combustor. The fuel inlet temperature to the combustor varied from 150 °C to 750 °C in order to represent the fuel gas after removal of particles by a cyclone and a filter. The results showed that the electrical power output increases when high fuel inlet temperatures to the combustor are used. Additionally, although it would be expected that fuels with higher LHV (lower heating value) show higher temperatures and higher output power, this does not always occur because of the composition of the fuels and their respective flue gas temperatures. The addition of methane does not have a large effect on the electrical power output. For a fixed temperature limit in the heat exchanger, the composition of the fuels does not play an important role. However, high fuel inlet temperatures to the combustor show slightly higher efficiencies. Additionally, the effect on the electrical power output of increasing the pressure drop as a result of increased thickness of deposit materials in the heat exchanger was analyzed.
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| 3. |
- Baina, Fabiola, et al.
(författare)
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Extended operability of a commercial air-staged burner using a synthetic mixture of biomass derived gas for application in an externally fired micro gas turbine
- 2015
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 150, s. 664-671
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Tidskriftsartikel (refereegranskat)abstract
- Biomass gasification converts solid biomass into a gaseous fuel that is more versatile and can be used in many applications. However, biomass gasification gas contains some contaminants and inert compounds. The contaminants can cause several problems in the downstream equipment and undesirable emissions while the inert compounds can affect the lower heating value of the gas. Because of these characteristics, there have been difficulties in finding a conversion technology using biomass gasification gas for heat and power generation. In this regard, externally fired gas turbines open a possibility for this combustible gas since due to its configuration, combustion takes place outside the conventional gas turbine cycle. For this reason, combustion studies of biomass derived gas are important. In this work the operability of a commercial air-staged natural gas burner is shown in terms of CO, UHC, and NOX emissions using a synthetic mixture of biomass gasification gas. Two fuel gas mixtures simulating the composition of biomass gasification gas are injected in the combustor. Each fuel gas contains different injection rates of benzene in order to represent tars and to understand their effect on the combustion performance. Additionally, the equivalence ratio is varied in a range of lean conditions in order to find an optimum operation point for the burner studied. The results showed that the presence of polyaromatic hydrocarbons such as benzene reduced the CO concentrations in the exhaust gas while it increased the concentrations of unburned hydrocarbons (UHC) at equivalence ratios lower than 0.68. Additionally, NOX emissions showed a relatively constant trend over the range of equivalence ratios studied for both fuels. It was also observed that NOX emissions increase with the addition of benzene in the fuel gas. An optimum point with regards CO and UHC concentrations was found for the fuels tested.
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| 9. |
- Myléus, Anna, MD PhD, et al.
(författare)
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Questionnaire showed that Swedish paediatric clinics complied well with the revised European guidelines for diagnosing coeliac disease
- 2019
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Ingår i: Acta Paediatrica. - : John Wiley & Sons. - 0803-5253 .- 1651-2227. ; 108:6, s. 1140-1143
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Tidskriftsartikel (refereegranskat)abstract
- Aim: In 2012, revised criteria for diagnosing childhood coeliac disease were published by the European Society for Paediatric Gastroenterology, Hepatology and Nutrition and incorporated into the revised Swedish guidelines the same year. These made it possible, in certain cases, to diagnose coeliac disease without taking small bowel biopsies. This survey assessed the extent to which the new guidelines were implemented by Swedish paediatric clinics two years after their introduction.Methods: In October 2014, we distributed a paper questionnaire including five questions on diagnostic routines to the 40 paediatric clinics in university or regional hospitals in Sweden that perform small bowel biopsies.Results: All 36 (90%) clinics that responded used anti-tissue transglutaminase antibodies as the initial diagnostic test and some also used serological markers. Most clinics (81%) used endoscopy and took multiple duodenal biopsies, whereas only a few (19%) occasionally employed a suction capsule. Almost all clinics (86%) omitted taking small bowel biopsies in symptomatic children with repeatedly high coeliac serology and positive genotyping, thereby avoiding the need for invasive endoscopy under anaesthesia.Conclusion: The 2012 Swedish Paediatric Coeliac Disease Diagnostic Guidelines had been widely accepted and implemented in routine health care two years after their introduction.
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| 10. |
- Ruiz-Puerta, Emily J., et al.
(författare)
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Holocene deglaciation drove rapid genetic diversification of Atlantic walrus
- 2023
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Ingår i: Proceedings of the Royal Society B: Biological Sciences. - 1471-2954. ; 290:2007, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Rapid global warming is severely impacting Arctic ecosystems and is predicted to transform the abundance, distribution and genetic diversity of Arctic species, though these linkages are poorly understood. We address this gap in knowledge using palaeogenomics to examine how earlier periods of global warming influenced the genetic diversity of Atlantic walrus (Odobenus rosmarus rosmarus), a species closely associated with sea ice and shallow-water habitats. We analysed 82 ancient and historical Atlantic walrus mitochondrial genomes (mitogenomes), including now-extinct populations in Iceland and the Canadian Maritimes, to reconstruct the Atlantic walrus’ response to Arctic deglaciation. Our results demonstrate that the phylogeography and genetic diversity of Atlantic walrus populations was initially shaped by the Last Glacial Maximum (LGM), surviving in distinct glacial refugia, and subsequently expanding rapidly in multiple migration waves during the late Pleistocene and early Holocene. The timing of diversification and establishment of distinct populations corresponds closely with the chronology of the glacial retreat, pointing to a strong link between walrus phylogeography and sea ice. Our results indicate that accelerated ice loss in the modern Arctic may trigger further dispersal events, likely increasing the connectivity of northern stocks while isolating more southerly stocks putatively caught in small pockets of suitable habitat.
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