| 1. |
- Andersson, Jan-Olof, et al.
(författare)
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Improved energy efficiency in juice production through waste heat recycling
- 2013
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Ingår i: International Conference on Applied Energy, ICAE 2013.
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Konferensbidrag (refereegranskat)abstract
- The global demand for Nordic wild berries has increased steadily, partly due to their healthy properties and their good taste. Juice concentrate is produced by pressing berries and heating up the juice. The by-products are berry skins and seeds. Traditionally, the by-products have been composted. Higher competiveness can be achieved by decreasing the production cost and increasing the product values. The berry skins and seeds have a commercial value since they are rich in vitamins and nutrients. To use and sell these by-products, they need to be separated from each other and dried to a moisture content of less than 10 %wt. A berry juice industry in the north of Sweden has been studied in order to increase the energy and resource efficiency and optimize the quality and yield of different berry fractions. This was done by means of process integration with thermodynamics and psychrometry along with measurements of the berry juice production processes. Our calculations show that the drying system could be operated at full without any external heat supply. This could be achieved by increasing the efficiency of the dryer by recirculating 80 % of the drying air and by heating the air with heat from the flue gases from the industrial boiler. This change would decrease the need for heat in the dryer with about 64 %. The total heat use for the plant could thereby be decreased from 1204 kW to 1039 kW. The proposed changes could be done without compromising the production quality or the lead time.
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| 2. |
- Elfgren, Erik, et al.
(författare)
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Exergy as a means for process integration in an integrated steel plant
- 2011
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Konferensbidrag (refereegranskat)abstract
- The Luleå energy system consists of SSAB (an integrated steel plant) – LuleKraft (the heat and power plant) – Luleå Energi (the district heating network). The exergy flows in the whole system have been studied and some possibilities on how to reduce the exergy losses are discussed. The exergy thermal efficiency of SSAB, LuleKraft and Luleå Energi are 70 %, 40 % and 30 % respectively. The relatively low exergy thermal efficiencies is a natural consequence of converting high-value chemical energy into heating water. In the integrated steel plant, the exergy losses are caused by the cooling of the steel prior to transport. In the heat and power plant, exergy is destroyed mainly in the furnace. In the district heating, exergy is destroyed mainly by the customer. A preliminary conclusion is that a lot of exergy is destroyed and lost in order to produce hot water, which doesn’t really need so much exergy. By lowering the water temperature of the district heating, a larger portion of the exergy can be converted to high-value electricity. Mapping by combined Exergy/energy analysis is important to find ways to improve energy efficiency. It can also be important to initiate regional energy collaboration.
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| 3. |
- Elfgren, Erik, et al.
(författare)
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Possibility to Combine Exergy with other Process Integration Methods for a Steelmaking Case
- 2010
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Ingår i: PRES 2010, 13th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction. - : AIDIC Servizi S.r.l.. - 9788895608051 ; , s. 1375-1380
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Konferensbidrag (refereegranskat)abstract
- The energy system of Luleå consists of the steel plant, a local CHP using process gases from the plant and the district heating system. Process integration work to improve the efficiency of the system is presently carried out by mathematical programming using a MILP tool (reMIND). Further improvements would need an improved possibility of the tool to consider the thermodynamic quality of the energy flows. This project aims to include exergy parameters in the node equations and object functions. This has been carried out for a test case, including a part of the system. Programming principles and some results are described.
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| 4. |
- Grip, Carl-Erik, et al.
(författare)
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Possibilities and problems in using exergy expressions in process integration
- 2011
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Ingår i: Proceedings of the World Renewable Energy Congress 2011 (WREC 2011), 9-13 May, Linköping.. - Linköping : Linköping University Electronic Press. ; , s. 1605-1612
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Konferensbidrag (refereegranskat)abstract
- Industrial energy systems are complicated networks, where changes in one process influence its neighboring processes. Saving energy in one unit does not necessarily lead to energy savings for the total system. A study has been carried out on the possibility to use the exergy concept in the analysis of industrial energy systems. The exergy concept defines the quality of an amount of energy in relation to its surrounding, expressing the part that could be converted into work. The study consists of literature studies and general evaluations, an extensive case study and an interview study. In the latter it was found that non technical factors are major obstacles to the introduction of exergy.
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| 5. |
- Agredo Chavez, Angelica Maria, et al.
(författare)
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Cracking and Fatigue of Heavy Loaded Prestressed Concrete Bridge in Sweden
- 2022
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Ingår i: IABSE Symposium Prague 2022: Challenges for Existing and Oncoming Structures - Report, International Association for Bridge and Structural Engineering. - Zürich : International Association for Bridge and Structural Engineering. ; , s. 792-799
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Konferensbidrag (refereegranskat)abstract
- A prestressed concrete bridge was built in 1963 with BBRV cables. It has three spans and a total length of 134.8 m. Due to mining activities the bridge was loaded with trucks with a total weight of 90 ton during 2012-2014 and from 2019. Crack development has been monitored manually and from 2020 with strain gauges and LVDTs.Cracks normally vary between 0.1 to 0.3 mm in width and grow in length with time. In November 2020 some of the strain gauges on the concrete showed alarming growth and the bridge was closed for traffic. Additional strain gauges were installed on vertical reinforcement bars and an assessment was carried out of the fatigue capacity of the bridge. It was found that the new strain gauges did not indicate any growth in strain and that the fatigue capacity was sufficient. The bridge could be opened again for traffic after being closed for five weeks. Monitoring drift in the strain gauges and fatigue are discussed.
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| 6. |
- Andersson, Jan-Olof, et al.
(författare)
-
Improved energy efficiency in juice production through waste heat recycling
- 2014
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 130:S1, s. 757-763
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Tidskriftsartikel (refereegranskat)abstract
- Berry juice concentrate is produced by pressing berries and heating up the juice. The by-products are berry skins and seeds in a press cake. Traditionally, these by-products have been composted, but due to their valuable nutrients, it could be profitable to sell them instead. The skins and seeds need to be separated and dried to a moisture content of less than 10 %wt (on dry basis) in order to avoid fermentation. A berry juice plant in the north of Sweden has been studied in order to increase the energy and resource efficiency, with special focus on the drying system. This was done by means of process integration with mass and energy balance, theory from thermodynamics and psychrometry along with measurements of the juice plant. Our study indicates that the drying system could be operated at full capacity without any external heat supply using waste heat supplied from the juice plant. This would be achieved by increasing the efficiency of the dryer by recirculation of the drying air and by heat supply from the flue gases of the industrial boiler. The recirculation would decrease the need of heat in the dryer with about 52%. The total heat use for the plant could thereby be decreased from 1262 kW to 1145 kW. The improvements could be done without compromising the production quality.
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| 7. |
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| 8. |
- Broms, Carl Erik, et al.
(författare)
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Skruvförankringar i maskinfundament
- 1983
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Ingår i: Byggmästaren. - 0007-7550. ; 62:9, s. 25-28
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 9. |
- Elfgren, Christina, et al.
(författare)
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Subjective experience of memory deficits related to clinical and neuroimaging findings.
- 2003
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Ingår i: Dementia and Geriatric Cognitive Disorders. - : S. Karger AG. - 1420-8008 .- 1421-9824. ; 16:2, s. 84-92
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to evaluate cognitive impairment, psychiatric symptoms and cerebral blood flow (CBF) patterns in middle-aged (35–64 years) and younger old patients (65–74 years) with subjective experience of memory deficits. The study group was heterogeneous with patients fulfilling criteria for dementia, as well as patients with mild cognitive impairment (MCI) and with non-verified cognitive impairment (non-MCI). Seventy per cent of the non-MCI patients reported long-lasting experiences of psychosocial stress tentatively causing the memory problems. The MCI patients were subdivided into two groups: MCI type 1 included patients with isolated memory impairment, while MCI type 2 included patients with memory impairment together with slight verbal and/or visuospatial impairments. CBF measurements comparing the two MCI groups with the non-MCI group were performed. The MCI type 2 showed reduced CBF in the left anterior medial temporal lobe as well as in parts of the posterior cingulate gyrus. The CBF pattern in MCI type 2 concurs with the pathophysiological process of Alzheimer’s disease. The results indicate that it is important to make a subdivision of MCI patients regarding the presence of isolated memory impairments or memory impairments together with other slight cognitive deficits.
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| 10. |
- Elfgren, Erik
(författare)
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Cosmic dust and heavy neutrinos
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Doctoral thesis treats two subjects. The first subject is the impact of early dust on the cosmic microwave background (CMB). The dust that is studied comes from the first generation of stars, which were hot and short-lived, ending their lives as giant supernovae. In the supernova explosions, heavy elements, produced through the fusion in the stars, were ejected into the interstellar medium. These heavy elements condensed to form dust, which can absorb and thus perturb the CMB radiation. The dust contribution to this radiation is calculated and found negligible. However, since the dust is produced within structures (like galaxy clusters), it will have a spatial correlation that could be used to detect it. This correlation is calculated with relevant assumptions. The planned Planck satellite could eventually detect and thus confirm this correlation. The second subject is heavy neutrinos and their impact on the diffuse gamma ray background. Neutrinos heavier than M_Z /2 ~ 45 GeV are not excluded by particle physics data. Stable neutrinos heavier than this might contribute to the cosmic gamma ray background through annihilation in distant galaxies as well as to the dark matter content of the universe. The evolution of the heavy neutrino density in the universe is calculated as a function of its mass, M_N, and then the subsequent gamma ray spectrum from annihilation of distant N-Nbar (from 0 < z < 5). The evolution of the heavy neutrino density in the universe is calculated numerically. In order to obtain the enhancement due to structure formation in the universe, the distribution of N is approximated to be proportional to that of dark matter in the GalICS model. The calculated gamma ray spectrum is compared to the measured EGRET data. A conservative exclusion region for the heavy neutrino mass is 100 to 200 GeV, both from EGRET data and our re-evalutation of the Kamiokande data. The heavy neutrino contribution to dark matter is found to be at most 15%. Finally, heavy neutrinos are considered within the context of a preon model for composite leptons and quarks, where such particles are natural. The consequences of these are discussed, with emphasis on existing data from the particle accelerator LEP at CERN. A numerical method for optimizing variable cuts in particle physics is also included in the thesis.
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