| 1. |
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| 2. |
- Göransson, Lisa, 1982, et al.
(author)
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Dispatch modeling of a regional power generation system - Integrating wind power
- 2009
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In: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 34:4, s. 1040-1049
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Journal article (peer-reviewed)abstract
- A modeling tool has been developed which can be used to analyze interaction between intermittent wind power generation and thermal power plant generation in a regional electricity grid system. The model uses a mixed integer programming (MIP) approach to determine the power plant dispatch strategy which yields the lowest systems costs. In the model, each large thermal plant is described separately, including properties such as start-up time, start-up cost and minimum load level. The model is evaluated using western Denmark as a case study.For western Denmark, it is found that the inclusion of start-up performance (i.e. start-up time and related costs) and minimum load level of the power generating units have a significant impact on the results. It is shown that the inclusion of these aspects influences the analysis of the effect of wind power variations on the production patterns of thermal units in the system. The model demonstrates how the introduction of wind power production and associated variations change the dispatch order of the large thermal power plants in the western Denmark system so that the unit with the lowest running costs no longer has the highest capacity factor. It is shown that this effect only is detected if start-up performance and minimum load level limitations are included in the optimization. it can also be concluded that start-up performance and minimum load level must be taken into account if the total system costs and emissions are not to be underestimated. The simulations show that if these aspects are disregarded, both total costs and total emissions of the power system are underestimated, with 5% in the case of western Denmark. Models such as the one developed in this work can be efficient tools to understand the effects of large-scale wind power integration in a power generation system with base load plants.
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| 3. |
- Hansson, Julia, 1978, et al.
(author)
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Co-firing biomass with coal for electricity generation—An assessment of the potential in EU27
- 2009
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In: Energy Policy. - : Elsevier BV. - 0301-4215. ; 37:4, s. 1444-1455
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Journal article (peer-reviewed)abstract
- The European Union aims to increase bioenergy use. Co-firing biomass with coal represents an attractive near-term option for electricity generation from renewable energy sources (RES-E). This study assesses the near-term technical potential for biomass co-firing with coal in the existing coal-fired power plant infrastructure in the EU27 Member States. The total technical potential for RES-E frombiomass co-firing amounts to approximately 50–90 TWh/yr, which requires a biomass supply of approximately 500–900 PJ/yr. The estimated co-firing potential in EU27 amounts to 20–35% of the estimated gap between current RES-E production and the RES-E target for 2010. However, for some member states the national co-firing potential is large enough to fill the national gap. The national biomass supply potential is considerably larger than the estimated biomass demand for co-firing for all member states. About 45% of the estimated biomass demand for co-firing comes from plants located close to the sea or near main navigable rivers and indicates the possibility for biomass import by sea transport. Thus, biomass co-firing has the potential to contribute substantially to the RES-E development in EU27.
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| 4. |
- Hansson, Julia, 1978, et al.
(author)
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The potential for biomass co-firing with coal in EU27
- 2008
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In: Proceedings of the 16th European Biomass Conference & Exhibition - From research to industry and markets, Feria Valencia, Spain, 2-6 June 2008..
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Conference paper (other academic/artistic)abstract
- The European Union (EU) aims to increase the use of bioenergy. An increased production of electricity from renewable energy sources (RES-E) is also being promoted within the EU. Biomass co-firing with coal represents an attractive near-term option for increasing the production of RES-E. This study assesses the near-term technical potential for biomass co-firing with coal in the existing coal-fired power plant infrastructure in the EU27 Member States (MS) and relates the potential to the national EU targets for RES-E by 2010. The possible contribution of RES-E from biomass co-firing to the RES-E target for 2010 for EU27 as a whole (expressed in absolute numbers) is about 10%. However, the contribution from the estimated co-firing potential to the gap between current RES-E levels and the RES-E target for 2010 is about 20-33% for EU27 (depending on assumptions made). For some MS the potential contribution is large enough to fill the gap. Biomass co-firing with coal has the potential to play an important role when increasing the amount of RES-E in EU27. However, considering how little time remains, it is unlikely that co-firing can actually make a considerable contribution to the 2010 RES-E targets.
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| 5. |
- Hjärtstam, Stefan, 1978, et al.
(author)
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Evaluation of gas radiation modeling in oxy-fired furnaces
- 2010
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In: Conference Proceedings; 2010 AIChE Annual Meeting, 10AIChE; Salt Lake City, UT; 7 November 2010 through 12 November 2010. - 9780816910656
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Conference paper (peer-reviewed)abstract
- Oxy-fuel fired furnaces will exhibit combustion conditions different from air-firing and this will have important effects on the radiative properties of the gas. In contrast to nitrogen (N2), carbon dioxide (CO 2) and water vapor (H2O) are strong infrared emitters and the radiative activity of the gas in oxy-fuel combustion is increased compared to air-firing. In an oxy-fired furnace the pressure path-lengths are several times larger than in an air-fired furnace and the ratio of H2O to CO2 can be significantly different. These differences between air and oxy-fuel combustion make the role of radiative heat transfer by gases in oxy-fired combustion different to air-firing, even in cases where the temperature distribution is similar to that of airfired combustion. These aspects are essential for design of oxy-fired furnaces and need to be accounted for when temperature and heat transfer conditions are determined by modeling. In comprehensive combustion models, for example CFD models, it is common to neglect the spectral variations of the gases and to treat the spectrum by a single average, i.e. a gray approximation. Approximate models frequently applied in combustion modeling, such as the Weighted-Sum-of-Gray-Gases (WSGG) model, are not suitable for oxy-fired boilers since their parameters are fitted to pressure path-lengths, and ratios of H2O to CO2, typical for airfired conditions. Different approximations used to account for gaseous radiation in CFD-simulations are investigated: temperature predictions by a gray model and a non-gray formulation of a WSGG model are compared in air- and oxy-fired conditions. The WSGG model used in this work is suitable for oxy-fuel conditions since it accounts for various ratios of H2O to CO 2 and the parameters are fitted to a broad range of pressure path-lengths. The modeled case is a propane flame in Chalmers 100 kW oxy-fuel rig. Two flames with similar temperature distribution are modeled and compared: an oxy-fuel case with 27 vol.% oxygen in the feed gas and an airfired reference case. To support the CFD-results, calculations of the radiative source term are carried out for a domain between two infinite plates with similar temperature and concentration profiles as in the CFD-simulations. In these calculations, the gray model and the non-gray formulation of the WSGG model are compared with a Statistical-Narrow-Band model. In addition, the role of radiative heat transfer is investigated by including soot radiation in the CFD-simulations to give an understanding of the relative importance of gaseous radiation when soot particles are present. It is shown that a use of a non-gray approach is motivated when modeling oxy-fuel combustion since the gray model fails in predicting the source term, which affects the predicted temperature field in CFD calculations. Furthermore, the inclusion of soot radiation is more crucial for the modeled flames than the use of a more rigorous description of the radiative properties of the gaseous components.
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| 6. |
- Johansson, Andreas, et al.
(author)
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Dynamics of furnace processes in a CFB boiler
- 2007
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In: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 62:1-2, s. 550-560
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Journal article (peer-reviewed)abstract
- With the aim of understanding the dynamics of combustion, this work examines simultaneous fluctuations in fluid dynamic parameters and gas composition measured in a CFB furnace operated with coal as a fuel. The fluid dynamic parameters investigated are pressure and air flow entering the furnace. Gas composition was recorded by a zirconia-cell probe and a gas suction probe connected to a mass spectrometer having a high time resolution (10 Hz). The principal fluctuations detected are around I Hz and below 0.3 Hz. The fluctuations below 0.3 Hz mostly originate from variations in the fuel-feed rate. These variations create periods of reducing conditions caused by a momentarily high fuel input accompanied by a pressure rise in the furnace and a reduction of the air feed, which occurs concurrent with the release of an enhanced quantity of volatiles. Modelled pressure fluctuations based on the relation between volatile release and pressure in the furnace give similar pressure fluctuations as the measured pressure fluctuations, with respect to amplitude and characteristic time scale of the fluctuations. There is also a correlation between reducing conditions and the concentration of hydrocarbons. (c) 2006 Elsevier Ltd. All rights reserved.
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| 7. |
- Johansson, Daniella, 1983, et al.
(author)
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Assessment of strategies for CO2 abatement in the European petroleum refining industry
- 2012
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In: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 42:1, s. 375-386
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Journal article (peer-reviewed)abstract
- Petroleum oil refineries account for almost 8% of the total CO2 emissions from industry in the European Union (EU). In this paper, the European petroleum refining industry is investigated and the prospects for future CO2 abatement in relation to associated infrastructure are assessed. A more efficient use of the adjacent infrastructure, e.g., district heating networks, natural gas grids, neighbouring industries, and CO2 transport and storage systems, could provide opportunities for additional CO2 emissions reduction. It is shown that access to infrastructures that can facilitate CO2 abatement varies significantly across countries and between individual refineries. The assessment shows that short-term mitigation options, i.e., fuel substitution and energy efficiency measures, could reduce CO2 emissions by 9-40 MtCO2/year (6-26% of the total refinery emissions). It is further shown that carbon capture and storage offers the greatest potential for more significant emission reductions in the longer term. However, the potential for CO2 capture varies significantly depending on the choice of technology, CO2 source, and scope of implementation (5-80% of the total refinery emissions).
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| 8. |
- Johansson, P., et al.
(author)
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Electricity dependency and CO2 emissions from heating in the Swedish building sector-Current trends in conflict with governmental policy?
- 2006
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In: Energy Policy. - : Elsevier BV. - 0301-4215. ; 34:17, s. 3049-3064
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Journal article (peer-reviewed)abstract
- Coal-condensing power is marginal production in the deregulated Nordic power market and an increase in electricity consumption will therefore result in increased CO2 emissions. One goal of the Swedish energy policy is to reduce the amount of electricity used for heating in the building sector. This paper investigates the potential for reduction in electricity dependency and CO2 emissions from heating, taking the energy infrastructure into account, here defined as the capital stock of the buildings and heating systems together with geographical variations in heat intensity. In order to include the energy infrastructure in the analysis the study is made on a regional level (Southern Sweden) applying a comprehensive database describing the energy infrastructure of the region. The paper compares two scenarios for converting the heating systems of the region: one employing energy savings and with the aim to phase out the oil and most of the electricity used for heating purposes and a second which illustrates the effect if the current trend in the heating market continues. Both scenarios apply commercially available technologies only. From the second scenario it is seen that the current trend-contrary to the aim of the Swedish Governmental policy-shows an increase in electricity dependency for heating, mainly due to a large diffusion of heat pumps, but also due to installations of electrical floor heating and electricity heating systems installed in newly constructed one- and two-dwelling buildings. However, the options proposed in first scenario show that it is possible to reach significant reductions in the electricity dependency due to heating and in corresponding CO2 emissions. An analysis of the age structure of the heating systems shows that the transformation of the heating system is not completed until the year 2025, if new investments for replacement of heating systems are made only provided they have reached their economical life time, and only applying heating technologies which at present are known to be economically competitive. It can be concluded that future policies on transforming the energy system should be based on an analysis that takes the entire energy infrastructure (in this case of heating system) into account (e.g. not directed towards single technologies). More specifically for the region studied, which is considered representative for Sweden as a whole, policies should aim at installing heat pumps to replace electricity heating only in regions with low heat density where district heating is not competitive, in contrary to the present situation where heat pumps replace all types of heating systems.
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| 9. |
- Johansson, P., et al.
(author)
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Primary energy use for heating in the Swedish building sector - Current trends and proposed target
- 2007
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In: Energy Policy. - : Elsevier BV. - 0301-4215. ; 35:2, s. 1386-1404
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Journal article (peer-reviewed)abstract
- One goal of the Swedish energy policy is to reduce the amount of electricity used for heating in the building sector. This means to reduce the primary energy used for heating which in this paper is analyzed in the context of various heating technologies and CO2 emissions. The analysis is applied to a region in Sweden (southern Sweden) for which detailed information on the energy infrastructure (the capital stock of the buildings and heating systems together with geographical variations in heat intensity) is available from a previous work [Johansson, P., Nylander, A., Johnsson, F., 2005. Electricity dependency and CO2 emissions from heating in the Swedish building sector-current trends in conflict with governmental policy? Energy policy] and which is large enough to be assumed representative for Sweden as a whole. The detailed mapping of the energy infrastructure allows a good estimate on the rate at which the energy system can be expected to be replaced with respect to economical lifetime of the capital stock (the year 2025 in this case). Two scenarios are investigated; a: target scenario for which energy savings are employed (e.g. improving climate shell in buildings) and oil and most of the electricity used for heating purposes are phased out and a second for which the current trend in the heating market continues. In the target scenario it is shown that although only applying commercially competitive heating technologies, it is possible to achieve a 47% reduction in primary energy use for heating with a 34% decrease in heat demand together with significant reduction in CO2 emissions. However, the scenario which continues the current trends on the heating market instead yields an increase (of about 10%) in primary energy use (reduction in conversion efficiency) of the heating system of the region over the period studied, in spite of a slight decrease in heat demand (9%, mainly due to energy efficiency measures) as well as in CO2 emissions. In light of the recently proposed introduction of energy performance certification of buildings in Sweden (and in EU), it can be concluded that such a certification system must take into account the primary energy use and local conditions. A politically acceptable way to do so would be to propose municipalities to develop "best strategies" on development of the heating market for various house types and districts within the municipality which can then be included as recommendations in the energy performance certification of the buildings. (c) 2006 Elsevier Ltd. All rights reserved.
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| 10. |
- Johansson, Robert, 1977, et al.
(author)
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THE INFLUENCE OF PARTICLE AND GASEOUS RADIATION IN OXY-FUEL COMBUSTION
- 2011
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In: The 36th International Technical Conference on Clean Coal & Fuel Systems, Clearwater USA, 5-9/6 2011.
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Conference paper (other academic/artistic)abstract
- This work focuses on radiation in oxy-fired conditions. Both gas and particle radiation is modeled in an axi-symmetric cross section of a cylinder and differences between air- and oxy-firing are investigated. The particle radiation is modeled by empirical correlations accounting for spectral properties of coal particles and scattering of the particles is assumed to be isotropic. For the gas radiation, a Statistical-Narrow-Band (SNB) model is applied as reference. Included in the analysis is also a non-gray or banded formulation of the Weighted-Sum-of-Gray-Gases (WSGG) model and grey approximations. The investigated cases cover both air-and oxy-fired conditions and the properties of the combustion gas are based on measured data from a lignite flame in Chalmers 100 kW rig. Wall fluxes and the radiative source term along the cylinder diameter are compared to evaluate differences in the radiative heat transfer between air- and oxy-fuel combustion. Special emphasis is put on the load and distribution of particles, with both in-flame conditions as well as furnace exit conditions being examined. The different approximations for gaseous radiation are evaluated to quantify the errors they result in when they are applied in conditions with a high particle load.
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