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1.
  • Andersson, Maria, 1965-, et al. (författare)
  • Cost-effective incentives for cooperation between participants in the electricity market
  • 1996
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 54:4, s. 301-313
  • Tidskriftsartikel (refereegranskat)abstract
    • In the Swedish electricity system there is a great potential for increasing the cost efficiency of electricity use. Today economic incentives, offered for instance by existing electricity tariffs, are too weak to improve the use of the system. On the Swedish electricity market, there are at least three different participants, the power producer, the distributor and the customer. Today these participants act separately owing to low awareness of the costs for electricity over the year and the day. If the participants are aware of the real electricity costs, cost-effective incentives for cooperation will arise. When participants cooperate, the introduction of end-use measures will reduce system costs for those participants that are involved in cooperation. We present a system analysis for cooperation between distributor and customers. We also present results from a project, where behaviours of an existing distributor and existing customers have been analysed. The results show that there exist cost-effective incentives for cooperation when end-use measures are introduced.
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2.
  • Gebremedhin, Alemayehu, et al. (författare)
  • Optimisation of merged district - heating systems - Benefits of co - operaion in the light of externality costs
  • 2002
  • Ingår i: Applied Energy. - 0306-2619 .- 1872-9118. ; 73:3-4, s. 223-235
  • Tidskriftsartikel (refereegranskat)abstract
    • Studies have shown that separate actors can benefit from co-operation around heat supply. Such co-operation, for example, might be between an industry selling waste heat to a districtheating system or two district-heating systems interconnecting their respective systems. Cooperation could also be expected to reduce the environmental impacts of the energy systems by choosing the plants with the lowest emissions. It is widely accepted that the production of heat and electricity causes damage to the environment. This damage often imposes a cost on society, but not on company responsible. In general, using a broader system perspective when analysing local energy systems results in a lower total cost, more e.cient use of plants and a greater potential for producing electricity in combined heat-and-power (CHP) plants. Internalising the externality costs in the energy system model facilitates the study of what cooperation can mean for reducing emissions. This study shows that co-operation between the two systems is on the whole cost-effective, but the benefits are greater when external costs are not included in the calculation. Considering externality costs in combination with current electricity prices would lead to a higher system cost, but the quantity of emission gases will be lower. If, on the other hand, the calculation is made taking externality costs and corresponding adjusted electricity prices (the adjustment being necessary to compensate for the additional cost due to externality costs) into consideration, the quantities of emission gases will rise because more heat-and-power will be generated by one of the CHP plants. © 2002 Elsevier Science Ltd. All rights reserved.
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3.
  • Gustafsson, Stig-Inge (författare)
  • Climate Influence on District Heat and Electricity Demands
  • 1992
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 42:4, s. 313-320
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper describes the district heating and electricity load of Kalmar, Sweden. Unfortunately, it has not been possible to examine one full year because the monitoring of the energy use for district heating and electricity, and the outdoor temperature, did not exactly overlap. However, more than 7200 h, of the 8760 in a full year, have been examined. It is shown that the district heat load has a far higher correlation with the outdoor temperature (a coefficient of 0·89), than has the electricity load (0·33). Thus, it is much easier to predict the influence of, e.g. an insulation retrofit for the building stock where district heating is used compared with electricity space heating. It is also shown how an estimate can be made of the thermal transmission factor for the total building stock.
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4.
  • Gustafsson, Stig-Inge, et al. (författare)
  • Insulation and Bivalent Heating System Optimization : Residential Housing Retrofits and Time-Of-Use Tariffs for Electricity
  • 1989
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 34:4, s. 303-315
  • Tidskriftsartikel (refereegranskat)abstract
    • Time-of-use tariffs, which reflect the cost of producing one extra unit of electricity, will be more common in the future. In Sweden the electricity unit price will be high during the winter and cheaper during the summer. A bivalent heating system, where an oil-fired boiler takes care of the peak load, when the electricity price is high, and a heat pump the base load, may decrease the cost of space heating substantially. However, insulation retrofits are also likely to reduce the peak space-heating load in a building. This paper shows how a bivalent heating system can be optimized while also considering the insulation measures. The optimization is elaborated by the use of a mixed integer programming model and the result is compared with a derivative optimization method used in the OPERA (optimal energy retrofit advisory) model. Both models use the life-cycle cost (LCC) as a ranking criterion, i.e. when the lowest LCC for the building is achieved, no better retrofit combination exists for the remaining life of the building.
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5.
  • Gustafsson, Stig-Inge, et al. (författare)
  • Is space heating in offices really necessary?
  • 1991
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 38:4, s. 283-291
  • Tidskriftsartikel (refereegranskat)abstract
    • New office buildings in Sweden are thoroughly insulated due to the Swedish building code. This code, however, does not consider the type of activity occurring in the building. This means that the heating equipment is designed as if no activity at all is going on. In modern offices there is a lot of equipment installed which uses electricity. This electricity is converted into heat which can be utilized for heating the premises, mostly in a direct way but also by the use of exhaust-air heat-pumps or heat exchangers. This paper deals with a modern office building plus office hotel complex located in Linköping, Sweden, about 200 km south of Stockholm. The tenants deal with the design of hard- and software for computers. The lighting and computers in the building use electricity which converts into heat. In this paper, it is shown that this electricity is all that is needed during normal conditions, i.e. when people work in the building. The building is also equipped with a district-heating system, which is designed as if no activity goes on in the building, so subsequently the heating equipment is larger than it need be. In this special case, it might have been better to install an electric heating device for hot-water heating and very cold winter conditions, instead of using district heating. This is so even if district heat is about half the unit price compared with that due to the dissipation of electricity. At present, when district heating is used, no measures for saving heat can be profitable due to the low district-heating price. The fact is that the tenants complain of too much heat instead of too little: the prevailing indoor temperature was about 24° C in January 1990 even though 20° C would have been sufficient. There is subsequently a need for a properly working regulation system. The one currently in use is designed to a modern standard, but is not able to maintain temperatures at a modest level.
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6.
  • Gustafsson, Stig-Inge (författare)
  • Mathematical modelling of district-heating and electricity loads
  • 1993
  • Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 46:2, s. 149-159
  • Tidskriftsartikel (refereegranskat)abstract
    • In recent years it has been more common to use linear or mixed-integer programming methods for finding optimal solutions to the complicated operating options in modern Combined Heat and Power (CHP) networks. Electricity may be bought from the national grid or it may be produced in ordinary condenser or CHP plants owned by the utility. In the same manner, district heat can be produced by the use of waste heat from industries or from a CHP plant. Other options are burning garbage in an incineration plant, using heat pumps in a sewage water plant or just burning fuels in an ordinary boiler. Combining these options and including the possibility of using conservation measures in industry or in the housing stock will result in a very complex situation if one tries to find the optimal solution characterized by the the lowest Life-Cycle Cost (LCC). Load management equipment, such as hot-water accumulators, will aggravate the problem even further. By the use of modern computers, complicated problems can be solved within a reasonable period of time. The bases for the mathematical models are the thermal and electrical loads. Splitting these loads into finer and finer segments will yield a model that will depict reality more closely. Two methods have been used frequently, one where the high and low unit price hours in each month have been lumped together, resulting in 24 segments plus one segment showing the influence of the maximum electricity demand. The other method tries to model the loads by lumping the energy demand in six electricity-tariff segments, but also using about 15 elements for a more versatile picture of the district-heating load. This paper describes the two methods using monitored data for 1990-1991 from Kalmar in the south of Sweden. It also discusses which of the methods is preferable or whether a combination must be elaborated upon in order to model reality closely enough for practical use.
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7.
  • Gustafsson, Stig-Inge (författare)
  • Sensitivity analysis of building energy retrofits
  • 1998
  • Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 61:1, s. 13-23
  • Tidskriftsartikel (refereegranskat)abstract
    • When a building is refurbished, energy conservation measures might be profitable to implement. The profitability depends, among other things, on the electricity and district-heating tariffs, the unit price for oil, etc. The cost for the retrofit is of course also important as well as the influence of the retrofit on the demand for heat in the building. By the use of a Mixed Integer Linear Programming model of a building, a number of different optimal retrofit strategies are found depending on the energy cost. The result shows that the Life-Cycle Cost for the building is subject only to small changes as long as the optimal strategies are chosen. Most important is the heating system, while building retrofits such as added insulation, are too expensive to take part in the optimal solution.
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8.
  • Gustafsson, Stig-Inge, et al. (författare)
  • Window Retrofits : Interaction and Life-Cycle Costing
  • 1991
  • Ingår i: Applied Energy. - 0306-2619 .- 1872-9118. ; 39:1, s. 21-29
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper deals with the interaction between different types of building energy retrofits. The means for finding this interaction has been via the OPERA model, which is used for energy retrofit optimization. The solution is an optimum when the total life-cycle cost, LCC, for the building, i.e. the sum of the building, maintenance and operating costs, is minimized. The model finds the candidates for the optimal strategy by calculating the total LCC for one retrofit after another, i.e., an incremental method is used. All the measures are implemented with respect to the building and the resulting LCC is calculated. Usually, the LCC for this combination is higher than the incremental LCC, i.e. the incremental way of calculation overestimates the savings. However, when window retrofits are considered, the opposite might happen due to the use of shading factors. These factors indicate the decrease in solar radiation through a window when an ordinary one is replaced by a window with enhanced thermal performance. The paper also shows that the interaction between the different measures usually can be neglected, as long as optimal retrofits are introduced.
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9.
  • Johansson, Lars, et al. (författare)
  • Energy efficient bio fuel drying with an open absorption system : parameter study in order to reduce investment costs
  • 2000
  • Ingår i: Applied Energy. - 0306-2619 .- 1872-9118. ; 67:3, s. 231-244
  • Tidskriftsartikel (refereegranskat)abstract
    • A pilot plant using the open absorption system for drying of timber and bio fuel has been realized at a sawmill located in the northern part of Sweden. The technique decreases the energy demand for the dryers considerably and the system has an availability of about 8000 h per year. Compared with other drying techniques, the investment cost is high due to large airflow and therefore large apparatus. The main part of the investment cost, i.e. about 70% originates from the bio fuel dryer and the absorbers. In order to decrease the initial cost a parameter study has been made to investigate the possibilities to reduce the airflow of the drying process, i.e. bio fuel dryer and absorber. Parameters studied are drying temperature, salt concentration and cooling of the airflow during the absorption process. Measured values from the pilot plant have been used as a reference case. The results show that it is possible to decreases the airflow by 31% when using a higher drying temperature. Higher salt concentration decreases the airflow by approximately 32% and cooling during absorption makes it possible to decrease the airflow by 50%. In order to minimize the airflow, the three parameters were combined. In this case it is possible to decrease the airflow by approximately 60%. The electrical input for the plant is also high due to large air and solution flows. By decreasing the airflow, the required electrical input will also decrease since the fan power is proportional to the volume airflow. The results clearly show that it is possible to reduce the airflow and therefore the investment costs compared with the pilot plant.
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10.
  • Johansson, Lars, et al. (författare)
  • Energy savings in indoor swimming-pools : comparison between different heat-recovery systems
  • 2001
  • Ingår i: Applied Energy. - 0306-2619 .- 1872-9118. ; 70:4, s. 281-303
  • Tidskriftsartikel (refereegranskat)abstract
    • In indoor swimming-pool facilities, the energy demand is large due to ventilation losses with the exhaust air. Since water is evaporated from the pool surface, the exhaust air has a high water content and specific enthalpy. Because of the low temperature, the heat from the evaporation is difficult to recover. In this paper, the energy demand for the conventional ventilation technique in indoor swimming pools is compared to two different heat-recovery techniques, the mechanical heat pump and the open absorption system. The mechanical heat-pump is the most widely used technique in Sweden today. The open absorption system is a new technique in this application. Calculations have been carried out on an hourly basis for the different techniques. Measurements from an absorption system pilot-plant installed in an indoor swimming pool in the northern part of Sweden have been used in the calculations. The results show that with the mechanical heat pump, the electrical input increases by 63 MWh/year and with the open absorption system 57 MWh/year. However, a mechanical heat-pump and an open absorption system decrease, the annual energy demand from 611 to 528 and 484 MWh respectively, which correspond to decreases of approximately 14 and 20% respectively. The electricity input will increase when using heat-recovery techniques. Changing the climate in the facility has also been investigated. An increased temperature decreases the energy demand when using the conventional ventilation technique. However, when either the mechanical heat-pump or the open absorption system is used, the energy demand is increased when the temperature is increased. Therefore increasing the temperature in the facility when using the conventional technique should be considered the first measure to reduce the energy demand.
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11.
  • Rolfsman, Björn (författare)
  • Combined heat-and-power plants and district heating in a deregulated electricity market
  • 2004
  • Ingår i: Applied Energy. - 0306-2619 .- 1872-9118. ; 78:1, s. 37-52
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, a municipality with district heating supplied via boilers and combined heat-and-power (CHP) plants is studied. The electricity load in the municipality is provided for by the CHP plant and electricity bought from the Nordic electricity market. It is therefore desirable to produce as much electricity as possible during periods when the price of electricity is high. The variations in the price of electricity over a 24-h period are significant. The idea presented in this paper is that heat storage can be used to maximise the amount of electricity produced in the CHP plants during peak-price periods. It can also be used to minimise the use of plants with higher operational costs. For storing heat, both a hot-water accumulator at the CHP plant and storage in the building stock are suggested. The situation is analysed using a mixed integer linear-programming model and a case study is presented for the city of Linköping, a City of approximately 130,000 inhabitants, situated 200 km south of Stockholm in Sweden. A simple model for forecasting the electricity price on the Nordic electricity market is also presented. © 2004 Elsevier Ltd. All rights reserved.
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12.
  • Sjödin, Jörgen, 1970-, et al. (författare)
  • Calculating the marginal costs of a district-heating utility
  • 2004
  • Ingår i: Applied Energy. - 0306-2619 .- 1872-9118. ; 78:1
  • Tidskriftsartikel (refereegranskat)abstract
    • District heating plays an important role in the Swedish heat-market. At the same time, the price of district heating varies considerably among different district-heating utilities. A case study is performed here in which a Swedish utility is analysed using three different methods for calculating the marginal costs of heat supply: a manual spreadsheet method, an optimising linear- programming model, and a least-cost dispatch simulation model. Calculated marginal-costs, obtained with the three methods, turn out to be similar. The calculated marginal-costs are also compared to the actual heat tariff in use by the utility. Using prices based on marginal costs should be able to bring about an efficient resource-allocation. It is found that the fixed rate the utility uses today should be replaced by a time-of-use rate, which would give a more accurate signal for customers to change their heat consumptions.
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13.
  • Söderholm, Patrik, et al. (författare)
  • A utility-eye view of the CO₂ compliance-decision process in the European power-sector
  • 2003
  • Ingår i: Applied Energy. - 0306-2619 .- 1872-9118. ; 75:3/4, s. 183-192
  • Tidskriftsartikel (refereegranskat)abstract
    • The purpose of this paper is to provide a utility eye-view of the European power-sector's CO2-compliance decision process under a tradable emissions scheme. The cost analysis indicates that, in the medium term, many utilities are likely to consider options based on traditional power technologies such as converting existing coal-fired capacity to burn gas, extending the lives of nuclear capacity, and replacing old coal-fired plants with more efficient gas- or even coal-fired units. The long-term economic potential of future options is highly uncertain, and utilities are likely to respond to this by maintaining flexibility in fuel choices and avoid large investments that lock them into a specific compliance method before more efficient and cleaner technologies have crystallized. Given the multitude of possible CO2-mitigation options, there is a strong case for emissions trading and for refraining from policies that build on mandatory fuel-requirements, higher rates of capital stock turnover and technology standards.
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14.
  • Westerlund, Lars, et al. (författare)
  • Absorbers in the open absorption system
  • 1994
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 48:1, s. 33-49
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper describes an experimental study of four different absorber designs in this type of system: cross-current and counter-current packed-absorbers, the spray absorber and fluid-bed absorber. In a laboratory pilot, plant, working lines for the absorbers were determined under adiabatic conditions. The influences of internal solution flow, gas flow, pressure drop and dissipation are discussed. The working lines represent the efficiency for each absorber. The highest performance occurs with the packed-bed absorbers, followed by the fluid-bed absorber and finally the spray absorber. For open absorption systems in air-conditioning applications (small scale) the fluid-bed absorber should be chosen
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15.
  • Westerlund, Lars, et al. (författare)
  • Open absorption system : experimental study in a laboratory pilot plant
  • 1991
  • Ingår i: Applied Energy. - 0306-2619 .- 1872-9118. ; 38:3, s. 215-229
  • Tidskriftsartikel (refereegranskat)abstract
    • The open absorption system is specially fitted in drying processes using air for the transport of the water. Advantages of the system are that different types of energy supply can be used, and that direct contact between the working media and the solution gives an effective absorber. This experimental study concerns measurements of the capacity of the system when a cross-flow absorber is used. Experiments were done under adiabatic and non-adiabatic conditions, and the results show that non-adiabatic conditions give a considerable increase in the absorption capacity. The dissipation of solution media increases strongly for air velocities over 2m/s. However, a demister can be used to reduce these losses. Investigation of the packing depth shows that the absorption takes place mainly in the first quarter of the packing. Different types of plastic packings were studied, the Telpac packing giving the best results.
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16.
  • Westerlund, Lars, et al. (författare)
  • Use of an open absorption heat-pump for energy conservation in a public swimming-pool
  • 1994
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 49:3, s. 275-300
  • Tidskriftsartikel (refereegranskat)abstract
    • A conventional climatization system at a public swimming-pool normally uses outdoor air to remove the moisture from the facility. This practice results in large heat losses. An open absorption heat-pump can dehumidify the outlet air from the building: this makes it possible to recirculate a larger amount of air and so reduce the heating requirement for the facility significantly. Measurements on two types of systems have been performed during approximately 4000 h in a bath house in northern Sweden. In 1990, the use of an open absorption heat-pump decreased the heat supply by 445 MWh (from 742 MWh), while the electricity supply was increased by 233 MWh. The uncertainty in the annual energy saving with the open system can be estimated to be in the range 10-15%. If the present electric energy supply to the generator is replaced by another energy source, for example natural gas, the electricity demand of the absorption system will decrease considerably. The results show that public baths are an interesting application area for the open absorption technique
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17.
  • Abdi, Amir, et al. (författare)
  • Numerical investigation of melting in a cavity with vertically oriented fins
  • 2019
  • Ingår i: Applied Energy. - : ELSEVIER SCI LTD. - 0306-2619 .- 1872-9118. ; 235, s. 1027-1040
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper investigates the effect of vertical fins, as an enhancement technique, on the heat transfer rate and energy density of a latent heat thermal energy storage system. This contributes with knowledge on the interaction of heat transfer surface with the storage material for optimizing storage capacity (energy) and power (heat transfer rate). For the assessment, numerical modeling is employed to study the melting process in a two-dimensional rectangular cavity. The cavity is considered heated isothermally from the bottom with surface temperatures of 55 degrees C, 60 degrees C or 70 degrees C, while the other surfaces are insulated from the surrounding. Aluminum and lauric acid are considered as fin/enclosure material and phase change material, respectively. Vertical fins attached to the bottom surface are employed to enhance the charging rate, and a parametric study is carried out by varying the fin length and number of fins. Thus, a broad range of data is provided to analyze the influence of fin configurations on contributing natural convection patterns, as well as the effects on melting time, enhanced heat transfer rate and accumulated energy. The results show that in addition to increasing the heat transfer surface area, the installation of vertically oriented fins does not suppress the natural convection mechanism. This is as opposed to horizontal fins which in previous studies have shown tendencies to reduce the impact of natural convection. This paper also highlights how using longer fins offers a higher rate of heat transfer and a better overall heat transfer coefficient rather than increasing the number of fins. Also, fins do not only enhance the heat transfer performance in the corresponding melting time, but also maintain similar total amount of stored energy as compared to the no-fin case. This paper discusses how this is the result of the enhanced heat transfer allowing a larger portion of sensible heat to be recovered. For example, in the case with long fins, the relative mean power enhancement is about 200% with merely 6% capacity reduction, even though the amount of PCM in the cavity has been reduced by 12% as compared to the no-fin case. Although the basis for these results stems from the principles of thermodynamics, this paper is bringing it forward with design consideration. This is because despite its importance for making appropriate comparisons among heat transfer enhancement techniques in latent heat thermal energy storage, it has not been previously discussed in the literature. In the end, the aim is to accomplish robust storage systems in terms of power and energy density.
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18.
  • Abrahamsson, Johanna, 1990, et al. (författare)
  • A Raman spectroscopic approach to investigate the production of biodiesel from soybean oil using 1-alkyl-3-methylimidazolium ionic liquids with intermediate chain length
  • 2015
  • Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 154, s. 763-770
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a Raman spectroscopic study of the conversion of soybean oil into biodiesel by methanol using the lipase B enzyme pseudomonas cepacia as the bio-catalyst and 1-alkyl-3-methylimidazolium ionic liquids (CnC1Im) as co-solvents, where the alkyl chain length is varied from ethyl (n=2) to decyl (n=10). We have limited this study to a low reaction temperature, 40°C, and a low enzyme concentration to investigate the possibility of producing biodiesel with low energy and cost demands. We also demonstrate that Raman spectroscopy is a powerful and straightforward method to estimate the yield of the transesterification reaction, by analysis of the characteristic CO stretching mode found in the range ~1730-1750cm-1. Our results indicate that both reaction yield and reaction rate increase with the chain length, but also that for chains longer than decyl further improvements are marginal. We discuss these results from the viewpoint of local interactions and local structure of the investigated ionic liquids.
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19.
  • Abubaker, Jamal, et al. (författare)
  • Biogas residues as fertilisers - Effects on wheat growth and soil microbial activities
  • 2012
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 99, s. 126-134
  • Tidskriftsartikel (refereegranskat)abstract
    • Residues from the biogas process are a relatively new type of organic fertiliser with composition varying with origin of the raw material fed into the biogas process. The performance of four different biogas residues (BRs) was evaluated and compared with that of pig slurry (PS) and mineral fertiliser (NPK) in pots filled with sandy soil and fertilised at rates corresponding to 35,70 and 140 kg NH4+-N ha(-1). After sowing with spring wheat, the pots were incubated in a growth chamber. Total biomass yield and relative yields of ear, straw and root fractions were measured at harvest. Nitrogen mineralisation capacity (NMC) and potential ammonium oxidation rate (PAO) in soil were assessed. The fertilisation based on NH4+-N led to high addition of Tot C, Org N, Tot P, Tot K, Tot Mg and Zn at application of PS compared with BR. Biomass yields generally increased with increasing fertiliser rate but the response varied between the fertilisers. The BR yields compared well with NPK, but PS resulted in significantly higher yields. PS gave lower relative biomass of ears and higher relative biomass of roots compared with BR and NPK. The BR treatment yielding the lowest overall biomass also produced plants with the lowest relative root biomass, but partly compensated for this by increasing the relative ear biomass with increasing fertiliser rate. The NMC and PAO in soil had increased by the end of the experiment in almost all treatments. The high NMC in the PS treatment resulted in calculated mineralised N corresponding to 50-82 kg ha(-1) during the experimental period. In conclusion, fertilisation with biogas residues gave similar biomass yields but increased NMC and PAO in soil compared with NPK. Pig slurry gave the overall highest yields and NMC, but a PAO comparable to most BR. (C) 2012 Elsevier Ltd. All rights reserved.
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20.
  • Acuña, José, 1982-, et al. (författare)
  • Distributed thermal response tests on pipe-in-pipe borehole heat exchangers
  • 2013
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 109:SI, s. 312-320
  • Tidskriftsartikel (refereegranskat)abstract
    • Borehole Thermal Energy Storage systems typically use U-pipe Borehole Heat Exchangers (BHE) having borehole thermal resistances of at least 0.06 K m/W. Obviously, there is room for improvement in the U-pipe design to decrease these values. Additionally, there is a need for methods of getting more detailed knowledge about the performance of BHEs. Performing Distributed Thermal Response Tests (DTRT) on new proposed designs helps to fill this gap, as the ground thermal conductivity and thermal resistances in a BHE can be determined at many instances in the borehole thanks to distributed temperature measurements along the depth. In this paper, results from three heat injection DTRTs carried out on two coaxial pipe-in-pipe BHEs at different flow rates are presented for the first time. The tested pipe-in-pipe geometry consists of a central tube inserted into a larger external flexible pipe, forming an annular space between them. The external pipe is pressed to the borehole wall by applying a slight overpressure at the inside, resulting in good thermal contact and at the same time opening up for a novel method for measuring the borehole wall temperature in situ, by squeezing a fiber optic cable between the external pipe and the borehole wall. A reflection about how to calculate borehole thermal resistance in pipe-in-pipe BHEs is presented. Detailed fluid and borehole wall temperatures along the depth during the whole duration of the DTRTs allowed to calculate local and effective borehole thermal resistances and ground thermal conductivities. Local thermal resistances were found to be almost negligible as compared to U-pipe BHEs, and the effective borehole resistance equal to about 0.03 K m/W. The injected power was found to be almost evenly distributed along the depth.
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21.
  • Ahlström, Johan, et al. (författare)
  • Value chains for integrated production of liquefied bio-SNG at sawmill sites – Techno-economic and carbon footprint evaluation
  • 2017
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 206, s. 1590-1608
  • Tidskriftsartikel (refereegranskat)abstract
    • Industry's increasing demand for liquefied natural gas could be met in the future by liquefied methane produced from biomass feedstock (LBG - liquefied biogas). This study presents results from an investigation of value chains for integrated production of LBG at a generic sawmill site, based on gasification of sawmill waste streams and forest residues. The objective was to investigate the cost for, as well as the carbon footprint reduction associated with, production and use of LBG as a fuel. Five different LBG plant sizes were investigated in combination with three different sawmill sizes. The resulting cases differ regarding biomass feedstock composition, biomass transportation distances, LBG plant sizes, how efficiently the excess heat from the LBG plant is used, and LBG distribution distances. Pinch technology was used to quantify the heat integration opportunities and to design the process steam network. The results show that efficient use of energy within the integrated process has the largest impact on the performance of the value chain in terms of carbon footprint. The fuel production cost are mainly determined by the investment cost of the plant, as well as feedstock transportation costs, which mainly affects larger plants. Production costs are shown to range from 68 to 156 EUR/MW hfuel and the carbon footprint ranges from 175 to 250 kg GHG-eq/MW hnet biomass assuming that the product is used to substitute fossil LNG fuel. The results indicate that process integration of an indirect biomass gasifier for LBG production is an effective way for a sawmill to utilize its by-products. Integration of this type of biorefinery can be done in such a way that the plant can still cover its heating needs whilst expanding its product portfolio in a competitive way, both from a carbon footprint and cost perspective. The results also indicate that the gains associated with efficient heat integration are important to achieve an efficient value chain.
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22.
  • Akbilgic, O., et al. (författare)
  • A meta-analysis of carbon capture and storage technology assessments: Understanding the driving factors of variability in cost estimates
  • 2015
  • Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 159, s. 11-18
  • Tidskriftsartikel (refereegranskat)abstract
    • The estimated cost of reducing carbon emissions through the deployment of carbon capture and storage (CCS) in power systems vary by a factor of five or more across studies published over the past 8 years. The objective of this paper is to understand the contribution of techno-economic variables and modeling assumptions to explain the large variability in the published international literature on cost of avoided CO2 (CACO2) using statistical methods. We carry out a meta-analysis of the variations in reported CACO2 for coal and natural gas power plants with CCS. We use regression and correlation analysis to explain the variation in reported CACO2. The regression models built in our analysis have strong predictive power (R2 > 0.90) for all power plant types. We find that the parameters that have high variability and large influence on the value of CACO2 estimated are levelized cost of electricity (LCOE) penalty, capital cost of CCS, and efficiency penalty. In addition, the selection of baseline technologies and more attention and transparency around the calculation of capital costs will reduce the variability across studies to better reflect technology uncertainty and improve comparability across studies.
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23.
  • Akhtar, Farid, et al. (författare)
  • Colloidal processing and CO2 capture performance of sacrificially templated zeolite monoliths
  • 2012
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 97, s. 289-296
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Sacrificial templating of suspension cast and subsequently thermally treated zeolite monoliths with glassy carbon spheres and fibers yielded zeolite 13X and silicalite-1 monoliths with macroporosities up to 50 vol%. Homogeneous distribution of the macroporosity in hierarchically porous monoliths was obtained by tailoring the surface chemistry of the carbon particles by polyelectrolyte-assisted adsorption of zeolite particles. The effect of amount of kaolin binder and temperature for the thermal treatment on the monoliths strength, surface area and CO2 uptake was studied by diametral compression tests, electron microscopy, X-ray diffraction and gas adsorption. Cyclic adsorption and regeneration measurements showed that zeolite 13X monoliths display a high CO2 uptake while the silicalite-1 monoliths could be regenerated with a relatively low energy penalty.
  •  
24.
  • Alamia, Alberto, 1984, et al. (författare)
  • Well-to-wheel analysis of bio-methane via gasification, in heavy duty engines within the transport sector of the European Union
  • 2016
  • Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 170, s. 445-454
  • Tidskriftsartikel (refereegranskat)abstract
    • Bio-methane from biomass gasification (bio-methane) is expected to play a major role as a biofuel in the heavy transport sector, since the production process has reached the technical maturity required for large-scale exploitation, and the fact that bio-methane can be distributed through the compressed natural gas (CNG) and liquefied natural gas (LNG) supply chains. Assuming that the burning of biomass is climate-neutral, we compared the well-to-wheel (WtW) emissions from the use of bio-methane in heavy duty engines with those from currently used fossil alternatives: CNG, LNG, and diesel. The well-to-tank (WtT) analysis of bio-methane is based on the case study of the new GoBiGas plant in Gothenburg (Sweden), which is the largest bio-methane plant in the world currently in operation. Finally, tank-to-wheel (TtW) section compares three different state-of-the-art heavy duty gas engines: a spark-ignited (SI) gas engine; a dual fuel (DF) engine; and a high-pressure direct injection (HPDI) engine.The WtT emissions for compressed bio-methane (bio-CNG) and liquefies bio-methane (bio-LNG) were estimated at 21.5 [gCO2e/MJbioCNG] and 26.2 [gCO2e/MJbioLNG]. As compared to diesel the WtW emissions from bio-methane were reduced by 60-67%, 43-47%, and 64% when used in SI, DF, and HPDI engines, respectively. HPDI and DF are the most efficient technologies for the utilization of biomass, reducing emissions by 39 gCO2e and 33-36 gCO2e per MJ of biomass, respectively, compared with the diesel case, whereas the SI engine gave an emissions saving of 29-31 gCO2e.
  •  
25.
  • Amiri, Shahnaz, et al. (författare)
  • Possibilities and consequences of deregulation of the European electricity market for connection of heat sparse areas to district heating systems
  • 2010
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 87:7, s. 2401-2410
  • Tidskriftsartikel (refereegranskat)abstract
    • The objective of the study is to analyse the conditions for connection of residential buildings in heat sparse areas to district heating systems in order to increase electricity production in municipal combined heat and power plants. The European electricity market has been assumed to be fully deregulated. The relation between connection of heat sparse areas, increased electricity and heat production as well as electricity prices, fuel prices and emissions rights is investigated. The results of the study show that there is potential to expand the district heating market to areas with lower heat concentrations in the cities of Gavle, Sandviken and Borlange in Sweden, with both economic and environmental benefits. The expansion provides a substantial heat demand of approximately 181 GWh/year, which results in an electricity power production of approximately 43 GWh/year. Since the detached and stand-alone houses in the studied heat sparse areas have been heated either by oil boiler or by direct electricity, connection to district heating also provides a substantial reduction in emissions of CO(2). The largest reductions in CO(2) emissions are found to be 211 ktonnes/year assuming coal-fired condensing power as marginal electricity production. Connection of heat sparse areas to district heating decrease the system costs and provide a profitability by approximately 22 million EURO/year for the studied municipalities if the price of electricity is at a European level, i.e. 110 EURO/MWh. Sensitivity analysis shows, among other things, that a strong relation exists between the price of electricity and the profitability of connecting heat sparse areas to district heating systems.
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26.
  • Amjadi, Golnaz, 1982-, et al. (författare)
  • Is industrial energy inefficiency transient or persistent? Evidence from Swedish manufacturing
  • 2022
  • Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 309
  • Tidskriftsartikel (refereegranskat)abstract
    • Energy inefficiency in production implies that the same level of goods and services could be produced using less energy. The potential energy inefficiency of a firm may be linked to long-term structural rigidities in the production process and/or systematic shortcomings in management (persistent inefficiency), or associated with temporary issues like misallocation of resources (transient inefficiency). Eliminating or mitigating different inefficiencies may require different policy measures. Studies measuring industrial energy inefficiency have mostly focused on overall inefficiencies and have paid little attention to distinctions between the types. The aim of this study was to assess whether energy inefficiency is transient and/or persistent in the Swedish manufacturing industry. I used a firm-level panel dataset covering fourteen industrial sectors from 1997 to 2008 and estimated a stochastic energy demand frontier model. The model included a four-component error term separating persistent and transient inefficiency from unobserved heterogeneity and random noise. I found that both transient and persistent energy inefficiencies exist in most sectors of the Swedish manufacturing industry. Overall, persistent energy inefficiency was larger than transient, but varied considerably in different manufacturing sectors. The results suggest that, generally, energy inefficiencies in the Swedish manufacturing industry were related to structural rigidities connected to technology and/or management practices.
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27.
  • Amuakwa-Mensah, Franklin, et al. (författare)
  • Role of banking sector performance in renewable energy consumption
  • 2022
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 306, Part B
  • Tidskriftsartikel (refereegranskat)abstract
    • To secure future universal access to modern energy, large investments in renewable energy technology are required. This paper estimates the impact of five banking sector performance indicators (return on asset, market capitalisation, asset quality, managerial efficiency and financial stability) on renewable energy consumption for a global panel consisting of 124 countries. The study used two-step system-GMM panel model to handle potential endogeneity and serial correlation. The paper considers three homogenous subpanels which are constructed based on the income group classification (high-, middle-, and low-income countries). Generally, our results show that improved banking sector performance enhances renewable energy consumption, with heterogenous effect across income group classification. For high -income (HI) countries, an increase in bank size together with improved asset quality and managerial efficiency have positive effects on renewable energy consumption. For middle-income (MI) and low-income (LI) countries, a high return on asset, an increase in bank size and financial stability are positive determinants of renewable energy consumption. We also find heterogenous effect of banking performance indicators across various renewable energy consumption types. The results highlight the importance of a well-functioning bank sector to achieve the investment in renewable energy needed to meet future energy demand and simultaneous decrease CO2 emissions.
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28.
  • Andersson, Jan-Olof, et al. (författare)
  • Improved energy efficiency in juice production through waste heat recycling
  • 2014
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 130:S1, s. 757-763
  • 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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29.
  • Andersson, Jan-Olof, et al. (författare)
  • Improved energy efficiency in sawmill drying system
  • 2014
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 113, s. 891-901
  • Tidskriftsartikel (refereegranskat)abstract
    • The worldwide use of biomass has increased drastically during the last decade. At Swedish sawmills about half of the entering timber becomes lumber, with the remainder considered as by-product (biomass). A significant part of this biomass is used for internal heat production, mainly for forced drying of lumber in drying kilns. Large heat losses in kilns arise due to difficulties in recovering evaporative heat in moist air at low temperatures. This paper addresses the impact of available state-of-the-art technologies of heat recycling on the most common drying schemes used in Swedish sawmills. Simulations of different technologies were performed on an hourly basis to compare the heat and electricity demand with the different technologies. This was executed for a total sawmill and finally to the national level to assess the potential effects upon energy efficiency and biomass consumption. Since some techniques produce a surplus of heat the comparison has to include the whole sawmill. The impact on a national level shows the potential of the different investigated techniques. The results show that if air heat exchangers were introduced across all sawmills in Sweden, the heat demand would decrease by 0.3 TWh/year. The mechanical heat pump technology would decrease the heat demand by 5.6 TWh/year and would also produce a surplus for external heat sinks, though electricity demand would increase by 1 TWh/year. The open absorption system decreases the heat demand by 3.4 TWh/year on a national level, though at the same time there is a moderate increase in electricity demand of 0.05 TWh/year. Introducing actual energy prices in Sweden gives an annual profit (investment cost excluded) on national level for the open absorption system of almost 580 million SEK. For the mechanical heat pump technology the profit is 204 million SEK and for the traditional heat exchanger the profit is significant lower. It has been found that a widespread implementation of available energy recovery technologies across Swedish sawmills would result in substantial savings of biomass for other purposes in the society
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30.
  • Andersson, Jan-Olof, et al. (författare)
  • Improving energy efficiency of sawmill industrial sites by integration with pellet and CHP plants
  • 2013
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 111, s. 791-800
  • Tidskriftsartikel (refereegranskat)abstract
    • An essential strategy to lower energy and resources consumption is the development of highly integrated industrial sites including different kind of plants complementing one another. Sawmills are huge biomass suppliers to other industries, such as pulp and paper mills, pellet plants and CHP plants, and part of the biomass is also used for the internal heat requirement. In this paper the integration of a sawmill with a pellet plant and a CHP plant is investigated using advanced process integration techniques, so that the thermal energy and the electricity produced in the CHP plant by burning part of the sawmill biomass output are used for the heat and power requirements of the other two industries. The results show that up to 18% of the biomass by-products from the sawmill can be saved, but from the economic point of view the ratio between prices of the thermal energy sold for district heating and the low quality biomass has to be lower than the present one to make the integrated design solution more attractive than separate plant operation.
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31.
  • Andersson, Jan-Olof, et al. (författare)
  • Surplus biomass through energy efficient kilns
  • 2011
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 88:12, s. 4848-4853
  • Tidskriftsartikel (refereegranskat)abstract
    • The use of biomass in the European Union has increased since the middle of the 1990s, mostly because of high subsidies and CO2 emission regulation through the Kyoto protocol. The sawmills are huge biomass suppliers to the market; out of the Swedish annual lumber production of 16.4 Mm3, 95% is produced by medium to large-volume sawmills with a lumber quotient of 47%. The remaining part is produced as biomass. An essential part (12%) of the entering timber is used for supply of heat in their production processes, mostly in the substantial drying process. The drying process is the most time and heat consuming process in the sawmill. This study was undertaken to determine the sawmills’ national use of energy and potential magnitude of improvements. If the drying process can be made more effective, sawmills’ own use of biomass can be decreased and allow a considerably larger supply to the biomass market through processed or unprocessed biomass, heat or electricity production. The national electricity and heat usage when drying the lumber have been analysed by theoretical evaluation and experimental validation at a batch kiln. The main conclusion is that the heat consumption for drying lumber among the Swedish sawmills is 4.9 TW h/year, and with available state-of-the-art techniques it is possible to decrease the national heat consumption by approximately 2.9 TW h. This additional amount of energy corresponds to the market’s desire for larger energy supply.
  •  
32.
  • Andersson, Johanna, et al. (författare)
  • Study on reduced process temperature for energy optimisation in mesophilic digestion : A lab to full-scale study
  • 2020
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 271
  • Tidskriftsartikel (refereegranskat)abstract
    • This unique study combined the lab and full scales to investigate how the anaerobic digestion process of sewage sludge was affected by a temperature change within the lower mesophilic temperature range (32–37.5 °C). Both scientific methane potential experiments and dewaterability studies were made to be used in changes of the operational conditions for a full-scale wastewater treatment plant. The aim of this study was to reduce anaerobic digestions heat consumption by altering the operational mesophilic temperature in first lab-scale experiments and then in continuation to full-scale conditions. The results of the study suggest that it is possible to save approximately 13% in heat energy demand each year by reducing the temperature for anaerobic digestion by 2.5 °C. At the lab scale, the effect of temperature on biogas production was tested in a batch experiment by measuring the biochemical methane production. At 32 °C, the production of biogas decreased by 11% compared to that at 37.5 °C. No significant difference was observed between 37.5 °C and 34.5 °C. The effect of temperature on sludge dewaterability was tested by measuring the capillary suction time, and no difference was detected between various temperatures. To confirm these results, the temperature in two full-scale digesters was gradually adjusted from 37.5 °C to 35 °C. No change was observed in biogas production, process stability, or dewaterability. The amount of heat energy that can be saved for the full-scale digesters was calculated using a heat balance. This study shows that it is possible to reduce the heat demand for AD in real applications without compromising the biogas production and process stability.
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33.
  • Andersson, Jim, et al. (författare)
  • Techno-economic analysis of ammonia production via integrated biomass gasification
  • 2014
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 130:S1, s. 484-490
  • Tidskriftsartikel (refereegranskat)abstract
    • Ammonia (NH3) can be produced by synthesis of nitrogen and hydrogen in the Haber–Bosch process, where the economic challenge is the hydrogen production. Currently, substantial amounts of greenhouse gases are emitted from the ammonia industry since the hydrogen production is almost exclusively based on fossil feedstocks. Hydrogen produced via gasification of lignocellulosic biomass is a more environmentally friendly alternative, but the economic performance is critical. The main objective of this work was to perform a techno-economic evaluation of ammonia production via integrated biomass gasification in an existing pulp and paper mill. The results were compared with a stand-alone production case to find potential technical and economic benefits deriving from the integration. The biomass gasifier and the subsequent NH3 production were modelled using the commercial software Aspen Plus. A process integration model based on Mixed Integer Linear Programming (MILP) was used to analyze the effects on the overall energy system of the pulp mill. Important modelling constraints were to maintain the pulp production and the steam balance of the mill. The results showed that the process economics and energy performance are favourable for the integrated case compared to stand-alone production. The main conclusion was however that a rather high NH3 selling price is required to make both production cases economically feasible.
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34.
  • Andersson, Martin, et al. (författare)
  • A Review of Cell-Scale Multiphase Flow Modelling, including Water Management, in Polymer Electrolyte Fuel Cells
  • 2016
  • Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 180, s. 757-778
  • Tidskriftsartikel (refereegranskat)abstract
    • The PEFC has emerged as the most viable fuel cell type for automotive and some portable applications, and also has potential back-up power unit applications due to its low operating temperature, comparative simplicity of construction, high power density, and ease of operation. In spite of tremendous scientific advances, as well as engineering progress over the last few decades, the commercialization of PEFCs remains unrealized, owing primarily to economic viability associated with the high prices of materials and components and technical problems relating primarily to water management. The difficulty in addressing the water management issues lies mostly in the two-phase multi-component flow involving phase-change in porous media, coupled heat and mass transfer, interactions between the porous layers and gas channel (GC) and the complex relationship between water content and cell performance. Due to the low temperature of operation, water generated by the electrochemical reactions often condenses into liquid form, potentially flooding the gas diffusion layer (GDL), GC or other components. Insight into the fundamental processes of liquid water evolution and transport is still lacking, preventing further enhanced PEFC development.The aim of this paper is to give a comprehensive introduction to PEFC modeling inside GCs and GDLs, with a focus on two-phase flow and related phase-change and transport processes. Relevant momentum, mass and heat transport processes are introduced and the microstructural effects on the transport processes inside the porous GDL are extensively discussed.The selection of a computational approach, for the two-phase flow within a GDL or GC, for example, should be based on the computational resources available, concerns about time and scale (microscale, cell scale, stack scale or system scale), as well as accuracy requirements. One important feature, included in some computational approaches, is the possibility to track the front between the liquid and the gas phases. To build a PEFC model, one must make a large number of assumptions. Some assumptions have a negligible effect on the results and reliability of the model. However, other assumptions may significantly affect the result. It is strongly recommended in any modeling paper to clearly state the assumptions being implemented, for others to be able to judge the work.It is important to note that a large fraction of the expressions that presently are used to describe the transport processes inside PEFC GDLs were originally developed to describe significantly different systems, such as sand or rocks. Moreover, the flow pattern maps and pressure drop correlations of two phase flow in micro channels may not be applicable for GCs due to one side wall being porous, with the resulting interaction between the GDL and GC.
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35.
  • Andersson, Malin, et al. (författare)
  • Electrochemical model-based aging-adaptive fast charging of automotive lithium-ion cells
  • 2024
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 372
  • Tidskriftsartikel (refereegranskat)abstract
    • Fast charging of electric vehicles remains a compromise between charging time and degradation penalty. Conventional battery management systems use experience-based charging protocols that are expected to meet vehicle lifetime goals. Novel electrochemical model-based battery fast charging uses a model to observe internal battery states. This enables control of charging rates based on states such as the lithium-plating potential but relies on an accurate model as well as accurate model parameters. However, the impact of battery degradation on the model's accuracy and therefore the fitness of the estimated optimal charging procedure is often not considered. In this work, we therefore investigate electrochemical model-based aging-adaptive fast charging of automotive lithium-ion cells. First, an electrochemical model is identified at the beginning of life for 6 automotive prototype cells and the electrochemically constrained fast-charge is designed. The model parameters are then periodically re-evaluated during a cycling study and the charging procedure is updated to account for cell degradation. The proposed method is compared with two reference protocols to investigate both the effectiveness of selected electrochemical constraints as well as the benefit of aging-adaptive usage. Finally, post-mortem characterization is presented to highlight the benefit of aging-adaptive battery utilization.
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36.
  • Andersson, Martin, et al. (författare)
  • Review on Modeling Development for Multiscale Chemical Reactions Coupled Transport Phenomena in Solid Oxide Fuel Cells
  • 2010
  • Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 87:5, s. 1461-1476
  • Forskningsöversikt (refereegranskat)abstract
    • A literature study is performed to compile the state-of-the-art, as well as future potential, in SOFC modeling. Principles behind various transport processes such as mass, heat, momentum and charge as well as for electrochemical and internal reforming reactions are described. A deeper investigation is made to find out potentials and challenges using a multiscale approach to model solid oxide fuel cells (SOFCs) and combine the accuracy at microscale with the calculation speed at macroscale to design SOFCs, based on a clear understanding of transport phenomena, chemical reactions and functional requirements. Suitable methods are studied to model SOFCs covering various length scales. Coupling methods between different approaches and length scales by multiscale models are outlined. Multiscale modeling increases the understanding for detailed transport phenomena, and can be used to make a correct decision on the specific design and control of operating conditions. It is expected that the development and production costs will be decreased and the energy efficiency be increased (reducing running cost) as the understanding of complex physical phenomena increases. It is concluded that the connection between numerical modeling and experiments is too rare and also that material parameters in most cases are valid only for standard materials and not for the actual SOFC component microstructures.
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37.
  • Anerud, Erik, et al. (författare)
  • Fuel quality of stored wood chips Influence of semi-permeable covering material
  • 2018
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 231, s. 628-634
  • Tidskriftsartikel (refereegranskat)abstract
    • Storage is an important component in securing the supply chain for forest fuels, but can result in substantial dry matter and energy losses that reduce the economic value of the material. This study examined fuel quality and amount of recovered energy during storage of forest-residue chips stored in a full-scale pile and the effect of covering the pile with a water-resistant, vapour-permeable fabric.Moisture content in the covered part declined continuously during the trial, while mean moisture content in the uncovered part did not change, due to rewetting at the surface. Average dry matter losses after seven months were 5.8% in the covered part and 7.3% in the uncovered part.Combined changes in fuel quality and dry matter decreased the amount of assessable energy (expressed as net calorific value as-received from an initial kg of dry base) by 5.3% in the uncovered part and 0.6% in the covered part. Thus covering the pile with a semi-permeable fabric provides opportunities to store wood chips at lower cost.
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38.
  • Araoz Ramos, Joseph A., et al. (författare)
  • Numerical simulation for the design analysis of kinematic Stirling engines
  • 2015
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 159, s. 633-650
  • Tidskriftsartikel (refereegranskat)abstract
    • The Stirling engine is a closed-cycle regenerative system that presents good theoretical properties. These include a high thermodynamic efficiency, low emissions levels thanks to a controlled external heat source, and multi-fuel capability among others. However, the performance of actual prototypes largely differs from the mentioned theoretical potential. Actual engine prototypes present low electrical power outputs and high energy losses. These are mainly attributed to the complex interaction between the different components of the engine, and the challenging heat transfer and fluid dynamics requirements. Furthermore, the integration of the engine into decentralized energy systems such as the Combined Heat and Power systems (CHP) entails additional complications. These has increased the need for engineering tools that could assess design improvements, considering a broader range of parameters that would influence the engine performance when integrated within overall systems. Following this trend, the current work aimed to implement an analysis that could integrate the thermodynamics, and the thermal and mechanical interactions that influence the performance of kinematic Stirling engines. In particular for their use in Combined Heat and Power systems. The mentioned analysis was applied for the study of an engine prototype that presented very low experimental performance. The numerical methodology was selected for the identification of possible causes that limited the performance. This analysis is based on a second order Stirling engine model that was previously developed and validated. The simulation allowed to evaluate the effect that different design and operational parameters have on the engine performance, and consequently different performance curves were obtained. These curves allowed to identify ranges for the charged pressure, temperature ratio, heat exchangers dimensions, crank phase angle and crank mechanical effectiveness, where the engine performance was improved. In addition, the curves also permitted to recognise ranges were the design parameters could drastically reduce the brake power and efficiency. The results also showed that the design of the engine is affected by the conditions imposed by the CHP interactions, and that the engine could reach a brake power closer to 832 W with a corresponding brake efficiency of 26% when the adequate design parameters were considered. On the other hand, the performance could also be very low; as the reported in experimental tests, with brake power measurements ranging 52-120W.
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39.
  • Arjmand, Mehdi, 1986, et al. (författare)
  • Investigation of Different Manganese Ores as Oxygen Carriers in Chemical-Looping Combustion (CLC) for Solid Fuels
  • 2014
  • Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 113, s. 1883-1894
  • Tidskriftsartikel (refereegranskat)abstract
    • The chemical-looping combustion (CLC) process is a novel solution for efficient combustion with direct capture of carbon dioxide. The process uses a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor, where the fuel reacts with the solid oxygen carrier. In this work, six different manganese ores are investigated as oxygen carriers for CLC application. The chemical-looping characteristics of the oxygen carriers were evaluated in a laboratory-scale fluidized-bed reactor in the temperature range of 900-970oC during alternating reducing and oxidizing conditions. Three of the manganese ores showed a small oxygen release in inert environment between 850 and 950oC. During reactivity tests, the gas yield with methane increased with the temperature and complete conversion of 50% CO in H2 was obtained for all of the ores. The rates of char gasification of two fuels, namely Mexican petroleum coke and Swedish wood char, were compared for the different manganese ores at 970oC and with 50% H2O in N2 as fluidizing gas. Ilmenite and a manufactured Mn-oxide oxygen carrier consisting of Mn3O4 and MgO-stabilized ZrO2 as support were also included for comparison. The char gasification rate and the gas conversion were higher with the manganese ores and the Mn-oxide oxygen carrier compared to ilmenite. However, the higher reactivity of the manganese ores with H2 and the ensuing decrease in H2 inhibition for manganese ores is not sufficient to explain their higher rate of char gasification. Surface analysis of partially gasified petcoke particles in the presence of manganese ores showed formation of cavities and channels as well as a uniform distribution of potassium and sodium elements. The rate of char gasification also increased with the concentration of potassium and sodium impurities in the manganese ores. Thus the results suggest that the increased rate of char conversion for manganese ores is due to alkali-catalyzed steam gasification. The increase in rate of char gasification, in combination with potentially low costs of these materials suggests that manganese ores could be interesting materials for CLC with solid fuels.
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40.
  • Armendariz, Mikel, et al. (författare)
  • Coordinated Microgrid Investment and Planning Process Considering the System Operator
  • 2017
  • Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 200, s. 132-140
  • Tidskriftsartikel (refereegranskat)abstract
    • Nowadays, a significant number of distribution systems are facing problems to accommodate more photovoltaic (PV) capacity, namely due to the overvoltages during the daylight periods. This has an impact on the private investments in distributed energy resources (DER), since it occurs exactly when the PV prices are becoming attractive, and the opportunity to an energy transition based on solar technologies is being wasted. In particular, this limitation of the networks is a barrier for larger consumers, such as commercial and public buildings, aiming at investing in PV capacity and start operating as microgrids connected to the MV network. To address this challenge, this paper presents a coordinated approach to the microgrid investment and planning problem, where the system operator and the microgrid owner collaborate to improve the voltage control capabilities of the distribution network, increasing the PV potential. The results prove that this collaboration has the benefit of increasing the value of the microgrid investments while improving the quality of service of the system and it should be considered in the future regulatory framework.
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41.
  • Aslani, Mohammad, et al. (författare)
  • Automatic identification of utilizable rooftop areas in digital surface models for photovoltaics potential assessment
  • 2022
  • Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 306
  • Tidskriftsartikel (refereegranskat)abstract
    • The considerable potential of rooftop photovoltaics (RPVs) for alleviating the high energy demand of cities has made them a proven technology in local energy networks. Identification of rooftop areas suitable for installing RPVs is of importance for energy planning. Having these suitable areas referred to as utilizable areas greatly assists in a reliable estimate of RPVs energy production. Within such a context, this research aims to propose a spatially detailed methodology that involves (a) automatic extraction of buildings footprint, (b) automatic segmentation of roof faces, and (c) automatic identification of utilizable areas of roof faces for solar infrastructure installation. Specifically, the innovations of this work are a new method for roof face segmentation and a new method for the identification of utilizable rooftop areas. The proposed methodology only requires digital surface models (DSMs) as input, and it is independent of other auxiliary spatial data to become more functional. A part of downtown Gothenburg composed of vegetation and high-rise buildings with complex shapes was selected to demonstrate the methodology performance. According to the experimental results, the proposed methodology has a high success rate in building extraction (about 95% correctness and completeness) and roof face segmentation (about 85% completeness and correctness). Additionally, the results suggest that the effects of roof occlusions and roof superstructures are satisfactorily considered in the identification of utilizable rooftop areas. Thus, the methodology is practically effective and relevant for the detailed RPVs assessments in arbitrary urban regions where only DSMs are accessible.
  •  
42.
  • Aydin, Murat, et al. (författare)
  • Experimental and computational investigation of multi U-tube boreholes
  • 2015
  • Ingår i: Applied Energy. - 0306-2619 .- 1872-9118. ; 145, s. 163-171
  • Tidskriftsartikel (refereegranskat)abstract
    • In ground source heat pump (GSHP) applications, borehole drilling cost constitutes an important part ofthe investment cost and it can be reduced by improving borehole performance. In vertical GSHP applications,usually double-U tube configurations are used to improve the heat transfer rate per unit length of aborehole, (unit HTR value). To determine the optimal number of U-tubes which maximizes the commercialand engineering benefits of multi U-tube applications, cost and performance analyses of multi U-tubeboreholes are crucial. In this study, a triple U-tube is used in a borehole of 50 m depth. Time variation ofunit HTR value of the borehole is experimentally measured when single, double and triple U-tubes are inoperation separately. Furthermore a computational model is calibrated by fitting the computationalresults to the experimental ones, and effects of using four and five U-tubes in a borehole are computationallyinvestigated. The relations between number of U tubes and time variation of unit HTR value ofa borehole as well as investment cost are analyzed. Long term borehole performance predictions aremade and compared for multi U-tube applications. Both experimental and computational results showedthat performance improvements are remarkable for 2U-tube and 3U-tube configurations while it isnearly insignificant for 4U and 5U ones. If the investment cost per thermal power is considered, 2U-tubeconfiguration is the optimal one if the prices of polyethylene pipes are relatively high, like in Turkey.When the cost of pipes decreases, then 3U-tube or even 4U–tube configuration can be the cheapestsolution.
  •  
43.
  • Ayele, Getnet Tadesse, et al. (författare)
  • An extended energy hub approach for load flow analysis of highly coupled district energy networks: Illustration with electricity and heating
  • 2018
  • Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 212, s. 850-867
  • Tidskriftsartikel (refereegranskat)abstract
    • Energy systems at district/urban level are getting more complex and diversified from time to time. Different energy carriers are coupled each other to meet various types of energy demands. The conventional way of analyzing energy networks independently does not reflect the true nature of the coupled networks. One of such a promising coupled multi-carrier energy system (MCES) is the combination of district heating and electricity networks. The coupling between these two networks is increasing due to the integration of co– and poly-generation technologies at the distribution networks. Recent literatures tried to address a load flow analysis for lightly coupled networks by formulating case-specific load flow models. This paper presents a more general and flexible tool developed using Matlab® which can be used to conduct the load flow analysis of highly coupled electricity and heating networks. An energy hub concept is extended further to formulate a general model in which local generations and detailed network parameters of MCES can be taken into account. Coupled heating and electricity networks are modeled in detail for illustration. The flexibility and generality of the model are then tested by considering case studies with different network topologies (tree and meshed). A comparison is also made with a model used in recent literature. The results show that the proposed model is more accurate. The main contribution of this paper can be summarized by the following five points: (1) Coupling matrices are used to relate network power flow equations of different energy carriers; (2) Hybrid hydraulic head and pipe flow equations are used to develop the hydraulic model which can be applied for both types of tree and meshed heating networks with the possibility of pumping units; (3) A general thermal model that relates steady state temperature drops and mass flow rates, even during change of flow direction, is developed for the heating network; (4) The electricity network is modeled with the possibility of tap changing transformers; (5) The overall system of equations are solved as a single problem using Newton-Raphson iterative method.
  •  
44.
  • Azimoh, Chukwuma Leonard, et al. (författare)
  • An assessment of unforeseen losses resulting from inappropriate use of solar home systems in South Africa
  • 2014
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 136, s. 336-346
  • Tidskriftsartikel (refereegranskat)abstract
    • One of the challenges to the sustainability of the Solar Home System (SHS) electrification program in South Africa is equipment theft. In response to this, communities susceptible to solar panel theft resort to mounting their panels flat on the ground so they can be looked after during the day and taken indoors at night for safe keeping. Other households use their security lights to illuminate their environment and provide security for pole and roof mounted solar panels at night. These actions have consequential effects on the performance of the SHS. Several studies have detected resentment from households regarding the low power quality from these systems. Most scientific contributions on the issue of low power from SHS have focused on the challenges based on the technical designs of the systems. The power losses due to the usage pattern of the system has not received much attention. This study therefore reports on the technical losses as a result of the deviation from the designed and installed specification of the system by the users in order to protect their systems. It also investigates the linkage between the technical and economic losses which affects the sustainability of SHS program. A case study was performed in Thlatlaganya village within Limpopo province in South Africa. Technical analysis using PVSYST solar software revealed that the energy output and performance of the battery is compromised as a result of these practices. Economic analysis indicates that the battery life and the economics of owning and operating SHS are affected negatively. The study recommends solutions to mitigate these losses, and proposes a cost effective way of optimizing the operation of SHS using a Bench-Rack system for mounting solar panels.
  •  
45.
  • Azimoh, Chukwuma Leonard, et al. (författare)
  • Illuminated but not electrified : An assessment of the impact of Solar Home System on rural households in South Africa
  • 2015
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 155, s. 354-364
  • Tidskriftsartikel (refereegranskat)abstract
    • The introduction of the off-grid electrification program in South Africa using the Solar Home System (SHS) was a central component of the government policy aimed at bringing development to un-electrified households. An assessment of the performance of SHS in many countries provided little evidence to support the development impact of the system. The general perception is that the SHS program is wasting government funds and has no hope of achieving the set objectives. Previous scientific reports have concluded that SHS is the most viable technology for bringing about socio-economic development to rural households. Most of these conclusions have been based on one sided arguments and largely on anecdotal evidence. This study provides a pluralistic view of the subject from the perspective of the energy service companies (ESCOs) and the households using the equipment. The development impact of SHS is subjected to scientific analysis by investigating the economic and social dimensions of the program. Additionally, the sustainability of the South African SHS program is assessed by investigating the challenges facing the ESCOs and the households. The study reveals that illumination provided by SHS electricity has profound impact on the livelihoods of rural households. Due to the limited capacity of SHS for productive and thermal use, there are limited direct economic benefits to the households. The associated economic impact is peripheral to the secondary usage of SHS electricity. SHS has improved the productivity of small scale business owners who utilize the light from SHS to do business at night. Irregularities in payment of subsidy funds and energy bills, high operation cost, non-optimal use of SHS, grid encroachment, and lack of customer satisfaction contribute to make the business unsustainable for the ESCOs.
  •  
46.
  • Bach-Oller, Albert, 1989-, et al. (författare)
  • On the role of potassium as a tar and soot inhibitor in biomass gasification
  • 2019
  • Ingår i: Applied Energy. - : Elsevier Ltd. - 0306-2619 .- 1872-9118. ; 254
  • Tidskriftsartikel (refereegranskat)abstract
    • The work investigates in a drop tube furnace the effect of potassium on carbon conversion for three different types of fuels: an ash lean stemwood, a calcium-rich bark and a silicon-rich straw. The study focuses on an optimal method for impregnating the biomass with potassium. The experiments are conducted for 3 different impregnation methods; wet impregnation, spray impregnation, and dry mixing to investigate different levels of contact between the fuel and the potassium. Potassium is found to catalyse both homogenous and heterogeneous reactions. All the impregnation methods showed a significant effect of potassium on heterogeneous reactions (char conversion). The fact that dry mixing of potassium in the biomass shows an effect reveals the existence of a gas-induced mechanism that supply and distributes potassium on the char particles. Concerning the effect of potassium on homogenous reactions, it is found that potassium in the gas phase leads to much lower yields of C2 hydrocarbons, heavy tars and soot. The results indicate that potassium reduces the likelihood of light aromatic to progress toward heavier polyaromatic hydrocarbons clusters, thereby inhibiting the formation of soot-like material. A moderate interaction between the added potassium and the inherent ash forming elements is also observed: Potassium has a smaller effect when the fuel is naturally rich in silicon. The combined results are of interest for the design of a gasification process that incorporates recirculation of naturally occurring potassium to improve entrained flow gasification of biomass. 
  •  
47.
  • Bacsik, Zoltan, et al. (författare)
  • Selective separation of CO2 and CH4 for biogas upgrading on zeolite NaKA and SAPO-56
  • 2016
  • Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 162, s. 613-621
  • Tidskriftsartikel (refereegranskat)abstract
    • Several commercial and potential adsorbents were investigated for the separation of CO2 from CH4, which is relevant for the upgrading of raw biogas. The main focus of the paper was on the working capacities and selectivities of the adsorbents for a generic vacuum swing adsorption (VSA) process. Zeolites 4A and 13X had good estimated CO2-over-CH4 selectivities and reasonably high working capacities for the removal of CO2. A variant of zeolite A - vertical bar Na12-Kx vertical bar-LTA (with 1.8 <= x <= 3.2), had at least the same working capacity as zeolite 4A but with a significantly improved selectivity. Hence, the environmentally important CH4 slip can be minimized with this vertical bar Na12-Kx vertical bar-LTA sorbent. If a high working capacity for CO2 removal is the most important characteristic for a VSA process, then silicoaluminum phosphate, specifically SAPO-56, appeared to be the best candidate among the studied sorbents. In addition, SAPO-56 had a substantially high estimated CO2-over-CH4 selectivity with a value between similar to 20 and 30.
  •  
48.
  • Bakhtiari, Hamed, et al. (författare)
  • Predicting the stochastic behavior of uncertainty sources in planning a stand-alone renewable energy-based microgrid using Metropolis–coupled Markov chain Monte Carlo simulation
  • 2021
  • Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 290
  • Tidskriftsartikel (refereegranskat)abstract
    • Due to the lack of available flexibility sources to cope with different uncertainties in the real-time operation of stand-alone renewable energy-based microgrids, the stochastic behavior of uncertainty sources needs to be included in the planning stage. Since there is a high association between some of the uncertainty sources, defining a proper time series to represent the behavior of each source of uncertainty is a challenging issue. Consequently, uncertainty sources should be modeled in such a way that the designed microgrid be able to cope with all scenarios from probability and impact viewpoints. This paper proposes a modified Metropolis–coupled Markov chain Monte Carlo (MC)3 simulation to predict the stochastic behavior of different uncertainty sources in the planning of a stand-alone renewable energy-based microgrid. Solar radiation, wind speed, the water flow of a river, load consumption, and electricity price have been considered as primary sources of uncertainty. A novel data classification method is introduced within the (MC)3 simulation to model the time-dependency and the association between different uncertainty sources. Moreover, a novel curve-fitting approach is proposed to improve the accuracy of representing the multimodal distribution functions, modeling the Markov chain states, and the long-term probability of uncertainty sources. The predicted representative time series with the proposed modified (MC)3 model is benchmarked against the retrospective model, the long-term historical data, and the simple Monte Carlo simulation model to capture the stochastic behavior of uncertainty sources. The results show that the proposed model represents the probability distribution function of each source of uncertainty, the continuity of samples, time dependency, the association between different uncertainty sources, short-term and long-term trends, and the seasonality of uncertainty sources. Finally, results confirm that the proposed modified (MC)3 can appropriately predict all scenarios with high probability and impact.
  •  
49.
  • Baldi, Francesco, 1986, et al. (författare)
  • Comparison of different procedures for the optimisation of a combined Diesel engine and organic Rankine cycle system based on ship operational profile
  • 2015
  • Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 110:Part B, s. 85-93
  • Tidskriftsartikel (refereegranskat)abstract
    • At a time of strong challenges for shipping in relation to economic and environmental performance, the potential of waste heat recovery has been identified as among the most important technologies to lower fuel consumption. This paper presents the comparison of four different procedures for the optimisation of a combined Diesel and organic Rankine cycle system with increasing attention to the ship operational profile and to the inclusion of engine control variables in the optimisation procedure. Measured data from two years of operations of a chemical tanker are used to test the application of the different procedures. The results indicate that for the investigated case study the application of an optimisation procedure which takes the operational profile into account can increase the savings of the installation of an organic Rankine cycle from 7.3% to 11.4% of the original yearly fuel consumption. The results of this study further show that (i) simulating the part-load behavior of the ORC is important to ensure its correct operations at low engine load and (ii) allowing the engine control strategy to be part of the optimisation procedure leads to significantly larger fuel savings than the optimisation of the waste recovery system alone.
  •  
50.
  • Baldi, Francesco, 1986, et al. (författare)
  • Development of a combined mean value-zero dimensional model and application for a large marine four-stroke Diesel engine simulation
  • 2015
  • Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 154, s. 402-415
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, a combined mean value–zero dimensional model is developed using a modular approach in the computational environment of Matlab/Simulink. According to that, only the closed cycle of one engine cylinder is modelled by following the zero-dimensional approach, whereas the cylinder open cycle as well as the other engine components are modelled according to the mean value concept. The proposed model combines the advantages of the mean value and zero-dimensional models allowing for the calculation of engine performance parameters including the in-cylinder ones in relatively short execution time and therefore, it can be used in cases where the mean value model exceeds its limitations. A large marine four-stroke Diesel engine steady state operation at constant speed was simulated and the results were validated against the engine shop trials data. The model provided results comparable to the respective ones obtained by using a mean value model. Then, a number of simulation runs were performed, so that the mapping of the brake specific fuel consumption for the whole operating envelope was derived. In addition, runs with varying turbocharger turbine geometric area were carried out and the influence of variable turbine geometry on the engine performance was evaluated. Finally, the developed model was used to investigated the propulsion system behaviour of a handymax size product carrier for constant and variable engine speed operation. The results are presented and discussed enlightening the most efficient strategies for the ship operation and quantifying the expected fuel savings.
  •  
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