| 1. |
- Ajdari, Sima, 1985, et al.
(author)
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Modeling the Nitrogen and Sulfur Chemistry in Pressurized Flue Gas Systems
- 2015
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 54:4, s. 1216-1227
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Journal article (peer-reviewed)abstract
- A rate-based model is developed to elucidate the chemistry behind the simultaneous absorption of NOx and SOx under pressurized conditions (pressures up to 30 bar) that are applicable to the flue gases obtained from CO2 capture systems. The studied flue gas conditions are relevant to oxy-fuel and chemical-looping combustion systems. The kinetics of the reactions implemented in the model is based on a thorough review of the literature. The chemistry of nitrogen, sulfur, and N-S interactions are evaluated in detail, and the most important reaction pathways are discussed. The effects of pH, pressure, and flue-gas composition on the liquid-phase chemistry are also examined and discussed. Simulations that use existing kinetic data reveal that the pH level has a strong influence on the reaction pathway that is followed and the types of products that are formed in the liquid phase. In addition, the pressure level and the presence of NOx significantly affect the removal of SO2 from the flue gas.
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| 2. |
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| 3. |
- Ajdari, Sima, 1985, et al.
(author)
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Reduced Mechanism for Nitrogen and Sulfur Chemistry in Pressurized Flue Gas Systems
- 2016
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 55:19, s. 5514-5525
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Journal article (peer-reviewed)abstract
- The gas- and liquid-phase chemistry of nitrogen and sulfur species under pressurized conditions is of high importance to the design and performance of the pressurized flue gas systems in carbon capture and storage (CCS) schemes. Yet, the available description of this chemistry is complex and difficult to apply in design studies for removal of NOx and SOx during the compression. This work proposes a reduced mechanism for engineering calculations of pressurized flue gas systems, a mechanism that is able to describe the relevant gas and liquid-phase chemistry as well as the S/N-product distribution. The reduced mechanism is derived by identifying the rate-limiting reactions using sensitivity analysis. The performance of the mechanism subsets are compared with results of a detailed mechanism. The identified rate-limiting reactions for the formation of key products form the basis for two different types of reduced mechanisms. The sets include one general reduced mechanism (valid for all pH conditions) and sets of pH-specific mechanisms. The general reduced mechanism and the pH-specific mechanisms perform satisfactorily compared to the detailed mechanism under different pH conditions. The results show that depending on the purpose of the modeling, whether it is to predict the pollutant removal (where sulfurous acid and nitrogen acids are mainly important) or capture the liquid composition, for which the N-S chemistry products are also important, different levels of simplification can be made. The number of reactions is reduced from 34 reactions (39 species) in the detailed mechanism to 12 reactions (20 species) in the general reduced mechanism and 7-8 (14-17 species) in the pH-specific mechanisms.
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| 4. |
- Alamia, Alberto, 1984, et al.
(author)
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Well-to-wheel analysis of bio-methane via gasification, in heavy duty engines within the transport sector of the European Union
- 2016
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In: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 170, s. 445-454
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Journal article (peer-reviewed)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.
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| 5. |
- Beiron, Johanna, 1992, et al.
(author)
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An assessment of the flexibility of combined heat and power plants in power systems with high shares of intermittent power sources
- 2018
-
Conference paper (other academic/artistic)abstract
- There is an urgent need to reduce anthropogenic CO2 emissions from the power sector as a climate change mitigating strategy. Thus, the share of renewable energy sources in power systems, for example wind power, is increasing. However, the variability in wind power generation poses a challenge to conventional thermal power plants, as well as yielding volatile electricity prices. Once in place, wind power with low operating cost will replace higher-cost electricity generation units in the merit order, while during low-wind periods the need for thermal plants remains. Traditionally designed for stable base load, thermal power plants might thus face a future with new demands for flexible operation to stay competitive. Combined heat and power (CHP) plants are thermal power plants that produce electricity and district heating simultaneously and, depending on plant type and fuel, they have different possibilities to vary the ratio between power and heat production. However, technical constraints place limitations on flexibility, including ramp rates and efficiency. The interconnection between the power and heat markets provides additional opportunities for load variation management. With the comparably slower dynamics of the heat market, and the possibility to store thermal energy, prospects of adapting to new and profitable operating strategies that can aid the balancing of the power system arise. This study focuses on how CHP plants can provide flexibility in a scenario with fluctuating power demand and associated volatility in electricity prices. Plant and market dynamics are analyzed to estimate the need for flexibility, and what is required of CHP units in terms of operation to meet these requirements. A CHP plant is modelled in detail with a boiler, steam cycle and its link to the district heating system, both under steady state and transient conditions, using the softwares Ebsilon and Dymola, respectively. The models are validated against operational data from a Swedish CHP plant. Transient responses to load ramps are characterized, as well as the flexibility in power-to-heat ratio, and their effects on efficiency.
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| 6. |
- Beiron, Johanna, 1992, et al.
(author)
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Dynamic modeling for assessment of steam cycle operation in waste-fired combined heat and power plants
- 2019
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In: Energy Conversion and Management. - : Elsevier BV. - 0196-8904. ; 198
-
Journal article (peer-reviewed)abstract
- As the share of non-dispatchable energy sources in power systems increases, thermal power plants are expected to experience load variations to a greater extent. Waste-fired combined heat and power has multiple products and is today primarily operated for waste incineration and to generate heat. To consider load variations in the power demand at these plants may be a way to provide system services and obtain revenue, however, the transient interaction between power and district heating generation for the type of steam systems used should be studied. This work describes the transient characteristics and timescales of cogeneration steam cycles to discuss the operational interactions between power and district heating generation. A dynamic model of the steam cycle of a 48 MW waste-fired combined heat and power plant is developed using physical equations and the modeling language Modelica. The model is successfully validated quantitatively for both steady-state and transient operation with data from a reference plant and is shown capable of characterizing the internal dynamics of combined heat and power plant processes. Simulations are performed to analyze steam cycle responses to step changes, ramps and sinusoidal disturbances of boiler load changes and variability in district heating inlet temperature and flow. The results give insight on the process timescales for the specific case studied; for example, with the present design a 10% boiler load change requires up to 15 min for responses to settle, while the corresponding time for a 10% change in district heating flow or temperature show settling times within 5 min. Furthermore, increasing the boiler ramp rate from 2 to 4%/min could reduce the rise time of power generation by 42%, which could be of economic significance in day-ahead power markets.
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| 7. |
- Beiron, Johanna, 1992, et al.
(author)
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Enhancement of CO2 Absorption in Water through pH Control and Carbonic Anhydrase - A Technical Assessment
- 2019
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 58:31, s. 14275-14283
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Journal article (peer-reviewed)abstract
- This paper provides an industrial-scale technical assessment of absorption of CO2 in water to react into bicarbonate (HCO3−), with the goal of storing HCO3− in the oceans as a carbon sequestration technology. A potential advantage of the process is that it will not require a CO2 transport and storage infrastructure that will be expensive for small-scale and remote emission sources. Process simulations are utilized to estimate absorber column length and for mass flow estimations of water and base required for a target capture rate of 90%. The results indicate that the process is technically feasible under specific conditions, with pH regulation being highly important, although the demand for base represents a limiting factor. Yet, a potential niche for the process is CO2 capture at smaller plants emitting small amounts of CO2.
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| 8. |
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| 9. |
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| 10. |
- Biermann, Max, 1989, et al.
(author)
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Evaluation of Steel Mills as Carbon Sinks
- 2018
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Conference paper (other academic/artistic)abstract
- The iron and steel industry is one of the industries with the largest global contribution to CO2 emissions. Possible mitigation options include use of biomass and carbon capture and storage. Combining these two mitigation options, this study evaluates the potential for BECCS at an integrated steel mill in Sweden. The injection of pulverized biocoal from torrefaction or pyrolysis into a blast furnace and CO2 capture by amine absorption of the blast furnace gas leaving at the top of the furnace can reduce CO2 site emissions by up to 61 %, when accounting for negative emissions (biogenic CO2 being captured). The mitigation cost are estimated to 43 – 100 € per tonne CO2 avoided, depending primarily on biomass prices and the share of biomass used in the process (the study assumes a cost effective capture rate of 84%). Besides a reduction in CO2 emissions, the study highlights the potential for green by-products from injecting biogenic carbon into the blast furnace in the form of renewable electricity and CO2 neutral steel. The study concludes that it is theoretically possible to reach carbon neutrality or even net-negative emissions in an integrated steel mill, but this would require considerable process changes and high demand of biomass. Nonetheless, the implementation of BECCS based on feasible biomass injection volumes in integrated steel mills is interesting as a near-term and possibly cost-effective option for CO2 mitigation.
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| 11. |
- Biermann, Maximilian, et al.
(author)
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Excess heat-driven carbon capture at an integrated steel mill : Considerations for capture cost optimization
- 2019
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In: International Journal of Greenhouse Gas Control. - : Elsevier. - 1750-5836 .- 1878-0148. ; 91
-
Journal article (peer-reviewed)abstract
- Primary steelmaking in blast and basic oxygen furnaces is inherently carbon-intensive. Partial capture, i.e., capturing only a share of the CO2, is discussed as an option to reduce the cost of carbon capture and storage (CCS) and to realize a near-term reduction in emissions from the steel industry. This work presents a techno-economic assessment of partial capture based on amine absorption of CO2. The cost of steam from excess heat is assessed in detail. Using this steam to drive the capture process yields costs of 28–50 €/t CO2-captured. Capture of CO2 from the blast furnace gas outperforms end-of-pipe capture from the combined-heat-and-power plant or hot stove flue gases onsite by 3–5 €/t CO2-captured. The study shows that partial capture driven exclusively by excess heat represents a lower cost for a steel mill owner, estimated in the range of 15–30 €/t CO2-captured, as compared to full capture driven by the combustion of extra fuel. In addition, the full-chain CCS cost (capture, transport and storage) for partial capture is discussed in light of future carbon prices. We conclude that implementation of partial capture in the steel industry in the 2020s is possible and economically viable if policymakers ensure long-term regulation of carbon prices in line with agreed emission reduction targets beyond Year 2030.
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| 12. |
- Biermann, Max, 1989, et al.
(author)
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Partial Carbon Capture by Absorption Cycle for Reduced Specific Capture Cost
- 2018
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 57:45, s. 15411-15422
-
Journal article (peer-reviewed)abstract
- For a sustainable-energy system, the industrial carbon emission should be zero or close to it. The partial capture of CO2, i.e., capturing only a share of the CO2, is discussed as an option for initiating the transition toward the decarbonization of industry by reducing the CO2 mitigation cost at industrial sites. This work models two approaches to achieving partial capture based on amine absorption: (1) capturing 90% CO2 from a split stream of the flue gas or (2) capturing less CO2 (≪90%) from the total flue-gas flow. A techno-economic analysis is carried out that considers scale, CO2 concentration, and process configurations (absorber intercooling and rich solvent splitting) when comparing the cost of partial capture to full capture, i.e., capturing close to all CO2 from the entire gas. Besides lowering absolute costs, the study shows that partial capture from CO2-rich gases may also lower specific cost (€ per tonne of CO2 captured) compared to full capture, despite the economy of scale, during certain market conditions. Operating expenditures, especially the cost of steam, are found to be dominating cost factors for partial capture, even for capture down to 200 000 tonnes per year.
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| 13. |
- Biermann, Max, 1989, et al.
(author)
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Scenario for near-term implementation of partial capture from blast furnace gases in Swedish steel industry
- 2019
-
Conference paper (other academic/artistic)abstract
- Iron-and-steel making is a carbon-intensive industry and responsible for about 8% of global CO2 emissions. Meeting CO2 reduction targets is challenging, since carbon is inherent in the dominating production route in blast furnaces. Long-term plans to phase out carbon and change production technique are under way, such as iron ore reduction with hydrogen[1][2] won from renewable energies or electro winning[3], however unlikely to be implemented at scale before 2040 [4]. Until a transition to such technologies is completed, carbon leakage will remain to be a threat to steel industry inside EU ETS system. CCS remains an option for steel industry to comply with reduction targets and meet rising allowance (EUA) prices, currently above 20 €/t. Most studies on CCS propose a capture rate of ≥ 90 %[5–7], however, CCS could be considered as a part of a series of measures (e.g. fuel change, energy efficiency measures) that together achieve a significant reduction in CO2 emissions until a carbon-neutral production is in place. This line of thought motivates the concept of partial capture, where only the most cost effective part of the CO2 emissions are separated for storage [8]. In steel industry, high CO2 concentrations at large flows and the availability of excess heat make partial capture attractive. Previous work on the steel mill in Luleå, Sweden, emits around 3.1 Mt CO2 per year, has found that 40-45 % of site emissions can be captured fueled by excess heat alone[9]. Therein, five heat recovery technologies were assessed, ranging from back pressure operation of CHP turbine to dry slag granulation. Promising CO2 sources on site include flue gases from hot stoves and the combined-heat and power plant, and the process gas originating from the blast furnace – blast furnace gas (BFG). BFG is a pressurized, low value fuel used for heating on site. CO2 separation from BFG requires less reboiler heat for MEA regeneration, and the enhanced heating value of the CO2 lean BFG increases energy efficiency of the steel mill [9]. This work discusses the near-term (the 2020s) implementation of partial capture at a Swedish steel mill and the economic viability of such implementation dependent on the energy price, carbon price, and required reductions in CO2 emissions. Based on previous work [9][10,11] on partial capture in steel industry a cost estimation of a capture system for the BFG is conducted including CAPEX and OPEX of the MEA capture unit, gas piping, and recovering heat from the steel mill. The costs are summarized as equivalent annualized capture cost (EAC) and set into relation to transport and storage costs as well as carbon emission costs to form the net abatement cost (NAC) according to Eq. (1) ???=???+ ?????????&??????? ???? −?????? ????? [€/???2] (1) Figure 1 shows how EAC for BFG varies with the capture rate and the cost of steam for different heat recovery technologies represented by the steps in the curve ( see explanation in [9]). Note that partial capture from BFG is more economical than the full capture benchmark. The most cost-efficient case of 28 €/t CO2 captured is achieved for BFG capture fueled by steam from back-pressure operation (at the expense of electricity production), flue gas heat recovery and flare gas combustion. The transport and storage cost applied in Eq (1) represent ship transport from the Bothnian Bay to a storage site in the Baltic Sea , according to Kjärstad et el.[12]. Transport and storage cost range within 17 – 27 €/t CO2 depending on scale. These installation and operation cost for capture, transport and storage are set into relation with various scenarios on future carbon and energy (electricity) prices in Europe and Sweden. For example, Figure 2 illustrates a scenario in line with IEA’s sustainable development scenario to restrict global warming to 2°C. The carbon prices are adapted from WEO 2018 [13] and increase from 20 € to 120 € per tonne CO2 by 2040 and the electricity prices of 42-52 €/MWh (increasing with time) are based on latest results from the NEPP project [14]. In this scenario, partial capture from BFG could become economic viable in 2029, construction in 2020 with operation from 2022/23 onwards is likely to pay off within a lifetime of 20 years only. This work demonstrates the viability of partial capture as cost-efficient mitigation measure for the steel industry and illustrates conditions for an early implementation in the 2020s. This work is part of the CO2stCap project (Cutting Cost of CO2 Capture in Process Industry) and funded by Gassnova (CLIMIT programme), the Swedish Energy Agency, and industry partners.
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| 14. |
- Cintas Sanchez, Olivia, 1982, et al.
(author)
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Geospatial supply-demand modeling of biomass residues for co-firing in European coal power plants
- 2018
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In: GCB Bioenergy. - : Wiley. - 1757-1707 .- 1757-1693. ; 10:11, s. 786-803
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Journal article (peer-reviewed)abstract
- Biomass co‐firing with coal is a near‐term option to displace fossil fuels and can facilitate development of biomass conversion and the build‐out of biomass supply infrastructure. A GIS‐based modeling framework (EU‐28, Norway, and Switzerland) is used to quantify and localize biomass demand for co‐firing in coal power plants and agricultural and forest residue supply potentials; supply and demand are then matched based on minimizing the total biomass transport costs (field‐to‐gate). Key datasets (e.g., land cover, land use, wood production) are available at 1,000 m or higher resolution, while some data (e.g., simulated yields) and assumptions (e.g., crop harvest index) have lower resolution and were re‐sampled to allow modeling at 1,000 m resolution. Biomass demand for co‐firing is estimated at 184 PJ in 2020, corresponding to an emissions reduction of 18 Mt CO2. In all countries except Italy and Spain, the sum of the forest and agricultural residues available at less than 300 km from a co‐firing plant exceeds the assessed biomass demand. The total cost of transporting residues to these plants is reduced if agricultural residues can be used, since transport distances are shorter. The total volume of forest residues less than 300 km from a co‐firing plant corresponds to about half of the assessed biomass demand. Almost 70% of the total biomass demand for co‐firing is found in Germany and Poland. The volumes of domestic forest residues in Germany (Poland) available within the cost range 2‐5 (1.5‐3.5) €/GJ biomass correspond to about 30% (70%) of the biomass demand. The volumes of domestic forest and agricultural residues in Germany (Poland) within the cost range 2‐4 (below 2) €/GJ biomass exceed the biomass demand for co‐firing. Half of the biomass demand is located within 50 km from ports, indicating that long‐distance biomass transport by sea is in many instances an option.
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| 15. |
- Cutz, Luis, 1986, et al.
(author)
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A techno-economic assessment of biomass co-firing in Czech Republic, France, Germany and Poland
- 2019
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In: Biofuels, Bioproducts and Biorefining. - : Wiley. - 1932-1031 .- 1932-104X. ; 13:5, s. 1289-1305
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Journal article (peer-reviewed)abstract
- Biomass co-firing with coal can help to reduce greenhouse gas emissions and can act as a low-cost stepping-stone for developing biomass supply infrastructures. This paper presents a techno-economic assessment of the biomass co-firing potential in coal-fired boilers in Czech Republic, France, Germany and Poland. The current coal power plant infrastructure is characterized by means of geographic location of the coal power plants, installed boiler capacity, type of boiler technology and year of commissioning, as extracted from the Chalmers Power Plant Database. The assessment considers type of boiler technology, type of biomass, co-firing fraction, implementation costs, breakeven prices for co-firing and an alkali index to determine the risk of high-temperature corrosion. The main factors affecting the co-firing potential are the biomass price, carbon price and alkali index. Results indicate that the total co-firing potential in the four countries is around 16 TWh year−1, with the largest potential from a conversion perspective in Germany, followed by Poland. Biomass co-firing with coal is estimated to be competitive at biomass prices below 13 € MWhinput−1 when the carbon price is 20 € t−1 CO2. On average, 1 TWh of electricity from biomass co-firing substitutes 0.9 Mt of fossil CO2 emissions. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.
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| 16. |
- Cutz, Luis, 1986, et al.
(author)
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Assessment of biomass energy sources and technologies: The case of Central America
- 2016
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In: Renewable and Sustainable Energy Reviews. - : Elsevier BV. - 1879-0690 .- 1364-0321. ; 58, s. 1411-1431
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Research review (peer-reviewed)abstract
- This paper reviews and assesses conditions for increased and efficient use of biomass in Central America (CA), providing an overview of conditions for biomass supply in each country. Then, a Fuzzy Multi-Actor Multi-Criteria Decision-Making (MCDM) method is applied to identify a portfolio of biomass conversion technologies appropriate for CA, considering technical, economic, environmental and socio-political aspects. The work is motivated by the relatively large availability of biomass in CA at the same time as current conversion of biomass is carried out in inefficient processes. The assessment of technologies includes thermochemical processes (pyrolysis, combustion and gasification) for production of different energy carriers, including improved cooking stoves (ICSs). The most promising biomass feedstocks in the region are residue based; animal (manure), forest and agricultural origin. We show that around 250 PJ/year could be available for the energy sector, which is equivalent to 34% of primary energy supply for CA. It is concluded that in the short term promoting and implementing ICSs will give the largest improvement in the efficiency of biomass use, whereas on the long term small combustion plants seem to be the best choice for transforming CA's biomass into a clean and sustainable energy carriers, boosting economy and industrial development. Results show that the introduction of ICSs will result in an annual saving in the range of 4-8 Mt of fuelwood (59-113 PJ). Moreover, even when the investment cost of the cooking stoves is considered, ICSs yield economic savings to fuelwood consumers compared to traditional stoves. The total savings during the first year of implementation would be in the range of 19-152 US$/stove. (C) 2016 Elsevier Ltd. All rights reserved.
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| 17. |
- Djerf, Tove, 1989, et al.
(author)
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Bottom-bed fluid dynamics – Influence on solids entrainment
- 2018
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In: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 173, s. 112-118
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Journal article (peer-reviewed)abstract
- In CFB boilers, the solids concentration along the riser and the external solids circulation are important design parameters. This work provides an experimental investigation on how the solids entrainment from the bottom region of a CFB riser is influenced by the fluidization conditions, in particular if there is a bottom bed or not. Measurements are carried out in a CFB riser with a height of 3 m and 0.45 m 2 in cross section. The solids inventory consists of glass spheres with a mean size of 112 μm, employing fluidization velocities up to 1.4 m/s and riser pressure drops in the range 0.15–1.5 kPa. The vertical distribution of solids concentration is determined through pressure drop measurements along the riser height. The external solids circulation is measured with a valve system in the return leg. The results show that the bottom region conditions govern how operational parameters influence the characteristics of the solids entrainment from the bottom. The vertical extension of the splash zone above the dense bed depends strongly on the dense bed height. In the absence of a dense bed, a bottom region with strong solids back-mixing is established which has similarities with the splash region.
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| 18. |
- Djerf, Tove, 1989, et al.
(author)
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Bottom-bed fluid dynamics - Influence on solids entrainment
- 2017
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In: 12th International Conference on Fluidized Bed Technology, CFB 2017. ; 2017, s. 183-190
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Conference paper (peer-reviewed)abstract
- In CFB boilers, the solids concentration along the riser and the external solids circulation are important design parameters, mainly in terms of the heat balance but also influencing the risk of wear on heat transfer surfaces. This work investigates experimentally how the amount of solids entrained from the bottom region of a CFB riser is influenced by the fluidization conditions, including the presence or absence of a dense bottom bed. The paper presents first measurements in a new cold lab-scale unit (3 m tall, 0.45 m2in cross section), which is a scale model of a large utility boiler. The solids inventory consists of glass spheres with a mean size of 112 µm. The operational range covers fluidization velocities between 0.1 and 1.4 m/s and riser pressure drops between 0.2 and 1.5 kPa. The vertical distribution of solids concentration is determined through pressure drop measurements between densely spaced pressure taps (15 in total) along the riser height. The external solids circulation is measured with an automatic valve system in the return leg. The results show that the presence or absence of a dense bed govern how operational parameters influence the characteristics of the solids entrainment from the bottom region. The vertical extension of the splash zone above the dense bed depends strongly on the dense bed height. In the absence of a dense bed, a bottom region with strong solids back-mixing is established which has similarities with the splash region.
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| 19. |
- Djerf, Tove, 1989, et al.
(author)
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Solids circulation in circulating fluidized beds with low riser aspect ratio and varying total solids inventory
- 2016
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In: Fluidization XV (2016), Quebec, Canada.
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Conference paper (other academic/artistic)abstract
- This paper presents an experimental study with the aim tounderstand the relation between the flow conditions - the riser pressure drop and fluidization velocity - in a CFB riser and the net (external)solids flux (Gs [kg/m2s]), applying a riser geometry and overall flow conditions similar to CFB boilers.The experiments are carried out in a CFB unit operated under ambient conditions. The riser has a cross section of 0.7 m x 0.12 m and a height of 8.5 m, yielding a riser height-to-width aspect ratio of 10.6 (in the wide dimension), similar to that of CFB boilers. The unit is equipped with densely spaced pressure taps providing a fine resolution of the measured vertical pressure profile along the riser and an automatic system to accurately measure Gs. The experiments cover fluidization velocities of 0.3-7 m/s, riser pressure drops of 1.7-10.5 kPa and loopseal fluidization velocities of 0.12-0.54 m/s (secondary air flows are not considered). These ranges correspond to conditions both with and without a dense bottom region.The results show that Gs is determined by the solids concentration at the riser top, which depends riser pressure drop and fluidization velocity, and the backflow effect, which depends on the configuration and flow conditions of the loop seal and the exit region. For operating conditions with a dense bottom bed present, Gs is independent of riser pressure drop, whereas when operating without a dense bed an increase in riser pressure drop yields an increase in Gs.
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| 20. |
- Djerf, Tove, 1989, et al.
(author)
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Solids circulation in circulating fluidized beds with low riser aspect ratio and varying total solids inventory
- 2017
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In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 316, s. 670-676
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Journal article (peer-reviewed)abstract
- This paper presents an experimental study with the aim to understand the relation between the flow conditions - the riser pressure drop and fluidization velocity - in a CFB riser and the net (external) solids flux (Gs [kg/m(2) s]), applying a riser geometry and overall flow conditions similar to CFB boilers. The experiments are carried out in a CFB unit operated under ambient conditions. The riser has a cross section of 0.7 m x 0.12 m and a height of 8.5 m, yielding a riser height-to-width aspect ratio of 10.6 (in the wide dimension), similar to that of CFB boilers. The unit is equipped with densely spaced pressure taps providing a fine resolution of the measured vertical pressure profile along the riser and an automatic system to accurately measure G5. The experiments cover fluidization velocities of 03-7 m/s, riser pressure drops of 1.7-10.5 kPa and loop-seal fluidization velocities of 0.12-0.54 m/s (secondary air flow is not included). These ranges correspond to conditions both with and without a dense bottom region. The results show that G(s) is determined by the solids concentration at the riser top, which in turn depends on riser pressure drop and fluidization velocity, and the backflow effect, which depends on the configuration and flow conditions of the loop seal and the exit region. For operating conditions with a dense bottom bed present, G(s) is independent of riser pressure drop at any fluidization velocity, whereas when operating without a dense bed an increase in riser pressure drop increases G(s).
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| 21. |
- Farzaneh, Meisam, 1982, et al.
(author)
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The crucial role of frictional stress models for simulation of bubbling fluidized beds
- 2015
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In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 270:Part A, s. 68-82
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Journal article (peer-reviewed)abstract
- In this paper we combine Eulerian-Lagrangian and Eulerian-Eulerian frameworks to simulate the behavior of a limited number of fuel particles in a bulk of inert particles in a bubbling gas-solid fluidized bed. The gas and the inert phase are treated as interpenetrating continua and resolved within the Eulerian-Eulerian framework, whereas the fuel particles are regarded as a discrete phase. The forces acting on a fuel particle are calculated by using the velocity and pressure fields of the inert solid and gas phases. We assume that the hydrodynamics of the bed are predominantly governed by the motion of the inert solid and gas phases. Therefore, emphasis in this work is on a correct description of the stress tensor of the inert particulate phase and, in particular, on the modeling of frictional stresses, which is of primary importance for continuum simulations of bubbling fluidized beds. Performance of two of the traditionally used frictional stress theories (Schaeffer [12] and Srivastava and Sundaresan [13]) and of the one more recently proposed (Jop et al. [18]) is investigated and the corresponding results are compared with experimental findings in the form of position and velocity of the fuel particles. In addition, preferential positions, the dispersion coefficient, and the average cycle time of the fuel particles motion are obtained by the simulations and compared with experiments. It is observed that the results of the visco-plastic model proposed by Jop et al. [18] are in good agreement with the experiments for prediction of the bed hydrodynamics and the movement of the fuel particles. The other two models underestimate the frictional stresses in the inert solid phase, leading to erroneous predictions of the stress tensor of the inert particulate phase and thus of the entire system.
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| 22. |
- Goop, Joel, 1986, et al.
(author)
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Distributed solar and wind power - Impact on distribution losses
- 2016
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In: Energy. - : Elsevier BV. - 0360-5442. ; 112, s. 273-284
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Journal article (peer-reviewed)abstract
- Introducing renewable electricity as distributed generation may be an attractive option in the shift towards a more sustainable electricity system. Yet, it is not clear to what extent an increased use of distributed generation is beneficial from a systems perspective. We therefore investigate the impacts from increased employment of distributed solar and wind power on losses and transformer capacity requirements in distribution systems. The analysis is based on a dispatch model with a simple representation of typical voltage levels in the distribution system. When electricity is transferred between voltage levels, we subtract losses estimated as the transferred energy times a constant loss factor. Our results show that the losses depend on how load is distributed between voltage levels. For total penetration levels up to 40–50% on an energy basis, we find that wind and solar power could potentially reduce distribution losses. Results further indicate that solar photovoltaic capacity in the low voltage level has a limited potential to decrease peak power flows between voltage levels in a setting where seasonal variations in demand and solar output are opposite to each other. Thereby distributed solar generation also has limited potential to defer investments in transformer capacity between voltage levels.
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| 23. |
- Goop, Joel, 1986, et al.
(author)
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The effect of high levels of solar generation on congestion in the European electricity transmission grid
- 2017
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In: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 205, s. 1128-1140
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Journal article (peer-reviewed)abstract
- The increasing levels of solar power affect the usage and development of electricity grids, both at local distribution level and with respect to potential congestion within the transmission grid. We use a cost-minimising investment model (ELIN) to determine the development of the European electricity generation system up to Year 2050, for two renewable-dominated scenarios: the Green Base scenario, with a Europe-wide, technology-neutral renewable certificate scheme; and the Net Metering scenario, with an additional net metering support scheme for solar power. The system compositions are extracted from the ELIN results for the years 2022 and 2032, and analysed in an hourly dispatch model (EPOD) to study the effects of solar power on marginal electricity costs and transmission congestion. From the results of the investment model, it is clear that the presence of a net metering subsidy scheme significantly affects both the pace at which solar power continues to expand and the geographical distribution of the new capacity. In the dispatch modelling, it can be seen that high penetration levels of solar power have a strong effect on the marginal costs of electricity, since production is concentrated around a few hours each day. At penetration levels of 20–30% of annual electricity demand, solar power production entails a predictable daily marginal cost difference between the solar peak and the evening price peak, which could make short-term storage competitive. Transmission congestion during summer is consistently higher in the systems from the Net Metering scenario than in those from the Green Base scenario, while the opposite is true during winter. Solar power production correlates strongly with congestion 6–9 h after the solar peak, whereas wind power correlates with congestion with respect to more slowly evolving and longer-term variations.
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| 24. |
- Göransson, Lisa, 1982, et al.
(author)
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A comparison of variation management strategies for wind power integration in different electricity system contexts
- 2018
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In: Wind Energy. - : Wiley. - 1099-1824 .- 1095-4244. ; 21:10, s. 837-854
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Journal article (peer-reviewed)abstract
- Variation management strategies improve the capability of the electricity system to meet variations both in the electricity demand and in the generation that relies on variable energy sources. In this work, we introduce a new, functionality-based, categorization of variation management strategies: shifting (eg, batteries), absorbing (eg, power-to-gas), and complementing (dispatchable generation, including reservoir hydropower) strategies. A dispatch model with European coverage (EU-27 plus Norway and Switzerland) is applied to compare the benefits of shifting and absorbing strategies on wind integration in regions with different amounts of complementing strategies in place. The benefits are measured in terms of the wind value factor, wind owner revenue, and average short-term generation cost. The results of the modeling show that the reduction in average short-term generation cost and the increase in revenue earned by the wind owner from shifting strategies, such as the use of batteries, are more substantial at low wind shares than at high wind shares. The opposite situation is found for absorbing strategies, such as power-to-gas, which are found to be more efficient at reducing the average generation cost and increasing profit for the wind owner as the wind share increases. In regions that have access to complementing strategies in the form of reservoir hydropower, variation management has a weak ability to reduce the average short-term generation cost, although it can increase significantly the revenue accrued by the wind power owner.
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| 25. |
- Göransson, Lisa, 1982, et al.
(author)
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Impact of thermal plant cycling on the cost-optimal composition of a regional electricity generation system
- 2017
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In: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 197, s. 230-240
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Journal article (peer-reviewed)abstract
- A regional cost-minimizing investment model that accounts for cycling properties (i.e., start-up time, minimum load level, start-up cost and emissions, and part-load costs and emissions) is developed to investigate the impact of thermal plant cycling on the cost-optimal composition of a regional electricity generation system. The model is applied to an electricity system that is rich in wind resources with and without accounting for cycling in two scenarios: one with favorable conditions for flexible bio-based generation (Bio scenario); and one in which base load is favored (Base load scenario) owing to high prices for biomass. Both scenarios are subject to a tight cap on carbon dioxide emissions, limiting the investment options to technologies that have low or no carbon emissions. We report that in the Bio scenario, the cost-optimal system is dominated by wind power and flexible bio-based generation, whereas base-load generation dominates the Base load scenario, in line with the assumptions made, and the level of wind power is reduced. In the Base load scenario, 19% of the capacity is cycling-dependent, i.e., for this share of installed capacity, the choice of technology is different if cycling properties are included, compared to a case in which they are omitted. In the Bio scenario, in which flexible bio-based generation is less costly, 9% of the capacity is cycling-dependent. We conclude that it is critical to include cycling properties in investment modeling, to assess investments in thermal generation technologies that compete at utilization times in the range of 2000–5000 h.
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