| 1. |
- Òsk Gardarsdòttir, Stefanìa, 1987, et al.
(författare)
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Improving the flexibility of coal-fired power generators: Impact on the composition of a cost-optimal electricity system
- 2018
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 209, s. 277-289
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Tidskriftsartikel (refereegranskat)abstract
- A transformation of the electricity generation system is required to drastically reduce the associated CO2 emissions. In future systems, variable renewable energy sources (wind and solar) are expected to provide a significant fraction of the electricity supply, increasing the requirement for variation management compared with today´s situation. This paper investigates the impacts of measures designed to increase the competitiveness of coal-fired power plants in future energy systems, which are facing restrictions related to CO2 emissions and variable operation as a consequence of high penetration levels of wind and solar power. We investigate the cost-optimal compositions of three regional electricity generation systems with different conditions for generation using renewables with a linear cost-minimizing investment model. The model is applied in two energy policy scenarios: one with a tight cap on CO2 emissions, and one with a stringent requirement for generation from renewables. In a system with a stringent requirement for electricity generation from renewables but without a CO2 cap, coal-based technologies with improved cycling properties provide variation management, given that the development of measures for ensuring improved flexibility continues and reaches full-scale implementation at moderate cost. The effects of improved cycling properties on the system composition are especially relevant for regions with moderate potential for wind and solar generation, in that they reduce wind curtailment and improve the underlying conditions for investments in solar power. In the system with a tight CO2 cap, only coal-based technologies with Carbon Capture and Storage (CCS) and co-firing of biomass are feasible. Increasing the share of biomass in co-firing technologies to achieve negative CO2 emissions increases the competitiveness of these technologies to a greater extent than if simply the cycling properties are improved. A larger co-firing fraction reduces the total system costs, since it facilitates the provision of low-cost flexibility by Natural Gas Combined Cycle (NGCC) plants, and it is especially important in regions where nuclear power is otherwise cost-competitive, as low-cost flexibility stimulates investments in wind and solar power at the expense of nuclear power.
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| 2. |
- Ajdari, Sima, 1985, et al.
(författare)
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Evaluation of Operating and Design Parameters of Pressurized Flue Gas Systems with Integrated Removal of NO x and so x
- 2019
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 33:4, s. 3339-3348
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the operating and design parameters of product gas compression and integrated control of nitrogen oxides (NO x ) and sulfur oxides (SO x ) in large-scale oxy-fuel and chemical looping combustion processes. A process model that includes a comprehensive description of nitrogen and sulfur chemistry and mass transfer is developed. The results show that the fraction of NO oxidation into NO 2 will be 10-50% in a multistage compressor to 30 bars (1-4% O 2 in the gas) depending on the residence times in intercoolers and pressure levels. At lower O 2 concentrations (>0.1% O 2 in the gas), the oxidation is limited but still active. Nitric acid formation in the compressor condensate is, thus, inevitable, although limited, as most water is condensed in the early stages, whereas the acid gases are formed in the later stages. The NO 2 /NO x ratio has an important effect on the total amount of NO x absorbed and extra residence time should be added after the compressor to increase this ratio. Evaluation of the process behavior in relation to simultaneous absorption of SO 2 and NO x revealed that increased SO 2 /NO x ratio and bottom liquid recycling enhanced the total NO x absorption. In addition, maintaining the pH in the absorbing solution above 5 improves the removal efficiencies of NO x and SO 2 . NO x removal rates of up to around 95% can be achieved for SO 2 /NO x > 1 in the flue gas with appropriate design of the absorber. For SO 2 /NO x < 1, increasing the packing height or addition of S(IV) solutions could enhance the NO x removal rates to 95% or more. The model predictions are compared with the experimental data from a laboratory-scale absorber. The process model developed in this work enables design studies and techno-economic evaluation of absorption-based NO x and SO x removal concepts.
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| 3. |
- Ajdari, Sima, 1985, et al.
(författare)
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Formation and Control of NOx and SOx in Pressurized Oxy-Combustion Systems
- 2015
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Ingår i: The Proceedings of the 40th International Technical Conference on Clean Coal & Fuel Systems, 31 May-4 June 2015, Clearwater, Florida, USA.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The formation and control of NOx and SOx in pressurized oxy-fuel combustion systems is discussed in the present work. The chemistry of nitrogen and sulfur species under pressurized conditions and the experiences gained from operating atmospheric oxy-fuel combustion pilot plants are reviewed in brief. In a conventional combustion and gas cleaning process, SO2 and NO are the principle NOx and SOx species. However, the oxidation of NO to NO2 and SO2 to SO3 is favored by low temperature and high pressure. In the present paper we will make a first modelling based of the altered oxidation conditions during both high and low temperature conditions in pressurized oxy-combustion. Besides the gas-phase oxidation, the liquid-phase N-S interactions will further enhance the formation of acids in the flue gas condensate. Thus, these low and high temperature processes will be discussed in the present work due to their relevance for the design of the flue gas compression and gas cleaning system in pressurized oxy-combustion.
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| 4. |
- Ajdari, Sima, 1985, et al.
(författare)
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Modeling the Nitrogen and Sulfur Chemistry in Pressurized Flue Gas Systems
- 2015
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 54:4, s. 1216-1227
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Tidskriftsartikel (refereegranskat)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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| 5. |
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| 6. |
- Ajdari, Sima, 1985, et al.
(författare)
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Reduced Mechanism for Nitrogen and Sulfur Chemistry in Pressurized Flue Gas Systems
- 2016
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 55:19, s. 5514-5525
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Alamia, Alberto, 1984, et al.
(författare)
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Efficiency Comparison of Large-Scale Standalone, Centralized, and Distributed Thermochemical Biorefineries
- 2017
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Ingår i: Energy Technology. - : Wiley. - 2194-4296 .- 2194-4288. ; 5:8, s. 1435-1448
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.We present a comparison of three strategies for the introduction of new biorefineries: standalone and centralized drop-in, which are placed within a cluster of chemical industries, and distributed drop-in, which is connected to other plants by a pipeline. The aim was to quantify the efficiencies and the production ranges to support local transition to a circular economy based on biomass usage. The products considered are biomethane (standalone) and hydrogen/biomethane and sustainable town gas (centralized drop-in and distributed drop-in). The analysis is based on a flow-sheet simulation of different process designs at the 100MWbiomass scale and includes the following aspects: advanced drying systems, the coproduction of ethanol, and power-to-gas conversion by direct heating or water electrolysis. For the standalone plant, the chemical efficiency was in the range of 78-82.8% LHVa.r.50% (lower heating value of the as-received biomass with 50% wet basis moisture), with a maximum production of 72MWCH4 , and for the centralized drop-in and distributed drop-in plants, the chemical efficiency was in the range of 82.8-98.5% LHVa.r.50% with maximum production levels of 85.6MWSTG and 22.5MWH2 /51MWCH4 , respectively. It is concluded that standalone plants offer no substantial advantages over distributed drop-in or centralized drop-in plants unless methane is the desired product.
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| 8. |
- Ali, Hassan, et al.
(författare)
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Cost Estimation of CO2 Absorption Plants for CO2 Mitigation – Method and Assumptions
- 2019
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 88, s. 10-23
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Tidskriftsartikel (refereegranskat)abstract
- The estimates of post combustion CO2 capture costs reported in the literature range from 50 €/tCO2 to 128 €/tCO2, reflecting differences in the cost estimation methods used, scopes of the analyses, and assumptions made. This variation in calculated costs is important when evaluating the feasibility of a technology and highlights the importance of ensuring consistency and transparency in cost estimations. This study establishes a cost estimation tool that highlights the effects of different assumptions on the overall cost of a capture plant and identifies the crucial technical and economic factors. The input is a simplified process flow diagram and equipment list. Detailed installation factors and the equipment cost are the two main elements used to derive the capital expenditures (CAPEX), which represent a fundamental component of the cost estimation approach. A detailed installation factor sheet is used for the capital cost estimation. The method is applied to a Base case that involves the capture of CO2 from the flue gas of a process industry, giving a capture cost of 62.5 €/tCO2. The Base case results reveal that the steam cost, electricity cost, and capital cost are the main contributors. This method can provide an overview of the main cost drivers, and a sensitivity analysis of the variable input parameters can be performed simply and quickly. The results obtained using this method can be valuable in the early phase of the project and contribute to decision making.
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| 9. |
- Ali, Hassan, et al.
(författare)
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Cost estimation of heat recovery networks for utilization of industrial excess heat for carbon dioxide absorption
- 2018
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 74, s. 219-228
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Tidskriftsartikel (refereegranskat)abstract
- The absorption of CO 2 using solvents (e.g., amines) is considered a state-of-the-art, albeit energy-intensive process for CO 2 capture. While it is generally recognized that the utilization of waste heat has potential to reduce the energy-associated costs for CO 2 capture, the cost of waste heat recovery is seldom quantified. In this work, the cost of heat-collecting steam networks for waste heat recovery for solvent regeneration is estimated. Two types of networks are applied to waste heat recovery from the flue gases of four process industries (cement, silicon, iron & steel, and pulp & paper) via a heat recovery steam generator (HRSG). A novel approach is presented that estimates the capital and operational expenditures for waste heat recovery from process industries. The results show that the overall cost (CAPEX + OPEX) of steam generated from one hot flue gas source is in the range of 1.1–4.1 €/t steam. The cost is sensitive to economic parameters, installation factors, the overall heat transfer coefficient, steam pressure, and to the complexity of the steam network. The cost of steam from an existing natural gas boiler is roughly 5–20-times higher than that of steam generated from recovered waste heat. The CAPEX required to collect the heat is the predominant factor in the cost of steam generation from waste heat. The major contributor to the CAPEX is the heat recovery steam generator, although the length of the steam pipeline (when heat is collected from two sources or over long distances) is also important for the CAPEX.
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| 10. |
- Allgurén, Thomas, 1986, et al.
(författare)
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NO formation during co-combustion of coal with two thermally treated biomasses
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The behavior of biomass as a fuel varies a lot. Not only between different sources of raw material, but also depending on if they have been pre-treated, and if so, also depending on the type of treatment. Two types of thermal pre-treatments of woody biomass used for combustion in suspension systems are torrefaction and steam explosion. These two types of pre-treated biomass were investigated in this work with focus on the nitrogen chemistry, and were investigated both experimentally in a 1.5MWth combustion unit and by performing detailed reaction simulations. Three different cases have been investigated. One case with 100% Utah Sufco coal and two cases where 15% of the coal (on a mass basis) has been replaced with either torrefied or steam exploded biomass. Even though only 15% of the coal has been substituted there is a clear difference in the amount of NO formed between the cases. The pure coal had the highest amount of NO formed which was expected due to the higher amount of fuel-bound nitrogen in the coal compared to the biomasses. The fuel analyses indicate that the nitrogen content is the same in the two investigated bio fuels. Despite this fact, the amount of NO formed was when coal was co-fired with torrefied biomass than with steam exploded biomass. The gas composition data from the in-flame measurements show that the concentration of volatile nitrogen species (HCN and NH3) varies between the cases, which is suggested as the reason for the difference in the NO formation. The importance of when and where the nitrogen species are released is also shown in the modelling work, supporting what was observed experimentally.
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