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Sökning: WFRF:(Ajdari Sima 1985)

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1.
  • Ajdari, Sima, 1985, et al. (författare)
  • Risk Evaluation of Household Hazardous Waste-A case study
  • 2009
  • Ingår i: Proceedings of International Symposium on Occupational Safety and Hygiene SHO 2009, 5-6 February, Guimarães, Portugal. - 9789729950452 ; , s. pp. 23-27
  • Konferensbidrag (refereegranskat)abstract
    • ABSTRACTCertain chemicals in household products, when not used up to the completion at homes, may have the potential to spread hazards. These chemicals consist of heavy metals, pesticides and various types of solvent which may be persistent and can cause severe damage to public and environment. These types of waste shall be collected separately from other waste and are in general destroyed in some kind of specific destruction plant. Everyone who creates hazardous waste is responsible for a proper collection. When it comes to household hazardous waste (HHW) this could be a problem since it assumes that everyone in the society has enough knowledge of how to make a proper collection. Some types of hazardous waste are well-known and easy to recognize, e.g. solvents and batteries, but many people do not have any idea about some of the harmful products which they use and waste. Due to the fact that the hazardous waste is spread out in all households and that everyone is responsible for their own collection, leakages into the environment are possible in today's system. Therefore, a fact finding study is needed to be conducted to see: what would be the main causes of the release of household hazardous wastes (HHW) into the environment during the collection and to evaluate the risks of such an event. This study is carried out based on two studies conducted at Chalmers University of Technology and focused on a case related to collection procedure of HHW in Gothenburg city, Sweden. The aim of the study is to develop a framework to find the most hazardous scenarios, the main causes of release of HHW into the environment. The goal is to propose a guide line to improve the collection procedure with lowest or acceptable risk.Initially, by using “what if” analysis the most important possible scenarios have been discovered. The results have been used in constructing a “fish bone” diagram to analyze the collection methods in Gothenburg city in order to discover the most important causes of the release of hazardous waste into the environment. Based on the fact that nearly 20% of the HHWs are not collected at all (reference), the most hazardous scenario is when “there is no attempt to collect the household hazardous waste”. Subsequently a few scenarios of release to nature have been chosen to be investigated by setting up a model for semi quantitative risk analysis. Risk ranking has been performed with the aim of determining areas associated with high and very high risks. Finally, potential improvements have been discussed.
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2.
  • Ajdari, Sima, 1985 (författare)
  • Chemistry and Process Design of Integrated Removal of Nitrogen and Sulfur oxides in Pressurized Flue Gas Systems
  • 2019
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Carbon capture and storage is vital to reach the climate goals to limit the increase in the global temperature. Among the carbon capture technologies, oxy-fuel and chemical looping combustion produce a stream mainly containing carbon dioxide (CO2) and water but also contaminants such as nitrogen oxides (NOx) and sulfur oxides (SOx). The carbon dioxide is compressed and separated from water and impurities to achieve suitable conditions for transport and storage. In addition to storage and transport system requirements, separation of NOx and SOx during the CO2-conditioning is required to avoid corrosion issues in various parts of the process. In addition to the emission control measures available for conventional power plants, there are new opportunities for control of NOx and SOx in pressurized flue gas systems of oxy-fuel and chemical looping combustion plants. The work presented in this thesis evaluates the chemistry and process design of NOx and SOx removal during CO2-conditioning in oxy-fuel and chemical looping combustion systems. The primary goals of this thesis are to expand the current understanding of NOx and SOx chemistry and identify favorable conditions for achieving cost-effective control processes. Analysis of the reaction system by a detailed chemistry model, uncovers the importance of pH level in the liquid for the selectivity of the integrated NOx and SOx removal process. Moreover, a reduced mechanism is proposed for engineering calculations of the pressurized flue gas systems that captures the effect of pH and describes the relevant gas and liquid-phase chemistry. Process simulations, which utilize the reduced mechanism, enable evaluation of design of the integrated removal of NOx and SOx in pressurized flue gas systems. Technical evaluation of the integrated process reveals that removal rates of >98% for SO2 and >90% for NOx may be achieved. Moreover, the efficiency of the NOx removal can be improved by the presence of SOx and increased concentration of O2 in the flue gas. A comparison of the economic performance of the integrated removal process and the conventional emission control measures, i.e., selective catalytic reduction and wet flue gas desulfurization with limestone, shows significantly lower costs of removal by the integrated process.
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3.
  • Ajdari, Sima, 1985, et al. (författare)
  • Evaluation of Operating and Design Parameters of Pressurized Flue Gas Systems with Integrated Removal of NO x and so x
  • 2019
  • Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 33:4, s. 3339-3348
  • 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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4.
  • Ajdari, Sima, 1985, et al. (författare)
  • Formation and Control of NOx and SOx in Pressurized Oxy-Combustion Systems
  • 2015
  • Ingår i: The Proceedings of the 40th International Technical Conference on Clean Coal & Fuel Systems, 31 May-4 June 2015, Clearwater, Florida, USA.
  • 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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6.
  • Ajdari, Sima, 1985, et al. (författare)
  • Modeling the Nitrogen and Sulfur Chemistry in Pressurized Flue Gas Systems
  • 2015
  • Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 54:4, s. 1216-1227
  • 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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8.
  • Ajdari, Sima, 1985, et al. (författare)
  • NOx AND SOx CHEMISTRY IN PRESSURIZED FLUE GAS SYSTEMS: IMPORTANCE FOR CHEMICAL LOOPING COMBUSTION
  • 2014
  • Ingår i: 3rd International Conference on Chemical Looping, 9-11 September 2014, Gothenburg, Sweden.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The control of NOx and SOx in chemical-looping combustion systems is discussed with the focus on the importance of the pressurized flue-gas train. The chemistry of nitrogen and sulfur under pressurized conditions and the experiences gained from operating oxy-fuel combustion pilot plants that pertain to chemical looping are reviewed. In the flue gases from the combustion process, SO2 and NO are the principle NOx and SOx species. The oxidation of NO to NO2 is favored by low temperature and high pressure and is enhanced during the compression of flue gases. The oxidation of NO to NO2 in the flue-gas train is significant at pressures >15 bar. The solubilities of NO2 and SO2 in water are high and results in the formation of acids. Once NOx and SOx are absorbed, the liquid-phase N-S interactions lead to the formation of sulfuric and nitric acids. Thus, the chemistry of NOx and SOx is of importance for flue-gas conditioning of chemical-looping combustion systems. Similar to oxy-fuel combustion, the conditions in the chemical-looping flue-gas train offer new opportunities for the design of NOx and SOx removal processes.
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  • Resultat 1-10 av 14

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