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Sökning: WFRF:(Malik Azhar)

  • Resultat 1-9 av 9
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  • Einvall, Jessica, et al. (författare)
  • Investigation of reforming catalyst deactivation by exposure to fly ash from biomass gasification in laboratory scale
  • 2007
  • Ingår i: Energy & Fuels. - American Chemical Society (ACS). - 0887-0624. ; 21:5, s. 2481-2488
  • Tidskriftsartikel (refereegranskat)abstract
    • Production of synthesis gas by catalytic reforming of product gas from biomass gasification can lead to catalyst deactivation by the exposure to ash compounds present in the flue gas. The impact of fly ash from biomass gasification on reforming catalysts was studied at the laboratory scale. The investigated catalyst was Pt/Rh based, and it was exposed to generated K2SO4 aerosol particles and to aerosol particles produced from the water-soluble part of biomass fly ash, originating from a commercial biomass combustion plant. The noble metal catalyst was also compared with a commercial Ni-based catalyst, exposed to aerosol particles of the same fashion. To investigate the deactivation by aerosol particles, a flow containing submicrometer-size selected aerosol particles was led through the catalyst bed. The particle size of the poison was measured prior to the catalytic reactor system. Fresh and aerosol particle exposed catalysts were characterized using BET surface area, XRPD (X-ray powder diffraction), and H2 chemisorption. The Pt/Rh catalyst was also investigated for activity in the steam methane reforming reaction. It was found that the method to deposit generated aerosol particles on reforming catalysts could be a useful procedure to investigate the impact of different compounds possibly present in the product gas from the gasifier, acting as potential catalyst poisons. The catalytic deactivation procedure by exposure to aerosol particles is somehow similar to what happens in a real plant, when a catalyst bed is located subsequent to a biomass gasifier or a combustion boiler. Using different environments (oxidizing, reducing, steam present, etc.) in the aerosol generation adds further flexibility to the suggested aerosol deactivation method. It is essential to investigate the deactivating effect at the laboratory scale before a full-scale plant is taken into operation to avoid operational problems.
  • Malik, Azhar (författare)
  • Characteristic Properties and Applications of Fine Particles in Biomass Gasification
  • 2011
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Many of the energy needs in today’s modern society are fulfilled by sources based on fossil fuels, including non-domestic oil and coal. It is well known that the increase in CO2 emission is the result of human activities, mostly fossil fuel consumption. The use of such fuels is unsustainable and has led to the phenomena such as climate change, political instability in some parts of the world and, most important of all, an imbalance in the natural environment – in which we humans live with other organisms. The shift to a sustainable way of living is much needed if we wish to safeguard the environment for future generations and still enjoy a modern and conscious living. There is growing public awareness of alternative energy sources, and bioenergy is one of the options that can help us combat global warming, reduce the emission of harmful gases, and exploit local energy sources. The thermochemical conversion of biomass has emerged as a suitable technology of choice. It has attracted a great deal of interest from the research and development community due to its potential to help meet energy demands in a sustainable way, mainly through the possibility of producing liquid and gaseous fuels. Further exploitation of this technology will result in a reduction of net greenhouse gas emissions and hence counteract global warming effect. The thermochemical conversion of biomass consists of combustion (to produce energy) and gasification (to produce heat, power, chemicals and vehicle fuel). This thesis deals with biomass gasification and the impact of the emitted impurities on downstream cleaning systems and catalytic upgrading processes. As with any other energy conversion process, biomass gasification is not without challenges and technical obstacles that must be overcome. The gaseous and particulate contaminants present in the produced gas threaten the performance of catalytic processes of producing biofuels, and integrated heat and power generation. There is a reasonable understanding and technological development available to handle gaseous poisonous compounds but the removal of contaminants in particulate form in the harsh environment inside the gasifier remains as serious problem. The high-temperature cleaning devices available do not optimally meet the requirements for the level of contaminants in the producer gas suitable for most applications. The research presented in this thesis describes the efforts made to understand the post-gasification handling of producer gas to remove particle contaminants, and the study of different mechanisms of particle formation in order to develop efficient filtration devices. Effects on the upgrading process have been studied, demonstrating a loss of catalytic activity due to the presence of harmful particulates in the post-gasifier streams. A method has been developed to characterize the particles in producer gas which can be used to evaluate the filtration efficiency of particle removal systems. The initial testing of developed method at a lab-scale gasifier has shown its ability to sample representative particles, from which useful information on their characteristic properties can be obtained. The developed soot-particles generator was also utilized in the application of soot sensor for online detection of soot in high-temperature processes, e.g. in a vehicle exhaust diesel particulate filter and combustion boilers. This scientific work constitutes a step forward in our understanding of the formation of particles, their impact on downstream technological systems, and the development of gas cleaning devices for biomass gasification applications. The knowledge gained through this work will aid the further development of gasification technology for bioenergy, and hence the shift towards a more sustainable society.
  • Malik, Azhar, et al. (författare)
  • Methodology for Sampling and Characterizing Internally Mixed Soot-Tar Particles Suspended in the Product Gas from Biomass Gasification Processes
  • 2011
  • Ingår i: Energy & Fuels. - ACS Publications (American Chemical Society Publications). ; 25:4, s. 1751-1758
  • Tidskriftsartikel (refereegranskat)abstract
    • When biomass is used to produce fuels and green products by thermochemical conversion, the ability to handle or remove the fine particle phase in the product gas is crucial. The product gas from biomass gasification contains relatively volatile organic compounds (“tar”) condensed on nonvolatile cores of, for example, aggregated soot particles and char. The problems are, for example, that particles will poison catalysts used for upgrading of the gas and loss of thermal energy occurs when carbonaceous particles are being formed. The aim of the work is to design and use novel methodologies to characterize the particles in the product gas stream. A methodology has been developed to sample and characterize fine particles by a sampling probe connected to either a denuder or a packed bed device. The system was designed to avoid condensation of organic compounds when diluting the sample and decreasing the temperature. A flame soot generator connected to a condensation−evaporation unit was used to produce internally mixed model particles, i.e., particles consisting of a core of soot with an outer layer of condensed volatile compounds. A scanning mobility particle sizer (SMPS) and a differential mobility analyzer followed by an aerosol particle mass analyzer (APM) were used to characterize the particles. Because of the agglomerated structure of soot, the SMPS system was not adequate to fully characterize the mass of volatiles condensed onto the soot core, and therefore the DMA-heater-APM technique was used to determine the mass fraction of the condensed phase on the soot particles. The two different configurations were studied, and the sampling system was shown to work at a high load of organic mass. In both cases, the organic removal efficiency was >99.5%. Minor condensation of organics on the sampled soot was found for the denuder but not the packed bed. On the other hand, the particle losses were substantially higher for the packed bed compared to the denuder. The results showed that the tested sampling methodology can be used to get sufficient characterization of particles in the product gas and to evaluate the performance of biomass product gas cleaning systems at high temperature.
  • Nilsson, Patrik, et al. (författare)
  • Laboratory evaluation of a gasifier particle sampling system using model compounds of different particle morphology
  • 2011
  • Ingår i: Biomass Conversion & Biorefinery. - Springer Verlag.
  • Tidskriftsartikel (refereegranskat)abstract
    • The objective of this work was to design and evaluate an experimental setup to be used for field studies of particle formation in biomass gasification processes. The setup includes a high-temperature dilution probe and a denuder to separate solid particles from condensable volatile material. The efficiency of the setup to remove volatile material from the sampled stream and the influence from condensation on particles with different morphologies is presented. In order to study the sampling setup model, aerosols were created with a nebulizer to produce compact and solid KCl particles and a diffusion flame burner to produce agglomerated and irregular soot particles. The nebulizer and soot generator was followed by an evaporation–condensation section where volatile material, dioctylsebacete (DOS), was added to the system as a tar model compound. The model aerosol particles were heated to 200°C to create a system containing both solid particles and volatile organic material in gas phase. The heated aerosol particles were sampled and diluted at the same temperature with the dilution probe. Downstream the probe, the DOS was adsorbed in the denuder. This was achieved by slowly decreasing the temperature of the diluted sample towards ambient level in the denuder. Thereby the supersaturation of organic vapors was reduced which decreased the probability for tar condensation and nucleation of new particles. Both the generation system and the sampling technique gave reproducible results. A DOS collection efficiency of >99% was achieved if the denuder inlet concentration was diluted to less than 1–6 mg/m3 depending on the denuder flow rate. Concentrations higher than that lead to significant impact on the resulting KCl size distribution. The choice of model compounds was done to study the effect from the particle morphology on the achieved particle characteristics after the sampling setup. When similar amounts of volatile material condensed on soot agglomerates and compact particles, a substantially smaller growth in mobility diameter was found for soot compared with compact KCl.
  • Nilsson, Patrik, et al. (författare)
  • Sampling and Characterization of Sub-Micrometer High-Temperature Particles Present in the Product Gas from a Circulating Fluidized-Bed Biomass Gasifier
  • 2013
  • Ingår i: Energy & Fuels. - American Chemical Society. - 0887-0624. ; 27:6, s. 3290-3295
  • Tidskriftsartikel (refereegranskat)abstract
    • The removal of particulate fine fractions by a proper high-temperature cleaning device is a very important issue in the development of the biorefinery concept. Therefore, in this investigation, particles from a 100 kW(th) steam-O-2 blown circulating fluidized-bed (CFB) gasifier were sampled and characterized. The sampling was performed with a specially designed heated dilution probe downstream of a high-temperature candle filter element. The dilution probe was followed by a bed of activated carbon to separate the condensed phase from the particle phase by reducing the supersahuation of the volatile material. Parallel measurements were performed by a scanning mobility particle sizer (SMPS) and sample collection by a cascade impactor assembly to obtain information about the particle size distribution and elemental analysis, respectively. The measured particle mass was found to be dominated by coarse particles from bed material together with high amounts of potassium, which is thought to have penetrated through the filter. The aim of this work is to validate the developed particle measuring setup by performing physical and chemical characterization of the fine-particle fraction that is not captured by the filtering system to avoid the catalytic deactivation of the downstream upgrading processing.
  • Raykova, Doroteya, et al. (författare)
  • Autosomal Recessive Transmission of a Rare KRT74 Variant Causes Hair and Nail Ectodermal Dysplasia
  • 2014
  • Ingår i: PLoS ONE. - 1932-6203. ; 9:4, s. e93607
  • Tidskriftsartikel (refereegranskat)abstract
    • Pure hair and nail ectodermal dysplasia (PHNED) comprises a heterogeneous group of rare heritable disorders characterized by brittle hair, hypotrichosis, onychodystrophy and micronychia. Autosomal recessive (AR) PHNED has previously been associated with mutations in either KRT85 or HOXC13 on chromosome 12p11.1-q14.3. We investigated a consanguineous Pakistani family with AR PHNED linked to the keratin gene cluster on 12p11.1 but without detectable mutations in KRT85 and HOXC13. Whole exome sequencing of affected individuals revealed homozygosity for a rare c.821T> C variant (p.Phe274Ser) in the KRT74 gene that segregates AR PHNED in the family. The transition alters the highly conserved Phe274 residue in the coil 1B domain required for long-range dimerization of keratins, suggesting that the mutation compromises the stability of intermediate filaments. Immunohistochemical (IHC) analyses confirmed a strong keratin-74 expression in the nail matrix, the nail bed and the hyponychium of mouse distal digits, as well as in normal human hair follicles. Furthermore, hair follicles and epidermis of an affected family member stained negative for Keratin-74 suggesting a loss of function mechanism mediated by the Phe274Ser substitution. Our observations show for the first time that homozygosity for a KRT74 missense variant may be associated with AR PHNED. Heterozygous KRT74 mutations have previously been associated with autosomal dominant woolly hair/ hypotrichosis simplex (ADWH). Thus, our findings expand the phenotypic spectrum associated with KRT74 mutations and imply that a subtype of AR PHNED is allelic with ADWH.
  • Rissler, Jenny, et al. (författare)
  • Effective Density Characterization of Soot Agglomerates from Various Sources and Comparison to Aggregation Theory
  • 2013
  • Ingår i: Aerosol Science and Technology. - Taylor & Francis Inc. - 0278-6826. ; 47:7, s. 792-805
  • Tidskriftsartikel (refereegranskat)abstract
    • Soot particle (black carbon) morphology is of dual interest, both from a health perspective and due to the influence of soot on the global climate. In this study, the mass-mobility relationships, and thus effective densities, of soot agglomerates from three types of soot emitting sources were determined in situ by combining a differential mobility analyzer (DMA) and an aerosol particle mass analyzer (APM). High-resolution transmission electron microscopy was also used. The soot sources were diesel engines, diffusion flame soot generators, and tapered candles, operated under varying conditions. The soot microstructure was found to be similar for all sources and settings tested, with a distance between the graphene layers of 3.7-3.8 angstrom. The particle specific surface area was found to vary from 100 to 260m(2)/g. The particle mass-mobility relationship could be described by a power law function with an average exponent of 2.3 (+/- 0.1) for sources with a volatile mass fraction <10% and primary particle sizes of 11-29nm. The diesel exhaust from a heavy duty engine at idling had a substantially higher volatile mass fraction and a higher mass-mobility exponent of 2.6. The mass-mobility exponent was essentially independent of the number of primary particles in the range covered (N-pp = 10-1000). Despite the similar exponents, the effective density varied substantially from source to source. Two parameters were found to alter the effective density: primary particle size and coating mass fraction. A correlation was found between primary particle size and mass-mobility relationship/effective density and an empirical expression relating these parameters is presented. The effects on the DMA-APM results of doubly charged particles and DMA agglomerate alignment were investigated and quantified. Finally, the dataset was compared to three theoretical approaches describing agglomerate particles' mass-mobility relationship. Copyright 2013 American Association for Aerosol Research
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