| 1. |
- Tranvik, AC, et al.
(författare)
-
Bed material deposition in cyclones of wood fuel fired circulating fluidized beds (CFBs)
- 2007
-
Ingår i: Energy & Fuels. - Washington : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 21:1, s. 104-109
-
Tidskriftsartikel (refereegranskat)abstract
- Bed material samples were collected at different times from a full-scale combustion boiler, and bed material deposits were taken from the cyclone and the riser at two different occasions from a wood-fired circulating fluidized bed boiler (104 MWth). The bed materials and the bed material deposits were analyzed with environmental scanning electron microscopy/energy-dispersive X-ray spectroscopy (ESEM/EDXS) to determine the characteristics of the formed bed particle layers and bed material deposits. On the basis of their elemental composition, the corresponding melting behavior was estimated, using data extracted from phase diagrams. The bed material was also fractionated by sieving, and the alkali metal concentration dependence on the particle size was determined. The bed material deposits found in the cyclone and the riser consisted of bed particles embedded in a low-temperature melting (sticky) alkali metal silicate (K and Na) that resemble the composition of the layer found around the cracks in older quartz bed particles. The alkali silicate formation, which is in progress in the vicinity of the formed cracks of older quartz bed particles, significantly transforms a large part of the bed particle and makes it less resistant against fragmentation. The results therefore suggest that elutriated alkali silicate-rich fragments from old quartz bed particles are responsible for bed material depositions in cyclones of wood-fired circulating fluidized beds (CFBs).
|
|
| 2. |
- 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 .- 1520-5029. ; 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.
|
|
| 3. |
- Fhager, Andreas, 1976, et al.
(författare)
-
A statistical approach to gradient scaling microwave tomography
- 2007
-
Ingår i: Proceedings of EMB 07, computational electromagnetis, methods and applications, Lund, Sweden. ; , s. 153-160, s. 153-160, s. 153-160
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 4. |
- Fhager, Andreas, 1976, et al.
(författare)
-
A Statistically Based Preconditioner for Two-Dimensional Microwave Tomography
- 2007
-
Ingår i: Proceedings of The Second International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP2007), Dec. 12-14 2007, St. Thomas, U.S. Virgin Islands. - 9781424417148 ; , s. 173-176
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 5. |
- Kirm, Ilham, et al.
(författare)
-
Shift catalysts in biomass generated synthesis gas
- 2007
-
Ingår i: Topics in catalysis. - : Springer verlag. - 1022-5528 .- 1572-9028. ; 45:1-4, s. 31-37
-
Tidskriftsartikel (refereegranskat)abstract
- One of the CHRISGAS project objectives is to study the shift catalysts in biomass-generated synthesis gas. The water gas shift reaction is ruled by equilibrium, and the state of the gas can for a given H2/CO ratio be shifted by addition/removal of water, CO2 and/or by a change in the temperature. Stability area in respect to gas composition, sulphur content, pressure and temperature for FeCr shift catalyst has been investigated by thermodynamic equilibrium calculations. The calculations show that carbide formation is favourable in the “Normal water” case without sulphur in the gas. If sulphur is present in the gas, the situation improves due to sulphide formation.
|
|
| 6. |
- Larsson, Ann-Charlotte, et al.
(författare)
-
Physical and chemical characterisation of potassium deactivation of a SCR catalyst for biomass combustion
- 2007
-
Ingår i: Topics in catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 45:1-4, s. 149-152
-
Tidskriftsartikel (refereegranskat)abstract
- The deactivation of a commercial Selective Catalytic Reduction (SCR) catalyst, of V2O5-WO3/TiO2 type, has been studied through comparisons with results from a full-scale biomass combustion plant to that with laboratory experiments. In the latter, the catalyst was exposed to KCl and K2SO4 by both wet impregnation with diluted salt solutions and deposition of generated submicrometer aerosol particles by means of an electrostatic field. The reactivity of fresh and deactivated samples was examined in the SCR reaction. Chemical and physical characterizations were focusing on internal structures and chemical composition. Deposition of submicrometer sized particles on the monolithic SCR catalyst was shown to induce deactivation with characteristics resembling those obtained in a commercial biomass combustion plant.
|
|
| 7. |
- Larsson, Ann-Charlotte, et al.
(författare)
-
Pilot-scale investigation of Pt/alumina catalysts deactivation by organosilicon in the total oxidation of hydrocarbons
- 2007
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 45:1-4, s. 121-124
-
Tidskriftsartikel (refereegranskat)abstract
- The deactivation of alumina-supported platinum catalyst for VOC oxidation by long-term exposure for hexamethyldisiloxane (HMDS) has been investigated in a pilot scale reactor for up to 1000 h of exposure. Catalyst samples were characterized by ICP-AES, BET and silicon deposition by SEM. Catalyst activity was investigated using oxidation of ethyl acetate showing deactivation of the catalyst samples as exposed to HMDS increasing with exposure time. Silicon was shown to deposit on the catalyst as well as on the blank alumina support. SEM investigation of an individual pellet revealed a radial eggshell silicon distribution. CO chemisorption showed strong decrease of Pt active sites after deactivation, while still maintaining reasonable oxidation levels of ethyl acetate.
|
|
| 8. |
- Cijvat, Pieternella, et al.
(författare)
-
A GaN HEMT power amplifier with variable gate bias for envelope and phase signals
- 2007
-
Ingår i: [Host publication title missing]. - Aalborg, Denmark : Institute of Electrical and Electronics Engineers (IEEE). - 9781424415168 ; , s. 108-111
-
Konferensbidrag (refereegranskat)abstract
- This paper describes the design, simulation and measurement of a GaN power amplifier suitable for envelope and phase signal combination. The low-frequency envelope signal is used to vary the gate (bias) voltage of the device, resulting in a pulse width modulated drain voltage, while modulation of supply voltage or current is avoided. The test circuit is implemented using a discrete GaN HEMT power amplifier and discrete surface-mount passive components assembled on a PCB. Measurements showed a maximum drain efficiency of 59% at 360 MHz, at an output power of 29 dBm. The output power as a function of the gate bias voltage varied between 3 and 29 dBm, with the drain efficiency varying between 6 and 59%.
|
|
| 9. |
- Johannesson, Björn, et al.
(författare)
-
Multi-species ionic diffusion in concrete with account to interaction between ions in the pore solution and the cement hydrates
- 2007
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 40:7, s. 651-665
-
Tidskriftsartikel (refereegranskat)abstract
- The penetration and leaching of ionic species in concrete are studied by using a model based on the Nernst-Planck equations. A finite element procedure is used to solve the coupled non-linear governing equations. A numerical example is performed in which the results are compared to measured electron probe micro analysis (EPMA) data. A close agreement of the simulated results to measured data is found for the specific studied example. The model includes the ionic species Cl-, Na+, OH-, Ca2+, K+ and SO42- and solid phases with variable composition. From the EPMA measurements the total concentration profiles of Cl-, CaO, SiO2, Na2O and SO3 are evaluated on samples exposed to a 3 wt% sodium chloride solution for 1 year. The main task in this investigation is to quantitatively understand the underlying mechanisms and find an accurate model that gives good correlation with the experimental results concerning the multi-species action during chloride penetration. In the model the chemical interaction between ions in solids and in pore solution is assumed governed by simple ion exchange processes only. The drawback using this approach is that the chemical part is lacking important physical relevance in terms of standard solubility thermodynamics. On the other hand the presented model is capable of accurately simulate the well documented peak behavior of the chloride profiles and the measured high content of calcium ions in pore solution under conditions when also chlorides is present. In this sense the established multi-species models for concrete based on standard solubility calculations alone is still incomplete.
|
|
| 10. |
- Larsson, Ann-Charlotte, et al.
(författare)
-
Deactivation of SCR Catalysts by Exposure to Aerosol Particles of Potassium and Zinc Salts
- 2007
-
Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 41:4, s. 369-379
-
Tidskriftsartikel (refereegranskat)abstract
- Generated aerosol particle deposition has been applied in laboratory scale to induce deactivation of commercial Selective Catalytic Reduction (SCR) catalysts Of V2O5-WO3/TiO2 monolithic type. The monolithic catalyst has been exposed to the generated submicrometer particle of inorganic salts, KCl, K2SO4, and ZnCl2 at 200 degrees C in a tubular reactor. The generated particles have been deposited on the catalytic surfaces by utilization of an electrostatic field. Physical characterization of the generated aerosol particles were conducted by Scanning Mobility Particle Sizer (SMPS) and Electric Low Pressure Impactor (ELPI) with and without catalyst in order to investigate the magnitude of the particle deposition. Particle charge distribution was also evaluated with a Tandem Differential Mobility Analyser (TDMA) set up.SCR is the most common method to commercially reduce NOx emissions from combustion processes. Catalyst lifetime is important for process economics and extending catalyst life can allow future strengthened emission legislation and diminished NOx emissions.Verification of particle deposition has been conducted through comparison with catalyst samples exposed to commercial biomass combustion condition.The reactivity of both fresh and exposed catalyst samples as well as commercially used samples was examined in SCR reaction and the methods of deposition as well as the influence of the different salts on catalytic performance have been explored.Catalyst samples have been evaluated with Scanning Electron Microscopy (SEM) with respect to surface morphology of the catalyst material. The laboratory deactivated catalyst samples showed resemblance with the commercially exposed catalyst sample with respect to salts concentration and deposition of the salts particles. The obtained influence on catalyst activity was comparable with commercially obtained catalyst activity reductions at comparable potassium concentration levels.
|
|
