| 1. |
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| 2. |
- van der Wijngaart, Wouter, et al.
(author)
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Valve-less diffuser fluid micropump
- 1999
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In: Gordon Research Conference 1999, Analytical Chemistry, New Hampshire, USA.
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Conference paper (peer-reviewed)
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| 3. |
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| 4. |
- Wik, Torsten, 1968, et al.
(author)
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Transfer functions for series of continuously stirred biofilm reactors
- 1997
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Reports (other academic/artistic)abstract
- There is an increasing interest in modeling and applications of biofilm reactors. Commonly, biofilm reactors are modeled as a single continuously stirred biofilm reactor (CSBR), or as a series of such. The models can be used to extract information about the reactor, for design and to predict reactor effluent characteristics as a function of influent characteristics. A CSBR consists of a stirred tank, which the bulk water flows through, and from which substrates diffuse into a biofilm where they may be transformed into new substances by bacteria living in the biofilm. Here, standard assumptions are used to derive a general and flexible dynamic model of CSBR-systems, where the reaction kinetics are of zero or first order. An exact, and an approximate transfer function, which enables easy simulations, analysis, and implementation in real-time softwares, is derived. Particular focus is on pulse responses, which is an important experimental procedure in control and reactor design. Explicit equations for the pulse responses are presented, and parameter dependancy is discussed. Experimental data from a pilot plant nitrifying trickling filter are used to illustrate the use of transfer functions for identification of reactor and biofilm parameters.
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| 5. |
- Wik, Torsten, 1968
(author)
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An investigation of the fast dynamics in a nitrifying trickling filter
- 1996
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Reports (other academic/artistic)abstract
- The fast dynamics of a large pilot scale nitrifying trickling filter (NTF) using effluent waste water from Rya Waste Water Treatment Plant in Göteborg, Sweden, has been investigated experimentally and by simulations. The plant is 7.2 m high, have a diameter of 2.7 m, and was filled with a cross-flow media with a specific surface area of 226 m^2/m^3. Continuous ammonium meters connected to the NTF measured influent and effluent ammonium concentrations.Two different phenomena may affect the fast dynamics in this type of biofilm reactors: The mixing in the bulk flow and the dynamics within the biofilm, i.e. the mixing in the biofilm and the response time for the bacteria to changes in substrate concentrations.Pulse response experiments conducted at two different flows (7.3 l/s and 14.5 l/s), where dissolved LiCl was used as trace substance, showed that the flow through the NTF could not be characterized as laminar, but significant mixing occurs inside the plant. The residence time distributions are well approximated by four identical continuously stirred tanks in series, and from the mean residence time the liquid film thickness was estimated to be 0.5 mm.Two experiments, where the influent ammonium concentration was rapidly increased while the flow was held constant at 14 l/s, were also conducted as well as an experiment where the flow was stochastically varied around 12 l/s. Comparisons are made between the measured effluent concentrations in these experiments and simulations of a model of the plant, where the NTF is divided into a series of continuously stirred tank reactors (CSTRs) having the total volume estimated from the pulse response experiments. The nitrification rate in each CSTR is modelled as a first order dynamic system driven by a physically derived expression of the stationary nitrification rate. Simulations for different values of the time constant of this dynamic system, and comparisons with the experimental data, shows that the dynamics within the biofilm are much faster than the dynamics of the mixing in the bulk. Implicitly, this means that the response times for the nitrifying bacteria to changes in ammonium bulk concentration were less than a few minutes. Hence, the fast dynamics in the biofilm can in many cases be neglected, which greatly facilitates simulations of many nitrifying biofilm reactors when more complex biofilm models are used.
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| 6. |
- Wik, Torsten, 1968
(author)
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Dynamic Modeling of Nitrifying Trickling Filters
- 1996
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Licentiate thesis (other academic/artistic)abstract
- Trickling filters, one kind of biofilm reactors, for removal of nitrogen in municipal wastewater are presently increasing in number in Sweden. For improved control and operation of wastewater treatment plants, where such reactors are used, dynamic models describing their behavior are necessary. In this thesis a physical dynamic model of cross-flow nitrifying trickling filters (NTFs), based on a general multi-species biofilm model, is presented. The model predicts effluent concentrations of ammonium, nitrite, nitrate, and alkalinity as functions of the corresponding influent concentrations, the water temperature, the flow, and the present state of the distribution of the nitrifying bacteria {\it Nitrosomonas} and {\it Nitrobacter} in the biofilm of the NTF. Efficient methods to solve the model equations, also in steady state, are presented. Experimental data achieved on a large pilot scale trickling filter are compared with model simulations, and model assumptions are experimentally validated. From the modeling and experiments it is concluded that the dynamics of the NTF can be divided into two modes: One fast mode that can be assumed to depend only on the mixing in the bulk, and one slow mode that depends on the bacterial growth and decay in the biofilm. The settling times of the two modes are separated by a factor of order 1000, which considerably simplifies model simulations. Comparisons between experimental data and a simplified version of the model show that it takes less than a few minutes for the nitrifying bacteria in the biofilm to change their substrate uptake rate after changes in substrate bulk concentrations.From pulse experiments and laminar flow theory analysis it is shown that the flow through the NTF is turbulent and, hence, significant mixing occurs inside the NTF. The residence time distribution can be approximated by a model of continuously stirred tanks in series.Comparisons between simulations and semi-stationary data show that the substrate flux into the biofilm is enhanced by an increase in flow, probably due to increased turbulence in the bulk. Analysis and simulation of steady-state multi-species biofilms in general indicate that bacterial coexistence is not only dependent on the bulk water substrate concentrations, but also on the biofilm thickness, which means that control of the biofilm thickness may be a way of controlling the bacterial composition in biofilms.
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| 7. |
- Wik, Torsten, 1968
(author)
-
Experiment utförda på en nitrifierande biobädd 1995
- 1996
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Reports (other academic/artistic)abstract
- A number of experiments was conducted on a pilot scale nitrifying trickling filter during 1995. The experiments aimed for better knowledge of the flow-dependent fast dynamics, and the slow bacterial dynamics.The residence time distribution was investigated by a number of impulse response experiments where dissolved LiCl was added to the influent. The experiments showed that the amount of water in the trickling filter is almost independent of the flow through the plant, and corresponds to a liquid film thickness of approximately 0.5 mm. The residence time distribution can be approximated by a model with four or five identical and ideally continuously stirred tanks.Based on the results of the impulse response experiments the plant is modelled by four continuously stirred tank reactors in series, where the nitrification in each tank is described by a physically derived nonlinear expression.Data from a few step response experiments, where the ammonium concentration in the influent was raised from a low constant level to a high constant level at a constant flow through the plant, was compared to model simulations. The comparisons showed that the fast dynamics in the biofilm can be neglected in comparison to the dynamics caused by the mixing in the bulk and the residence time distribution. Implicitly, this means that the response time for the active nitrifying bacteria to changes in ammonium concentration is less than a few minutes, also when the ammonium load has been very low for a long time.An experiment, where the flow was stochastically varied around an operating point during one day, showed that the simple model derived sufficiently well describe the fast dynamics of nitrifying trickling filter also when the flow changes. When the ammonium concentration in the effluent is low, a model where the nitrification rate is assumed constant is not sufficient.The slow dynamics that depend on the growth and decay of the active nitrifying bacteria was investigated by a three months long step response experiment, where the ammonium concentration in the influent first was held at a high level (not full nitrification) for approximately one month and then at a low level (approximately 50% of the nitrifying capacity) for one month, and finally at the same high level as before for one more month. In spite of several practical problems, the experiment indicated that it takes one to two weeks for the concentration of active bacteria in the biofilm to increase to a new higher concentration after the raise in influent ammonium concentration. The corresponding increase in nitrification rate is approximately 20%.The two periods of the same high influent ammonium concentration was during periods with different water temperature. Comparisons of the nitrification rate between the two periods indicated a stronger dependency on the temperature than has earlier been observed. The standard temperature dependency of the maximum growth rate for nitrifying bacteria that are used for laboratory scale experiments may well apply also for this large scale process.During periods of the experiment the ammonium sensors were not working. Therefore the possibility to determine the influent ammonium concentration based on the flow into the plant was investigated. Both black box models and a physically based model was fitted to data. The investigation showed that with a good model of the influent flow to the plant it may be possible to predict the ammonium concentration with quite good accuracy.The trickling filter was flooded weekly for a couple of hours for predator control. An investigation of the nitrification rate before and after the floodings showed no short term effects of the flooding.When the pilot plant was taken out of operation at the end of the year the uppermost meter of the plant was investigated. It was observed that the biofilm thickness was approximately 0.5mm and no bare surfaces without biofilm could be observed.
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| 8. |
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| 9. |
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| 11. |
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| 12. |
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Enoksson, Peter, 1957, et al.
(author)
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Microfluid Device Research at KTH
- 1996
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In: Micro Structure Workshop 1996 (MSW’96), March 26-27, Uppsala, Sweden..
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Conference paper (peer-reviewed)
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| 17. |
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| 18. |
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| 19. |
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| 20. |
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| 21. |
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| 22. |
- Olsson, Anders, et al.
(author)
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A valve-less planar pump in silicon
- 1995
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In: The 8th International Conference on Solid-State Sensors (TRANSDUCERS'95), Stockholm, Sweden, June 25-29. ; , s. 291-294
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Conference paper (peer-reviewed)
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| 23. |
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| 24. |
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| 25. |
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| 26. |
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| 27. |
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| 28. |
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| 29. |
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| 30. |
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| 31. |
- Fröling, Morgan, 1966, et al.
(author)
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Oily Waste Composting
- 1996
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In: AUZO'96 International Conferece on Analysis and Utilisation of Oily Wastes.
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Conference paper (other academic/artistic)
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| 32. |
- Kriz, Dario, et al.
(author)
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Preparation and characterization of composite polymers exhibiting both selective molecular recognition and electrical conductivity
- 1995
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In: Biomimetics. - 2313-7673. ; 3:2, s. 81-90
-
Journal article (peer-reviewed)abstract
- Electrically conducting composite particles were manufactured consisting of a morphine-imprinted methacrylic acid-ethyleneglycoldimethacrylate copolymer interpenetrated with a polypyrrole network. The imprinted polymer was first prepared and then used as a host polymer into which pyrrole monomer was adsorbed. After partial drying of the pyrrole-saturated host polymer, an oxidant was adsorbed, whence polymerization took place. The resulting composite was found to have retained its molecular recognition properties and obtained electrical conductivity. Characterization of the composite particles was performed by scanning electron microscopy, energy-dispersive X-ray analysis, pore volume and surface area measurements, and elemental analysis. Potential applications of these composite polymers, especially in sensor technology, are discussed.
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| 33. |
- Pettersson, Thomas, 1966
(author)
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The effects of variations of water quality on the partioning of heavy metals in a stormwater pond
- 1999
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In: In: Proc. 8th International Conference on Urban Storm Drainage, Sydney, Australia, 30 August-3 September 1999. ; 4, s. 1943-1946
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Conference paper (peer-reviewed)abstract
- Heavy metals are contaminants of stormwater and significant concentrations are found in the dissolved phase, which has a biological importance. Stormwater ponds have been used more and more for treatment of urban runoff to reduce hazardous constituents such as heavy metals. In this study the partitioning of heavy metals in particulate-bound and dissolved phases are investigated in relation to varying water quality parameters such as pH, dissolved oxygen contents and specific conductivity in a stormwater pond in Göteborg, Sweden. The results show a clear variation in heavy metal partitioning and that lead seems to be more extensively particulate-bound due to high specific conductivity.
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| 34. |
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| 35. |
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| 36. |
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| 37. |
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| 38. |
- Jeppsson, Ulf, et al.
(author)
-
On the modelling of the dynamic propagation of biological components in the secondary clarifier
- 1996
-
In: Water Science and Technology. - : IWA Publishing. - 0273-1223. ; 34:5, s. 85-92
-
Journal article (peer-reviewed)abstract
- When coupling a model of the biological reactor to a model of the settler, difficulties appear because of the different representations used for the particulate material. A combined model of the entire activated sludge process needs to include an algorithm for the dynamic propagation of the biological components of the particulate material through the secondary clarifier. In particular, this is of importance for an accurate description of the sludge that is recycled to the biological reactor. Two one-dimensional algorithms have been evaluated by means of numerical simulations. The first algorithm investigated is the one by Otterpohl and Freund in 1992 and some inherent problems of this method are discussed. For example, it will produce oscillating solutions as the number of layers in the settler model increases. Therefore, an alternative algorithm is proposed. It is based on a percentage vector that describes the different particulate biological components as fractions of the total suspended solids concentration. The vector is updated for every layer in the settler model by a robust numerical method. The algorithm is derived analytically, is computationally efficient and does not exhibit any oscillatory behaviour.
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| 39. |
- Karlsson, Camilla
(author)
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Fouling and cleaning of solid surfaces. The influence of surface characteristics and operating conditions
- 1999
-
Doctoral thesis (other academic/artistic)abstract
- The severe fouling common in food processing puts high demands on equipment cleaning. Adsorption of the protein betalactoglobulin to solid surfaces and its subsequent removal were followed using in situ ellipsometry. Most experiments were done in a stirred cuvette. Additionally, a flow cell was designed, which was employed in some work. The characteristics of the surface were shown to influence protein adsorption and removal. While differences between chromium oxide and stainless steel were small, methylated silica showed significantly different adsorption, desorption during rinsing and cleanability. Near the betalactoglobulin denaturation temperature, rapid multilayer build-up was observed, and the importance of the bare surface properties appeared to decrease. On metal oxides, a lag phase preceded the build-up, while on methylated silica an initial phase of slower adsorption was seen. Prolonged adsorption times gave less desorption during rinsing from metal oxides. For methylated silica, increasing the betalactoglobulin residence time on the surface led to lower removal by the anionic surfactant SDS. Increasing the NaOH concentration gave enhanced cleaning rates and better cleanability of the stainless steel. Combining SDS with NaOH resulted in improved cleaning compared to if using the individual components. Adsorption and removal at high temperature resulted in lower cleanability compared to at room temperature, due to heat-induced alterations in the protein. No correlation was found between the bulk composition or the surface finish of the stainless steel and the fouling tendency or the cleanability. Differences in NaOH-induced protein removal were striking between surfaces subjected to different pretreatments. Passivated surfaces were less cleanable than surfaces pretreated with strong alkali or plasma-cleaned. After repeated fouling and cleaning without renewed pretreatment, differences decreased. While the cleanability of alkali-precleaned surfaces decreased when reused, changes for passivated surfaces were smaller. The initial betalactoglobulin adsorption in turbulent flow was found to be kinetically controlled. At the laminar flow rate, results indicated effects of both mass transport limitations and adsorption kinetics. No significant influence on rinsing or cleaning was evident, and effects on the amounts adsorbed were small. All NaOH concentrations tested caused significant protein removal, and the performance of the two highest concentrations was comparable.
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| 40. |
- Ståhl Wernersson, Eva
(author)
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Some Fluid Dynamic Characteristics in the Scale-up of Rushton Turbine-Agitated Tanks
- 1997
-
Doctoral thesis (other academic/artistic)abstract
- Turbine-agitated tanks are used in chemical and biochemical applications to increase mixing which, in turn, affects the yield, productivity and product quality. The purpose of this work was to study the hydrodynamic influence on the scale-up of turbine-agitated tanks, commonly used in fermentation. Local turbulent flow parameters, the turbulent kinetic energy and the local energy dissipation rate, were related to the global scale-up parameters: the impeller tip speed, impeller diameter and power per unit mass, and to the local flow parameter, the calculated convective velocity. A system for turbulent velocity measurements was designed using constant-temperature anemometry as the measuring method. A split-film probe was used which enabled velocity measurements to be made in two directions simultaneously. Measurements were performed in three tanks of different geometries and sizes (0.75 m3, 12 m3 and 30 m3). Different operating conditions, in regard of power input per unit mass, were used, comparable both to commercial fermentation and bench-scale units. Several estimates and hypothesis for the convective velocity were evaluated. Different methods for calculating the local energy dissipation rate were compared for measurements performed both in the impeller region and the bulk region of the tanks. It was shown that there was a correlation between the local turbulent parameters, turbulent kinetic energy and energy dissipation rate, and the local flow parameter, the convective velocity Uconv, independent of the tank size, the tank geometry or position in the tank, which confirms the similarity of the flows at high turbulent Reynolds numbers. The similarity of the flow conditions at high turbulent Reynolds numbers was also evidenced by scaling of energy spectra in the space domain for tanks of different geometries, sizes and at different positions in the tanks. Correlations are given for the scaling of local flow parameters, the turbulent kinetic energy and the energy dissipation rate, in the impeller region of the tank, using global scale-up parameters. Long-term characteristics have been detected in the mean flow and in the turbulent flow in the impeller and bulk zones. Increasing the power supplied to a process affects the impeller region more than the bulk region, and therefore increases the turbulent mixing in the process. This was shown by the higher values of the slopes of turbulent parameters compared with global parameters.
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| 41. |
- Ramström, Olof, et al.
(author)
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Recent Advances in the Use of Molecularly Imprinted Materials in Separation and Synthesis
- 1998
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In: Molecular and Ionic Recognition with Imprinted Polymers. - Washington, DC : American Chemical Society. - 0097-6156. - 9780841235748 - 9780841216853 ; 703, s. 82-89
-
Book chapter (peer-reviewed)abstract
- Molecularly imprinted materials, prepared using self-assembly imprinting protocols using only non-covalent interactions, can be used as chromatography media in aqueous phase. The recognition properties are highly dependent on the interacting species used in the imprinting protocol. Ionic interactions, together with strong hydrogen bonding, represent useful means of obtaining recognition. With increasing levels of water in the recognition media, the hydrophobic effect comes into play. Molecularly imprinted materials can furthermore be used as auxiliary agents in enzymatic syntheses in water-saturated organic phases. When materials molecularly imprinted for the reaction product were applied to the thermolysin-catalyzed aspartame synthesis, an increase in yield was observed. Introduction of a thermodynamic trap provided by the molecularly imprinted matrices allowed a non-favorable equilibrium for the thermolysin reaction to be pushed in the forward direction.
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| 42. |
- Svanström, Magdalena, 1969, et al.
(author)
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A Method for Analysing the Gas Phase in Polyurethane Foam
- 1995
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In: Journal of Cellular Plastics. ; 31, s. 375-388
-
Journal article (peer-reviewed)abstract
- A method for analyzing the gas phase in polyurethane foam is described. The gas content of the foam sample is released by grinding in a special sampling equipment made from a metal pipe. The grinding is effected by pressing the cylindrical sample towards a rotating edge at the end of the pipe. The gas released during grinding is collected in a glass syringe, permitting the total gas volume to be determined. The syringe is connected to two gas sampling valves of a gas chromatograph. In the chromatograph, the gas is analysed on two different columns. For the qualitative analysis of samples with unknown gases and for the identification of impurities, a gas chromatograph—mass spectrometer system is used. Since the sampling equipment, with the sample inserted, is flushed with an inert gas before grinding, the "true" volume of the sample can be determined and the pressure in the cells can be calculated.
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| 43. |
- Svanström, Magdalena, 1969, et al.
(author)
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Determination of the Blowing Agent Distribution in Rigid Polyurethane Foam
- 1996
-
In: Journal of Cellular Plastics. ; 32, s. 159-171
-
Journal article (peer-reviewed)abstract
- The amount and distribution of blowing agent in rigid polyurethane foam were determined by several methods, which are described and compared. A method for solvent extraction with subsequent gas chromatographic analysis was developed and found to be advantageous for CFC-blown foam along with a combustion method (the Schoniger method), where the chloride ions formed were determined by titration. The solvent extraction method was successfully applied to blowing agents in CFC-free foams as well. Three methods involving heating and weight-loss determination were evaluated. They are easy to use, but corrections for thermal decomposition of the polymer are needed. About half of the total amount of CFC-11 in the investigated polyurethane foams from district heating pipes was found to be dissolved in the polymer matrix.
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| 44. |
- Tobias, Peter
(author)
-
Silicon carbide field-effect devices studied as gas sensors for exhaust gas monitoring
- 1999
-
Doctoral thesis (other academic/artistic)abstract
- Metal-insulator-silicon carbide (MIS) structures have been studied as gas sensors. We have investigated how the sensors detect gases, how fast they do that, and how they could be used for exhaust gas monitoring.We have prepared simple field-effect devices, MIS-capacitors and Schottky diodes, on silicon carbide with platinum gates. We have tested the gas sensitivity by measuring the electrical characteristics of the devices in oxygen and in hydrogen and sometimes carbon monoxide (representing oxidising and reducing gases). The flat-band voltage of a MIS-capacitor is more positive in oxygen than in hydrogen. Hydrogen or carbon monoxide changes the current-voltage characteristics of a Schottky diode on n-type SiC in a way typical for a lowering of the barrier height. For Schottky diodes on p-type SiC, the apparent barrier height increases in hydrogen. We have determined values of barrier heights for different platinum-insulator combinations, but they differ from each other depending on the measurement method used. We conclude that the thermionic emission model does not describe the MISiC sensors well. In the introductory chapters, a mechanism is discussed how gas exposure might change the electrical characteristics of Schottky diodes and capacitors.When we expose a MIS capacitor to hydrogen, not only the field effect influences the properties of silicon carbide. At temperatures above 600°C, the inversion capacitance of an n-type MIS capacitor decreases with increasing hydrogen pressure. We have measured and analysed the effectfor 6H and 4H n-type silicon carbide. We have suggested that the influence of hydrogen is due to a decreased minority-carrier generation in the semiconductor. For p-type material, the capacitors apparently do not build up an inversion layer.We have studied sensor signals also in more complex gas mixtures. We have measured the effects of compounds of synthetic exhaust gas systematically using an experimental design. For each sensor temperature, we could identify one gas compound that influences the sensor signal most. To understand the origin of these effects, we have studied more closely a mixture of oxygen and carbon monoxide. We could explain the sensor behaviour qualitatively with the relative sizes of reaction kinetics and mass transport. For a medium temperature, e.g.400 °C, and high nominal gas concentrations, the oxidation of carbon monoxide is kinetically controlled: The sensor surface is covered with carbon monoxide even if oxygen is in excess, because carbon monoxide has a higher sticking coefficient on platinum. At a high temperature, e.g.500 °C, the oxidation on the platinum is very efficient. Only the gas inexcess is present on the sensor surface and dominates the sensor signal. The possibility is discussed to use an sensor array for the multicomponent analysis in exhaust gases, e.g. for the diagnosis of a catalytic converter. Not alone the sensor temperature determines the selectivity of the sensor but also the presence of reactive surfaces close to the sensor, which change the local gas concentrations.We have investigated the response times of some MISiC sensors to see if they can be used as fast binary A-sensors for cylinder-specific monitoring of a car engine. We have invented a new method for measuring response times of fast gas sensors in the laboratory, i.e. the moving gas outlets. At temperatures of 650°C and higher, the MISiC sensors react to a change in the ambient in less than three milliseconds. Measurements in the exhaust of a bench engine have confirmed this finding.
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| 45. |
- Franck, Per-Åke, 1953, et al.
(author)
-
Analys av vissa konsekvenser av långsiktiga avtal som styrmedel att effektivisera energianvändningen i industrin
- 1999
-
Reports (other academic/artistic)abstract
- Föreliggande rapport utgör en del av ett första steg i att ta fram förslag till långsiktiga avtal mellan stat och näringsliv inom området effektivare energiutnyttjande. Syftet med detta första steg är att utröna om det är möjligt och rimligt att utnyttja långsiktiga avtal i Sverige.I denna rapport analyseras konsekvenserna av att med långsiktiga avtal stimulera genomförandet av åtgärder som inte skulle genomförts utan intervention från staten. Analysen genomförs med utgångspunkt från tre fallstudier där åtgärder identifierats genom energikartläggningar.I ett första steg, applicerat på de tre fallstudierna, analyseras hur skatter fungerar som styrmedel och incitament att genomföra besparingsåtgärder. I denna del inkluderas hur emissionerna kan kvantifieras.I ett andra steg, utgående från fallstudiernas karakteristik avseende investeringar och besparingar, analyseras i detalj konsekvenserna av långsiktiga avtal. Dessa avtal innebär att industrin får utnyttja en del av koldioxidskatten för investeringar i åtgärder som inte skulle genomförts utan intervention från staten.
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| 46. |
- Kassman, Håkan, 1962, et al.
(author)
-
Secondary effects in sampling ammonia during measurements in a circulationg fluidised-bed combustor
- 1997
-
In: Journal of the Institute of Energy. ; :70, s. 95-101
-
Journal article (peer-reviewed)abstract
- A previous paper presented the results of measuring the ammonia (NH3) concentration in the combustion chamber of a circulating fluidised-bed (CFB) boiler. Two sampling techniques were used: a gas-quenching (GQ) probe where the sample is quenched directly in the probe tip by a circulating trapper solution, and a gas-sampling probe connected to a Fourier-transform infra-red (FTIR) instrument. In this paper, an attempt is made to estimate the influence of potential secondary reactions with NH3 in the GQ probe tip by means of a plug-flow model. The calculations showed that heterogeneous and homogeneous reactions could be of importance to the accuracy of the measurement. This contradicts the almost identical results relative to the parallel FTIR measurement, and the conversion of NH3 is probably overestimated by the model. In addition, transients obtained during the FTIR measurement were used to study the accuracy of the gas-sampling probe.
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| 47. |
- Lyngfelt, Anders, 1955, et al.
(author)
-
Low N2O, NO and SO2 emissions from circulating fluidized bed boilers
- 1995
-
In: Proc. Int. Conf. Fluid. Bed Combustion. - 0197-453X. - 0791813053 ; 13, s. 1049-1057
-
Conference paper (other academic/artistic)abstract
- A new method, reversed staging, for decreasing N2O without increasing the emission of the other pollutants, NOx and SO2, was investigated in the 12 MW circulating fluidized bed boiler at Chalmers University of Technology. It was possible to reduce the emission of N2O to one fourth (25 ppm), NO to half (about 40 ppm) compared to normal staging and normal temperature, without significantly affecting the sulphur capture efficiency (about 90%). Air staging, which is normally used in circulating fluidized bed boilers means that only a part of the combustion air, primary air, is added to the bottom zone, resulting in a lower oxygen concentration in the bottom part, while the secondary air results in more oxidizing conditions in the upper part of the combustion chamber and the cyclone. The principal idea of reversed staging is to reverse the conditions in top and bottom, i.e. to decrease the oxygen concentration in the upper part and to increase it in the bottom part. Such a reversal is accomplished by adding air in the bottom corresponding to an air ratio of approximately unity. No secondary air is added to the combustion chamber which means that the oxygen concentration will be low in the upper part of the combustion chamber and the cyclone. Air for final combustion is added in the cyclone outlet.
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| 48. |
- Lyngfelt, Anders, 1955, et al.
(author)
-
Methods for reducing the emission of nitrous oxide from circulating fluidized bed combustion
- 1996
-
In: Energy Conversion and Management. - : Elsevier BV. - 0196-8904. ; 37:6-8, s. 1297-1302
-
Journal article (peer-reviewed)abstract
- Abstract - Two methods for the reduction of nitrous oxide emissions, afterbuming and reversed air staging, are investigated in a 12 MW circulating fluidized bed boiler. With afterburning the N2O emission can be reduced by 90% or more, using an amount of secondary fuel corresponding to 10% of the total energy input. With reversed air staging it is possible to reduce the emission of N2O to one fourth (25 ppm), without significantly affecting the other emissions. With reversed air staging no secondary air is used in the combustor and an air-ratio of about unity is maintained throughout the combustion chamber. Air for final combustion is added in the cyclone outlet.
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| 49. |
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| 50. |
- Lyngfelt, Anders, 1955, et al.
(author)
-
Progress of combustion in the furnace of a circulating fluidised bed boiler
- 1996
-
In: Twenty-sixth Symposium (International) on Combustion. ; , s. 3253-3259
-
Conference paper (peer-reviewed)abstract
- Gas concentrations were measured in the combustion chamber of a circulating fluidized bed boiler(FBB ). Sieved fractions of solid material sampled at different heights were analyzed for combustible matter. Together with the bulk density profile obtained from pressure drop measurements, these data were used to obtain the distribution of combustible matter in the combustion chamber. High concentrations of combustible gases and low concentrations of oxygen Were found in the bottom part, indicating that the bed material to a large extent is subject to reducing conditions. From the gas concentration profile, the degree of combustion/fuel conversion versus boiler height was deduced. This procedure, however, involves a major error since measured concentrations gin, a misrepresentation of the concentrations of the gas flow. This is explained by a through flow of gas through bubbles or voids in the bottom bed with high velocity and high concentration of oxygen. A correction for the hn1ass flow was attempted, which increases the 02 concentration in the lowest position from 2.5 to 11%. This correction compared favorably with the fuel conversion versus height, derived from the distribution of solid combustibles (char) in the combustion chamber. The results show that the concentrations measured in the bottom part of the combustion chamber do not represent the flow and cannot, accordingly, be directly used in mass balanees. This misrepresentation has consequences for the interpretation of gas measurements in the bottom part of FBBs.
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