Co-combustion of Miscanthus in a pulverised coal combustor: Experiments in a droptube furnace

In this study, the devolatilisation process of Miscanthus particles inside a pulverised coal combustion chamber is characterised with the aim of finding conditions for which the devolatilisation rate of coal and Miscanthus is similar. However, choosing a power station as an experimental set-up for research is awkward because of the scale of operation (> 500 MWel). Therefore, BTG has designed and constructed a droptube reactor for well-controlled Miscanthus devolatilisation experiments with operational conditions that resemble those of a pulverised coal combustor. The droptube reactor has an internal diameter of 0.050 m and a maximum heated length of 1.6 m. Parameters which have been varied are: the droptube temperature (1000°, 1200°, 1300°, 1400°C); the heated droptube length (0.4, 0.8, 1.2, 1.6 m); and the particle size or sieve fraction (0.6¿1, 1¿2, 2¿2.8 mm). For a droptube length of 1.6 m, this results in a particle residence time of approximately 1 s.\ud \ud The experimental study on high-temperature Miscanthus decomposition in the droptube showed that Miscanthus particles which belong to the smallest sieve fraction (0.6¿1 mm) could be devolatilised completely in a 1.6 m long droptube. Apart from the experimental investigation, a numerical model has been developed. Samples of Miscanthus particles, representing grass-/straw-like crops, have been characterised in detail with respect to their size distribution. These data have been used to validate the numerical model with the results from the droptube experiments. The validation was successful. The model was then applied to predict the Miscanthus devolatilisation behaviour in a pulverised coal power station. The model predicts full conversion of Miscanthus particles for particles with a diameter smaller than 3 mm, in the core of the coal flame. Feeding of Miscanthus particles with a diameter up to 3 mm can therefore be recommended. Miscanthus particles with a diameter larger than 3 mm contribute to a geometrical extension of the coal flame in the upward direction. This should be avoided and firing of such large particles in a pulverised coal combustor is discouraged

Particle dynamics and gas-phase hydrodynamics in a rotating cone reactor.

The rotating cone reactor is a novel reactor type which can be used for rapid thermal solids processing. This paper focuses on particle dynamics and gas-phase hydrodynamics in a rotating cone reactor as a first stage to obtain a basic understanding of the processes that govern the performance of this reactor. Therefore, the flow of nearly spherical monosized PVC powder in a cold-flow rotating cone reactor has been studied under variation of the particle diameter (140¿780 ¿m), the cone rotational speed (up to 1800 rpm) and two different cone top-angles (60 and 90°). The gas flow created by the rotating cone showed a marked influence on motion of particles smaller than 200 ¿m. A mathematical model is presented using a single-particle description, and a turbulent gas flow description near the wall according to the universal velocity profile. The experimentally observed residence time of the particles inside the present reactor is typically in the order of 0.2 s

Investigating membrane breakdown of neuronal cells exposed to nonuniform electric fields by finite-element modeling and experiments

High electric field strengths may induce high cell membrane potentials. At a certain breakdown level the membrane potential becomes constant due to the transition from an insulating state into a high conductivity and high permeability state. Pores are thought to be created through which molecules may be transported into and out of the cell interior. Membrane rupture may follow due to the expansion of pores or the creation of many small pores across a certain part of the membrane surface. In nonuniform electric fields, it is difficult to predict the electroporated membrane area. Therefore, in this study the induced membrane potential and the membrane area where this potential exceeds the breakdown level is investigated by finite-element modeling. Results from experiments in which the collapse of neuronal cells was detected were combined with the computed field strengths in order to investigate membrane breakdown and membrane rupture. It was found that in nonuniform fields membrane rupture is position dependent, especially at higher breakdown levels. This indicates that the size of the membrane site that is affected by electroporation determines rupture

The rotating cone reactor: For rapid thermal solids processing

The rotating cone is a novel type of reactor for flash pyrolysis of biomass developed especially to maximize the bio-oil production. Wood particles fed to the bottom of the rotating cone together with an excess of inert heat carrier particles, are converted while being transported spirally upwards along the hot cone wall. Products obtained from the flash pyrolysis of wood dust in a rotating cone reactor are non-condensable gases, bio-oil and char. Specific features of this reactor are: rapid heating (5000 K/s) of the solids, a short residence time of the solids (0.5 s) and a small gas phase residence time (0.3 s). Since no carrier gas is required the pyrolysis products are not diluted. Reduction of the gas phase volume inside the rotating cone is possible by blocking a part of the volume inside the routing cone; it reduces the gas phase residence time in the reactor by which the secondary tar cracking is suppressed. Apart from biomass conversion, other promising areas of application of the routing cone technology are: the pyrolysis of coal or oil shale and the thermal cracking of polymers or oil residues. Also physical operations are possible like the drying of slurries by evaporation. For some of the chapters in this thesis separate abstracts have been prepared

Novel method for noncontact measurement of particle temperatures

A nonintrusive temperature measurement technique is developed for noncontact measurement of the temperature of single particles with < 200 m dia. It is based on the temperature dependence of the fluorescence spectrum resulting from irradiation of a certain phosphor mixture with UV light by applying a mixture of two phosphors with fluorescence colors (blue and green) and a color shift from green to blue (with temperature increase from 20 to 280°C). An experimental setup is described for temperature measurement of particles based on the fluorescence color, together with the calibration of this system. The fluoroptic technique is applied to measure the temperature decrease of hot particles flowing down a cold chute. The measurements agree very well with thermocouple measurements. This novel technique can be applied to nonintrusive measurement of particle temperatures in (dense) multiparticle systems as encountered in packed and fluidized beds