Combustion in Vortex Chambers with a Fluidized Particle Bed

Confined bed comminution in high-pressure grinding rollers (HPGRs) and vertical roller mills (VRMs) was previously used preferably for grinding comparably homogeneous materials such as coal or clinker. Meanwhile, it started to complement or even replace tumbling mills in ore beneficiation with ore and gangue particles of rather different breakage behaviors. The selectivity in the comminution of a mixture of particles with different strengths but similar particle size distribution (PSD) of the constituents in a particle bed was investigated earlier. The strength of a material is, however, also a function of particle size. Finer particles tend to be more competent than coarser ones of the same material. In industrial ore processing using confined bed comminution, this effect cannot be neglected but even be exploited to increase efficiency. This paper presents research results on this topic based on experimental investigations with model materials and with natural particles, which were stressed in a piston–die press. It appeared that the comminution result substantially depends on the material characteristics, the composition of the mixture and the PSD of the constituents. Conclusions will be drawn for the future applications of selective comminution in mineral processing.

Download Full-text

Grain-based DEM for Particle Bed Comminution

Minerals ◽

10.3390/min11030306 ◽

2021 ◽

Vol 11 (3) ◽

pp. 306

Author(s):

Michael Klichowicz ◽

Holger Lieberwirth

Keyword(s):

Grain Size ◽

Discrete Element Method ◽

Specific Energy ◽

Coarse Particles ◽

Full Understanding ◽

Real Experiment ◽

Helpful Tool ◽

Ore Processing ◽

Comminution Process ◽

Particle Bed

The comminution at the grain size level for liberating the valuable minerals usually requires the highest size-specific energy. Therefore, a full understanding of the comminution process at this level is essential. Models based on the Discrete Element Method (DEM) can become a helpful tool for this purpose. One major concern, however, is the missing representativeness of mineral microstructures in the simulations. In this study, a method to overcome this limitation is presented. The authors show how a realistic microstructure can be implemented into a particle bed comminution simulation using grain-based models in DEM (GBM-DEM). The improved algorithm-based modeling approach is exemplarily compared to an equivalent real experiment. The simulated results obtained within the presented study show that it is possible to reproduce the interfacial breakage observed in real experiments at the grain size level. This is of particular interest as the aim of comminution in mineral processing is not only the size reduction of coarse particles, but often an efficient liberation of valuable components. Simulations with automatically generated real mineral microstructures will help to further improve the efficiency of ore processing.

Download Full-text

Aiming Strategy on a Prototype-Scale Solar Receiver: Coupling of Tabu Search, Ray-Tracing and Thermal Models

Sustainability ◽

10.3390/su13073920 ◽

2021 ◽

Vol 13 (7) ◽

pp. 3920

Author(s):

Benjamin Grange ◽

Gilles Flamant

Keyword(s):

Tabu Search ◽

Ray Tracing ◽

Wall Temperature ◽

Gradual Increase ◽

Particle Temperature ◽

Outlet Temperature ◽

Operation Conditions ◽

Start Up ◽

Fluidized Particle ◽

Solar Receiver

An aiming point strategy applied to a prototype-scale power tower is analyzed in this paper to define the operation conditions and to preserve the lifetime of the solar receiver developed in the framework of the Next-commercial solar power (CSP) H2020 project. This innovative solar receiver involves the fluidized particle-in-tube concept. The aiming solution is compared to the case without the aiming strategy. Due to the complex tubular geometry of the receiver, results of the Tabu search for the aiming point strategy are combined with a ray-tracing software, and these results are then coupled with a simplified thermal model of the receiver to evaluate its performance. Daily and hourly aiming strategies are compared, and different objective normalized flux distributions are applied to quantify their influence on the receiver wall temperature distribution, thermal efficiency and particle outlet temperature. A gradual increase in the solar incident power on the receiver is analyzed in order to keep a uniform outlet particle temperature during the start-up. Results show that a tradeoff must be respected between wall temperature and particle outlet temperature.

Download Full-text

Performance of CVD and CVR Coated Carbon-Carbon in High Temperature Hydrogen

MRS Proceedings ◽

10.1557/proc-327-139 ◽

1993 ◽

Vol 327 ◽

Author(s):

J. W. Adams ◽

R. E. Barlettia ◽

J. Svandrlik ◽

P. E. Vanier

Keyword(s):

Development Process ◽

Chemical Vapor ◽

Screening Tests ◽

Carbon Structure ◽

Carbon Substrates ◽

Component Development ◽

Flowing Hydrogen ◽

Deposition Processes ◽

Particle Bed ◽

Coated Carbon

AbstractAs a part of the component development process for the particle bed reactor (PBR), it is necessary to develop coatings which will be time and temperature stable at extremely high temperatures in flowing hydrogen. These coatings must protect the underlying carbon structure from attack by the hydrogen coolant. Degradation which causes small changes in the reactor component, e.g. hole diameter in the hot frit, can have a profound effect on operation. The ability of a component to withstand repeated temperature cycles is also a coating development issue. Coatings which crack or spall under these conditions would be unacceptable. While refractory carbides appear to be the coating material of choice for carbon substrates being used in PBR components, the method of applying these coatings can have a large effect on their performance. Two deposition processes for these refractory carbides, chemical vapor deposition (CVD) and chemical vapor reaction (CVR) have been evaluated.Screening tests for these coatings consisted of testing of coated 2-D and 3-D weave carbon-carbon in flowing hot hydrogen at one atmosphere. Carbon loss from these samples was measured as a function of time. Exposure temperatures up to 3000 K were used and samples were exposed in a cyclical fashion, cooling to room temperature between exposures. The results of these measurements are presented along with an evaluation of the relative merits of CVR and CVD coatings for this application.

Download Full-text