1,433 research outputs found
Using a magnete to seperate plastics
No full textFundamental research into magnetic fluids spans more than thirty years, in the course of which a number of practical applications have emerged. Magnetic fluids become heavier when exposed to a magnetic field and can thus be used to separate materials of different densities, with lighter materials floating to the surface. However, since practical fluids took a long time to appear on the scene, development was faltering. Raw materials technologist Dr Peter Rem discovered a new approach, in which separation becomes a viable option for applications like the recycling of plastics and metals, and for refining diamonds. Instead of bulky, energy-hungry electromagnets, the system uses permanent magnets. A patent has been applied for
Magnetic Density Separation of Polyolefin Wastes
No full textPolymer recycling has significantly positive impacts on the environment, economics and society. Using recycled polymer to replace virgins reduces the growing amount of post-consumer polymer wastes, decreases the demand for fossil fuel and creates local jobs. As the most used polymer types, polyolefins certainly have attracted attention of recycling. Mechanical sorting has been pointed out as the preferred route for the recovery of relatively clean and homogeneous plastic waste streams. Whereas washing and compounding technologies for polymer scrap have dramatically improved over the last decade, there is as yet no sorting technology commercially available that is both cheap and effective. Consequently, the amount of recycled post-consumer mixed plastics remains low and the recycled polymer value is even worse. Innovative recycling technologies for post-consumer wastes should be extremely powerful, simple, cost-effective and accurate enough to create high quality products. Magnetic density separation (MDS) is such a technology. Early research showed that MDS has the potential to turn around the poor image of polyolefin recycling. However substantial research was needed to improve the separation process before high quality secondary polyolefins could be obtained from complex waste mixtures. This thesis starts with the characterization of the main resources of secondary polyolefins to determine the proper input streams for MDS. Concerning the lifetimes and the total consumption of polyolefin applications, household packaging and car components are two interesting streams for MDS. To reach the necessary separation accuracy for gaining high quality secondary PP and PE in one single step, MDS needs to be sensitive to very small differences in the physical properties of the input materials. Therefore, three main aspects influencing the separation process were studied: wettability of polymers, quality of the process liquid and flow turbulence. For this thesis, a new wetting process to eliminate the effect of air bubbles on the apparent polymer density was developed, a simple method to avoid the segregation of the process liquid was provided, and the sources of turbulence were studied and reduced. Based on all of these achievements, two MDS setups were designed and their performance on the post-consumer polyolefins was evaluated. For both setups, over 98% of the polyolefin waste can be successfully recycled with sufficient separation accuracy: 10 kg/m3. The output products of the MDS were analysed to assess their quality: composition, rheological and mechanical properties. According to the analyses, the derived products from MDS were high purity PP and PE. Based on the mechanical analyses, the separated household wastes showed good and consistent properties, independently from their origin, which were comparable with neat polymers. A model that simulates the MDS process was constructed on the basis of the fundamental principle of MDS and the major factors affecting the process. The study concluded that the separation accuracy of MDS in polymer recycling is determined by the flow turbulence and the uneven magnetic field. The combined effect of these two factors indicates that for most of the polymers turbulence is the major cause of an inaccurate separation. Both the experiments and the simulations concluded that MDS can accurately separate polyolefin mixtures based on their density. With such high accuracies in density, polyolefin mixtures can be separated into different polymers according to their type by MDS in a single step.Structural EngineeringCivil Engineering and Geoscience
Ultrasound imaging for quantitative evaluation of magnetic density separation
No full textThis thesis is dedicated to an investigation of the potential and technological possibilities of an inline ultrasound system as a quality control system for wet recycling of solid waste. The main targeted recycling technology is magnetic density separation (MDS), a novel technique that was investigated and technologically matured in a project running in parallel to this work. In MDS, the easily magnetisable ferrofluid is used as the separation medium to sort different materials based on their mass densities. The MDS is very accurate compared to conventional recycling separation techniques as it is effective even when the densities are very close (< 1 weight percent), such as for different polyolefin plastics. The special attention for plastics in this work is motivated by the economical and environmental gains that are obtained from the separation of plastics from large waste flows such as automobile scrap and household waste. Due to the inherent optical opaqueness of ferrofluid, the ultrasound imaging system is the only effective method that allows accurate observation and study of the waste particles as they separate in the channel. Moreover, the intrinsic properties of ultrasound make it suitable for quantitative analyses, such as particle tracking and measurement of particle sizes, volume and density distributions as the particles flow in large quantities towards the extraction units. The main objectives for this work have been achieved. It was shown that commercial medical 2D ultrasonic imaging systems provide a good technological point of departure for the desired inline system. They are capable of generating good quality images of moving particles, provided the view of the probe onto the particles is well controlled. Moreover, it has been shown that real-time ultrasound is capable of delivering online quantitative information that is crucial to the performance of an MDS. In particular, image processing techniques have been applied on the real-time ultrasound video-streams to evaluate the particles density distribution in the channel, measure the particle velocity and to analyze their motion behaviour as they float in the ferrofluid. The limitations of the medical commercial technology are that it cannot serve as a reliable stand-alone machine and also cannot provide all types of quantitative analyses that are desirable in an industrial recycling operation. As a next step, the investigation turned towards the imaging methods themselves. For that purpose the general linear acoustic theory for waves in ferrrofluids and acoustic imaging was reviewed, first to establish the basic physics and main principles of imaging. The potential of quantitative ultrasound analysis was determined by focusing on cross-section imaging, which is the biggest challenge for accurate 2D imaging. It has been shown that probe positioning and the overall data acquisition strategy deserve due consideration, since data quality proved paramount for good quality images. For the imaging research, the most technologically promising ultrasound methods were adapted from the fields of seismology, medical ultrasound and non-destructive testing. These imaging methods were developed in either the space-time domain or the Fourier domain, as each approach proved to have its own advantages and limitations for data requirements and computational costs. The methods were implemented in Matlab and supplied with raw ultrasound data, scanned from static scenes with just a few generic test objects. These objects were generic in the sense that all possible shapes and size-dependent acoustic wave effects were captured that could be expected with ‘real’ waste particles. Two complementary data sets were used to investigate the possible benefits of having either a wider sensor array aperture during transmission (pulse-echo data) or during data reception (plane wave data). The resulting images were evaluated in terms of performance indicators, which were introduced to obtain a more objective judgement of image quality. This research showed that accurate ultrasound cross-section imaging is quite feasible if good quality data can be scanned, i.e. if the data contain the necessary acoustic information. In particular, the availability of acoustic information from both front and back surfaces was found to be the key factor for good quality data. It is also concluded that all the imaging methods tested in this work are in principle capable of delivering good image quality, provided the data are of sufficient quality. What sets them apart are the substantial differences in computational costs and the ability to process different types of data. Finally, the research conducted in this thesis has also led to the compilation of a set of recommendations for future realization of an ultrasound system, dedicated to inline quality control in recycling.Structural EngineeringCivil Engineering and Geoscience
Werkwijze voor het winnen van metaal-houdende deeltjes uit bodemas
No full textRecovery of non-ferrous metal particles from a stream to yield non-ferrous metal-enriched and metal depleted fractions involves putting the stream onto a conveyor belt (1) as a mono-layer such that with the help of water at least the non-ferrous metal particles get adhered to the belt; subjecting the moist mono-layer to magnetic field rotating in the same direction of the belt for the separation; and removing the adhered particlesCivil Engineering and Geoscience
Werkwijze voor het scheiden van deeltjes en inrichting daarvoor
No full textSeparation of particle fraction from particle stream in a fluid e.g. aqueous liquid medium under gravitational force based on difference in vertical velocity involves passing the fluid and particle in horizontal direction defining relative direction of movement; collecting first particle fraction and second particle fraction in respective collective device with baffles (5), which causes the fluid to move in the relative direction of movement. An Independent claim is included for an apparatus for the separation of particles comprising a vessel provided with baffles.Civil Engineering and Geoscience
Pebble milling of crushed concrete fines
No full textConcrete is the most commonly used building material in our time. For every person on earth, more than one cubic meter of concrete is produced every year. Cement is the main feedstock for the production of concrete. Cement makes up about 15% of the mass of concrete. The consumption of concrete will grow in the coming decennia [2]. Beside these developments, there is another issue going on, the issue of recycling concrete - from demolition of buildings or from construction materials(C&DW). Therefore it is worthwhile to examine these material streams. The major part of the demolition waste is now used for the construction of new roads. The objective of this thesis is to recycle the cement, by the means of liberation and separation. The focus of the investigation will be on (pebble) milling. By performing milling experiments, XRF analysis and the determination of the particle sizes more insight is gained in the milling and liberation of cement (calcium). During the milling experiments, variables like speed of the mill, size of the pebbles, fill rate of the feed and temperatures were varied to investigate the influence of these variables. To back up the results some ESEM images were taken and a TGA in combination with mass spectrometry was performed. The main actions performed during the experiments are summarised in a flow sheet. Most of the results were as one would expect. But still some of the XRF analysis and TGA analyses have unexpected results. The milling experiments showed that pebble milling does cause size reduction of the concrete fines. It also showed that heating of the material is not worthwhile. The performed experiments provide a good basis for further research. From this thesis it can be concluded that milling with bigger pebbles (16-64mm) and great mill speed, improve the milling efficiency. And that the residence of the feed in the mill should be around five minutesMaterials and EnvironmentGeotechnologyCivil Engineering and Geoscience
REM and NREM mentation: Nielsen's model once again supports the supremacy of REM
No full textNielsen's model presents a new isomorphic brain-mind viewpoint, according to which the sole dream generator is found in a REM-on (explicit or covert REM) mechanism. Such a model cannot explain the dreamlike activity during SWS (slow wave sleep), SO (sleep onset) and in the last period of sleep. Moreover the hypothesis contrasts with Solms's data, which show that dreaming is present also in case of destruction of the REM generator.[Nielsen; Solms]</jats:p
Upgrading of post-consumer steel scrap
No full textPost-consumer steel scrap resulting from End-of-Life Vehicles (ELV), Waste from Electric and Electronic Equipment (WEEE) and Incineration Bottom Ash (IBA) is often hand picked for copper, stone, cloth and other contaminants, in order to meet the specifications of the steelmakers. At capacities of 20 t/h of scrap or more, the efficiency of hand sorting generally becomes problematic, hence, leaving half of the copper in the steel product. New technologies are presently being proposed to facilitate or even eliminate hand sorting of these types of scrap, allowing operators to increase revenues from copper, expand plant capacity, realize a higher and more consistent steel product quality or avoid legal constraints associated with hand pickers. A shape-sensitive magnetic separator called "Clean Scrap Machine" (CSM) pre-sorts the scrap into a bulky thin-walled steel fraction of consistently high purity and a volumetrically much smaller flow of relatively heavy parts in which the contaminants are concentrated. The latter flow can either be sorted by a much smaller number of hand pickers, by sensor sorting, or it can be sold directly to specialized sorters to extract the copper. Detailed results are reported for mid-sized IBA scrap
The Delta dryer: Theoretical and technological development of an energy-efficient dryer for sludge
No full textThe annual production of watery waste streams is significant. Considerable fractions are contaminated and cannot simply be disposed off. They must be stored or further treated. The latter option usually involves a thermal drying step, which renders the residue suitable as a resource: 1. Sludge with high organic content can serve as biofuel. 2. Mineral sludge can be converted into secondary building materials. Unfortunately, however, thermal drying is an energy-intensive and expensive process step. The Delta Dryer concept was developed to overcome the disadvantages of existing techniques. It mixes the mechanically dewatered sludge cake with hot steel balls, dries the mixture in a vacuum atmosphere, and then separates the dried product. The balls provide large heat transferring surfaces, allowing low drying temperatures. Part of the heat of evaporation is recovered by a process of multiple stage evaporation. The study aimed to broaden the knowledge on the Delta drying process, to explore the potential of the concept, and to develop the accompanying technology towards an operational installation. The process was found to rely on the interplay of thermodynamic, kinetic and mechanical aspects, to be influenced by various design details, operational parameters and properties of the feed.Design & ConstructionCivil Engineering and Geoscience
ADR: The use of Advanced Dry Recovery in recycling fine moist granular materials
No full textEffective recycling of municipal solid waste incinerator bottom ashes (MSWI-BA) and construction and demolition wastes (CDW) has proven to be a challenge, despite the high potential for recovering valuable metals in MSWI-BA and reducing the carbon footprint of the construction industry. The fundamental problem is caused by the combined presence of fines (-1 mm) and moisture. This combination forms agglomerates and fouls screens and other separation equipment, making it notoriously difficult to recover value from these waste-streams.<br/
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