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Technical Director: Environmental) 1 , C D Chapman (Technical Director), S A Ismail (Process Engineer), M L H Wise (Technical Manager) and H Ly (Process Engineer). Tetronics Limited, 5 Lechlade Road, Faringdon, Oxfordshire, England, SN7 8AL 1 SYNOPSIS The use of plasma arc technologies, especially in the treatment of hazardous wastes, is set to exp...
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... manual measurement of particulate matter gave a mean particle emission of 2.24 mg Nm . Speciated organics determined using a charcoal tube and a gas chromatograph were below the limits of detection as were hydrogen chloride and hydrogen fluoride emissions. The different generic stages of the trial are summarised in Table 3. At all times the installation remained within compliance of the WID with minimal off-gas abatement. Various quantitative analyses were undertaken to validate the effectiveness of the plasma process for asbestos vitrification, the aim being to establish whether any asbestos minerals were present in the plasma vitrified materials. Exposure to temperatures greater than 500-600 C affects the physical properties of asbestos. Consequently, as the extreme temperatures involved in the plasma vitrification process were likely to render polarised light microscopy (PLM) characterisation techniques, such as birefringence and sign- of-elongation, ineffective, X-Ray Diffraction (XRD) was used for bulk crystallographic characterisation and Scanning Electron Microscopy (SEM) for topographic characterisation at the Institute of Occupational Medicine (IOM), Edinburgh. Five samples were examined in line with HSG 248 Asbestos (The analysts' guide for sampling, analysis and clearance procedures) which forms the current basis of the UKAS accreditation, specified above. The aim of the HSE publication “HSG 248 ‘Asbestos: The analysts’ guide for sampling, analysis and clearance procedures’” is to combine a number of HSE asbestos guidance documents into a single publication, including the methods used for sampling and evaluation of fibres in air, and the sampling and identification of asbestos in bulk materials. A summary of the method of analysis for asbestos within the bulk sample, according to HSG 248 follows: analysis is initially by x10 Low Power Stereo Microscopy (LPSM), then detailed examination by PLM to a minimum x 80 magnification. Should a sample show positive to all the signs, the assessment will indicate the sample as containing a definite asbestos type. Should any of the indicators prove negative then the result will be assessed as ‘No Asbestos Detected’. A certificate indicating the results was issued to Tetronics in accordance with UKAS accredited procedures. The five product slag samples were taken for non-asbestos certification by mineralogical analysis. Portions of each sample were finely ground to create samples of uniform particle size for X-ray diffraction phase analysis then resultant diffraction patterns were compared with standard reference materials and search-match indices. A certificate indicating the results was issued to Tetronics in accordance with UKAS accredited procedures. Two random product slag samples (2 Pour and 5 Pour) were taken for non-asbestos certification by micro-structural analysis. Portions of the two samples were mounted on 25 mm SEM sample stubs, coated with a thin layer of conductive gold and examined by SEM. Energy dispersive X-ray (EDX) analysis was used to indicate the elemental composition of the samples and electronic images of their structure were recorded. A certificate indicating the results was issued to Tetronics in accordance with UKAS accredited procedures. The analysis, conducted in accordance with HSG 248 ‘Asbestos: The analysts’ guide for sampling, analysis and clearance procedures’, is summarised in Table 3: The five tap samples which were solidified in cast iron moulds are shown in Figure 9 together with the still hot sampling spoon. Samples from the slag bin are shown in Figure 10. These samples were dense and opaque with a vitreous lustre and fine crystalline facets on some fracture surfaces. The XRD traces for all five samples were the same and the annotated diffractograms of samples 2 and 5 are shown in Figure 11. Most of the material appeared to be crystalline and was identified from the diffraction pattern to be Akermanite (the Akermanite-Gehlenite geological series has the following generic chemical formula (Ca,Na) 2 (Al,Mg,Fe) 2+ [(Al,Si)SiO 7 ]). No peaks corresponding to any of the primary peaks of the original asbestos minerals were detected in the sample diffraction patterns. The XRD scanning (2 ) range considered for diagnostic purposes was more extensive than usually employed for the determination of the absence of asbestiforms. The 2 θ range 5 - 30 degrees shows the first two gehlenite/akermanite lines as well as the asbestiform ...
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Citations
... This phenomenon is called pseudomorphosis (Giacobbe et al., 2010). The existing literature reports an impressive number of processes at the laboratory and pilot plant scale and of patents based on the thermal transformation of ACMs (see for example Abruzzese et al., 1998; Borderes, 2000; Boccacini et al., 2007; Deegan et al., 2006; Dellisanti et al., 2009; Bernardo et al., 2011; Gualtieri et al., 2008a). The cementasbestos (CA) product of thermal transformation at 1200ºC is described in Gualtieri et al. (2011). ...
Selected samples of asbestos-containing material (ACM) with different Ca/Si ratios have been treated thermally at 1200°C for 15 min to obtain an 'end of waste geo-inspired material'. Before and after treatment, micro-Raman spectroscopy allowed the investigation of both powdered
and massive samples by directing the laser beam onto crystals with elongated morphology, thin fibres and the matrix. In the raw samples, chrysotile and/or crocidolite were detected. After the thermal treatment, no asbestos phases were identified in the Raman spectra collected on fibrous or
fibre-like morphologies. The scanning electron microscopy/energy dispersive spectroscopy investigations confirmed the onset of a pseudomorphic process during annealing, leading to the complete transformation of asbestos minerals into non-hazardous magnesium or calcium magnesium silicates such
as forsterite, monticellite, a˚kermanite and merwinite. The identification of such mineral assemblages was inspired by the close inspection of a natural counterpart, the high-temperature contact metamorphic imprint due to the intrusion of a sill into carbonate rocks. The process turned
out to occur largely at the solid state and involved substantial mobilization of Ca and Mg to form a spinel phase (namely MgFe2O4) which was recognized in the matrix and within, or close to elongated morphologies.
... There are numerous transferred arc reactor designs available for waste treatment, several of them based on successful developments for metallurgical plasma processes. Tetronics (Faringdon, UK) offers two types of reactors, single-torch reactors and twin-torch reactors181920 63]. In the single-torch reactor, the arc is transferred from one electrode to the melt, the electrode is usually the cathode, and can be either water-cooled metal or graphite. ...
... Operating powers range from 200 to 1200 kW for metal cathode torches and up to 2.75 MW for high current graphite cathodes (up to 9800 A). Corresponding treatment rates range from 200 kg h −1 to over 5800 kg h −1 .Figure 11 [63] shows a schematic of one of these single-torch transferred arc reactors. A schematic of the Tetronics ash vitrification installation is shown in figure 12 [23]. ...
Plasma waste treatment has over the past decade become a more prominent technology because of the increasing problems with waste disposal and because of the realization of opportunities to generate valuable co-products. Plasma vitrification of hazardous slags has been a commercial technology for several years, and volume reduction of hazardous wastes using plasma processes is increasingly being used. Plasma gasification of wastes with low negative values has attracted interest as a source of energy and spawned process developments for treatment of even municipal solid wastes. Numerous technologies and approaches exist for plasma treatment of wastes. This review summarizes the approaches that have been developed, presents some of the basic physical principles, provides details of some specific processes and considers the advantages and disadvantages of thermal plasmas in waste treatment applications.
The disposal of End-of-Life Vehicles (ELVs) results in a highly heterogeneous polymeric waste stream of Automobile shredder residue (ASR). Within Europe, strict legislation, such as the End-of-Life Vehicle Directive and the Landfill Directive, has imposed targets for reducing this waste stream and diverting the material away from landfill. One pathway open to recyclers is to thermally process these wastes, but the presence of chlorine and metallic species can present challenges to traditional incineration technologies. This paper discusses the use of Gasplasma®, an advanced thermal treatment technology, comprising fluidised bed oxy-steam gasification followed by plasma treatment, for ASR, refuse derived fuel (RDF) and blends of ASR and RDF wastes.The work demonstrates the ability to process these highly heterogeneous materials achieving high energy conversion (87–94%) and virtually complete carbon conversion, producing a calorific synthetic gas (syngas) capable of being used for power generation or as a chemical feedstock. The actual conversion efficiency achieved is dependent on feed chemistry and properties. The study also shows that ash components of the feed material can be transformed into an environmentally stable vitrified product.
Plasma Arc Technology is finding wider application in the treatment of hazardous waste materials an area which has a lot of synergy with radioactive waste management. It is being stimulated by the increasing demands of regulatory and economic drivers; currently, within the Integrated Waste Management (IWM) sector, there is a climate of rising costs, limited numbers of technological solutions, restricted access to traditional disposal based solutions and a significant levels of market consolidation. Traditionally, the IWM sector has operated with basic mixing technology solutions: e.g. physiochemical consolidation, physiochemical separation, neutralisation and basic material bulking, with ultimate reliance on landfill, cement based encapsulation and high temperature incineration (HTI). The impact of national statutes, the value of national liabilities and infra-structural deficiencies is demanding constant technological advancement for continued regulatory compliance. This paper presents information on Tetronics' plasma based solution, for the treatment of Asbestos Containing Materials (ACM) and Plutonium Containing Material (PCM). (authors)
The disposal of Municipal Solid Waste (MSW) is an increasingly difficult challenge for communities. Advanced thermal treatment (ATT) technologies, such as Gasplasma®, have been specifically developed to effectively utilise wastes to generate clean electrical power. An added beneficial feature of this process is the conversion of ash-type materials in the MSW to environmentally-stable products capable of reuse in various applications, closing the recycling loop. This paper discusses this application of Gasplasma®. Also discussed is the use of plasma technology to thermo-chemically treat hazardous Air Pollution Control (APC) residues, derived from the gaseous abatement systems of MSW thermal treatment technologies to produce ceramic products.
This review describes the current status of waste treatment using thermal plasma technology. A comprehensive analysis of the available scientific and technical literature on waste plasma treatment is presented, including the treatment of a variety of hazardous wastes, such as residues from municipal solid waste incineration, slag and dust from steel production, asbestos-containing wastes, health care wastes and organic liquid wastes. The principles of thermal plasma generation and the technologies available are outlined, together with potential applications for plasma vitrified products. There have been continued advances in the application of plasma technology for waste treatment, and this is now a viable alternative to other potential treatment/disposal options. Regulatory, economic and socio-political drivers are promoting adoption of advanced thermal conversion techniques such as thermal plasma technology and these are expected to become increasingly commercially viable in the future.
