Industrial atomisation

GC-AAS has found late acceptance because of the relatively low sensitivity of the flame graphite furnaces have also been proposed as detectors. The quartz tube atomiser (QTA) [186], in particular the version heated with a hydrogen-oxygen flame (QF), is particularly effective [187] and is used nowadays almost exclusively for GC-AAS. The major problem associated with coupling of GC with AAS is the limited volume of measurement solution that can be injected on to the column (about 100 xL). Virtually no GC-AAS applications have been reported. As for GC-plasma source techniques for element-selective detection, GC-ICP-MS and GC-MIP-AES dominate for organometallic analysis and are complementary to PDA, FTIR and MS analysis for structural elucidation of unknowns. Only a few industrial laboratories are active in this field for the purpose of polymer/additive analysis. GC-AES is generally the most helpful for the identification of additives on the basis of elemental detection, but applications are limited mainly to tin compounds as PVC stabilisers. 

Besides plasmas, which are at the forefront of thermal atomisation devices, other excitation processes can be used. These methods rely on sparks or electrical arcs. They are less sensitive and take longer to use than methods that operate with samples in solution. These excitation techniques, with low throughputs, are mostly used in semi-quantitative analysis in industry (Fig. 15.2). Compared to the plasma torch, thermal homogeneity in these techniques is more difficult to master. 

The flame is still by far the most popular and convenient atomisation source employed in AAS. It provides sufficient sensitivity for most trace metal analysis requirements met in the petroleum industry. Methods are described for use with both aur-acetylene and nitrous oxide—acetylene flames. The properties of these flames are described in Chapter 2. 

Although drenching, spraying or atomisation may find limited application in the food industry, they are by far the major methods used for surface applied natural liquid smoke flavourings in the meat and fish industries. Drenching and spraying are widely accepted practices on continuous line operations where large volumes of product are produced in tunnel-type ovens. 

CONTENTS 1. Basic Principles (J. W. Robinson). 2. Instrumental Requirements and Optimisation (J. E. Cantle). 3. Practical Techniques (J. E. Cantle). 4a. Water and Effluents (B. J. Farey and L A. Nelson). 4b. Marine Analysis by AAS (H. Haraguchi and K. Fuwa). 4c. Analysis of Airborne Particles in the Workplace and Ambient Atmospheres (T.J. Kneip and M. T. Kleinman). 4d. Application of AAS to the Analysis of Foodstuffs (M. Ihnat). 4e. Applications of AAS in Ferrous Metallurgy (K. Ohis and D. Sommer). 4f. The Analysis of Non-ferrous Metals by AAS (F.J. Bano). 4g. Atomic Absorption Methods in Applied Geochemistry (M. Thompson and S. J. Wood). 4h. Applications of AAS in the Petroleum Industry W. C. Campbell). 4i. Methods forthe Analysis of Glasses and Ceramics by Atomic Spectroscopy (W. M. Wise et al.). 4j. Clinical Applications of Flame Techniques (B.E. Walker). 4k. Elemental Analysis of Body Fluids and Tissues by Electrothermal Atomisation and AAS (H. T. Delves). 4I. Forensic Science (U. Dale). 4m. Fine, Industrial and Other Chemicals. Subject Index. (All chapters begin with an Introduction and end with References.)... 

Whitehead et al [1983] point out that the Conradson carbon residue test has a poor correlation with measured particles in the combustion gases. They suggest that the differences are probably due to the very different conditions in the laboratory bench test compared with the practical combustion conditions. In an industrial furnace the oil droplets undergo a high heating rate and under these conditions the level of pyrolysis residue (coke) formed can be considerably reduced. Droplet size (a fonction of atomiser design and performance) is likely to be an important factor that affects the droplet heating rate as described earlier. 

An alternative method that has been used to prepare ferrite particles in a single step is the evaporative decomposition of the solutions, or spray-roasting (Ruthner, 1977). The solutions were mixed and atomised, and the droplets fell through a reaction chamber at 900-1050 °C. The solvent evaporated and the salts decomposed to oxides. The process took 3-5 s. By using a roasting furnace for industrial production, agglomerates of 40-200 pm containing 1 pm ferrite particles were obtained. The furnace feedstock was an aqueous suspension of the oxides, carbonates or hydroxides of the desired composition. However, the residence time was insufficient and complete transformation to the desired ferrite was not achieved. 

Spray drying is a technique with many existing and potential applications in the food industry. In spray drying the incoming feed material is atomised to form a spray (Masters, 1991). Evaporation takes place as the droplets in the spray come into contact with warm air in the dryer. Moisture is lost from the surface and replaced by water migrating from the centre of the droplet. Eventually, a dry shell is formed around the droplet and the loss of moisture slows. The dried particle is then removed from the air stream. 

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