Ashing method advantages

A fluidized bed combustion system (FBC) is one that has a high temperature (1500 F to 1600 F) inert material, such as sand, ash, or limestone, occupying the bottom of the chamber.14 Figure 2-3 illustrates a typical fluidized bed boiler. Limestone, either as primary bed material, or as an addition, provides the additional advantage of S02 scrubbing.14,15 The advantage of fluidized bed combustion over the other 3 boiler types is that the fluidization of the inert bed material allows fuels with higher moisture and ash content to be burned, and still yield nearly complete combustion. Further, SOx control is easily and efficiently accomplished. The bed material is fluidized by one of two methods as described below. 

Apart from its high sensitivity, the ETA method has a number of additional advantages in the analysis of water and effluents for metals, (a) Only very small samples (1—100 jul) are required for the analysis, (b) Since the sample is dried and ashed in the electrothermal atomiser, pretreatment procedures prior to analysis are often not required. It is possible to introduce waters containing a high level of organic matter directly into the atomiser. 

In the circulation method, the same solution is continuously passed through the sample, also with continuous monitoring of the concentration, until equilibrium is reached (see Figure 5.15d) (Kurbanbekov et al., 1969 Ash et al., 1973). Although this method requires a less conventional set-up than the immersion or open-flow methods, it presents the following advantages ... 

Dry ashing is rarely applied now and has largely been replaced by wet decomposition (ashing) because it has several disadvantages, such as losses caused by volatilization, very low ashing of some materials, difficult dissolution of ashed materials, and contamination. Advantages of this method are that no reagents are used and little operator attention is required. 

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