Devolatilization phenomena

If the mobile phase is present in a significant concentration, as suggested by the results of solvent extraction studies (1,8), the practical meaning of the mobile phase to coal conversion processes may be profound. In coal liquefaction, two stage processes emphasizing the mobile phase and the macromolecular structure separately could well be most economical. In devolatilization kinetics, at least two sets of kinetic parameters are necessary to model the devolatilization phenomena associated with the mobile phase and the macromolecular structure respectively since the mobile phase components devolatilize at much lower temperatures than the macromolecular structure components 0. In addition, the mobile phase appears to have a significant influence on the thermoplastic properties of coal (0 and thereby on coke quality. 

There are relatively few phase equilibrium data relating to concentrated polymer solutions containing several solvents. Nevertheless, In polymer devolatilization, such cases are often of prime Interest. One of the complicating features of such cases Is that. In many Instances, one of the solvents preferentially solvates the polymer molecules, partially excluding the other solvents from Interaction directly with the polymer molecules. This phenomenon Is known as "gathering". 

Figures 4-1 through 4-3 show the devolatilization or pyrolysis reactivity profiles of sawdust and urban wood waste note that there is a two-stage devolatilization for tiie sawdust this is not true for the urban wood waste where the matmal has been subjected to drying and weathering. The low temperature devolatilization is largely convicted before the urban wood becomes a fuel. The consequence of tfiis phenomenon is that the fresh sawdust has an even greater potential for NOx reduction than the urban wood waste.

In a combustor the release of sulfur is not uniformly throughout the bed it may vary with the radial and axial bed position caused by the fact that the devolatilization time of a coal batch added to a fluid bed is in general less than 20% of the total birmout time and consequently in the same order as the particle mixing time (10-20 sec.). This implies that the volatiles-sitlfur is released predominantly aroimd the coal feed points, while the char-sitlfur is released throughout the bed. This phenomenon has consequences for the combustor design and operation e g. the position of sorbent feed and removal, the pitch of the heat exchanger pipes etc. 

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