Agglomeration partial

Fig. 1.11 The external surface of the individual particles in I is partially converted into an internal surface (denoted by heavy lines) when the agglomerate in II is formed.

The population balanee eoneept enables the ealeulation of CSD to be made from basie kinetie data of erystal growth and nueleation and the development of this has been expounded by Randolph and Larson (1988), as summarized in Chapters 2 and 3. Bateh operation is, of eourse, inherently in the unsteady-state so the dynamie form of the equations must be used. For a well-mixed bateh erystallizer in whieh erystal breakage and agglomeration may be negleeted, applieation of the population balanee leads to the partial differential equation (Bransom and Dunning, 1949)... 

There are disadvantages with suspension polymerisation. In particular, for polymers that are very soluble in their monomer, stirring has to be extremely vigorous, otherwise the partially reacted droplets undergo agglomeration. Also, tacky polymers (such as synthetic elastomers) are very prone to undergo agglomeration, so that suspension polymerisation cannot be used for these polymers. 

The polymer/additive system in combination with the proposed extraction technique determines the preferred solvent. In ASE the solvent must swell but not dissolve the polymer, whereas MAE requires a high dielectric solvent or solvent component. This makes solvent selection for MAE more problematical than for ASE . Therefore, MAE may be the preferred method for a plant laboratory analysing large numbers of similar samples (e.g. nonpolar or polar additives in polyolefins [210]). At variance to ASE , in MAE dissolution of the polymer will not block any transfer lines. Complete dissolution of the sample leads to rapid extractions, the polymer precipitating when the solvent cools. However, partial dissolution and softening of the polymer will result in agglomeration of particles and a reduction in extraction rate. 

It is well known that during liquefaction there is always some amount of material which appears as insoluble, residual solids (65,71). These materials are composed of mixtures of coal-related minerals, unreacted (or partially reacted) macerals and a diverse range of solids that are formed during processing. Practical experience obtained in liquefaction pilot plant operations has frequently shown that these materials are not completely eluted out of reaction vessels. Thus, there is a net accumulation of solids within vessels and fluid transfer lines in the form of agglomerated masses and wall deposits. These materials are often referred to as reactor solids. It is important to understand the phenomena involved in reactor solids retention for several reasons. Firstly, they can be detrimental to the successful operation of a plant because extensive accumulation can lead to reduced conversion, enhanced abrasion rates, poor heat transfer and, in severe cases, reactor plugging. Secondly, some retention of minerals, especially pyrrhotites, may be desirable because of their potential catalytic activity. 

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