Thermal decrepitation

Size Reauction Three major size-reduction mechanisms occur in the fluidized bed. These are attrition, impact, and thermal decrepitation. 

Thermal decrepitation occurs frequently when crystals are rearranged because of transition from one form to another or when new compounds are formed (i.e., calcination of limestone). Sometimes the strains in cases such as this are sufficient to reduce the particle to the basic ciystal size. 

Analysis of Volatile Matter Evolved. An attempt was made to establish the particular volatile component or components responsible for decrepitation by using a Beckman gas chromatography apparatus as described below. It was considered that comparing the analyses obtained at different temperatures with the corresponding rate of volatile matter evolution from the experimental work described previously would perhaps indicate the presence of a thermal decomposition reaction of controlling importance. 

The chief differences in the methods for the determination of volatile matter emanating from the thermal decomposition of coal are (1) variations in the size, weight, and materials of the crucibles used (2) the rate of temperature rise (3) the final temperature (4) the duration of heating and (5) any modifications that are required for coals which are known to decrepitate or which may lose particles as a result of the sudden release of moisture or other volatile materials. In essence, all of these variables are capable of markedly affecting the result of the tests, and it is, therefore, very necessary that the standard procedures be followed closely. 

Studies of x-ray diffraction (5-7), optical properties (6, 8), thermal expansion (, 9), thermal analysis (10-14). enthalpy (1), and decrepitation of single crystals (6, 9, ) indicate the existence of a reversible transition near 2100 C. 0-BeO is tetragonal with a structure related to rutile (5), while a-BeO is hexagonal close-packed with a wurtzite-type structure (1, IT). ... 

Decrepitation refers to the cracking, or breaking-up of lumps of limestone during heating. It is caused by differential thermal expansion. 

This technique provides a visual depiction of the entire glass forming process in a video. If the technique is properly executed it can provide a surprising amount of information. The physical behavior of the batch can be observed. Things like batch expansion, the presence of decrepitation (the violent fragmentation of crystals caused by different levels of thermal... 

Extra carbon is added to the coke layer as unbumed coke from the burner to make up for consumption by the reduction reactions. Coal or coke at a particle size in excess of 5 mm is usually added for this purpose, and is carbonised in the shaft but is not burned to any significant extent. Since the shallow coke layer has minimal strength requirements, as distinct from a shaft furnace, it is not necessary to conform to normal rigid coking coal specifications. On the other hand it is still necessary for the carbon to arrive at the coke layer in granular form. If it decrepitates to a fine powder under the thermal shock of entering the burner flame, it is more likely to be carried out in the gas stream than enter the coke layer. It would appear that any low volatile coal with reasonable coking properties is a suitable reductant for the Kivcet process. 

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