Heat of cracking

Cycloaliphatic Diene CPD—DCPD. Cycloatiphatic diene-based hydrocarbon resias are typically produced from the thermal or catalytic polymerization of cyclopeatadieae (CPD) and dicyclopentadiene (DCPD). Upon controlled heating, CPD may be dimerized to DCPD or cracked back to the monomer. The heat of cracking for DCPD is 24.6 kJ / mol (5.88 kcal/mol). In steam cracking processes, CPD is removed from C-5 and... 

The stripped catalyst is picked up by a stream of air and carried into the regenerator where the carbon is burned at temperamres about 1100-1300°F. Entrained catalyst is again removed by cyclones and the flue gas goes out the stack. The hot, regenerated catalyst leaves the regenerator and takes with it much of the heat of combustion. This is carried over to the reactor to vaporize the feed and to balance the endothermic heat of cracking. Thus, the process is heat balanced. 

The hot regenerated catalyst supplies the bulk of the heat required to vaporize the liquid feed (and any recycle) to provide the overall endothermic heat of cracking, and to raise the temperature of dispersion steam and inert gases to the reactor temperature. 

Heat of Cracking is the amount of energy required to convert FCC feed to the desired products. 

The overall endothermic heat of cracking is described by the equation... 

The heats of cracking that are generally used are based on the complete cracking of hydrocarbons to carbon and hydrogen and thus they are overestimated. We modify the heats of cracking so that they are closer to the industrial values obtained empirically. 

USY Catalysts. USY catalysts are advertised by catalyst vendors, as low coke/high octane catalysts. This behavior results from the smaller zeolite unit cell size due to dealumination (21.221. The controlled dealumination leads to fewer but stronger acid sites resulting in increased cracking relative to H-transfer. The decrease in the extent of the exothermic H-transfer reactions also results in net increase in the endothermic heat of cracking for USY catalysts (211. 

From the API data book and a heat of cracking of 332Btu/(lb gas + gasoline) ... 

A heat balance around the catalyst-case area of a Houdry plant indicates that 69% of the heat from combustion of coke is used to generate steam, and 14% to preheat regeneration air. Heat of cracking absorbs 7 %, and minor amounts are removed by oil vapors, regeneration gases, and radiation losses (238). A typical temperature pattern during a complete cycle is shown in Figure 7. 

The heat of cracking increases from about 100 B.t.u./lb. of charge at... 

Generally, FCC units operate in a heat-balanced mode whereby the heat generated by the burning of coke is equal to the heat needed for the vaporization of the feed plus the heat of cracking. Also, the pressure balance of an FCC unit is very important to ensure proper catalyst circulation and to prevent contact between the hydrocarbons (reactor) and air (regenerator). Overall, this makes the optimal operation of a unit a very interesting challenge. 

The heat transfer coefficient was obtained by using the analogy for mass and heat transfer iD-jn)- The overall heat of cracking reactions was assumed to be 380 kJ/kg gas oil converted. In addition, the heat flux by radiation from the reactor tube to the surface of the catalyst particles was accounted for by the Stefan-Boltzmann law [10]. 

Model parameters include AHer = Heat of cracking... 

Verma and Walker [97] selected propylene as the preferred organic source of pyrolytic carbon since its heat of cracking AH) is low, and the gas is easy to handle imder ambient temperature. A few additional organic sources for chemical vapor deposition (CVD) and their application conditiorrs are summarized in Table 4.17. 

Dart and Oblad, Heat of Cracking and Regeneration. . . , Chem. Eng, Progr.f February, 1949, p. 110. 

An important check of the calibration appears in Figure 4.86. The theoretical and apparent heat of cracking should not be significantly different (< 5% relative error). If we meet this error threshold, we conclude that the calibration procedure is successful. 

---