Ind. Eng. Chem. Res. 2009, 48, 7453
7453
CORRESPONDENCE Comment on “Dynamic and Control of Fluidized Catalytic Crackers. 1. Modeling of the Current Generation of FCC’s” Amin Bashi, Jafar Sadeghi,* Abdolreza Samimi, and Mohammad Khorram Department of Chemical Engineering, Faculty of Engineering, UniVersity of Sistan and Baluchestan, Zahedan, P.O. Box 98164-161, Iran Sir: Seemingly, there is a conflict in the steady state and dynamic investigation of fluid catalytic cracking (FCC) by Arbel et al.1 They have analyzed steady state and dynamic modeling of FCC in both partial and full combustion. Their steady state analysis showed that the slopes of changing of both riser and regenerator temperatures versus the flow rate of air entering the regenerator were positive in partial combustion and negative in full combustion. This has also been mentioned by Han and Chung.2 The above statement seems to be true because • In partial combustion, more air to the regenerator encourages more conversion of coke to CO and CO to CO2; therefore, the regenerator temperature must be increased. • But in full combustion, the majority of the coke and CO are converted to CO2 and more air causes the regenerator temperature to decrease. This is due to the fact that there is no more released heat, from converting coke, to warm up the excess air, where the temperature is lower than the regenerator temperature. • Any change of the regenerator temperature finally influences the riser temperature in the same manner. * To whom correspondence should be addressed. E-mail: jsadeghi@ hamoon.usb.ac.ir.
However, in the dynamic investigation of Arbel et al.,1 the comparison between two steady states (the initial steady state and the steady state after transition response) shows different results. The temperatures of the riser and regenerator increase monotonously with the increasing flow rate of air entering the regenerator and settle at a higher value, for both partial and full combustions. At first glance, this appears to be a typographical error in the text (page 1236 paragraph 3), but the plot of dynamic properties of their model in Figure 12 (page 1236) confirms the text. This is a conflict between the steady state and dynamic investigations in full combustion. It seems that there may be some errors in the simulations whereby the results of the paper and the conclusion have been affected accordingly. Literature Cited (1) Arbel, A.; Huang, Z.; Rinard, I. H.; Shinnar, R. Dynamic and Control of Fluidized Catalytic Crackers. 1. Modeling of the Current Generation of FCC’s. Ind. Eng. Chem. Res. 1995, 34, 1228–1243. (2) Han, I.-S.; Chung, C.-B. Dynamic Modeling and Simulation of a Fluidized Catalytic Cracking Process. Part II: Process Modeling. Chem. Eng. Sci. 2001, 56, 1973–1990.
IE8019104
10.1021/ie8019104 CCC: $40.75 2009 American Chemical Society Published on Web 07/13/2009
