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Ind. Eng. Chem. Res. 2009, 48, 7454
Reply to “Comment on ‘Dynamic and Control of Fluidized Catalytic Crackers. 1. Modeling of the Current Generation of FCC’s’” Reuel Shinnar* Department of Chemical Engineering, The City College of New York, New York, New York 10031 I am happy that my paper from 1995 still draws attention, but, it should be read with greater care. Dr. Sadeghi1 is correct that when the air rate is increased and all other controllers are kept at constant settings, the temperature will drop. Such a case, however, is outside the scope of my paper, and thus, Dr Sadeghi’s observation is irrelevant to the discussion. My paper discusses the control of a reactor which lacks a CO boiler; in such cases, the CO in the effluent must be kept below a certain limit. This can be achieved by controlling the air rate and measuring the CO in the effluent. In feedback control, the only other variables are the temperature of the reactor (which is controlled by the recirculation rate) and the feed rate and feed temperature to the reactor (which are also controlled at a fixed rate). This paper focuses on what happens when a heavier feedstock with a higher rate of coke formation is introduced into the unit. To combust the higher rate of coke completely, the air rate and * To whom correspondence should be addressed. E-mail: shinnar@ ccny.cuny.edu.
the reregenerator temperature need to be increased. The air controller does this automatically. As a result, the temperature of the air in the regenerator and the temperature of the catalyst are increased. This causes a severe problem. The temperature of the catalyst in the complete CO oxidation reactor is already higher than in a conventional FCC with a CO boiler. At higher temperatures (>1500 F) catalysts that are in current use lose activity rapidly. This limits the types of feed that can be used to lower coking but, the problem has been completely solved by adding a catalyst cooler that provides control of the regenerator temperature independent of the air rate. This is the only case in the paper that discusses an increase in air rate, and it is of considerable interest. Literature Cited (1) Bashi, A.; Sadeghi, J.; Samimi, A.; Khorram, M. Comment on “Dynamic and Control of Fluidized Catalytic Crackers. 1. Modeling of the Current Generation of FCC’s”. Ind. Eng. Chem. Res., http://dx.doi.org/ 10.1021/ie8019104.
IE900749F
10.1021/ie900749f CCC: $40.75 2009 American Chemical Society Published on Web 07/13/2009
