Economics of Series CSTRs

To quantitatively demonstrate the economic effects of adding more reactors, let us consider the results found in Section 2.6. The three flowsheets considered have one, two, or three reactors in series. Reactor temperatures are 350 K, and the conversion is 98%. The specific reaction rate fc35o is 8.185 x 10-4 s-1. 

The respective volumes are 262 m3 for the 1-CSTR process, 32.5 m3 in each of the two vessels in the 2-CSTR process, and 14.4 m3 in each of the three vessels in the 3-CSTR process. The vessel diameters are 5.5, 2.74, and 2.09 m, respectively. 

What is the capital investment for each of these flowsheets The cost ( ) of a plain stainless-steel pressure vessel of length L (m) and diameter D (m) is 

We assume that the reactor is constructed from fairly exotic material and has heat transfer equipment (jacket or coil) and an agitator. So the capital cost is estimated at 10 times the basic vessel cost. The total capital costs of the reactors in the three different flowsheets are 7,429,000, 4,043,000, and 3,657,000 for the 1-CSTR, 2-CSTR, and 3-CSTR processes, respectively. You can see that the reduction in cost between the 2-CSTR and the 3-CSTR processes is quite small. The cost of a 4-CSTR process could be somewhat higher because of having more vessels, even if each is somewhat smaller. 

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