化学反应工程Chapter 7.ppt

PROBLEMSp?~?, ?~? 化 学 反 应 工 程 The flow in the reactor follows. (a) Plug flow (b) Mixed flow (c) The best of the four plug-mixed contacting schemes of Example 7.1. 化 学 反 应 工 程 SOLUTION As a warning, be careful to get the concentrations right when you mix streams. We show this in the three sketches for this problem. Also, the instantaneous fractional yield of the desired compound is Now let us proceed. 化 学 反 应 工 程 (a) Plug Flow Referring to Fig.E7.2a, noting that the starting concentration of each reactant in the combined feed is CA0 = CB0 = 10 mol/liter and that CA = CB everywhere, we find from Eq.9 that Figure E7.2a 化 学 反 应 工 程 Let , then and . Replacing CA by x in the above expression gives 化 学 反 应 工 程 Therefore Eq.13 gives Referring to Fig. E7.2b, we have from Eq.10, for CA = CB . (b) Mixed Flow 化 学 反 应 工 程 Figure E7.2b 化 学 反 应 工 程 (c) Plug Flow A - Mixed Flow B Assuming that B is introduced into the reactor in such a way that CB = 1 mol/liter throughout, we find concentrations as shown in Fig. E7.2c. Then accounting for the changing CA in the reactor, we find 化 学 反 应 工 程 Figure E7.2c 化 学 反 应 工 程 Therefore 化 学 反 应 工 程 To summarize For plug flow: and and and For mixed flow: For the optimum: Note. These results verify the qualitative findings of Example 7.1. 化 学 反 应 工 程 The Side Entry Reactor To evaluate how best to distribute the side entry feed and how to calculate the corresponding conversion equation is a rather complex problem. For this type of contacting in general see Westerterp et al. (1984). To actually build a commercial-size side entry reactor is another problem. Chem. Eng. News (1997) reports on how this was cleverly done by using a reactor somewhat like a shell-and-tube heat exchanger which used porous walled tubes. 化 学 反 应 工 程 Reactant A flowed through the tubes which contained baffles(折流板) to encourage lateral(横向的,径向的) mixing of fluid and approach to plug flow. Reactant B