Case 22 of the 2012 professional examination (an organosilicon plant producing two streams of exhaust gas containing HCl)

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22. During the production process of a certain silicone plant, two streams of exhaust gas containing HCl are generated. It is planned to use clean water at 20°C in an absorption tower to recover the HCl from these two streams; one of these streams has a flow rate of 146 kmol/h, with a HCl content of 10% (on a molar basis), and this stream is introduced into the tower from the bottom； Another flow rate of 108 kmol/h, with a 4% HCl content, is added separately at the optimal feeding point of the absorber. The absorber operates at atmospheric pressure, and the Henry’s coefficient under these operating conditions is 2.786×10^5 Pa. If a total HCl recovery rate of not less than 95% is required, the actual liquid-to-gas ratio in the upper section of the absorber should be 1.2 times the minimum liquid-to-gas ratio. What is the value (in kmol/h) of the absorption dose that needs to be applied to the absorber? A 254 B 698 C 754 D 838 This question was discussed before, and answer B was ultimately chosen. The process is calculated based on a feed material concentration of 4%. However, based on the absorption process as indicated in the question, the concentration in the gas phase should gradually decrease; therefore, the feed concentration should be taken as 10%. The result obtained through this calculation is 737, so the correct answer should be C.