申論題

Problem 3 In typical semiconductor manufacturing processes, for instances, chemical vapor deposition (CVD), etching, ion implantation and epitaxy, there are usually several sorts of toxic gases generated, such as AsH3, SiH4, PH3, B2H6 and SiH2Cl2. The absorption tower is one of the general equipment adopted to remove these gases. The most popular absorbents to fill the tower are active coal, silica, aluminum hydroxide gel, or zeolite. To improve the flow behavior, steam is usually injected alongside the toxic gases. In such a gas removal unit, a flux of 100kg toxic gases-steam mixture with a concentration of 43% gases (wt%) is treated per day and lowered down to a 5% outlet stream. How long can the absorption tower last until a need to switch from Tower B to the other flash and ready-to-use Tower A, if a batch of the absorbent’s absorption capacity is 153kg of toxic gases.     43% gases 5% gases 57% steam 95% steam 100 kg/day P kg/day Tower A B Step (1) 153 kg gases Fresh (3) absorbents absorbed loading Shut down and discharge absorbents (2) Running absorption