Lecture 12 9-19-11 - Exam #1(Closed Book) Wednesday,...

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1 Chapter 4: Material Balances Multiple-Unit Processes Recycle, Bypass, Purge Streams Exam #1(Closed Book) Wednesday, September 21, 2011 7:00 - 9:00 p.m. PHSC Room 108 Review Session for Exam #1 Monday, September 19, 2011 6:00 - 8:00 p.m. SEC N202A Find the kg of recycle/kg fresh feed if the amount of waste (W) is 60 kg of A. Basis: 60 kg of waste Unknowns: F, P, R, G F = P + W F = P + 60 kg (Eq 1) Plan: Assumptions: No chemical rxn, steady state Input - Output + Generation - Consumption = Accumulation Input = Output What system boundaries could we define? Overall Mass Balance on Entire Process Use Material Balance Equation F 0.8 kg B kg = P 0.95 kg B kg (Eq 2) P + 60 kg ( ) 0.8 kg B kg = P 0.95 kg B kg (Eq 2) 48 kg B = P 0.15 kg B kg P = 320 kg, F = 380 kg Substitute Eq 1 into Eq 2 Mass Balance on B for Entire Process F + R = G R = G - F = 506.7 kg - 380 kg =126.7 kg F 0.8 kg B kg = G 0.60 kg B kg G = 380 kg 0.8 kg B kg 0.60 kg B kg = 506.7 kg R F = 126.7 kg 380 kg = 0.333 kg recycle kg feed What’s another system that we can define? Overall Mass Balance at mixing point Mass Balance on B for at mixing point
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2 Solving Recycle and Bypass Problems The methods for solving recycle and bypass problems are basically the same. In the steady state, there is no buildup or depletion of material within the system or recycle stream of a properly designed and operated process. Only three of these will be independent (the fourth is a linear combination). In particular, when you write the balance around the entire process system, terms describing the recycle/bypass stream do not appear; only the fresh feed and the product are required. Recycle When solving, you can write balances (total material or component) around: the entire process structure the mixing point the splitter the processing unit (inside the recycle/bypass) Stoichiometry Objectives: 1. Write and balance chemical reaction equations 2. Calculate the stoichiometric quantities of reactants and products given the chemical reaction. 3. Define excess reactant, limiting reactant, conversion, degree of completion. 4. Know the products of common reactions given the reactants We understand chemical reactions by keeping track of the number (not mass) of molecules involved …. . Chemical Reactions
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Lecture 12 9-19-11 - Exam #1(Closed Book) Wednesday,...

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