ECH51SecondPracticeExam_2013 - HANOI UNIVERSITY OF MINING...

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Unformatted text preview: HANOI UNIVERSITY OF MINING AND GEOLOGY ECH 51 Material Balances Second Practice Exam (Closed book and closed notes, calculators allowed) Prof. Brian G. Higgins April 2013 Given for Exam: Total Mass Balance Ρ V t Ρ v t w n A 0 t Species balance with Reaction cA V cA vA w n A RA V, A 1, 2, …, N t t t t Axiom II: NJA RA A 0, J 1, 2, …, Τ 1 Note: Exam will have 3 problems Problem 1 (10 pts) Titanium dioxide, TiO2 is a white pigment used in the paint and paper industries. A new pigment plant processes an intermediate stream consisting of TiO2 precipitate suspended in an aqueous salt solution (stream #1). The salt removal is to be accomplished by washing the precipitate with pure water (stream #2). The raw pigment stream (#1) contains 40% by mass of TiO2 , 20% by mass salt, and the rest water. The washed pigment stream (#4) is upon settling, projected to consist of about 50% (by mass) TiO2 solids and it is determined that the wash water utilization should be 6 lb H2 O lb feed. The process is designed so that stream #4 produces 4000 lb/hr dry product (TiO2 salt) that contains on a water free basis, at most 100 parts per million (1 ppm=mass fraction of 10 6 ) of salt. Determine the compositions and flow rates of all streams. A schematic of the process is shown in figure below 2 ECH51SecondPracticeExam_2013.nb Problem 2 (15 points) A fuel with the following formula: C X SY OZ is to be used in a combuustion process. The combustion products are SO2 and CO2 . The NJA matrix for this fuel is X 0 1 0 Y 0 0 1 Z 2 2 2 NJA You may assume that the row reduced echelon form of NJA is given by 1 0 0 NJA 0 1 0 0 0 1 1 Y 2X 2Y Z 2Y X Y (a) Compute the minimum theoretical oxygen to obtain complete combustion of C X SY OZ . (b) If the fuel consists of 35% CS2 , 10% SO2 , and 55% H2 O, You may assume that the air stream composition is 79 N2 , 21 O2 Assume the complete combustion of the carbon disulfide is obtained. For this system we have the following species CS2 , SO2 , N2 , O2 , H2 O, CO2 . The NJA matrix for this system is NJA 1 0 2 0 0 0 0 1 2 0 0 2 0 1 0 0 0 0 0 2 0 0 0 2 0 1 0 0 2 0 where the rows represent the atomic species C, H, S, O, N and the columns the molecular species CS2 , SO2 , H2 O, N2 , O2 , CO2 . The row reduced echelon form for NJA is NJA 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 1 1 2 0 0 3 (i) compute the constraints on the species rates of production Ri (ii) What are the species balance equations for complete combustion of CS2 (iii) If the air stream is 100 mol/hr, calculate the minimum percent excess air that must be used if the local air pollution regulations limit SO2 in the stack gas to 2%. Problem 3 (15 Points) This problem deals with the hydrodealkylation of aromatics by reaction with hydrogen to form the parent aromatic compound. The potential reactions are converting toluene (C6 H5 CH3 ) to benzene (C6 H6 ), xylene (C6 H4 CH3 2 ) to toluene (C6 H5 CH3 ), and pseudocumene (C6 H3 CH3 3 ,called C9 ) to xylene (C6 H4 CH3 2 ). In this particular application a reformate stream #1 consisting of 5% benzene, 20% toluene, 35% xylene and 40% C9 is fed to a reactor with a hydrogen stream #2. Stream #2 has 5 mol H2 per mol of stream #1. The conversion of toluene is 80%, the conversion of xylene is 74% and the conversion of C9 is 70%. The product stream #3 contains toluene, benzene, xylene pseudocumene, hydrogen, methane CH4 as well as a small amount, 0.1% diphenyl ( C6 H5 2 ) as a consequence of a side reaction. ECH51SecondPracticeExam_2013.nb 3 In this particular application a reformate stream #1 consisting of 5% benzene, 20% toluene, 35% xylene and 40% C9 is fed to a reactor with a hydrogen stream #2. Stream #2 has 5 mol H2 per mol of stream #1. The conversion of toluene is 80%, the conversion of xylene is 74% and the conversion of C9 is 70%. The product stream #3 contains toluene, benzene, xylene pseudocumene, hydrogen, methane CH4 as well as a small amount, 0.1% diphenyl ( C6 H5 2 ) as a consequence of a side reaction. (i) Determine the constraints on the rates of productions Ri for this system. (ii) Select a suitable control volume and write down the species balances. (iii) What is the composition (in terms of species molar flow rates) of the reactor exit stream #3 if the exit stream contains 12.3% benzene. Assume the stream #1 has a molar flow rate of 100 mol/hr Problem 4 (15 points) In the air drier illustrated in figure below, part of the effluent stream is to be recycled in an effort to control the inlet humidity. The solids entering the drier (stream #3) contain 20 % water on a mass basis and the mass flow rate of the wet solids entering the drier is 1000 lbm hr. The dried solids (stream #4) are to contain a maximum of 5% water on a mass basis. The partial pressure of water vapor in the fresh air leaving the drier (stream #5) must not exceed 200 mm of mercury. In this particular problem the flow rate of the recycle stream (stream #6) is to be regulated so that the partial pressure of water vapor in the air entering the drier is equivalent to 50 mm Hg. For this condition calculate the total molar flow rate of fresh air entering the system (stream #1) and the total molar flow rate of the recycle stream (stream #6). You may assume that the process operates at 1 atm. Data: Molar mass of water: 18 lb/mol; 1atm =760 mm Hg; 1 lbm 453.59 g ...
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  • Summer '13
  • LeThuy
  • Combustion, Benzene, stream, NJA

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