USEFUL EQUATIONS           +++− +−+− − −−+ = ]11[2 ]11[2 ln)1( )1()1(ln1 2 2 2 RRS RRS R RSSR FT ; )( )( 12 21 tt TT R − − = ; )( )( 11 12 tT tt S − − = PP TT V V         −=    ...

In the file


USEFUL EQUATIONS           +++− +−+− − −−+ = ]11[2 ]11[2 ln)1( )1()1(ln1 2 2 2 RRS RRS R RSSR FT ; )( )( 12 21 tt TT R − − = ; )( )( 11 12 tT tt S − − = PP TT V V         −=        =    11 2 42 *   k xqg NuGrGr wxxx == 4/1 32 )( sin 943.0         − = wB TTL kg h   3/1 32 2 sin         = kg hCo   ln /c c-)N + N(/ N /c c-)N + N(/ N z c N + N N = N A1BAA A2BAAAB BA A A D t 2 y erfc = c-c c-c AB0AAi 0AA D t 4 y- t )c - c( = N AB 2 AB 0AAiA         D D exp  x - y dx = F W = L dL x x W F w F        ln 1 - q z - x 1 - q q = y F         +      − − − − = AAmxy mxy A NOG 11 1ln 11 1 22 21 ( )       +− − − − AA myx myx A = NOL 1 / / ln 1 1 11 12               A 1 + A 1 - 1 mx - y mx - y A = N 1+NN 1+N0 IP IPIP IPln ln 1 H A + H = H LGOG 1 HA + H = H GLOL 1+R x + x G L =y D n1+n A = s s mG L Question 1. A flow of 50,000 kg/hr of liquid ethanol at 75 °C and 190 kPa (F1) is preheated to become saturated liquid ethanol at 95 °C and 190 kPa using a shell and tube heat exchanger (HEX-1). The saturated liquid is then vaporized using a kettle-type reboiler (REB-1). The resulting vapor is not superheated (V). A reboiler station with four operating units was designed to provide the required superheated steam at 200 °C and 3 bara (H1). The generated steam flows in the tubes of REB-1 and saturated water at 3 bara leaves the tubes (H2). This saturated liquid subsequently enters the tubes of HEX-1 to utilize its remaining energy and heat up the liquid ethanol stream (F1). The physical properties of both ethanol vapour and liquid ethanol at 190 kPa are provided at the end of the paper. a) Determine the required steam mass flow rate. (5 marks) b) Calculate the temperature of stream H3. You may assume that the hot water has a constant heat capacity of 4.2 kJ/kg.K. (5 marks) c) Calculate the length of the tubes in HEX-1, assuming that the heat transfer coefficient on the shell side is 7,800 W/m2K for a clean system and the conductivity of the tube walls is 45 W/m·K, with a thickness of 2 mm. The Nusselt number (Nu) inside the tube can be calculated by: ?? = 0.012(??0.87 − 280)??0.4 Assume fouling is negligible on both sides. The HEX-1 heat exchanger contains 100 horizontal tubes with an outside diameter of 2 cm. (20 marks) d) There was a sudden failure of HEX-1 and ethanol at 75 °C and 190 kPa directly entered the REB-1 without being preheated. To keep the ethanol vapor production capacity constant, the operator decided to increase the steam flow rate coming from the reboiler. Calculate the amount of steam make-up required. You may assume that the hot water has a constant heat capacity of 4.2 kJ/kg.K. (10 marks) (Total for Question 1 = 40 marks) Question 2. A gas stream contains 2% (vol) H2S. It has a flow rate of 800 m 3/hr at 30 °C. A counter- current absorption column is used to reduce H2S concentration to 0.1% (vol) with clean water as the scrubbing agent, where the rest of the gas components are inert. The process is operated at 25 °C and 120 kPa. The equilibrium solubility of H2S in water can be considered as a dilute system and the equilibrium of the system follows Henry’s Law with a relation of Ye = 3 X. Ideal gas constant R = 8.31447??−1???−1 a) What is the Henry’s Law constant H (in the unit of kPa) at the above conditions? (2 marks) b) Determine the recovery of H2S by the scrubber. (3 marks) c) What is the minimum liquid flow required for this task? Unit in m3/h. Liquid density 1 kg/L. (5 marks) d) We choose 1.2 times of the theoretical minimum liquid as the operation condition. What is the composition (in terms of mole ratio) of the liquid leaving the scrubber? (4 marks) e) Then, what is the flow rate of water required for this task in m3/h? (3 marks) f) Try to determine the number of overall gas phase transfer units N. (5 marks) g) It is known the internal diameter of the packed column is 0.97m, the gas phase mass transfer coefficient is 0.001 kmol m-2 s-1, and the liquid phase mass transfer coefficient is 0.003 kmol m-2 s-1. The random packings used in the column provide a wetted area of 100 m2/m3. Determine the overall gas phase mass transfer coefficient on unit volume basis, KOY a, in kmol m -3 s-1, and determine the height of the transfer unit in overall gas phase. (6 marks) h) what is the height of the packing required. (2 marks) (Total for Question 2 = 30 marks) Question 3. Many of the Australian natural gases in Northwest Shelf are high in carbon dioxide. You are asked by the client to design a demonstration membrane unit to reduce the carbon dioxide concentration from 10 mol% to 2 mol%, the specifications of pipeline gases. The flowrate of this CH4/CO2 binary gas mixture is 120 mol/min, and pressure of 40 bar. A dense membrane with an active layer thickness of 0.5 micron is employed. The CO2/CH4 selectivity is 80, and the CO2 permeability PA = 5 x 10 -14 kmol.m.m-2.s-1.kPa-1. The pressure of the permeate is 1.5 bar absolute. a) If both sides of the membrane can be considered mixed flow, and retentate pressure equal to that of the feed, what is the composition of the permeate? (7 marks) b) What is the stage cut for this scenario? (4 marks) c) What is the area of the membrane required? (4 marks) d) Using a shortcut method, what is the stage cut and area of membrane for a countercurrent asymmetric membrane module operating under the same conditions? (8 marks) (Total for Question 3 = 23 marks) (Total for Paper = 93 marks)