of 10 mmol O 2 /g-dry wt-h are to be cultured. The critical

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1 Cork Insttute of Technology achelor of Engneerng n Chemcal & Process Engneerng - ward Summer 00 CE4.6 Chemcal & ochemcal Reactors (Tme: Hours) Instructons nswer any FOUR questons. Use separate answer books for Q1 and Q4 6. Examners: Mr. I. O Sullvan Dr. S. M. Rassan Prof. R. Ocone Mr. S. Kelly Q1. (a) () Estmate the requred coolng-water flow rate for a fermenter wth an workng volume when the rate of oxygen consumpton s 100 mmol O /1-h. (b) The desred operatng temperature s 5 C. coolng col s to be used. The mnmum allowable temperature dfferental between the coolng water and the broth s 5 C. Coolng water s avalable at 15 C. The heat capactes of the broth and the coolng water are roughly equal. () Estmate the requred length of coolng col f the col has a.5-cm dameter and the overall heat transfer coeffcent s 140 J/s-m - C. value of k L a 0 h -1 has been determned for a fermenter at ts maxmum practcal agtator rotatonal speed and wth ar beng sparged at gas/1 reactor volumemn. E. col wth a q o of 10 mmol O /g-dry wt-h are to be cultured. The crtcal dssolved oxygen concentraton s 0. mg/l. The solublty of oxygen from ar n the fermentaton broth s 7. mg/l at 0 C. (a) What maxmum concentraton of E. col can be sustaned n ths fermenter under aerobc condtons? (b) What concentraton could be mantaned f pure oxygen was used to sparge the reactor?

2 Q. bochemcal engneer has determned n hs/her lab that the optmal productvty of a valuable antbotc s acheved when the carbon nutrent, n ths case molasses, s metered nto the fermenter at a rate proportonal to the growth rate. However, he/she cannot mplement hs/her dscovery n the antbotc plant, snce there s not relable way to measure the growth rate (dx/dt) or bomass concentraton (X) durng the course of the fermentaton. It s suggested the an oxygen analyser be nstalled on the plant fermenters so that the OUR (oxygen uptake rate g/l-h) may be measured. (a) Derve expressons that may be used to estmate X and dx/dt from OUR and tme data, assumng that a smple yeld and mantenance model may be used to descrbe the rate of oxygen consumpton by the culture. (b) Calculate value for the yeld ( Y ) and mantenance ( m X / O o ) parameters from the followng data: OUR X Tme (g/h) (g/1)

3 Q. (a) fludsed-bed, mmoblsed-cell boreactor s used for the converson of glucose to enthanol by Z.mobls cells mmblzed n k-carrageenan el beads. The dmensons of the bed are 10 cm (dameter) by 00 cm. Snce the reactor s fed from the bottom of the column and because of CO gas evoluton substrate and cell concentratons decrease wth the heght of the column. The average cell concentraton at the bottom of the column s X 0 45 g/l and the average cell concentraton decreases wth the column heght accordng to the followng equaton: X X 0 ( Z) where Z s the column heght (cm). The specfc rate of substrate consumpton s q s g S/g cells h. The feed flow rate and glucose concentraton n the feed are 5 1/h and 160 g glucose/l respectvely. (a) Determne the substrate (glucose) concentraton n the effluent. (b) Determne the ethanol concentraton n the effluent and ethanol productvty (g/l h) f Y P/S 0.48 g ethanol/g glucose. Q. (b) Penclln s produced by P. chryogenum n a fed-batch culture wth the ntermttent addton of glucose soluton to the culture medum. The ntal culture volume at quassteady state s V O and glucose-contanng nutrent soluton s added wth a flow rate of F 50 1/h. Glucose concentraton n the feed soluton and ntal cell concentraton are S O 00 g/l and X O 0 g/l, respectvely. The knetc and yeld coeffcents of the organsm are µ m 0. h -1, K S 0.5 g/l, and Y X/S 0. g dw/g glucose. (a) Determne the culture volume at t 10 h. (b) Determne the concentraton of glucose at t 10 h at quas-steady state. (c) Determne the concentraton and total amount of cells at quas-steady state when t 10 h. (d) If q p 0.05 g product/g cells h and P g/l. determne the product concentraton n the vessel at t 10 h. Q4. Explan, wth ad of sketches, dagrams, etc; (a) Cold-shot coolng (1 Marks) (b) Desgn of a two-stage adabatc packed bed reactor wth nterstage coolng for a reversble exothermc reacton. (1 Marks)

4 Q5. (a) Show that for sphercal partcles of unchangng sze, wth the unreacted core model, when surface reacton s controllng the rate, then; t rc 1 1 (1 x ) R 1 t tme for partcle to react to r c tme for complete converson of partcle. R partcle radus. x converson of partcle for the reacton; (flud) + b (sold) Products (10 Marks) (b) Partcles of unform sze are 60% converted nto product accordng to the shrnkng core model wth reacton control n a sngle fludsed bed. () If the reactor s made twce as large but wth the same gas envronment what would be the converson of solds? (7 Marks) () If the output from the frst reactor s ntroduced nto a second reactor of same sze and gas envronment what would be the converson? (8 Marks) For a sngle fludsed bed x t e For mult-stage fludsed bed x t e t where t mean resdence tme of solds n a stage. 4

5 Q6. The H S content of a gas s to be reduced from 1% down to 1 ppm (1 x 10-6 ) by contact n a packed bed wth an aquous soluton contanng 0.5 mol/l of methanolamne (ME). Determne a reasonable L/G to use and the heght of tower needed. Data: H S and ME react as follows H S + R NH H S + R NH + ( + Products) Ths reacton s rreversble and nstantaneous, n whch case: -r DL C P + DL b H k a H k a L r ( k a) P or when k L k ap C b s a reasonable gas flow rate, take G x 10 - mol/cm s. lso, from experments, take k L a 0.0 s k a 6 x 10-5 mol/cc.s. atmos. k b L C D D L L D L 1.5 x 10-5 cm /s D L 10-5 cm /s H l.atmos./mol. Take total concentraton C T 55.5 mol/l. ssume column operates at atmospherc pressure. N.. t a reasonable L the reacton front moves to nterface. G 5