Design of stirred batch reactor

1. Design Of Stirred Batch Reactor Presented By: SAQIB RAUF

2. What is bio-reactor A bioreactor may refer to any manufactured or engineered device or system that supports a biologically active environment In one case, a bioreactor is a vessel in which a chemical process is carried out which involves organisms or biochemically active substances derived from such organisms. This process can either be aerobic or anaerobic . These bioreactors are commonly cylindrical, ranging in size from litres to cubic metres , and are often made of stainless steel .

3. Cont.. A bioreactor may also refer to a device or system meant to grow cells or tissues in the context of cell culture . These devices are being developed for use in tissue engineering or biochemical engineering

4. Classification of bio-reactors On the basis of mode of operation , bioreactor may be classified as B atch F ed batch continuous O rganisms growing in bioreactors may be Suspended Immobilized

5. WHAT IS FERMENTATION? Enzymes break down starch into simple sugars, and yeast ferments sugars into ethanol, giving off carbon dioxide gas as a by product. The process has been used since civilization began. Starch is made up of long chains of glucose molecules coiled together. The starch must be broken down into sugars that are only one or two molecules long for the yeast to feed on. REACTION 305 K C 6 H 12 O 6 (l) ------------------> 2C 2 H 5 OH (l) + 2CO 2 (g) 180 kPa ∆H r = -285 kJ /kg C 2 H 5 OH

6. Reactor Selection Process Design Mechanical Design Heat Calculation Specification Sheet REACTOR DESIGN REF: Chemical Process Engineering Design and Economics By Harry Silla

7. SELECTION OF REACTOR Our system is gas-liquid system. We select a batch stirred tank reactor. This is due to the following reasons: We need to have the bio mass and molasses in contact with each other for a long time. Need to mix the nutrients, bio mass and molasses well together. Visited MURREY BREWERY INDUSTRY RAWALPINDI where batch process was taking place. Concentration and temperature of the species is uniform through out. REF: Chemical Process Engineering Design and Economics By Harry Silla

8. The following table tells us that a stirred batch reactor is common for gas-liquid systems. SELECTION OF REACTOR REF: Chemical Process Engineering Design and Economics By Harry Silla

9. BATCH REACTOR REF: Chemical Process Engineering Design and Economics By Harry Silla

10. Fermenter modeled as a batch reactor. Batch reactor consists of an agitator and a jacket around it for cooling purposes. Reactants are filled in and allowed to react for a certain period of time without them exiting. Jacket consists of agitation nozzles for providing higher turbulence and hence better heat transfer. REF: Chemical Process Engineering Design and Economics By Harry Silla BATCH REACTOR

11. Fermenter modeled as a batch reactor. Batch reactor consists of an agitator and a jacket around it for cooling purposes. Reactants are filled in and allowed to react for a certain period of time without them exiting. Jacket consists of agitation nozzles for providing higher turbulence and hence better heat transfer. REF: Chemical Process Engineering Design and Economics By Harry Silla BATCH REACTOR

12. There are 2 fermenters installed in parallel. According to a journal, the conversion is 70 % and for that conversion the reaction time is 48 hrs. 2 fermenters are used because 1 would give us very large dimensions. BATCH REACTOR

13. PROCESS DESIGN

14. PROCESS DESIGN In sizing of a batch reactor, the following rate equations have to be followed to calculate the reaction time; REF: Chemical Reaction Engineering By Octave Levenspiel

15. PROCESS DESIGN The yeast being used is Saccharomyces cerevisiae. According to an experimental research paper, for a conversion of 70%, the time taken for the batch reaction is 48 hrs. The following equation was then used to calculate the entire batch time. Where; t F ’ = Time needed for filling. t R = Time taken for reaction. t C ’ = Time taken to cool. t E ’ = Time taken for emptying and cleaning. t B = Time taken for the entire batch operation. REF: Chemical Process Engineering Design and Economics By Harry Silla REF: Journal of Tokyo University of Fisheries, Vol 90, pp. 23-30, 2003

16. Time required for the entire batch operation: Charging time ( t F ’ ): 2 hrs. Cooling time ( t C ’) : 1.5 hrs. Reaction time ( t R ): 48 hrs. Emptying and cleaning time ( t E ’) : 0.5 hrs. Total time for batch ( t B ) : 2 + 1.5 + 48 + 0.5 = 52 hrs. REF: Crystalline Chemical Industries

17. PROCESS DESIGN Volume of Fermenter : Conversion = 70%. Reaction Time = 48 hrs. Batch Time ( t B ) = 52 hrs. No. of Fermenters used = 2 Working Pressure of Vessel (P) = 180 kPa Temperature of Reaction = 32 o C. pH = 4.8 Mass flow rate in (m l ’) = 6700 Kg/hr. Density of Material in Fermenter ( ρ ’) = 1200 Kg/m 3 .

18. Now; t B = 52 hrs. Density of Feed ( ρ ’) = 1200 Kg/m 3 . Now; m l ’ = 6700 Kg/hr Therefore; V r = 6700 x 52 1200 V r = 290 m 3 . REF: Chemical Process Engineering Design and Economics By Harry Silla VOLUME OF FERMENTER

19. Now; We allow 30% of volume of fluid as the free space in the fermenter. Hence; With 30% allowance; V T = 1.30 x V r = 1.30 x 290 = 377 m 3 . REF: Chemical Process Engineering Design and Economics By Harry Silla

20. Dimensions : H/D = 1.5 V T = Π x (D 2 /4) x L = Π x (D 2 /4) x 1.5D = (3/8) Π x (D 3 ) V T = 377 m 3 . Hence , putting in above equation; D = 6.8 m. H = 10 m

21. Now; Height of Dished Bottom = 1 m ( From Literature) Therefore; Total Height = 10 + 1 = 11 m.

22. MECHANICAL DESIGN

23. Static Pressure (P s ) = ρ ’ x g x H = (1200 x 9.81 x 10)/1000 = 129 kPa . Total Pressure at base = P s + P = 309 kPa . Maximum allowable pressure = 1.33 (309) = 410 kPa . MECHANICAL DESIGN WALL THICKNESS For the calculation of wall thickness we have to calculate the total pressure which is the sum of static pressure and operating pressure of the fermenter. REF: Plant Design and Economics for Chemical Engineers Max S. Peters et al.

24. Wall thickness = P x ri + C c SE j – 0.6P Material = Carbon Steel. Working Stress of Carbon Steel,S = 94408 KN/m 2 . Joint Efficiency, E j = 0.85 Internal Radius, ri = 3.4 m Corrosion allowance = 2mm. Therefore wall thickness = 0.017 + C c = 0.017 + 0.002 = 0.019 m = 19 mm. Therefore outside diameter = D i + 2t = 6.84 m. WALL THICKNESS REF: Plant Design and Economics for Chemical Engineers Max S. Peters et al.

25. REACTOR HEAD There are three types of heads: Ellipsoidal Head. Torispherical Head. Hemispherical Head. Ellipsoidal head is used for pressure greater than 150 psi and for less than that pressure we use Torispherical head. That is why we have selected a Torispherical head. REF: Coulson & Richard Chemical Engineering, Vol 6. REF: Chemical Process Engineering Design and Economics By Harry Silla

26. TORISPHERICAL HEAD = 0.019 + 0.002 = 0.021 m = 21 mm. REF: Coulson & Richard Chemical Engineering, Vol 6. REF: Chemical Process Engineering Design and Economics By Harry Silla

27. MECHANICAL DESIGN AGITATOR DESIGN Agitator Dimensions are: Impeller Diameter D a = D t /3 = 2.2 m Impeller Height above Vessel floor E = D a = 2.2 m Length of Impeller Blade L = D a /4 = 0.6 m Width of Impeller Blade W = D a /5 = 0.4 m Width of Baffle J = D t /10 = 0.68 m No. of Impellers = 3 No. of Impeller blades = 6 Distance between 2 consecutive impellers = 2.2 m Shape Factors are S 1 = D a /D t = 1/3 S 2 = E/ D t = 1/3 S 3 = L/D a = 0.27 S 4 = W/D a = 1/5 S 5 = J/ D t = 1/10 S 6 = H/D t = 1.5 Tip Velocity = 3 – 6 m/sec Tip Velocity = 5 m/sec Tip Velocity = π x D a x N Speed of Impeller = N = [5/( π x 2.2)] x 60 = 44 RPM REF: Unit Processes in Chemical Engineering By Mccabe, Smith & Harriot REF: Heuristics in Chemical Engineering Edited for On-Line Use by G. J. Suppes, 2002

28. Power no (N p )= 6. Shaft RPM (N)= 44 RPM = 0.7 rev/sec Power = (N p x N 3 x D a 5 x ρ )/g c = 52 hp. Now, Assuming the impeller is 85 % efficient: Actual Power required = 52/0.85 = 60 hp. POWER REQUIREMENT

29. No. of baffles = 4. Width of one baffle = D t / 10 = 0.68 m. Height of baffle = 10 m. BAFFLE DESIGN

30. VISUAL DISPLAY OF AGITATOR WITH DIMENSIONS

31. VISUAL DISPLAY OF FERMENTER WITH DIMENSIONS FRONT VIEW

32. VISUAL DISPLAY OF FERMENTER WITH DIMENSIONS TOP VIEW 6.84 m 2.2 m 0.68 m 6.80 m Width of Baffle Agitator Cooling Jacket

33. Cooling fluid used = Cooling Water. Cooling Jacket area available (A) = 17 m 2 This area is obtained from Table 7.3 in “ Chemical Process Engineering Design and Economics by Harry Silla ” CW inlet temp = 20 o C CW outlet temp = 28 o C Approaches; ΔT 1 = 32 – 20 = 12 C ΔT 2 = 32 – 28 = 4 C LMTD = 7.3 C = 7.3 K HEAT TRANSFER CALCULATION REF: Chemical Process Engineering Design and Economics By Harry Silla

34. Heat of Reaction; Q = ∆H r = 1.1 x 10 6 kJ/hr Design Overall Coefficient = U D = 170 W/ m 2 . K Now; Heat Removable by Jacket; Q j = U D x A x LMTD = 23579 W = 8.5 x 10 7 kJ/hr Since the heat of reaction (1.1 x 10 6 kJ/hr) < heat removable by jacket (8.5 x 10 7 kJ/hr ) Our design for a cooling jacket is justified in comparison with a cooling coil. Now Cooling water Flow rate can be calculated as: Heat to be removed from reactor = 1.1 x 10 6 kJ/hr Mass flow rate of water = Q/( CpΔT M ) = 33 Tons/hr HEAT TRANSFER CALCULATION REF: Chemical Process Engineering Design and Economics By Harry Silla

35. SPECIFICATION SHEET

36. Identification Item Fermenter Item Name R-101 No. Required 8 Function Production of Industrial Alcohol by Fermentation Operation Batch Type Jacketed, Stirred Tank Reactor Volume 377 m 3 Height 10 m Diameter 6.8 m Temperature 32 o C Working Pressure 1.8 atm Batch Time 52 hrs Height to Diameter Ratio 1.5 Type of Head Torispherical Depth of Dished Bottom 1 m Wall Thickness 0.019 m Head Thickness 0.021 m No. of Baffles 4 Width of Baffle 0.68 m Height of Baffle 10 m Material of Construction of Fermenter Carbon Steel

37. Identification Item Agitator Type Three 6-bladed Flat Turbine Number of Blades 6 Impeller Diameter 2.2 m Length of Blade 0.6 m Width of Blade 0.4 m Impeller Above Vessel Floor 2.2 m Speed of Impeller 44 RPM Power Required 60 hp Identification Item Cooling Jacket Fluid Handled Cooling Water Inlet Temperature 20 o C Outlet Temperature 28 o C Flow Rate 33 Tons/hr. Heat Transfer Area 17 m 2 U D 30 BTU/hr.ft 2 . o F R D 0.001 hr.ft 2 . o F/BTU