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Design Of Stirred Batch ReactorPresented By: SAQIB RAUF

What is bio-reactorA bioreactor may refer to any manufactured or engineered device or system that supports a biologically active environmentIn 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.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 engineeringClassification of bio-reactorsOn the basis of mode of operation, bioreactor may be classified as BatchFed batchcontinuousOrganisms growing in bioreactors may beSuspended Immobilized

(e.g. a continuous stirred-tank reactor model). An example of a continuous bioreactor is the chemostat6WHAT 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 KC6H12O6 (l)------------------> 2C2H5OH (l) + 2CO2 (g) 180 kPa

H0r = -285 kJ /kg C2H5OH

Reactor SelectionProcess DesignMechanical DesignHeat CalculationSpecification Sheet

REACTOR DESIGNREF: Chemical Process Engineering Design and Economics By Harry SillaSELECTION OF REACTOROur 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

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

BATCH REACTORREF: Chemical Process Engineering Design and Economics By Harry SillaFermenter 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 SillaBATCH REACTORFermenter 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 SillaBATCH REACTOR13There 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 REACTORPROCESS DESIGN

PROCESS DESIGNIn sizing of a batch reactor, the following rate equations have to be followed to calculate the reaction time;

REF: Chemical Reaction Engineering By Octave LevenspielPROCESS DESIGNThe 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;

tF= Time needed for filling.tR= Time taken for reaction.tC= Time taken to cool.tE= Time taken for emptying and cleaning.tB = Time taken for the entire batch operation.

REF: Chemical Process Engineering Design and Economics By Harry SillaREF: Journal of Tokyo University of Fisheries, Vol 90, pp. 23-30, 2003Time required for the entire batch operation:

Charging time (tF ):2 hrs.Cooling time (tC) :1.5 hrs.Reaction time (tR):48 hrs.Emptying and cleaning time (tE) :0.5 hrs.

Total time for batch (tB): 2 + 1.5 + 48 + 0.5 = 52 hrs.REF: Crystalline Chemical IndustriesPROCESS DESIGNVolume of Fermenter:

Conversion= 70%.

Reaction Time= 48 hrs.

Batch Time (tB)= 52 hrs.

No. of Fermenters used= 2

Working Pressure of Vessel (P)= 180 kPa

Temperature of Reaction= 32 oC.

pH= 4.8

Mass flow rate in (ml)= 6700 Kg/hr.

Density of Material in Fermenter () = 1200 Kg/m3.

Now;tB =52 hrs.Density of Feed ()=1200 Kg/m3.

Now;ml= 6700 Kg/hrTherefore;Vr= 6700 x 52 1200 Vr= 290 m3.

REF: Chemical Process Engineering Design and Economics By Harry SillaVOLUME OF FERMENTERNow;

We allow 30% of volume of fluid as the free space in the fermenter.

Hence;With 30% allowance; VT= 1.30 x Vr= 1.30 x 290= 377 m3.REF: Chemical Process Engineering Design and Economics By Harry Silla Dimensions:

H/D= 1.5 VT= x (D2/4) x L= x (D2/4) x 1.5D= (3/8) x (D3)VT= 377 m3.

Hence, putting in above equation;

D= 6.8 m.

H= 10 mNow;

Height of Dished Bottom= 1 m( From Literature)

Therefore;

Total Height= 10 + 1 = 11 m.MECHANICAL DESIGNStatic Pressure (Ps)= x g x H= (1200 x 9.81 x 10)/1000= 129 kPa.

Total Pressure at base= Ps + P= 309 kPa.

Maximum allowable pressure = 1.33 (309) = 410 kPa.

MECHANICAL DESIGNWALL THICKNESSFor 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.Wall thickness= P x ri + CcSEj 0.6PMaterial= Carbon Steel.Working Stress of Carbon Steel,S= 94408 KN/m2.Joint Efficiency, Ej= 0.85Internal Radius, ri= 3.4 m

Corrosion allowance= 2mm.

Therefore wall thickness= 0.017 + Cc= 0.017 + 0.002= 0.019 m = 19 mm.Therefore outside diameter= Di + 2t = 6.84 m.WALL THICKNESSREF: Plant Design and Economics for Chemical Engineers Max S. Peters et al.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 SillaTORISPHERICAL 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 SillaMECHANICAL DESIGNAGITATOR DESIGNAgitator Dimensions are:Impeller Diameter Da = Dt/3= 2.2 mImpeller Height above Vessel floor E = Da = 2.2 mLength of Impeller Blade L = Da /4 = 0.6 mWidth of Impeller Blade W = Da /5 = 0.4 mWidth of Baffle J = Dt/10 = 0.68 mNo. of Impellers= 3No. of Impeller blades= 6Distance between 2 consecutive impellers= 2.2 m

Shape Factors are S1 = Da/Dt = 1/3 S2 = E/Dt = 1/3S3 = L/Da = 0.27S4 = W/Da = 1/5S5 = J/Dt = 1/10S6 = H/Dt = 1.5

Tip Velocity = 3 6 m/secTip Velocity = 5 m/secTip Velocity = x Da x NSpeed of Impeller = N = [5/( x 2.2)] x 60 = 44 RPM REF: Unit Processes in Chemical Engineering By Mccabe, Smith & HarriotREF: Heuristics in Chemical Engineering Edited for On-Line Use by G. J. Suppes, 2002Power no (Np )= 6.

Shaft RPM (N)= 44 RPM = 0.7 rev/sec

Power = (Np x N3 x Da5 x )/gc = 52 hp.

Now,

Assuming the impeller is 85 % efficient:

Actual Power required = 52/0.85 = 60 hp.

POWER REQUIREMENTNo. of baffles= 4.

Width of one baffle= Dt / 10= 0.68 m.

Height of baffle= 10 m.BAFFLE DESIGNVISUAL DISPLAY OF AGITATOR WITH DIMENSIONS

VISUAL DISPLAY OF FERMENTER WITH DIMENSIONSFRONT VIEWVISUAL DISPLAY OF FERMENTER WITH DIMENSIONSTOP VIEW6.84 m2.2 m0.68 m6.80 mWidth of BaffleAgitatorCooling JacketCooling fluid used = Cooling Water.

Cooling Jacket area available (A) = 17 m2

This area is obtained from Table 7.3 in Chemical Process Engineering Design and Economics by Harry Silla

CW inlet temp = 20 oCCW outlet temp = 28 oC

Approaches;T1= 32 20 = 12 0C T2= 32 28 = 4 0CLMTD = 7.3 0C = 7.3 0KHEAT TRANSFER CALCULATIONREF: Chemical Process Engineering Design and Economics By Harry SillaHeat of Reaction;Q = Hr = 1.1 x 106 kJ/hr Design Overall Coefficient = UD = 170 W/ m2. 0K

Now; Heat Removable by Jacket;Qj = UD x A x LMTD = 23579 W = 8.5 x 107 kJ/hr

Since the heat of reaction (1.1 x 106 kJ/hr) < heat removable by jacket (8.5 x 107 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 106 kJ/hrMass flow rate of water = Q/( CpTM) = 33 Tons/hr

HEAT TRANSFER CALCULATIONREF: Chemical Process Engineering Design and Economics By Harry SillaSPECIFICATION SHEETIdentificationItemFermenterItem NameR-101No. Required8FunctionProduction of Industrial Alcohol by FermentationOperationBatchTypeJacketed, Stirred Tank ReactorVolume 377 m3Height10 mDiameter6.8 mTemperature32oCWorking Pressure1.8 atmBatch Time52 hrsHeight to Diameter Ratio1.5Type of HeadTorisphericalDepth of Dished Bottom1 mWall Thickness0.019 mHead Thickness0.021 mNo. of Baffles4Width of Baffle0.68 mHeight of Baffle10 mMaterial of Construction of FermenterCarbon SteelIdentificationItemAgitatorTypeThree 6-bladed Flat TurbineNumber of Blades6Impeller Diameter2.2 mLength of Blade0.6 m Width of Blade0.4 mImpeller Above Vessel Floor2.2 mSpeed of Impeller44 RPMPower Required60 hpIdentificationItemCooling JacketFluid HandledCooling WaterInlet Temperature20oCOutlet Temperature28oCFlow Rate33 Tons/hr.Heat Transfer Area17 m2UD30 BTU/hr.ft2.oFRD0.001 hr.ft2.oF/BTU