MANUFACTURE OF POLY VINYL ALCOHOL

[1 TONNE PER DAY]

THIRD REVIEW REPORT

PROJECT GUIDE

Dr.K.V.RADHA,ASSOCIATE PROFESSOR

Department of Chemical Engineering,AC Tech, Anna University,

Chennai-25

SUBMITTED BY

KISHEN RAFIZ (20080927)

B.TECH, CHEMICAL– VIII SEM

DESIGN OF EQUIPMENTS

POLYMERISATION REACTOR 1

Reaction vessels are often the most important elements in many industrial plants. They provide a structural facility for many functions including separation, mixing, blending, chemical reactions, treating and regeneration. The design of the reaction vessel depends mainly on the nature of the reaction.

REACTION KINETICS AND SIZING OF THE REACTOR:

In this reactor the monomer of Vinyl Acetate is polymerised to Poly Vinyl Acetate. This is a liquid phase, First Order reaction. The reaction is exothermic and thus, a cooling water jacket envelops the reactor. The reactor conversion is 25%, as referred from the literature.

Reaction rate : -rA= k.CA

Where CA – Concentration of VAM (moles/lit )

K - rate constant ( 0.274 hr-1 )

Design Equation:

VF Ao

= X A−r A

Where FA0 – initial molar flow rate ( mol/hr)

XA – percentage conversion

-rA – reaction rate ( mol/lit.hr)

V – Volume(lit)

VOLUME OF THE REACTOR:

Feed Specification:

Vinyl Acetate Monomer- 94.1kg/hr

Methanol- 35.58kg/hr

AIBN (Initiator) - 8.2kg/hr

Volumetric feed rate of vinyl acetate = (94.1*1000)/ (933.8) = 100.77litres/hr

Volumetric feed rate of Methanol = (35.88*1000)/ (791.7) = 45.32lt/hr

Volumetric feed rate of AIBN = (8.2*1000)/ (820) = 10lt/hr

Total Volumetric Feed Rate(Vo) = 156.09lt/hr

Initial Concentration:

CA0 = FA0/ Vo

= (94.1*1000)/ (86.088*156.09)

CA0 = 7.01 gm mol/ lit

Final Concentration:

-rA = KCA

CA= CA0 * ( 1- XA )

= 7.01(1- 0.25)

= 5.25 gm mole/ lit

VF Ao

= X A−r A =

VF Ao

= X AKC A

V = X AKC A

* CA0 * Vo

= 0.25

.274∗5.25 * 7.01 * 156.09

= 189.78 lit

= .189m3

Diameter and Height of the vessel ;

We assume that the reaction vessel is cylindrical in nature and ignore the volume due to dished end.

Volume of vessel = π D2H/ 4

Where D – diameter of the vessel

H – height of the vessel

Let H/D ratio = 2

Volume of the Reactor(theoretical) = .189m3

Volume (25% extra) = .189 * 0.25

= 0.047m3

Actual Volume (Theoritical +25%) = 0.2362 m3

0.2363= π D3/ 2

D = 0.53 m

H = 1.06 m

MECHANICAL DESIGN

1. SHELL THICKNESS:

Shell thickness = PDi

2 fJ−P

Where P – design pressure

f – permissible stress of the material

J – joint efficiency

Di – inside diameter

The operation pressure is 1 atm ( 101325 N/m2 )

Material of construction - mild steel

Design pressure (P) - 101325 N/ m2

Inside Diameter ( Di ) - 1.76 m

Joint efficiency (J) - 85 %

Tensile strength for mild steel- 93.95 * 105 N/m2

Safety factor - 3

Hence permissible stress - 310.6595 * 105 N / m2

Shell thickness (t) = 101325∗0.53∗1000

(2∗310.65∗105∗0.85 )−101325

t = 1.02 mm

Thickness of head

Since the operating pressure is less, it is sufficient to use torispherical head.

The thickness is given by :

t = P∗Rc∗W

2∗f∗J

P – design pressure ( N/ m2)

RC – crown radius ( m)

W- intensification factor

W= 14

*[3+√RcR1

]

R1 – knuckle radius

Torispherical heads have dish crown radius equal to or less than the diameter of the head to reduce the stresses at the corner of the head, a knuckle is formed with radius of 6% of the inside diameter.

Hence Rc = Di = 0.53 m

R1 = 0.53 * 0.06 = 0.03 m

W = 14

*[3+√RcR1

]

W = 14

*[3+√0.53

0.0318 ]

W = 1.7706

Thickness (t) = P∗Rc∗W

2∗f∗J

= 101325∗0.53∗1.77

2∗310∗105∗0.85

Head thickness (t) = 1.89 mm

Attachment of head and shell :

The bottom head is welded to the reactor and the top head is flanged with the shell.

2. NOZZLE:

Nozzle thickness:

tZ = P*Do/(2fJ+P)

Where,

P= Design pressure in kg/cm2

Do= Diameter of the nozzle in cm

J= weld joint efficiency

Let,

P=1atm: Do= 30cm: J=0.96

Therefore,

tf=(1*30*1.03367)/(2*950*0.96+1*1.00367)

= 0.198mm

Actual thickness of nozzle= 5*tZ

= 2.122mm = 3mm

3. GASKET DESIGN:

Material of gasket = rubber T - section ring

Gasket factor ( m) = 9

Yield stress ( Y ) = 2.8 N /mm2 = 2.8 * 106 N /m2

d 0di

= √Y−P∗MY−P(M+1)

do – outside diameter of gasket ring

di – vessel inside diameter

d 0di

= √2.8∗106−101325∗92.8∗106−P(M+1)

do = 1.03 * 0.53

do = 0.5459m

FLANGE THICKNESS:

Blind flanges are often used as cover plates for circular openings. The thickness of the flange is given as

tf = G√Pk∗f + C

k = 1

[0.3+1.5WM∗hg/HG ]

G – diameter of gasket load reaction

p – design pressure

f – permissible stress

B – bolt circle dia

c – corrosion allowance

Wm2 - total bolt load

hg - radial distance from gasket load reaction to bolt circle

hg =( B-G)/2

H = total hydrostatic end force

H = 0.79746 * 105 N

hg =(R-G)/2=(120.32-96.1)/2

= 12.1 cm

Wm = 13.45 * 105 N

G = 96.1 cm

K = 1/(0.3 + (1.5 *13.45 * 10 5 * 12.1 ) / ( 0.02515 * 10 5 * 96.1 ))

= 9.87 * 10-3

tf = G(P/Kf)0.5+ C

With low pressure, the thickness of flange may work out to be negligible. It is necessary however, to promote a minimum thickness. The minimum flange thickness for mild steel is 20 mm.

Hence flange thickness = 20 mm

4. IMPELLAR DESIGN:-

Agitator blades – 6 (n)

Width of the blade – 40 mm (w)

Thickness of blade – 5 mm (t)

Shaft material – commercial cold rolled steel

Permissible shear stress in shaft – 550 Kg/cm2

Elastic limit in tension – 2460 Kg/cm2

Modulus of elasticity – 19.5 x 10^5 Kg/cm2 (E)

Permissible stress for key (carbon steel)

Shear – 630 Kg/cm2

Crushing – 1300 Kg/cm2

Stuffing box (carbon steel) - 950 Kg/cm2

Studs and bolts (hot rolled carbon steel)

Permissible stress – 587 Kg/cm2

Flange extension = (D/5) = 0.106m

Da- Distance between impeller edges.

Dt- Diameter of Tank.

(Da/Dt) = (1/3)

Da = 0.53/3 = 0.176m

J- Baffle thickness

J/Dt = 1/12

J = 0.53/12 = 0.044m

E- Distance between tank base and centre of the impeller.

E/Dt = 1/3

E = 0.53/3 = 0.176m

W- Impeller Width

W/Da = 1/5

W = 0.53/5 = 0.106m

H- Length of the Impeller

H/Da = ¼

H = 0.53/4 = 0.1325m

5. POWER REQUIREMENT:

a. impeller Reynolds number

Re = ρ N Da2/µ

N- Rotational speed rps

Da – agitator diameter m

ρ – fluid density kg /m3

µ – viscosity kg / ms

Feed components Specific gravity Mass rate Mass fraction

VAM 0.933 94.1 0.68MeOH 0.8 35.58 0.25AIBN 1.1 8.2 0.06Total 137.88 1

Average specific gravity = (0.933 * 0.68 + 0.8 * 0.25 + 1.1 * 0.06)

= 0.90

Average feed viscosity = (0.158*10-3*0.33+0.203*10-3*0.018+8*10-4*0.66)

= 3.66*10-3 kg/ms

Speed of impeller = 35 rpm

Agitator diameter = 35 cm

Re = (830.9*(35/60)*0.72632)/ 3.66*10-3

Re = 69800.36

From graph between power no and Re

Power number P0 = 6

Power P = (P0 ρ N3 Da5 )*hp/(75*g)

= (6*830.9*(35/60)3*0.72635)/(75*9.8)

= 4.2 hp

Given allowance for transmission and other losses(25%) , we take the rated power of impeller = 5.25 hp.

6. JACKET:

Total reactor surface area covered by jacket = (π*D*l)+(π *D2/4)

= (π*0.53*1.614)+(π*0.532/4)

= 2.90 m2

Temperature difference in cooling water = Q / U * A

∆T = (3203.72*1000)/(500*2.90*3600)

= 298.45 K

Spacing between jacked and vessel = 50 mm (assumed )

Diameter of jacket = 0.53 + (2 * 50* 10-3)

= 0.63 m

Pressure inside jacket = 1.01325*105+0.026 bar(water pressure at 27°C)

= 1.04*105 N/m2

Jacket thickness = P*D/(2f j-P)

= (1.04*105*0.53)/(2*183.3*106*0.85-1.04*105)

= 0.2 mm

The jacket thickness obtained is less, so minimum jacked thickness of 2 mm is assumed with corrosion allowance of 4 mm.

Therefore, Total Jacked thickness = 6 mm

FLASH DRUM

The Flash Drum is used to separate the Acetic Acid liquid solution from the gaseous Vinyl Acetate Monomer (VAM). The design will consist of finding the Maximum Design Vapor Velocity, which in turn will set the Diameter of the column. The position of the inlet is be placed just somewhat above the column centre as per standard design norms.

A vapor-liquid separator drum is a vertical vessel into which a liquid and vapor mixture (or a flashing liquid) is fed and wherein the liquid is separated by gravity, falls to the bottom of the vessel, and is withdrawn. The vapor travels upward at a design velocity which minimizes the entrainment of any liquid droplets in the vapor as it exits the top of the vessel. 

Design Procedure:-The size of a flash drum (or knock-out pot, or vapor-liquid separator) should be dictated by the anticipated flow rate of vapor and liquid from the drum. The following sizing methodology is based on the assumption that those flow rates are known. 

For the maximum design vapor velocity (which will set the drum's diameter), I have used

the Souders-Brown equation: 

Vmax = (k) [ (dL - dV) / dV ]^0.5

where: Vmax = maximum design vapor velocity, kg/m3dL = liquid density, kg/m3dV = vapor density, kg/m3k = 0.35 (when the drum includes a de-entraining mesh pad) 

Notes(from GPSA engineering handbook):1. K = 0.35 at 100 psig; subtract 0.01 for every 100 psi above 100 psig2. For glycol or amine solutions, multiply above K values by 0.6 – 0.8.3. Typically use one-half of the above K values for approximate sizing of vertical separators without mesh pads.4. For compressor suction scrubbers and expander inlet separators, multiply K by 0.7 – 0.8

 Thus, the cross-sectional area (A) of the vertical flash drum will be:

A, m^2 = (V, m^3/sec) ÷ (Vmax, m/sec) 

Knowing the cross-sectional area A in square meters, you can then calculate the vessel diameter in m (D).

H, m= (2) (L, m^3/min) & divide; (A, m^2)

Where, cubic feet per minute of liquid (L) that will be leaving the bottom of the flash vessel is known.

Now, we have the height and the diameter of the vessel. If that height to diameter ratio is about 3 to 4, the design is satisfactory. If it is less than 3 to 4, increase the length of the vapor section above the liquid inventory. If it is more than 3 to 4, you may have to consider lowering the amount of liquid inventory so as to shorten the vessel or perhaps even swaging the liquid storage section to a larger diameter. 

SIZING CALCULATIONS:-

To find the maximum design vapor velocity:- Vmax = (k) [ (dL - dV) / dV ]^0.5

Vmax= 0.175 [(1050-800)/800]^0.5

Vmax=0.099m/s

Now, the area is found by:-

A, m^2 = (V, m^3/sec) ÷ (Vmax, m/sec) 

Where V=[(6220kg/sec)/(80kg/m3)]/(3600sec)=0.2m^3/sec

A= 0.2/0.099

A= 2.02 m^2(cross-sectional area)

Thus, the Vessel Diameter is:-

A= (π * D^2)/4

2.02= (π * D^2)/4

D= 1.61m

Now, the height of the Column is:-

Now, assuming the Height to Diameter ratio as 3.6.This will assure that the gas - liquid separation is effective.

Thus, the height of the column will be =3.6 * 1.61 = 5.796m

The liquid flow rate(L) to the column can be found out as,

L=[(141293kg/sec)/(10500kg/m3)]/(3600sec)=0.004m^3/sec

Allowing a hold up time of 10 minutes, for the liquid

Thus, Volume of Liquid held in the vessel will be = 0.004 * 10 * 60= 2.4m^3

Liquid Depth in the Column = Volume held in the vessel / Area of the Vessel

= 2.4 / 2.02= 1.01m.

Distance of Inlet Nozzle from the Liquid Level= D/2 =0.8 m

Distance of Mesh Pad from Inlet Nozzle = D= 1.6m

Thickness of Mesh Pad= D/3= 0.54m

Distance between Gas outlet and Mesh pad= 5.79- 3.94= 1.86m

Now, assuming the Height to Diameter ratio as 3.6.This will assure that the gas - liquid separation is effective.

Thus, the height of the column will be =3.6 * 1.61 = 5.796m

MECHANICAL DESIGN

1. SHELL THICKNESS:

Shell thickness = PDi

2 fJ−P

Where P – design pressure

f – permissible stress of the material

J – joint efficiency

Di – inside diameter

The operation pressure is 1 atm ( 101325 N/m2 )

Material of construction - mild steel

Design pressure (P) - 101325 N/ m2

Inside Diameter ( Di ) - 1.61 m

Joint efficiency (J) - 85 %

Tensile strength for mild steel- 93.95 * 105 N/m2

Safety factor - 3

Hence permissible stress - 310.6595 * 105 N / m2

Shell thickness (t) = 101325∗1.61∗1000

(2∗310.65∗105∗0.85 )−101325

t = 3.356 mm

Thickness of head

Since the operating pressure is less, it is sufficient to use torispherical head.

The thickness is given by :

t = P∗Rc∗W

2∗f∗J

P – design pressure ( N/ m2)

RC – crown radius ( m)

W- intensification factor

W= 14

*[3+√RcR1

]

R1 – knuckle radius

Torispherical heads have dish crown radius equal to or less than the diameter of the head to reduce the stresses at the corner of the head, a knuckle is formed with radius of 6% of the inside diameter.

Hence Rc = Di = 1.61 m

R1 = 1. * 0.06 = 0.096 m

W = 14

*[3+√RcR1

]

W = 14

*[3+√1.76

0.096 ]

W = 1.523

Thickness (t) = P∗Rc∗W

2∗f∗J

= 101325∗1.61∗1.77

2∗310∗105∗0.85

Head thickness (t) = 5.87 mm

Attachment of head and shell :

The bottom head is welded to the bottom and the top head is flanged with the top.

2. NOZZLE:

Nozzle thickness:

tZ = P*Do/(2fJ+P)

Where,

P= Design pressure in kg/cm2

Do= Diameter of the nozzle in cm

J= weld joint efficiency

Let,

P=2.5atm: Do= 30cm: J=0.96

Therefore,

tf=(2.5*30*1.03367)/(2*950*0.96+2.5*1.00367)

= 0.4244mm

Actual thickness of nozzle= 5*tZ

= 2.122mm = 3mm

3. GASKET DESIGN:

Material of gasket = rubber T - section ring

Gasket factor ( m) = 9

Yield stress ( Y ) = 2.8 N /mm2 = 2.8 * 106 N /m2

d 0di

= √Y−P∗MY−P(M+1)

do – outside diameter of gasket ring

di – vessel inside diameter

d 0di

= √2.8∗106−101325∗92.8∗106−P(M+1)

do = 1.03 * 1.61

do = 1.6583 m

width of gasket (bg ) = do−di

2 =

1.658−1.612

bg = 0.02 m

4. CALCULATION OF BOLT LOAD :(1) W m2 : Load to seat gasket 0.0264 m

W m2 = π∗b∗ y*g

b – Effective gasket width = 60 ; b0 < 6.3 mm

= 2.5 *√ 60;bo>6.3 mm

b0 – Basic gasket seating width = bg/2

b0 = bg /2 = 0.0264 /2 = 0.0132 m

b = 2.5*√ bo =2.5*√ 0.0132 = 0.2872m

mean gasket dia G = di + b0

= 1.61 + 0.0132

= 1.6232 m

Wm2 = π∗0.287∗2.8*106

= 44.73 * 105N

(2) Load to keep the joint tight under operation (Hp)

Hp = π∗2∗b∗G*M*P

= π∗2∗0.15∗1.632*9.1*1.1*105

= 10.65*105N

(3) Load from internal pressure (H)

H = π /4∗P∗G2

= π4∗1.1∗105∗1.6322

= 1.56*105N

(4) Wm1 = H + Hp

= 0.79746 * 105 + 9.727 * 105

= 10.52 * 105 N

Wm2 is greater than Wm1

Hence Wm2 is the operating load. It will create a tensile stress in the cross section of the bolt.

5. CALCULATION OF BOLT AREA AND NO OF BOLTS:(1) Bolt material is hot rolled carbon steel

Permissible stress = fb = 53.465 * 10 6 N /m2

In bolt under operating conditions

Cross sectional area (AM2 ) of bolt = Wm2 / fb = 13.45 * 105 / 53.465* 106

= 0.02515 m2

(2) Number of bolts = G / 2.5

= ( 1.632 * 102 / 2.5) = 39.67

Number of bolts are always rounded to the next multiple of four.

Number of bolts = 40

BOLT DIAMETER AND SPACING(1) BOLT DIAMETER :

D = √4∗AM 2π∗N

= (0.025*4/(3.14*40))0.5

= 0.03cm

(2) BOLT SPACING

Recommended bolt spacing is given by the formula

Bs = 2d +6TM+0.5

d- nominal bolt diameter (cm)

m- gasket factor

t – flange thickness ( cm)

Bs = 2*(0.03*102) + 6∗2

9+0.5

Bs = 7.26 cm

(3) BOLT CIRCLE DIAMETER

BCD = d0 + 12 *bolt dia + 1.2

d0 = outside dia of gasket

BCD = 1.813 * 102 + 12* 0.03 * 102 + 1.2

BCD = 120.32 cm

6. FLANGE THICKNESS:

Blind flanges are often used as cover plates for circular openings. The thickness of the flange is given as

tf = G√Pk∗f + C

k = 1

[0.3+1.5WM∗hg/HG ]

G – diameter of gasket load reaction

p – design pressure

f – permissible stress

B – bolt circle dia

c – corrosion allowance

Wm2 - total bolt load

hg - radial distance from gasket load reaction to bolt circle

hg =( B-G)/2

H = total hydrostatic end force

H = 0.79746 * 105 N

hg =(R-G)/2=(120.32-163.2)/2

= 14.1 cm

Wm = 13.45 * 105 N

G = 163.2 cm

K = 1/(0.3 + (1.5 *13.45 * 10 5 * 12.1 ) / ( 0.02515 * 10 5 * 163.2 ))

= 11.24 * 10-3

tf = G(P/Kf)0.5+ C

With low pressure, the thickness of flange may work out to be negligible. It is necessary however, to promote a minimum thickness. The minimum flange thickness for mild steel is 20 mm.

Hence flange thickness = 23 mm