Monday 11 April 2011

PREHEATER DESIGN


Mixed fresh feed and recycled stream from pressure vessel is pumped to Preheater where the stream is preheated to temperature required to carry out reaction in reactor. For this purpose large heating area is required, so we have selected shell and tube heat exchanger.
Flow rate of EO           =21866 kg/hr
Flow rate of Water       = 107342 kg/hr
Total flow rate of feed=m= 129208 kg/hr
Wt  % of EO = 16.92
Wt % of water = 83.08

 Heat Balance
Inlet temp of feed = t1= 401 K
Outlet temp of feed = t2= 468 K
Avg Temp= (t1 + t2)/2 = 434.5 K

 HEAT CAPACITY DATA
Cp of EO at Avg temp = 2.47 kJ/kg.K
Cp of water at Avg temp = 4.61 kJ/kg.K
Cp of mixture =Cp of water* Wt % of Water + Cp of EO * Wt % of EO                          
=4.27 kJ/kg
Q = mCpDt                                           
Dt = t2 – t1 = 67 K
Q = 3.7x 107 kJ/hr

STEAM CALCULATIONS
Temp of steam = 486 K
Latent heat of steam of steam  = l= 1880 kJ/kg
Q= msl
m= 2x 10 4 kg/hr
DESIGN CALCULATIONS
Heat transfer Area
 Q= U.A.LMTD                               
A = Q/(U.LMTD)

LMTD                
LMTD =          43 K
Estimated UD
 UD= 1448 W/m2.K
  A= 195 m2

Tube sheet layout
Tube length  =  16 feet
Tube Dia      = 1 inch
Pitch             = 1 ¼ inch triangular
BWG            = 14
Surface area per lin ft   = 0.2618 ft2
Surface Area of 1 tube = 0.2618 x 16 = 4.19 ft2 =0.3893 m2
Number of tubes = Nt = Total Area /Surface area of 1 tube
Nt =  501    , Nearest tube count =  522
Number of passes =  2


SHELL SIDE CALCULATION
Cold  fluid – EO/water Mixture
Shell Dia  = 33 inch = 0.8382 m
Number of shell passes = 1
as=      area of shell – area of tubes
as=      [ pDs2/4 -  NtpDt2/4]1/144     
as =      0.288  m2
Gas Velocity (for pressure drop only)
Gs = m/as                                                                           
Gs   = 448866 kg/hr.m2
Reynold’s Number
Res                = DeGs/m                                                    
De                  =  4 as /wetted perimeter                           
Wetted perimeter  = Nt.p.Odt/12                              
Wetted perimeter  = 41.76 m2
De     =0.0277 m
m = 0.0522 kg/m.hr
Res   =  239032
Factor for heat transfer
   JH  =320
ho calculation
ho   =      jH  .   k/ De  .   (Cpm/k)1/3.fs                             
k = 0.606 W/m.K
 ho / fs = 575
 fs  calculations
fs =  (m/mw)0.14                                                               
mw   is calculated at tw
tw  =tc + hio/(hio+ho) .(Ta – tc)                 
for steam hio = 8518 W/m2.K
Rd  0.001
tc = 434.2 K
ta = 434.2 K
Ta = 486  K
ho = ?
 hio*ho/(hio+ho) = UD/(1 – UDRd )        
ho = 2521.2  W/m2.K
tw  = 474 K
mw  = 0.44 kg/m.hr
fs =  0.742
Calculated ho
ho / fs = 575
ho  = 427 W/m2.K


TUBE SIDE  CALCULATION
Hot fluid- steam
Nt = 522
OD= 1 inch
Wall thickness = 0.083 inch
Number of passes = n = 2
 at` = 0.0139 m
 at  = Nt*at`/144*n          
 at  = 0.092 m2
 Gas Velocity
Gt = m/at                                                                                 
Gt =  251517 kg/hr.m2
Ta = 486 K
μsteam   =  0.061 kg/m.hr
ID = D = .0212 m
Ret = DGt/μ                                                  
hio = 8518 W/m2.K
Calculated UD
1/ UD = hio+ho/(hio*ho) + Rd                                  
UD = 1420 W/m2.K
PRESSURE DROP CALCULATIONS

SHELL SIDE PRESSURE DROP CALCULATION
ΔPs = f*Gs2*Ds*(N+1)/5.22*1010*De*s*fs 
N+1 = 12*L/B                                           
L = length of tube
B = baffle spacing
B = 21 inch
N+1 = 9
F= 0.0012
Ds = 0.8382 m
De = 0.0277 m
Gs = 448866 kg/hr.m
fs     =  0.742
Specific gravity = s =ρ/62.5      
ρ =  850 kg/m3
s =  0.85
ΔPs = 0.915 kN/m2

TUBE SIDE PRESSURE DROP
ΔPt  = f*Gt2*L*n/5.22*1010*De*s*ft                           
S= 0.0101
Gt =  251517 kg/hr.m2
L= 16 ft
n = 2
f = 0.00015
De = 0.0277 m
ft  =1
ΔPt  =  0.1862 kN/m2

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