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_T  = m_sl

m_s  = 2x 10 ⁴ kg/hr

DESIGN CALCULATIONS

Heat transfer Area

 Q= U.A.LMTD                               

A = Q/(U.LMTD)

LMTD                

LMTD =          43 K

Estimated U_D

 U_D= 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

a_s=      area of shell – area of tubes

a_s=      [ pD_s²/4 -  NtpD_t²/4]1/144     

a_s =      0.288  m²

Gas Velocity (for pressure drop only)

Gs = m/a_s                                                                           

Gs   = 448866 kg/hr.m²

Reynold’s Number

Re_s                = D_eGs/m                                                    

D_e                  =  4 a_s /wetted perimeter                           

Wetted perimeter  = Nt.p.Od_t/12                              

Wetted perimeter  = 41.76 m²

D_e     =0.0277 m

m = 0.0522 kg/m.hr

Re_s   =  239032

Factor for heat transfer

   JH  =320

h_o calculation

h_{o   =}      j_{H  .}   k/ D_{e  .}   (Cpm/k)^1/3.f_s                             

k = 0.606 W/m.K

 h_o / f_s = 575

 f_s  calculations

f_s =  (m/m_w)^0.14                                                               

m_w   is calculated at t_w

t_w  =tc + hio/(hio+ho) .(Ta – tc)                 

for steam hio = 8518 W/m².K

R_d  0.001

tc = 434.2 K

ta = 434.2 K

Ta = 486  K

ho = ?

 hio*ho/(hio+ho) = U_D/(1 – U_DR_d )        

ho = 2521.2  W/m².K

t_w  = 474 K

m_w  = 0.44 kg/m.hr

f_s =  0.742

Calculated ho

h_o / f_s = 575

h_o  = 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

 a_t` = 0.0139 m

 a_t  = Nt*a_t`/144*n          

 a_t  = 0.092 m2

 Gas Velocity

G_t = m/a_t                                                                                 

G_t =  251517 kg/hr.m²

Ta = 486 K

μ_steam   =  0.061 kg/m.hr

ID = D = .0212 m

Re_t = DG_t/μ                                                  

hio = 8518 W/m².K

Calculated U_D

1/ U_D = hio+ho/(hio*ho) + R_d                                  

U_D = 1420 W/m².K

PRESSURE DROP CALCULATIONS

SHELL SIDE PRESSURE DROP CALCULATION

ΔP_s = f*G_s²*D_s*(N+1)/5.22*10¹⁰*D_e*s*f_s 

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

f_s     =  0.742

Specific gravity = s =ρ/62.5      

ρ =  850 kg/m³

s =  0.85

ΔP_s = 0.915 kN/m²

TUBE SIDE PRESSURE DROP

ΔP_t  = f*G_t²*L*n/5.22*10¹⁰*De*s*f_t                           

S= 0.0101

G_t =  251517 kg/hr.m²

L= 16 ft

n = 2

f = 0.00015

De = 0.0277 m

f_t  =1

ΔP_t  =  0.1862 kN/m²