REBOILER DESIGN

Calculate Heat Duty – Q

Shell Side: (cold)                                        Tube Side: (hot)

MEG & DEG                                                  Steam

Inlet  Temp of cold fluid  = t₁ =    90  ^oC

Outlet Temp of cold fluid= t₂ =    157  ^oC

ta =  123.5 ^oC

Inlet Temp of hot fluid    =  T₁ = Ta=     212^oC

Outlet Temp of hot fluid =   T₂ =Ta =    212^oC

Preheat = Q1=mCp∆t = 9238925 KJ/hr

Latent Heat = Q2 = m λ = 38649042 kJ/ hr

Total Heat =Q = 47887967 kJ/ hr

LMTD

LMTD 1= ((Ta-t1)-(Ta-t2)) / Ln ((Ta-t1)/(Ta-t2))= 84.0982 ^oC

LMTD 2 =  54 ^oC

Weighted LMTD = Qt / ((Q1/LMTD1) + (Q2/LMTD2))

Weighted LMTD = 58.9341 ^oC

DesignOverall heat transfer Coefficient

Assumed  Ud=1.3639e+003 W /m² K

Ud=1.3639e+003 W /m² K             Ud1=374.1021 W /m² K

Ud2=481.5266 W /m² K

ESTIMATED AREA

A=Q/(Ud*LMTD)*1000/3600 Ac1=Q1*1000/(Ud1*lmtd1*3600)

Ac1 = 81.57 m²

Ac2=Q2*1000/(Ud2*lmtd2*3600)

A=Qtotal/(Ud*wlmtd)*1000/3600

A = 165.49m2

TUBE SIDE CALCULATIONS

Tubes: ¾ in. dia  . 14 BWG

Effective Length of the tubes L=18ft = 5.486 m

O.D of the tubes=0.75 in  = 0.0625   ft   = 0.01905 m

I.D of the tubes =0.584 in = 0.04867 ft = 0.01484 m

SURFACE AREA PER LINEAR FT OF TUBE

 =0.1963 ft2/ft = 2.3556 in2/in =0.0598m2/m

Surface area =at =  5*0.0598 = 0.328 m2

NO OF TUBES

nt=A/at =165.49/0.328=  504.54

Corrected number of tubes nt =506

No of Tubes pass

No of tube passes tp = 2

Corresponding Shell  ID  = 25 in =0.635 m

CORRECTED A

A=nt*a t= 506*0.328= 165.968m²

CORRECTED Ud 

Ud  = Q/(A_cor*wLMTD)*1000/3600

Ud   = 1360 W/m² K

Inside tube heat transfer coefficient based on the outer dia                

 hio= 8509W/m² K

SHELL SIDE CALCULATIONS:

PREHEATING

Shell Diameter =25 in = 0.635 m

Pitch = Pt =15/16 in =0.0238 m

B =ID =0.635 m

Number of  baffles  = n_b =L/B = 5.486/0.635=8.639

Corrected baffle number = 9

O.D of the tubes = 0.75 in = 0.0625 ft   = 0.01905 m

Clearance     C = pt-OD = 0.0238 - 0.01905 = 0.00475 m= 0.1875 in

B = L/nb     B = 5.486 / 9= 0.609 m= 23.97 in                                                                                                                                  

Shell Cross sectional Area

PREHEATING

a_s = ((pi*ID²/4) - (n_t*pi*OD²/4))

a_s = ((3.14*0.635²/4) - (506*3.14*.01905²/4))

a_s = 0.1725 m²

Mass Flow rate = w_f =29919 kg/hr

MASS VELOCITY

G_s = w_f/a_s

G_s = 53391.179 / 0.1725

G_s =173490 kg/m²hr

EQUIVALENT DIAMETER

D_e= 4*as /  (nt*pi*OD)

D_e= 4*0.1725/ (506*3.14*0.01905)

D_e=0.0228 m

Properties at  Temperature ta=123.5 ⁰C

μ=0.0016 kg/m sec

Reynolds Number

R_e.s  = D_e G_s / m

R_e.s  = (0.0228*173490)/(0.0016*3600)

R_e.s  = 686.1363

J_H FACTOR

j_H    =  13

ho   = j_H *k/D  (cm / k) ^1/3 (m / m_w)^0.14

(m / m_w)^0.14 = ?

DIRT FACTOR

Rd= 0.001/5.6812;

Rd = 0.000176 m² K/W

Ud1=374.1021 W /m² K

ESTIMATED OVER ALL CLEAN COEFFICIENT

Uc1 =Ud1/(1-Ud1*Rd)

Uc1= 374.1/(1-374.1021*0.000176)

Uc 1 = 400.5137 W/m²k

hio=    8509 W/m² K

OUTSIDE FILM COEFFICIENT 

Estimation

ho=Uc1*hio/(hio-Uc1)

400.5*8509/ (8509-400.51)

ho = 420.2968 W/m² K

WALL TEMPERATURE

Bubble point Temperature =ta=123.5 ⁰C

Steam Temperature =Ta=212 ^oC

μ=1.6 Cp = 0.0016 kg/m sec

tw=ta+hio/(hio+ho)*(Ta-ta)

tw = 123.5+8509/(8509+420.29)*(212-123.5)

tw =207 ^oC

μ_w=1.2 Cp = 0.0012 kg/m sec

k=0.2596 W/m k

= 2936.6 J /kg k

 j_H   =  13

CORRECTED OUT SIDE FILM COEFFICIENT

ho=JH*k/De*(c* μ / k^)(1/3) * ( μ / μ_w)^0.14

ho=13*0.2596/0.0228*(2936.6 *(2936.6 *0.0016/ 0.2596 /^)(1/3) * 0.0016  / 0.0012)^0.14

ho= 404.9497 W/m² K

CORRECTED OVERALL CLEAN COEFFICIENT

hio=    8509 W/m² K

Uc 1=hio*ho/(hio+ho)

Uc 1=8509*404.9497/(8509+404.9497)

Uc 1= 386.5533W/m² K

Rd = 0.000176 m² K/W

CORRECTED OVER ALL DIRT COEFFICIENT

Ud 1=Uc1 / (1+Uc 1*Rd)

Ud 1=386.5533 / (1+386.5533*0.000176)

Ud 1= 361.8942 W/m² K

CORRECTED AREA

Ac1=Q1*1000/(Ud1*lmtd1*3600)

Ac1 = 84.32 m²

EVAPORATION

Properties at  saturation Temperature ta=157 ⁰C

μ=0.000902 kg/m sec

Reynold Number

R _e.s = D_e G_s / m

R_e.s  = (0.0228*173490)/(0.000902*3600)

R_e.s  = 1217.1

J_H FACTOR

j_H     =  18

ho = j_H *k/D  (cm / k) ^1/3 (m / m_w)^0.14

(m / m_w)^0.14 = ?

DIRT FACTOR

Rd= 0.001/5.6812;

Rd = 0.000176 m² K/W

Ud2=481.5266 W /m² K

ESTIMATED OVER ALL CLEAN COEFFICIENT

Uc2 =Ud 2/(1-Ud2*Rd)

Uc2= 481.5266/(1-481.5266*0.000176)

Uc2 = 526.1898 W/m²k

 hio=    8509 W/m² K

OUTSIDE FILM COEFFICIENT 

Estimation

ho=Uc2*hio/(hio-Uc2)

ho=526.1898*8509/ (8509-526.1898)

ho = 560.87 W/m²

WALL TEMPERATURE

Bubble point Temperature =ta=157 ⁰C

Steam Temperature =Ta=212 ^oC

μ=0.902 Cp = 0.000902 kg/m sec

tw=ta+hio/(hio+ho)*(Ta-ta)

tw = 157+8509/(8509+560.87)*(212-157)

tw =208 ^oC

μ_w=0.9 Cp = 0.0009 kg/m sec

k=0.3594 W/m k

c = 3066.8 J /kg k

j_H   =  18

CORRECTED OUT SIDE FILM COEFFICIENT

ho=JH*k/De*(c* μ / k^)(1/3) * ( μ / μ_w)^0.14

ho=18*0.3594/0.0228*(3066.8 *0.0009/ 0.3594 /^)(1/3) * (0.000902  / 0.0009)^0.14

ho= 560.1898 W/m² K

CORRECTED OVERALL CLEAN COEFFICIENT

hio=    8509 W/m² K

Uc 2=hio*ho/(hio+ho)

Uc 2=8509* 560.8738/(8509+ 560.8738)

Uc 2= 526.1898W/m² K

Rd = 0.000176 m² K/W

CORRECTED OVER ALL DIRT COEFFICIENT

Ud 2=Uc2 / (1+Uc 2*Rd)

Ud 2=526.1898 / (1+526.1898*0.000176)

Ud 2= 481.5266 W/m² K

CORRECTED AREA

Ac2=Q2*1000/(Ud2*lmtd2*3600)

Ac2 = 370.9635m²   

TOTAL CORRECTED AREA

Ac=Ac1+Ac2;

Ac = 84.32+37.9635

Ac =122.2835 m²

    

CLEAN OVERALL COEFFICIENT

Uc=(Q1 /LMTD1+Q2 / LMTD2)/Ac

Uc=1784.7 W/m² K

     

DESIGN OVERALL COEFFICIENT

Ud=Uc/(1+Uc*Rd)

Rd=1357.6  W/m² K

      

TOTAL AREA

A=Qtotal/(Ud*wlmtd)*1000/3600

maxflux=Qtotal/A;

A=166.2560 m²