Process Systems Engineering

Process Systems Engineering

Prof. Davide Manca

Dipartimento di Chimica, Materiali e Ingegneria Chimica “G. Natta”

Politecnico di Milano

Exercise # 6

Calculate the economic potential of the fourth level by the following correlations, whereas the total cost of the column is given by the installation cost, and the fillers cost.

 Pressure vessels, Columns, Reactors

See Tutorial # 4

 Distillation Tray-Columns

& 1.55

. . 4.7

trays 280 TOT c

M S

C I   D H F

with D and H_TOT in [ft]. H_TOT is the total height of the column:





TOT trays Spacing between trays Top Bottom

H  N  H H _

with H_{Top Bottom}  4 5 m.

The factor F_c is calculated as the sum of three factors: F_c F_s F_t F_m.

Tray spacing [in] 24 18 12

Fs 1.0 1.4 2.2

Tray type No down- comer

Sieve Valve Bubble cap “Koch

Kaskade”

Ft 0.0 0.0 0.4 1.8 3.9

Tray Material Carbon Steel Stainless Steel Monel

Fm 0.0 1.7 8.9

 Heat exchangers

Cost of purchase: & ^0.65

. . 101.3

280 ^c

M S

C A   A F

  

Cost of installation: ^{. . & 101.3 0.65}





280 ^c

M S

C I   A F with A = Area of heat transfer in [ft²], e ^{Fc }





Material Shell Tube

CS CS

CS Brass

CS Mo

CS SS

SS SS

CS Monel

Monel Monel

CS Ti

Ti Ti

Fm 1 1.3 2.15 2.81 3.75 3.1 4.25 8.95 13.05

N.B.: Brass = Brass, Mo = Molybdenum, Ti = Titanium

Pressure [psi] ≤ 150 300 400 800 1000

Fp 0 0.1 0.25 0.52 0.55

Heat exchanger type

Kettle Floating Head U-tube Fixed tube

Fd 1.35 1.00 0.85 0.8

The operative costs can be calculated considering that the cost of 30 bar steam is 1.65 € 1000lb, while that of the steam 70 bar is 2.25 € 1000lb. The cost of cooling water is 0.06 € 1000gal. For the calculation of heat exchange area, the heat exchanged in the condenser is:

   

2 , 2

c c c ml H O p H O out in ev cond

Q U A T W c T T  H T V

where U_c is the global heat transfer coefficient, A_c is the exchange area of the condenser, T_ml is the logarithmic mean temperature difference,

H O2

W is the flowrate of cooling water, Tin and Tout

are the temperatures in inlet and outlet to the condenser (generally, T_in  30 C e T_out  50 C), V is the condensing flowrate at the column head.

The latent heat of condensation can be calculated as:

   

1 NC

i

ev cond i ev cond

i

H T x H T



 



The logarithmic mean temperature difference is calculated as:

   

log

cond out cond in

ml

cond out

cond in

T T T T

T T T

T T

  

  



Consider U_c 580 W m K² .

In the case of stabilizer it is important to understand that T_out cannot be greater than that of condensation of the column head. We recommend T_out  38 C.

For the calculation of the heat exchange area is considered that the heat exchanged in the reboiler can be calculated as:

 

steam

r r r ml steam ev ev reb

Q U A T W H  H T V

in which W_steam is the flow rate of steam to the reboiler, V is the evaporating flow rate in the reboiler.

Consider U_r T_r 11250 Btu h ft²

The logarithmic mean temperature difference is calculated as:T_ml T_steamT_reb.