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 fourth level by applying 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 HTOT in [ft]. HTOT is the total height of the column:
1
TOT trays Spacing between trays Top Bottom
H N H H
with HTop Bottom 4 5 m.
The factor Fc is calculated as the sum of three factors: Fc Fs Ft Fm.
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
Purchased cost: & 0.65
. . 101.3
280 c
M S
C A A F
Installed cost: . . & 101.3 0.65
2.29
280 c
M S
C I A F [equipment cost + installation cost]
with A = Area of heat transfer in [ft2], e Fc
Fd Fp
FmThe so called “installed cost” is the sum of the purchase cost and the installation cost.
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 € 1000 lb, while that of the steam 70 bar is 2.25 € 1000 lb. The cost of cooling water is 0.06 € 1000 gal.
For the calculation of heat exchange area, the heat exchanged in the condenser is:
Qc U A Tc c ml WH O2 cp H O, 2
ToutTin
Hev
Tcond
Vwhere Uc is the global heat transfer coefficient, Ac is the exchange area of the condenser, Tml 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, Tin 30 C e Tout 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 Uc 580 W m K2 .
In the case of stabilizer it is important to understand that Tout cannot be greater than that of condensation of the column head. We recommend Tout . 38 C
For the calculation of the heat exchange area is considered that the heat exchanged in the reboiler can be calculated as:
Qr U A Tr r r WsteamHevsteam Hev
Treb Vin which Wsteam is the flow rate of steam to the reboiler, V is the evaporating flow rate in the reboiler. Consider Ur Tr 11250 Btu h ft2 .