Economics

The column is sized using the procedures in Rathore, et al., A.I.Ch.E. J. 20 491 [1974]. Capital costs are scaled accordingly to the CE index. Operating costs are scaled with the price of steam, cooling water, and refrigerant. The utility temperatures are set by a schedule depending on the bottoms and overhead temperatures.

Column Cost

Condenser overall heat transfer coefficient = 100 Btu/hr.ft 2 oF

Reboiler overall heat transfer coefficient = 80 Btu/hr.ft 2 oF

Operating costs

Basis: 8500 hours operation per year

cooling water at 24 cents per 1000 gallons ($0.60/10 6 Btu); heated from 70 to 120oF

refrigerant at - 40oF costs $10.80 /10 6 Btu

steam at 1250 psia costs $3.61 /1000 lb. ($6.00/10 6 Btu)

Adjustments to operating costs are made according to the following schedule

Condenser	Coolant	Temp.	Cost
Temp (oF)	In (oF)	Out(oF)	($/106 Btu)
140 ² T	70	120	0.6
100 ² T < 140	70	T - 20	0.6 x 50/(T-90)
	Refrigeration
40 ² T < 100	20	20	5.61
10 ² T < 40	-10	-10	8.04
-20 ² T < 10	-40	-40	10.8
-80 ² T < -20	-100	-100	17.61
-130 ² T < -80	-150	-150	25.32
T < -130	T - 20	T - 20	8.44 (330/T(oR))3

Reboiler operating costs

Reboiler	Steam		Cost
Temp (oF)	Temp(oF)	pres.(psia)	($/106 Btu)
552 ² T	1540	fired heater	6
450 ² T < 552	572 1250	6
428 ² T < 450	470	515	5.22
346 ² T < 428	448	420	4.98
273 ² T < 346	366	165	3.75
220 ² T < 273	293	60	2.79
192 ² T < 220	240	25	2.03
70 ² T < 192	212	14.7	1.302
50 ² T < 70	use hot cooling water
	tin=120-T	tout-100-T	-0.6 x 50/(100-T)
T < 50	tin = 120-T	tout=70-T	-0.6

Equivalent Uniform Annual Cost (EUAC)

where

E = operating expenses

R = revenue (here zero)

t = tax rate (default 40% )

D = depreciation ( here = (W - Sv) / n )

Sv = salvage value ( default 0.1W )

io = internal interest rate (default 9% )

n = project lifetime (default 5 years )

W = capital cost = purchased cost x Lang factor (default 5.0)

( J.F. Valle - Riestra, Project evaluation in the Chemical Process Industries,

McGraw-Hill, 1983, p. 569.